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[Question] [ A century ago, after a catastrophic event on our planet, many of us were were forced to find a new home. There was one world that caught our attention: a tidally-locked blue planet orbiting a red dwarf. Since the planet was 70% ocean, had an ideal atmosphere (thanks to its strong magnetic field), and orbited a low-intensity star, our astrophysicists predicted that the sun-side would be more or less habitable. The wind and the heat took a bit of getting used to, but it was better than the nuclear winter back home. Solar panel and wind turbine industries are booming nowadays, so at least the environmentalists are pretty happy. There's just one teeny tiny problem we discovered recently... the dark side of the planet is populated by hideous Lovecraftian monstrosities. Just our luck, right? They avoid the light, but we've found archaeological evidence to suggest that they might have migrated through our side of the planet at multiple points in the past. We're wearing our brown pants. What could have possibly casted darkness on the sun-side of our world long enough for the Horrors to be able to visit? We're thinking for days at a time, or even possibly weeks. [Answer] **Ash clouds from a supervolcano or many volcanoes** This one has all the flexibility and trappings that you need: * Increasing seismic activity, smoke and/or minor eruptions as ominous warning signs * Storms now bring darkness or blow it away at peak drama. * It can cover as small or large of an area as you want * The eruptions and ash clouds can last as long as you want. * It can optionally be triggered by humanity's hubris (giant Geothermal Powerplant supposed to power the whole planet) **Lovecraftian Periodic Cicadas** If volcanoes are just too mundane... For a completely different approach, you can have the sky fill with clouds of [Periodic Cicadas](https://en.wikipedia.org/wiki/Periodical_cicadas). The Earth versions live underground for 13-17 years and then the entire species/brood emerges at once and takes to the skies, to meet, mate, lay eggs and die. Your planet's bugs are more... *Lovecraft*. They have been sleeping underground for hundreds or even thousands of years, waiting for a sign of some kind. It might be a big solar flare, passing meteor or mortals disturbing the ground with their construction activities. Now, they rise from the ground, take to the skies and head for the light side, blocking out the sun with their swarms. Oh btw, they are also the size of cars, not coins. **A comet** If you want the darkness to be external to the planet, here is a somewhat weaker scenario. The solar system has a big outer planet that keeps slinging balls of dust and ice at the sun. Big ones. None of these was or is on a collision course with the planet, but they have the unfortunate tendency to break apart into clouds of highly reflective dust somewhat inside the planet's orbit, leaving the planet in the shadow until they disperse. [Answer] # Rings First, observe this picture of Saturn. [](https://i.stack.imgur.com/bxOyF.jpg) This is a picture of Saturn's rings casting a shadow upon the cloud tops. If your planet: 1. Has rings 2. The rings are tilted slightly relative to the planet's orbital plane The rings will cast a shadow taking the form of a long arc stretching from sunrise to sunset, while the rest of that side of the planet is lit. This will take the form of a very narrow line twice per year when the rings line up with the star, and will then transition into an arc, growing thicker and more arced while migrating northward, then it will retreat slowly back towards the equator and continue the same thing in reverse over the southern hemisphere, and back. This would cause the dark regions near the equator to be very short lived and narrow, while further from the equator the shadow will be very wide and last much longer. The exact arc depends on the size of the planet, size of the rings, how wide the rings are, and how tilted they are with respect to the planet's rotation axis and orbital plane, how long the planet's year is, etc. But this would be a cool effect if you need your monsters to have made this trek across the light side often, and in specific paths. The particular scenario I've described would favor paths away from the equator, further north or south. **Edit:** @David Dubois seems to have found a cool simulation of this, if you are willing to download and run Wolfram Alpha's software. See his comment below. If you don't want to or don't have time, [I found a picture that might be helpful.](https://upload.wikimedia.org/wikipedia/commons/c/c6/Saturnoppositions.jpg) It shows how Saturn's rings are oriented as seen coming from the direction of the sun as it goes about its year. You can imagine that the shadows are directly behind the rings in each image. [Original source here.](https://en.wikiversity.org/wiki/Saturn) [](https://upload.wikimedia.org/wikipedia/commons/c/c6/Saturnoppositions.jpg) [Answer] **You've already written the answer** If you're in orbit around a "low-intensity star" then that, to me, sounds like a Red Dwarf. Red Dwarf sunspots can dim the effective brightness by 40% for anything from days to months. Make your planet the right distance away or make the creatures tolerate *low* light levels and you're sorted. [Answer] What you need is an eclipse. However being a tidally locked planet you're not going to have a moon, at least your people would have been idiots for settling on a tidally locked planet with a moon as it would be unstable as discussed in this question: (<https://physics.stackexchange.com/questions/25577/stability-of-moons-around-tidally-locked-exoplanets>) Edit: As mentioned in the comments; early in the planet's life it would be stable enough. But at the point that you have day to week long eclipses you can be fairly sure that the planet's biosphere is dying. Depending on the size and distances between the planet, moon, and sun; the planet and moon might even hit the Roche limit and be destroyed before this ever happens. The next possibility for an eclipse is a large planet inside the orbit of your planet. But if this planet was close enough to cause an eclipse then the two planets' gravity would likely be ripping each other apart every time they passed. Again if you settled on a planet like this you'd be an idiot. A third and probably most plausible possibility would involve a space mega-structure near to the sun. Something like a Dyson swarm might do it if the swarm members were large enough but you'd need to do some size and distance calculations that I can't do at the moment to confirm. Personally if someone had built a mega-structure in a star system I would stay well away until I had done some investigation, however, if you were desperate enough you might settle on this planet. [Answer] You have wind and heat, therefore sand and dust are widely available. Planet wide sandstorms, the same kind happening on [Mars](https://www.nasa.gov/feature/goddard/the-fact-and-fiction-of-martian-dust-storms), can cast darkness over long time, independently from astronomical situation. > > “Every year there are some moderately big dust storms that pop up on > Mars and they cover continent-sized areas and last for weeks at a > time,” said Michael Smith, a planetary scientist at NASA’s Goddard > Space Flight Center in Greenbelt, Maryland. > > > [Answer] # The planet may only recently have become tidally locked. Tidally locked planets don't start out that way. All planets lose their rotational momentum over time as they orbit their star. Planets that are smaller and closer to their host lose it more quickly, so it not inconceivable that while your planet may be tidally locked now, it may not have been so in its recent past. Even the Earth's current 24 hour period is decreasing, resulting in the length of a day getting longer by 1.7 milliseconds per century. Nothing to worry about there, then. But for a smaller planet close-in around a red dwarf star, the decrease in spin would be many times quicker than that. Having a moon (or moons) will also affect it. Your planet is tidally locked, but has only become so very recently. In fact, it isn't really tidally locked yet; it still had some residual spin, resulting in a "day" that lasted maybe several thousands of years. It would be moving almost imperceptibly; to the point that the settlers may not even realise at first, but it might affect their long-term planning -- ie that city you build now will start moving into the night zone after a couple of hundred years time. [Answer] A [space sunshade](https://en.wikipedia.org/wiki/Space_sunshade) in orbit around the red dwarf that periodically comes between the planet and its primary star. > > > > > > A space sunshade or sunshield is a parasol that diverts or otherwise reduces some of a star's radiation, preventing them from hitting a > > spacecraft or planet and thereby reducing its insolation, which > > results in reduced heating. Light can be diverted by different > > methods. First proposed in 1989, the original space sunshade concept > > involves putting a large occulting disc, or technology of equivalent > > purpose at the L1 gravitation point between the Earth and Sun. > > > > > > > > > A sunshade is of particular interest as a climate engineering method > for mitigating global warming through solar radiation management. Such > shades could also be used to produce space solar power, acting as > solar power satellites. Proposed shade designs include a single-piece > shade and a shade made by a great number of small objects. > > > This should be capable of bringing darkness to the planet's dayside and allow the Lovecraftian monstrosities ease of access. I most definitely agree with Static's comment about not settling in a planetary system where someone or something has installed or constructed a megastructure. This should be taken as a sign that effectively says "Lesser lifeforms keep out. Enter at your peril." As your settlers do seem to have out. [Answer] # **Giant Lovecraftian Space Monster** You're already going with Lovecraftian Horrors as your antagonists, use one as your catalyst as well. This system is home to some massive Space Kraken that has periods of dormancy and activity. While dormant it curls in on itself and lazily orbits the star, perhaps farther out than your planet, nearly invisible against backdrop of space. When it wakes it uses it own unknowable propulsion to migrate closer to the star in order to feed on the stellar radiation/commune with the other cosmic entity that lives within the stellar mass/etc... In order to more thoroughly feast upon the radiation of the star it unfurls it's bulk, stretching massive fleshy sails/wings/polyps and creating a massive shadow between the planet and the star. Make this happen close enough to the planet to cast an eclipse and you've got your darkness. Plus this feeding could take as long as you wish and because it's not a regular spherical mass but rather an undulating writhing creature you can also have irregular period of light when some part of the creature moves and lets light past. Extra points for the beasties on your planet being cast offs shed by this monster as it flies past on it's periods migration thus also allowing for an occasional re-population of monsters if your humans decide to get organized about wiping out the monsters. [Answer] Eclipse from another planet in orbital resonance. There's a large planet - like a gas giant - on a lower orbit. The orbit of that planet has a rather high eccentricity; in particular such, that when near aphelion it moves at a speed very similar to ours. Its gravitational influence put our planet in a resonant orbit: every *n* orbits of the central planet, they make "closest approach", and that results in an eclipse that lasts several days or weeks, until the giant begins its descent towards its perihelion, and our planet (in a circular orbit) continues on its merry way. [Answer] Every few thousand years, one of the Horrors sheds its skin. It casts it into space, and it drifts in orbit around the planet until it de-orbits. This creates repetitive periods of darkness, not a continuous dark period. [Answer] Very occasionally, the creatures go to war on each other along factions, at large scale. One of their wartime activities bring up gargantuan amounts of dust. Nuclear explosions come to mind, maybe a giant creature that eats and purifies uranium until it reaches supercriticality. But could be something else. The dust is spread by the wind, and blocks the sun. The war then spills to the entire planet. The war ends, and the dust gradually settles. [Answer] How about a swarm of asteroids/comets on an elliptical orbit that crosses between the star and planet every "so often". The swarm wouldn't need to be dense - it could be quite sparse - it would just need to create opacity between star and planet. If the trajectory passed the planet at "steep" angle (nearly straight into the star) it could stay between star and planet for a while. I realize the swarm would need to be "quite big" to do this, considering that the further it got from the planet, the larger it would need to be to shade the planet, and the velocities it would be traveling would work against a long duration of shade. Also, you would expect a lot of surface impacts with that much crap in overlapping orbits - maybe the locals can deflect those destined to collide with the planet. It's a little thin, but maybe someone can save (or condemn) the idea with hard physics. [Answer] **Non-euclidean space** The space around the lovecraftian monsters is reputedly quite non-euclidean. This could bend light away from the sun. Giving a more detailed science based answer to questions involving lovecraftian monsters is a bit hard since scientists who study such things tend to be a little *odd*. Best guess is that the non-euclideaness results from a cluster of black hole like objects in a chaotic orbit. Mostly this just results in flickering, and moving the stars round, but like most chaotic systems it is hard to say how long the blackness would last, or when it would start. When pressed as to when the great darkness might begin the scientist would just say things like "when the stars are right", "probably in the past; objectively we are almost certainly dead, just don't look at the sun, lest it looks back and collapses the wave function.". Eventually they just insist that they are a cat in a box, and laugh maniacally until the people in white coats come to take them away. On the other hand, Lovecraftian monstrosities can be quite crafty. Why would they need the whole planet to be dark, when it is quite dark inside human skin? Think carefully, do you remember ever seeing your neighbours blink? [Answer] As others have mentioned, an inner planet causing an eclipse would work. The TRAPPIST-1 system has seven tidally locked planets. [See here](https://en.wikipedia.org/wiki/TRAPPIST-1) for general information on the system. If one of the inner planets is sufficiently large enough, it could cause the eclipse. The TRAPPIST-1 planets likely encounter frequent eclipses and transits. The question is, how far out is the resident planet (how long does it take to make one complete revolution around its host star)? If it takes a year or two, then the inner planet would be able to block the star light long enough to allow Lovecraft's hordes plenty of time for a little light-side exploration/destruction. Mercury is tidally locked, but it is small and close in. All of the TRAPPIST-1 planets are closer than that to their host star. The longest TRAPPIST-1 "year" is only 20 days, meaning that any eclipses would last only a few minutes. [Answer] # A large moon with an eccentric orbit The planet has a moon that is large enough to cause a total eclipse. The orbit of this moon is eccentric, meaning that actual eclipses are rare events, but when they do happen, the monsters can break out of the dark side by following the path of the eclipse and wreaking havoc along the line of totality. [Answer] ## Some kind of light on the dark side So you say the monsters don't like the light and stick to the dark side. Fair enough, but what happens if the dark side were to become illuminated? If that happened, I can imagine the monsters fleeing across the whole planet, even the daylight side, desperately trying to escape the light and causing chaos as they go. So what could happen to light up the dark side of the planet? Here are some ideas: * Fire: every few hundred years, a massive fire sweeps across the dark side of the planet. Lighting it up and driving the monsters across to the opposite side of the planet for a week or so until it subsides. The fire could also generate a global smog cloud that would darken the whole planet and make the light side more tolerable for the monsters. * Asteroid impact: Similar to the fire above; major planetary disturbance with ash blocking out the sun for weeks or months. The whole planet becomes dark so the monsters get free reign * Solar flare: a major solar flare could cause bright aurora even quite a long way round the back of the planet. They may not be as bright as daylight, but in a world of perpetual darkness, and where they don't happen often they could easily be the trigger to unleash the fury of the monsters. * Binary star. Maybe the red dwarf is just one star of a binary system? The layout of the system could mean that the 'dark side' of the planet alternates between being in complete darkness and being illuminated by the second star. Each could be last for a period of several thousands or even tens of thousands of years at a time, but the switch-over between the two states could be fairly quick (a sunrise of the second star that lasts maybe a few days or weeks? The second star would give much less light than the main star even if it was a brighter star, simply due to the distance, but it would be enough to create a gloomy daylight on the dark side, but that should be enough to stir the monsters into action. * Other significant light source elsewhere in the system: You could also achieve a similar effect with one of the outer gas giants in the system. You could have a planet that normally just looks like Jupiter, but every now and then can be triggered to produce its own light for a time by some external event; maybe a solar flare or comet impact. So normally it just looks like another point of light in the starfield, but randomly every fifty or five-hundred years, it bursts into light and illuminates the dark side of the planet for a few weeks. ]

[Question] [ ## Let's say a species of naive, yet well-intentioned aliens came across the Earth. They generally like humans and decide to try to increase their happiness by supplying the thing which they have deduced all people clearly most desire: **Money**. As they are wonderfully advanced, generating and deploying huge quantities of these rectangular pieces of fabric/polymer is absolutely no biggy. In fact after collecting a few samples and observing the world's different communities, they can recreate all banknotes perfectly (structurally, chemically, atomically) and have also learned which tribal groups like which types. And so they fly their majestic space ships over all significant population centers (all the while wondering why the bipeds have suddenly started running about) and gently release our "gift". We're talking trillions of dollars worth of notes spewed across the roofs and streets of almost all cities, towns and villages; totalling several quadrilions (1,000,000,000,000,000) worth in all. Now these aliens are really nice, if a government decides to change the design of their money and abolish the old one, then the aliens will just assume they've met the demand and now the natives all want this new flavor of rectangle: which they'll again graciously supply enormous quantities of, of course. --- So here's the question: while these kindly aliens try to understand this new and very bizzare cultural phenomenon called an "€con@mee" (*sounds so exotic doesn't it!*), **what concrete effects would this event have and what policies would the world's various administrations put in place?** I am also very open to answers only explaining what would happen in specific countries. The US, for example. **Note:** *Just to be clear, when I say "Totalling quadrillions", I mean the total worth of the money dropped. Not the number of individual bills. These aliens aren't just making it rain with $1 notes people!* [Answer] > > what policies would the world's various administrations put in place? > > > 1. Switch to digital currencies and eliminate paper money. 2. Explain to the nice aliens that we were just settling on paper money. What we really wanted were Star Trek replicators and non-polluting power sources that don't require fuel. Thanks! ...and some of us would like spaceships too. We appreciate your attention! [Answer] If the governments of the world are in any way intelligent (which is a stretch), they would quickly switch to using a combination of highly nutritious, pre packaged food bars, and fully charged high efficiency batteries as currency. Using the batteries and eating the food would remove some from circulation, helping them to retain their value. In the meantime, food and energy crises are taken care of. [Answer] * What effects would this massive increase of physical currency have on the modern world? The "local" economy would be wrecked or on the road to become so unless policies are quickly put into place. * What policies would the world's various administrations put in place? Immediate lock on any non-electronic currency exchange, and that would be done by the banks refusing to accept (but very willing to disburse, I bet) paper they well know has become worthless, even before the government had time to intervene. Then, a sort of "looting" would follow in which people would try to exchange money into "real" goods. This would be no great mischief in the developed countries where most shops already accept plastic. Elsewhere, you'd need to institute quotas and probably face riots and return to barter economy on a local scale. In the medium run, change the currency, but that isn't something you can do easily. Also, compensation for people *claiming* to have had paper money before the Event and wanting it converted to spendable electronic credit would make for interesting times for lawyers and attorneys. * How would people/governments react towards these aliens? Try to contact them and explain, and be quite convinced in their heart of hearts that the aliens knew exactly what they're doing and did this on purpose. Also, try and ask whether there's some way of telling their money from "real" money - for example from its isotopic spectrum, if it has been manufactured from raw materials coming from outside the Solar System; or they could supply the whole Earth with very efficient 14C detectors. I expect forgers to try smearing ancient graphite on alien money to make it seem older. Or they could supply very fast and memory-endowed OCRs loaded with a white/blacklist of serial numbers. Also, they'd dearly love to get their hands on **replicator technology**. That would be probably asked as a stopgap measure to supply medicines and first-aid necessities to the worst struck countries. * Would there be significant changes in the popular perception of wealth? No. Wealth is not *hard currency* in most people's minds. The perception of physical currency might change, though. * What would be the general cultural and social impact of this event? The *Currency Rain* - promptly co-dubbed the *Currency Ruin* - would have a large effect, but **nothing** compared with the *arrival of an alien culture*. --- **Scenario** The world would be split in three camps overnight. Really backward countries where barter economy is still thriving, and which would be split between cities (where this wouldn't work) and the country (where it would work). These countries would likely suffer from internecine warfare, with people from the cities trying to force agricultural producers to give them food, and the latter unwilling to do so in exchange for paper which might or might not be worth something. Advanced countries where most business already uses plastic and you can already live without hard currency. These would be inconvenienced, but on the whole would emerge unscathed. Emergency shipments of POS readers could take care of most crises. Banks tend to not keep paper money (actually, lots of people *wanting* paper money all of a sudden would be a catastrophe because the banks *do not have* it as they already loaned it). They would simply refuse to *accept* paper money, and be left with just the currency in their vaults that would have become worthless. And even so, if that paper had been kept sealed and untouched inside since the day of the Money Rain, and it could be proved - given a bank's pull, their say-so would likely suffice - then they might argue that *that* money is still worth its face value; it's just people outside's that isn't. So, no great bank crash -- not there and then, at least. And finally middling countries where the economy, at the citizen level, is almost completely currency based and plastic money is next to unheard of. Those would descend into chaos, as no shop would accept money and, if it did, would quickly find itself crammed with worthless paper; in effect, every seller would have the choice between **giving away** its merchandise or **hoard** it and revert to barter for personal and familiar survival. I expect most would do the latter, which leaves a large part of the population with no real, *legal* way of procuring food and necessities. Civil war would almost immediately break out. Shortly after that, it would be waves upon waves of refugees... and that's where bordering advanced countries would find themselves *not so unaffected after all*, and likely quickly become unwilling to shoulder the burden of their neighbours' welfare. [Answer] You needn't look any further than many failed states. When a country can't pay its debts, the typical response of the government is to just print money. This causes [Hyperinflation](https://en.wikipedia.org/wiki/Hyperinflation) and causes everyone to try to divest themselves of the useless currency. In other words, the currency itself becomes worthless. Assets still have the value they always had, such as food, clothing, and fuel. Some items that have real value but are also durable and portable may actually rise in value because they can be used as a new form of money. Historically this has been gold, but it could be anything. Cigarettes are a form of currency in prisons. Batteries, non-perishable food, and medicine seem like great candidates. A lot of people's investments aren't actually money, but stocks. If you own a stock, you own a portion of a company, which is really an asset. Assuming that company can figure out how to stay in business and produce their product for some kind of profit, then that stock still has value. If nothing else, that stock may entitle you to a share of their assets if they liquidate (but it depends on the type of share). There are other alternatives to cash though. Let's say as soon as the aliens started dropping money, the government declared that all cash was worthless, but all deposits were still valid. A bank, for instance, only keeps 5% of the on-deposit money as cash. When you deposit \$100 in your account, the bank loans out \$95 of that, and that person typically deposits it in their bank account (or spends it meaning the seller deposits the money) and then the bank loans out 95% of that \$95, and so on. The net result is called the "money multiplier" and it ultimately means that the amount of money in circulation is only 5% cash. It's hard for me to understand what this would mean, if suddenly only that 5% became worthless. Could we just switch to a cashless society? How does the government continue to manage the money supply? One option would be something like [Bitcoin](https://en.wikipedia.org/wiki/Bitcoin). One could imagine a crypto-currency where only the government had the keys necessary to authenticate a transaction. This would be some kind of centralized electronic currency (instead of the distributed nature of Bitcoin). Countries have gone through periods of Hyperinflation and then stabilized by [issuing a new currency](https://en.wikipedia.org/wiki/Hyperinflation_in_the_Weimar_Republic). If you immediately say "cash" is worthless but money on deposit has value, and you immediately start issuing a new digitally-authenticated currency where the value was one-to-one the same as your existing denominations, and you offered some kind of replacement plan for the banks that hold most of the cash currency (the amount they have on hand at the moment the aliens started dropping cash could probably be authenticated by an audit) then it just might work, and the world could avoid big financial system problems. [Answer] Since we need oxygen, why wouldn't they replace all of the nitrogen in our atmosphere with oxygen? Since we need (and "everybody" likes) water, why wouldn't they just increase sea level by oh, say 20 km? Your premise assumes they're idiots, or in a comic book way, villains (the road to Hell is paved with good intentions). There was an old old TV show "WKRP in Cincinnati" (iirc) a comedy which had what I consider one of the funniest sketches on TV. It's Thanksgiving (US Autumn holiday feast day). They're having a free Turkey give-away (traditional main course) but the birds are live. The reporter/news anchor giving them away in some parking lot is arriving by helicopter with the birds. He decides it would be more 'festive' (suspend disbelief here) to let the birds fly down and land in the parking lot, so he releases them at several thousand feet altitude. One problem is, turkeys don't fly. Of course, a 10 or 20 pound object can cause quite a bit of damage on impact from a height (although to be honest, I'd guess that terminal velocity for a bird, even a turkey, is not extreme). --- So, first question is what do you mean 'replicate'? As you probably know, each note has a unique serial number. I assume there's some magical process which allows the aliens to not only exactly duplicate freshly printed notes, but notes which have been in use and are worn and torn, and marked-up and creased. Magic, indeed. In the USA, there are about 40 billion notes in circulation with a value of about $1.5 trillion. If we assume the rest of the world has a proportionate amount of paper currency, then since the US is 4% of the world population, we're talking about 1 trillion notes or a value of 37 trillion USD. But you're talking quadrillions. So we need to multiply that by a factor of what? 100? 500? Say 100. So they dump 100 trillion notes, and assuming each note weighs 1 gram, that's 100 billion grams or 100 million kilograms. That is about 20 years worth of space dust accumulation, which could have a small effect on our orbit and possibly our spin (not my area of expertise). Its fall would probably also lead to a bump up in temperature (potential energy converted to kinetic), but I'd guess not enough to be easily measured. A lot of it would blow into bodies of water, causing massive pollution, reduced light transmission, and various ecological effects as well as clogging drainage systems leading to flooding, disease and death. Accumulations of it would cause fires and power line shorts and more people would die. --- But I agree that the economic effects would be the most significant. Paper money would become worthless. This would be equivalent to a kind of hyperinflation. People would lose their jobs, their businesses, their health insurance. People would die. --- To answer some of your questions: Physical effects are (somewhat) predictable. Banks would refuse to accept banknotes, coins would become more valuable. Only businesses accepting electronic payments would survive. Small operators - a lot of them -would fail. With the demise of paper money, some economies would go to cards or electronics others to metal coinage. Would purses become universal? IDK. I think the effect would be larger than the 9/11 attacks were on the US mood/world view, but over the entire globe. Rural populations - those who missed the mana, would probably suffer even more, but that's another area outside my expertise. There'd be a period of adjustment, and things would go back pretty much to (a new) normal. Mugging would decrease, identity theft and online hacking explode. There would be all sorts of reactions and side-effects. It's impossible to predict accurately, imho. So much of the initial reaction would be ill advised. More centralized governments? probably. National ID cards? Maybe. Bitcoin? A big winner. Perception of aliens? Generally hostile, I expect. Effect on society? Well, I don't believe technology changes human nature. So we'd still be the apes in suits we've always been. Lying, cheating, stealing, giving, caring, loving, and hating. [Answer] I think this would totally devastate the financial systems of the world until the governments learned how to communicate with the aliens or how to adapt to this. I think you would see a shift back to commodities like gold and silver. Not necessarily coins, but bars. If the aliens started producing those too, I think the world would put two and two together and they could get the aliens to produce literally any element they needed by making their currency out of rare materials. Naturally, this would be a very positive outcome in the long run. If the aliens could replicate any currency you would see money become useless and we would go back to the old days of barter, land ownership and power being the way the economy works. I think administrations would start restricting things related to currency in the beginning, and you would see them start to horde things of value, like equipment. I would not be surprised if some governments reacted with hostility, shortly before the aliens started dropping notes. I think the aliens would be seen differently depending on how they reacted to hostility, if the governments could contact them, and what kinds of "currency" they could replicate. [Answer] The clever country immediately changes their currency to something actually useful. An alloy of useful metals, for example. Gems. CPUs. 3d printers. Atomic clocks. 3d printing raw material spools. Cutlery. Whatever. Then the aliens rain down this new "currency", which they put to use. The country then rotates to a new "currency". Manufacture a few 1000s of something, get millions or billions or more of it. Design an electronic currency to handle the rest of the economy. Maybe require that trading the currency along with a set of physical tokens (cash) to emulate the old way of trading, thus encouraging more "mana from heaven". [Answer] It would be incredibly annoying and throw the world into panic mode for a bit, but then everyone will just switch to completely digital currencies like 92% of world currencies are. That panic mode would go something like... - "oh I got this large amount of money. let me put it in the bank/spend it" - if they spend it then yay they get a bunch of free stuff which no one really notices is free other than all the computers say "more than what we expected was bought here so produce/send more here" which wastes resources when noone buys it the next cycle which inflates the currency by some ammount. And that small inflation is done millions of times across all systems. Or because so many people all of a sudden get money all at once it also can create a run on products through someone buying too much or too many people wanting it at the same time which raises the price which causes inflation too. - If on the other hand people instead deposit this money then the computers will go "ding this person suddenly has more than 10,000 they are putting in the bank, where is it coming from?" which will then be investigated and someone will know what happened and as a result all these large transactions that are out of place will be rolled back. There is also the possibility, though very unlikely that it could lead to a good stimulis by way of the rich realizing what is happening and just deciding to take the lose and simply work with the government and bank to figure out how much currency was "added" and simply remove that as a type of tax on the company to balance the books. The reason this would be good is that most of the problem as it stands is that the economic system of the world has a blockage in the arteries which is keeping all the capital in the hands of a few, whether they want it or not. A sudden influx of capital to the poor and the rich just taking this hit would be like creating a temporary new artery around the blockage, but considering they wouldn't do this it doesn't really matter. Another possibility is that some people realize that depositing 10k+ probably isn't a wise idea, especially not soon after event and they'd hold onto the currency and deposit it in smaller amounts. Not enough people would do this to make a difference, but if you were to do this you'd have to do it within about a year or two window, before everyone goes to all digital and will no longer accept physical currency... --- Also, this is less of a problem than you might think because all physical currency has marking of some sort that set each piece apart from any other piece. Much of the "money" would be useless because these markings wouldn't mean anything to them and reproducing it would result in random symbols that would be unusable or would be duplicates of bills that already exist and you could just invalidate all bills which are known to be duplicates. The Legitimate holders would be unhappy, but more than likely the legitimate holders would be the aliens if they don't try to duplicate the security marking patterns so it would just take a short period to realize then issue a statement that those aren't legitimate. [Answer] Other answers are only addressing the economic ramifications of these helpful aliens. However there are other impacts to our planet as well: Earth has roughly [150,000,000 sq km of land mass](http://hypertextbook.com/facts/2001/DanielChen.shtml) and [95% of humans inhabit 10%](https://www.quora.com/Philosophy-of-Everyday-Life-What-percentage-of-the-worlds-land-is-populated-by-humans) of that, which means 95% of your currency will be rained down on a 15,000,000 sq km area. So 950,000,000,000,000 bills divided by a 15,000,000 sq km area gives you 63,333,333 per sq km or 63.33 per sq meter. A US dollar bill is approx 15 cm X 6.5 cm. Assuming all bills are the same size, evenly distribution in the populated areas, and I did my math correctly then that means it will be covering 61.7% of the surface of populated areas. This is **very bad**. 61.7% of road ways are going to be covered with money, this is going to cause all kinds of accidents all over the planet. People will be slamming on their breaks to collect the money, paper bills will help blind drivers and cause them to hit the cars that decided it was a good idea to stop on an interstate. People will have trouble collecting all the money that was printed and so the money not collected will cause environmental damage (essentially it will be litter at this point since its value will be gone). Paper money is also a fire hazard and if the money catches on fire it can help fuel a fire storm causing property damage. [Answer] Worldwide littering? As if the normal sort wasn't bad enough. To say nothing of the fire hazard, what will happen when all that paper starts to rot? I suspect you'd have more immediate problems than runaway inflation. Let's say your average note is ~20 by 10 cm, on 100 gsm paper or lighter polymer. That's $0.02 \times 100 = 2$ grams. $10^{13}$ notes is therefore $2 \times10^7$ tonnes of paper and polymer (assuming same weight). At least half the world's cities will burn down overnight. The rest will declare a state of emergency and call out the military. Think of a major natural disaster like [Katrina](https://en.wikipedia.org/wiki/Hurricane_Katrina), but worldwide, only this time the stuff left behind catches fire. Major oil refineries and stores will have to shut down, as will any gas fields near population centres. Internal combustion vehicles and thermal power plants will need to be regulated. Since transport into population centres is being regulated, within a day, you'll start having shortages, as the limited electricity means stored food will start to spoil. Riots and fights over resources will start breaking out, since they can't use cash for exchange, and electricity is being rationed to avoid starting fires (no electronic payments). As I said, this is just Day 1. Day 2 will double the disaster,even if the aliens don't start litter bombing again. Several areas will start spraying down the streets and buildings to avoid fires starting. Several tonnes of soggy paper and polymer will block the sewage system, then start to rot (the paper, at least; the polymer will simply block the pipes), producing methane, while the sewage already present will start to overflow. Waterborne diseases will become epidemic, moreso since the last couple of generations haven't developed immunity thanks to water purification. Soon though, the methane itself will start becoming a problem in the lower areas of the cities--even if it doesn't explode, it's still poisonous. Forget the economy, every major population centre will become uninhabitable, forcing people into the country, where presumably the aliens will target the next largest population concentrations. ...Are you sure they aren't invaders? EDIT: Changed $10^{15}$ to $10^{13}$ and consequently $10^9$ to $10^7$ in response to comments below [Answer] I am assuming that alien can somehow produce fake credit card that always get accepted by a POS. Short term a bit of chaos. One thing the government could do to govern the situation is to create a board devoted to estimating and making public the amount of money put in circulation by the alien. If their estimates are good enough they can then, at least as a temporary measure, dictate prices for all goods and peg them at the inflow of alien money. It's a bit of an hassle but can keep things reasonable for a while. People would of course attempt to kill each other as they try to skew the uniform distribution of money from aliens toward themselves. The government might want to say something on this kind of behavior, assuming (unlikely) the various minister are not too busy collecting the money from the ground. [Answer] 20 years ago this question might have been interesting but it's 2017 so ask yourself this - How many people do you know who depend on *bank notes* for their survival? Sure you might depend on physical cash if you're a fruit picker, prostitute, drug dealer or selling beans on the side of the road but for most of us "money" means a plastic card with numbers on it and a bank account tied to numbers in a computer. What would actually happen is that the wealthy elite, with their money in bank accounts, trusts, shares, bonds and property would simply use the event as an excuse to stomp down harder on those who do rely on physical bills (ie, the poor and fringes of society). Banks and governments would simply declare cash worthless and move on with their lives. [Answer] Actually, it would have very little impact. In the western world, actually cash money is no longer used for anything other than quite trivial transaction between individuals. By trivial, I mean to the economy, not to the individuals involved. For example, the foreign exchange markets trade over five trillion dollars a day, but the total cash in circulation on the planet is only about four trillion dollars. Major currency upsets are quite common, for example, India took the most common cash notes out of circulation all together and with very little notice and while it caused problems for some, the country are still fine. If the aliens actually wanted to disrupt the world economy through 'kindness', they would have much better results by giving away free power sources. Drop a few clean fusion reactors into some developing countries and watch the world turn upside down. [Answer] Money with unique ID on banknotes is not falsifiable in that each banknote is unique and can be disabled if detected duplicate (banknote usage at two distant spaces in a small amount of time), and exact duplication (atom-wise) of a banknote is not a technology that can destabilize this system. Also, IDs need not be printed or be numbers, see the systems that analyze the paper fibers arrangement, that are somewhat random, and extract unique IDs from these. ]

[Question] [ We all know that the universe is going to die one day: all the stars will die, all the black holes will evaporate and life will be gone. But hypothetically speaking, if a super advanced alien race (let's say a few billion years more advanced than us) wanted to prevent this from happening, and protect all life within the universe, would they be able to do it? Or is the death of the universe inevitable and it doesn't matter how advanced you are? [Answer] Going a bit more out there, say the aliens have discovered undeniable proof that the simulation theory is actually true. And they have figured out how to get access to some of the API from inside the simulation. They can't get out, because you have to have a body to exist on the outside, but they do have a bit of control over the default parameters, so long as they don't do something really crazy and draw attention to the fact that they've figured it out, they can tweak things in small ways. Like change the rate of universe decay from 1 to -1, so that the universe starts getting younger instead of older. They just have to remember to switch it back every few billion years so that the universe doesn't get too young and hot. Edit: All this depends on the point of the simulation being to study life, not the universe. Another fun possibility that it allows is for the creator(s) to be able to take up an avatar in the simulation, which could lead to things like the greek gods. [Answer] We can't answer this question as we do not know how any of those things work. Since we know the universe exists, there must be some way to create it in the first place but whether that can be accessed from within is completely unknown. There's an old and famous sci-fi short story that explores this question: *The Last Question* by *Isaac Asimov*. <http://www.multivax.com/last_question.html> At the point we are at in the story Multivac answers your question with: > > INSUFFICIENT DATA FOR MEANINGFUL ANSWER > > > [Answer] ## You can achieve trillions of years of power beyond the point where the universe goes dark, by harvesting matter. Even after all the black holes are gone there will still be asteroids, planets, and all kinds of other cosmic junk that has mass. This mass can be converted via `E=mc^2` to energy. Using antimatter, for example, would be one way to achieve very high efficiency conversion of mass to energy. The energy generated from these reactions, and the incomprehensible amount of matter in a single galaxy, let alone the universe guarantees a near infinite amount of energy for any galactic civilization that can harvest it. While this amount of energy will eventually run out, after for example 10^50 years, the time frame is so long that the galaxy will have "died", as we know it now, a trillion times over by the time our selected galactic civilization runs out of a means to survive. By that time one would assume that they would have found a way to create a new universe, or to hop between them. The universe might die, but the species that live within it don't necessarily have to. **Edit:** A Kugelblitz is another way to harvest energy from mass efficiently, via hawking radiation: <https://en.wikipedia.org/wiki/Kugelblitz_(astrophysics)> Thank you @Ryan\_L for bringing up the idea of using a blackhole instead of antimatter: > > You are best off slowly dumping these planets and asteroids into the > black holes and living off the Hawking radiation. This is because many > systems are most efficient at very low temperatures; particularly > computation. en.wikipedia.org/wiki/Landauer%27s\_principle > > > Also of interest: > > The universe could possibly avoid eternal heat death through random > quantum tunnelling and quantum fluctuations, given the non-zero > probability of producing a new Big Bang in roughly 10^10^10^56 years.[41] > <https://en.wikipedia.org/wiki/Future_of_an_expanding_universe#Dark_Era_and_Photon_Age> > > > [Answer] # We don't know: possibly not First, I want to say that we are nothing compared to that super advanced civilization, so how you dare to think we could actually have **any** kind of idea of how to prevent the Heat Death of the universe? Actually, we have some ideas, possibles or not is another matter: ## [Turn matter into energy](https://en.wikipedia.org/wiki/Mass%E2%80%93energy_equivalence) Even if starts die and everything gets frozen, the matter will be there -at least for a while (we aren't sure if the matter is unstable)- and **we could convert it into energy.** [Mass energy equivalence](https://en.wikipedia.org/wiki/Mass%E2%80%93energy_equivalence)! $$\text{E} = \text{mc}^2$$ Each gram of matter has 89,875,517,873,681,764 Joules of energy, that is, **90 petajoules**. We could use matter as ultimate fuel for some time. ## Escape from the universe If our universe is dying we should make portal/spaceships and **travel to another young universe** in order to escape from death. I strongly don't recommend this idea because it could be really dangerous, since we don't know how physical laws work on other universes. With a minimal change in some physical constant, we could stop existing. So I have another idea: ## Drain energy from other universes Heat death means all the suns will die by inability to continue fusion and all the entropy will reach its maximum level, meaning all the universe will have a constant of 2.7 kelvins everywhere. So we just need a **new energy source to draw from it: another universe**. Draining energy from a younger universe, making our universe an open system, is safer than travel there because we aren't exposed to their laws. That will let us buy more time until death again, but again we have problems. If our entropy is increasing and we still keep draining more energy from other universes, our universe will start inflating like a balloon of energy until something bad happens. * Either we die cooked because of that 2.7 K of passive heat increase into something so hot that even with thermal pumps (AKA: AC) we can't survive. * Or we adapt to the heat and then the universe blows up or cracks due to massive energy because that "2.7 k" of passive heat ends reaching the Plank temperature... a bit worried... * Or the expansion of the universe is forced and accelerated even more: in order to increase the universe volume ($\text{V} = \frac{3}{4}\pi\text{r}^3$) and that decrease the energy density. * Or, our passive heat (2.7 k) becomes so hot that we are not more able to drain energy from other universes because the heat flows becomes the opposite ($\text{T}\_{\text{our}} > \text{T}\_{\text{their}}$). To prevent this we have another solution, which is to artificially provoke the last alternative. If we keep draining energy from other younger universes, our universe will keep inflating in energy, so we just need to transfer it passively to another older universe already in its Heat Death. **Now the matter would be if there is an infinite or finite amount of universe to gather and expel energy.** ## [Quantum tunnelling](https://en.wikipedia.org/wiki/Quantum_tunnelling) and [Heisenberg uncertainty principle](https://en.wikipedia.org/wiki/Uncertainty_principle) I've already explained quantum tunneling today in [this answer](https://worldbuilding.stackexchange.com/a/118530/35041), so I don't want to explain it again. Easy: particles are able to teleport to anyplace where it doesn't consume more energy than they have, even if in order to do that they must move through a barrier which in classical physic they wouldn't be able. Combining the [Quantum tunnelling](https://en.wikipedia.org/wiki/Quantum_tunnelling) and the [Heisenberg uncertainty principle](https://en.wikipedia.org/wiki/Uncertainty_principle) we could archive it. We just need to learn how to do manipulate them at will artificially. **If that is possible, we could reverse Heat Death at the cost of statistics, it will be just a matter of time reverse it.** ## [Big Bounce](https://en.wikipedia.org/wiki/Big_Bounce) Artificially or maybe naturally if gravity is stronger than the universe expansion, in some time all the mass of the universe will fall into a huge supermassive black hole (that would provoke a [big crunch](https://en.wikipedia.org/wiki/Big_Crunch)), and if that happened, we could have the "hope" of that will produce a [big bang](https://en.wikipedia.org/wiki/Big_Bang), **effectively resetting the universe**. Now it will be a matter of how to produce the big bounce and how to survive it (we will need to escape from the explosion zone and the gravitational well), maybe they could use wormhole technology, FTL drives, Warping space around themselves, etc. ## Dark energy generator If we get deeper into science fiction, we could develop a way to convert [dark energy](https://en.wikipedia.org/wiki/Dark_energy) into normal energy. If that is true, we are saved because dark energy is infinite. If we could gather this high amount of energy (around $68.63\text{%}$ of the universe) from its low but constant density ($~7\times10^{−30}\text{ g/cm}3$) and turn into energy we would archive endless energy. Dark energy is quite peculiar because it is born from space itself and also produce more space. Dark energy produces a negative pressure in the container its hold -the universe-, that means that dark energy is pushing the "boundaries" of the universe making it bigger. And also, we already know that the universe expansion is accelerating, **so the dark energy is being produced from somewhere. We just need to gather it!** ## Vacuum energy Without the need to get close to science fiction we could try to gather [vacuum energy](https://en.wikipedia.org/wiki/Vacuum_energy) which has a density between $10^{-9}\text{ j/m}^3$ and $10^{113}\text{ j/m}^3$... scientist still aren't agree and have a [problem](https://en.wikipedia.org/wiki/Cosmological_constant_problem). Do you remember that above I said dark energy births from space? Well, I lie, because vacuum energy births from space itself and this produce dark energy. Vacuum energy could be said that its the mother or dark energy. But it's even better. Vacuum energy isn't a normal energy, it's an intrinsical property of space itself. Space has the magical property to produce more space, everywhere, always, all the time. That is why the expansion is getting faster, because each time there is more space, which is producing more space, which that is producing more space..., per second, per second... per second. The vacuum energy is how scientists explain this space replication property ## [Virtual Particle](https://en.wikipedia.org/wiki/Virtual_particle) Generator Do you what is a [virtual particle](https://en.wikipedia.org/wiki/Virtual_particle)? It's again another way to interpret vacuum energy. This way of thinking states that void isn't vacuum, it has particles. Not exactly normal particles but virtual particles. But, what happens if we capture one of this particles? Well, black holes already do that in the way os [Hawking radiation](https://en.wikipedia.org/wiki/Hawking_radiation). A pair of particles spawns one of them inside the even of the horizon while the other outside. That particle escape producing energy, so in order to not break the conservation law, the black hole pays the energy price. That is the explanation of why black holes evaporate over time. If we could artificially create virtual particles without a black hole, something inside our universe must be obligated to pay the energy price disintegrating itself. If we are lucky and that victim isn't us we could generate energy even after the Heat Death of the universe. Just pray to not be the next victim of energy price. [Answer] **Maybe** Assuming all mass and energy don't collapse back in on themselves due to gravity and the universe resets with a big bang. (Leading to the separate question of how do you survive the Big Bang) The entropy and disorder of any *closed* system is always going to increase. The universe will eventually degrade to a random jumble on neutrinos and photons of progressively lower energies that spread away from each other occupying a larger and larger space. The hyper-advanced life that you posit might be able to make the cold scatter universe livable by changing the fundamental assumption of closedness. Opening the bottle as it were to another universe would allow for the importation of yummy highly structured and ordered matter and energy. This would decrease the entropy to the hyper-advanced life's universe and increase the entropy of the other universe by a greater amount so everything is cool physics wise. The owners of pilfered stars and galaxies would probably disagree though. [Answer] I offer as an answer, this quote from Daniel Moynihan: "everyone is entitled to his own opinion, but not his own Facts..." To suppose that a Type III (Or greater ) Civilization has an understanding of Physical Laws superior to ours is a given, however they are the *same* laws we have. Entropy flows in a single direction, *only*, therefore, No, they could not. For an interesting side read ( only 13 pages) see Isaac Asimov's brilliant short story " The Last Question" - it addresses a nearly identical question as you have posed. [Answer] **Maybe** We currently think that entropy is inexorable. That the universe will certainly continue expanding and cooling, and eventually all that will remain is an incredibly sparse expanse of fundamental particles a fraction of a degree above absolute zero, no matter what we do. But we've only been really studying the universe for a few hundred years. I think it's far too early to say with any certainty that the end of the universe is actually truly unavoidable. We have trillions of years left until the stars burn out, and even that isn't the end. We could have civilizations around black holes, living on the Hawking Radiation, which would also last for trillions of years. And during all this time, we could be searching for a way to reverse entropy. Sure, we haven't found a way to do that given ~400 years of study. But how about after 10^12 years? [Answer] **We don't really know.** Our current models of how the universe works say the answer is a definite **NO**. As Joe points out entropy is one directional. The trouble is all we know about the universe are models. Even if we ignore the pure philosophical questions of a Plato's cave, the thing we call Laws in physics, Conservation Laws, Law of Entropy etc. are really "just" models/theories. (Got rid of gertruding here) The models we currently have we've been developing for, very optimistically, 4000 ($4\*10^3$) years. We have at least 400 ($4\*10^8$) million years before the sun becomes a problem for us in terms of it's own decay (it won't decay for much longer but that's an order of magnitude guess at when we start having trouble). We are talking about 5 orders of magnitude difference here. Given the knowledge we had of the universe even 400 years ago vs. now, the answer to "Will the models we have now still hold after another 40000 years?" seems completely unknowable much less 400 million years in the future when we must confront our sun or the couple billion years when we start having to confront deaths of many stars. [Answer] Yes, and there's two or three ways that require finagling. The first is to let it happen and become a spontaneously occurring omnipotent brain that decides the heat death never happened. This, although pretty dumb, is based on an actually theory in physics. Essentially, since time scales will be infinite after the heat death of the universe, everything can and will happen so this is plausible. Perhaps a sufficiently advanced civilization would be able to figure out how to do this intentionally, and how exactly the heat death didn't occur. The second is to simply find another universe or dimension, and use that universe to get rid of the entropy in our universe. Entropy is always generated by everything. That means that in a closed system like our universe it always rises. Finding another universe or dimension would give the aliens a way to make our universe an open system. That means, like with all other open systems, that the total entropy can be lowered even though entropy is always generated. Functionally, this is literally just lowering our univers's entropy by putting it somewhere else. A "or third way" would be limiting the amount of entropy created by unreasonable levels of micromanaging followed by handing the issue to some other hyper advanced civilization. This would be the universal equivalent of the "Kicking the can" approach. Certain governments consider this a solution, while individuals usually see this as an easy cop out. [Answer] The real answer is, we dont know. But if it is possible. Vacuüm energy is a likely candidate: <https://en.m.wikipedia.org/wiki/Vacuum_energy> One theory about the universe is that it first started as a quantum fluctuation. If you read "implication" of the wiki page it may be that Black holes are theoretically creating matter on its event horizon by sucking up either the particle or antiparticle before they can annihilate eachother back into nothingness. This wouldnt stop entropy, but it would be a way for matter and energy to enter the universe and keep it going. [Answer] Everybody so far has focused on the universe-scale problem. I will try to talk about smaller scale: solar system-level For life on Earth to continue to exist, theoretically there is no need for any other star to be still burning other than the Sun. If all the stars in Universe are dead but the Sun is still running strong, we're fine. The night sky will be dark, but that will not be much of a change from what a city dweller sees today because of the light pollution. So the problem is smaller: keeping one star running. The Sun produces energy by using a fusion reaction: it fuses two atoms of hydrogen to produce one atom of helium and a ton of energy. When most of the hydrogen in the Sun is gone, the Sun will start fusing helium and it will start growing large enough that it will engulf Earth, and turn into a red giant. To keep life going on Earth, the alien race would have to have a technology that restores the hydrogen in the Sun, without any catastrophic side effects (exploding Sun, or massive gamma radiation, or anything like that.) While something like that would be a massive undertaking (and I have no idea what it would take to do it), it seems to me that this is a much smaller problem than keeping the entire Universe alive, and possibly achievable by a much more scientifically advanced race. [Answer] **Maybe** See, the whole idea behind heat death is that since the universe is expanding, matter will spread out and eventually reach an equilibrium. *If* our super advanced aliens could somehow reverse this expansion, they could cause an artificial 'crunch', where all matter is again reduced to a single, bright point. And from there the big bang would occur, and Bing bang boom heat death delayed. How the aliens would go about this or even persevere in order to enjoy this newly re-created universe is definitely beyond me, as I have not based this portion of the answer in real scientific laws. They could always just delay the inevitable. If these aliens found particles with negative mass and energy, as outlined in the [Newsweek article](https://www.newsweek.com/time-travel-possible-wormhole-black-hole-astrophysicist-715038), the aliens could create a wormhole connecting two different points in time, and simply travel back in time, effectively delaying heat death forever, at the cost of being stuck in this small loop of time. This is entering the territory of theoretical physics, though. In short, without the use of theoretical physics or fantastical means, these super advanced aliens cannot stop the heat death of the universe from occurring. > > **Sources** > > > [Time Travel Is Possible Through Wormholes—but You Can Only Ever Go Backward](https://www.newsweek.com/time-travel-possible-wormhole-black-hole-astrophysicist-715038) > > > [Answer] i once read a story with similar problem, summarizing from memory (if anyone recognizes it id appreciate the title and author) Some billions of years ago the basic constants of the universe were different, in such a way that the universe was way smaller, and its fate was to collapse back onto itself to result in a new big-bang in not that long. The universe was housing only one very advanced species which take an issue to that scenario and developed a way to change the universal constants in such a way that the universe would expand forever, thus not avoiding the death of the universe per-se but postponing it to way later. A consequence of this action was that those changes also affected all of then-existing physics and basically would mean that that alien race had ceased to exist. So the idea would be not to make the aliens save the universe from current death scenarios but to have them prevent something even worse or earlier. [Answer] What if our universe is just a pocket universe used to harvest energy from. We don't know how long until we are disposed like an empty battery. That disposal, it probably means death to our universe. --- It was quite a pleasant night. Kinda hot for this time of the year but still pleasant. Suddenly the City went dark. All of it. The City never was dark. For centuries the lights didn't went out. Until now. I stood there, in awe and uncertainty. This must be a dream. My comm device suddenly screamed at me, ordering me to report to closest emergency station. I had a faint idea that those things could turn themselves on, in cases of highest emergency, but never saw it happen. Well, i never saw the City blackout too. Everyone at the station was clueless, some helpers even terrified. Commander appeared before us, but before he could start the breefing one of the rookies screamed "What the hell is going on? How comes the City is dark?" "There was an accident at the power station. One of the pocket universes become unstable and broke though the containment field" the commander responded without even lektioning the rookie. Things were way out of order to waste time on discipline. "No-one know what exactly happened, but the universe detached itself from the stem and is rapidly expanding into our own space. The reactor core is already gone, and if the expansion rate keeps entire City will be gone in two hours." commander continue. "How do we stop it?" i shouted "The scientists don't know. The containment field cant stop it anymore, the pocket just ignores it. Its a lost cause. We already lost two teams in the power plant trying to set up a perimiter." He paused "Those were good people." he nodded to himself. Raising his voice he proclaimed "Just so you all understand: this is an evacuation, we get everyone off this planet and probably out of the entire system." "We just run and leave everything behind?!" asked the guy beside me in disbelief. "Yes, we do. We played god and this is our punishment." [Answer] > > If Big Rip doesn't happen long before that then the "heat death" situation could be avoided **if there is a method or mechanism to regenerate hydrogen atoms** from radiation, dark matter, dark energy, zero-point energy, or other sources so that star formation and heat transfer can continue to avoid a gradual running down of the universe due to the conversion of matter into energy and heavier elements in stellar processes and the absorption of matter by black holes and their subsequent evaporation as Hawking radiation. > > > – [Heat death of the universe](https://en.wikipedia.org/wiki/Heat_death_of_the_universe) > > > [Answer] Easy. Build a smaller universe. The heat death of the universe is only a thing at scales on the order of humans. However, as space as we know it expands, and entropy gets very large in a box the size of our galaxy - entropy in a box with an inscribed photon remains yet small. The energy contained in that box is yet orderly and compact. As the Planck Length expands along with space, who knows what will emerge from that tiny photon, and what physical constants will govern the world in which it exists? Since the photon is on the size scales of light as we know it, the speed of light as we know it is moot in photon-world, and all new interesting physical constants govern material relationships in the photoniverse. Perhaps there are even tinier particles of micro-photons within the photons that travel at the speed of micro-light. As space expands, and the heat death of our world really sets in, the size of a micro-photon might now be comparable with the size of the photons of ages past, and the speed of micro-light might be the new speed of "our" light. From the point of view of anyone living in the photoniverse, their entire reality would have originated sometime around our lifetime, when their entire universe fit into the space of a single particle.... Of course, I wouldn't bank on it being anything like the universe WE live in, or even anything at all, but this is Worldbuilding stackexchange, so some imaginative liberty is in order. [Answer] This is a very deep question and from a formal scientific basis we indeed do not have adequate information to formulate an answer. However the Hindu philosophy (and some others) instructs us that there are various 'levels' of creation that encompass the respective level below. The Hindu philosophy (perhaps others, I have not had occasion to investigate) also tells that at certain periods there are 'Lesser Dissolutions' and '[Greater Dissolutions](https://en.wikipedia.org/wiki/Pralaya)' that are used to reset the levels below a certain point. Various mystics have described these things in times past and some a bit more contemporaneously. The time frames are long, it seems some of them are of the same order as [the age of the known universe](https://en.wikipedia.org/wiki/Kalpa_(aeon)), it makes one think a bit. Perhaps the 'Lesser Dissolution' corresponds to what we in science expect to happen to the known universe at the time of the 'Big Crunch' and this is cyclic and part of the philosophy. While all of this is diverting the telling point is that the souls that have reached a level that is not subject to that turn of dissolution will persist while all the souls in lower levels are in essence 'reset' and have to start their path to god realisation anew (sort of like stage extras in the play of life that are just there to help the main cast) from single cellular organisms over millennia until they incarnate into self aware beings and can strive to reach the higher levels. For this reason the Hindu philosophy places a fair amount of emphasis on spiritual advancement to achieve access to those levels that are safe from the Dissolution. So in essence the aliens are the denizens of the higher levels and their emissaries, the various Masters, who come to visit and the technique they use to avoid the heat death of the universe is to maintain a backup copy of their soul in a fire proof safe, knowing when the fire is coming. The Masters trying to get us mere mortals to also try to prepare a backup. Granted this is not a scientific answer unless one delves into the 'Science of the Soul' movement but is could make for a great storyline that can cover the life of a universe and still have observers. [Answer] Yes, they can prevent it for a long time, but maybe not forever. We are barely,if even that, cave people compared to your aliens. It is highly possible that they could save, if not the universe, large portions of it given how sparsely populated it currently is. Most of humanity major inventions have been discovered in the last 100 years, sure galieo, newton, and etc had discoveries but not at the level and rate we have achieved in the last 100 years or so. Right now, we think "dark energy" which is a replacement for "don't know" is pushing the universe apart. Clearly the alien race will have a far better if not complete understanding of this. Possibilities 1. Destroy dark energy 2. Move the dark energy around 3. Convert the dark energy Converting "dark energy"/"dark matter" to real matter will cause it to again produce gravity. Thus things will start pulling themselves together. The universe has expanded a lot so, they can slowly contract it over millions of years if necessary. Re-distribution matter will also help. For example, if you have a force you can't contain pushing the universe apart throw a black hole/sun at it. Boom, a giant source of gravity to either counter-act the forces pushing the universe apart. The sun/black hole may also be able to convert the unknown enery/matter back into real matter as a bonus. Also the alien can probably pull energy from other universes, and possibly from the fabric of space time itself. They can probably convert energy to mass and visa versa further extending there dominance on the universe. So there only problems are running out of mass or energy at some point down the road. Side note: We don't really know what is going on at the edge of our universe. We can see the light, measure the forces, and etc but all of that happened 13 billion years ago. We have no idea what its doing today. [Answer] We do not know what is outside of the universe. If we could say nothing is out there, then we would have a strong indication that heat death will be the end. BUT, our Universe and everything within it is the Universe with every law and particle we know. So if there was something outside of it...we would not know. Point is, we have no real proof rather we are expanding like the surface of a balloon or growing like a crystal. If we are growing like a crystal... the heat death is unlikely as our growth would be attributed to "feeding" on something else (or even being fed by something else)... with the food no longer available, the expansion would probably stop. Another thing to note is the idea that we could live in a simulation. If that is the case then the creators could have a program that would prevent heat death by changing the laws of the universe. The idea that gravity was a repulsive force during the big bang can be viewed as an example of them changing a law. Or maybe they would not need to directly change a law... perhaps the laws are already designed to behave differently under specific conditions. [Answer] It depends. If multiverse is a reality then they may be able to travel from one universe to another, if instead there is only one Universe and taking into account that it is expanding at a higher pace than expected then most probably they wouldn't be able to stop that since they would need a huge amount of energy and that energy is spread at higher distances as time goes by. If creating wormholes is a posibility the amount of energy to create them would also be huge and they should be able to get more energy the place where that wormwhole takes them. So I really don't think they could. [Answer] If your future aliens could manipulate space-time then yes, I see no reason why not. I'm imagining the use of technologies to fold the vast spaces between galaxies into pocket universes, then expel any energy contained within out into the Prime universe. Essentially creating something resembling a White Hole pouring energy in the form of radiative heat in vast quantities into the now much smaller universe. It'd be sort of like giving the universe a Nip and Tuck in its old age, or if you prefer, wringing out a towel to collect water. An alternative is to do this to the *entire* universe all at once, piping all of its energy through a pinchpoint and out the other side to create a new universe with a new Big Bang. In concept like forcing a playdough sculpture through a pipe, the sculpture is destroyed but it's formless again and ready to sculpt anew. The most important point is that this approach doesn't violate thermodynamics that I can see. ]

[Question] [ **Locked**. Comments on this question have been disabled, but it is still accepting new answers and other interactions. [Learn more](/help/locked-posts). **A time machine malfunctions and spits a traveller from ~2015AD out in 500BC northern France. With nothing but the clothes on his back, and minimising contact with the locals (as that may risk altering timelines), how can he best determine his approximate location and time period?** His pockets contains only coins, a wallet with both Canadian and US money and credit cards, keys, and a few dirty tissues. He's wearing business attire - black jacket, black shoes, tie, button up blue shirt, nice pants. He knows a little bit of modern French (He can navigate a Quebec café menu), and a few touristy Spanish phrases, but not the languages that may have been spoken in this time period in this place. He doesn't know Celtic, or Greek, or Latin or Italian. He probably can't even recognise them if he hears them. His main language is Canadian English. He's never been to France but has definitely read the odd relevant Wikipedia page. He is in his 40s, and has few cuts and bruises from the time-mishap, but otherwise is in great physical condition. He's a star at his local gym where he can basically bench press the other customers. He's mentally sharp, ex-military, ex-police, basically [the guy from this related question about a tough smart guy making a time determination](https://worldbuilding.stackexchange.com/q/185746/78800) but a few years senior. His time machine has previously only connected his 2 offices located at two different points in history, where he has separate past-and-present identities and has been slowly transferring knowledge back in time to accumulate wealth for himself through a series of lucky stock market plays and "insightful" patents. He has no idea why it malfunctioned and sent him to some random point in time on the other side of the globe. [Answer] ouf, hard one. There are MANY ways to obtain this detail, but all of them require in-depth and specialist knowledge by the traveler. There is a well-established local population, though very sparse by modern standards. Iron age technology. Somewhat warlike, hill-forts with attendant settlements. Language Celtic and Germanic, with some Greek along the coasts. Your traveler will understand, even recognize, nothing from the language. Romans exist, but only as rumors of a tribe over the mountains, they would have no influence in France yet. Geographically, he will see forested hills, and forested plains, and swamps, and grassy plains. Maybe get a glimpse of some true mountains to the south. He should be able to get a rough idea of latitude from the sun position and at night from the stars. But none of this will tell him whether he is in Europe, or Ukraine, or China, or North America. If he was a gonzo amateur astronomer he could get exact latitude and place the date to within 50 years, by measuring the deviation of Polaris from the celestial northpole, but how many of us know how to do that? And this would still give no clue as to longitude. Plantlife will give him both location and timespan, but... Just how many people can even tell the difference between the various plants' subspecies, much less recall where they originated and when the plants were spread by humans to other regions? For example, the absence of rice and maize and potato but presence of lowgrowing Barley and really tall Wheat will tell him he is in central Europe between 1000bc and 200bc. But... can he even see the difference between Wheat and Barley of any kind? Most people cannot. Unless your traveler has specialized, obscure knowledge in either ancient languages, or historic biology, or astronomy with a keen observation eye and knowledge of Earth's orbital precession, etc... He will most likely remain rather lost. And also, will likely not survive long enough to learn. Primitive tribes tended to behave unkindly to strangely-dressed people speaking nonsense, and the wildlife will only care about his calories, not his origin. --- Example: If this were to happen to me, I would die. But give me an armed escort, and some survival supplies... I could determine north/south hemisphere and rough latitude within one day, from sunsticks. This will also give me compass directions more accurate than any magnetic compass(who knows *where* the magnetic northpole would be, at unknown date in the past?). I could determine the latitude within the first cloudless night, accurate to about 2-3 degrees. 500BC is an opportune time, as right about then (+-80 years) the celestial north pole was squarely on the brightest star of the little dipper's bowl. So after one sunny day and one cloudless night I would know my latitude, and the date. (Yes, I'm a bit of an astronomy geek). The Climate and Plantlife would tell me I'm somewhere in Europe, or western Asia. Possibly even regions of China. But nothing better than that. Ditto for observing or interacting with natives. I know in theory what languages they should be speaking, but to actually *recognize* them, much less intelligent conversations? Nope. Pity we are not a bit further south, I would recognize the old Latin of the Romans(although they are more like their ancestors the Etruscans than the Imperial Rome we think of). Would not be able to speak it well enough to make myself understood, but at least they would see that I'm trying. But the older Celtic and Germanic languages? I have no clue! So, for my specific case, I would be able to place the date and latitude very closely, the longitude only +- 6000 kilometers. And that's from someone having specialist knowledge (astronomy), and keen interest (ancient civilizations and sciences) [Answer] ### How to tell you're in northern France? You're going to need to explore a bit a spot a landmark that you can recognise. You have no idea when you are so this could be either a town name or some writing style or something visually familiar - otherwise you're waiting for information to come to you (which it never does outside of the movies) or giving up. The best advice I have is to either walk in a spiral slowly exploring and expanding out from where you landed, or head straight towards the nearest coast (follow water downstream). Both paths are decent attempts to try to recognise landmarks or named ports. Assuming you're north of Amiens but not in Belgium (because that's where Google scaled the map when I searched "northern france"), the most interesting map feature is the coastline towards to your north-west, and also towards the coast, so you should find it with either strategy. [](https://i.stack.imgur.com/VobJn.png) When you get there, the white cliffs of Dover are fairly unique and notable out to sea. [](https://i.stack.imgur.com/Qr1Ka.png) I do not know if this view is *unique*, but for much of the coastline in the north of France, for Berck to Wimereux to Dunkirk, you should be able to see some weird white cliffs on the horizon. I've been to this area and can confirm they are very visible so long as there isn't fog or rain over the channel. I think this is the only way you can determine your location in under a month in this rough area without knowing when you are. (You could wait up to a year and get a very accurate latitude reading at the equinox - buts that's a long way away). ### How do you tell it's 500BC? This is only accurate to a few hundred years, but if he has a decent common knowledge of cultures of the world, and has determined hes opposite Dover on the northern French coast, hell have the shock of his life when he looks at the sky next. He will see part of the southern hemispheres culture clearly in the sky of the northern hemisphere. He can then know an approximate timing from the fact that you can see the [Southern Cross](https://en.wikipedia.org/wiki/Crux) from France. Two very bright pointer stars pointing to the arms of a cross: [](https://i.stack.imgur.com/r0EDW.png) With the feet of the cross pointing southwards-ish. In the time period you left, this was only visible in the Southern hemisphere, it's on the Australian and NZ (and more) flag. If it was visible in Europe, why is it part of Australias identidy? And Why is this up so far North? In one of the Wikipedia pages you read you happened to note that the [Southern Cross was visible as far north as Britain up until 400BC](https://en.wikipedia.org/wiki/Crux#History). I've read a lot of random wikipedia pages and its nice to imagine that all that stuff will one day be useful. [Answer] # He Doesn't First, our hero is an ordinary 21st century man. Gym rat, has had military and police experience though no stated special survival skills. He is basically fit but has travelled into the deep past without the knowledge to survive the first 48 hours of a plunge into the deep darks of any primeval landscape, chances are good your time traveller will either be killed by a native or be eaten by a bear. Secondly, without soap and clean water, those wounds will fester. Without antibiotics, those festering wounds will become infected and perhaps balloon into gangrene and sepsis. This is the wilds of primeval Europe, not the local provincial park with sanitary restroom facilities. Thirdly, without a source of clean and safe drinking water, your time traveller will almost certainly begin to suffer from Sjorgall's Revenge and will end up squatting trousers down more often than trying to find out where he is trousers up. Best plan of action he can do is just find a comfortable spot to lay down, pull out that wad of Canadian twenty dollar notes and inhale the maple syrupy goodness as a last reminder of home, because there is suddenly a whole lot less life before him than there was yesterday evening. (But that's what you get for using a time machine to play the stock market!) The long and short of it is: your time traveller will make for a very smartly dressed corpse. [Answer] In my opinon he shouldn't be able to prove his is in Gaul (not France), but he could be able to determne he was in northwestern continental Eurasia fairly easy, if he meets natives and they don't kill him. The first men he meets would probably be hunters or farmers, and so probably be rather tanned, but he could probably tell that they weren't very dark skinned people. And their facial features, if he gets close enough to see them clearly without being killed, should look rather Caucasian instead of belonging to other races. If prehistoric men take him to their camp or permanent village, or if he meets women and children gathering food in a forest, or working in fields, he should note that the women and children are lighter skinned than the men, since they spend more time indoors and haven't been tanned so much, and since women tend to have lighter skin then men in order to make more vitamin D for the health of their children. Thus he should calculate that he is in northern Eurasia, and also in western Eurasia, since there would be few groups with such light skin in East Asia. So if he can tell his latitude by the height of the Sun at noontime during this season of the year, and by the stars at night, and if he doesn't see any large bodies of saltwater to the north, he can guess that he is in northern Continental Eurasia. If he can tell his latitude closely enough, he might know that he is near the latitude of the English channel, and maybe even be certain that he is south of it. So he might be able to deduce that he is in continental Eurasia, somewhere south of the latitude of the English Channel, along a belt of latitude which stretches from northern Gaul east for thousands of miles to as far east as he imagines there might be people who look like that. And he should be able to deduce the rough historical era by the technology of the natives, if they don't kill him. The use of iron spread north and west in Europe, and the Iron Age in remote Ireland, among the last regions to use Iron, began about the date he finds himself in, around 500 BC. Thus the use of iron should be common in northern Gaul by the time he arrives there. So the use of iron tools & weapons should tell him he is in a time period after about 1000 BC. Lack of evidence of Christianity or Islam should tell him that the date is before either religion came to the area, and so before AD 1500 at the latest. And lack of any evidence of classical culture should tell him that it is before the time that the Romans conquered this unknown region - if they ever did. Most parts of Eurasia that far north were never part of the Roman Empire. And if the natives don't kill him and he learns a bit of their language, he might possibly deduce that he is in northern Gaul from their description of a channel to the north and a large island beyond that channel, and of an ocean not too far to the west. And I think that some answers exaggerate the probability that bears or wolves would eat him, since the natives would have been hunting bears and wolves for more than 10,000 years and they would usually avoid humans. [Answer] For location, you basically need him to get lucky. He happens to arrive somewhere that has a world-famous landmark that existed 2,500 years ago. In France, that probably means either the White Cliffs of Dover or the Lascaux cave (which was buried in recent history until 1940, but might have been more accessible 2,500 years ago) (I hope he has a torch/flashlight on his keychain). Edited to add: There are also the megalithic complexes at Carnac in Brittany, but unless he’s sufficiently expert to recognise a much younger version of them, that just tells him that he’s somewhere in Britain, Ireland or Brittany. A Canadian layman would probably think “Stonehenge” and be wrong. If he can arrive further south and knows a bit of history, Marseille exists in 500BC and is a Greek city called Massilia, which name he can probably get from the locals with mime and sign language. [Answer] We'll presume the traveler carries a smart phone -- even six years ago in our timeline, these were pretty remarkable devices. Even with zero connectivity, most installed apps will still work, at least as long as the battery charge lasts. If he's thinking, he'll put the device in "airplane mode", shutting down all the radio hardware to extend battery life, as soon as he realizes he's in an unknown time/location and has no signal -- perhaps checking for signal periodically before he knows when he is -- or he might well be in the habit of doing so before going to his "early" office anyway, since if it's before the early 2000s there won't be any compatible signals. If he has any kind of star map software already loaded, he can use that to get close on the date (at least to the millennium, likely to the century) based on what constellations are where in relation to others. Once he has that, he can use things like sunrise/sunset times to get an approximate time of year, then solar noon angle to arrive at latitude -- this will take at least some days, so being able to use his smart phone for the task will depend as much on battery conservation as on the software already installed. I doubt he'd be able to get as far as "northern France" based on sky data alone without a fairly precise time reference, however. Something like "36 degrees north, give or take two or three degrees" is likely as close as he'll come. However, the climate didn't change all that much from the 5th century BCE to the present (aside from the Little Ice Age of the 14th century or so), so he might be able to recognize vegetation common to Western Europe to narrow things down to either France, or Italy/Corsica, or the Balkans -- and separating those based on landforms and vegetation shouldn't be hard, if he's traveled a bit. So now, our lost traveler has some idea when he is, and knows roughly where he is. Unless his time machine is one he carries with him, he's probably still stuck; he can't leave a message for the future without risking massive alteration to the time lines. [Answer] If your traveler realises that he has moved in both time and space, but is still on the same planet, all of which you've already either implied or specified, he's already in a better position than someone without that knowledge. If he can survive and remain unnoticed for two days and the skies are cloudless, he can at least determine the compass directions, whether he is in the northern or southern hemisphere and the approximate time of year using primary school level knowledge and good observation skills. It would just be tedious. Tracking the path of the sun, determining the length of day, etc. - sun sticks, counting seconds, finding the spot in the sky the stars seem to rotate around, all the fun stuff. If he's wearing a watch or has a cellphone and it's still working, you can eliminate a lot of the tedious counting, too. Seeing the Southern Cross in the night sky after already knowing he's in the Northern hemisphere will tell him he's somewhere prior to 400BCE, spotting any worked iron will tel him it's definitely after 1000BCE, and probably later than 800BCE. If he spots a Greek trading party (up from the South) he might know it was between 600 and 400 BCE, i.e. after the establishment of Greek presence on the Medetiranean, but prior to the disruption of trade to the north, but that might be pushing it. Since you specified avoiding the natives, well, not much else he can figure out easily. For anything more detailed, you'd have to either give him specialized knowledge & skills or have him get lucky. There are many ways to do this. You can drop him somewhere he's been (which you already ruled out) or somewhere he has extensive knowledge of, which has a distinctive natural or archeological landmark he can recognize. This would be easiest if he's near the coast, as there are a few distinctive areas such as the white chalk Etretat cliffs, pink granite coast, view of the white cliffs of Dover accross the channel, etc. heck, maybe Mont San Michel is even recognizable. Maybe he recognizes a piece of coastline, distinctive rock formation or whatever because he once reasearched the area thinking to plan a vacation there, or you dropped him in the middle of the Carnac stones in the northwest or near the coast of the English Channel in the north where he can spot the cliffs of Dover. Or he was fascinated by the allied landings in Normandy in WWII and recognizes something he saw when studying maps and photos of the area. You could make him a survivalist type who knows everything there is to know about finding your way anywhere - including in a doomsday scenario where there was polar reversal .... He could be a history buff or just a fan of celtic history and be able to tell from the style of the hill fort spotted in the distance that it is celtic and from around 600-400BCE. Or a Julian May fan who has a fascination with the geography of France throughout history from the Pliocene up to the present. Amateur botanist or lepidopterist who recognizes a plant or butterfly native to the region, astronomy geek who can determine the date from the differences in the night sky due to precession, there are many possibilities. Build a believable backstory for why he knows it, and you can give him a method he can use or a lucky break to do the job for him. [Answer] I will focus on the main question: the easiest way, from a storytelling perspective, to have the time traveller identify his location, is to have him accidentally stumble on a relevant landmark. For Northern France, two come to mind: * the White Cliffs of Dover as seen accross the English Channel (already mentioned above, and a very iconic landmark, that I would except a Canadian to know about, given cultural links between Canada and the UK) * the Carnac Stones (not so Northern, as it's in Brittany, but interesting as a unique man-made landmark that did already exist in 500BC). A bit of a niche piece of knowledge, but since it's a popular tourist spot, maybe our guy got a friend send him a postcard from there while on holidays. As for the date, I guess spotting some locals would be your best bet. The lack of Roman influence (don't speak latin, no Roman roads, etc.) would tell you it's BC, not AD. But the fact they have iron tools (not just bronze) would indicate it's the Iron Age, so circa 500AD (plus or minus a few centuries...) is a good bet. I don't think you'd be able to get a more precise date. You need to be a bit of a history geek to know all that, but this is primary school level of knowledge for British kids (not sure about Canada), or stuff you could easily pick from a BBC TV documentary. Edit: you could have your guy gather clues about the date without meeting people directly, by stumbling on relevant artefacts (someone's lost bag). E.g. a few iron tools (or other metal objects, like a brooch, a belt), and some celtic coinage, but no roman coins. [Answer] His best chances? Through dumb luck he lands in a religious sanctuary of some kind at a point in time at which it will be clearly seen that he appears out of nowhere. His foreign clothes and strange talk are therefore manifestations of the divine. That gives him a much needed in with the locals. Also, it gives him the best odds of finding locals with astronomy knowledge, which was needed for calendars. (Both the Greeks and the Romans, though a bit later, said that their religious leaders, the Druids, were good astronomers.) He could pose as judging how well they have studied the matter on behalf of the gods. (That is, fit in with their culture to minimize change.) He should devote himself to learning the language and the places. His best bet would be traders. Some place names still have continuity, and he can work out history. Mind you, this was the days of the Persian empire, though Rome was expanding. You'd have to give him some knowledge of history to work it out. [Answer] Finding the location would depend on luck and knowledge, finding the time on the available knowledge. **LOCATION:** Assuming he has a detailed knowledge of the local geography, he can search for relevant landmarks. For example being able to see the Mont Ventoux would be a strong indicator he is somewhere in Provence. While searching for food and shelter, he should try to finding a vantage point from where he can see his surroundings and try to find some relevant feature, like a river, a lake, a mountain. I am not familiar with the landscapes of northern France to point a few of them. If he manages to find it, he can try to communicate with the locals and find the name they give to it. If he has the knowledge, he can track back the name of the landmark to the location. For [example](https://en.wikipedia.org/wiki/Meuse) > > The name Meuse is derived from the French name of the river, derived from its Latin name, Mosa, which ultimately derives from the Celtic or Proto-Celtic name \*Mosā. > > > **TIME:** Once he has determined the approximate place where he is staying, he can browse his memory and find a list of relevant astronomical events which can help him narrow down the period in which he is. Something like an eclipse, a conjunction or the celestial coordinates of known constellations can help him find the period of time where he ended. Quicker and rougher, he can simply check the tech level of the fellas he will meet on his venture. If he manages to not get killed, he can tell if they are stone age, bronze age or iron age, and if iron age also which culture they belong to. All in all, it would require him to be some Pico della Mirandola to be able to store and retrieve all those information in his memory. [Answer] If the time traveller spies on the people, then there will be druids performing ceremonies, perhaps some holy mistletoe someplace, people wearing silver, bronze and gold torques, rings and bracelets, celtic inscribed rocks, fine bronzework, weird celtic military and decorated helmets, plaid clothes, perhaps someone running off saying Teutatis, the name of a god. Perhaps the most obvious ways to tell that they are in France will be if they walk a while near the charriot tracks and sees lots of dolmens and obelisks. Perhaps the traveller is questioned and held captive for long enough to recognize vaguely some words like "Brigand"(brigantii tribe), "rocs", "Chariot"("Kars"),"Aurocs","mouton","ambassade","bouche","chamois","gobelet","Glaive","lance","javelot"... carpenter/carbanto, chene, dague, ... Some words have slight resemblence to the celtic of 500BC, and it would be possible to figure some of them out. Perhaps you can hear geographic names like the name of a river and places, Bayeux, Armorique, Ardoise, Amiens, Bourbon, Cantal, Auvergne, Geneve, Caen, the Parisii celts, which are all words that come from pre-roman france. For the timing of 500BC, there was a celtic calender started in about 800BC and documented by romans, but it's very mysterious. The locals wouldn't use coinage until about 350BC, they would trade in semi precious metals and exchange livestock, it's the middle of the transition from bronze to iron, some some of the iron working could still be a bit crude, and still experimenting with iron to make it better than bronze. [Answer] **Hide a GPS-like system at some known time in the past for emergencies exactly like this** Send back in time and hide a long-lived hidden transponder system that contains an atomic clock and trilateration capabilities. Possibly on the moon where it won't interfere with history. Unlike GPS, to keep itself hidden and to preserve power, it only responds when when polled responds by giving you the time and your location. You could also design an electronic mailbox into the probe so users use it to relay an SOS message into the future to call for rescue. Whatever agency in the future maintains the probe can monitor the mailbox. [Answer] ## Identify the Culture If your time traveller is an ancient cultures enthusiast, he could figure it out without actually being able to talk to the locals. He'd just need to see them and their artwork. ### Hair Styles The Ancient Gauls are known for having a distinct hairstyle that to the best of my knowledge is not common in any other culture in history. Using lime, they would style their hair into white spikes or horse manes. The closest pre-modern civilization would probably be the Mohawkians, but they plucked the sides of their head to create a strip and did not actually stand them up or dye them white; so, if your time traveler is not very well educated he might erroneously assume Native Americans, but not only if he does not know anything about the Ancient Gauls. By seeing both white horse manes and white spiked hair, your traveler could infer he is probably dealing with Gallic Celts some time before the Roman conquest. This single datapoint will get you a lot more precise than most answers on here and only takes knowing a single piece of trivia that anyone could possibly know. ### The Hallstatt Art Style The hair would tell him where he is, but the artwork could narrow it down much better. The prevalence of iron over bronze would tell your explorer than he arrived after the end of the Bronze Age, but before the rise of curvilinear artwork that rose in the La Tène period. With a strong art history background paired with the clue of the hair, the explorer could further determine the date to be somewhere between 800-450 BCE. [Answer] ## He finds his journal. Most of the text has been lost to mishap and water damage over the years, but what is left gives a sense of his miserable travels across the continent, his brushes with death, his map-making, his recollection and deduction of the rules by which the North Star would pass from (he recalls) Vega to Polaris. Eventually he concluded a great deal about his time and place. But none of that helped him to defeat the key problem that the wake of his errant time machine lands only in close vicinity to one place, one time, one wretched spot in the ancient world, with no trace of the machine to be found or hint of where it went next. And his note that, lacking any other idea, and feeling the ravages of years of injury and disease, he is going to simply keep walking into the traces of the stream that he has mapped until he either lands in the vicinity of his lost machine, wherever and whenever it might have been lost, or arrives ... embedded in the stone, within ten minutes' walk of the place where he first arrived, his skeletal hand protruding and holding forth the journal that will inspire him to begin his researches into a means of escape. [Answer] ## Cave Paintings It might necessitate a change in the story, but let's say your time traveler is visiting one of the many sites in France where there are ancient Paleolithic and Neolithic cave paintings when he gets transported back. Some of these are as much as 20,000 years old, but others are less so. If he sees these paintings in modern times, and then gets transported back and sees either the same cave wall unpainted, or even *sees the person painting it*, that would give a very clear signal as to how far back he's traveled, without requiring any kind of expertise or equipment he happened to bring with him. (Let's say before he was transported back, a tour guide was telling him how old these paintings were estimated to be.) [Answer] Here's some quick ideas: You can work out east and west by it rising and setting easily enough, and you can probably tell which half of the sky it's in. In the UK it's fairly obvious, but since France is at a lower latitude, I'm not sure if that's the case, so he might need to observe the shadows of something during midday to work it out. However, knowing the sun is to the south of him, and that it's not all day or all night, should be a good indication that he's somewhere between the equator and the arctic circle. Places of worship. Looking for places where people worship or bury their dead should give a pretty good indication of when you are. Arabic Numerals were only introduced to Europe in the 12th century AD, and neither christianity nor latin were particularly present before the spread of the roman empire. You're also likely to run into written language of another form: Runes. Your Time Traveller might not know the difference between different types of runes, but gaulish runes look similar enough to norse runes, which most people would probably have a decent grasp on what they look like given how often vikings show up in pop culture, and like the bluetooth symbol. So that should narrow it down to "I'm in northern europe". That's probably the best bet for guessing when and where you are. Wildlife: There are multiple forms of wildlife that should help narrow down where he is to north-western europe. Badgers are a pretty obvious one. European Badgers look drastically different to North American Badgers, which narrows things down to europe and asia, as do Red Squirrels, as grey squirrels were only recently introduced to eurasia. What would really help though is finding a Yew Tree. Yew Trees are very much limited to Europe, and Brittany in northern france is one place they were originally native to. Even if he doesn't know exactly which parts of europe they're from, that definitely narrows things down to a single continent. None of this is particularly specific to "I'm in -5th century france" but it should help determine "I'm in europe and somewhere/somewhen where latin hasn't come to yet" without any specialist knowledge. Although, as others have noted, running into a landmark he recognises like seeing the cliffs of dover across the channel would probably help with nailing down the specific place. [Answer] I think the easiest way to solve this problem is to have an artifact travel with him which gives him the information. It could be the control interface, for instance, which he was holding at the time of the mishap. From it he gets the settings at transference, and thus his own new circumstances. This solves the problem, introduces a potential future plot device (a small piece of technological kit) and requires no further explanation. [Answer] Other answers already pointed out how to determine the geographical latitude, I will give a hint on how to get at the longitude without accidentally landing on a well-known touristic spot: **Birdwatching** The birds are all foreign, therefore he can exclude the North American continent. There is a twin species of crows, Carrion crow (all black) and Hooded crow (black and grey) with a peculiar East-West distribution pattern. By spotting crows the time traveller can decide whether he is East or West of the dividing line. Seeing Black crows he can infer he is stranded in West Germany, France, or South England. ]

[Question] [ I've been doing a little research (including reading Howard Curtis' *[Orbital Mechanics for Engineering Students](http://www.nssc.ac.cn/wxzygx/weixin/201607/P020160718380095698873.pdf)*) because I want to build a solar system with a planet that has a true three-dimensional orbit. Regrettably, I'm not far enough into Curtis' book to answer this question, if it is answerable from it. I understand that orbits occur in three dimensions, however, the examples I've found so far are all 2D in the plane of the elliptic. In other words, the orbit is actually two-dimensional, it simply can be rotated as a flat plane in lots of different directions. **Question:** Is it possible to set up a series of stars and/or planets such that one planet has an actual three-dimensional orbit, meaning the orbit is not flat (two-dimensional) in the plane of the elliptic? *For illustration purposes only* Here's our solar system showing Neptune's normal orbit. Notice that both Neptune and Pluto can be thought of as 2D orbits in the plane of their elliptic. It only becomes 3D when you compare the two orbits. [](https://i.stack.imgur.com/cj3xs.jpg) And here' a modified mock-up showing Neptune's orbit as a 3D orbit (gravity well causing this behavior not shown). Neptune's orbit is no longer on a flat plane. [](https://i.stack.imgur.com/FhMMr.jpg) --- **If you're tempted to edit my question and change every instance of "elliptic" to "ecliptic..." please don't do it:** It is incorrect as "ecliptic" refers the the *solar plane,* not the orbital plane of an individual planet. Pluto does not orbit on the ecliptic plane, but it does orbit on its own elliptic plane. The gist of my question can be summarized as follows: if you press all of the orbits to the ecliptic plane without modifying the basic shape of the orbit itself, what you get in our solar system is a 2D orbital example (the ecliptic and elliptic planes would coincide). If you flatten my example of Neptune, above, it's 3D because part of the orbit sweeps out of the ecliptic plane. In other words, the orbit I'm interested in does not inhabit a single elliptic plane and could not be contained within the ecliptic plane if pushed into it. [Answer] **There are no known orbits of this kind, but they aren't proven to be impossible.** You need to have 3 objects in order to have a 3d orbit, and it's known that the general 3-body problem is chaotic and difficult to work with. However, researchers do explore restricted 3-body problems. In these problems, we assume that one object is negligable in mass to the others (mathematically, we treat it as massless). That means two of the objects orbit in a predictable 2-body configuration, and the 3rd smaller object flits around between them. There are two classes of problems you are looking at: 3D CR3BP and 3D ER3BP. Yes, they gave the names. The 3D part is what you are interested in: the solutions aren't planar. The CR and ER refer to a circular obit restriction and an elliptical orbit restriction, referring to how the large two objects orbit each other. 3BP references the fact that it's a 3 body problem. So you're looking for non-planar solutions with either circular or elliptical orbits for the 2 main bodies in a 3 body problem. \*Phew\*\* First the good news. A shout out to b.Lorenz and [their answer](https://worldbuilding.stackexchange.com/a/122195/2252), because it suggests there's some possibility of it working. The paper [cited](https://www.researchgate.net/publication/283604199_Design_of_transfers_trajectories_between_resonant_orbits_in_the_restricted_problem_with_application_to_the_Earth-Moon_system?_sg=a5tc3YpypXvOBq1fCAQs7OHQZ19kxsictvt4IuVrzRXtDD1VXftWD2-_duA02DgxwWW-XtSA5g) explores a 3D CR3BP problem, specifically the Earth/Moon system. It also has some glorious looking pictures showing 3d movement resonating around these two massive objects, suggesting interesting parking orbits. [](https://i.stack.imgur.com/mUXQF.png) However, there's some bad news.If you note, these orbits get "pinched" in some places. None of the orbits found in this paper were stable. They decayed in dozens or hundreds of orbital periods. For a planet, you need something that remains stable for millions or even billions of periods! Indeed, it appears we have not yet found a stable 3D ER3BP orbit, as of [this paper published in August 2015](https://arxiv.org/pdf/1508.02312.pdf): > > A few families of periodic orbits in the elliptic Hill problem were discovered by Ichtiaroglou [1981], who found all of them to be highly unstable. In more recent work, Voyatzis et al. [2012] calculated a large > set of families of periodic orbits in the elliptic Hill problem, determined their stability and applied the results to motions of a satellite around a planet. > > > Reading the [Voyatzis et al. paper](https://arxiv.org/pdf/1111.3843.pdf), we find that they did indeed find stable ER3BP solutions, but they were concerned with the planar ER3BP problem, not the 3D one. Indeed, it appears that has been enough of a search for 3D ER3BP solutions that the paper pays a substantial amount of attention to periodic ejection-collision orbits in the 3D ER3BP space. Many papers have indeed found such orbits, but by their nature, they cause the small object to pass so close to one of the massive ones that there will either be a collision or the small object will be ejected out of the system. So overall, we've found nothing which prevents us from finding a stable 3D ER3BP solution. However, in the current art, such a solution has yet to be found. The paper I cited does mention that some of the solutions used to approach planar ER3BP problems show promise for continuation into the 3d problem. But, as of publication, the authors had not yet seen this done in any journal. [Answer] [It is indeed possible.](https://www.researchgate.net/publication/283604199_Design_of_transfers_trajectories_between_resonant_orbits_in_the_restricted_problem_with_application_to_the_Earth-Moon_system?_sg=a5tc3YpypXvOBq1fCAQs7OHQZ19kxsictvt4IuVrzRXtDD1VXftWD2-_duA02DgxwWW-XtSA5g) This is for Earth-Moon system, but shows that a small object can orbit two others in a 3d way. And since the third (the spaceship considered) is so small, the other two's motion is nonchaotic. You would need luck to get a planet on such an orbit, but as you see, the article is quite above KSP-level astrogation, thus fulfilling your desire for pain.in the ass navigation. As Justin Thyme's insightful answer pointed out, you would need probably more than a bit of luck, as the almost-planar structure of the solar system is the result of the angular momentum of the gas cloud of which it was formed. Perhaps a giant space station with station-keeping engines would be a better candidate for these orbits, as it would have reason to be there, and means to fight orbital instability and remain there. [Answer] [Lissajous orbits](https://en.wikipedia.org/wiki/Lissajous_orbit) and [Halo orbits](https://en.wikipedia.org/wiki/Halo_orbit) seem to be relevant here. > > Lyapunov orbits around a Lagrangian point are curved paths that lie entirely in the plane of the two primary bodies. In contrast, Lissajous orbits include components in this plane and perpendicular to it, and follow a Lissajous curve. Halo orbits also include components perpendicular to the plane, but they are periodic, while Lissajous orbits are not. > > > As others have mentioned, the "third body" in these three-body problems seems to have negligible mass. These particular orbits don't conform exactly to the example in your image, but they do demonstrate that orbits don't necessarily have to take place in a 2D plane. [Answer] # Try the [Kozai mechanism](https://en.wikipedia.org/wiki/Kozai_mechanism) The basis for the Kozai mechanism is that in a binary system, a third orbiting body - with a much lower mass than the other two - has a quantity that doesn't change in time: $$L\_z=\sqrt{1-e^2}\cos i$$ where $e$ is the orbital eccentricity and $i$ is the orbital inclination - the amount it tilts in comparison to a reference plane. As the planet orbits the main body - in this case, a star - the second body perturbs it such that the planet's eccentricity and inclination oscillate in time, with a characteristic period. Both orbital elements are changing, but $L\_z$ remains constant. Therefore, even though the planet's orbit is at a given point in time Keplerian, it's actually following a much more complex path in three dimensions. There are two scenarios where this is commonly considered: * A Jupiter-like planet perturbing minor bodies, such as asteroids. * A brown dwarf perturbing the orbit of a planet orbiting a companion star. In your case, I think adding a brown dwarf would be a good idea. If the system is largely compact with the exception of one planet, and the brown dwarf is far enough away from the star, the inner planets wouldn't be affected, and their orbits would be stable and Keplerian. The farther-out planet, with the greater period, would be far more likely to be perturbed by the brown dwarf, and would indeed execute a strange three-dimensional orbit. Here's an example of how eccentricity changes with time, from [Takeda & Rasio (2005)](http://faculty.wcas.northwestern.edu/rasio/Papers/106.pdf): [](https://i.stack.imgur.com/sNNMc.png) Figure 2, Takeda & Rasio. The two curves show two different scenarios, illustrating how the Kozai timescale can be large or small. If you know $L\_z$, you can calculate $i(t)$ from the values of $e(t)$ for any given $t$. # Example: TRAPPIST-1 The [TRAPPIST-1 system](https://en.wikipedia.org/wiki/TRAPPIST-1) is an appealing example. It is extremely compact - all seven planets have semi-major axes less than 0.07 AU. They're held stable by resonances. What if we were to put another planet in orbit at, say, 2 AU, and to add a brown dwarf companion at 8 AU? The mass of TRAPPIST-1 is $0.089M\_{\odot}$; a brown dwarf might have a mass of $0.02M\_{\odot}$. Kepler's third law tells us that the planet's orbit is 9.48 years. [The period of Kozai oscillations is](http://large.stanford.edu/courses/2007/ph210/raman1/), in the case where the brown dwarf is much more massive than the planet, $$P\_{\text{Koz}}=P\_p\frac{M\_\*}{M\_b}\left(\frac{a\_b}{a\_p}\right)^3(1-e\_p^2)^{3/2}$$ where the subscripts $p$ and $b$ refer to the planet and brown dwarf. Say the initial eccentricity is $0.5$. For us, this turns out to be $185P$, or 1785 years. In other words, noticeable inclination changes could happen in less than two millennia, which is fairly small on astronomical timescales. The oscillations will happen quicker if 1. $M\_\*/M\_b$ is small, which means a low-mass star (like a red dwarf) is a safe bet for the primary, or 2. $a\_b/a\_p$ isn't too large. If we substituted the Sun in for TRAPPIST-1, the effects would be much different, and the period of oscillation would increase by more than an order of magnitude, producing less drastic changes. The maximum eccentricity is a function of the initial inclination of the planet: $$e\_{\text{max}}\simeq\sqrt{1-(5/3)\cos^2(i\_0)}$$ If, say, $i\_0=75^{\circ}$, we find that $e\_{\text{max}}=0.94$, which is enormous. We then calculate that if $e\_0=0.5$ and $i\_0=75^{\circ}$, $L\_z=0.058$. We can then graph $e(t)$ and $i(t)$: [](https://i.stack.imgur.com/ciFmB.png) [](https://i.stack.imgur.com/rdQZ3.png) This assumes that the eccentricity varies sinusoidally; it's likely that the period motions are more complicated than that. [Answer] I would suggest that the solution would involve another significant gravity source outside of the elliptical. I am thinking perhaps FOUR suns forming a 3-D triangle, with the planets weaving between them. Or perhaps a major planet rotating around a sun in an orbit on the z-x or x-y axis, with other major planets orbiting on the x-y planar axis. Thus, the smaller planet would seem to wobble as the influence of each major planet came closer to it. I suspect such a system would need a computer simulation to model. I am thinking along the lines of, after the planetary system were formed, a galactic wanderer came in to the system high above the elliptic, and was captured by the star in some orbit not on the elliptic. That is, suppose Pluto were an absolutely massive planet. As it orbited off the elliptical, it would deform the orbit of the other smaller planets in some strange wobbly way. [Answer] I am not an expert on orbital mechanics, but I can suggest a possible situation in which a star system has some three dimensional orbits. I can point out that from one point of view all the planets, asteroids, comets, etc. in our solar system have 3 D orbits. They orbit around the Sun, each orbit being apparently 2D, while the Sun orbits around the center of the Galaxy in a 200,000,000 year or so long orbit. And the plane where the Sun orbits and the plane of the planetary orbits are very much non co planer. So instead of moving in closed elliptical orbits, the planets, etc. in our solar system actually movie in orbits that are open helices from the point of view of the galaxy. And there is another factor that actually makes the orbits of all bodies in the Solar System slightly 3 D. The planets, asteroids, comets, etc., don't all orbit in the same plane. They orbit in planes that are very closely aligned but still slightly tilted in various directions compared to other orbital planes. And because the orbit of another planet is tilted slightly with respect to Earth's orbit, half the time that other planet will seems to be In a direction that could be arbitrarily called "above" Earth's orbital plane, and half the time that other planet will seem to be in a direction that could be arbitrarily called "below" Earth's orbital plane. And because Earth and that other planet are attracting each other with gravity all the time, they are constantly "pulling" on the plane of each other's orbit and tilting the orbits a little more toward each other. But since their relative positions are constantly changing as they orbit the sun separately the relative directions of that pull are constantly changing. And because the mass of Jupiter is much greater than the pass of all other planets combined, the ever changing direction and distance to Jupiter is the main factor that determines how much force in pulling on Earth and in which direction, but the changing directions and distances to the other planets modify the strength and direction of that force. And so the tilt of Earth's orbital plane compared to the equatorial plane of the Sun is constantly changing very slightly in one direction or another. Now image a solar system with two stars, and planets orbiting each star, instead of orbiting both stars. When planets orbit one star in a binary system they are said to have "S-type" orbits instead of "P-Type" or "circumbinary" orbits. In which planes will the planets orbit? The planets of each star in "S-type" orbits will orbit in planes tilted only slightly to the equatorial plans of their stars, since the vast mass of the equatorial bulges of the stars will gradually pull the planetary orbital planes closer and closer to the equatorial planes of the stars. So can two stars in a binary system have different equatorial planes? If the two stars formed in the same collapsing protostar nebula then they are likely to have very similar equatorial planes which should also be very similar to the orbital plane in which they revolve around each other. But possibly various factors can make the three planes varying by much more than a few degrees. Stars tend to form in vast collapsing nebulae that contain many smaller collapsing protostar nebulae that form the individual stars. And after all the stars are formed they make up an open star cluster, which gradually dissipates over hundreds of millions of years as the gravity of other stars pull the cluster apart. And while the new stars are orbiting each other in a relatively dense star cluster for tens and hundreds of millions of years there are any opportunities for gravitational interactions to make two stars capture each other and form a binary star. In any case it seems that it might be possible for the orbital plane that two stars in a binary orbit around each other in to be very highly tilted compared to the orbital plane of any planets in S-type orbits around either of the stars. In some cases the orbit of the other star could be tilted approximately 90 degrees compared to the orbit of a planet around its star. And thus the gravity of the other star, many times more massive than Jupiter, should pull the orbital plane of a planet "up" on one side and thus "down" on the other, since it has to stay centered on its own sun. But since the years of the planet as it orbits its star close in will be many times shorter than the orbital period of the other star several times farther out, when the planet moves to the other side fr its orbit the other star's pull will now pull the other side of the orbital plane "up". Thus I picture the orbital plane of the planet wobbling from side to side, going in one direction for half a planetary year and then going in the other direction for the other half of the planetary year. Any other planets that orbit the same star as this planet will also experience wobbling of their orbital planes, but to greater or lesser degrees, the lesser degrees closer to their star, and the greater degrees farther from their star. And I think that it might be possible, under some conditions, for some or all of the planets that orbit Star A to have their orbital planes do a full circle around Star A at about 90 degrees to the equatorial plane of Star A. Thus each planet might have an orbit around star A lasting one planetary year in the planet's orbital plane, and also a much longer orbit of its orbital plane as that orbital plane rotates around Star A at an angle of about 90 degrees. And to me that seems like it might be considered a three dimensional orbit. [Answer] You could use a binary planet. Then the planets would describe a 2D orbit around a common center of gravity, and this would too describe a 2D orbit around the primary. The resulting orbit could be fully three-dimensional. [Answer] I think it cannot happen. When you have a single attractor, the force it exerts, combined with the motion of the planet, defines a plane, which is the ecliptic. When you have multiple attractors, you can have two different situations: 1. the planet is far enough from them to be simply attracted by the center of mass of the attractors, ending up in the single attractor case. Think something like the Earth in the system Sun-Jupiter-Earth 2. the planet is closer to one of the attractors so that the others can be neglected, but in this case we would again be in the single attractor case. Think something like the Moon in the system Sun-Jupiter-Earth-Moon Worrying about the attractors being out of the plane of the ecliptic is not needed. For the solar system the plane of the ecliptic is tilted with respect to the galactical plane. Still the orbits we see are contained in a plane. [Answer] While it seems next to impossible to have a stable orbit that deviates significantly from a planar ellipse, some orbits are truly 3D in a different way: They precess in interesting ways. Around the earth, there is one especially important class of these precessing orbits, the [Sun-synchronous orbits](https://en.wikipedia.org/wiki/Sun-synchronous_orbit). These orbits (which happen to pass near earth's poles) are arranged in such a way that the plane of their orbit rotates slowly around the earth's axis due to the equatorial bulge of the earth. This rotation is exactly as fast as earth's rotation around the sun, so the satellite always crosses the equator at the same local time. Satellites that need a lot of power (= sun light on their collectors) just love the Sun-synchronous orbits. They allow them to avoid earth's shadow entirely. True 24/7 power by an orbit that traces across an entire sphere (relative to earth) over the course of a year. In the coordinate system of the sun the motion can be quite complex. --- What are the prerequisites? * You actually only need two celestial bodies, a big one, and a tiny one (compared to the big one). More won't hurt, as long as your small body stays close to the big one. * The big body must have a bulge. This is easiest to achieve with some smart rotation. Earth's rotation is enough to provide enough bulge for a full precession within a year. Spin the big body faster, and you enable faster precession. * The orbit must have a significant inclination relative to the bulge of the big body. As far as rotational speed goes, the gas giant [Jupiter](https://en.wikipedia.org/wiki/Jupiter) turns around its axis once every ten hours. So that's what's totally believable for a celestial body. It's enough to give Jupiter a visible vertical squeeze, and it should be easy to find some fast precessing orbits around this planet. The problem with a fast precessing orbit is, that it cannot result from planet formation from an accretion disk. You need a significant inclination to get meaningful precession, and that's what an accretion disk does not provide. So, your small body must have been caught by the big body to explain the inclination. This also means that the small body will move through the equatorial plane at very significant speeds. If there's anything in its way, you get a nice big explosion. In the long run, these collisions would change the parameters of the orbit to make it more equatorial. So, there must be no remnants of an accretion disk remaining around the big body. (Sorry, Jupiter won't do with its wonderful rings...) --- So, take a fast spinning gas giant like Jupiter, subtract rings, add a moon that was caught from interstellar space which happens to have entered a highly inclined orbit. This moon's orbit will precess around the gas giant in a matter of months, giving you your true 3D orbit. [Answer] # Yes, a binary pair of planets can have a crown-shaped orbit. [](https://i.stack.imgur.com/h8ucK.png) Imagine two planets of equal mass $m=m'$. They mutually orbit each other in a circle of radius $r$, centered on their mutual center of mass (barycenter), 180° out of phase with each other. Let's call this circle the "wheel". This binary pair orbits a star of mass $M>>m$ at a radius $R$. The "axle" of the "wheel" runs along the radius to the star $R$. In other words, the plane of the "wheel" is inclined 90° to the orbit around the star. If $R>>r$, then the orbits should be stable. The gravitational force radial to the star is essentially only that of the star; thus, each planet orbits the star as if the other planet is absent. The gravitational force tangential to the star is essentially that of only the other planet; thus, the planets orbit each other as if the star was not there. The path of each planet is a [trochoid](https://en.wikipedia.org/wiki/Trochoid) wrapped around a cylinder. This makes a 3-dimensional "crown" shape. It is not planar, although in order for $R>>r$, it would likely be fairly "flat". Pluto and its "moon" Charon are close examples to such a system. Their barycenter is outside of either body, and their orbit round each other is inclined about 120° to Pluto's orbit around the Sun. [Answer] I got a very loose idea to get your "impossible to nagivate" world that's not immediately disprovable. Set your fiction in a globular cluster. The stars in a globular cluster have box orbits around the center of the cluster. The thing about box orbits is they don't really repeat and you quickly get a mess. You would want several inhabitable worlds (gotta make em G stars but as big as you dare with your planets as close as you dare without becoming implausible in that direction) and no outer planets at all. Every few years you get a system-system encounter where another star passes 10-20 of your AU (measured by your home planet of course) away. Getting from one inhabitable planet to another is quite the challenge as the energy and time efficient methods probably involve slingshots off other (quite probably larger) stars. Make sure when setting up your worlds you give them all *really* strong magnetic fields. The radiation is going to be something else. [Answer] The orbit of the Moon (or the Earth) around the Sun is 3D as the Earth-Moon system has 5.145° inclination to the ecliptic. Tidal forces caused the Moon to become tidally locked to Earth (=the Moon always points one side towards Earth). Similarly also Earth will become tidally locked to the Moon (this already happened with Pluto and Charon). This will also change Earth's equator to match the Earth-Moon orbit. Since angular momentum is conserved this change in Earths axis has to change the Earth-Moon orbital axis to keep the overall angular momentum constant. So even in a two body system the orbit can be 3D, although since we need to deal with real bodies that can flex, bulge, break and have friction, the gravity of all the particles (atoms) excerted on each other is relevant and their electromagnetic interactions (chemical bonds, repulsion, attraction) which give these bodies their consistency (hard rocks, oceans) over a gas. IIRC the Sun will go red giant before this finishes and possibly destroy the Earth-Moon system. [Tidal locking](https://en.wikipedia.org/wiki/Tidal_locking) [Angular momentum](https://en.wikipedia.org/wiki/Angular_momentum) [Answer] This phenomenon is observed in the case of the moons of Jupiter - Janus and Epimetheus. Source: <http://www.planetary.org/blogs/emily-lakdawalla/2006/janus-epimetheus-swap.html> Two moons swap their orbits, so these orbits are 3D. [Answer] One example comes to mind: There are several earth observing satellites that are in sun-synchronous orbits. See <https://en.wikipedia.org/wiki/Sun-synchronous_orbit> The orbit is nearly polar, and is chosen so that it precesses due to the non-spherical earth. This probably isn't useful to you: For earth, the typical altitude is about 600-800 km, and orbital inclination is about 98 degrees. For a planet the star would have to be seriously oblate. 2 hour orbits tend to make for toasty temperatures around a star (Yes, it would be longer than 2 hours,due to lower density of stars, but still *way* too close for comfort. Put on your silvered asbestos long johns.) I suspect that having a jupiter mass inner planet would give the effect of an obese primary. E.g. put a jupiter mass in Mercury's orbit, then orient your planet at 95 degrees to the ecliptic. Note: You need to explain the unusual inclination. However for story purposes, you can state it as an observation, and claim that the mechanics of how it got that way are still being investigated by the boffins. ]

[Question] [ Back in the day, during a writing jam, I started wondering it'd be good if a culture in my world would have loafs of bread resembling a hexagon-based tube. Almost like a cylinder, but with six well distinguishable sides. In terms of practical approach in bakery, how and/or when can it be useful or even working? Or it's just a matter of tase, and I can bake hexagon-shaped breads whenever I want? [Answer] **The hexagon is an efficient way to mass-produce identical loaves** Following a period of widespread bread alteration (think allum) the king has given a list of decrees to control the bread market. Apart from limiting the ingredients to flour, water, yeast and salt, he has demanded that all 1-penny loaves be identical. A 1-penny loaf on this side of the kingdom is the same as a 1-penny loaf on the other side. The bakers were not happy. . . . Problem #1: All loaves must be the same weight. Solution #1: Make the dough in large amounts. Slice into equal kilo-weights and put them all in the oven. Problem #2: Loaves must be the same shape. Solution #2: Use a mould. Think an upside-down cake tin with the raw dough placed under. As the dough rises it expands to match the shape of the container. Problem #3: Having many molds uses up lots of material and they don't fit properly in the oven. Solution #3: Only have one big mold. A wide one with many same-shape cavities in it. Put a lump of dough under each and put the whole thing in the oven. An hour later you have a hundred identical loaves side-by-side. Now there are many ways to arrange the same shape over a plane. For example the square: [](https://i.stack.imgur.com/k063J.jpg) and the hexagon: [](https://i.stack.imgur.com/02fTd.jpg) and many others. So to solve all 3 problems you can use a square or hexagon loaf or some other shape. So why one and not the other? Problem #4: Shortage of materials to make moulds. Solution #4: The hexagon pattern is known to minimise the total length of the 'walls'. This is why bees use hex-comb rather than square comb. So hundreds of bakers each use dozens of inverted honeycombs to produce thousands of identical 1-penny loaves every day of the year. I think that answers the question nicely. [Answer] **It really depends on the scale you're aiming at** *Bread as we know it*: Making this the main-form for bread in that culture would be impractical. The loaf as we know it developed from the fact that it is very easy to just heat up a ball of dough until it is done. You can control the time it takes to bake it by adjusting the thickness of your loaf, and as there's no holes whatsoever, the heat will evenly distribute. *Hexagonal bread*: Making a hexagonal bread, at least the way you describe it, will be a tad more difficult and ultimately less practical. As your goal is to attain a hexagonal shape you will need to do something along the line of sticking 7 rods of dough into 3 layers of 2, then 3, then 2 rods again on top of each other. [](https://i.stack.imgur.com/rezCe.jpg) The issue here is that you need some way to keep the weight of the upper dough rods from crashing the lower rods. The best way to do this would likely be to bake the bread in a vertical position, e.g. inside a basket or maybe a hole in your oven, this will lead to further issues regarding heat, etc. But it can ultimately be solved. Considering the additional effort and the specialized equipment this would need, it seems more likely that this sort of bread would develop as a bread for special occasions (e.g. for the mess on Sundays, birthday festivities, catering for guests, etc.) similar to e.g. [the Zopf](https://en.wikipedia.org/wiki/Zopf). An *alternative* to your tube-based bread would be to arrange multiple balls of dough like a flower, and thus create a flat bread that has the distinct shape: [](https://i.stack.imgur.com/VXpwY.jpg) Image taken from: <http://www.wunderkessel.de/media/brotblume.12725/> [Answer] It is done, just the way you described it. See the [manufacturer's website](http://www.gswarta.pl/page/31/) and a [shop that sells it](http://www.ecotrade.pl/chleb-gwarek-z-orkiszem). So **yes**, by all means it makes sense. They have been baking and selling it for years, at least since 2010 - the best proof it can work. For why, I admit I'm clueless, but you wanted a reality check, and here you have it: it's real. About the bread: it's a sourdough bread, made of Triticum spelta ([spelt](https://en.wikipedia.org/wiki/Spelt)) and common [wheat](https://en.wikipedia.org/wiki/Wheat). Spelt is low on gluten so it needs to be baked in forms, and that's the case here. It is baked in hexagon forms with a crust similar to that of rye breads (baked in forms), not white bread (baked as free standing loaves). In [this image](http://www.gswarta.pl/file_download/15/) you can see the top of this bread. Sadly, it is not licensed in a way that would let me include the image directly in my answer. [](https://i.stack.imgur.com/yZDBd.jpg) [Answer] As others have noted, the reasonable starting point is stacking. If you need to stack lots of bread for significant periods of time, you want a shape that does not waste space. So the cross-section would be a triangle, a rectangle, or a hexagon. The problem is that pretty much all storage spaces where we would stack things are rectangular and will store rectangular bread more efficiently. Only advantage a hex has over a square is that it has less crust per volume. So we need some reason to minimize the amount of crust. The easy solution is that the crust is actually inedible. Considering that this is bread that is stored long enough that stacking efficiency is a major issue, the bread itself is probably completely dry, extremely dense, and hard enough that you need to soak it for a while before you can eat it. More a biscuit than bread. For the crust to be inedible in comparison, it must be toxic. As in, rats gnaw at it and die. As noted in a comment, a toxic crust would also be an added cost and would give an added reason to minimize the surface area. So if you use such crust a hexagonal bread will be better than a rectangular. This actually makes sense. Any bread stored long enough that stacking efficiency matters would have to be protected from spoilage. It should be rat proof, insect proof, mould proof, and water proof. Being fireproof would be nice, but given the extreme dryness would be hard to achieve. So after it has been baked in a metallic mould, it is lacquered with a lacquer that is either toxic enough to kill rats itself or has some arsenic added to it. Once the lacquer dries it forms a hard insect and water proof surface. The toxicity gives protection from rats and other vermin. The smooth hardened surface also makes storage slightly easier. Since the bread itself is very dense the poison will not penetrate beyond the surface layer. This kind of bread should store for a very long time. And you would not need to worry about keeping the storage dry and free of vermin. This is important because it combines with high stacking efficiency to make long term storage cheap enough to be practical. Then after you are out of everything that is actually edible, you go to the farthest corner of the basement, pick some of these hexagonal rods your grand father stacked there, cut off the brightly coloured (probably red/ochre) crust with a saw, then use a **clean** saw to cut the rod into thin slices, boil some water, soak the slices in the water, eat the slices once they have softened enough, and pray to all Gods you can remember that you will not die. You could call this the "red bread of last resort", I guess. Although I imagine it could be some sort of gourmet delicacy, if it was spiced in some way. Since it can be stored for a long time, the taste could mature over time. A bread equivalent of fine wines or cheese. I thought some about what possible disaster would make such emergency food make sense and by coincidence saw a video about medieval castles. Sieges were prolonged affairs and properly designed castles could hold out until the defenders run out of supplies. The amount of food stored when the siege starts would then be of crucial importance. This would give real value to food that can be stored for long periods of time. Castles were also fairly expensive to build. This means that spending some extra money on making food store better might be practical and that food that stores efficiently would have real value because space was at premium inside castles. [Answer] Here are many different, separate reasons for this that I could come up with. * The moulds for this exist in nature and do not have to be made, as in there is an easily accessible fireproof something that can be used for this purpose for any kind of bread, the effect of which is better, more evenly cooked bread even for the poor without a good oven. + Expanding on this, perhaps there isn't a lot of wood, and this material, in this shape, can cook bread faster, which is needed because there isn't much fuel. * The guild insists upon it. It's a weird shape to prevent pretenders from being bakers. There's a baker's mafia. * The shape is important in the culture, and hexes are used for certain festivals/popular for celebration feasts/said to be lucky/are considered better than "poor round bread." * As @Ville Niemi covered, because this form is good for storage. I would expand on this to say it would be good for harsh winters, and there might be other things baked into it, such as dried meat or mushrooms to make a kind of "stew bread" in desperate times. * There's nothing people fight over more than food, especially bread. @Daron's suggestion of a king's decree for standardization is not surprising, since in history there were plenty of laws governing bread in early times. * Finally, and this is a weird one, food as currency. If it's as indestructible as @Ville Niemi says and takes a good soaking to break down, it actually might be a good stand-in for MONEY. The weird shape is a bonus, making it more difficult to forge (and the ingredients cost money...so...) Here's a list of all the food used for [currency](https://www.cryptocoinsnews.com/12-types-currency-throughout-history-eat-drink-smoke/) in history. Not as a trade item, mind. (I talk about [food as currency in this answer here](https://worldbuilding.stackexchange.com/questions/79559/post-apocalypse-currency/79572#79572) on our site). [Answer] ## Cultural norms often define things for no readily apparent reason. Things often grow organically from earlier things. Think how railroad gauges chose an arbitrary width that hearkens back to horse cart widths, which are fairly standardized because of the width of horses... everything grows from something older. So you have *hex shaped bread loaves* and want to reverse that back to a reason why. Why would most (all?) bakers standardize on a hex-shaped loaf pan? Early bakers didn't use pans at all. They used ovens and slid bread dough into the oven without a pan. As near as I can determine, bread pans are a relatively modern idea. It appears they are most commonly used in England, Scotland, the US. It appears that [bread pans](http://www.foodtimeline.org/foodbreads.html#breadpans) date back to roughly the 16th century England/Scotland. That link cites the earliest known English reference to baking *bread* in pans as 1807, but states it was surely a common practice before then. I mention that, because to get hexagonal bread, you need a hexagonal bread pan. Otherwise, you get a vaguely hexagonal round loaf, since forming the loaf into a perfect hex while it is still dough won't matter during the rising or baking stages. As for *why,* others have supplied answers that basically talk about efficient use of oven space. This really doesn't matter until your society reaches mass production. As long as your baker can bake sufficient quantities to supply his/her local customers for the day, then standard baking practices with ovens and no baking pans will work. No, if you want to get hexagonal loaves before mass production, you need a different cause than efficiency. If your society [worships bees](https://en.wikipedia.org/wiki/Bee_(mythology)), they would have a reason to introduce bee-based shapes into their society. Perhaps they build everything on a hexagonal pattern. So you have hex houses with hex plates and bowls and they bake hex-shaped bread from hex-shaped stoneware. [Answer] The most efficient way to place *round* bolls of dough on a plate is to use a hexagonal pattern. During the baking process, the dough will rise to the sides and automatically form hexagons. This not only works with bread, multiple times I ended up baking hexagonal cookies because I placed too many on the same plate while baking. [Answer] Considering that [this heart-shaped monstrosity](http://rads.stackoverflow.com/amzn/click/B001BINZ8E) is quite doable, I'm very much inclined to say it is indeed possible. Cooking bread in such molds generally requires a fair amount of cleanup, though, so I'm not convinced doing so would be especially practical. If your society is capable of making the bread come out easily without sticking or leaving residue, though, I could see using the hexagon shape as being practical. Make an oven with heating elements between each mold, and optionally integrate it with the ability to push the bread out and get more dough. You get loafs of bread that store compactly, and are produced in a relatively space-efficient way. That said, I don't think the hexagon shape would be particularly superior in any respect to the standard square-ish thing we have today. [Answer] So these answers focus on a mold, but there is one really large problem. You have to bake the stuff. Normal white bread will not do well if it's "fat in the middle" The narrower top and bottom will be done long before the middle of the loaf. The crust will be harder and more dry, while the center will still be "raw". Normal white bread (that we generally eat these days) just won't work if it's not "mostly" uniform. This is true for older breads too, that's why many breads were made as a blob of dough on a flat surface. The bread wasn't as much rectangle (like we think of today) but round. It would "flatten" out a bit as it cooked, and you would get a short fat blop of bread. The "modern" bread that you get at the grocery is a joke compared to real bread. Even real bread made in a loaf pan tend to be uniform in nature or the cook poorly. The loaf pans primary job is to constrain the rising bread and make it "mushroom" at the top. In fact when placing the dough in the pan there should be lots of room "around" the dough to allow for it to expand (lots is relative). So, a Hex shaped tube, or any non circular tube isn't going to work well for "modern" bread. But don't fear there are options. Wet or moist breads (think banana bread) won't have this problem, at least not as bad. Flat breads also won't matter much. Any bread that doesn't leaven (rise with yeast) should work quite well so long as you can account for thicker middle of the loaf. Leavening breads may still work if the tube allows some poof out the top like a loaf pan does IRL. It would be tricky though. Historically, breads wanted a thick, hard, dense, tough, crust. This is how it stayed fresh. Specially for traveling, you would want a crust you wouldn't actually eat. You would peal back the crust and eat the squishy bit inside. Much like a orange. The only difference is that the crust could then be used (some times) in soups or stews. Other times it was too moldy and just discarded. If that is a feature your looking for the a hex shape may not be bad. The center could need more time to cook, and thus your crust would be thick and hardy. [Answer] One of the difficulties with bread baking involve the equal application of heat over the surface area, nobody wants bread that is burnt, but it happens, especially in big wood ovens. So what do you do? Create a clam-shell like mold that closes into a hexagonal tube with flat ends. This is the important bit though: When closed, it has 3 edges with a hole for a hook to attach. This would be the same hook that is in many old time fireplaces where you could hang a kettle. The closed design has many benefits. First, it keeps embers and other debris from the fireplace out of the loaf. Next, being able to turn the loaf to each of the 3 hook points gives the baker much better control over heat distribution. These molds, most likely being mad from cast iron, are likely to become heirloom pieces, passed from generation to generation, like your grandmothers jelly mold. The stackablility is just a by product of the shape that allows for a quality loaf. Stackability, heirloom molds, plus inertia (We've always done it that way) should carry the traditional hex loaf forward through time. [Answer] Rectangle is perfect shape for storing (as it works like building blocks). Hexagons would require more work as it's hard to produce bread in semi-perfect hexagon shape and can't really be placed in a container not to waste space. Rectangular shape has no such imperfection and is much more easier measurable. [Answer] One of the answers already shows that it is being done (although it seems like rye bread) ## Shapes for safety Many breads are just different shapes to distinguish between the different types since if all bread looked the same you wouldn't be able to tell which scones are burger buns from a commoner's perspective. Perhaps squishing it to see if its soft but nobody wants to eat bread that dirty commoner hands have touched. So I would say that there was a some kind of rectangular bread that was brought in, maybe a foreigners bread and they want people to sell local. (or maybe the local wheat was safe while the outside bread could be made from plague wheat) so one day the local folk decide to make their bread hexagonal to differentiate it from normal bread in the stores so people know they can trust it. This could be the history and the in the world's modern day it just stayed hexagonal without the original reason for it being that way as being common knowledge [Answer] In terms of low-tech bakeries (typical medieval bakeries for instance) the oven would be internally fired to get it hot and the bread 'just' plopped down in free-form dollop shapes onto the oven floor. There's no expense of buying tins to bake in, there's no effort needed to clean the tins and no need to store tins for each type of loaf that is made. And if fashion changes and a 'new' shape loaf becomes fashionable then you'd need a whole new set of tins. Given the absence of cheap tin-plate, bread tins would be heavy, take a lot of heating up and therefore take a lot of heat out of the oven. When it comes to transporting bread... sacks don't pack hexagons much better than dollops. All in all, there's no benefit in making bulk bread in medieval times in tins. Also if you're using an artisanal flour with your own variety of yeast, the behaviour of the dough won;t be consistent. Making consistent loaves from inconsistent ingredients would be an extra overhead. Now if you accept uniform ingredients and cheap tin plate you can more easily make a hexagonal tin (a closed two-part tin with ends) and make a consistent hexagonal loaf. In the UK there's a loaf called 'milk roll' that is mould-made in this way... as a ribbed cylinder with flat ends. But it's dependent on knowing that an amount of bread will rise in a given time to fill the tin completely, that the oven temperature will be reliable and consistent across the loaves cooking at any time. It's a high-tech loaf rather than a low-tech loaf. If you want to consider authorities imposing dimensions on bread... consider the laws in France about dimensions and weights of baguettes. See for instance <http://www.frenchdesire.com.au/facts/bread/> that hints at the law. So it can be done, but not in hexagonal tins! [Answer] If question is about industrial bread production for mass consumption, hexagon molds will cost magnitudes more for earlier eras and are less useful if you aim to authomatise baking later. Conveyor line handles rectangles much better than hexagons. It will make machines like these twice as complicated for no real benefit. <https://www.youtube.com/watch?v=3UjUWfwWAC4&t=220> If question is not about bread industy, then there isn't any problems with hexagons. Cylindrical bread are common through history, and they are pretty close to hexagonal in shape and mass. ]

[Question] [ A ring species is a species, in which a population migrates in two directions and the population remains continuous as it migrates so that each sub-population can breed with its neighbors, however when the two ends of the population meet they are different enough that they cannot interbreed. I was thinking of a similar situation with a language, in which the people who speak a certain language spread out in two different directions, and as they spread everyone who speaks that language continues to be able to understand their neighbors; however, when people from the two ends of the region that speaks this language meet after several hundred years they are no longer able to understand each other because their languages are mutually unintelligible, even though they are the exception to everyone in this region speaking the same language of their neighbors, and are each other's neighbors' neighbors' neighbors' neighbors' . . . neighbors. Would such a scenario be possible? [Answer] It’s not only possible, it exists as you describe. Italian, French (Provençal, really), Catalan, Spanish and Portuguese (and many local dialects thereof) merge continuously into each other, and everyone can understand their near neighbours in both directions, even across international borders where the language nominally changes, but Sicilians and Portuguese can’t understand each other. National broadcast media are reducing this by standardising language within each country, so your world should have a lower technology level. [Answer] ### Old Norse and Old English It's basically how languages spread in pre-modern times. Have you seen "Vikings"? There is a scene in the first season when Ragnar lands in England and meets a local landlord and his soldiers on the beach. They're not able to communicate immediately. The vikings speak Old Norse, the English - well, Old English. It's exactly the situation you described: these are both languages coming form the common proto-Germanic roots, but they are separated by hundreds or maybe a thousand years of development. The only difference from what you wrote is that no language stays the same - the "original" language of people who were left behind in Scandinavia also evolved in time. I wrote an article about it for a Polish linguistic website woofla.pl, but it's in Polish. All I have in English is an animation showing the development of Germanic languages: <https://www.youtube.com/watch?v=UzYjsuvHx4c> In short, Germanic people settled in about 2000-1500BCE in the area of the modern Denmark and southern Sweden, and lived there in relative isolation until around 500-200BCE. The isolation contributed to the differences between Germanic and all other Indo-European families of languages. At the end of that period a dialectal continuum emerged with people who dwelt in southern and western parts on one end of the spectrum, and population in the Scandinavia on the other. From the first group, Western Germanic languages emerged, from the second, Old Norse. Western Germanic languages were also a continuum for a long time (even until the modern times to be precise - even in the 18th century the border between Dutch and Low German was kinda fuzzy). In the south, close to the Alps, Old High German started to develop. In the north, Low German dialects. One of them was Saxon which was probably close or the same as the languages of Angles, and together these two peoples invaded Britain in the 5th-6th century CE. Old English developed as a merger of Old Saxon, Old Frisian, and some other, smaller dialects of people who joined the invaders. Some of them might have even spoken the northern dialects. In the same time Old Norse was developing as well, but in a more conservative fashion. In the times of Ragnar, late 8th and early 9th century, it was still one language with just some differences between east and west Scandinavia. Even now Danish, Swedish and Norwegian (which has its own interesting story and is divided into two main "versions", Bokmal and Nynorsk) are quite intelligible. Anyway, when the vikings invaded England it was as if the linguistic history made a full circle. And now both peoples needed translators. But not for long: the languages were still similar enough that probably after a few years of learning a Dane was able to speak Old English quite well, and vice versa. Only the later Norman invasion introduced a lot of (Norman) French vocabulary and put English on a very different track. [Answer] It's almost like Slavic languages, though the reason has more to do with history of literacy, political changes and assimilation. Slovak is mutually intelligible with modern heavily Slovakized Rusyn, which is mutually intelligible with Rusyn as spoken in Transcarpathia, which is *almost* mutually intelligible with standard Ukrainian, which is mutually intelligible with Surzhik, which is mutually intelligible with Russian, which is mutually intelligible with Belarussian, which is not really, but somewhat mutually intelligible with Polish, which is almost mutually intelligible with Góral language (at the Polish side of the border), which is basically the same as the Góral language at the Slovak side of the border, which is kind of mutually intelligible with standard Slovak. Apart from the broken link between Belarussian and Polish (which in an alternative history of surviving Polish-Lithuanian Commonwealth could exist), there is almost a complete ring. Going the southern route, central Slovak has some tenuous connection with Croatian (though mutual intelligibility has been already lost to history); Croatian blends into other (neo-štokavian) Balkan languages, transitions into Macedonian, which is mutually intelligible with Bulgarian, which is surprisingly close in lexica to Russian, because of the heavy influence of Old Church Slavonic on Russian. From Russian, the usual route via Surzhik->Ukrainian->Transcarpathian Russyn->Slovak Russyn->Slovak closes the ring. There is the missing step from Croatian to Slovak, and the connection between Bulgarian and Russian is rather weak. But still. [Answer] I think that what you are asking is more or less what happened with Latin and neo-Latin languages. Take Romanian, French and Italian. They are all from Latin origin: an Italian can understand some French and some Romanian (actually Romanian sounds really similar to some South Italian dialects, while some Northern Italy dialects sound really close to French), but I doubt a Romanian and a French would had the same level of partial understanding. [Answer] ## Czech-Polish dialect continuum [](https://i.stack.imgur.com/kNfOj.jpg) *(Wikimedia Commons, GDFL)* Czech and Polish are, for most native speakers of both languages, not mutually intelligible. However, in the easternmost corner of the Czech Republic, there is a transitional Cieszyn Silesian dialect (G2 in the map above). It is mutually intelligible with the Silesian dialect spoken on the Polish side of the border (G1) and, to a lesser extent, also with the Lachian dialects (C4) on the Czech side. So, there seems to be a well established dialect continuum in this region. However, this continuum does not exist all along the Czech-Polish border. In fact, there are basically no transitional dialects outside the Cieszyn region. The thing is, most of what is now the Czech-Polish border region used to be a predominantly German speaking area. After the expulsion of Germans from Czechoslovakia, new settlers from all over the country arrived to the region, bringing their own dialects, which eventually merged into what is now described as the mixed dialects (C5). A similar process took place on the Polish side where the so called Recovered Territories were settled from central and eastern Poland, again creating mixed dialects (B4). These new dialects of Czech and Polish are about as far apart as the respective standard languages are. So, no cross-border mutual intelligibility. Not without a significant exposure to the other language, anyway. [Answer] This situation exists in Japan. While the dialect of Tokyo has become the standard language via radio and television, each region also has local dialects. As described, occupants of neighboring regions can understand one another, but travel any significant distance, and the local dialects become mutually incomprehensible. I recall a conversation with a man who was about 7 years old when evacuee children from Tokyo arrived and lived in local temples. He said they could not understand one another at all. He also said that he preferred to speak the local dialect; that he felt more himself while doing so. [Answer] I would like to add another comparison in a lateral direction - time. This is exactly how language development over time works. Grandparents and their grandchildren can communicate, but if you were to move through a few generations, you wouldn't be able to understand your ancestors anymore and vice versa, even though every 'temporal subset' was able to understand each other. [Answer] Definitely possible, although I don't know real examples from our world. The Slavonic languages on the Balkans form a somewhat broken ring, almost encircling the Hungarian and Romanian language area: Going counterclockwise from Ukrainian via Ruthenian and Slovak to (first gap in the ring) Slovene, Croatian, Serbian, Macedonian and Bulgarian there is a dialect continuum. Between Bulgarian and Ukrainian is the second gap in the ring, when it were closed along the Black sea coast, Bulgarian and Ukrainian would exhibit a hard language boundary. [Answer] Yet another real world example: Arabic is widely spoken, but Moroccans and Iraqis cannot understand each other's (spoken) dialects. The film industry in Egypt thrives in part because all native speakers of Arabic can understand the Egyptian dialect. However, if migration patterns around, say, a large ocean caused speakers of incompatible languages or dialects with a common root to live next to each other, there would likely be Creolization within a generation unless there were significant cultural barriers. [Answer] More examples for you to use for research, since everyone has answered this well: Quebec French, Creole French, and French are all completely distinct. In China, there are over 104 (?) dialects. They are distinct enough that not even neighbors can understand each other, so they communicate in English instead. In Japan, the main island has it's form of Japanese, with a dialect in the Osaka prefecture being like American Southern English, as well as the Ryukyuan Islands having distinct languages that are Japonic, however are also unintelligible to Japanese-speakers. [Answer] For such a language to exist, it is sufficient that the dialects differ on at least two dimensions (principal components). Given the complexity of language, this is obviously possible. For example language L1 could share set of words S1 with L2. L2 shares S2 with L2. L3 shares S3 with L1. S1, S2 and S3 are all disjoint. [Answer] This sort of dialectal ring continuum might happen naturally for a population with homogeneous language origins living on a contiguously traversable, toroidal world with very limited travel distances. Essentially, a people speaking one language landed as one group on a donut without any great oceans separating its land masses. You might also be able to pull this off on a world which can only be traversed or inhabited along its equatorial zone, so long as it remains reasonably contiguous. The more you increase the distance the average person travels, the more you dilute the dialects. To get the most varied continuum, reduce the average person to a walking distance (*cf.* "God Emperor of Dune"). Speakers of neighboring dialects will tend to retain mutually intelligibility and, since no one lives in a vacuum, there will be some "cross-pollination" of dialects across the spectrum. As these people spread across the face of this world, the dialects will diverge. Eventually, the population will expand until one extreme meets the other. The first encounter would likely be between mutually unintelligible dialects. Whether they initially meet with war or trade, those two groups will gradually reach a point of relative stasis and a pidgin will emerge. This will develop into its own dialect and start propagating along the continuum. Of course, so long as the average person doesn't travel very far, these propagations will rapidly diminish with distance. ]

[Question] [ On a mythical world almost identical to our own, deep space telescopes notice as an object appears out near the orbit of Jupiter. In the instance after its appearance, the light which bounced off it during its FTL entry into the solar system finally catches up with it, allowing the telescopes to see what general direction the ship came from. Scientists determine that the ship is decelerating at such a pace and trajectory that it will pass close to the world while staying just outside of lunar orbit distance. Over the course of the next hour, the ship does just that. Then with every telescope in the world pointed at it, the ship re-accelerates to FTL, effectively vanishing. Never to be seen again. Question : What can the scientists of this world learn from the event? More specifically, what does absolute proof that FTL is possible do to current scientific understanding? Would there be any immediate advancements or resulting technologies which might quickly become visible to a layman, non-physicist? [Answer] Hmm. Let's try to understand what we *actually* see. 1. *"Deep space telescopes notice as an object appears out near the orbit of Jupiter":* That's either one *biggg* object, or at least a veeery luminous object. The chances of any reasonably sized spacecraft being detected near the orbit of Jupiter are between zero and infinitesimally small. Anyway, and wherever the object is first detected, nobody will have any reason to suspect that the object just materialized in normal space. Everybody will more naturally assume that it had always been in normal space. It's not as if we have a complete catalog of stuff moving about in the outer solar system and beyond. 2. *"The ship is decelerating at a pace and trajectory that it will pass close to the world while staying just outside of lunar orbit distance":* So we notice that an extra-terrestrial object is maneuvering and we now know for certain that extraterrestrial intelligent life exists; or at least that it existed thousands of years ago when the ship was launched in some star system far, far away. Depending on how exactly the ship is maneuvering we may learn quite a bit about their technology. Do they use some sort of reaction engine? We will see the spectrum of the exhaust, and we can measure its chemical composition and temperature. Do they use some sort of reactionless drive? *That* would be shocking, and will give a very strong impulse to conduct research in fundamental physics. A secondary effect of equal importance is that we will know now for certain that our defense systems are pitiful. Expect a *huge* investment in defense by all the great powers. 3. *"With every telescope in the world pointed at it, the ship re-accelerates to FTL, effectively vanishing":* What we see in reality is that the ship accelerates and then vanishes. Nobody will ever suspect that it went FTL. What the relevant military agencies will deduce is that stealth in space is possible after all. This will downgrade the impression of our defense systems from being pitiful to being a very bad joke. Expect even *larger* investment in fundamental research in physics and in advanced weapons platforms. The point is that at present we are absolutely confident that faster than light travel is impossible and even nonsensical. We would be ready to accept that an advanced artificial intelligence is piloting the ship, that the aliens have some sort of stasis technology, or that they can build functional generation ships; all those possibilities are consistent with what we think we know for certain. Faster than light travel is so far out of our understanding of physics that no serious scientist will suggest it, and those who *will* suggest it will be labelled cranks and exiled to the remote corners of the Internet discussion forums. [Answer] Obviously exciting things: * FTL is possible without the need for chunks of exotic matter than weigh more than the visible universe. * Interstellar travel appears to be possible and practical. * There exist intelligent beings capable of building such a device. Possibly interesting things: * It probably isn't made of antimatter, or we'd see lots of gamma rays shooting out of it due to interplanetary dust and gas hitting it. Alternatively, it has a magical deflector shield. I'm not sure if we could tell if the latter existed or not, unless we actually spotted it hitting something, which we almost certainly will not. * If we get a good look at the object, we might be able to get a handle on the most minimal obvious requirements for FTL travel. Does it seem to have a huge shielding bumper? Massive heatsinks? Does it have any sort of design to minimise its cross section? Does it appear to be made of something that behaves like regular matter does? We might even be able to tell *what* it is made of, looking at the spectrum of light being reflected off it. * It almost certainly *cannot* use reaction engines to brake into and accelerate out of our system. If it does, there will be a *really exciting* amount of gamma rays, and we'll learn that whilst FTL appears to be possible, reactionless drives are not. If there is any exhaust, we'll be able to get a grip on what sort of rockets it uses. * If it *does* use reactionless drives, we might be able to see some sort of warping or frame-dragging distorting the view of the stars behind the object, if it uses some kind of warp-motor. If it does, we know that warp drives are possible, and may or may not be the same mechanism for FTL travel. If it does not, it suggests that our understanding of physics is even *more* lacking than we initially thought, because there's a non-warping yet still reactionless mechanism for travel through space. * If we can see the object accelerating smoothly up to the speed of light, that probably tells us that our understanding of relativity is deeply inadequate. What we see *might* be able to inform new theories. But beyond that, I think things stay pretty murky. Whilst FTL *implies* that timetravel is *possible*, it doesn't guarantee it (see also various chronology protection conjectures). I'm not at all sure whether analysis of the object and its trajectory can tell you whether it was travelling back in time or not. If it *was* travelling back in time, the people who made it might have been us, in the future, so the question of whether there is intelligent life elsewhere in the universe *right now* remains unanswered. > > What can the scientists of this world learn from the event? > > > Huge amounts. There's decades worth of research to be done, I'm sure. As to the *specifics*, I can't say, because a) I am not an omnidisciplinary scientist and b) you left the nature of the object and its propulsion unspecified ;-) > > More specifically, what does absolute proof that FTL is possible do to current scientific understanding? > > > It wouldn't *totally* upend it. It would upset various bits of theoretical physics, that's for sure, but the rest of reality will keep on working pretty much as it always did. If we see the object violating relativity, that'll be interesting, but *in most circumstances* we already know that general and special relativity hold true (see also: how GPS satellites were designed). > > Would there be any immediate advancements or resulting technologies which might quickly become visible to a layman, non-physicist? > > > Who knows? It might produce a bunch of amazing things immediately, or it might take *decades* for actual end-products to appear. How long is a piece of string? [Answer] The first thing that scientists will learn, is that there is a severely blueshifted object near Jupiter. This will be extremely bright for the same reason that a sonic boom is loud. This "luminal boom" will not be noticed by most people on Earth, though. The blueshift will be far outside of the visible range, well past X-rays, and into Gamma rays. The broad-spectrum gamma ray observatories -- satellites that are tasked with detecting the Gamma Ray Bursts associated with hypernovas, and the double-spikes of gamma radiation associated with nuclear weapons testing -- will be the first to detect the blueshifted light from our FTL ship as it decelerates through the transluminal barrier. In minutes, the directional gamma ray observatories will be retasked to observe the extremely strange signal... Extremely strange, because it's the only gamma ray source that isn't just a huge, short lived spike of high energy photons at some arbitrary wavelength, but is a long lasting source that is changing its wavelength very, very, very quickly. If they're lucky, they'll notice the streak of very high energy gamma radiation traveling away from the point where the FTL ship crossed the transluminal barrier, but this signal will likely be completely lost in the huge amount of gamma -- then X-ray photons that the FTL ship is reflecting. As the ship slows down, we'll be able to better resolve it -- both because it's closer, and because our abilities to focus photons improves as the frequency goes down. It won't be in visible wavelengths until it's at least .25c, though. Our scientists will know that something is very strange. Some will suggest FTL. Most will say that FTL shouldn't be possible. Unless we notice (and understand) the stream of gamma radiation that's traveling away from the point where the ship crossed the transluminal barrier, though, there will be no proof that the ship ever travelled faster than light, since simply travelling near the speed of light, then decelerating as it nears Jupiter will have the same effect. Even if instruments do record that telltale FTL echo, it isn't *conclusive* proof, as the same signal could be produced from a high energy communications pulse being reflected by interplanetary dust, perhaps letting their homeworld know that they've arrived. As the ship starts to depart our system, it will be severely redshifted, quickly becoming undetectable in the visible spectrum as the photons elongate out to radio frequencies. If it happened to have a clock on the rear, we would notice the clock slowing. Even though the redshift will happen at the same rate that we'd expect a ship traveling at *near* the speed of light will happen, the brightness will drop faster than we'd expect. This will be another hotly debated but still inconclusive detail in academia. In all, several people will be convinced that FTL is possible -- a minority of physicists will deeply consider the implications but, unless they can replicate it, the only papers in journals will be theoretical discussions that conclude that more research is necessary. However, seeing the object accelerate from (presumably) .999g to a relative standstill in the course of an hour, then back up to speed again over the next hour will generate a LOT of buzz. Physics will be turned over. I can't even begin to imagine the technology it would take to shove that much energy into a spacecraft in such a short amount of time without it turning into a stream of highly ionized and definitely-not-spacecraft-shaped dust. Cats-and-dogs-living-together scales of mass hysteria. [Answer] **FTL can be achieved!** This is no pipe dream and providing resources to the investigation of Faster than light travel is now humanity's top priority. * All observatories pointing over it means a full spectre of radiation was recorded. From gravitational sensors, microwaves, even the shift on the lunar regolith can hold clues. * Fermi Paradox got an answer, we are **not** alone. * Militaries the world over want lasers and weapons able to shoot down such spaceship. * Chaos! Religions worldwide claiming an act of his/her/their gods. Churches burning down. Average Joe will see a ton of Star Fleet paraphernalia and kids will fight over Kirk vs Picard. [Answer] The most obvious thing that will be discovered from the passage of the FTL spacecraft from Jupiter orbit to close to the Earth will be that the spacecraft travelled that distance at an average velocity of around half-lightspeed. This indicates an acceleration of the order of approximately 9,000 gee. Similarly, it will accelerate away from the Earth at the same acceleration. This is sufficiently remarkable in and of itself. The power required to accelerate a spacecraft is incredibly huge. However, the most important aspect of the vehicle's FTL travel is the fact something that is made of bradyonic matter can pass through the lightspeed barrier. Going from, as it has been observed, above lightspeed to below it, and then transition from below lightspeed to above it. This will imply that two of theories which allow for certain kinds of FTL travel may be possible. These will be the initial theories scientists will investigate in an attempt to explain the phenomenon. Extended special relativity which assumes the existence of tachyons, and the Alcubierre metric which might permit a kind of warp drive. The observations made of the FTL vessel may be able to either distinguish between these two theories or, possibly, discount both of them or give indications of an otherwise novel physical basis for faster-than-light technology. Theoretical physicists will have the proverbial field day in concocting a whole slew of new theories to explain FTL physics. These will endeavour to reconcile whatever observations and measurements were made of the FTL spacecraft during its flyby of planet Earth, with science as we know it, and to extend it beyond what we do know at present. The querent's post doesn't give a complete enough picture of the FTL spacecraft to determine what could be discovered from observing it. That will determine what its impact will be upon science so massively that it is nigh impossible to predict what the changes to science will be. [Answer] **Many existing scientific theories would need to be revisited.** Any sort of FTL travel would be so fundamentally at odds with known physics; many of its theories (or even laws) would need to be revisited and rethought. There would be an enormous flurry of activity in the academic world due to this one discovery. **The ship's pattern of movement would open lines of investigation.** In order for this ship to interact with the local environment, it would need, at least sometimes, to be traveling at a sublight speed. At one moment the ship would appear to be travelling very fast, but still at sublight speeds-- but then the ship would vanish and appear impossibly far away. **Hidden variables.** Given this pattern of behavior, scientists would want search for any evidence of hidden variables. For example, it would be of interest to know whether the frequency of disappearances is periodic, and if it is, if it is periodic with respect to time or distance traveled. Inconsistencies in the periodicity would give rise to additional theoretical hidden variables; for example, perhaps they occur more frequently near other objects or fields of radiation, suggesting that the FTL drive relies in part on its immediate environment to operate. **Environmental side effects** may indicate some clue as to how it operates. For example, perhaps the ship does not interact gravitationally with nearby bodies, or light reflected from its surface has unusual characteristics, or it releases a radio burst each time it disappears. **Does it "jump?** Of considerable interest would be whether there are any environmental effects evident in the space between where it disappears and reappears. A complete absence of any environmental effects in these areas would suggest the FTL drive relies on some of of "jump" or "skip" effect, in contrast to continuous movement that is simply too fast to witness except by its trail. **The shape of the vessel** may give several sorts of clues: * Is the vessel occupied by biological life? * How could they possibly survive under such extreme acceleration or in the presence of exotic physical effects? * Is there evidence of shielding, or are the engines houses in an outboard structure of some kind? * Does the vessel carry fuel, or collect it? * Is it driven by thrusters of some kind, or operate a sail? **Historical or mythological implications.** Is it possible the vessel has been by the Earth before? Is it shaped like any known mythological create or archeological symbol? [Answer] It's been said that you can have relativity, causality, or FTL. [Pick any two.](http://www.projectrho.com/public_html/rocket/fasterlight.php#id--Introduction--Causality) We have numerous things that require that relativity be true(one example being the GPS system), thus causality cannot be true. This then implies that time travel is also possible. The problem with a new scientific theory that implies FTL is that it must also explain all our current understanding of physics as well. This is known as the [correspondence principle](http://www.projectrho.com/public_html/rocket/respectscience.php#id--"Maybe_A_Future_Scientific_Breakthrough_Will_Let_Me_Have_My_Way"), and also applies to the thermodynamics problem of stealth spaceships. [Answer] Regarding first detection and the telescope observations: As someone before me pointed out, us detecting a sensible sized ship at Jupiter's distance is next to impossible without some heavy immediate clues. We indeed don't have that good knowledge of stuff flying around there. Luckily there are plausible clues! There are automatic alarm mechanisms and equipment in space to detect a few types of short-lived interesting events. One of the best for this purpose are gamma flash detection satellites. They were first developed and deployed to enforce ban of atmospheric nuclear testing. They made detections, which turned out to be of astronomical origin, and so we found gamma bursts. Your ship exiting FTL speeds might emit such a signal. Another more modern - and in that sense cooler - prospect are the gravitational wave detectors! Similarly, we could see a signal there that is either strange in shape, or strength and that pokes curiosity. With current detectors we can already manage some poor direction finding, but with some more detectors around the world, and improving sensitivity, it is already estimated that we will soon be able to point exactly where a gravitational wave came from Additionally there is the point that if there is any fleeting chance of fitting FTL to our current understanding of physics, it involves excessive abuse of general relativity, and gravitational signatures would be more than expected of such exploits. [Answer] Let's take a step back, because it is much easier to imagine people less smart and knowledgeable: You barely managed to get your stone axe mostly fixed to that piece of wood and just then see a bird fly by. What would you learn from that event? Almost nothing useful - that flight is possible for birds, and that's about it. The same would happen here. Assuming ship gradually continuously accelerates from 0 to c (and beyond), then yeah, it might be the simplest explanation is that FTL is indeed possible, winning against competing "they have super-duper broadband cloak they turned on just when they reached almost c". But beyond making a huge mess in physics, best case nothing would really change for science. For example, LHC results might be possibly useful to laymen in several decades. Or perhaps never. We shall see. Cosmology and particle physics are more about pushing boundaries of knowledge than anything useful - these are experimental math. And these are results we have managed to produce ourselves (so we knew what to search for, where is the boundary and so on), unlike an one-off event. What could change is that we now know others have FTL and know how to get to our solar system. Maybe leading to a lot of money for science and defense. But this would be a political development, not a scientific one. [Answer] Assuming that coming out of FTL is a pretty energetic event, what you'd first detect is probably a massive(?) gamma ray burst, so that's the context in which the observations will happen. We don't expect GRBs to move, so by the time the source of the GRB is pinpointed in the sky and optical telescopes repoint themselves to the indicated coordinates, they'll find nothing. Optical sky survey telescopes might pick out the object at some later time (depending on how big or luminous it is), but if it still moves much faster than the orbital velocity of more or less anything in our solar sytem (e.g. >1000km/s), it's unlikely it will be flagged up as a single moving object at first, in fact it might be discarded as a bad pixel. It will take years if not decades for someone to piece the puzzle together, the strange GRB without any optical counterpart and the systematic "bad pixels" in subsequent survey photos, and chances are they won't publish it anywhere because it sounds so crazy. *p.s.: Of course the above scenario isn't what would definitely happen, like most sci-fi authors, I cheated. I started out with my own (not too flattering) view of human society, and worked my way backwards from there.* *p.p.s: It is also feasible that such an event also generates gravitational waves, which combined with the GRB would point towards a black hole merge scenario, except it would very quickly become apparent that the waves don't match the pattern we know about the mergers. It could be this anomaly that sets someone off to check the sky survey photos.* [Answer] One very important discovery would be: Not only are we alone in the universe, but an alien civilization definitely knows we exist. Traveling "just outside the lunar orbit" almost certainly puts the ship within the sphere of influence of the planet. Given the great distance traveled, the incredible speeds, the fact that it decelerates and accelerates at the planet, and the tiny sphere of influence of the planet, the people of the planet will be able to be absolutely certain that the ship was sent to observe the planet. This will cause a huge increase in SETI-like activity, as well as a huge increase in planetary defense spending, and spending on looking for exoplanets and general astronomical observation. ]

[Question] [ **Closed.** This question is [off-topic](/help/closed-questions). It is not currently accepting answers. --- This question does not appear to be about worldbuilding, within the scope defined in the [help center](https://worldbuilding.stackexchange.com/help). Closed 3 years ago. [Improve this question](/posts/76274/edit) In my world, having a nuclear reactor at your own house is legal, in fact government donates money in the form of subsidies ( So no constraints of funds). This might have been practical because of energy crisis and lack of expert engineers, or might just be a kind of revolution. Rest of the things are normal. I am high school teenager and I want to build a nuclear reactor efficient enough to power up a house (about 8 kW). What are all the things I require and how can I get them? What are possible ways of disposing the waste generated which can be carried out by an individual? P.S. - Consider 'I' as a hypothetical child prodigy (not me). [Answer] In this case, it'd probably be common practice to use a Liquid Fluoride Thorium Reactor (LFTR pronounced "lifter"). It's a kind of Molten Salt Reactor (MSR) that enriches Thorium (~3x more abundant than Uranium in Earth's crust) in a liquid salt and then burns the product of that enriched material (now U-233) in a liquid salt. Or perhaps some other (even better) kind of MSR we haven't come up with yet. This kind of reactor was researched in the 60's - lack of funding and foresight (as well as widespread and bad information) have prevented it from becoming a reality here in the USA. A LFTR is safer and cheaper than our current pressurized water reactors by a large margin. It also produces less waste - and that waste is dangerous for much less time. While I don't expect a scenario like this to occur in reality since the proliferation risk of U-233 is a thing (thus still requiring centralized, guarded reactor facilities), I'd expect that in your proposed scenario, the private sector would have commercialized these reactors to a point that they'd be very cheap, very easy to install, and very easy to operate. If such commercialized products weren't available for whatever reason, you'd need knowledge of the chemistry of the reactor, the pipes to hold the salt, a freeze valve and a heat-dump reservoir, lots of concrete for shielding, a reactor core blueprint, the salt (+Thorium), and additional concrete-enclosed space for the waste. And general radiation equipment such as detectors, suits, etc. It's worth noting that the waste material even for a family's entire life would be miniscule assuming current energy use rates, so storing that waste may not be a priority other than keeping it in a sealed radiation-blocking box under the back patio. I'd encourage you to look up LFTR's on the Internet - you will probably find a lot of useful (and interesting!) information out there. There's a bit of a cult surrounding these reactors - its proponents make it sound like it's the solution to every problem ever. While these reactors could solve a lot of Big Problems at once, there are some technical issues that we haven't worked out yet on the R&D side, and there's a sh\*t ton of gov't policy to wade through even if we do. <https://en.wikipedia.org/wiki/Liquid_fluoride_thorium_reactor> [Answer] # You don't Not without handwaving. ## Teenage and 8 kW This is a first issue. I don't know any country that would allow teenagers to operate power plants on their own. High school teenagers usually can't even become licensed electricians. There was a time when you bought electrical appliances without the plug, and installed plug on your own, at home. But these times are gone now, because this was just a bit too difficult for general public. And we are talking about really, really smaller power and much simpler operation. ## Nuclear reactor size Smallest presumably safe I've heard about is [Chinese cargo container reactor](http://www.dailymail.co.uk/sciencetech/article-3832725/World-s-smallest-nuclear-power-plant-China-developing-reactor-tiny-fit-shipping-container.html). > > The tiny power plant would fit inside a shipping container and could generate 10 megawatts of heat - enough to power 50,000 households. > > > Given that you can't get any cheaper or smaller and still have good security against leakage etc. This means it won't be cheaper. If single unit won't be cheaper, then your idea is 50,000 times more expensive. No government will ever fund it, when they could fund something so much cheaper with similar effect. There are [other designs](https://en.wikipedia.org/wiki/Small_modular_reactor) but the problem is the same - with a single unit, you will be able to power up a whole town, and going smaller doesn't make it any cheaper, and not much safer. ## Obtaining materials You need to handwave weapons of mass destruction and dirty bomb terrorism risks from your world. This is a really, really big handwave. Currently, any fission materials are (supposed to be) tracked as national security issues. ## Waste disposal Surprisingly, this one is only a small issue. If you can have a safe cargo container reactor, you can just send it for refueling, and have waste processed the way it is now. [Answer] For many technical reasons using nuclear power for individual houses is not a great idea. With nuclear power you either get too few energy to power a house (RTG's), or way too many and it's incredibly wasteful (fission, fusion). And while operating an already built nuclear reactor is not that hard - sailors do in nuclear ships and submarines, and they don't demand a physics grade to work in the navy - building it DIY-style it's not going to end well. To start with, mining the fissile material is a pain in the ass. Several tonnes of rock are needed for every kilo of uranium, and most of it it's **U-238**. You'll need to refine it to augment the quantity of U-235 in the mix, or the chain reaction won't be sustainable (how high the percentage of U-235 depends on the type of reactor; it's higher for BWR than PWR, for example). And centrifuging uranium it's not something you can do in your washing-machine. Building the uranium rods that you need in order to run your reactor is a very long and complex process, and then you have to put them in a reactor carefully designed to fit them at precise positions and geometry. In short, you *could* buy the reactor and the fuel and run your own nuclear plant with some handwaving here and there - after all, it's all run by computers, nowadays - but for building one with spare parts, I'd say "No". [Answer] You can draw inspiration from what Enrico Fermi's team did in the lab of via Panisperna. Assuming you have some fixile material, you would also need: * a neutron generator * a neutron moderator (Fermi used paraffine, but also water could do) if you put the fixile material in water and irradiate it wit a flux of neutrons, you will end up breaking some atomic nucleus and generate energy. That energy will warm up the water. If you want to scale up and build an atomic pile, like Fermi did in the US with [CP-1](https://en.wikipedia.org/wiki/Chicago_Pile-1), the size will grow up and you won't be able to host it in your backyard. [](https://i.stack.imgur.com/Bk2Aj.jpg) > > It contained 45,000 graphite blocks weighing 400 short tons (360 t) used as neutron moderators, and was fueled by 6 short tons (5.4 t) of uranium metal and 50 short tons (45 t) of uranium oxide. > > > and > > The pile had run for about 4.5 minutes at about 0.5 watts. On 12 December 1942 CP-1's power output was increased to 200 W, enough to power a light bulb. Lacking shielding of any kind, it was a radiation hazard for everyone in the vicinity, and further testing was continued at 0.5 W. > > > [Answer] # They could, but they will not be allowed to Physically, in your world, it would be possible for your high-school to build it. As long as they get access to the material they will be able to pile it together — literally so; the first reactor ever was in fact called [Chicago Pile-1](https://en.wikipedia.org/wiki/Chicago_Pile-1) — and get a chain reaction going. And even **today**, [high-schoolers are doing nuclear reactor experiments](https://en.wikipedia.org/wiki/Fusor#/media/File:Homemade_fusion_reactor.JPG), constructing so called [fusors](https://en.wikipedia.org/wiki/Fusor). [](https://i.stack.imgur.com/nAC0k.jpg) *This is a fusion reactor made by a high-school student* The main problem is that these fusors to not have a $Q > 1$, which is to say they use more energy than they produce. Never the less: high school students are creating nuclear fusion. The thing that will trip up your intrepid high-school student is not that they will not physically be able to, but that **they will not be allowed** to. As hinted in [Fight Club](https://en.wikipedia.org/wiki/Fight_Club), you can make quite destructive things with household items. [Sweden's own version of the Radioactive Boy Scout](http://www.businessinsider.com/sweden-nuclear-reactor-angelholm-2011-8?IR=T) not only managed to call the attention to the [Swedish Radiation Safety Authority](http://www.stralsakerhetsmyndigheten.se/in-english/about-the-swedish-radiation-safety-authority1/) for trying to make a reactor out of discarded smoke detectors, he also did other things, such as make [ricin](https://en.wikipedia.org/wiki/Ricin). This is — of course — not permitted. When it comes to handling substances that can be dangerous to life and the environment, this is usually regulated. You will need to seek a permit in order to engage in any such enterprise. This applies especially if your enterprise will leave any kind of hazardous waste. You say "but I will just have him deal with the waste". Well no, this is not acceptable. He could do it, simply by just depositing it 10 meters down in the ground. From a physical point of view this would perfectly safe. But the regulatory authorities would throw a fit about it because this is not allowed. When it comes to waste of this sort, it needs to be dealt with in a professional, monitored and approved manner. Also fissionable materials — such as uranium — are **very highly regulated** and cannot be obtained willy nilly at the nearest Nukes'R'Us. Even if you never intend to put the Uranium in a reactor, the it is a toxic heavy metal, and you may not play around with that, at least not legally. [Answer] Ken Silverstein: The Radioactive Boy Scout: The Frightening True Story of a Whiz Kid and His Homemade Nuclear Reactor. This book is the answer in depth to your question. In 1993 David Hahn did just that. The book is his story. Book was published for the first time in 2004 (and later on the 11th January of 2005 as publisher's 33673rd edition) by Villard with ISBN-10: 0812966600. [Answer] 1.7 billion years ago, nature assembled a natural fission reactor at a location now called Oklo. Back then, there was more U235 in natural Uranium than there is today, and so creating a high enough concentration of natural Uranium is all that was needed. <https://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor> This is Worldbuilding, so you might be an intelligent humanoid alien living on a planet where progress from supernova-dust to solar system to life to people moved faster than here on Earth. In which case, your society is going to have some interesting possibilities and problems. It's also possible that evolution has made you somewhat more radiation-tolerant than us Earthlings, if there are natural nuclear-geothermal heat sources dotted around all over the place, along with shorter-lived fission fragments in your groundwater. (Note: little of Earth's crust today is 1.7 billion years or older, so the Oklo event was probably not the only such instance, just the only one that we have evidence for). [Answer] Your biggest issue with building a reactor would be that they've got a minimum output, well in excess of what you could use. You could build an RTG (<https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator>) instead, though it'd probably be well below what you could use. You'd just need: * something to convert heat to electricity, e.g. + peliter heat pump + turbines, which could be bought pre-assembled + a steam engine linked up to drive a generator * a large lump of radioactive stuff; I'm not sure how critical it'd be what you picked, as long as it got warm, and didn't go critical. A large pile of smoke detector samples might work. Assuming your world where this was legal, you could presumably buy a suitable source. And then you'd probably need chemo, unless you'd been extremely careful... [Answer] The problem with your basic premis: promoting household reactors are two fold. 1. Reactors benefit from economies of scale. It costs almost as much to make a reactor for one house as it does to make one for ten houses. This would be a very inefficient policy. 2. There isn't enough uranium in the world to supply widespread use for any reasonable length of time. You could use thorium which is much more common but it has other issues (that you may be able to hand wave). That being said, thorium is very easy to get. The US and China have piles of it sitting around as the leftovers from mining rare earth elements (they tend to be found together). Home made reactors are likely to be "low output" reactors. The more you concentrate the neutrons, the faster the reaction. By having the radioactive sources more spread out, they will decay at a slower rate. They would be bigger for any given output but wouldn't need to be as complex. Current reactors run on a needle point balance. Since the low efficiency reactors wouldn't burn through their fuel source as fast, there would be less radioactive waste and the waste would be easier to handle. Current "spent" rods are still quite hot. They often need to be kept in a water bath of flowing water to keep the water from boiling off (why they don't make a steam generator from that, I've wondered about since I was 10). If home made reactors are legal there is likely some sort of radioactive waste disposal infrastructure. You would only need a pick up every 10 or so years. Just call 1-800-GLOW-GON. [Answer] Starting up a nuclear reactor requires that you have enough fissile material for a critical reaction. This amount is know as the [Critical Mass](https://en.wikipedia.org/wiki/Critical_mass). Many people are suggesting using the normal Uranium 235 fuel cycle, but the critical mass for low grade uranium ore (i.e. the percentage of the Uranium that is 235 vs 238 or other isotopes) is very high, at 15% it is over 600lbs, and that requires a lot of enrichment, natural 235 is only around 0.75%. This is why nuclear reactors are not usually built in small power outputs, there are fundamental limits on how small you can make them. As far as the waste disposal portion of the question, the standard method of nuclear waste disposal is essentially to contain the material and put it somewhere isolated until it isn't radioactive anymore, for longer lived wastes this is still an unsolved problem requiring tens of thousands of years of isolation, this isn't likely to work well in your backyard either. [Answer] There are several simple (loosely defined) ways to accomplish this without a bulky reactor plant. Use the heat from radioactive decay to create power. It eliminates the need for the reactor vessel and a cooling structure. I understand this is not a nuclear reactor, but it is a way a home consumer could access nuclear power. **Advanced Stirling Radioisotope Generator** An Advanced Stirling Radioisotope Generator (ASRG) is a radioisotope power system developed at NASA's Glenn Research Center. It's based on an idea of creating power from the heat of radioactive decay from plutonium. It uses a Stirling power conversion technology to convert the radioactive-decay heat into electricity for use on spacecraft. A Stirling engine is a closed-cycle regenerative heat engine with a permanently gaseous working fluid. Closed-cycle, in this context, means a thermodynamic system in which the working fluid is permanently contained within the system, and regenerative describes the use of a specific type of internal heat exchanger and thermal store, known as the regenerator. The inclusion of a regenerator differentiates the Stirling engine from other closed cycle hot air engines. [](https://i.stack.imgur.com/RF45V.gif) The positive is this a pretty simple mechanical system. The drawback is that this unit will produce 130 watts of power from 1.2 kilos of plutonium-238-dioxide. To meet your power goals, you would need to run several in series, or perhaps in your world, the technical limitations were overcome and one unit will produce the required power. For more information, check out: <https://en.wikipedia.org/wiki/Advanced_Stirling_radioisotope_generator> [](https://i.stack.imgur.com/pT8NZ.jpg) **Radioisotope thermoelectric generator** Another existing power source is the Radioisotope thermoelectric generator. The positives are this can be created with no moving parts. The drawback is a low power yield. <https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator> **Thermovoltaic** A Thermovoltaic generator captures the light given off the thermal source and translates that into power. The positives are that thermovoltaics provide consistent and reliable power without large amounts of fuel. The drawback is that they are not very efficient. If your power source was in a sphere of thermal-voltaic cells, you could run them in series to produce the energy you need. Perhaps in your world, there's a more efficient source of thermovoltaic cells, which could produce the 8,000 watts of desired power. <https://en.wikipedia.org/wiki/Thermophotovoltaic> [Answer] First, what do you mean by "efficient enough" ? The meaning of efficiency is getting high yield out of less amount of fuel. This will require a highly refined system, which is...unlikely for anyone below specialised company to achieve. As for building a reactor: you need four basic components. A reactor proper - meaning container of fissile material, is the first one. Second one is cooling system, both to help carry off energy to convert into electicity, and for your reactor proper not melting down within minutes to seconds from putting together enough fissile mass for it to achieve criticality. Third is a power generator. This one is easy - any steam turbine will do the trick. Fourth one is shielding. For a teenager, only the generator component would be understandable, and somewhat possible to construct. Most problematic ones are the ones that are most crucial - the reactor itself (if only due to, really, insane level of metalurgy required. Just a steel tube will not do the trick. Correct materials used are also a must, because radiation-material interaction can be very damaging to both reactor, and anyone around it, esp. in the long run). Radiation protection is even more tricky, not to mention work and knowledge required to be able to run the system in a stable configuration (for reference, if you get an unstable configuration, Chernobyl happens...rapidly). This might be doable on a college level, MAYBE. And thats stretching it. [Answer] Iff you can handwave the fuel problem, particularly the fuel problem for a relatively highly enriched fuel (U235 or Pu239 or a mix would do) then the actual machine is not particularly complicated, but you will want to be able to pour significant concrete for a biological shield. A single fuel element, (Heavy) water cooled with a surrounding neutron reflector close enough that the thing is slightly under moderated (Important to have a negative void coefficient), in a sealed stainless steel tube maybe 10M long with the water level extending to maybe 5M above the fuel could I suspect be made to run in equilibrium between the steam (subtracting reactivity due to the negative void coefficient) and the slightly above delayed criticality of the system. The steam generator for the secondary loop would wrap around the top few meters of the thing (Doubles as biological shield for the gamma from the nitrogen decay chain). Add some boron compound to the heavy water to allow the thing to be throttled by tweaking the water chemistry and to extend fuel life by reducing the poisoning as the burn up increases? There might also be some tricks you can play with doppler broadening to make the thing more reliably self regulating. @10kW thermal, you would have to **REALLY** work to get a meltdown and could probably design in sufficient thermal mass to deal with the short term decay heat long enough for the decay heat to drop to the point that convection and conduction would keep the fuel from melting. IIRC there was a (Soviet?) criticality accident that left them with a PU bomb core running as a reactor for some time with the control being the equalibrium between the core expanding as it heated and the increased neutron losses from the surface area, I suspect they eventually sent someone in to knock the thing apart with a stick! Iff you can handwave a low energy cost efficient muon source then a muon catalyzed fusion machine may just be possible, not sure that Hirch/Farnsworth does it even then, but Bussard polywell just might. Not sure most 14 year olds have the combination of maths, physics and mechanical skills to put a reactor together (I certainly would not have been able to do it back then). [Answer] There are two massive problems that make this completely non-viable and a third that's going to limit you. 1) Uranium-based reactors require a critical mass of uranium to work. This sets a minimum size for the reactor and from a practical standpoint a minimum power. Trying to power a house from a uranium reactor is like trying to power your toy boat with the engine out of a yacht. This can be avoided with a neutron-induced thorium reaction. No critical mass is necessary and thus it can run at lower power levels. 2) Shielding. It matters not whether you're producing a 8kw or 8gw, your shielding thickness is almost the same. Your containment is the same. If you want something safe to be around it's simply going to be too big for home use. 3) Cooling pools. Again, a shielding issue. They're big to put enough water between you and the hot stuff. Once again, something that won't fit in a home. [Answer] The key problem with building a backyard nuclear power plant is getting sufficient quantities of fissile material of sufficient purity to easily achieve criticality with a crude reactor design. Naturally occurring deposits of fissile materials burn themselves out fairly early in a planet's lifetime, so by the time 4+ billion years has passed, all that is left is the stuff that takes quite a bit of processing to burn, and it is safe to say that processing of natural ores in their current state into nuclear fuel is something that is well outside the capabilities of even the most industrious and precocious teen. But OP did not specify that this planet was Earth. If we assume his world is a geologically much younger planet (about 2 billion years old, give or take a few hundred million), then it is conceivable that naturally occurring deposits of fissionables are still lying about that can be purified by simple chemical processes that any child can accomplish. For example, she could crush the ores with a hammer or some other means, wash the crushed ore in acid to put the fissionables into solution, filter out the crud from her solution, and then raise the pH of the solution with lye to make the fissionables precipitate out. If she is starting with high enough grade ores to begin with, then this should be all that is needed to get nuclear fuel that can achieve criticality. Then our young atomic engineer needs an atomic pile, and that can just be a pile... as in a pile of dirt. Run some plumbing through the pile to extract heat to drive whatever heat engine she chooses, and some other plumbing through which she can maneuver moderators/neutron sinks to regulate the power output by pushing them through the pile to where her fuel is buried. She might also want to bury some thermocouples and maybe other detectors in near the fuel to get an idea what is going on while she is shuffling her makeshift control rods about. The resulting nuclear power plant would be crude, and the chances of prompt criticality accidents sterilizing the entire neighborhood would be ludicrously high, but this is a young planet, which means the inhabitants are colonists from someplace else as the only things which would have had a chance to evolve there yet would be things like algae and bacteria. This leaves open the possibility of a fairly low population density (very, VERY large backyards), and thus relatively limited concern over what the neighbor does on their side of the hedge. If your nearest neighbor is a few miles away and they are not downwind, then what do they care if you mess up and make a glowing crater behind your house? [Answer] Buy an old ship diesel engine (2 stroke as they are) with a generator attached to it. Drill the bottom of the cylinders with reduced diameter. Thread the extra centimeters. Buy a bunch of thin pure plutonium screws with 100g weight each with the same diameter. Screw some of them in each cylinder from the bottom - on top of each other using a long tool and a horizontal bar; I guess it will be about 40 of them per cylinder needed. 12 cylinders, 4 kg plutonium each. When your "screwdriver" comes out of the cylinder glowing hot, you put enough plutonium in that cylinder. Over to the next one. Use water as fuel (use the fuel pump to pump it from your well or lake) and start the "engine" using its original starter. If it's not running fast enough, put some more plutonium "screws" in. The plutonium will last for long enough that you don't have to worry about its disposal. [Answer] ### You Can Do This First get hold of some fissile material. Uranium-235 can be dug up. Make sure it's quite pure, and ideally buy it in rods. Now stick those rods into a boiler attached to a steam engine. Use the engine to drive your electricity generator. Extra marks for re-using the water by condensing it from the steam outlet. You can use waste heat to warm the house, or for heating the swimming pool, as you like. [Answer] By far the easiest way would be to buy up a power company that is already planning to build a nuclear power station. When the security fence goes up, build an actual dwellinghouse for yourself at the entry instead of the usual prefab security hut. Have the back door open inside the fence. Now you can build the nuclear reactor in your backyard. [Answer] It's easy to build and run a nuclear reactor. I don't have the answer on how to build it because it's classified. The problem is after you've run it for a while. Neutrons propagate and everything starts to become radio-active. The water you use to cool it becomes radio-active. The shielding to stop the radiation becomes radio-active. The radiation degrades electronics similar to the way human cells die from radiation exposure. [See Chernobyl cleanup problems](http://www.the-scientist.com/?articles.view/articleNo/10861/title/Soviet-Official-Admits-That-Robots-Couldn-t-Handle-Chernobyl-Cleanup/) ]

[Question] [ So: We all know about the Labyrinth and the Minotaur. One is a maze of stone tunnels, and one is a half-man half-bull killing machine. It's reasonable to assume that the Minotaur requires a decent amount of energy to keep going (Lets assume about 3000 KCal a day), and it's also reasonable to assume that he needs to eat a lot of protein (I mean, what kind of dread guardian *doesn't* have biceps the size of a normal man's head?). The issue here is that the Labyrinth this particular minotaur lives in is stone walled (with decent mortaring), subterranean and lit by endless torchlight. The Minotaur can't get to the outside world (stupid small doorways), but he knows the tunnels like the back of his hand. Also: Nobody comes to feed him ever since he ate an acolyte that was irritating him. **How does the Minotaur reliably meet his dietary requirements? What sort of ecosystem will the Labyrinth need in order to support one Minotaur sized Apex predator?** [Answer] The [myth of the Minotaur](https://en.wikipedia.org/wiki/Minotaur) states that the monster must eat humans for sustenance. It also states that Athens was obliged to provide seven young noblemen and seven noble maidens each one, seven or nine years (sources differ) as a sacrifice to feed to the minotaur. Assuming that the minotaur requires 3000kcal per day as per the OP's question, [and that a 70kg human provides 750 mj, or 179254 kcal](http://cosmoquest.org/forum/archive/index.php/t-97026.html). Thus, we have: 179254 \* 14 / 3000 = 836.52 Thus, one batch of Athenian sacrifices might feed the OP's Minotaur for 2.29 years. Given these energetics, the minotaur could either be bigger and require more energy (up to 6870.79 kcal/day) and have yearly sacrifices to feed him, or he would need his diet supplemented by additional human sacrifices sourced from elsewhere. Given the pragmatics of the situation, I'd go with the more (locally) popular option of feeding the minotaur yearly foreign sacrifices. So, if we play with the input parameters of [this](https://www.bcm.edu/cnrc-apps/caloriesneed.cfm) online calculator, based on the presumption of a 21 year old male, the Minotaur could be 300cm tall (if standing fully upright), weighing 250kg, and considering that he would be only lightly active - given the need to run down and kill a sacrifice for a few hours each 26 days - these yearly sacrifices would be entirely sufficient to last him all year. As an additional factor, the online calculator I used states that at the height and weight I proposed, the Minotaur would be overweight, with a BMI of 27.7. Since the Minotaur would be fed once each 26 days, and may well eat a sacrifice in less than this amount of time, having fat reserves would be useful. His weight would obviously fluctuate [Answer] **Insects** Tasty tasty insects. If insects aren't plentiful enough in the Labyrinth, he can supplement his diet with spiders. [](https://i.stack.imgur.com/ptCEi.jpg) The Minotaur needs food which is calorically dense, but doesn't require sharp, meat eating teeth. Insects, specifically cooked ones, are the perfect solution. They can be crunched up and eaten, providing a high protein high calorie diet, but aren't too chewy, like red meat can be. They're also abundant and can be efficiently farmed in confined areas, like the dark twisting passageways of a maze. Insects are also far less likely to carry parasites that can be passed on to the Minotaur than mammalian food would be, so if he doesn't have access to cooking facilities, they could fairly safely be eaten raw, especially if he mostly stocks his insect farms with fungus or vegetable matter. [Answer] It's going to be very difficult for the Minotaur to be self-reliant. As you state, this maze is not a very good place to grow food. So here's how you do it: **Jurassic Park Style** Have a narrow, vertical shaft leading down into the heart of the maze (its existence can be a closely guarded secret). Lower chunks of meat in for the Minotaur to feed on. **Only One Entrance** Alternatively, if you ***really*** want a single way in/out simply lead animals such as sheep or cows into the labyrinth a little way, and run out. If you don't want to risk even stepping foot inside then rig up a pulley system (anchored inside the labyrinth) and pull the animals in from the outside. > > All you'd need is a long loop of chain and a ring firmly affixed in the wall of the labyrinth. You tie the animal to the chain and pull, leading it inside. Once the Minotaur rips the animal off the chain you can cycle it through the ring and pull in the next one. (you could potentially have to fix the ring/chain every once in a while, but the Minotaur would probably let you, or even help you do it) > > > **Alternate Food Source** Another way to provide the Minotaur with food is to have animals stumble into the labyrinth through some sort of natural cave system. It would make the food source unreliable/hit and miss, but it would be a lot more realistic than having your fearsome murder-pet lick lichen off the walls. **Rat Burgers** Realistically the Minotaur won't be able to sustain itself unless it's quite intelligent and resourceful. However, assuming that you really want a hands-off approach then it would probably set up traps for the many pests roaming the underground tunnels. Eventually it can even start breeding rats or other pests for a food source. **You Should Feed It** If you are the one feeding this thing then you have leverage over it. It has a reason to at least ***pretend*** to obey you. You also have some very real power over it. If it becomes too rebellious you cut its food rations and discipline it. If it tries to attack you, or goes berserk simply withhold all food and watch it slowly starve to death. A self reliant Minotaur is not stuck inside the maze - it's ***in charge*** of a maze you can't get it out of. [Answer] The maze isn't place to keep the Minotaur trapped. The maze is a Minotaur nest. The Minotaur is a mythical beast. It is an infovore: it eats information, and excretes mazes (information waste). It is attracted to civilization because civilization generates tasty highly abstract information: lists of goods, taxes, areas, names of citizens, salaries, calendars, etc. If not careful, the Minotaur gorges itself on the information content of a civilization, leading to the civilization collapsing in bureaucracy, corruption and disorganization. Minotaurs that adapt to their prey build a nest -- a maze of digested waste information (and emergency rations) and a distance buffer to keep their appetite in check -- and only eat enough to keep themselves healthy. Highly organized structures, like humans, provide a tasty dessert like snack on top of the ambient abstract information of the civilization itself. Humans who have complex plans have a better fragrance. The Minotaur isn't trapped in the maze: the civilization is a domesticated information factory owned by the Minotaur. [Answer] The top half of a Minotaur, including his digestive system, is bull, so one would assume that the natural diet of a Minotaur is very similar to that of a cow: approximately 2% of their body weight in foliage a day. Gorillas are another example of highly muscular animals that achieve their physique despite a pure vegetarian diet, disproving the need for high protein. That said, the subterranean nature of the labyrinth is problematic- that may limit things to fungi and roots from larger plants growing above. Maybe the Minotaur has found a way to sustainably tap into the rich sap of trees above. Apart from that, burrowing animals and insects are your alternative potential food sources. Given the static location of a maze, it would really have to serve as a less-dangerous location compared to predators above ground. If the Minotaur's hunting ground is too small, he will starve himself by over-feeding or scaring off potential prey in that regards. The third alternative is domestication of animals that could fetch food on his behalf. Maybe the Minotaur is an avid bee keeper (if we're going to stick to the supernatural, perhaps he blows smoke out from his nostrils for just this reason) or looks after honey-making ants. Perhaps he keeps cats that bring him kills and keep him fed. Well-trained monkeys that steal from the populace? There's a lot of potential there. [Answer] I thought the whole point of the story was that the Minotaur ate people, the various condemned prisoners sent to die in the Maze. If you want to get all sciency-y and realistic about it, you could speculate that when there aren't enough prisoners to sustain him, they force some animals into the Maze. Presumably they'd be trapped there as easily as people, and the Minotaur could find and eat them. Of course the Minotaur is supposed to be half man and half bull, and in real life neither men nor bulls are carnivores. But I don't think the writer of the original worried overly match about that. He's a fictional monster: giving him inconsistent eating habits is the least of the unreality about him. [Answer] The answers provided above are excellent - serious debates about calorie per sacrifice breakdowns and positing that the Minotaur is probably running the labyrinth while keeping bees, are reasons why I love human logic. However, I think the answer is already in the question: "and lit by endless torchlight." Torches need maintenance - new ones need lighting, burnt out ones need replacing, piles of old torches to be cleared away. This, given the era, means low-level servants. Quite possibly slaves, even. Disposable. ...lunch. Depending on how rapacious the Minotaur is when he eats the torch-bearers, this also explains the smoke he breathes out. Nothing more than literal heartburn. [Answer] There are other minotaurs than the classic Greek one. Consider the [Dr. Who](http://tardis.wikia.com/wiki/Minotaur) versions. * Second Doctor: The Mind Robber - [fictional Minotaur](http://tardis.wikia.com/wiki/The_Mind_Robber) * Third Doctor: The Time Monster - [transformed being](http://tardis.wikia.com/wiki/The_Time_Monster) * Fourth Doctor: The Creature from the Pit - [variation on Greek](http://tardis.wikia.com/wiki/The_Horns_of_Nimon) * Eighth Doctor: Caerdroia - [an illusion](http://tardis.wikia.com/wiki/Caerdroia_(audio_story)) * Eleventh Doctor: The God complex - [a psychovore alien](http://tardis.wikia.com/wiki/The_God_Complex) shown below They eat different things: time lords, victims, electricity, worship. [](https://i.stack.imgur.com/k676N.jpg) <http://www.bbc.co.uk/programmes/profiles/447FRsQ0z5StssHllhppp4R/minotaur> [Answer] It would be very, very difficult for a large creature to survive on a diet of periodically sacrificed humans if it was regularly active. My guess is that the Minotaur's lifestyle would probably be a lot like a spider - it would spend most of its time dormant, saving energy for the rare occasions when a victim enters the labyrinth. It would need to have excellent hearing, both to know when there is a victim to be caught and to locate the victim quickly and efficiently. If it had a means of attracting small prey like insects or rodents in order to eat them while expending very little energy (producing a smell, perhaps) that would be helpful as well in staving off hunger. Alternatively, since the sacrifices were regular, perhaps the Minotaur spends most of its time in hibernation, and the sacrifices are coordinated to occur when it wakes up. [Answer] First, i think you forgot that labyrinth wasn't made from natural cave systems, but according to Homer (not Simpson) it was designed and built by Daedalus. As it was designed by one of the greatest minds who lived in that period, we can assume there was a safe way to provide food for the Minotaur. When I was child, I got comic book about Daedalus. In that comic book, in the labyrinth there was some kind of "dining room" with a large hole in ceiling. Through that hole, servants were dropping baskets with food for the Minotaur. Later, obviously, he got yummy Athenians, but that was different story. [Answer] Not sure this is a good answer, but myths don't really stack up to modern realities. Remember that the Minotaur was born because a woman got hot for a bull, and built a cow-shaped frame she could tie herself inside so that the bull would have sex with her. Then she got pregnant and gave birth to a half-human half-bull creature. (Yes, this particular bit of Greek myth tends not to get published as much!) My point is that the genetics of that simply don't work, because the two species aren't compatible that way to produce viable offspring. So if we discount all that, we're left with "because it's magic". And really that's as much detail as Homer and his mates would ever have gone into. ]

[Question] [ Humanity has just developed a star drive and begun sending their first probes, and have now discovered an unstoppable force of doom approaching to destroy the solar system. Their only option is to escape to another star system, but they don't have the resources or the time to build a fleet that can evacuate Earth before it's destroyed. Instead, they decide to simply move the entire planet. A star nearly identical to the sun - about 1000 light-years away - is chosen as the target, and a series of drive installations are constructed. The drive can safely teleport Earth, but not all the way to its destination. Instead, it will jump to a point in interstellar space about halfway there, and then the drive will be recharged before jumping the rest of the way. This process will take approximately 5 minutes. So, what happens in those 5 minutes? * The drive teleports the Earth instantaneously and with no perceivable motion. * Any change in velocity is made during the jump without applying any acceleration. * The Earth will appear exactly in its new orbit after the second jump. * The jump field extends about 200km above the surface (anything orbiting inside it also jumps, if it matters). * The Moon is left behind. Everything I've been able to find related to this is some variation of "what if the sun disappeared?", and the answers are always "We would all freeze and die.". I'm pretty sure that the Earth retains heat well enough that 5 minutes without sunlight won't cause a catastrophic temperature drop (But correct me if I'm wrong), so in this case I'm more interested in what effects the sudden disappearance (and reappearance) of the Sun's gravitation pull causes, and what effects losing the Moon has. PS this is my first question here, tips are welcome! [Answer] Short term effects are pretty much covered in the other answers and are probably nothing of interest. Then again, a great deal of things to fix later: * The night sky will be completely different. Most of the naked-eye-visible stars are closer than 1000ly. Some satellites, some animals and some people will lose orientation. Animals will need a great deal of time to adapt. Some of them will fail. No sat communications, weather forecasts, GPS, etc... for a while. Aviation and marines in really deep trouble. Of course, some of the technology and activities can be prepared in advance, but a lot of everything will fail anyway. * Tides. A lot of things on Earth are powered by them, including, but not limited to, aquatic animals lifecycles, ocean water deep mixing, plate tectonics, etc, etc... There are solar tides, but they are like 1/4 of the magnitude. It would be easier to bring the Moon along than deal with everything tide-based. * Long term orbital stability. Earth is in an orbital resonance with Mercury and Venus and, to some extent, Mars. Since you managed to move the Earth, you will be probably able to fine-tune its orbit later (subject to budget cuts and political hassle). * How much solar activity to expect from the new star? A Carrington event yearly? Or a Maunder minimum? Either of these is quite a hassle. * How old and mature is the new solar system? Do we get a meteorite shower out of a sudden? * How old and mature are the neighboring stars? We don't want a supernova nearby, do we? * Subtle changes in the climate. p.s. while at it, you may as well fix the calendar. Integer number of days per year, please. 350 is good - the weeks will align favorably. --- p.s.2 inspired by the comments: The knowledge that the year is not exactly 360 days is rather recent anyway. On the other hand, we want a main sequence star and they have fixed mass/age/luminosity/temperature interdependence. We also want an Earth at most 1C hotter or colder than before so the star mass determines the distance where it is exactly warm enough and thus the orbital period. The year/day ratio can be changed by changing either * the Earth rotation rate (disastrous instantly) * the orbital radius and consequently the solar constant (this is the total solar power per area at the particular orbit distance from the star, disastrous for the climate in very short term) * the mass + surface temperature + luminosity + spectrum of the star (unknown, but I am sure we don't have this much freedom here either). Well, the point about the calendar was a joke. The project is hard as hell without bells and whistles. [Answer] Absolutely nothing happens except that it's night for about 5 minutes everywhere on Earth. It would take several days for the tides to even out. It would take several months for the foodweb to collapse. It would take several years for the planet to cool below freezing. It would take several millennia for all of the oxygen produced by photosynthesis to be used up. At most you'll see wind patterns change as the temperature diffusion across the planet changes with no day side providing heating. However, in 5 minutes, even this effect is likely to be extremely small. Think of it in terms of a solar eclipse but on a planetary scale. In fact, 5 minutes is about an average time for a solar eclipse. Bugs will come out early, birds will think it's night time and go to sleep, animals might bed down, winds shift slightly, etc... But overall, solar eclipses have no real lasting effects, and neither would your scenario. [Answer] Stix's answer is almost correct, but doesn't take the [Earth Tide](https://en.wikipedia.org/wiki/Earth_tide) into account. To summarise, the Sun and Moon cause tides in the "solid" body of the Earth. It isn't *rigid* - nothing is on that scale - and the surface flexes up and down twice a day. The maximum movement is about 55 centimetres each day at the equator. The flexing can be ignored for most purposes, but matters for things like the design of large particle accelerators, very precise GPS positions, and long-baseline interferometry. It also occasionally [triggers](https://en.wikipedia.org/wiki/Tidal_triggering_of_earthquakes) small earthquakes. The sudden loss of the Sun and Moon's gravity will cause the Earth to start to slump back towards the shape it would "naturally" have without them. This probably won't trigger any major 'quakes, but it's something that has never happened before, so it would be unwise to make strong predictions. It will be worthwhile to make the Earth appear after the second jump with the new star in the same position relative to Earth as the Sun would have been without the jumps, so that the slump gets stopped and Earth moves back towards its customary shape. The lack of a Moon will make things seem different, though. Is there a plan to send a mission back to fetch it? Also, most medium- and high-orbit satellites will have been left behind. We'll have lost geosynchronous communications satellites, GPS, and various other things. Launching new ones may take a year or two. [Answer] Mostly agree with sentiments so far not a lot will happen, other than the likely earthquake from the loss of tidal forces on tectonic plates. The sizes of the quakes are completely up to the OP, as no one knows when "The Big One" will hit, this might or might not set one ten or none off. More concerned of placing a planetary body into the orbit of an existing solar ecosystem. Sol came into its present state though Aeons of a violent, truly catastrophic natural-orbital-selection. Now it operates like fine clockwork, most everything that could have went wrong did so billions of years ago. See theories like: [Grand tack hypothesis](https://en.wikipedia.org/wiki/Grand_tack_hypothesis). Now take another solar system likely in the same state, it's worked out its bugs. And throw our little blue mote of dust into the finely tuned gears of that celestial dance. You may now find yourself out of the frying pan and in the fire. Very little of this mind you would be immediate. But for sure dropping a new gravity well into an established solar system will have it's consequences. [Answer] ## 5 minutes of night during the day That's about it. There's nothing really wild about interstellar space that could cause Earth harm. There'd be a fractionally higher exposure to cosmic rays, maybe. Not enough to matter in the span of 5 minutes. We endure 10-12 hours of night on a daily basis without much worse for wear. [Answer] One thing I can't believe no one's mentioned is the interstellar medium and its likely effects. Everyone's always happy about what the Earth's magnetic field does to protect us from solar winds—no one stops to wonder what it is that the *sun's magnetic field is protecting us from*. We're all so caught up on what suddenly isn't there, we aren't considering the big thing that now is. The interstellar medium has a lot of different regions in it, with phases distinguished by the nature of the small amount of matter it contains—atomic, molecular, and in the worst case ionic. The reason these phases change so much in a relative vacuum is because of the enormous amount of interstellar radiation. True cosmic rays, not the watered-down stuff we get intra-stellarly. To give you an idea of an approximate scale, the rems per year absorbed by a person traveling through interstellar space has been estimated to be about 70; the safe amount is at most 5-10. This is in a shielded vessel, which is a fairly nebulous concept. Unshielded, there are pockets of interstellar gas reaching hundreds of thousands of rems per second, on account of no stellar magnetic referee. It is the electromagnetic badlands, the radiation wild west. That's not different from the inside of a live fission reactor. Whether our own planet's magnetic field would provide an adequate front against it over a five minute exposure is difficult to determine, but it's a huge risk. You would *definitely* see cancer rates rise. If we're in the wrong spot, we might actually not make it the five minutes. Given electrical interference from relativistic ions, you would also most certainly want to have every computer shut down that can be shut down, and would probably see a number of overloaded transformers and fires within that period. The solar wind is what's batting this stuff back, and when it takes out a satellite or causes a power outage, that's just tough love. While there's always some handwavium involved (at least until our hands can finally do it), I want to highlight that the relative reference frame of the planet is also important. If you're in the reference frame of the average radiation, your concerns are still significant but relatively minimal; if you're outside of this, you need to consider that the planet could be hammered by relativistic nucleons. My speculative-fiction side wouldn't be surprised if we started seeing Cherenkov-blue streaks in the sky in some regions, as charge particles slammed into our atmosphere and were forced to slow down due to the relative change in speed-of-light. So in short, what I am certain of is that cancer rates would spike over the next forty years from the massive amount of unbuffered radiation exposure, we would experience global power outages (something your wormhole might want to take into account), and probably some significant climate change down the line. There's a neat paper speculating on the subject of relativistic ships crossing the interstellar medium, by Oleg G. Semyonov. You can find it at <https://arxiv.org/pdf/physics/0610030.pdf> . It isn't quite your question, but it's very related. This is excellent story material, so I encourage you to give it a read. [Answer] One thing that is being forgotten is the effect of the solar wind on the Earth's magnetic field. The sudden loss of the pressure of the solar wind on the magnetic field of Earth, and the sudden change to the solar wind of a new star would be considerable. The magnetic field would move and probably damage all sattelites. IDK about electronics on the surface of the Earth. There would probably be some damage to the electrical infrastructure akin to what would happen during a severe solar flare, but without the aurora caused by the charged particles in the solar wind ( because there is none in interstellar space ). [Answer] As a supplementary answer, here is an image representation of what would happen, whole Earth at night: [](https://i.stack.imgur.com/rtxG1.jpg) *high resolution* Composite map of the world assembled from data acquired by the Suomi NPP satellite in April and October 2012. Credit: NASA Earth Observatory/NOAA NGDC <https://www.nasa.gov/mission_pages/NPP/news/earth-at-night.html> ]

[Question] [ My mermen & women (fish from waist down and human from waist up, but breathe only in water) are at WWII era warfare and interested in their version of 'underwater,' meaning they want out-of-sea vehicles (sorry, there is no antonym to submarine) to fight over land similar to our attempts to occupy the seas with submarines. I would like it to be the equivalent of a U-Boat / Submarine in an attempt to extend military dominance over land territory. Definitely not air (as in airplanes or jet fighters) .. yet. The merpeople live between 100m & 1m underwater. They want to have military dominance against other merpeople over what we call land. There are no humans, but there are plants, trees and animals on land, in the sea, and in the air. The predecessor to this question is [a comment on a previous question](https://worldbuilding.stackexchange.com/questions/25648/what-would-out-of-water-warfare-look-like-for-underwater-people), in which @bellerophone mentioned a 'water-filled truck.' I'd like the antithesis of a submarine with WWII-level technology. I don't know that steel and titanium would be practical. **What would a water-filled "landmarine" look like?** Assumptions include our typical mermaid and men, population, politics, industrial resources, and geography similar to Earth: I understand that these are all a dramatic stretch, to say the least, but this is worldbuilding.se They want dominance over the land. There are no air-breathing humans, and these merpeople cannot breathe air. +1 to anyone who can find what the heck this thing would be called. Landrover? O-Boat? Are there any terms in literature for this? [Answer] ## I'm sorry to disappoint you but they wouldn't look like anything special. Unlike crafts designed to operate underwater, these supermarines (yes, that is indeed what they are called, I will have my +1, thank you) would not need to contend with enormous pressures. Further more these supermarines would not need any fancy mechanisms to keep the water sealed. Just a simple box filled with water would suffice. They wouldn't even need to periodically refill with oxygen. Just having some elongated tubes coming out from the top letting the air dissolve into the water would work. You could even open the top of the supermarine every once and a while. --- So yeah, in short what you're looking for is a light tank-like vehicle with a retractable top, or weird tube things sticking out. Instead of a mounted gun (no human to shoot after all) just have an excavator hand on the front to collect resources with. --- You know if you want more entertaining responses, you have to give us something fun to work with. What do you expect they would look like? [Answer] A water-filled tank would be both heavy and fragile. Heavy : if you put it on wheels, it would require roads to be built first. I imagine that building roads on earth is as difficult for merpeople as it is for us to build under the sea (French Commandant Cousteau once did a trial without much success). Caterpillar tracks would be a better option. Fragile : just drill a hole into it and it will leak and cause the death of the merpeople inside. Solution : I would rather think of a scuba-like device allowing merpeople to carry water with them and have their gill kept wet enough with a built-in system to let O2 into the water and CO2 out of it. Merpeople are however adapted to water, not to air. As a consequence, they do not only need water to breathe but also to move. That makes it more complicated than its human equivalent as it seems to me easier to take air underwater inside of a submarine (air is light and water carries the submarine and the air inside) than to take water outside to the surface. Diverting a little bit form the original question and looking at its goal (domination), I would think at what we use submarines for : initially, to sink ships by carrying a bomb close enough and let it explode, causing damage to the hull. The bombs eventually became a torpedo. The torpedo eventually evolved into a missile to allow sea-air and sea-land attacks. But let's stick to the initial purpose of sinking ships. Ships are used to move from one shore to another. Let's thus imagine that merpeople from the mediterranean want to conquer the red sea. They would be interested in getting over and later controlling that stretch of land into which the Suez canal was dug. A first option would be to dig a canal similar to the one that de Lesseps made. Tough job for merpeople but at least it would solve the problem of breathing and would allow for the transportation of many people at the same time as opposed to vehicles. In conclusion, my answer to your question would be : merman, don't try to build complicated vehicles, just dig a canal through narrow stretches of land in order to move faster from one sea to another. [Answer] Their technology would probably be vastly different: even if they have gained technology that relies on air since the industrial revolution, they will have a long history of building things differently. So they won’t have a steel box — steel will be reserved for the engine block and critical parts that require it. The vehicle will be adapted from what they use normally. Perhaps it will be made from bioengineered shell or some kind of concrete. Rather than carry a truck filled with water, which is heavy and can fail catastrophically, they will use suits that keep the necessary breathing parts wet with fresh water, and cover any sensitive areas or use a personal drip system. Getting around and bearing their weight will be a handicap when working dry. Maybe it will look like a wheelchair. [Answer] A fish tank on wheels. That would be the basic design. The outside would be made of steel not glass course ( except for a few Windows that allow the crew to look outside). The inside will be a mini you water environment I would have everything you will need to survive a extended stay on land. Including plants to provide food and oxygen to the water, a device on top made to stir up the surface of the water so that oxygen can also be taken from the air, a machine pumping air into the top of the submarine to supply first source of oxygen maybe even some sort of water filtration system prevent disease caused by waste buildup. Certain sea creatures could also be brought to complete the environment serving as a sort of source of live food and as the way to clean up waste. The sub will not be completely full of water though they would be at air pockets at the top provide contact with the air and exchange of oxygen from it. The outside would look more like a sub mets tank. Mainly made of steel few windows lots of guns. [Answer] I would imagine that your water-bound creatures would have the type of airships that are used in the Iron Man and Captain American and S.H.I.E.L.D. Movies. They only show an aircraft carrier, but instead of the atmosphere inside being a gas, it would be a liquid. A sub as a simple cigar shape that is reminiscent of all the USO's (Unidentified Sea Objects) that people report either entering the ocean from the air or vise versa. Your describe your world Earth-like, so it will have a gaseous atmosphere. That means for your submarine to fly, it will need wings. So it may look like a passenger aircraft, but it holds in water. With WWII technology though, you don't have jet engines or fans big enough to move what would be a very heavy object around. Take your German WWII submarine. It weights 871 tons. Let's say the interior space measures 250-feet long by 25-feet wide. The volume of a cylinder in cubic feet for a 250 by 25 foot submarine is 917,995.46 Your submarine will have to be small if your world has 1G like Earth. 1 cubic foot of water equal about 30 quarts. And 30 quarts of water weights about 63 lbs. Besides the 871 tons that the sub weighs empty, add to it another 29 tons of water weight ([used this to calculate volume](http://www.handymath.com/cgi-bin/cylinder.cgi?submit=Entry)) and if you keep to the size of a German U-Boat, it would weigh 900 tons. A lot of weight to get off the ground, never mind keeping it airborne. I concentrated on airborne solution because any land-based craft with the added weight of water still, like a car or tanker, has to navigate the hazards of a battlefield, filled with craters, uneven terrain, and the energy required just to get something that heavy moving would probably be Saturn-V like in nature. The mini subs of Japan that held two people and even the "Turtle" during the Revolutionary War will make more sense. You see, if the year was 2525, then anti-gravity may have been perfected and size and weight not an issue. But with WWII technology, your mermen and women will have to operate smaller vehicles with the current world you descibed. And I like the name Turtles. Even if they are small, just the weight of the water will make them move as fast as turtles. [Answer] Not considering the supporting world, just the technical problem of a water-filled, mobile vehicle. There is a biological question tho': Do the merfolk need to be completely submerged? Do they breath with gill-like organs? Wouldn't it be sufficient to keep the gills wet? Many fish an survive for extended periods if their gills remain moist--gas exchange still works across the gill surfaces. If the vehicle were a refuge for rest and shelter, the merfolk could make forays across the terrain with a water-filled breathing apparatus. Let's call this vehicle a **terrameris**. 1. The terrameris vehicle doesn't need to be sealed--wouldn't want this anyway as a sealed container will present problems of gas exchange. So let's imagine an recumbent cylindrical container with a hatch or hatches along the top edge. 2. Water is very heavy, so minimizing the structural support mass will be important. The walls of the vehicle can be a clear polymer with external reinforcement. The cylinder has hoop-like ribs at regular intervals along its length. Rigid components could be ceramic or carbonate or manganese or a combination of all three. 3. Since the polymer can be flexible, this would allow segments of the cylinder to be articulated with large wheels or tracks supporting each segment. This will allow the vehicle to move across uneven terrain. 4. Power for moving the terrameris has to come from somewhere. You're going to need to imagine how the merfolk have developed motors, fabrication capabilities, etc. What are their fuel sources? Hydrogen fuel cells perhaps? If you split the water molecule, you get hydrogen, which can be re-oxidized (with O2 from the atmosphere) for power, producing water as a byproduct. So power comes from hydrogen cells, and the 'waste' water helps to maintain the internal environment of the terrameris. Perhaps each segment of the vehicle has a separate power train. In summary, I see the terrameris vehicle as a giant caterpillar-like form with articulated segments that moves rather slowly, powered by hydrogen fuel cells, and propelled by a series of wheels or tracks. Each segment has a hatch for egress and gas exchange. Perhaps the segments can separate and rejoin as needed. [Answer] The answers here all assume the merfolk can perform metalwork, which I think is unreasonable. So my answer attempts to provide a viable solution. --They chew plastic-- Our oceans are filled with plastic waste. If the merfolk could chew the plastic and secrete a mild acetone, benzine or dichloromethane in their saliva (or other glands) they could soften certain plastics (like polyethyline) so it could bond with itself. It's possible that cyanoacrylate (superglue) works underwater too, enabling bonding with other plastics and rubber. Have the merfolk chew enough plastic into a paste and form the supermarine in a process like paper mache. It might be possible for the merfolk to take plated steel from sunken ships, bend and deform it to shape, and seal the edges with their chewed plastic goop. Maybe they could use other excreted substances as a sealant, too. To move around on the land requires a means of propulsion. Again, merfolk cannot fabricate metal parts and internal combustion engines, and even wheels on axles would be hard (and not commonly found on sunken ships either). A simple locomotion system would involve punting the vehicle around using long poles which they hang over the sides (think like a barge in venice) but this would be painfully difficult without decent wheels and all but the tiniest of vessels (minimum weight for a one person bathtub is going to be close to a half ton). Given these locomotion restrictions, I think that the merfolk are going to be limited to a floating vessel which operates in water only. Essentially a floating bathtub driven with long poles and hooks, it would allow the merfolk to explore coastal water and move up a river estuary, possibly reaching a freshwater lake (I assume freshwater is poisonous to them, so this is an achievement for their explorers). As saltwater won't float on freshwater, they will need air filled ballast tanks to keep afloat (alternatively, bottom crawling with the use of poles and hooks may also work, but I assume they want to see the surface). [Answer] You haven't adequately described your world. The first tool we had was our hands and we made hand tools. OK, mermaids can do that. The next was fire. A problem. So, what do we do about internal combustion, or worse, the Iron or Bronze age? Or glass? Or chemistry. I suspect development of a technological society under the sea would progress through biological means. Use of animals for energy, use of electric eels (say) as batteries. There's no reason that such a society wouldn't "invent" sailboats or dirigibles. The idea that our subs "occupy" the oceans is so laughable, that I won't say anything more about it. The merpeople have no need to "occupy" the land...how many undersea colonies are you aware of? They would no more want to live up here than we would down there. I'd suggest that sailing balloons is the way to go. They could only go as far as their feeble (unless you give them nuclear or petrochemical engines) energy sources would allow. But with enough caching along the way, it might be only a moderate problem - to organized (ie governmental) groups. [Answer] I would take a more contrarian view; they would be very challenged to get onto land. The issue is that when we went undersea in 1941, we took batteries to power our life support systems. We recharge the batteries using diesel engines on the surface. The surface - AKA air - is everywhere. Our submarines were never more than 500' from air. I think, then, that "a truck full of water" is a poorly thought-out answer. Where's the food? Where's the fresh (breathable) water? Where's the power supply? it isn't like IC engines (or pouring cast iron for them) is a natural thing for undersea dwellers. Without thinking through this, posters are creating a [Turtle](http://www.drgeorgepc.com/TurtleSub.gif) that would be even less effective than the original. I am assuming that like a WW2 submarine, the vessel must be able to be "out" for up to 6 weeks. How will they keep their water breathable? How will they dispose of waste? German subs in WW2 were supposed to be 'fragrant' by the time they returned to port. Imagine living in your own filth... How does it move across land? Treads? Made of what? There are no roads, unless the Merfolk are making them. How does it power itself? It is hard to imagine there are IC engines. What's the fuel? How is the food stored? WW2 submarines hard a larder of dead things and cans. What will our Merfolk eat? How fast is the vessel intended to travel? How far from the sea is the vessel intended to journey? How will the vessel communicate with 'home'? [Answer] The reason for the use of submarines in real life military operations is not to occupy the seas, but simply stealth. Yes, there is sonar, but this could be evaded in WW2 as well as today. One important concept is the thermocline, a boundary in the water with a pronounced difference in temperature between the water above and below it. This will reflect sound, so passive and active sonar are much less effective across this boundary. How do the merman "see"? Do they use sonar, optical vision, smell? Would the rumbling noise of a land-based vessel prevent its use as a stealth weapon platform? Another option for a sneaky attack via land might be the building of canals or tunnels (below water level, or above water level with locks, like in rivers where ships need to traverse sudden changes in water levels). These might start out as civil trading routes, but could also be re-purposed in case of military conflicts (like autobahns). Unmanned vessels (rockets, specifically) could be used both tactically as well as strategically. They can move faster than torpedoes, might be invisible to the mermen during most of their flight phase and an explosion in water is probably more harmful to sea life than it would be in air/on land to land life ("fishing with dynamite"). Back to the out-of-water submarine: I suspect that the lack of land-based, air breathing humans would mean that large areas of the land would either be covered by forests or be deserts. Forests might prevent the easy passage of any vehicles. Deserts might be an issue because of the large temperature ranges encountered there. If the vehicle carries enough water mass, it could possibly mitigate the effects of cold nights and hot days. I assume that the merman are poikilotherm, like fish. They cannot sweat in water, so they might be in real trouble when the water gets too warm, and swimming into colder water regions is not an option if you are caught in a land-based vehicle. The fun part is, of course, that this weakness might be of use in combat, where one side might try to heat up the enemy vessel by directing sunlight on it (via mirrors), or by using Napalm-like weaponry. This will be a very slow process, however. The "sunlight heat ray" option might or might not work for a larger land-based base, depending on whether attackers can move fast enough during the night (before they hibernate before they get too cold, or because the range of the heat ray is so large and the land-based vessels so slow that they will be sitting duck when the sun rises again. Obviously, attack vehicles could have a mirror surface, and equally obvious, their enemies could carry paint bomb to combat the mirror surface. So, perhaps a dry ice reserve in the land-based vessels and a coal/oil/gas heater to cope with adverse temperatures? Or an "air condition" for the water? Well, for short excursions onto the land, a rubber bubble filled with water might be sufficient, propelled by the merman walking inside. Dangerous, as the bubble might burst, the water might get too warm or the oxygen in the water might get used up before they can return to their natural environment. For longer excursions, a vessel might be a wheel, or rather a cylinder, filled with water. Unlike a real-life submarine, which has a form to minimize the drag of the relatively dense water, this cylinder would roll on the land and not care about a less than aerodynamic form. To allow for some sort of controlled movement, several cylinders (or wheels) could be connected. One famous example of a land-based vehicle with two connected "cylinder wheels" is the Flintstone car: <https://en.wikipedia.org/wiki/The_Flintstones_(film)#/media/File:Flintstones_ver2.jpg> Just imagine that the "cylinder wheels" are large enough to carry machinery, merman, supplies and that no cavemen ride on top this thing. Steering would still be a pain. However, real life military submarines aren't known for their cornering abilities, too. [Answer] Yes, there are already umpteen answers to this question. However, I will attempt to answer it in a way that none have yet done. --- You say that your merfolk are at “WWII era warfare” — I take that to mean that they are at the second part of the Great War, and therefore are a parody of our own history, or some version of it. Therefore, I shall suppose that the human nations and empires of that era were moved over to the eastern ocean: the Americas are in the Atlantic, Africa is in the south of India, Europe is off the coast of Japan and China — with the Isles conveniently separated from the main ocean by the ‘Nippon Insurmountain’? Obviously it isn't a perfect conversion, because freshwater lakes do not have properties which equate them to islands for us, and I base my answer on the premise that these merfolk require salty water. I'll say that they cannot control a heterostatic pressure of their bodily cells, and so are unable to venture from their home depth — which is what? Are these merfolk bathic, occupying the deepest depths and possibly surviving off the sulfurous hot vents issuing forth from the cracks in the trenches? Are they less extreme, and living at the transition from lit oceans to the dark depths? Feeding from the detrius which rains down from above, like mana from the heavens? Or, are they shallow folk, farming the phytoplankton for nutrients? Whatever the case may be, they are limited to it, and so it merely serves to provide them with larger expanses if they can occupy the seas above continental shelves. Now, being as they are a parodical version of our history, you ask for a description of their **Überlandkarts** (U-boat, Unterseeboot). Well, keep in mind that these people have probably already discovered a way to travel under, over, or through the massive obstacles of land. Why? Because these merfolk like to expand their limits. If nobody else has done it yet, then to do so is to reduce the competition and to allow previously stifled people a chance to thrive. If they were shallow, it is quite simple. They've already begun colonizing the land with big umbilici which they've built against the rivers flowing into their oceans — remember that I suppose they require salty water. The same technology can be used to build bubbles on the land: waystations off the roads, where planktons can be cultivated. Ah, yes, their technology. I will say that these people have technology which is much nearer their own biomechanical systems than anything else. Okay, so they aren't exactly like people, naked mediocre and extracting their living from the unwilling earth about them. The deeper merfolk would be the ones who would require vessels to travel out of their stratum. I don't think digging would be an optimal method of expansion — though it certainly wouldn't be unattempted, especially with the folk huddling around the hot vents. Those ones are the most promising, so I'll go with them. The hot vents, or hydrothermal vents (see to [Wikipedia](https://en.wikipedia.org/wiki/Hydrothermal_vent), [NOAA](http://oceanservice.noaa.gov/facts/vents.html), or [PMEL](http://www.pmel.noaa.gov/eoi/nemo/explorer/concepts/hydrothermal.html)), which exist on the ocean floor exude water heated to temperatures anywhere about the range of roughly 300 to 400°F, saturated with minerals, and with a basic pH. From my recent reading, many of the characteristic mineral chimneys which occur at these focused vents are mostly made of a copper–iron sulfide e.g. chalcopyrite on the insides — and zinc sulfides on the outside of the porous chimney walls. Now, whether the merpeople are able to smelt any of the abundant ore or not relies on whether they are able to employ a means by which to separate the ionic metals from their companions to produce elementally pure metallic compounds. There are two major ways by which to extract metal from ore. The first is chemical: chemically, whereby you introduce an ionic compound which causes the undesired components of the molten ore to either float or precipitate away, leaving the metallic elements alone; electrically or galvanically, whereby you use electric voltage to perform the separation, attracting the metal to the cathodes of your galvanic cell. Well, anyways. These merfolk, establishing their cities around the hot vents, would eventually learn that they could gather minerals from the distant brine pools. The brine is laden with alkali halide minerals, e.g. sodium chloride, bring them to the vents, and create voltaic batteries by separating the copper and zinc ions by their specific elemental gravities. I've not worked out whether this is entirely possible, mind, but depending on the rigor of your world's scientific consistency, you may be able to simply say that it happens. Suffice it to say that these merfolk would've already been building metalcraft in great smithies constructed over artificial extensions to the hydrothermal vents. They would build vessels contain their own native pressures and allow them to venture upwards out of their depths, discovering the vast anti-depths above them. I figure that they would take comfort in the presence of a floor, much as we do, and so would eventually learn that it climbs upward. They'd be establishing colonies all along the continental shelves — this is during the ages of 1600..1900. Here, I must raise issue with the plausibility of them developing Überlandkarts, or even Überseeboots, which would venture to the surface of the oceans. See, most of our submarine vessels didn't venture far from the ocean surface. The differences of pressure which they were built to withstand at even 1500 feet were in the ballpark of 660 psi absolute: $$P\_a = \rho h + 14.7\frac{\text{lb}}{\text{in}^2}$$ A very simplified version of the equation for the relationship between absolute pressure ($P\_a$) in a liquid of a certain density ($\rho$) at a depth ($h$), and is valid for static pressures in a range of depths below Mean Sea Level where the water has negligible change occuring with its density. Most of our submarines don't go so deep. Going to the benthic depths was not a routine activity during 1940. Nowadays, we do built vessels capable of holding pressures in excess of 3000 psi, but those are built much differently than a submarine. Submarines have much more complex shapes and many more necessary seals to prevent leakage and to withstand buckling where the shape deviates from a perfect sphere. Enclosing greater pressures on the inside is easier than keeping them out, yes, but there is yet a large differential between the pressure at 30,000 feet below Mean Sea Level and at MSL. I don't expect that these merfolk would be straying on the land any time soon. You know why so few specimens of deep see creatures are adequately studied by us? Because they deteriorate when brought up to our comparatively low–pressure atmosphere, and must be kept in hyperbaric chambers to maintain their integrity. [Answer] I imagine it would look like a tank with a little bit larger window openings. Heavy construction would allow it to be pressurized and tank treads would allow it to travel without roads. They wouldn't want the sides completely open to the light because underwater the light is filtered down to a less intense level so they would want some shielding from the bright surface light. They would need some means to communicate but we have underwater microphones so that's no problem. It would have mechanical arms to manipulate objects outside of the vehicle. Name suggestions: **exaqua** or **interra** In Latin "ex aqua" means "out of water" and "in terra" means "on land" . [Answer] The Santini Box A real-life surface transport for dolphins. <http://www.aquaticmammalsjournal.org/share/AquaticMammalsIssueArchives/1972/Aquatic_Mammals_1_1/Dudok2.pdf> Regardless of this specific implementation, the general approach for the surface transport of dolphins is to have a hammock (with cutouts for the fins) and a shower which keeps the dolphin from drying out. The "traditional" depiction of mermaids and merman indicate that they can survive outside the water for short periods of time. If they evolved from lungfish, perhaps even longer (some African lungfish can survive for four years in dried mud, recycling their water, keeping their tail fin over their eyes to prevent these from drying out and breathing regular air). Since, in real life, dolphins are not used in military surface operations, the actual vehicles are standard trucks or vans. For military surface use of dolphin, I presume something like an **M113 armored personnel carrier** could be used. Note: I am aware that the OP specified that no humans live on the planet. The only conceivable way I can think of that the mer people would use names like "Santini Box" or "M113" would be some sort of contact with humans, possibly from off-world visitors, long range communication or reception of radio transmission, not necessarily specifically meant for them (like TV shows being transmitted to an other planet or solar system, or to a space vessel on the way to some solar system, to keep the crew entertained during their sub-lightspeed journey). [Answer] What about using normal land-based vehicles fitted for their possible lack of feet (driving with a joystick) and giving everyone their own life support suit like this guy in addition to a common one (water sprinklers or something like that)? [](https://i.stack.imgur.com/8Q7Dv.png) That way they are more efficient as a simple puncture on the hull could kill everybody. Since they are soldiers they are expected to be able to fight at closed quarters eventually. But, if they got no way to move on land beside crawling (hello there, *surgically split legs*) they will be an easy group target, so less people per vehicle is better to minimize personnel losses during manouvers. Maybe a lot of individual tanks (with internal life support system, in addition to the backup suit) similar to the one below. Or a modular big one. [](https://i.stack.imgur.com/4VDqw.jpg) [Answer] If nobody has mentioned it yet, a fishtank on wheels is very little different from a car, and a car is not a submarine. At best you could say it corresponds to a boat in that it will ride on the surface of land instead of water. A submarine operates at *any depth* (within limits) underwater, so, by comparison a "supermarine" should operate at any depth (within limits) abovewater. This makes it more like an airship than a car. Without going into extensive analysis of underwater chemistry, or conducting chemical manufacture underwater, it is good to note that it would need to be "launched." Light gases come to mind, which work as well below as above the water. The depth issue applies, but since submarines are launched at sea level, so could supermarines--just in the opposite direction. A major difference is that water is heavier than air, so instead of being like a submarine and filled with air and a purification system for same, the supermarine may have a much more contained life support system filled with water due to its weight. [Answer] The vehicle itself wouldn't need special adaptations for the water-breathing merfolk. Instead, they could wear [wet-suits](https://s-media-cache-ak0.pinimg.com/736x/70/01/de/7001de50969aa83fc9c42b9d2694bf2a.jpg) with water-filled "re-breather" water tanks to keep their bodies at the appropriate pressure and wetness levels and keep sufficient oxygen in the water to keep their gills happy. These might look like deep-sea diving rigs (see link). They will have a bigger issue with making the vehicle itself. Propulsion systems that work under water are much less effective on land. They might have better luck stealing land vehicles, unless they have pretty solid R&D division. [Answer] Amphibious **out-of-water submarine** would look like a **submarine fused with hoovercraft** where propellers may act as pushing fans on ground and air in float tanks could be used in bellow action. ]

[Question] [ It's 2016, but for some reason, the Cold War never ended. You've been inspired by your (for some inexplicable reason) favorite movie, Indiana Jones 4, to start a new business: building refrigerators. However, the market is so saturated that in order to distinguish yourself with a nice marketing campaign, you decide to make them **NUKEPROOF!** The refrigerator should be: 1. Usable as a real refrigerator would be. 2. No bigger than standard double door refrigerator, so no room-sized walk-in refrigerator. Though, you *can* add some additional size for additional armor, for example, in **reasonable** margins, so nothing like 10 meters of iron from one side. 3. Protect one person from up to 1.2 megatonnes of a TNT nuke at a minimum distance of 2 km from the explosion. How are you going to design it and what materials are you going to use? [Answer] **It's Not Possible** You have asked for a **Science-Based** answer, and it's just not going to happen. Despite what Indiana Jones says, it's impossible to build a nuke-proof fridge. Even if the fridge itself is basically OK, the concussive force it went under would jar it severely (and rattle anyone inside of it to death) - or the heat of the blast would cook you inside of it. So to answer your question about what I would make it out of, since I'm selling snake oil anyway I would build it with the CHEAPEST things I could, put a basic lead plating around it all so people thought it was built in a sturdy fashion, then make profit. And shortly after selling a few I'd close up shop and drop the alias I was using. If I were to try to answer this more to the spirit of your question than how it was asked, to survive the nuke you would want to build the fridge out of lead (obviously). Your trouble would come where you would want your fridge to have enough air to breathe for awhile (you know the nuke is coming, but not exactly when, so you would hide in there for a bit). At that point you can either make holes in your fridge - drastically reducing its efficacy as a food chiller and as a life saving device - or install some kind of oxygen tank and air scrubber. Those however are going to take up a lot of space. Some other downsides: The air tank may explode due to the concussive force of the blast. And when your house is on fire, opening a door and releasing a lot of oxygen into the room will result in you being lit on fire. Of course, not opening the door will ALSO result in your death because that fridge will heat up as the house burns. If your house collapses though, it's a bit of a moot point as you'll be trapped in your fridge and won't have to worry about picking one or there other. . **Update\*** Because the comments pointed out the OP updated the question with a specific distance a nuclear yield, let's make sure it's still impossible. According to [NUKEMAP](http://nuclearsecrecy.com/nukemap/) a 1.2 Megaton nuke has the following effects at 2km: **Outside of Fireball Radius (1.04km)** Well, that's good! **Inside or Radiation Radius (2.56km)** Less good. 500rem (5 Sv) of radiation - [that's lethal](https://www.standeyo.com/News_Files/NBC/Roentgen.chart.html)! We need to get that down to about 200rem (2 Sv; the "largest dose that does not cause illness severe enough to require medical care in over 90% of people" per previous link). The best possible shielding wouldn't be Lead, it would actually be Tungsten. To be safe, we'll use two halving-factors, which would actually reduce radiation to ~125rem (1.25 Sv; a hair over the "Smallest dose causing loss of hair after 2 weeks in at least 10% of people"). Link: [Half-Value Layers](https://www.nde-ed.org/EducationResources/CommunityCollege/Radiography/Physics/HalfValueLayer.htm) If we used Lead, we would need to line the fridge with: 0.98" (24.9 mm; let's call it 1" or 25.4 mm to be safe). If we used Tungsten, we would need to line the fridge with: 0.62" (15.8 mm; let's call it 0.7" or 17.8 mm to be safe). Well, that's possible to accommodate - you're still alive! **Inside 20PSI (138 kPa) Air Blast Radius (3km)** Per NUKEMAP, at 20PSI (138 kPa) heavy concrete buildings are severely damaged or demolished. Unless you are living underground or in a very fortunate large concrete building, **per [FEMA](http://www.fema.gov/pdf/plan/prevent/rms/155/e155_unit_vi.pdf), you are dead**. You cannot expect the fridge to withstand this blast. **Inside 5PSI (34.5 kPa) Air Blast Radius (7.4km)** Per NUKEMAP, at 5PSI (34.5 kPa) residential buildings can be expected to collapse. If you are in your fridge and cannot escape due to the roof having collapsed in front of the door, **you will be trapped and die**. **Inside the Thermal Radiation Radius (13.6km)** Per NUKEMAP, within this radius 3rd degree burns can be expected. At this point your house has collapsed on you and spontaneously combusted. If you were lucky enough to survive the pressure (doubtful), **you are now roasting alive in your Tungsten-lined tomb**. ***There is no such thing as being "safe" 2km from any instrument of mass thermonuclear war, least of all in a REFRIGERATOR.*** [Answer] It's George Lucas's marketing manager here. We are now working on a new Indiana Jones movie: Indiana Jones and the Blastproof Fridge, where Indiana Jones goes for a quest to find the sacred Superfridge, made by God himself. We're now developing a new blastproof fridge, which will not only be used in our movie, but also put into sale. Here's how it looks like inside: [](https://i.stack.imgur.com/2Rh4j.png) Notes: * the water is accessible from the food storage * the oxygen is stored in liquid/solid state, at around 30K. This provides a cooling feature on top of all - cold air circulates from the tanks (if it melts from heat inside the fridge) to the fridge, and then back through the air filter. * The cushioning would be ideally made from polystyren, because it also isolates the inside (but that's for a 10% surcharge) How it looks on the outside ([source](http://www.heyuguys.com/indiana-jones-5-what-they-need-to-get-right/)): [](https://i.stack.imgur.com/IGAnH.jpg) Hope this helped will get us some money! [Answer] Well, I'm going to say, my refrigerator is a SpaceX dragon launch abort system with a baggy of ice inside. The total volume of the capsule is 25 cubic meters, which is the equivalent of a 2.9m x 2.9m x 3.0m cube, or a refrigerated room, as seen in grocery stores. According to the spaceX website, the capsule can move a crew (of 3) vertically upwards about 5000 feet (0.9 miles, or 1.5km), which means that it could travel about 7070 feet (2.15km) laterally. This would carry you out from 2km off the blast range to 4.15km. While most buildings would still be completely demolished, you, being in the air, would be perfectly fine with no debris to fall on you. Maybe a bit toasty, but hey, why do you think it has a bag of Ice? [Answer] GrinningX has quite a good answer but I would like to amend it slightly. The stats quoted appear to refer to a ground burst. Ground bursts are not thought to be targeted against cities because air bursts are more damaging to them. Ground bursts are expected to be used against hardened targets like ICBM silos. However, if a 1.2MT ground burst did occur in your city it the fridge owner would die for sure. Ground bursts generate enormous quantities of fallout. (Air bursts generate almost no fallout.) Fallout is created when energetic neutrons in the fireball touch heavy matter, converting it into unstable isotopes. Air burst neutrons interact with gasses, and the radioactive isotopes they make from this gas tends to stay aloft. The fallout from such a ground burst would be lethal for weeks to months - far too long to be hiding inside a refrigerator. On the other hand, an air burst produces almost no radiation on the ground (neither prompt nor fallout) so the radiation shielding would be largely unneeded. The most important need would be (in this following order of events) 1) protection from the flash (just being inside your house and away from windows is probably good enough), 2) protection from blast (sturdy steel construction and being securely bolted to a sturdy foundation would keep you alive), 3) protection from the heat and fumes from your house burning down, and 4) a mechanism to allow you to exit the fridge even though it has been buried by the debris of your house. Numbers 3 and 4 are quite a bit more difficult and complicated than 1 and 2. For surviving the fire, maybe some kind of hand-cranked air pump which pulled air in from outside and percolated it through a container of water (to cool the air and remove smoke)? That would help, but would not do anything to reduce carbon monoxide or lethal carbon dioxide levels. Heat would be less of a problem. Fridges are designed to be insulated, so just make sure the gaskets are fire resistant and increase the R value enough to survive. I'm honestly not sure how to handle egress. It's hard to guess what debris will be on the fridge and how it will be shaped. I don't have any good ideas for this one. [Answer] Your customers will need to: Put your fridge underground in the cellar; Reinforce the cellar walls to withstand the shockwave of the blast and the collapse of the house on top. Add shielding in 2 layers, preferably tungsten, 0.5" each layer, since lead is just messy, on the outer side of the body, and on the inside, just behind the fibreglass interior. Put the insulation in between the two layers of tungsten. The piping and wiring to the outside from the inner compartment should leave through the bottom of the fridge. Recommend buyers get **TWO** fridges, or one for every member of the family and a spare for actually keeping food in. [Answer] While the it's-not-possible answers are correct for the question you intended to ask lets try another approach: For colder climates it's technically possible (but economic insanity) to build a refrigerator that contains no cooling element at all. Lets make the Green Fridge (tm): No ozone-destroying Freon! No toxic ammonia! No risk of incomplete combustion of the propane causing CO poisoning! Uses far less electricity than a normal refrigerator! You'll be safe against anything less than a direct hit by a nuke! Dig a big, deep hole. In the hole we put a large, very well insulated, very strong walk-in cooled space. Note that this will be at at least the sub-basement level, ideally it would be accessed by stairs or a ramp going down so as to minimize the air spill when the door is opened. There are two holes in the ceiling of the cooled space. Above the cooled space, separated by the insulation layer is a large concrete box. One of the holes from the ceiling connects to a U-shaped pipe (so the opening points down) in one corner of the box, the other to a pipe in the opposite corner that connects to the top, again with a U on the end. There is a large bimetallic thermometer on the first pipe that opens or closes a baffle in the pipe. There also must be a drain for the box. A pipe heading up goes into the third corner of the box, the box is filled with large gravel, a pipe is added in the last corner and it's roofed over and likewise very well insulated. Pipe #3 is insulated and extended to a surface air intake. There is a fan in this pipe (the only powered component in the whole thing!) that turns on when the outside air is colder than the air in the box. The final pipe vents back to the surface, ideally after running a bit through the ground first to dump its cold into the soil. Now the whole thing is covered over except for the vent pipes and however you plan to get to your storage space. You want some feet of dirt and then a moisture barrier layer and more dirt. Assuming you sized it big enough and the winters are cold enough this will work--you get a cold space for no more operating costs than running a fan in the winter. Note that so long as you are dealing with an airburst this should survive anything, although escape might be problematic. You have basically perfect radiation shielding, the only modification you'll need to make to ride out the nuke attack is to add a supply of compressed air to use while the firestorm burns overhead. (Note: In practice you would put the cold space on the bottom and use a fan to bring up the air, I was going for ultimate green. Also, the thermal mass needed is simply too great to be worth it. However, a related idea is in actual use by some people: Bury your house as indicated, run the air feeds through enough ground and you can climate-control your house with nothing but a fan. While the total heating/cooling needed is a lot greater the outside air will be in the right direction far more often and the natural ground temperature isn't too far below what you want for your house anyway.) [Answer] The it's not possible answers are correct if you interpret the requirements strictly in light of the scene from the movie, where the fridge is directly exposed to the nuclear explosion. Having said that, your company could legitimately market a fridge that would be of benefit, within certain limitations. 1. The fridge would require to be installed in a cellar, or ideally in a reinforced shelter dug into your garden. At a time of heightened nuclear tension digging a shelter may be something people are prepared to do, similarly to how Anderson shelters were dug in many gardens in the UK in World War 2. A shelter intended for protection from a nuclear device should ideally have a zigzag tunnel leading to it: the earth will provides a significant amount of protection from direct gamma, neutron and thermal radiation. 2. The fridge should have a large dedicated compartment for fresh water, sufficient for an entire family to drink for at least a couple of days while you trek out of the fallout zone. 3. The fridge should have a (non-refrigerated) compartment for other emergency supplies, particularly enough P-3 particulate masks for the entire family. As above, these will be used during the first couple of days after the explosion while you trek out of the fallout zone, to prevent internal contamination. Other useful items: ear plugs (your eardrums will likely rupture thus providing a route for contamination particles into the lungs / stomach, so you will want to block your ears), disposable razors (contamination will be trapped quite effectively in hair so you will need to ensure everybody gets a close all-over shave, to reduce contamination), basic medical kit including splints and burns dressings. 4. The fridge should have a lead-acid battery backup, for when the power goes down, and beefy EMP protection. 5. The fridge should feature a pull-out strong metal frame so that it can serve the function of a Morrison shelter and protect the users from falling rubble if the building above collapses on the cellar, or the roof of the garden shelter falls in. It should also have a shovel and combination hammer / crowbar / wrench in case you need to dig your way out of the rubble. It doesn't really work in the same way as the Indiana Jones fridge, but I'd still be pretty happy to have such a fridge in a shelter in my garden if I was worried about possible nuclear attack. Obviously nothing would protect you from a direct hit, but the fridge would considerably enhance a shelter capable of supporting survival in the scenario you outlined as long as sufficient warning was provided to allow you to get into your shelter before the blast. [Answer] Add an asterisk to "Protect": > > Protect\* one person from up to 1.2 megatonnes of a TNT nuke at a minimum distance of 2 km from the explosion. > > > \* Protect: the explosion will not kill you and the nuke will leave no lasting ill effects. Protection may also apply to others near fridge. Simply make a normal fridge with small extra box with a piece of string hanging out. "Nuke conversion"-kits also sold separately. In the event of an imminent nearby nuclear explosion simply enter the fridge, pull the string and the 40 kg of TNT in the box will explode, preventing the nuclear blast from killing you. Double your money back if the nuke kills you, upon personal application. ]

[Question] [ Background: Nearly all low-wage labor is done by humanoid robots (retail, factories, transport, sanitation, construction, mining, and similar fields). These robots have all the physical capabilities of humans and more, but jobs that require ingenuity and adaptation such as design, management, etc are still done by humans, and technology allowing robots to fill these jobs is millennia away. Problem: Housing, sustenance, and other necessities of life are not free or subsidized and members of society still need to work for these in some way. With menial low-wage jobs being taken by robots, there's no longer a low entry point into the job market, and the design/management/etc professions that aren't filled by robots require advanced training that is not available to the poorer portions of society. How would the population have adapted to allow robots to do low-wage labor? Would all of these people have died off or moved elsewhere? Would society have naturally create large numbers of jobs that require ingenuity but little training? If so, what would these jobs be? Society is still functioning at this point, and there's a government and workers' rights groups, so Matrix-esque human farming and similar things are out of the question. Edit: This is not a duplicate of [this question](https://worldbuilding.stackexchange.com/questions/38603/what-would-the-transition-to-a-jobless-society-look-like). The linked question concerns removing humans from the workforce entirely and a money-free society. The aim of this question is human adaptation to a society where money is still present and robots only occupy low-wage labor, and jobs that require ingenuity are still done by humans as initially mentioned in the first paragraph. [Answer] Well, this wouldn't be a sudden change. Robots aren't free -- and likely aren't cheap. So this is something that we can easily assume would take years, if not decades or generations to really happen. Based on this assumption I offer you my thoughts (hypothesis) on a plausible progression. It would start in factories where there is currently a high(er) error occurrence or low(er) error tolerance. Think welding, assembly and such (many of which are already being done by machines today, but not unanimously). These are jobs that (usually) require quite some training, but are fairly low-entry. Then it would take over the construction industry (starting with high-risk, such as high-rise buildings), but slowly working its way into all niches of the construction industry. Farmers would soon start considering buying a few robots. Starting with the bigger farms, because they have bigger budgets. Slowly, all the jobs usually offered to those with lower educational backgrounds, will no longer need them. So those with learning disabilities, low socio-economical backgrounds, and yes immigrants, will slowly be phased out of the workforce. They will be forced to start getting more and more creative over time, because everything they can do, a robot can do better, for longer, and over long periods will be done cheaper. This will start a period of social unrest. People with higher positions will start getting nervous, people will start complaining. This happens with all forms of change, but especially now because robots seem to be everywhere. Suddenly you'll start noticing robots in restaurants, replacing waitresses. Customers (especially those who've felt the sting of being replaced) will complain about the 'trash compactor' that brought the wrong order (or purposely giving them the wrong order just to make them look bad). There might even be those who find it funny (kids especially, but plenty of adults) that will start talking funny just to throw off the robots' speech recognition software. It's around this point in the transition that society would have to make a decision. After all, more and more people are starting to file for unemployment. More and more small business owners that can't afford to buy robots will file for bankruptcy because they can no longer compete. The government might start an initiative to offer financial aid to small businesses to help they buy a robot, or there might be a tax cut offered to those who hire unemployed people. Maybe both. Slowly, people who don't want to starve or become homeless will be forced to go back to school. I'm sure the government would have to offer some kind of financial aid in this, or risk entire social groups being unable to do anything but collect unemployment. So, over the course of a few generations, more and more people would have to work their way up from 'low social classes', to middle class or preferably upper middle class. This hypothesis is based on what happened during the industrial revolution, though extrapolated slightly because of the more socially geared society we (seem to) live in. Take away the 'easy road', and people will be forced to work themselves up, or risk starving in the long run. Let alone the risk of no longer being a 'viable mate' by their preferred gender (should they have one). Social pressure is a hell of a motivator, but this is only one plausible route. You could go for a more dystopian route, where the lower classes are systematically sabotaged and slowly start to either die out (not likely) or find other means of survival. It could even go so far as to develop a fringe society, tribal almost. They'd be forced to either steal to survive, or the more prideful of them would develop new means of farming. Most would find a balance between the two. [Answer] When robots are producing products much cheaper than humans could, it becomes trivial to afford the necessities of life. There are plenty of things possible for people to do which might seem absurd to us now - if I described the concept of a "let's play" video or unboxing videos to someone 50 years ago, and asked them to guess how many people could make a living just doing that... they would probably find the concept laughable. Right now, some people make several thousand dollars a month just videoing themselves eating. What kind of memes or entertainments will be popular 100 years from now? Current trends in social isolation suggest that companionship will probably be a massive industry (even compared to it's current extent) - this is already evident in many places. I'm not just talking about Japanese style host/hostess clubs, or Korean muk-bang videos, but online chats where people pay to 'hang-out' with people, and not just online live porn streams with a tip jar (though sex work will still be as big as ever). Also, think how much of a price premium some wealthier professionals pay for 'local organic sustainable' products. While society might stratify into wealthier educated professionals and an underclass, there will be status signaling in buying human-produced goods and services. The cheaper products become through automation, the easier it is to afford them, the more money in society for spending on unnecessary expenditures for less than optimal products - only the underclass will eat the cheap manufactured food products or use anything not handmade by human 'artisans', even if robots have a lower error rate on better products (we can already see this when we consider those 'accidental thumbprints' in some pottery making it *more* valuable because it signals it supposedly wasn't made by machine). The value of positional goods and status signals is their cost - anything machine made would be cheap, and thus the affluent would find it rather gauche (despite being objectively higher quality). People will need to be adaptable, but people will adapt. The problem is not finding things to do, the problem is regulatory - how does government control adapt to most people having very flexible ad hoc informal employment rather than highly controlled full-time employment by a corporation? Minimum wages and various employment restrictions get tricky when it becomes hard to define who is even an 'employee' or what counts as 'work'. [Answer] **many low-skilled jobs will never be replaced by a robot**. mostly jobs that are valued due to their "human" element. examples of human-required jobs include: 1. artist (actor, author, painter, etc.) 2. child care provider, elder care provider, etc. 3. teacher, tutor, coach, etc. 4. security guard, life guard, etc. 5. bar tender (this job could have been replaced by a machine years ago) 6. masseur, fortune teller, greeter, u-tube star, etc. note: some of the jobs listed above are currently not low-skill positions (e.g. teacher). however, after the automation revolution they will be able to afford to hire a lot of low-skilled assistants (e.g. 1 assistant per child in a private school). similarly, low-skilled versions of the positions might become economically viable (e.g. low-skilled after-school tutors). **everyone with a high-skill job will hire a team of low-skilled personal assistants**. with automation driving the productivity of high-skilled jobs up, even the middle class will be able to afford a team of low-skilled assistants who understand their own personal taste. for example: 1. personal shopper (finds clothes, furniture, etc. that match your style) 2. personal chef (cooks foods that you personally prefer) 3. personal restaurant critic (recommends restaurants you will like) 4. personal media curator (tells you what music and movies you will like) **extensive education will be the key to success**. 500 years ago, most people didn't think they were smart enough to learn how to read. today, basic literacy is nearly universal. even entry level jobs like ticket taker or cashier require some literacy. in the post-automation world, learning to identify and solve problems robots can't will be a basic skill that everyone learns. today most first world children receive between 12 and 23 years of education. in the post-automation world, people may receive at 20-30 years of education before they are considered "qualified" for a skilled career. in addition to subsidizing education, the government will probably implement a **[universal basic income](https://en.wikipedia.org/wiki/Basic_income)**. this would allow everyone to buy minimal food, clothing and shelter. in fact, a similar scheme was [proposed in the united states in 1969](https://decorrespondent.nl/4503/The-bizarre-tale-of-President-Nixon-and-his-basic-income-bill-/173117835-c34d6145) (killed in the senate) and [recently voted on in switzerland](https://en.wikipedia.org/wiki/Swiss_referendums,_2016#Basic_income_referendum) (only 23% in favor). **income disparity will increase exponentially**. ever since the invention of the plow, income disparity has been getting exponentially larger because technology has allowed some people to become more productive than other people. while no one is likely to starve to death in the post-automation world, there will be people who only have the basics. in contrast, the super-rich are likely to have [their own](http://www.thisiscolossal.com/2016/08/freedom-cove-island-house/) private [floating island](http://thecreatorsproject.vice.com/blog/private-floating-islands-are-the-new-luxury-mega-yachts). on the plus side, those same super-rich will probably spend a lot of time making life better for the desperately poor (e.g. [by eradicating malaria](https://www.gatesnotes.com/Health/Eradicating-Malaria-in-a-Generation)). **or maybe it would be a utopia**. if all manual labor is really done by robots, then in theory that includes building robots. in which case [robots would be virtually free](https://pando.com/2014/03/10/will-technological-progress-lead-to-greater-wealth-inequality/) so surely some rich person will give one to everyone on the planet. life would be pretty easy if everyone had their own personal robot slave. with the cost of manual labor dirt cheap, anyone could grow all their own food, and build their own floating island. the only scarce resources would be raw materials and energy. and considering the abundant aluminum silicates in the earth's crust are easily made into aluminum and glass given enough energy, really **only energy would be scarce**. [Answer] Since this is essentially the start of a post scarcity society, there will be lots of unexpected effects. Party politics as we understand this will become increasingly irrelevant, since politics (as defined in organizational theory) is a means of allocating limited resources. Fundamentally, the only resource which cannot be changed is time, so people will be able to meet their basic needs and eventually will be "rewarded" by how efficiently they allocate their time. By analogy, imagine a very famous person who has millions of social media "friends" and receives thousands of emails a day. They can not respond to more than a fraction of their emails and requests, so you getting an email is like winning a lottery or discovering a rich relative. Your receiving attention , social networking and other skills will be the source of "wealth" in a post scarcity environment. This also has other implications, since these are very different social and cognitive skill sets than what makes people successful in today's economy. If you think the vulgar rich are something now, imagine a future where reality TV stars are the "new" wealthy class that everyone emulates (oh, wait....). Being a cranky, isolated super genius isn't going to make the cut in a post scarcity environment, although these people are not going to starve either. Since people's interactions are generally going to be limited to those people who share similar interests, then society as a whole will break up into a more tribal structure. If we imagine reputation points on Worldbuilding Stack Exchange as being a form of currency, how well would that translate for people on "Romance Novels Stack Exchange"? Your "Reputation" or time management currency will be rather situational, unless some sort of elaborate exchange mechanism is developed. What is really frightening abut this is the bell curve. The social and cognitive skills needed to succeed are distributed in the normal population on a "bell curve", so only a small number of people on the right hand edge of the curve will really succeed, there will be a mass of people who just muddle through and a left hand edge of pole who simply cannot navigate this environment, and would be homeless or disabled people in an earlier society. Regardless of how large or small the population becomes, there will always be people who won't be able to cope. The danger in a post scarcity environment is they could simply be warehoused in an institution and left to caretaker robots, and abandoned by the larger society. [Answer] My guess would be that society would invest more and more in education. The reasons being: * low wage jobs are most of the time (but definitly not always) for the less educated people. * All these robots will need maintenance. for the low level stuff (like replacing a robot arm or refilling the oil) less educated (you don't need a master for that) people will do but the higher end stuff like designing new functionalities will require higher educated engineers but if everybody is an engineer then wages will drop and even educated people will fall into poverty. Other possibility would be a more dystopian-chaotic scenario: You'll have the very rich classes who got rich because of these robots or other means and the lower class people who probably will hate the robots for taking their jobs. > > They took 'er jobs! > > > This will result in uprisings against the rich upper class in which the upper class might even use the same robots used to replace people to kill them, civil war, massive emigrations, etc.. I'm pretty sure there are movies which handle subjects like these but i can't think of any right now. At first the countries will try to compensate for the loss of wealth by for example increasing military personnel this is short term as this is extremely expensive but can stimulate the economy for a period of time (think of pre-WW2 Germany). Increased militaries around the world might feed global discontent and may even start a new World War. it's also possible that world leaders might abolish the use of robots in certain fields of work to make sure the economy doesn't collapse. These are just things that i think might happen, i'm sure many more things are possible. [Answer] I think the best way to think of this is not as something that started in the future; **it really started in the industrial revolution and just kept going.** In the early 1800s there was a group in England called the Luddites, who went around smashing machinery they thought was taking their jobs. The term is even synonymous with someone who doesn't use/like technology. **And the thing is, there's a lot of evidence that those machines really *were* taking their jobs.** But far from being the end of the world, **the labor market slowly adjusted.** Some people lost their jobs, but others got new jobs that hadn't existed before. On top of that, *everyone got more and cheaper goods*. The world you're describing would have been the result of a very long, multi-century (or millennia if you're far enough in the future) process. There would have been lots of periods of adjustment, likely often accompanied by upheaval such as the Luddites, or the decline of the middle class we're glimpsing now. **Labor as an Exit from Poverty** --- One thing your world might suffer from is a lack of a way out of poverty. In the US, low-skill trades like the auto industry were a path to the middle class for millions. Later those jobs moved to places where people work for much lower wages. There's actually some evidence in development economics that China is currently "clogging" this path for everyone else; if you're a small poor country somewhere interested in expanding manufacturing for your people, how are you going to compete with China, and particularly their infrastructure? So maybe in your world no countries that didn't already escape from poverty can find a way out. They're just poor countries that stay afloat on volatile commodities markets and international aid - only now the thing blocking their way out isn't China, it's that the entire world has cheap robot labor. **Cheap Stuff** --- If robots are so good at everything that they've entirely replaced low-skilled labor, it's likely that manufactured stuff is *cheap*. You say people still need to work to get by, but how cheap would it be to send a bunch of construction robots over to whip up a new tenement when needed? They don't need breaks or lunch hours, don't go on strike, presumably make near-zero mistakes, and don't particularly worry about their own safety. Are massive farming operations completely automated by these same tireless robots? What does that do to food prices? And so on. It seems very likely to me that a subsistence level of living would be widely available. Large swaths of people would probably be miserable due to a lack prospects for upward mobility, but they almost certainly don't lack for basic necessities. **Shifting Labor Market** --- This has been mentioned in a few other places, but it's possible that the fields that machines *aren't* able to do well, like music or art, would just... expand. If there's tons of wealthy people who have easy access to the things that robots *can* do, what do they do with their disposable income? Hire yourself an artist, or spend way more time going to things artists do. Get a nanny, or heck, get two. Maybe machines can handle fairly boring food for everyone, like going to eat at Ruby Tuesdays or something, but what people really want is their own human chef to show off to their friends! Or maybe even new jobs we can't imagine? Could Luddites have envisioned computer programming jobs? Maybe it becomes en vogue to have your own personal self-esteem person, who follows you around and tells you how great you are at every turn. **Increased Productivity** --- Think of productivity as the number of people working it takes to support everyone. Our **standards of living can increase across the board as long as our productivity increases proportionally.** That is, if some new innovation makes everyone twice as productive, we can basically double living standards for everyone. Likewise, **we can reduce the number of people working as long as the people who *are* working are proportionally more productive.** That is, if some new innovation makes everyone twice as productive, we can maintain living standards by having half as many people work. Then imagine how your society falls on this scale. Essentially robots have made productivity go off the charts. How that productivity gets used is what will dictate your answer. [Answer] That depends on what you call "low-wage." It also depends on the limits of what robots are able to do. If a robot can 100% mimic human form and actions, *Fallout 4*-style, then yeah, 99% of us are screwed. However, if they appear to be stuck in the [Uncanny Valley](https://en.wikipedia.org/wiki/Uncanny_valley), then there are plenty of jobs in which a "human touch" will be necessary, or at the very least, desired: * Maids * Food service * Personal grooming (hairdressers, etc) * Prostitutes (if legal, it would be like Uber for your body) * Lifestyle coaches * Brand managers * Baristas (those little cappuccino hearts don't have the same feel when they're made by BUXBOT-M5-U4823) The problem is, as today, we don't generally value this kind of human labor. In the United States, workers in professions that expect tips can be paid almost as low as $2 an hour. If we accept that the cost of a higher standard of living from cooking all of our own food and brewing all of our own coffee means that the people who do so for you are paid a living wage, then we wouldn't have these kinds of problems in the long term that we do today. [Answer] in a way we already so this - only with "slave labour" (ie very low-paid wages to immigrants or foreign workers). So I can buy a t-shirt today for £1 because someone far away got paid 1p for making it. So what would a society look like - well, it'd look a lot like where we are already. Now there is an issue with robots taking the jobs that these people would otherwise have been paid for, but this assumes that the robots are cheaper than the cheap workers - in the UK there's been a lot of talk about immigrant farm workers, its become clear that there are crop picking machinery available that could do the job these migrants do, but as the machines are expensive, and the immigrants are cheap... the farmers do not buy the machines. Same argument works for robots. Similarly, look at what we do with current workers, we provide more and more welfare in the form of part-time job top-ups. In the UK there is very high employment, but an increasing amount of it is provided for from part-time workers obtaining in-work benefits. I'm not sure how sustainable it would be if robots took over even more work though. the end result of robots taking all work is that the economy would have to be rebalanced with the economic output of the robots being taxed to provide support for the population. Universal Basic Income anyone? [Answer] “...the design/management/etc professions that aren't filled by robots require advanced training that is not available to the poorer portions of society.” I’ve been hiring computer programmers for two decades. Having paid for formal education is absolutely no indicator of whether candidates are qualified for the job. Those who can afford education can get a lot out of it *if* they apply themselves. Many, however, manage to graduate without being employable. With technology and information becoming more accessible, those who can’t afford an education can still become employable *if* they apply themselves to learning and practicing on their own. (I had one boss who—based on our experience of this—actively discouraged aspiring programmers from going to college.) [Answer] The answer to this question is very important because it's happening now. Millions of truck drivers will wake up some day in the next decade to find that self driving trucks have replaced them. I can't find the article now, but I saw recently that driver wages comprise 80% of ground freight costs. The day it's possible, basically every truck driver will be out of work. Other industries will change more gradually, but manufacturing robots are getting much more flexible and cheap. When that goes you're left with service positions. Those too are ripe for disruption. Ordering by screen is becoming more and more normal. Imagine a day where you walk into a restaurant, order and pay with a phone on your app, the food is prepared robotically (there's a high end robotic pizza place in Palo Alto) and delivered by a roomba thing with a serving tray. All of these technologies exist and they're getting cheaper and better every day. What happens to high school kids when those jobs are not available anymore? How do they get work experience? Perhaps children will grow up learning to herd robots, perhaps everyone will learn to program, or orchestration tools will get good enough that people without traditional technical skills can use their natural human talents in conjunction with the fast and strong, but uncreative talents of robots. Our society will need to rethink preparation for working life around different sorts of entry level work. There will always be work to do, but the entry level will be shifted up a floor. But as in any massive change many people will resist the change, fail to adapt, stubbornly stay put (see the coal miners in Kentuckey refusing to acknowledge the world's gradual shift away from coal, see Pacific islander's refusal to acknowledge steadily rising seas, see people in Louisiana refusing to leave even in the face of yearly devastating hurricanes). And these people will suffer if there isn't a social safety net to catch them. Then we as a culture need to ask ourselves, do we throw those unlucky people away or do we try to find a place for them to do gratifying, meaningful work. I know which I'd wish for, but wishing won't make it so and we have a distressing history of voting in the throw people away policies. [Answer] With all the production work mostly done by robots, very little time would need to be invested per person to produce enough food and keep it all running. People could earn their basic needs (housing, food and medical care) and a little bit of purchasing power through a "civic duty" of maybe one day per week or one shift per week. Any additional money needs to be earned by finding other work, but a person may just as well go for volunteer activities or community stuff. Since on your world A.I. research has stalled somehow *("technology allowing robots to fill these jobs is millennia away")*, there will be plenty of work in the healthcare, education and other people-focused sectors. [Answer] Welcome to the bloody preface to the post-scarcity economy. With the arrival of automation, the availability of jobs decline. Theoretically, that decline is countered by an increase in available resources and resulting lower prices, eventually approaching zero price for basic life needs. But the relationship between supply and price is very tenuous, especially when basic life needs are involved. My body demands 2000 calories per day, regardless of how much grain is in the silos and warehouses. The planet could be drowning in food, but if I lack the right to eat any of it, that surplus means nothing. A week after my most recent meal, any food owner can request my life savings for a bowl of cereal, and I will pay it! With robots making all the products and robot-owners owning everything that is made, there are going to be a few people who have everything and a vast majority who have nothing. Historically, that is a recipe for revolution. If we are lucky, the starving will attack the robot-owners, leaving the production lines intact. In this scenario, there is at least a chance that we can create a true post-scarcity economy. If the starving attack the robots, then everyone starves. [Answer] Most answers are concerned about what will happen to the unskilled workers. But what about the skilled workers? The skilled workers are going to be able to demand a lot of money in terms of compensation. Enough that for many of them, after working a few years, they'll be happy to live on the investment returns. They'll exit the labor market and pursue whatever they deem to be their life's calling. There will be a constant shortage of enough people to take on the skilled jobs. Companies will do everything they can to get more skilled people. They will probably pay for the education of anyone who has the neccessary aptitudes. Even if not, taking out a student loan to get such an education becomes a no-brainer. [Answer] ## Robots can frame a house, but they can't grow a 2x4. Ultimately there is going to be *some* sort of resource constraint. ## Compassion is still a thing. Even moreso because it's cheaper. No matter how things are shaken up, a significant amount of resources will be used to help the needy. This will happen via charity and government entitlements. In fact, the automation of this will allow this to be greatly expanded. Homelessness will cease to exist (at least insofar as those willing to be helped) as housing stocks are quickly grown by robot labor. It's a lot easier to feed the poor quality food when harvesting quality food is automated, as is the delivery and cooking. A lot of why they grow high mechanization low-nutritional-value foods like corn and soybeans is that healthier foods require much more hand labor. Which is good, because human-only work will only become more expensive, including medicine. Ending the new epidemics caused by low quality foods, like obesity, diabetes, kidney issues, heart disease etc. will be important to the society remaining solvent. ## Capitalism is still a thing too. There will still be plenty of people using (their) robots to create wealth that is *their own* wealth. I'm quite sure robber-barons will still exist. I think they will find it difficult to monopolize in quite the same ways. ## Disillusion and communism is still a thing too. There will be plenty who refuse to engage the capital economy which is their birthright and "how we do things here", and choose instead to hate and blame. They will read Karl Marx and complain about the system and intentionally refuse to thrive on general principle. Some of them will start revolutions. In short: ## The human condition is still a thing. [Answer] One option that I'm not seeing covered is the Government Buyout. As more and more jobs are being automated, and the income disparity grows seemingly without bound, governments start buying up (or just seizing, depending on the specifics of their internal politics) robotic factories, automated diners, mechanized house builders etc. *en masse*, and use the profits from the now government-owned businesses to pay for people's livelihood, essentially paying people *not* to work, in an effort to stabilize society. [Answer] ## Tax the robots. This is the answer to all of the social difficulties caused by the steady encroachment of robots into society. *"The robots are taking our jobs?"* Well, if you put a sufficiently high tax on them, they won't be as obviously cost-saving compared with the human worker, so the jobs crisis will be slowed. More and more jobs will still go to robots, but the pace of change will be much slower, allowing society to adapt more easily. *"I don't have any money because the robots took my job!"* Redistribute the tax as a social welfare payment for the unemployed, and suddenly people realise it's not so bad after all. They're getting paid but they've got all this free time! It's great. They go out and spend the money doing fun stuff like sitting in a cafe getting served by robots; the economy grows; more robots are brought into service; more taxes generated; higher social security payments; more spending; it's a cycle of never-ending growth. Well, in theory, anyway. *"Who are the real winners here?"* Obviously, those who own the robots stand the most to gain. They're the ones who already had lots of money to start with, so they'll bitch about the taxes, even though they actually benefit from them in the long run. They will continue getting richer. Not much change there then. Low wage earners will benefit because in order for the whole thing to work the social security payments will need be higher than they could earn doing the menial jobs that the robots have taken. Maybe not to start with, but certainly in the long term. There will be a large-scale upward shift in the class dynamic. Conversely, the middle-class will be the losers, because many of them they will also lose their jobs but the social payments won't cover their losses. At least they'll have more free time though so they won't feel too bad, although they will wish that the cafes weren't so crowded these days. [Answer] I think you would see different results in different countries/societies based on existing values. Societies with a very capitalistic bend will likely experience severe political polarization and social unrest as huge parts of the population gets unemployed and the rich gets richer. Although it could develop in other ways. It depends on the level of equality already existing on society. A society with more resourceful and richer lower class will likely turn into a society of only capital owners. The lower class will simply own robots doing their former jobs, and get income from that. In essence the whole society will change from mainly being made up of wage workers to capitalist owners. The benefits of scale, anti-trust regulations etc might affect whether this happens at all or whether power will just accumulate in a small class of capitalist owners. The latter will likely descend into political chaos. Although with such advance robots the rich might be able to build military and police robots to control and subjugate the masses. In a more social democratic or mixed economy type of society I suspect social programs will simply expand as people become unemployed. More wealth will be taxed and redistributed to the rest of the population to sustain them. A third possible way is that the poor will bound together in a collectivist manner to buy and own means of production which can give them an income according to their needs. A sort of voluntarily communism. Although I don't see it as likely as there would be no benefit in admitting new members with limited means. [Answer] A robot might be able to cut my hair as well as a human but hit won't give me the same experience has a hair dresses that talks to me while it makes my hair. The same goes for low-wage workers like baby sitters that provide a service that inherently needs a human. We might also see a comeback of buttlers and similar human services if the price is low enough. [Answer] Not everybody will use robots because they will be expensive. It's not just the initial outlay of capital to buy them, but the additional ongoing expenses for maintenance contracts, programming fees, and patching. For some mom-and-pop operations, it still will make sense to bring on part-time help. As the supply of labor increases, the price will decrease. You'll see a surge in under-the-table, black market employment. There will be a surge of jobs supporting robots. There will be new sectors emerge to recondition and repair cast-offs, non-sanctioned repairs, and training that will absorb some of the excess labor supply as well. Governments and private industry will offer training programs. Crime will increase, as will the need for police (which affects the labor pool.) The disruption will last for a generation or so until society reaches a new equilibrium. Maybe compulsory higher education would emerge, or mandatory military service to train skills. [Answer] Let’s go back 100 years; a farm worker from that time would consider our tractors etc to be “robots”. Go back a bit more to when waiving was done by hand, our current waiving machines will be considered robots to them. In both cases “capital” has got richer, however also in both case people “with nothing” are now better off in most european countries (including UK) then most of the worker were before the robots took their jobs. What people expect from life seems to increase just as fast as we are able to automate jobs with tool, machines, now just renamed to robots. [Answer] Most importantly, we need is a Scientific Approach to deal with this question of "How would humans adapt if low-wage labor was done by robots?" And the historical perspective of this situation. “Think Out Of The Box”. Read the following theoretical article in two parts on [this page](http://anticorruptionfight.blogspot.in/2016/08/artificial-intelligence-robots-make.html) and [this page](http://anticorruptionfight.blogspot.in/2016/08/artificial-intelligence-robots-make_6.html). The gist of the theory is; there must be A Gradual Reduction in Working Hours. In the present situation, ENACTMENT of A THREE-DAY/24/HOUR WORK WEEK Before which, the principle behind my theory is; the fruits of the societies technological progress should not be appropriated only by a few elite but it is their historical responsibility to see to it that the benefit should be equally shared among all members of the society. ]

[Question] [ **Story background** The government has chosen to use a constructed language as a part of the process of building national identity. They don't want to use a foreign language. They also don't want to use local dialects because they are quite similar with the languages of the neighboring countries. The time setting is decolonization after 1945. Most of the citizens are illiterate. Those few that could read & write use the language of the former colonial masters. **Question** The government of a former colony, which recently gained its independence, decided to replace local dialects with a constructed language as the official language. The new language doesn't have any similarity with any local dialect nor with any other language in the world. How should a country introduce a constructed language as the official language? [Answer] # With patience They would have to know in advance that the process would take at least a generation. As people grow older it becomes harder for them to learn a new language and be proficient in it. So it's better to teach the kids, and to do that you need to give them the tools, and the motivation. **tools**: this is the easy part. The education system's whole purpose is to pass on knowledge that fits the government's whims, so use it to teach them the new language. **motivation**: of course, you want the kids to speak the language fluently, not just enough to get a good grade. So they need a reason to want to learn, or for their parents to push them to learn. Examples include: * all university studies are in the new language * all government services are in the new language * entertainment like TV, movies etc are in the new language ## Real life examples: As mentioned, when Israel was founded the Hebrew language didn't even exist as it is today, and now it's the official language. Many immigrants don't speak it very well (almost all the population are immigrants or 2-3 generation in the country) but their children all do. The Italian language was also introduced in an attempt to unite all the various cultures under one language, which obviously was a success Another example from Israel: when you speak to people (mostly girls) at the ages 25-30 they have a really good knowledge of Spanish. The sole reason being a series of Spanish soap operas that were the best thing to watch for kids in the 90s. ## What about illiterates? You mentioned that the population is mostly illiterate. The thing about this is, if you don't have education it's really hard to pass on knowledge. Some system needs to be in place in order to teach kids the language. If your determined to teach the language and keep the population illiterate, my best suggestion is an army of nannies that speak the language and provide free (perhaps even mandatory) child-care. There's no better way to learn than to have someone speak to you when you're a kid. Then, you also need to keep some motivation for the kids to keep practicing the new language, as mentioned above. The fact that every kids speaks a language that none of the parent do might act in your favor actually. [Answer] > > Languages take immense effort to learn, and people will only learn > them if it's socially or economically inescapable. [Zompist](http://www.zompist.com/whylang.html) > > > Choose a combination of stick and carrot depending of how powerfull the government is and how dirty they wanna play: 1. Train and license teachers that will strictly teach in the conlang. 2. Open schools that will educate students in the conlang. 3. Make knowing conlang obligatory for anyone who wants government job. Most of the people are risk averse and steady government paycheck is the only ticket to middle class. 4. Make all official documents & legal contracts only in the conlang. 5. Organize campaign of eradication of illiteracy, see [Likbez](https://en.wikipedia.org/wiki/Likbez) . Where illiterate means can't use the conlang. 6. All schools must use the conlang as language of instruction. Ban those who won't. 7. Propagate the glory of the official language. 8. Make all the print (newspapers, books) conlang only. 9. Make all radio & tv programs conlang only. 10. Invest in conlang literature (prose, poetry, dramas). 11. Invest in conlang music, radio dramas, movies. 12. Mock all those who refuse to learn the conlang as backward, stupid or enemy of the state. See supression of French regional dialects as an [example](http://www.france-property-and-information.com/dialects_of_the_french_language.htm) If you prefer to use national pride take a look at [Revival](https://infogalactic.com/info/Revival_of_the_Hebrew_language) of the [Hebrew language](http://www.jpost.com/Jewish-World/Jewish-News/This-week-in-history-Revival-of-the-Hebrew-language) its not a conlang, but its the only language that was brought from sacred language to a spoken and written language used for daily life. [Answer] When we speak of constructed languages we tend to think of languages invented *ex nihilo*, such as Esperanto or [Volapük](https://en.wikipedia.org/wiki/Volap%C3%BCk); such languages have never taken roots solid enough to make them serious candidates for the role of the official language of a reasonably large political structure. (Esperanto, the most successful wholly invented language, was at a certain point proposed as the official language of [Neutral Moresnet](https://en.wikipedia.org/wiki/Neutral_Moresnet) (1816–1920), a tiny tiny neutral territory wedged between Belgium and Germany. It was also somewhat favored by certain left-wing political movements in the first half of the 20th century.) There is however another class of constructed languages, namely those built on the basis of a natural language. Such half-natural half-artificial languages have certain advantages compared to those which are fully artificial: they come with a ready-made cultural tradition, and with an obvious target population of potential speakers. Two of those languages, Modern Hebrew and Purified Greek, actually became the official languages of Israel and Greece; in Israel, Modern Hebrew took root, endured and flourished; in Greece, Purified Greek fought bravely but eventually lost in favor of its natural rival, Modern Greek. * An example of success: [Modern Hebrew](https://en.wikipedia.org/wiki/Modern_Hebrew). At the beginning of the 19th century Hebrew had been a dead language for two millenia, [plus or minus a few centuries](https://en.wikipedia.org/wiki/Hebrew_language#Aramaic_displaces_Hebrew_as_a_spoken_language). (Some scholars think that Hebrew was already dead in the time of Alexander the Great, others say that it may have still survived in some communities until the 2nd century CE.) In the second half of the 19th century a movement to [revive Hebrew](https://en.wikipedia.org/wiki/Revival_of_the_Hebrew_language) arose among some Jewish scholars and ideologists, spearheaded by [Eliezer Ben-Yehuda](https://en.wikipedia.org/wiki/Eliezer_Ben-Yehuda). The task was ample; nobody had spoken Hebrew in real life since the Antiquity; the language lacked words for modern concepts and objects; and there was no commonly agreed pronounciation. The movement had a very slow start, but eventually it gained the support of educators, and when Israel proclaimed its independence the newly revived language was the obvious choice as the official language of the new country. (It was the obvious choice for the people who led the independence movement; the practical choice would have been Yiddish, but Yiddish was considered ideologically inappropriate.) Modern Hebrew has a [simpler phonology](https://en.wikipedia.org/wiki/Modern_Hebrew_phonology) than Biblical Hebrew, simpler morphology, and somewhat different syntax. It includes a large number of loan-words from European languages, to make up for the gap between the Antiquity and the modern world. While most linguists classify Modern Hebrew as a purely Semitic language, there is a significant minority who view it as "genealogically a hybrid with Indo-European" (from Wikipedia) -- but they can't agree *with what specific Indo-European* family; some say that the decisive influence came for Germanic Yiddish; others see obvious Slavic traits. What is clear is that Modern Hebrew is a new language, created by the collective efforts of scholars, writers and educators between the second half of the 19th century and the middle of the 20th. And it has successfully been adopted as their official and everyday language by an entire nation. * Another half-successful example is [Nynorsk](https://en.wikipedia.org/wiki/Nynorsk) (New Norwegian), constructed towards the middle of the 19th century by Ivar Aasen and intended to represent a true form of Norwegian, free from Danish influence. Today the language is co-official in Norway alongside [Bokmål](https://en.wikipedia.org/wiki/Bokm%C3%A5l), the Danish-like language used by 85% of the population. * An example of failure: Purified Greek ([Katharevousa](https://en.wikipedia.org/wiki/Katharevousa)). Conceived around 1800 by [Adamantios Korais](https://en.wikipedia.org/wiki/Adamantios_Korais), Katharevousa was intended to bridge the gap between wild exuberance of Modern Greek or [Demotic](https://en.wikipedia.org/wiki/Demotic_Greek) (which, at the time, was uncodified, split into several different dialects, and essentially unwritten) and the deadly stuffiness of the Byzantine form of Ancient Greek which was the only acceptable written form of Greek. The name of the language means "Purifying"; it was built to reflect what its developer considered to be the course of evolution from Ancient in the absence of external influences. As a half-way language, Katharevousa had simpler grammar than Ancient, and its phonetics was mostly similar with Modern Greek. When Greece achieved independence in 1830, Katharevousa became the official language of the kingdom. The acceptance of Katharevousa was far from universal; tellingly, it never gained the favor of writers. While all children were supposed to learn it in school, few people used it as their everyday language. The [Greek language question](https://en.wikipedia.org/wiki/Greek_language_question) remained unresolved for one century and a half, until in 1976 the Greek government capitulated and accepted defeat, and, in an article of Law Number 309 (written in Katharevousa, ironically) declared Demotic to be the official language of the country. Today Katharevousa survives as the language used by the Church of Greece in public communications. (The liturgical language is still [Koine Greek](https://en.wikipedia.org/wiki/Koine_Greek), the form of Ancient Greek spoken in the days of the Roman Empire.) What can be seen from those examples is that *ideology matters*, and gaining the favor of educators and writers is crucial. It is essential to gain a foothold in schools and to grow a generation of native speakers; equally important is to gain mind-share among the target population and to position the new language as an essential attribute of national identity. [Answer] # Make them want it You need some heavy propaganda to make people believe that learning is beneficial for them. No similarities means five to eight years to fluency [citation needed] . They must have really strong feeling this is good and that this time would pay for itself in future. # Make them hate old languages If you don't, they will stick to them, and "official language" will be only a legal fiction,or a tool for lawyers. # Make your new language easy, precise, rich and capable of beauty This one is mostly self - contradictory and impossible, but at the same time you have to do it. Easy to introduce it in few generations. Precise because you need people with different language backgrounds to understand each other well. Rich and capable of beauty because if it isn't, people will fall back to other languages. [Answer] Mustafa Kemal Atatürk implemented a sweeping [reform](http://countrystudies.us/turkey/25.htm) to the Turkish language in the 1930's, including large vocabulary changes as well as a [switch from the Arabic alphabet to the Roman alphabet](http://www.docblog.ottomanhistorypodcast.com/2013/12/language-reform-turkey.html). The change was largely implemented via the public school systems. This answer is based on my [answer on History.SE](https://history.stackexchange.com/questions/522/are-there-confirmed-cases-where-a-country-changed-its-language-without-being-con/33083#33083) covering this. I made an argument in my History.SE answer that this change could be considered a switch to a new language, and if it was a new language it could certainly be considered a conlang as it was purpose-built by the government. A society that is mostly illiterate is less likely to want to keep an old writing system alive since the average citizen will have no significant investment in it, and many illiterate citizens would jump at the chance to learn to read and write at all, not caring what script. In your world, be sure to fund the public schools well enough to ensure that there is an adequate Adult Education department to teach the alphabet to all the illiterate adults, and that you don't allow too many illiterate children to graduate high school by cheating! [Answer] The [History of Esperanto](https://en.wikipedia.org/wiki/Esperanto#Later_history) would be a good read for you. It was proposed as the official language of [Neutral Moresnet](https://en.wikipedia.org/wiki/Neutral_Moresnet), and if not for WWI, it likely would have taken hold. Using that as a real world example, your government should cast suspicion on anyone using a local dialect. Spread some propaganda that anyone speaking XYZ could be a spy from XYZonia. All *TRUE* ABCians only speak the new ABC language. [Answer] Beside teaching and broadcasting in the new language, it's important that new words are firstly invented in the new language. But it would be difficult for government officials to do that themselves. It would be easier if the country originally consisted of many small tribes that have used significantly different languages. If not, another slightly extreme approach is to dictate the original language. You may create so many taboos on using the original language that makes most "creative" uses, such as borrowing new words, naming new things, or even humors impossible. But you leave the language usable enough that most people could survive with it in everyday life, so they are less likely to risk breaking the law. Finally young people would find the workaround by just using the new language, if it is taught anyway. That might seem quite bad. But it's not something so easy to begin with. [Answer] If you take a broad view of the question, you might include **Newspeak**, the language being forced on the denizens of Oceania in 1984. Of course, 1984 is fiction, and Newspeak is an adaptation of English rather than a new language. But it does have a couple of points that are worth considering. First, it's promoted in the furtherance of a specific ideology. And second, it's designed to limit communication instead of broadening it. [Answer] **Biopower.** Foucault's idea: the norms of behavior are better enforced than any law, because everyone knows how one is supposed to act, and enforces it. My understanding (from a class in 1995) is that English before Elizabeth I (and Shakespeare) was very different. She worked to be a champion of the arts that glorified her government. She benefitted from being lucky in war, and for coming after a period of civil strife. Ways changed, because people wanted to get away from the bad old days. Shakespeare's fame is a side-effect of Elizabeth's success. Atatürk and Mao also succeeded, and they also had personality cults. Mao used modern propaganda, but his rule was unpleasant, so his changes were inconclusive. The Greek reform failed: no sun king, no buy-in from the artists. So: civil war, resolved by a god-king, who rules for long happy decades, and controls all the good writers. [Answer] Brigham Young created a phonetic alphabet for all the Mormon immigrants moving to the Utah area so all of the immigrants could learn English more easily. This was done using a university and local schools. It may be worth researching his efforts. Here is the Wikipedia article. <https://en.wikipedia.org/wiki/Deseret_alphabet> [Answer] I think SapirWorf should look up the Indonesian Language. <https://en.wikipedia.org/wiki/Indonesian_language> It is constructed from an existing lingua franca, but mostly seems to qualify for what he is looking for. [Answer] **Belief in Sapir-Whorfianism** In the country in question, the Sapir-Whorf hypothesis is held in great esteem and popular. So, the conlang to be introduced is designed with the Sapir-Whorf hypothesis in mind and shall express the culture and the values of the new country in a specific way. The people want the language, because it is marketed to them as the expression of themselves while all other languages have shortcomings in this respect. They will also have the feeling of self-improvement by acquiring the new language. [Answer] Your biggest enemy here is spoken language. Your people might be mostly illiterate, but they still can speak languages. Have all the kids between 2-5 to government facilities where they will be exposed only to conlang. The caretakers in the facilities are loyal government agents, thus the kids has no way to learn language other than conlang. Release them...ahem...I mean they can graduate after they are 18 or so. For the masses, introduce this as a government program to ensure that every child has equal access to nutritional food, and education. The reason why the government have to do this is because they have to catch up with the other nations fast or else they risk being colonialized again. Those who still against it, well...eliminate them silently. As for those above 5 (which means they most probably has been exposed to other languages enough), re-educate them by conditioning things so that like it or not they must use conlang. 1. All stores must use conlang. Those who don't will have their shop fined. Repeat offender will have their shop closed down. To enforce this, regularly do inspection on random shop. Disguise the agent as customer. 2. All literature accessible to the masses, including even a piece of flyer, must be in conlang. Using language other than conlang is deemed serious crime. Those who created and/or distributed the said literature can be jailed for several years. Since only a few people in your country are literate, you can apply this immediately without risking riot. If those few got angry with this, let's make it that they have unfortunate incidents. 3. Promote conlang by gradually change broadcasts (TV and radio) to use conlang. Adversite it like a cigarette. Conlang is cool those who don't use it are lame-o. Gradually change this into those who don't use it are enemy of the state, spies from another countries. 4. Have schools teach conlang. It is accessible by people of all age. Make it so that for the first 5 years of its inception this schools are free. Since everything is now in conlang, this will accelerate the change (well people love free stuffs). 5. Under the pretense of rezoning, have the older generation move to the more remote part of the country. Once they are all gone your whole country would use conlang since you have the younger generation grows in it. 6. Have the kidnapped...ahem...government cared kids send letter to their families in conlang. Now for the sake of hearing from them the family would have to study conlang. All letters should be screened. Those that includes language other than conlang will not be delivered. ]

[Question] [ Suppose a group of people get transported back in time (say 2500 years). Then, in a manner reminiscent of *A Connecticut Yankee in King Arthur's Court*, they try to re-design modern technology. Assume that there's no shortage of labor or materials; the only real lack is knowledge. What kind of group would have enough knowledge to recreate modern technology within 50 years? Would one average college-educated person be enough, or would it take hundreds of experts? Would there be any particular points that they would get stuck at? For argument's sake, we can define modern technology as: laptop computers, kidney transplants, DNA sequencing, artificial satellites, and nuclear power plants. [Answer] Our intrepid time-travelers really have their work cut out for them! To make this possible, let's hand wave the problem of language and religion, and say they got really lucky and wound up in a country that is eager to learn and listen. This is a big hand wave, but let's at least give them a shot to try before getting executed straight away or having to overcome a language barrier. The big thing they will need to realize is that it will be simply impossible to jump straight from 500BC to 2000AD all in one straight step! Let's use the Wikipedia handy-handy [List of Technologies](http://en.wikipedia.org/wiki/List_of_technologies) to see what we can hope for in 500BC! According to the [History of Metallurgy](http://www.historyworld.net/wrldhis/PlainTextHistories.asp?HistoryID=ab16&paragraphid=bax#bax), we can say that our locals have access to iron and have been using it for a while, and a it is pointed out that even steel has been discovered and used! However, until right around 500BC in China no one had a furnace that could actually melt steel, so no cast iron - but that's right when we arrived! Note that the first iron foundry in Europe as put at 1161 AD - 1600 years after China. That could cause us a problem if we land in Europe... But let's hand wave this little geographic problem and pretend we have actual access to iron, charcoal, and a furnace hot enough to make limited amounts of cast iron and steel. To further orient ourselves, consider that we have to hope to be in an area where [petroleum](http://en.wikipedia.org/wiki/History_of_the_petroleum_industry#Early_history) is available to us for things like tar and asphalt, which is actually possible - hey, China did it! It sure seems easier to land in China in 500BC and get to work there, doesn't it? Anyway, we've got clean running water, iron, a hot furnace, oil, copper, bronze...holy crap, we don't even have PAPER? We're about 1000 years before the first [Persian windmills?](http://telosnet.com/wind/early.html) Well, we've got papyrus and animal skins and clay tablets for writing, so I guess we'll make do. ## Let's Make a Computer! ...right, so remember what I said about not trying to jump ahead? Obviously we are going to need some silicon to get any kind of recognizable computer made, and that stuff is just sand, right? Well, not exactly. Remember that great iron melting furnace? Iron melts above 1500 Celsius, but to refine even [metallurgy grade silicon](http://en.wikipedia.org/wiki/Silicon) we need to get over 1900. We now need to make a kiln hot enough to make glass, which the internetz say is way hotter than needed to make cast iron. Which is weird, because the internetz say cast iron was so hard to make because they couldn't get the furnace hot enough to melt iron, and yet they could melt glass? Hm. Hand wave, we build a furnace to melt glass! Now we could get this far in a few months, with lots of labor help I'm sure. But now we have a problem. We can now make glass and even get ourselves some silicon, but it isn't pure enough to use in even friggin' basic electronics - much less computers! We supposedly need over 95% pure silicon for basic electronics, which was first done [seemingly around the early to mid 1900s](http://books.google.com/books?id=ATFo8Pr67uIC&pg=PA33#v=onepage&q&f=false). I honestly can't understand half the real technical material, so this college-educated single person with the internet at his hands would fail right here. I think we need to try crushing and putting through an acid bath, but where do we get such pure acids? That will take refinement, and a whole ton of chemistry, I honestly don't know how hard it is or how long it will take to get enough, pure enough, to get even remotely close to pure enough silicon. And the thing is, [that isn't nearly enough](http://www.madehow.com/Volume-2/Integrated-Circuit.html). We are going to need a handful of weird elements sourced and purified, from aluminum and boron to gallium. We need a clean room, air filtration, anti-static measures - these people don't have air filters! We will need electricity here, and how can we know without trial and error we got it right and have things pure enough? This is going to soak up a lot of time and specialist man power unless we have special instruments and ultra-precise tools to help us - and guess how much work that will take to build? I'd say that with a team of specialists, all the worlds combined internet knowledge and the library of congress, we are at least a few years in and don't even have silicon of the proper grade. I don't know that with trial and error alone that it'd be doable, so we probably can't even progress here until we go backwards and invent some pre-requisites. ## It's Not All Just Knowledge Another problem we run into very soon is that it isn't all about knowledge itself, but arts, crafts, and skills. If you want useful chemistry and/or refinement, you're going to need thing like suitable lab equipment, such as test tubes and piping. Using crude metal scruples will contaminate the process and ruin it (or will fail spectacularly as with acids for advanced chemistry in metal or stone containers), as will crude methods of providing heat and flame unless you seal things properly. When it comes down to it, glass-working and metallurgy are arts too - especially without functioning preprogrammed robots! You'll need skilled craftsmen to even begin to shape stuff resembling what you'll need for crude methods, and without automation or mass production they'll need trained assistants and heavy labor and months or years to handcraft the stuff we're going to need. ## This Is Getting Toxic What's worse, to start moving towards the first electronic devices we start facing some amazingly dangerous substances. Poisons, strong acids, aerosols, particulates, flammable/explosive gasses, toxins - without the right tools, pure hard work and persistence will kill everyone involved. Safety measures will be needed. We're probably going to need some pretty good plastics to get out of this process alive, and... ## We Are Going To Need A Bigger Boat The thing is, our technology has pre-requisites - a history. It's easy for us not to think about it, but the things we have now are refinements and combinations of things that were invented before, which themselves are refinements and combinations of other things from before that, and on and on...all the way back to ancient history. While we can certainly speed things up as development didn't take a straight line (and never will), it isn't the result of a few brilliant insights. It took many thousands of smart people, who learned methods from thousands of smart people who came before, who learned from thousands of smart people who came before, who together labored for effectively thousands of life times and drew together the work of hundreds of thousands of people across the last 2500 years just to get from "what's paper?" to "OK, Google". There are lots of cool stuff we could have known about that others have pointed out (from soap and the importance of washing your hands and the importance of sanitation), but also is might be naive of us to think it's just because people didn't know they shouldn't throw corpses in with the drinking water; it was the result of a lot more than mere ignorance. Lots of awesome improvements could be made, but fast-forwarding 2500 years in 50 years is going to take a herculean effort from many people, and they are definitely going to need more than the knowledge that they carry around in their head. This is definitely something you can make an interesting story from, but the ultimate answer to the beginning question is: hundreds or thousands of experts, probably a lot more than 50 years, and they are going to need more than their own knowledge and memory - Wikipedia won't be enough, I assure you! [Answer] ## New answer: Good luck! So if you wanted to offer your creative scheme to bring Lolcatz to a more civilized age, you would probably need a plan to show the local king to suggest that your plan is feasible. There is an entire school of thought dedicated to how to make high level timelines like Gantt charts. Let's look at what it would take. A key limiting factor here is manufacturing. While you can store all sorts of knowledge and work on designs in parallel, when it comes to building things you have to have enough capabilities to actually do the job. You don't get to make a mill or lathe that is square to 1/10000th of an inch straight off. You have to build several predecessors first, each more precise than the last. And building a computer is unforgiving... you won't get away with being less precise than that. Another limiting factor is skilled labor. Free access to indentured servants is useful and all, but if you want someone to manage the temperature of a furnace by eye (because digital thermometers don't come until later), you're going to have to do it yourself with one of your precious future-people. As a rough outline, I would divide my 50 years into epochs. Each epoch is responsible for a very wide class of tasks, because it takes a lot of infrastructure to get to where it is possible to build a computer. After that, you are free to staff-up those epochs. --- ## Kickoff Epoch **Products:** Iron casting, skilled surveyors (for future metalic needs) Sorry to those who were hopeful. Just because we have labor doesn't mean we get to start swinging hammers. We need to take inventory of what is around. If your 2500y.a. metric is actually what you're looking for, that's just at the end of the "early" iron age. You're going to need quality iron, and fast. You will need to educate the local people as to what makes good or bad ores, and start explaining to them how amazing steel is going to be within their lifetime. You're also going to have to get them started searching for high grade trace metals like Vandium. They'll need the head start before other phases need such materials. --- ## The machinist Epoch **Products:** Steel machine tools It's really hard to make reasonable machine tools with horrible base metals. Now that you've spent a few years working with the peasants to have some base materials on par with the base needs for [Gingery's machine tools books](http://en.wikipedia.org/wiki/David_J._Gingery), you're ready to start making machine tools. Just remember that the next few epochs are going to call for strange things like vacuum tight glass/metal seals that call for extraordinary precision. Expect to reinvent the entire set of machine tools (lathe, mill, drill press, etc.) several times during this epoch. Each time, you can use the precision of the previous set of tools to drive closer to the quality product needed for the next epoch. --- ## The Power Epoch **Products:** Electricity, generators, power tools It's not really reasonable to approach the building of electrical generators without machine tools. The precision needed to have a shaft spin at 60Hz for any reasonable amount of time is very demanding. At the very least we're shooting for steam-era power sources. That's not a lot (compared to the needs of modern foundaries), but its at least something. Your computers are going nowhere without electricity. This step is not trivial. You are going to have to not only remember how power stations are built, but actually build one big enough to power your work in future epochs. There are a lot of processes which do not scale down well (such as every process required to build a computer), so this is going to have to be a reasonable sized power station. It doesn't have to be anywhere near a 500MW plant (a small modern plant), but if you're less than a MW, you'll be unhappy with the results. This is the first time your exercising your new machine tools to do big things, so don't be surprised if you have to do things a few times to get it right. --- ## The Purity Epoch **Products:** Reasonable grade stainless steel, aluminum, glass, copper, etc. Now that we have enough power to run a reasonable sized foundary without a brownout, it's time to let the Chemists have their day. Climbing towards computers requires quality. If you have low quality metals, your vacuum tubes will burn out too fast, and your computers wont be of any use. You need to give the chemists enough time to not only make reasonably pure aluminum, silicon, and copper, but to isolate the Nickel, Chromium, Vandium, and Molybdenum to make reasonable stainless steel. Consider that the upcoming foundry and fab work is some of the more demanding material requirements around, so low-grade stainless steel is not going to cut it. That's just the steel. I'm going to ignore the requirements needed to turn Bauxite into aluminum, and the [oxygen-free coppe](http://en.wikipedia.org/wiki/Oxygen-free_copper#Industrial_applications)r needed for some of the vacuum processes we're going to see in the foundries. --- ## The Computation Era **Products:** COMPUTERS! Finally! We get to make computers. But it's not so easy. The 486 has over a million transistors. You are NOT laying those by hand, so you're going to need to do this in generations. Minimizing the number of generations, you're going to want some vacuum tube based computers to bootstrap the extreme demands of monocrystaline-silicon manufacturing (without these 14+ inch wide crystals, integrated circuits just don't happen... and monocrystaline silicon is not an option without computer-grade temperature controls). Then you're going to need to make something along the lines of an Intel 4004 (the first "monolithic integrated chip CPU"). If you're gusty, you can skip a few million man hours worth of work and jump straight to a 486. With a 486, you're in a reasonable position to start talking about laying out the 1.7 BILLION transistors of a core2 duo. Of course, while doing this, we're assuming you'll go through at least 4 or 5 completely new fabs to transition from the 10um processes of the 1970s to the 20-30nm processes needed for a modern laptop. I'm going to hand-wave away the software requirements like VHDL here. You'll need to have a software team keeping ahead of the hardware so that they have something to make the next generation of hardware with. --- ## The Prodigal Son Era **Products:** Software I'm a software engineer by trade. I can tell you that it doesn't matter how much you *think* you know about a piece of software you want to copy - it takes time to produce it. Unfortunately, we have run into an interesting problem here due to the nature of the question. Life expectancy in mideval times was low, so I don't see people living very long past their 60's in 300BC. The real problem is medicine. Without hundreds of years of medical practice, people are going to die. If you're bringing "experts," rather than college students who know theory but not application, you're looking at people in their late 30s and early 40s. 50 years later, those people are 80 and 90... you're going to have lots of deaths due to diseases that are preventable in modern times, but well beyond the medicine we can scrounge together in 50 years. The last few steps, building software to run on the laptop, are going to have to be done by pesants who were *taught* how to program software, not crack-shot developers in their senile years. Likely we would have to take children out of their family, and raise them to do nothing but produce code. --- ## So what does it all mean? We have 6 phases: * Kickoff Era * Machinist Era * Power Era * Purity Era * Computation Era * Prodigal Son/Software Era We can't really do these in parallel. Each phase is really quite annoyingly dependent on the previous era's final product. It'd be wonderful to try to blend the kickoff and the machinist eras, but honestly it's not a reasonable estimate. There *will* be a blend, but my estimates are also hyper conservative because \*I have included *very little discovery time* in my schedule, which is always a sign that the schedule is hopelessly optimistic. Given this, we need to allocate 50 years between 6 eras. I am uncomfortable giving anything less than 10 years to the Software Era. It's going to have to be done by a bunch of pesants *who have never programmed in their life until now.* I consider 10 years an *eggregously aggressive schedule*. Realistically I'd like 100-200 years to develop enough of a knowledge base in the pesants to do this task, but we're going to allocate 10 years. The Computation Era cannot be rushed as well. You are going to have no not only develop 4-6 unrelated computer architectures in order to realistically accomplish the goal, but you're going to have to debug each and every one before using it to move on to the next. I choose to give it 2 shares worth of time, compared to the other epochs getting 1 So the final schedule is (with a few handwaved allocations): * Kickoff Era - 3 years * Machinist Era - 6 years * Power Era - 8 years * Purity Era - 9 years * Computation Era - 14 years * Prodigal Son/Software Era - 10 years **What did I just suggest?** * We are going to have to go from wood fired brick stoves to steam-powered 60Hz generators in 8 years * We are going to have to go from "the best iron we can find in this era" to "the abiltiy to fabricate 100lb+ single crystals of silicon" in 9 years. * Somehow we will need to average somewhere between 2 and 3.5 years to completely develop, test, and integrate an entire computing architecture (which had thousands of engineers to develop in the first place). We will need to average that over 4-6 architectures * We will need to manage to teach an entire generation of pesants how to program for computers *that do not exist yet* until they are 20-30 years old. This class of pesants will have 10 years to reproduce Linux, Office, and maybe even a Web Browser. --- ## Realism check? The time-frames needed to meet the 50 year deadline are *hopelessly* extreme. The only way to get around this is to stack the deck. If you bring a glut of individuals over, each of which is carefully assigned their portion of the task, you stand a chance of succeeding. The only way you can succeed is if you manage to do epochs in parallel. The only way to do this is to remember how to build everything *in such detail* that it can be built as fast as materials are available, and without a single mistake. The only way to do that is to treat humans as over-priced books, and fill their heads with the fine details of "Foundary Design: Volume MXVI." --- **Original Answer** This is my original answer. It is rather pessimistic because I actually tried to answer the original question of "N people in 50 years" instead of the modified question "how would you lay out the tasks?" In light of the time-frames above, I think you can see why I consider such high personel-counts reasonable. **You could do okay if you transported the entire population of the Earth, along with all of our books and computers.** While a *reasonable* sized group could remember a lot of the really difficult leaps (Electricity comes to mind), vast swaths of what you look to do is simply out of the scope of such a small crowd. One of the challenges you will face is the need to do things right the first time, or a very small number of times. Not all technologies can be made in paralell, so your 50yr budget is going to have to get sliced up into little pieces to deal with such ordering. Let's take your laptop example. * I need a CPU, north bridge, south bridge, graphics card, hard drive controller, and memory. Each of these has to be coded in VHDL. Modern hardware is not simple. There are a lot of really difficult details to remember. There's a good reason intel hires so many of the best designers each year. I'd estimate 300 PhDs would be enough to remember all of the fine details. A team of 2000-3000 engineers working round the clock should be able to redesign a Core2Duo in 10 years or so (hopefully they'll remember enough details, because they lack the libraries of information the original teams had). Unfortunately, Engineering like that isn't exactly a skill you can just teach your average commoner, so you'll have to bring all of your engineers yourself. * Of course they'll make mistakes in the VHDL code, so we need a simulation to test on, which means you need a computer. Oh wait, you're building one. Okay, so we need to build a simpler computer. Unfortunately, we don't get to re-use the engineers before... their brains are full of a decade's worth of innovation. We need a few engineers and PhDs to remember how it was done old-school, before we had all that extra processing power. An additional 100PhDs and 1000 engineers should be able to boot strap you. * Unfortunately, even this computer is going to need a computer to operate on. We probably need some vacuum tube logic to bootstrap that. Vacuum tubes are tempremental beasts with all sorts of hard-to-explain behaviors. I'd say 50PhDs to remember the details of how to make them work well, 50 technicians/glassblowers to remember all the details of how to manufacture them. * We'll do a gimmie on the wires, since that's part of the mining block of tasks (probably 40-50k people's worth of information, but it's distributed across all of the things you need to build with the fancy minerals). * Wait, what's VHDL again? We don't have specs, so we're going to have to recall what VHDL is from memory. It took hundreds of people to get it right the first time. We might get away with 30 really sharp VHDL people to write the spec down again. * But VHDL has to be processed. We need C/C++ to write a decent VHDL simulator or printer. I think 70PhDs and 200 coders should be enough to remember all of the fine reasons WHY each C/C++ behavior existed and code them all up over 10 years or so. Remember, this has to be bootstrapped, so they're goign to write it 4 or 5 times. Fortunately, this can be done in paralell with the hardware team! You now see that I have a small city forming. I haven't even begun to design a screen, or fill it with software. And, in my opinion, I am highly conservative in these numbers. I'd say my original estimate might be high. If you had 50 years to reproduce a reasonable set of technology, you might make do by taking the top 10 or 20 million smartest individuals. You'd have to pick them carefully, because some of those people are going to die within 50 years, so you need overlap. I'm also removing nuclear power from the reasonable list. Because of how long it would take to identify nuclear fuel, and how hard it is to build nuclear power plants *while* you are building computers, I'd say 50 million individuals carrying carefully worded instructions from today's modern NRC workers could remember enough details to build a reactor cold-turkey in time for your deadline. It can't be done by bringing just the smart people, because the smart people had computers to work with; this has to be done from sheer memory. [Answer] No one can do it. Even if they all knew *EVERYTHING* about our modern technology, were perfectly orginized, and had the resources of a kingdom backing them up it couldn't be done in 50 years. The problem is that of building tools. I can't just build a computer with the help of a blacksmith. I need *very* exact tools to fit 10^8 circuits per square centimeter of chip. To build automated tools that exact I would need, in turn, other special tools, which I would need specialized tools to build etc etc. Even doing everything perfectly it's just not possible to go from middle age tools to computer age tools in 50 years, it takes too long to build all the intermediate, slightly more resigned, tools in succession. There is also, as already pointed, we are a very specialized society. No one person knows everything, or anything remotely close to everything, about technology. Even if you sent all of NASA, YALE and Harvard, and MENSA back in time you would still be loosing the vast majority of our knowledge. EDIT: as BrianDHall said kidney transplants are not quite as doable as I thought. However, many other surgeries would be plausible, though less effective, If a surgeon trained in the older surgery techniques were sent back. Surgery is more about knowing the body and how it works, it is less dependent on specialized tools (relatively speaking!!). The biggest issue would be lack of proper anesthesia, limited ability for sanitation (basic boiled water can be used, but it's not the same as a proper sterile operation enviroment), and lack of drugs to control infection and/or body immune response(though as I said a basic antibiotic could theoretically be created in a few years, penicillin was just moldy bread after all!) . This means a lower success rate of surgeries, but if it was life or death then a surgery with risk of infection is still better then death! Which surgeries are possible and which aren't really comes down to rather they needed specialized drugs pre or post operation, and how hard it is to operate on a patient that is not under anesthesia (ie that could move while your doing a percise cut) I would assume. I admit I'm less knowledgeable in this area. Some cool things that *could* be theoretically done by a lone person with any STEM education, intellect, some support from the 'natives', and perhaps an interest in science (but no very unique or specialized skills beyond high school) are: 1) curing lots of diseases. Penicillin is just mold on bread. Smallpox can be cured by having everyone make good friends with cows and their polka-doted milk maids. MANY diseases could be cured by teaching people sanitation and to not defecate into their drinking water. Others can be survived by getting rid of rats and misquto infestations. If someone recognized a particular disease they could help to cure it. The idea of a vaccination *may* be possible to generalize to any virus (give me my high school knowledge, 5 years, and a kingdom's support and I could try a few tricks to make vaccines that might actually be partially effective, though I feel sorry for my first test subjects). All of these would take trial and error, not a do-right-first-time thing, but could possible be done. For that matter basic sanitation like having people who are doing surgery or delivery babies wash their hands first could save a massive number of lives! 2) teach scientific method and advanced math. None of these change life directly, but the concepts are what make the Renaissance and industrial revolution possible. You can rapidly accelerate human development with these concepts 3) teach high school science. Really, Newtons first book on Newtonian physics came out right after the middle ages had officially ended (just barely), so they don't know physics yet! Calculus was discovered a century after that! Germ theory was figured out sometime between the two. 4) Teach evolution. This is one science that is very easy to explain, it's not based off of any complex math and could be understood by anyone who has an open mind without much other scientific basis. Of course managing to reveal it in a way that doesn't make you the enemy of religious orthodoxy is another issue, remember the catholic church was VERY powerful for much of the middle ages and was not afraid to excommunicate or worse those that they didn't like 5) Get people to believe you are from the future just with the clothes off your back (and phone in your pocket). Imagine what a watch would do. Imagine what a scientific calculator or laptop would do!! Sure they would run out of power eventually, but you would have convinced everyone who you are by then and used them for good effect. 6) helped design gunpowder and the gun. It's entirely possible someone would remember most of the gunpowder's ingredients. You won't know fully how to build a gun or even gun powder, but the principles and ingredients given over to well-funded experimenters of the day could perhaps make a gun happen? 7) cure scurvy. Scurvy is interesting, the 'secret' to curing it was discovered and forgotten many times. Since we didn't know what it was about fruit that cured scurvy experiments with using cheaper fruits (that didn't have vitamin C), or cooking or filtering our storing it in such a way that the vitamin C was lost occurred many times in an effort to cut costs 8) 'discover' the New World. That one isn't even hard to do. "hey king guy, I'm the dude that can make people move and talk on a magic screen by pressing button and just cured a deadly disease. I tell you that if you send 3 ships in that direction with lots of food they will find something awesome." 9) correct stupid misconceptions like blood letting that were getting people killed and maimed for no reason. 10) tell the 'future' by remembering your history. Though keep in mind that the more one does this the more they change history to make this not work. Plus we all tend to be taught rather inaccurate history in high school, someone trying this may find out that real-life wasn't quite like the bastardized euro-centric version we were taught if they aren't careful. [Answer] In Eric Flint's 1632, a town of about 30,000 from West Virginia gets transported back in time (you guessed it, to 1632) in Central Germany. They retain the physical infrastructure of the town. I won't spoil the book further than to say that, absent the library of Congress or somesuch, the best they can aspire to is a low 1800 technology within a decade or so, with the cooperation of the locals. Modern technology is so distributed and interconnected, that even a pencil requires materials from half a dozen countries to build. They would simply not have the infrastructure base to maintain, never mind develop 20th or 21st century tech for generations, even with perfect libraries. [Answer] Let me start with a quick 'no' to the average college-educated person possibility. I'd like to think of myself as above average, and I'm continually learning post-graduation. One of the gauges I use to decide what to learn next is the question, "How much of the modern world could I recreate if I found myself in the dark ages?" I could only do two of these and help out a bit with a third. Okay, 2500 years ago, so for the best labor and access to materials, we're talking about Greek, Roman, Babylonian, Egyptian or Chinese. It would be awesome if at least one of your team was fluent with the ancient form of one of their dialects. That's pretty specific. You'd also need someone to convince the locals to do all this work for you and that you are not, in fact, demonic in nature. So you have metallurgy and basic mining, architectural, smithing and very primitive loom work. You will need to upgrade that, and pretty much any college student could quickly get them up to Dark Ages level. Anyone in the sciences could probably start them working with electricity, but it does take specialized knowledge of how to extrude metal into wire. You need someone who could figure out where to start drilling for fossil fuels to make plastics from, and a chem major to take the raw ingredient and get a finished product from it. You wouldn't need a biology major to do the DNA sequencing, but you would need someone who knew how to build a centrifuge (fairly simple) and a mass spectrometer (extremely complicated) and a lot of steps in between. The same person could probably build a Geiger counter to find fissionable material to power you reactor, and could certainly build a satellite (getting it into orbit is a separate issue). Probably a radio for communicating with it. This is getting long, so I'm going to stop trying to figure out how many people it would take, and tell you how many specialized disciplines you are talking about. Linguistics and sociology, electrical engineering, computer programming, chemistry (with knowledge of refining metals, making plastics, ceramics and glass and rocket propellant), surgery, lens grinding, tool machining, familiarity with the parts involved. Let me point out that the same guy with the specialized knowledge to coat your wiring in the right mix of distilled fossil fuels is probably not the same guy who is comfortable working with liquid fuel mixtures. Also, the guy who could machine the parts for your mass spectrometer probably doesn't know his way around a containment chamber for your power plant. [Answer] If you look at history, you'll see that technology grows in leaps, not steadily. Some of that comes from new knowledge, but quite a bit is tied to the tools used to create more technology. The huge rush of new technology in the last hundred years wouldn't have been possible without reliable vehicles and roads, air travel, and computers. To build even one of those things - say, a computer - you'll have to start at raw materials. 2500 years ago, the best tool available was barely at "pliers" technology, which means that every tool you'll need - including more tools to build those tools - will need to be designed from the ground up. First, the raw materials need to be gathered. Since some of the materials for circuit design are very, very rare, or only come from certain parts of the world, you'll need someone who is a top-level mining expert, who has worked both in the field and in the office. That's at least one person. The raw materials will be bound to rock or other minerals, so you need to know how to extract the materials from the dirt you dug them up with. To do that, your best bet would be a chemical engineer, with broad knowledge of how to obtain, create, and manage the chemicals required to extract or create the metals and other materials you'll need. Very few chemical engineers are also mining experts, so that makes two people. In fact, you'll probably need a scientist and an engineer, so three people thus far. Now that you have your materials - and they will most likely be very low quality - you need to actually build the circuits of... your machinery. Circuit boards of today can't be built by hand, and for the first iteration of tools will have to be built that way. So, you'll need an engineer to build the production machines. You should be able to find someone with a broad knowledge of mechanical and electrical design to build a power station, the machines, and warehouses to hold it all; but, such a person probably isn't cross-skilled in chemistry or mining, so that's a fourth person. After several iterations of machinery to build more precise machines and tools, you should have the materials available to build some simple electronics. At this point, you'll also need a master of circuit design, with deep knowledge of computers, circuitry, and everything that goes with it. The electrical engineer could help to design some of the circuits, but really, you'll need an expert for this, too. That makes five people, thus far. Given those four experts, you should be able to build a working prototype within 50 years - possibly less time, but I expect the mining and refining to take a decade at least. Some materials may take even longer to find or refine. However, they will need a lot of help from the local population - while the mining expert is digging for ore, the rest of the experts should be training students of all ages to replace them and to assist them. For safety's sake, I would bring two or three times that number of people; you never know who will die from illness, injury, or old age. Of course, that's only the computer. The other technologies need similar hard-to-manufacture tools, and more experts that wouldn't have similar skills: * A kidney transplant would need at least four people (surgeon, nurse, sanitizing expert, and a chemist for basic medication), and many more if you intend to teach others how. * The artificial satellite is actually not that difficult; one person with knowledge of physics and another with knowledge of how to find or create fuel would be all you need. Refining the metal required isn't that hard, and one or both would know how to create it. * DNA sequencing, however, would need working computers from the first group, along with more chemical engineers, scientists, and biologists. We are only barely able to sequence DNA today, which means it will be very difficult to manage with rudimentary tools. * Nuclear power plants would also be difficult... at least, as long as you want to be safe. Without computer-driven safety controls, nuclear power is not all that difficult. Just slap a couple pieces of uranium together underwater, and bam! Instant steam power! The locals you'd need to run the controls wouldn't last long, but nuclear power could be available with no more than a nuclear engineer and a physicist. It would take a little while to find some uranium, but once found, a functioning nuclear power plant could be created in a few months. Which is a good thing, because that's about how long your workers would live. It would be a lot safer in the long run to start with coal power, and work up from there. The biggest problems with creating modern technology from scratch will always be materials. You may have the knowledge to build a computer, but even two hundred years ago, the materials you'd need to even make a simple diode wouldn't be available, let alone complex circuitry. The second biggest problem would be tools; the tools we use now are at least four iterations past hand tools. You'd need to hand-build one machine, which would be used to create another, more precise machine, which would be used to create yet another, even more precise machine, and then you would finally be able to reliably create a single tool we use today. Multiply that by the hundreds of tools needed to build a computer, or operate on a person, and you already have years of construction and design, regardless of the number of people you have. [Answer] The first thing to notice, is that you cannot do it the capitalist way in 50 years. No way\*. Empirically, looking at our world's history, I see only one other social organisation which is amazingly effective in precisely this task: bringing the semi-feudal, agrarian-type society to produce their own computers and nuclear power in 50 years. Forget college-educated, you need very specific skills. About 1% of your group needs to be a staff of dedicated people with "cool heads, hot hearts and clean hands", if you know [what I mean](https://www.google.pl/?gws_rd=ssl#safe=off&q=cool%20heads%2C%20hot%20hearts%20and%20clean%20hands). It won't look nice, it won't look scientific, there would be prisons, there would be tortures, there would be purges, both inside and outside, the heads are going to roll. Next you need a larger force (~10%) of trained and obedient police, and they need to be good at martial arts to exert their power on the main group, because they wouldn't have anything else initially. About 30% should be farmers trained in the archaic farming techniques. Without these basic prerequisites, your group would soon get some centrifugal force and wouldn't remain a monolith. All your cherished nuclear physicists might just wake up one day in the year 3 and decide they're fed up, they don't want the humanity to get to the proper version of future and they would walk the land, just like that, to become a successful hunters-gatherers somewhere in the central European plain. Historically, such problems were a major pain in the 1600s in North America, where Indians openly despised the powerful Western civilization, but there was quite a substantial number of whites who run away to voluntarily join Indian tribes. Situation can quickly get dramatic with your farmers, as they see more than a half of their food taken away from them and (initially) get nothing in return except of diseases and early-spring hunger. Constant terror is the only way to get this kind of taxation. Speaking of diseases, you would probably bring some modern mutations of viruses and bacteria to exchange with the ancients. While your people would be possibly in better situation (or maybe just slightly better), you would most likely do the same thing to the ancient cities that was done to American cities: you would kill 90-95% of inhabitants before you could even see them. --- [\*] Basic pre-requisite of capitalism is a large consumer market. By consumer market I mean >1 million of greedy people, the kind that would buy a shirt just to display their status despite they already have two other proper shirts. In 500 BCE you wouldn't have these people available, and it would take more than 50 years to "convert" the existing population to the consumer way. And computers are not made of silicon and science and need. Computers are made of silicon and consumer market, period. We've got silicon for billions of years on this planet, we've got the need from the very beginning, we've got science for thousands of years. But just as we developed consumer market, it took only about 300 years of clean sequential progress to have computers. Science is just a side effect. [Answer] It may not be possible to create the laptops of today in 50 years - the entire population of Earth 51 years ago, with all the infrastructure and knowledge in place, couldn't do it in 50 years. However, a small number of people from today can in 50 years kick off a technological revolution that will lead to an advancement of the level we have today in the shortest amount of time that is practically possible. There were a number of ideas throughout history that had a huge impact on the advancement of technology and are very simple to explain and obvious in retrospect, but no one thought of them before. Some examples: **The Printing Press:** Very simple to explain to a society that is already using stamps for wax or coins and using ink for writing. Getting them to set up printing presses will mean that information can start to spread more quickly and the knowledge from the future can be preserved and distributed widely for when the infrastructure will be ready to implement them. **The Steam Engine:** Very simple to explain the basic process to people who are already using fire and know how to boil water. They can then build railroads and other machinery required to produce and transport materials for other technologies. **The Scientific Method:** No science is required to explain it, but the world was stuck with the Aristotelian method for a long time. Explaining it to people 2000 years ago and showing them that science works would immediately advance them 1000 years. They can then proceed with their own advancement, boosted by having had a peak at the future. **Math:** Practically all the math knowledge that this group of people will have can be taught to smart people in the past, even though it took a very long time to develop in the forward direction. Even something as simple as our number system can have a huge impact. There are many others and there's also a number of other non-scientific advancements that we've made throughout history, such as democracy and equality, that have an impact on the advancement of science [Answer] It won't work if there is no market for it. A modern laptop computer can only be made because billions of processors are produced. You require an industry to make the tools to make computers, and you need another industry to produce the tools to make the tools for it, and so on. You could, however, create a late 19th/early 20th century technological base pretty quickly, in at most a few years. From then on, you would need to create a pretty globalized society to create the necessary markets, otherwise no single kingdom could achieve it. To make an early vacuum-tube computer with all the resources of a medieval kingdom? Maybe achievable. Modern consumer electronics? Not a chance without a large enough market for it. A lot of technology wasn't invented sooner, not because the idea didn't come to anyone, but because they didn't have the tools for it. All the mathematics necessary for a moon mission could be calculated in the 19th century, possibly sooner, they just didn't have the industry to produce the tools to build rockets large and efficient enough. [Answer] I'm gonna say it wouldn't happen, at least on the computational level. While a doctor, jeweler (for making the scalpel, needle, etc), geochemist (for mining and refining the materials needed by the jeweler), microbiologist (for penicillin to fight infections) and textile factory worker (Where do you think you get the threads for stitches?) may be able to get together to make a Kidney transplant happen, computers would be way more complicated. Every CS college grad at least in some way understand Turing machines and bit-wise operations, but the entire computer science industry is standing on the shoulders of giants. If you got the right group of highly advanced specialists (Manufacturing, hyper-mathematics, programmers, system designers), it could be done, but if you just took an average sampling of people, I'd be highly incredulous if you said you got the right people to build a computer. [Answer] ## So you want an uplift package Well, there's a lot of work that needs to be done. Now, technological development is not a straight line; there's a lot of things you can forgo and bypass, if you have specific goals, but let's just say we want some of our modern conveniences and see how far we can get. **TL;DR: you can get most of what you wanted, after a fashion, but not on today's level in 50 years.** Let's start out by listing who we need. I have the good fortune to be teaching (and researching) at a technical university, so I'm going to base my estimates on the type of requirements we have for our graduates. Here we have to stop for a minute and examine our basic assumptions; the first question is whether you get to pick who exactly you get to take back. If so, we can reduce the manpower requirements immensely, if not, you need to take enough people that you will get the required expertise by random chance. I'm going to do an ass-pull and estimate that about 1% of the population have the required skill on a required level, so if you're sampling randomly, multiply the numbers by 100. On the other hand, the extra people with modern education would also help, as you could send them off to do some less complicated tasks. Let's also assume that the entire population of the area is at your beck and call and will provide their work and whatever expertise they have per your instructions. I'm further going to assume that the area you're in is something like Europe, since that's where I'm from and it will make things easier on me to have a geographical point of reference. That said, here's a list of people you're going to need: ## 1. Metallurgists To get pretty much anything done or built, you're going to need steel. Tooling steel for things that make things, stainless steel for industrial chemistry and the like. Right now, we're in the bronze age, so people from the more advanced localities (eg. Greek city states) know something about smelting and alloys; your guys will need to teach them to make steel. Fortunately, iron ore is abundant and coal is not too hard to come by either. Unfortunately, to get good steel you'll need to get picky about the ore and the additives you use. Bottom line, you'll quickly be able to produce *some* steel, and later you'll use that to make yourself the tools to make better steel, repeat ad nauseam. This iterative principle is something you'll be seeing a lot of. Using modern knowledge, we can get the development started and get it running pretty well, but the later steps will get progressively more difficult. Whether 50 years is enough time to get to 21st century levels is anyone's guess; I'd say that in this case, and probably most of the others, you can get to 19th/20th century levels before the process slows to a crawl. ## 2. Civil engineers This bunch you'll need to make useful things out of the steel you now have. Mostly tools, then fabrication machines, engines to drive the factories you'll need (powered first by water and wind, later by steam as you can machine pistons) and ultimately the tools to make our desired goodies. They will also be building things; as a side effect of this enterprise, you'll probably be building a transportation network, so there will be roads, ships and barges, wagons, and such. A logistics expert would help here, but you could also just brute-force this. When your builders aren't busy, you can have them build aqueducts and sewer systems. You'll probably end up building cities around your eventual factories and it would be a good idea to get them some basic sanitation; cholera epidemics can really set you back. These guys will also be of use when you're digging mines to get further raw materials, and on their downtime they can be designing the thousands of tiny conveniences that will make your life a little more bearable. The nice thing about civil engineering is that if you have underlings who can follow instructions, a single engineer can get a pretty big project done. After all, that's how it was up until the late 19th century, when we finally ran out of the big projects and more specialisation was required from that point on. ## 3. (Bio)chemists These you will *really* need to get anything done. Most material science is based on chemistry, so you'll want industrial chemists to design the processes that fabricate your silicon, fuels and whatnot. A petrochemist will be required and a geologists wouldn't go amiss for prospecting. Some of your chemists should also be pharmacists; an unmedicated black plague can really put a damper on things and you want to get your hands on - at least - some antibiotics and vaccinations soonest. Yes, penicillin is just bread mold, but it's pretty much impossible to tell *which* bread mold it is without testing (otherwise you could just as easily poison your patient) and you want to be able to produce it in quantity. Of course, most of this work will require stainless steel vats to produce anything usable in quantity, which is why I listed metallurgists and civil engineers first. Another important thing that you can get your chemists to do are artificial fertilizers. If you have some guano at hand, you can start from that, otherwise you'll need to first implement the [Haber-Bosch process](http://en.wikipedia.org/wiki/Haber_process). If you do this, however, you'll also have your first ingredient for high explosives, which will come in handy later. ## 4. Agriculture experts Now, farming does not directly contribute to your goal, but it is necessary to keep your working population well fed. Increasing yields by improving your crop breeds and judicious use of fertilizer and pesticides (as soon as you can get them) can make sure a famine will not wipe you out. Furthermore, before the Industrial revolution, a significant fraction of the population (80% probably isn't far off) *had* to work in agriculture just to support what population level there was; improving yields not only staves off famine, but frees up a significant workforce that you can employ elsewhere. ## 5. Electric engineers Eventually, you'll have to introduce electricity (if you really want to run those computers, that is). These people will be there to build some power plants for you, design and run the power grid a build engines (or, for instance, furnaces) that run on that sweet electricity you now have and can be used in your factories and elsewhere. Electric engineers can also help you with telecommunications, which can help increase your industrial output by improving coordination. Of course, for most electric machines, you're going to need at least some copper for conductors and rubber for isolation (this can be replaced by layered silk or in some cases resin, but you want rubber for best effect), which your metallurgists and chemists need to take care of first. With these, you should be able to churn out some late 19th century engines and appliances pretty quickly. ## 6. Computer engineers and mathematicians I am lumping these into a single category because there will be a lot of overlap in what they will be doing, at least initially. Counterintuitively, computer science is not all that dependent on computers (that is, electronic microcomputers that we know today). The same theory applies to [mechanical computers](http://en.wikipedia.org/wiki/Mechanical_computer), or even [human computers](http://en.wikipedia.org/wiki/Human_computer). Now, you won't be playing World of Warcraft on any of these just yet, but any ability to perform more complex calculations is going to help; many of the folks above are going to be relying on calculations of their own, and the more of those they can make more precisely, the tighter they can make their tolerances. This can in turn decrease costs and/or improve results of whatever it is they are doing. Keep in mind that at this point, you're not *just* without electronic computers - you don't have any calculators either, so any time you need to use the value of pi or e, or calculate a sine or a logarithm, you have to do it the old way, which is, consult a [table](http://en.wikipedia.org/wiki/Mathematical_table). Of course, the more precise you want the result to be, the thicker your tables get. It was not entirely unusual to have multiple volumes of just the logarithmic tables, the logarithm being quite important in the pre-calculator era. Aside from that, tables of random numbers might come in handy, and ideally you want to avoid producing all of these by hand, as this is fairly error-prone. This is in fact the problem the [Babbage engine](http://en.wikipedia.org/wiki/Difference_engine) was meant to solve, so you can build something like that in the meantime. Statistical analysis might also be useful in managing your new industrial empire, and computer science is also used to improve telecommunication by developing codes (to compress information or protect it from transmission errors) and ciphers (to keep prying eyes from reading it). As for computers themselves, you can start building some as soon as you have reasonably precise mechanics, and then transition perhaps to hydraulics, and finally electronics as you can manufacture them. ## What about the goals? Well, let's walk through them one by one. **Laptop computer** While I'm pretty confident you can have computers, even programmable ones, fairly early on, you are not getting a 2014 laptop within 50 years from scratch. It might be possible to design it, sure, but the big problem are going to be semiconductors and transistors, which require a lot of advanced manufacturing. Even once you have those, the speed of modern computers is achieved not so much by design (though that helps a lot), as it is by making the basic building blocks really teeny tiny - this shortens the so-called "critical paths" and lets you set a higher clock speed (if you just go ahead and set a higher clock speed anyway, you start getting errors, because all the circuits do not have enough time to appropriately change their state in response to the input). So I would say you should be able to get electric computers (picture ENIAC), and that those will help, but even with semiconductors, the best you'd get, by my most optimistic guess, is an 8086. The more advanced stuff would be on the way, but would require too many additional "iterations" to fit in your timeframe. Then again, browsing stackexchange probably isn't going to be a priority. **Kidney transplants** Any good surgeon with a couple of tools can perform a kidney transplant in field conditions (with some luck, the patient might even survive). To do this the proper way from scratch, you'll just need some sterile tools (preferably made from surgical steel) and a couple of chemicals (disinfectants for starters, and if I were to be the patient, I would hold out for anesthesia). The problem here is making it stick. Even if you find a "compatible" donor, the recipient will likely be on [immunosuppressants](http://en.wikipedia.org/wiki/Immunosuppressive_drug) for the rest of their life. Otherwise, their body will reject the kidney and they will die painfully. These are fairly advanced drugs, and I dare not hazard a guess on whether you can get them in 50 years, but perhaps you can get something more rudimentary that could also work. You might also luck out completely and have no symptoms of organ rejection; basically all the better drugs will get you is a higher success rate, so when exactly you can say you can perform a kidney transplant is rather nebulous. **DNA sequencing** This is probably contingent on having reasonably fast computers and other electronics to operate the mass spectrometer someone else mentioned. I'm leaning towards "no", because of the above answer on computers. **artificial satellites** As soon as you can make gunpowder (which can be fairly early on, depending mostly on whether you have sulphur available) you can start launching rockets. Build one that's big enough and you can try launching an artificial satellite. There are just two minor caveats: Initially, most of your launches will end in explosions. This will improve as you are able to make more consistent gunpowder, so you can build bigger rockets that maybe don't blow up more often than they do, and eventually you might get into space. Other solid fuels will gradually become available, but liquid-fuel rockets, which get the highest efficiencies, require cryogenics and (essentially) super high-speed plumbing, so you will only have those available fairly late. Solid rockets, however, are enough to get you into orbit (in fact, in the early 20th century, there was a pretty well thought out proposal to ride a solid-fuel rocket *to the Moon*), if you can get over the next obstacle: Guidance. By machining the rocket really carefully and balancing it and installing stabilizer wings just so, you might be able to get it to fly in a straight line. However, what you really need it to do to get into orbit is to perform a maneuver called the [gravity turn](http://en.wikipedia.org/wiki/Gravity_turn); basically, it needs to burn straight up for a while and then horizontally a lot longer, and you need to build it so that it knows when to do that, when to separate stages, and so forth. This requires a guidance system (staging might be accomplished with a series of fuses), which was a technology not perfected until about the sixties. This is, incidentally, the reason why V2 missed its target more often than not: their big issue was precisely the guidance system. These days, rockets process input from a plethora of sensors and calculate corrections on the fly. You might be able to get away with a clockwork mechanism that performs preprogrammed steering at preset intervals, but this sacrifices the ability to react to changes, meaning again, you will crash and burn quite a lot. But, develop a good closed-loop guidance system (and the sensors to go with it), or launch enough rockets with a simple one and you will eventually launch an artificial satellite. What good it will do without advanced electronics on board is another question entirely. **nuclear power plants** Getting a nuclear reaction running is fairly easy. All you need is a bit of fissionable material (say, some convenient oxide of U-235), some moderator (regular old graphite will do). Mix these up and make a big enough pile, and you have a chain reaction going. What, you want to control it? Oh well, that will require a more advanced setup. You need to encase the fuel in good inert rods, so you can better manipulate it (=metallurgy), do the same for the moderator and also throw in some regulator rods, if you're the safety-minded type, attach all of these to a mechanism that lets you manipulate the rods and you have a reactor. To make it into a power-plant, you put the entire setup into a boiler and use the generated steam to drive a turbine. Connoisseurs will note that I just described the broad strokes of the Chernobyl setup, but once you get the knack of building these high-pressure vessels, you can go straight to the safer pressurized water reactors. The above glosses over the important point that fissionable material is *really fricking hard to isolate*. You might be able to mine some uranium in Bohemia and chemically purify it from the ore, but separating the isotopes is usually done in huge centrifuges with really precise control, which likely require electricity and probably also electronics. Once you can build a turbine and a generator, you can start using coal or water power from electricity, which solves the bootstrap problem, but that just lets you start on the path towards nuclear power. Furthermore lot of a nuclear power plant is the various control electronics, which might be more complicated to develop than the nuclear fuel itself; but you can ultimately make do without them, if you relax your safety requirements enough. Still, seeing as you will not be needing so much power to warrant working through all these issues, you will probably look for electricity elsewhere So there you have it! As a final note, there is also a bunch of other technologies that pretty much anyone from the modern times can "invent" if they are so inclined, and another thing to keep in mind is that you will probably end up with a very different overall setup than what we have today. Still, it is good fun exploring these scenarios. [Answer] Even having thousands of experts with college-level education would not be enough - because **their knowledge is related to current supply chains where you can order special material and tools.** All that would be missing, so most of the knowledge many of them have would be **completely useless and not applicable**. Instead of aiming for 21st century technology, better aim for level about start of industrial revolution at some 1800. It would take few years to develop manufacturing base to start industrial revolution, using just primitive hand-crafted iron tools - and your people need to eat right now. So your first goal would be to produce something quickly usable, easy to manufacture from low-technology materials available, to pay your upkeep - **gun powder**. It would be smart to align yourself with protection of some local warlord - but it can be also risky if you bet on wrong side, which will lose war even with help of your advanced technology (like Archimedes in Syracuse). Don't underestimate huge numbers of fighters with less advanced weapons (like British underestimated Zulu warriors). One simple weapon to deal with such danger would be nuclear weapon - easy to manufacture with right knowledge. Another goal to attempt would be to take over some island with good resources for industrial revolution, like British Islands, if you can. It will take decades to build technology up to 1900. And you would have better luck to **recruit not only average college educated persons, but current skilled craftsmen, and people who re-enact medieval technologies.** There would be huge amount of building and improvising needed, developing one technology to bootstrap next. Likely your first generation will die out before reaching level of 1900, so big part of your task would be to preserve their knowledge and educate new generation. From about 1900 you would not have any advances in knowing future, because you will need to develop technologies to be able to get to new level. [Answer] This is the kind of question take leads us to a romantic burgeoise dream. It would allow us to recreate history without the inconveniences of ignorance. Its a kind of revisited Noah, but with modern technology. But, as most conjectures of such kind, normal answers are biased with ideology and a shallow understanding of our world and history. Human history is not the history of ideas, at least not of ideas not rooted in reality. Human history is an history of accumulation and work. Work accumulated as goods allows us to have new ideas of how to change our world. And then those ideas get applied in our work to change reality even more (creating better and new goods). So, what happens with a group of enlightened individuals decide to come back in time to recreate history ? You get a floor plan of how to recreate society, but you still have to deal with all problems related to the accumulation of work (as goods) and the need for all sorts of specialists. Our modern society is rooted into a miriad of professions and specialities that makes the hope of recreating it in a short span of time a dream, not a true possibility. Take a transistor as example. To make one transistor you need refined silicon. To have refined silicon you need a refinery etc. All those tools are made out of work from someone. And this work usually needs tools that are the result of the work done by someone else. Even if some current tools can make it simpler to build some items, those tools, somewhere in history, where the result of tools that are not used currently anymore... So, you have work, from thousands of generations accumulated as goods (capital goods being a prime example because they are tools). You might say that current modernity is the result of a short time span relatively to our total time in our world. But you might them forget about the time it too for our species to reach the population levels needed to start a industrial revolution. If you have only five persons left, you need to divide the tasks between five people, like, farming, hunting, etc. You need to set priorities. And quickly you would realize that you cannot create modern tools and farm/hunt at the same time with only five people. Theres something called surplus work. A single person can hunt enough for himself and generate some surplus. Another person can farm and generate some surplus. Both persons can exchange the result of their work, so that both have meat and wheat (for example). With three persons someone can work as hut builder/repairer. And so on. So, even knowing the technology involved, living in a real world and recreating current technology levels, you need a pyramid of workers where each level produces basic goods needed for higher levels. And this means you need a population big enough to sustain the development of modern goods. [Answer] Everyone has some fancyful unrealistic dreams, one of mine is to travel back in time and do something like that. Not because I really want to do that, but it's a nice "what would be when"-idea for me. So I often think about that. I will not go to deep into technical detail. You just cant build thinks that you do not know much about or you have no access to their resources. Additional, it's depending on the time you 'land' in. I will go over these points and write about general topics. The "Group" factor is another thing I do not write about, due this, clearly gives you better knowledge, survival and laborforce, but beside that, this will not change anything. What mostly comes to my mind are these ideas: You will not be able to build up the whole technological evolution in your livespan on your own. You will hardly be able to build a modern computer, so how should you build a sattelite? **Convince the people** This means you need help, the more the better. Depending on the peoples believes you will seen as some kind of evil (inquisition), god (you set fire bevore early human know how to do that, or whatever. If you can convince them thatn you are a timetraveler there might be a better chance that they believe the strange things you are talking about. To prove your knowledge about powerfull stuff you could build a steammachine (very easy but powerfull). **Get help** If you gained their trust, you must teach them. Teaching others to help you is the essential key just because construction is hard labor and you need any help you can get. Help them helping you! At any time in history, people have been busy maintaining ther subsistence. If you build a letterpress, the savants have less affort on that topic and are able to help you. Building some simple ploughing-machines gives the peasants a big advantage and thus you'll get a massive laborforce. **You need military advantage** Assumed the people trust you, they're just one party in the world. They have enemies or tradingpartners. Some of them will notice the improvements of your party and may be harmed by that. This means your improvements will raise enemies, thus you must arm your people in a defensive way so no one can kill them with ease. But be carefull! If you give them to much advantage, they might think that they do not need you anymore or they start conquering other lands. Last point can be an improvment of your situation due this can bring you more laborforce but also this will lead to big harm in the world. If you want that, okay but consider the consequences. **Do not underestimate politic** So at that point people trust you, you might think. But no! There are always people frightened by change. Depending on their political force, they might speed you down or, even worse, prevent your work or kill you. You should use your technical advantage to improve your personal security. This is the most essential point! Your live is in danger all the time! [Answer] Each of those items you listed requires certain people with expertise in different fields. Here's who you'd need for each one: * **Laptop:** Give me (a relative layman) an electrician, a couple programmers, a computer chip expert, a draftsman and two or three skilled metalworkers/glassblowers and I can most likely churn out the first laptop in - say - three years. Minimum. With all of us working round-the-clock hours, without sleep, leisure time, etc. And assuming that we have all the raw materials delivered to us whenever we need them, and all the tools we need. I need the metalworkers/glassblowers to take some raw materials and turn them into something useful. I may only be given a block of copper; I need to turn that into a lot of wiring. The metalworkers/glassblowers also need to be able to make glass and other things used to build the laptop. The computer chip expert would need to figure out some way of creating chips. Silicon is all very well and good, but current methods of making chips rely on UV light. Figuring out how to get *that* will take him/her a while. The draftsman will be needed to plan things out. You can't just shove some chips together, place them in a box and expect something special to happen. The electrician will be there for the wiring - and finding a source of electricity - and the programmers will be there to build software from the ground up. They'll be running on java to create Java. Are there any people that can do the tasks of and two people doing different jobs? I doubt it. * **Kidney transplants:** One surgeon, two nurses, a patient and donor (well, duh), five or so auxiliary staff, an electrical engineer or two and a lot of luck could get you this one. Oh, plus roughly 1,000 lab rats. Estimate: 6 months. We need to figure out how to do this. Chances are, the doctor won't be able to perfectly perform a transplant without all the modern tech we have today, so s/he will have to practice using more primitive instruments. That's where the rats come in. The nurses will be there to do more research but primarily to help during the operation. The auxiliary guys will be doing the R & D leading up to all this, and preparing for any accidents. The engineers will work on creating the surgical tools necessary. This perhaps has a lot of redundancy, but when someone's life is on the line, you want redundancy. Redundant redundancy, actually. * **DNA sequencing:** Everyone from the first two groups. Estimate: 18 months DNA sequencing, to the best of my knowledge, is pretty hard. You need to extract the DNA, then analyze it (preferably with an advanced computer) and then record and interpret the data. Joe Schmo isn't going to be able to do this alone. The surgeon will be needed to extract the DNA. Well, sort of. People (and animals) leave bits of DNA almost everywhere, but it takes a delicate hand (hence the surgeon) to isolate it. The nurses and others have a background in medicine, which would seem to indicate a knowledge of biology. Obviously, they know what DNA is, but they might not know about DNA sequencing. Give them a few years and they'll perfect the extraction and isolation. You need everyone from groups number one to build the instruments to analyze the stuff. DNA sequencing isn't just recording some data; it's about measuring the data and interpreting it. For that, you'll need various scientific instruments and a couple computers. The auxiliary guys might be able to cobble together to medical tools needed. * **Artificial satellites:** Everyone from group one, plus a dozen or so aerospace engineers and a smattering of physicists, the same amount of chemists and chemical engineers, and a dozen or so folks knowledgeable about computers (besides the guys from group one). Estimate: 5 years. Minimum. The physicists and aerospace engineers will do the calculations and experimenting to see if a rocket can be built, and how to build it. The chemists will work on fuels, which are even more important. Group one will work on computers, communication systems and assorted electronics (give me more electricians and electrical engineers!), as will the computer guys. The five years is actually an optimistic estimate. Think of how long it took humans - countries in their prime, funneling loads of money into projects - to get something into a sub-orbital trajectory. Here, you have less than 50 people. So you'll need a lot of trial and error. Perhaps ten years would be a better guess. I'd say that you won't make any rockets in the first two; for the next three years, you might get one every six months. After that, I can see production rate doubling as tests get better. * **Nuclear power plants:** This will take the most people. Everyone from group one plus 50 physicists, 20 electrical engineers, 50 mechanical and civil engineers, 150 auxiliary staff, and 100 technicians. Minimum. Estimate: 15 years. Again, nuclear fission was the result of expensive projects and lots of money and resources. You need to build sophisticated equipment just to interact with matter on the atomic scale, let alone manipulate it. The physicists and some technicians will be hard at work for this. I'd give it seven years, starting from scratch. Then the mechanical and civil engineers have to plan the plant out, as do the electricians. It needs to be built (with that unlimited labor force) and wired - hence the electricians. You want computers running systems in case of emergencies, and you need skilled technicians as well. 15 years is in part because people will be so nervous about doing something that is perceived as inherently unsafe. They (and you) will want to be careful. [Answer] I don’t think it can be done in such short period of time if group is even close to being modest size (round 100 experts).It is not just a question of tehnology.Simply it takes some time for people mind frame to adjust to radical changes and to even roughly understand how something work, not to be afraid of it etc. Technology in past had it leaps, but between there were long periods of time during which knowledge accumulated preparing the next leap. Furthermore those labors must be learned how to use modern materials no matter how simple they really are. For example think how could you build hospital in which transplantation can be performed? First you need engineer (design and contractor), but let’s assume that those are „visitors“. Then you need machines and operator of those machines. That leads us further: you need factory for those machines. After that you need concrete, meaning cement. Then you need to produce bricks. Just imagine how much time it would take to learn cave man to build with bricks, to prepare plaster. Story goes on and on. And let me remind you: you are JUST building a hospital! It is empty; no instruments, no nothing; just a shell.TO give a short answer it cannot be done because, like I said between those big leaps in past are numerous tiny steps. [Answer] I think it is not possible to fully recreate modern technology in a way that you probably expect. You also need to make all people smarter, educate them. The problem is not only technology, but also moral and social environment, which creates the main ground for developing science. You must persuade people, that slavery is bad, sacrificing humans is bad, raping is bad, killing each other for stupid reasons (stealing, swearing, homosexuality) is bad ... and that is very hard. [Answer] I think that no matter how many of the best people you can find on modern Earth, and sent them back 2500 years with no modern equipment or infrastructure, that they have no hope at all of recreating 21st Century technology within 50 years. Even if you just wanted them to record everything they knew, good luck even having the safety and survival skills, and having time to even find materials to write information down. Have fun with the language barrier with the locals. Have fun with them not treating you as foreign invaders or slaves. Even if your people had no political or resource problems or environmental/situational problems, and they were all single-mindedly obsessed with helping you with your goal of recreating technology, and were brilliantly organized, didn't have to worry about disease, and were given infinite translators and slave labor... the materials available circa 500 B.C. are woefully inadequate to get very far. Cutting edge is iron, copper, bronze, papyrus to write on. Hand-waving all the situational problems, I'd say you might get up to about the 15th to 18th Century in 50 years. [Answer] Not going to answer this in any long fashion, but wanted to point out a couple of consistent flaws in the top rated answers # Language barrier Not much of an issue, I mean, it will indeed take off a year from the 50 years, but that same year will be spend setting up a basic group structure either way. # Jumping ahead Obvious, like the other answers state, jumping ahead in one big jump from 1500 years ago in one jump to modern technology isn't possible. Racing along at a crazy speed however is quite reasonably possible. This does mean you would simply jump from one scientific hurdle in the past to the next one. Of course this would require the enslavement of the locals in some way and setting up some kind of international trade system, however if you're able to build a plane like construction... getting people to worship you should be quite doable (just don't run afoul of an actual God :P , plus people in your group might disagree with this, so you would have to lock up a big portion of your group as well (still seems the best plan if your goal is just to quickly make as much technology work as possible)). # Group that will get furthest Beyond the standard experts in various fields it would be extremely important to throw in a lot of people who are experts in the history of sciences and add to that a couple of re-enacters from various time periods (e.g. a couple of individuals that re-enact renaissance times, a couple from the middle ages, a couple from roman times). These last people not only will be able to communicate a lot of the cultural norms, but more importantly will have an extremely good idea how the technology for their period was made and how it worked. # Conclusion Either way, I agree 50 years will likely not be enough. However such a colony should be able to get to around 1800 within 50 years, to 1950 within another 50 years and maybe to 2050 within another 100 years (the last being mostly dependent on how much people they can enslave and how geographically reaching their influence is). [Answer] One thing all of the answers seems to be missing is communication between the team and for that you need 1. A skilled technical **writer**. 2. A skilled **architect**. Their primary job will be to communicate highly complex technical ideas in a simple fashion. P.S. They don't need paper, they can use **a stick and the ground**. [Answer] I think the other answers have given good reasons why achieving modern technology in 50 years is not feasible. I'd like to look at this from a different angle. This transplant of a group of modern people into the past is very unlikely to end peacefully. There is not a good historical track record for interactions between societies with different levels of technology. Even if the modern people wanted to be peaceful, it is incredibly unlikely they'd be able to convince the local ruler to run the country their way. Also, freedom of religion by-and-large didn't exist. From the perspective of the natives we have the sudden appearance of a group of giants (proper nutrition during childhood makes a huge difference) that are clearly foreign and have magic (technology). Being labelled as heathens would be an improvement, these people are probably going to be known as hell-spawn. With that in mind, I think instead of college grads / scientists, a specially trained armed force should be sent back. This is going to end up looking like an invasion, so we might as well prepare for it properly. A good baseline for training would be a variation of <https://en.wikipedia.org/wiki/Genoese_crossbowmen>. Crossbows could be developed from scratch much more quickly than firearms. This force should also be trained in medieval siege warfare. I'd recommend launching this invasion in England. Once the island is pacified, improved naval technology should be able to keep the force relatively safe. Aside from troops, the force should contain a large number of teachers (child-hood, adult re-education, and language instructors). It will likely take multiple generations to reach modern technology, so knowledge transfer is extremely important. For the initial advancements, we should focus on things that will keep us safe (military/navy) followed by things that will keep us healthy (sanitation/health care/sewers/nutrition). This combination will trigger a population boom into a super-charged renaissance. ]

[Question] [ Last week, a young woman came by my physics lab. She demonstrated the telekinetic ability to rotate things from a distance. We did some quick tests, but we couldn't find any previously known phenomena which could explain this. Now, she had to run off to do some sort of superheroics, but she promised to return for more research. I'm not looking for you to provide an explanation for me (I do have to find something to publish, after all), but I'd like to know how I could use her power to discover new physics. Of course, there are some constraints. She seems resistant to being dissected (even for science), and she strongly dislikes needles and other medical equipment. Using her power does take energy, and it's not terribly strong. We have plenty of lab space, but grants are hard to come by, so we can't get too much expensive equipment. What experiments could I perform with her that would be most useful for developing new physics? I'm looking for the most direct route from "person with (these) superpowers" to "revision of the current model of the universe". Edit: To narrow the scope a bit, here are the results from some of the tests that have already been suggested: * While it's possible to use her to study other things, I have an unexplained phenomenon literally asking me to study it, so I'd prefer to study the physics of her powers. * She has difficulty moving sufficiently small things ("Have you ever tried grabbing an atom?"). * She can spin things behind glass with minimal difficulty. * She can rotate things from where she can see them to where she can't, and so long as she doesn't "let go," she can rotate them back. However, she hasn't been able to turn things she can't see to begin with. * She can rotate two or three things at once with difficulty, but she can't focus on more than that. If she loses focus on anything, it just stops spinning. * Her power decreases with distance, but not as fast as the inverse-square. * We can't measure when she starts using her power precisely enough to check for a speed of light lag. * She does have to rotate herself (at least her hands) a bit to get an object to start turning or to change its speed, but once it's going, it only requires focus. * She can rotate non-rigid objects and parts of objects. * She cannot turn herself. * There's no noticeable effect from applying electric or magnetic fields. [Answer] **Test her limits.** 1. Can she move more than one thing at once? If so, how many? 2. How large of a thing can she move, both by weight and by volume? 3. Is there a minimum size an object has to be, or could she move individual atoms if she wanted to. 4. How fast can she make an object move? 5. Are there any range limits on her telekinesis? 6. Can she move an object she cannot see? A coin in a box right in front of her? A coin on the other side of the planet? What if she has a line-of-sight to the object but the room is too dark? What if she has a view of the object via webcam, but not in person? What if she can only see the object's reflection in a mirror? 7. If no to the previous test, are any materials transparent to her telekinesis or are all opaque? 8. Can she move a subset of a collection of objects? Like some of the water in a pool, or some of the sand in a pile of sand? 9. Can she directly control how hot or cold an object is by controlling how quickly its constituent atoms vibrate? 10. Can she use it on herself? **Test if she violates any known laws of physics.** 1. Does she violate Newton's Laws of Motion? If she picks an object up with her telekinesis, does she get pushed down? 2. Does she violate the laws of thermodynamics? Does it cost her less energy to lift an object than it gains in potential energy? What about when moving a conductor through a magnetic field? 3. Does she violate the laws of general relativity? By this I mean could her telekinesis be used to send information faster than the speed of light? Does it take time for the telekinesis to happen if the object being moved is some distance away, or does the object move instantly? 4. Does she violate the Heisenberg Uncertainty Principle? Can she place an object more precisely than the HUP would normally allow? **Test her biology.** 1. Do an fMRI on her while she uses telekinesis; see which areas of her brain light up while she does it. 2. Get a DNA sample and see if there are any previously unknown genes in her genome. 3. See how many calories she burns while using telekinesis. This is different than in the thermodynamics test, it tells you how efficiently she can transfer energy from herself to an object. 4. Are her abilities affected by mind-altering substances? 5. Can she use telekinesis while asleep? If she sleepwalks, could she sleep-telekinesis? 6. Are her abilities affected by sleep deprivation? Last, I would have her try to teach someone else how to do it. Maybe it's not unique to her? [Answer] 1. Try to determine how her power changes over distance. Does she have a maximum amount of weight she can move? Does this change with distance? Is the effect immediate or it propagates at the speed of light? 2. Try to determine if the medium between her and the object influences the power. 3. Try to determine if the object has to be in her line of sight. 4. Try to determine if electromagnetic fields influence her ability. 5. Try to determine the size range of the object she can move (can you use her to move nuclei to relativistic speeds? You know, cyclotrons are expensive...) 6. Try to determine how her metabolic/mental conditions influence her ability. [Answer] Exploration of the physical universe begins at it's boundaries. Long ago, we learned about fire, initially by discovering which objects burned and which ones didn't. Later we arranged the tested objects by how well they burned and thus determined what properties of each object was influential in its' combustibility. You will want to find some boundaries to your super heroine's telekinesis. Can she move objects viewed through clear glass. If so, what if the glass is only translucent? What if it is opaque? What if it is made of lead? Continue to place boundaries between her mind and the object to be moved until you find someway to limit her power. Then, from the properties of those limiting barriers, you may be able to ferret out some previously unknown scientific premises. [Answer] I would add to the other great ideas: Attempt to trick, or deceive her power: * Apply variable resistance to the rotation and see what, if any, physiological response she has upon the application of resistance. * Lie about the nature of the object she is rotating and see if this affects her ability to rotate it. * Describe the location of an object to rotate but only allow her to see it through a video feed. Can she rotate it? What if the video feed is not actually of the object in the described location? * How does her power work on non-rigid objects? Can she rotate a string at a given point? * Can she rotate objects while she is being rotated? Can she rotate individual objects which is revolving around another object? * Try to break her focus while she is rotating in different ways? Will a sudden surprise or shock cause it to rotate faster or behave erratically, or does the force simply stop? * Can she fly by rotating air around her? Swim by rotating water? If not what devices could you create for her to utilize? Rotor blades to fly, etc. Could she capture villains simply by rotating their clothes around them? Or just throwing a rope at them and rotating it to ensnare them? [Answer] As I understood the question, you are **not** interested in scientific research on her superpower per se, but want to use it as a tool to discover new laws of physics or falsify current theories or such like, i.e. your results should be independent of her, she is just a convenient tool to get at them. For this, you would look at things that we are currently trying to accomplish and results are not yet perfect. Can she accelerate very small things to considerable fractions of the speed of light? You say her power is not very strong, but what if you apply it to tiny things? That would allow you to do particle physics without the billion dollar accelerators. You might want to get some protective chambers around the experiment area, though. Can she control plasma? If so, can you use her as a temporary containment field for a fusion experiment? We're currently doing not so well in that area, despite the task to be done ("keep the plasma in this area") being reasonably simple. Then, of course, there are all kinds of experiments where being able to manipulate something without being exposed to it would be really, really useful. Think radioactive, toxic or both. You could discover new uses for Plutonium that we're not aware of because nobody wants to deal with the stuff. There are other substances from hell. [Answer] **MATH MATH MATH** Everything is about math. What you need is to find mathematical equations that describe her powers. Then you use those equations and compare them to what we have right now. Do they match to any theoretical work? It is very likely that her powers match up to something in theoretical physics. Something predicted but never observed. From there you may quickly be able to flesh out missing parts of physics and update our theories. To go more into the math topics. As far as we understand we can describe reality with math. This means that if we come up with a mathematical model for something it may exist in our universe or it may not. We could have math describing other possible universes. But **nothing** can happen that can't be described by math. So what theoretical physics does it they make up possible universes. Then the practical physicists do experiments to try to figure out which one of those universes is the one we live in. This is the hard part as it takes incredible amounts of energy to do these experiments, thus the LHC. There superhero experiments should quickly let us discard some models and support others, letting us make amazing breakthroughs. **So what I am really trying to say is that if her powers can be described by math, someone in theoretical physics probably already did it. They will be happy to know they is right.** If on the other hand her powers can't be described by math, then they would truly be magic. In that case we can probably just throw all our science books out. [Answer] That she can't rotate herself is puzzling. Where does the angular momentum come from. When she loses focus it stops? E.g. it didn't have any angular momentum? This implies that it was never moving but was teleported to a new location rotated from the previous one. Is it easier to do two objects if they are rotated in opposite directions? Does the mass of the object affect the speed of it's rotation? Can she still not rotate herself if she is in a chair hung from a fine wire so that it takes very little energy to rotate? Can she rotate things she sees in a mirror? Can she rotate herself if she she sees herself in a mirror. Repeat last two, but substitute video camera for mirror. Does the effect go down with the real distance or the perceived distance. ]

[Question] [ Trying to create horns which are both ornamental and defensive, I've read somewhere that beards evolved in humans because we punch each other so much that even just a minuscule amount of hair cushion can make the difference between you dying with a broken jaw or surviving with a few broken teeth but no internal bleeding. With these in mind, one would think that human males are min-maxed for violence. I'm trying to push the meta even further beyond, by giving people horns; each horn is pointy, and these pointy horns also have sharp and pointy protuberances. In real life if you punch someone barehanded and hit their chin, unless you are considerably heavier than your opponent, you are more likely to crush your own fingers and break them against the sharp jawline of your adversary. Or at least it happens more often when both the victim and the aggressor weigh the same: that's kind of the point of why boxers use gloves. Following this logic, the jaw horns follow the jawline and then bend down both to expose the pointy protuberances forward and to cover part of the neck. The top horns exist to block attacks from predators. Historically predators used to pounce on people from behind and bite them in the top of the head. The prototype also shows some smaller barbs on the neck, which I will remove and place with a 2D textured version but the concept still remains. I want the horns to be made of either dentine or iron-enriched bone, like the teeth of beavers or scaly foot gastropods. As of now, there are 8 big horns; can it get up to 16 before it becomes unliveable? What am I trying to achieve? Basically these situations: * You hit this person with a sword in the head; your sword gets stuck between the horns and then she proceeds to beat you with your own weapon. * You punch her face; your fist bleeds and breaks. * You kick her face; you don't walk any more. * You watched too much Twilight and want to bite her neck; her neck bites back. [](https://i.stack.imgur.com/iZYmJ.jpg) Also, the rest of the body will be covered in external bony round/flat plates, of the same materials as the horns; it will cover mostly the thighs, back, belly, shins, forearms and chest [Answer] ## You have the wrong horns for your stated goal of defense. Long pointed horns a bad for defense, and even worse on the head of a biped. There is a reason humans only ever put horns on ceremonial helmets, they make the head more vulnerable to blows. The horns you have would make weapon attacks against the head MORE likely to injure the head and neck. They provide leverage to the blows and make them more likely to hit the head; there is little chance of getting your weapon caught. Worse, your horns are attached to the weakest part of the skull, so simply cracking the skull wide open is very likely, making them more vulnerable, not less. The lower horns are just as bad - they are attached to the zygomatic arch (literally can't be attached to anything else in that area) which is fairly weak, so a blow will simply rip them off the head along with bone and jaw muscle. This is doubly dangerous as it will prevent them from being able to chew properly. Even worse, the horns would provide leverage to grab the head, which is a huge liability to a creature with hands - why punch someone when I can just grab their horns and wrench them sideways, twisting the whole head and neck. Some minor cuts on the hand are nothing if I can literally snap their neck or even just knock them off their feet. The last thing you want on an upright biped with a thin neck is easy-to-grab leverage on the head. The small horns on the neck are fine and may help with defense; something like that has evolved more than once even in mammals. Small widely spaced scales are the best you can get in order to keep neck flexibility. But if your goal is to protect the head, you want broad flat horns - like those of a musk-ox or mouflon. Or you can have lots of tiny interlocking spikes, similar to those of a horny toad. Either would make grabbing or biting the head difficult, and provide a helmet-like extra layer of protection. The YouTube *Unnatural History Channel* created a great video about how horns function, titled [Spec evo short : the practical uses of horns and antlers](https://www.youtube.com/watch?v=QnwtP3Mjp3k). According to their terminology, you seem to have put jousting horns on something that can't use them, so they can only be pure ornamentation. **So which is more important to you? If you want the shape, they are pure ornamentation and a huge disadvantage in a fight. If you want the function, you need a drastically different shape and layout.** Also just FYI small horn covered bones covering the body are called either scutes or scales, depending on which layer of the skin they originate from. Horn, scales, and even hair and feathers are all made of the exact same material, Keratin. [Answer] You can cover the whole body with sharp, pointy horns if you want... but before you do that, you may need to justify yourself. How did these horns get there? Did they evolve? If they evolved, what evolutionary pressures led to their evolution? Did the ancestor species have horns that could have evolved into these horns? Maybe they were bioengineered... However, you need to consider the cost. Babies can't be born with horns, otherwise they and their mothers will die in childbirth, so they have to grow later. Growing horns has a cost, the most basic cost being a higher protein intake required to feed the growth of the horns. However, that's not the only cost. Humans engage in body contact a lot for social bonding, and lots of horns are going to make a person literally too prickly to hug or kiss... so you're going to have to change fundamental social bonding rituals. Also, if these horns evolved, the environment would have to be so hostile that any negative pressures from looking different and feeling prickly to the individuals' mates would be outweighed by the increased survivability of the individuals. Then, don't forget that evolution is *slow*. It might take millions of years for horns such as these to evolve... has there been time? Are these 'horny hominids' even human any more, and would they need to be? It's far more likely that, given that no hominids, apes or primates have horns, some *other* mechanism of defence or avoidance of injury might evolve than horns. This puts the question of horned hominids into the realm of traits that have appeared as the result of bioengineering or magic. If that's the case, then the limits of how many horns the hominid can bear comes down to practicalities of their protein intake and how social bonding rituals have been modified to allow for this spiky defence. Your horned humans *may* be *genetically* human, but with all those horns and armour, they're going to become a separate species pretty quickly, since regular humans and these people are going to see the others as being pretty different and unapproachable. Then don't forget that all this horn has weight. Your horned hominids are going to need either more muscle to carry it all, or they are going to need lower muscle-joint lever ratios to allow them to be stronger for a given mass of muscle... which will make them slower. Either way, it's a trade-off... more muscle, needing a higher protein and energy intake... or slower than normal humans, or something in between. You don't get something for nothing. Further, humans have evolved to have the best cooling system and greatest physical endurance of all terrestrial animals, due to their ability to sweat in order to lose body heat. However, covering the body with horn and adding all that mass would reduce the cooling capacity and increase the body mass, thus reducing endurance. Horned hominids would *not* be as good at persistence hunting as humans. Horns are sexual signals for many species, and are in effect saying to potential mates, 'Look at me, I can afford to carry these huge, otherwise useless things around and still be healthy, so I must be good breeding material!' As a rule of thumb, any time a biologist sees a huge, expensive, flamboyant and otherwise useless structure on an animal, sexual selection is probably involved. **TL;DR** So, how horny can humans become? As horny as they can be before less horny humans aren't horny for them any more... at which point, the horny hominids aren't human any more. [Answer] ## Anything more than a handful is too much. Humans have something no horned animal has: prehensile hands. Any horns large enough to be grabbed will be a massive disadvantage in a fight, giving the opponent an easy way to grab and control the head, and thus the whole body. It's doubtful any horns small enough not to produce this problem would be much use, but they could evolve as sexual markers. [Answer] # The dangers and advantages of exoskeletons There is something important you've glossed over at the start. You've mentioned that a beard cushions the blow. A horn will be more Newtons cradle. Those balls on wires that show how a force is moved through other balls to the outer ones. It shows why a hard surface in itself is not necessarily a good protection, as any force can as easily be passed through. Check out wounds of people shot while having a bullet proof vest. It's not pretty, despite them being alive. A fist against a horn will definitely dissuade pummelling your opponent, so it will be better in the long run. But a single strike against the neck will be better bearded than horned for the receiver. That being said, that is only when all else is equal. Evolution will likely step into cushion the blow. It is advantageous to catch a blow with a larger surface area as well as over distance. That means you can have the horn move to force of the blow to skin beneath it, which has evolved a clever layer to cushion blows. A larger surface area thanks to the horn means it can be a thinner layer, giving the explanation why it's better than just having such layer on top. The horn is also better suited against sharp things, which might be more important in a world where sharp horn edges can frequently come close. Unfortunately horns provide one really bad property. Weight. They can make people top heavy, requiring much more muscles to stay upright. With a thicker neck it can also make it more difficult to turn a head. Having horns is a costly business in not just growing, but even without it growing after maturity it has a large cost on the body and movement as well. Finally there's the plates on the rest of the body. These have the same problems as the horns with transferring energy and being heavy. Humans only have an 'exoskeleton' around the brain and a layer to cushion blows. This is because at a certain size, an exoskeleton for the rest of the body is simply too heavy. Your proposition of plates is even worse. Not only does it transfer the energy and is heavy, but it's also not used as an exoskeleton. So now you have in essence two skeletons to maintain, of which the outer one would be too heavy even without the inner skeleton. That being said, I would always choose story over reality. For a good story people will ignore or not think about such trifling things. [Answer] I'd be interested to see the evidence that a beard provides any significant cushioning to being punched in the face. A beard would have to be VERY thick for this to work. I find the theory that a beard helps keep your face warm in cold weather much more plausible. On the other hand I don't notice feeling any colder when I go outside in winter since I shaved off my beard. I always found that the main advantage of a beard was that it helped to hide my face so women didn't notice how unattractive I am. :-) That said ... As others have noted, a long horn can be a disadvantage in combat: an opponent can grab it and use it to control your head (or whatever part of the body). If you had a hundred horns all over your body, these would likely get in the way of performing routine tasks. Likewise large horns could be heavy and weigh you down. There's probably a reason why no real animal has a hundred horns. Yes, a horn could get in the way of some other creature trying to attack you. But a better defense would probably be a thick skull. Which in fact people already have. One could always say it would be better if it was thicker still, but then again you have trade offs. At some point it becomes so heavy that it takes a lot of muscles just to move your head. It suddenly occurs to me that when people make defensive armor, they do NOT put horns on it. (Viking helmets with horns were a product of fiction, a Wagner opera, and were never used in real life.) If horns were a good defense, surely armor with horns would have proven effective and become popular. ]

[Question] [ From an answer to a previous question of mine: > > A planet spinning fast enough to allow geostationary orbit near the surface would result in odd side effects. Any object at rest on the equator would be moving at speed near to orbital speed. It would have weight but much less than similar objects at the poles. A planet that formed spinning that fast would be flattened, with the equator at higher altitude. A planet spun up to that speed after solidifying as a sphere would result in any object just North or South of the equator experiencing a force towards the equator, resulting in a drift of loose rocks towards the equator. If the height of geostationary orbit was only just above the ground level, this could result in rocks finding their way into orbit simply by drifting towards the equator and then piling up. > <https://worldbuilding.stackexchange.com/a/303/90> by *@githubphagocyte* > > > 1. How would such a planet look like, geography and climate wise? 2. Could earth-like biology evolve in such an intense context? 3. Would this planet be short lived? (Maybe so much so that actual evolution doesn't have time to take place...) [Answer] I'm taking "near ground" as meaning "the height over ground is negligible compared to the radius of the planet". That is, we can as good approximation we can assume that the radius of the geostationary orbit is the same as the radius of the equator. # tl;dr Such a planet would likely be a dead, airless rock, but with interesting physical effects. Nice to put a space station on, but not developing life on its own. # Needed rotational speed Let's first look at a perfectly spherical planet (ignoring for the moment that a planet under those extreme conditions won't be perfectly spherical). The relevant quantities for such a planet are its mass $M$, its radius $R$ and its angular velocity (rotational speed) $\omega$. We also assume the geostationary orbit at height $h\ll R$ above the equator (note that on earth, that condition would still be fulfilled at the top of Mount Everest, so it is not too limiting). The condition of a circular orbit (which the geostationary orbit is) is that the centripetal acceleration equals the gravitational acceleration. The centripetal force is given by > > $$a = \omega^2 (R+h)$$ > > > and the gravitational acceleration is > > $$g = \frac{G M}{(R+h)^2}$$ > > > where $G = 6.7\cdot 10^{-11}\,\rm m^3\, kg^{-1}\, s^{-2}$ is the [gravitational constant](https://en.wikipedia.org/wiki/Gravitational_constant). So the planet would have to spin at the angular velocity of > > $$\omega = \sqrt{\frac{G M}{(R+h)^3}} \approx \sqrt{\frac{GM}{R^3}} \left(1 - \frac{3}{2} \frac{h}{R}\right)$$ > > > To see what this means, let's insert a few numbers. First, let's assume we've got a planet of [earth mass](https://en.wikipedia.org/wiki/Earth_mass), about $6.0\cdot 10^{24}\,\rm kg$ ($GM = 4.0\cdot 10^{14}\,\rm m^3/s^2$), and [earth radius](https://en.wikipedia.org/wiki/Earth_radius), about $6.4\cdot 10^6\,\rm m$. Then we have > > $$\omega = 1.2\cdot 10^{-3}\,\rm s^{-1},$$ > > > that is, you'd have one full rotation every 1.4 hours. Note that I neglected the height of the orbit here, since it would end up in the rounding error anyway. Actually that's a lot less than I would have expected (but thinking again, the actual geostationary orbit's radius is just about 7 times the earth radius, so it should not have been *that* surprising). Interestingly, if you look at the formula for omega, you see that the relevant quantity is the density of the planet. So we if we give the density of a planet as multiple of the earth density, omega scales with the square root of that number. So a planet of four times the earth's density would have twice the angular velocity, and thus have one rotation about every 42 minutes. On the other hand, a planet with only 1/4 of the earth's density would have 2.8 hours for each rotation. If you want to have an earth-length day (24 hours, neglecting the fact that you'd have to consider the sidereal instead of the solar day), the planet's density would have to be 0.34% of earth's density, or 19 kg/m^3. That's about 1/48 of the [density of Styrofoam](http://www.aqua-calc.com/page/density-table/substance/styrofoam). A planet made completely of Styrofoam would therefore need to have a rotational period of 3.5 hours. (**Note:** It would be nice if someone cross-checked my numbers.) # The effects of such a rotational speed OK, so what would be the effects of such a rotation on the planet's surface? Well, the two forces to consider are the effective gravitational force (that is, gravitation + centrifugal), and the Coriolis force. As before, I'll use accelerations instead of forces; to get the force onto an object just multiply with its mass. ## Effective gravitation The effects of course depend on the latitude, which I'll call $\phi$, in accordance to geographical conventions. It makes sense to split the acceleration into a vertical and a horizontal component, relative to the ground. The gravitational acceleration is, of course, always vertical and always the same (since we assume a spherical planet). The formula I've already given above (now we of course set $h=0$, since we are interested on the gravitation on the surface), but now we have to be careful about the direction: It points downwards, so we add a minus sign. > > $$g = -G M/R^2$$ > > > The absolute value of the centrifugal force depends on the distance from the rotation axis, which is > > $$d = R \cos(\phi)$$ > > > Otherwise, it's just the formula above, with $R$ replaced by $d$ (on the equator, of course we have $d=R$): > > $$a = \omega^2 d = \omega^2 R \cos(\phi)$$ > > > However, its direction is away from the axis, which means that we have to split it into a horizontal and a vertical component. The horizontal component is $a\sin(\phi)$, and the vertical component is $a\cos(\phi)$. Putting everything together, we get the total vertical acceleration > > $$g\_{\text{eff}} = -\frac{G M}{R^2} + \omega^2 R \cos^2(\phi)$$ > > > or, after inserting the "geostationary equator condition": > > $$g\_{\text{eff}} = \frac{G M}{R^2} \left(1 - \cos^2 \phi \left(1 - \frac{3}{2} \frac{h}{R}\right)^2\right) \approx \frac{G M}{R^2} \sin^2 \phi - 3 \cos^2 \phi = g \sin^2(\phi) - 3 \frac{h}{R} \cos(\phi)$$ > > > This is exactly as expected, you're heaviest on the pole (where the rotation has no effect), and lightest at the equator (and for $h=0$, you'd be weightless at the equator). And the force toward the equator is > > $$a\_{\text{eff}} = \omega^2 R \cos(\phi) \sin(\phi) \approx \frac{1}{2} \frac{G M}{R^2} \sin(2 \phi)) \left(1 - \frac{3}{2} \frac{h}{R}\right)^2 \approx \frac{g}{2} \sin(2 \phi) \left(1 - 3 \frac{h}{R}\right)$$ > > > Note that this force is zero both at the equator and at the poles, and maximal at a latitude of 45°. At that latitude it would be half of the polar gravitation, so it would be a quite strong force. Indeed, at that latitude, the horizontal floor would have an apparent tilt of about 27°. ## Coriolis force The [Coriolis force](https://en.wikipedia.org/wiki/Coriolis_effect) is velocity-dependent. It is the force which is responsible for the rotation of air around high/low pressure regions (and thus also in part responsible for things like hurricanes). The Coriolis force is always perpendicular both to the axis of rotation, and to the direction of movement. Therefore we now not only have to consider the position where we are, but also the direction we are running. I'll define the cardinal directions as on the earth: The sun rises in the east and settles in the west. The poles are in the north and south. This means that the angular momentum vector points to the north. The formula for the Coriolis acceleration is > > $$\vec a\_C = 2\, \vec v \times \vec\omega.$$ > > > The horizontal direction of the Coriolis force is to the right on the northern hemisphere, and to the left on the southern hemisphere. So for example if you are running towards the closest pole (to the north on the northern hemisphere, or to the south on the southern hemisphere), the force will push you in east direction. The most interesting part is the vertical component, which will become relevant on the equator when you're running left or right. When running on the equator in east or west direction, all of the Coriolis force is vertical; you'll get > > $$a\_c = 2 v \omega = 2 \frac{v}{V} R \omega^2 \approx 2 \frac{v}{V} g \left(1-\frac{3}{2} \frac{h}{R}\right) = \frac{v}{V} g \left(2 - 3 \frac{h}{R}\right).$$ > > > where I've introduced the equatorial speed $V = R \omega$. Note that when running to the east, the force will go downwards (make you more heavy), while when running to the west, it will go upwards (make you lighter). Compare with the effective force on the equator (see above): > > $$g\_{\text{eff}} = -3 g \frac{h}{R}$$ > > > So you get an effective *upwards* force if you run eastwards and $a\_c > g\_{\text{eff}}$, that is, > > $$\frac{v}{V} > \frac{3 \frac{h}{R}}{2 - 3 \frac{h}{R}} \approx \frac{3}{2} \frac{h}{R}$$ > > > Let's calculate that with earth mass/radius, and a geostationary orbit at 8000 meter height (about Mount Everest height): > > $$V = R \omega \approx \sqrt{\frac{G M}{R}} = 7.9\,\rm km/s$$ > > > $$\implies v > 0.015\,\mathrm{km/s} = 53\,\rm km/h.$$ > > > That's slightly above the allowed maximum driving speed inside a settlement in Germany. It's definitely much below what cars are able to do. # Would such a planet be able to develop life? Given that above the equator there's a "gravitational leak" due to the centrifugal force, I'd not expect that planet to be able to hold an atmosphere. So if there were life on such a planet, it would certainly not be on the surface. Without much of an atmosphere, I guess also water would evaporate quite quickly, so I'd expect the planet to be mostly a dead rock. Without air, there would, of course, also not much of a climate. # What advantage would such a planet have for colonization? Despite the disadvantage of having an effectively space-like environment, such a planet could have the advantage that you have very low launch requirements, so it would be relatively cheap to get onto/off the planet. For a space station (and possibly mining), that would be ideal. [Answer] With real-world physics, and not invoking any unknown or fantasy effects, a rocky planet would need to be very small before it could spin stably at such a speed. What would happen to a world that would be spherical when spinning slowly would be dramatic - within hours it [would transform into a pancake of spinning debris](https://physics.stackexchange.com/questions/10670/what-nonlinear-deformations-will-a-fast-rotating-planet-exhibit). The high angular momentum would rebalance as a more extended set of objects in orbit around a common point. I am not sure of the practical size limit/cutoff for this effect, but I think it will be quite small, lower than anything which could support liquid water or an atmosphere. Update: [this link has some clear maths](http://farside.ph.utexas.edu/teaching/336L/Fluidhtml/node38.html) on the stability of rotating objects, and [this page has run through the calculations including some nice graphics](http://www.josleys.com/show_gallery.php?galid=313), but unfortunately without working though the details of possible orbits and where geostationary ones would be. To make a large world practical you need to invoke some kind of fix to this problem. These things are pretty common in (non-"hard") science fiction and fantasy: * Ignore or modify the problem physics, and focus on exploring consequences of a less extreme version. * Posit some super-powerful materials or forces which keep the situation stable. You can then follow through with conjectures about experience of living in the environment, trusting to the magic you have invented to keep things stabe enough that life could evolve etc. If we assume you work around the physical impossibility as above, then you can make some conjectures about life-forms on a planet which is somehow stabilised as a flattened spheroid with centrifugal (or centripetal if you prefer) force balancing. The following things occur to me: * There will be extreme forces operating in atmosphere towards the equator. Hyper-powerful vortexes hurricanes, tornadoes or some kinds of weird weather not experienced in "normal" planets. This would likely be too extreme for living creatures if you did the maths to figure out likely forces, but again you could reduce that to something that might work in a more fanciful description. * The combination of powerful weather and low gravity should cause a major flow of material (basically masses of the atmosphere and whatever the world is made of) to make it into orbit at the equator, where it would either settle into an extended ring around the planet, or be recycled north or south to fall back onto the surface. You may need to posit this recycling scheme in order for the world to seem stable, and it could occur smoothly as a kind of weather, or in chaotic episodes, as catastrophic events, or likely both. * A flattened world would experience more extremes of angles in sunlight. The effects of this will depend on angle of planet's spin to its orbit around the star. If you assume an Earth-like tilt, essentially a large proportion of the world's land surface would experience daylight similar to our Artic and Antartic circles. That doesn't necessarily mean "cold", that could be balanced by a closer position to the star . . . * There would be a lot of atmosphere and debris in a band around the equator. Not a high atmospheric pressure though - in fact the opposite, the air would be highly rarified around the equator and creatures comfortable at the poles might not be able to breathe there. The extra air mass and debris should filter starlight that travels through it though, and the nature of the light would be very different in different parts of the planet. Sunsets might not even happen, so much as the "sun" would move towards the horizon becoming discoloured (more red in an Earth-like atmosphere), and more diffuse until it disappeared from view. At the equator it might be permanently shaded in dim red light with only a vague sense of where the sun is. * Whether or not my conjectures above are on target, I would expect extreme banding of environments between pole and equator to influence the nature of any plants and creatures much more dramatically than on earth. [Answer] The other answers are excellent but there is one important thing to add - the shape of the planet. Planets normally form a sphere as they are condensing from a liquid form and gravity pulls it into a flat sphere as it does so. In this case though it would actually form a very squashed sphere, it may even form what looks a lot like a disk, as the level "effective gravity" point is modified by the spin. At the extremes you are talking here the planet may only be (for example) 1 km tall and 6 million km wide. You would have very low experienced gravity no matter where you went on the surface. This would be modified a little depending on whether the planet cooled before or after it acquired this extreme spin though. [Answer] Some additional observations: 1. Rapidly rotating planets could be cigar-shaped as well as pancake-shaped. Haumea in the outer solar system rotates in about 4 hours and is thought to be like something between a cigar and a rugby ball. 2. Planets are in hydrostatic equilibrium. This means that, if it's big enough to be considered a planet, then it acts as a fluid over geologic timescales. Even solids deform under the pressure of their own weight, and after a billion years or so (maybe much less, I'm not sure) it will have reached equilibrium. This in turn means that rocks will not roll towards the equator any more - on average, the ground will be level. (There will still be mountains and valleys where it isn't level, just like on Earth.) The combined vector of gravitational and centrifugal force will be (on average) perpendicular to the ground. 3. You can adjust the parameters of the problem so as to retain an atmosphere by loosening your definition of "close" in the requirement that the geostationary orbit be close to the surface. I don't think the conditions for a planet to keep an atmosphere are totally known, but I bet something like 0.8 g at the equator and geostationary 1000 km up might be possible (please forgive the speculation). That seems pretty far, but it would make a space elevator much more feasible. ]

[Question] [ Very narrow question: assuming an immortality treatment keeping people at a biological age of a fit 30's, free of infections and cancers & ruling out death by aging, how long would people live (in the US) before dying from an accident (including crimes)? My understanding is that assuming no changes from our current society, the statistical risks set a hard limit around 300 years or so...? [Answer] The CDC [estimates](http://www.cdc.gov/injury/overview/leading_cod.html) 187,000 people in the USA die from "injury" every year -- basically that includes homicide, suicide, vehicle accidents, and other forms of accidental death. This works out to a chance of about 1/1600 of an individual dying from injury in any given year. So the chance of *survival* is 0.999375. After 300 years, your chance of remaining alive is $(0.999375)^{300} = 83\%$. After 1109 years, your chance of survival has dropped to 49.99%. After 5000 years, your chance of survival is only 4.3%. After 32,000 years, individual chance of survival is 1 in 488 million. By this time, it is likely that all of the 300 million Americans alive when the immortality serum was discovered would have died off. Of course, none of this accounts for fairly radical changes in society likely to result from biological immortality (not to mention other social change over thousands of years), which could drastically change the rate of death by injury. [Answer] Aside from Royal Canadian Bandit answer to the chance of people dying from accidents there is another problem to consider: how will people's brains age? You might have noticed time seems to speed up as you age. A year when you were 8 years old was nearly endless. But by now you will probably have noticed that years actually do pass in a reasonable amount of time (1 year to be exact). Now as you grow older and older this will likely continue. As you near your 100th birth day it becomes very difficult to actually keep track of what happens around you, this is because your brain has a finite amount of space to store memories in. So you either store less or lose older memories making the years seem shorter. This combines with the fact that you have probably already seen most things in the world by your 150th year. Making the rest of your life seem like a grey bluer. This is likely to result in people not wanting to live beyond 150/200 years. Sure some people can and will choose the longer life but many will cut it short. As such a cure would also greatly increase the population size we can also expect that suicide will become a lot more socially acceptable for those who are 80+ since otherwise we would have to deal with massive overpopulation. Of course if you have some way of keeping the brain in stasis as well or perhaps offloading memories onto a computer for later retrieval than this could be avoided. [Answer] Are we talking about a treatment that everyone can afford and everyone has to take only once, so basically everyone who is at adult age today, plus everyone who turns 18 in the future, will never die of old age? And since you cannot age forever, the ageing process would eventually stop? The problem would be that you can't have an exponentially growing population, so at some point number of deaths and number of births must be the same, one way or another. If this is handled carelessly then there will be initial growth, total destruction of resources, total disaster and a small and possibly primitive civilisation left. If handled careful, there will be either most brutal birth control, or some means to get rid of many people who lived long. Since it is the long living adults and not the newborns making the decision, I'd expect brutal birth control. Secretly having a baby without permission would probably be a good way to end your life and the baby's life. Violent crime, or reckless driving, would likely be seen as 100 times more abhorrent than today and get you culled. I'd expect some people to be careless and clumsy and die off rather quickly, leading to a different kind of evolution: The fittest would be surviving longest, so you would have some oldies who have already lived very long and carefully, and their numbers slowly filling up with newcomers. So while current statistics could be applied for 50 years, someone who is 200 (and still 25 year old fit) won't die in a skiing accident, or a car crash, or taking drugs easily. Forgot to answer the actual question: I'd say if all goes well, the ones living dangerously will be taken out of the equation within a short time (I could mention one motorist that I saw a short while ago who will *not* live for another ten years no matter what immortality drugs you could give him), say 200 years, and the remaining population will be the careful ones who can go on for many thousand years. [Answer] As a simple addition to the already good answers, you should think about Suicide. In any culture where life could be extended so long suicide would likely become more accepted. Maybe after 300 years people get bored. Maybe people get physically crippled and the prospect of living like that for an eternity is harder to bear? Maybe suicide is ENCOURAGED, because there aren't enough resources to provide for a constantly growing population and anyone that isn't consuming resources, and making more of the next generation, slows the inevitable over-popluated distopia that would be created. Maybe people would be refused treatment after 300 years just to keep the population slightly controlled. In any case culturally agreed upon suicide as a way of saying "I lived long enough, I'm bored and want to move on" would likely become a significant impact. It may even be a large percentage of deaths in the world. [Answer] As long as they want of course, in human measure. The question states that an immortality treatment is a given. So in my view it would include a superior backup of ones body and mind, to start with, otherwise there is not much immortality to discuss. After this the sky is the limit. Probably literally, because our particular Universe is not standing still. We could start attempts to recreate ourselves to -in the end- overcome entropy and break out of the particular surroundings of our dimensions and laws of nature. <http://en.wikipedia.org/wiki/Entropy> It would not do to stay as we are, mortals in a mortal Universe. The Multi Universe is out there. <http://www.space.com/25100-multiverse-cosmic-inflation-gravitational-waves.html> Our IQ's and other options could use an update to go forward, but for now, in my limited time, -I like to have a coffee-, the question is answered. ]

[Question] [ If an earth-sized planet were tidally locked to a star, and was in the life zone of its star with an earth-like atmosphere, what would its wind patterns be like? The planet would have one hot hemisphere and one cold hemisphere, so intuitively it seems like air currents would drive from the hot side to the cold side, but this seems like it should be counterbalanced by some stream of air from the cold side to the hot side. Would Coriolis effect be strong enough to direct these air currents? What would these wind patterns look like? [Answer] There is many studies (e. g. [Yang 2013](http://arxiv.org/pdf/1307.0515v1.pdf), [Hu & Yang 2013](https://www.pnas.org/content/pnas/111/2/629.full.pdf), indirectly [Joshi 1997](http://crack.seismo.unr.edu/ftp/pub/gillett/joshi.pdf) or [Joshi 2003](http://www.geo.brown.edu/classes/geol1950g/Joshi2003.pdf)) that investigate this in context of tidally-locked planets of red dwarf stars. The reason is that such planets have to be very close to their parent star in order to maintain liquid water. Their orbital periods are short (15 - 40 days) and tidal-locking occurs quickly and naturally. Because of the quick rotation period, which is the same as the orbital period, **the Coriolis force is crucial**. The most important feature, already pointed out by PipperChip and Vincent, is that the hot air is rising at the substellar point, which causes lot of rains, and the upper winds move towards the dark side. The winds at the level of ground move towards the substellar point, replacing the missing air. However, the Coriolis force turns the winds in the direction of rotation, which causes strong westward winds and maybe even superrotation as on Venus.  *Image from Yongyun Hu and Jun Yang, PNAS 111 629–634 (2013), doi: 10.1073/pnas.1315215111* You can notice on this Figure from meteorological model od [Hu & Yang](http://www.geo.brown.edu/classes/geol1950g/Joshi2003.pdf) that the substellar point is not the hottest place, thanks to the wind. The hottest places are two points just above and below it. However, if Earth got tidally locked, the Coriolis force would be almost non-existent and the most dominant feature would be air rising at substellar point and near-ground winds moving towards it. (There some videos exploring this scenario [1](http://vimeo.com/19458103), [2](http://vimeo.com/19458029), [3](http://vimeo.com/19458068), although not the wind pattern itself.) This situation was described in Vincent's and PipperChips answers. **Do not miss:** The transition from wind pattern of slow rotating planets without Coriolis force and quickly rotating planets of red dwarfs is nicely illustrated in [Oceaniis' post at the Forum of Speculative Evolution](http://s1.zetaboards.com/Conceptual_Evolution/single/?p=1024983&t=5047443). Interesting source is also [this post](http://en.spaceengine.org/forum/8-1986-1) at the SpaceEngine forum. Interesting source for deeper study is also thesis of [R. A. Edson](https://etda.libraries.psu.edu/paper/8129/4476). Recent work of [Lewis et al.](https://arxiv.org/pdf/1802.00378.pdf) contains interesting statistics about influence of continent in the substellar point, including maps of cloud coverage. [Answer] *Note:* While this isn't a complete answer, it turns out that your intuition is mostly right. **The Wind** Wind currents would, generally, go from the day side to the night side. This depends, however, on a lot of factors. Such factors can be temperature of the star, landmasses, density and composition of the atmosphere, oceans, and others. Cornell University did a neat study on [tidally locked planets](http://arxiv.org/abs/1001.5117), if you would like to take a look. They even address Coriolis Effects! As a simplification and summary, the faster your planet goes around your star, the more your winds get mixed up. We know that, eventually, the air from the cold side will "want" to go to the warm side, due to pressure, gravity, and diffusion. This may form the equivalent of [Hadley, Ferrel, and Polar Air cells](http://en.wikipedia.org/wiki/Atmospheric_circulation), except it involves air going from the day side to the night side instead of equator to pole. It turns out modern simulations find that such circulation would actually keep the night side quite warmer than previously thought. See the wikipedia article about [the Habitability of Red Dwarf Systems](http://en.wikipedia.org/wiki/Habitability_of_red_dwarf_systems#Tidal_effects). **The Air Cells** It would be generally assumed that the air cells on our tidally-locked planet would look like Hadley/Ferrel/Polar Air cells going from the day side to the night side. Some people think there would be areas of permanent rain where hot/cold air meet, and that there would at least be a ring of habitability somewhere around there. **Climate Models Are Complicated** You should therefore recognize that this answer has some assumptions built in. The Atmosphere needs to be neither too thick or too thin. It appears that oceans ought to exist to make it habitable. [Many](http://astrobites.org/2014/11/07/habitability-still-a-go-on-tidally-locked-terrestrial-exoplanets/) [studies](http://www.pnas.org/content/111/2/629.abstract) don't actually look at wind, but rather heat transfer or other [effects](http://arxiv.org/pdf/1405.1025.pdf). Your question is closely tied to exoplanet study, and it is a huge field. ]

[Question] [ I have an alternate history epoch taking place in [10th Century Islamic Renaissance](https://en.wikipedia.org/wiki/Islamic_Golden_Age), but I have a large Bedouin tribe that does not use anything to indicate a person's name or identity. This is a big Catch 22 every time I try to wrap my head about it. I don't want a number or symbol, I want it to be foreign for this tribe to refer to someone specifically. Historically, they might say they are son or daughter of so-and-so (Bin So-and-so / Bint So-and-so), but I want to avoid any way to name a person. In an effort to prevent this from being idea-generating or too-broad, and to be able to select a correct answer, I'll narrow it with the following: * Our 10th Century Arabic world; * People must be able to provide a response; if asked by the Caliphate "who did this," they cannot answer; * Numbers or symbols are not acceptable, as this would give identity. In the end, I need a mechanism to make it **impossible for someone in the tribe to name someone when questioned at length about 'whodunnit'** even if they wanted to. I think that this is impossible, so I'm bringing it to our WB brains. [Answer] People would be referred to in a *relative* manner only. So the person being questioned could refer to “my father”, “my second teacher”, “my kind neighbor” etc. But a stranger could not go back to this town and use the same labels. It would be “X's father”, but then who is X? Without producing him, they cannot get a base for relative designations. Without knowing the town’s people in some detail, such references don’t even make sense when used by people there. These people would have to carefully use *only* designations that are relative to themselves. Referring to something absolute, like “the mayor” (when there is only one) is a taboo. There is still some intermediate ground though—the outsider might kill *all* the barbers because the target is “X’s barber”. [Answer] So you want to do away with [personal names](https://en.wikipedia.org/wiki/Personal_name)? Seems like a daunting task. Names relate directly to a fundamental element of intelligence: identity. Humans aren't even unique in the animal kingdom in that they have names; [dolphins have them too](https://en.wikipedia.org/wiki/Personal_name#Dolphin_names_for_each_other). If you remove the capacity of a culture to be able to identify the perpetrator of an event, then you must strip away any concept of individualism within the society. There would be no 'me,' 'you,' or 'him.' Instead of: > > Michael planted the tree. > > > She painted the *Hills of San Jose*. > > > You would have: > > The tree was planted. > > > The *Hills of San Jose* was painted. > > > This has interesting ramifications. If the society needs to identify, then it will identify as a collective: > > We planted the tree. > > > We painted the *Hills of San Jose*. > > > There's no longer assignment of blame or accolades for a job well done. The Community succeeded. The Community failed. There is only The ~~Borg~~ Community. [Answer] The answer is **you**. If the tribe have no names, the only way they could refer to each other is direct communication: "You have food?", "You make fire", etc. In this instance, **everyone is you** and no-one is individually identifiable. Note that in this instance, it would be impossible for a member of the tribe to talk about someone else in the third person. That might limit their communication somewhat, but it gets you out of your *whodunnit* conundrum. [Answer] You seem to want a society where people still can interact and have meaningful relations, but an outsider without knowing the people beforehand can't know who is who, as they have no normal names. ## The relations define who you are. We start with no use for names; everything that has a name and can be named is an object. Our people are not objects nor animals, therefore we don't use names. Maybe outsiders do, but they are strange and not favored by Allah. Gossip is going to happen, but we refer only to others by an unique, for the relation, thing that happened. So when two people talk about a third that they both know, they would use a different designation. For Allah knows his interactions. *Also, this works because our tribe is not big, so every one knows one an other. And we have excellent memories.* And the last rule is we don't talk about the past to strangers. Allah knows our relations and motions, past and present, so do we. Our shared history is precious in our harts. To talk about it to strangers is sacrilege. **Tribesman & Stranger:** > > Stranger: "Who made this beautiful dagger?" > > > Tribesman: "It is indeed a beautiful dagger." > > > Stranger: "But who made it?" > > > Tribesman: "The one who made it." > > > Stranger; "Yes, I understand, but what is his name?" > > > Tribesman: gets angry; "Do you want to bring a curse?" > > > Stranger: "What? Me? Surely not!" > > > Tribesman: "Good." > > > **Tribesmen:** > > "That is a beautiful dagger, can I see it?" > > > "Here you are, nice, isn't it?" > > > "Yes it is, where did you get it from?" > > > "From 'cheated with dice', he is good with metal." > > > "Yes, I know 'bumbed his toe on the camel' well. If I need a new dagger I will go to him." > > > *Our Allah might not be the same as in their koran* [Answer] Refer to them by role and rank. First smith, second smith, first Carpenter, fifth shepard. Rank and role changes with time. You are what you do, not who you are. Or similar refer to them by family title. My brother, my sister, my father. This requires a reference person to point to someone. If those aren't known they can't be named. [Answer] English names refer to a time when we referred to a person by the deeds that person does, probably for a living. Wainwright. Weaver. Baker. Smith. Some native American groups have last names that tell more about the person - "Has No Horse" for example is not an uncommon name. Names can be deeds or qualities. I propose you use that: name the person by his or her deeds. I like the idea of a person referring to another person from one of an assemblage of deeds or doings, known mostly or only to the person being asked. He is the one who ran from his own dog. He is the one who looks at my cousin. He is the one who can drink more than me. He is the one who borrowed my soft pants when his testicles swelled up after he rode all day. Because his saddle was too hard. He is the one who brought me a bird he killed. The person being asked will recount from that own persons experiences with the individual in question. My recounting of you will be different from the next person and from the next. I name you for my own use with my own subjective experiences of you. Ideally that naming turns into a long and rambling story. Such a system is not very useful if I ask you "who has your soft pants? I need them please." But maybe with a friend (me, I hope; I need those pants!) you would refer to the third person with a description of an event shared by both of us - "He is the one who could drink as much as both of us, but then he fell into the fire and we had to roll him out.". [Answer] A language which only has three numbers (one, two, many) and three persons (you, me, they) would work, and be consistent. * Caliph: "Who did this?" * Ug: "They did." (meaning: it was not you or I, but another). * Caliph: "Oh, damnitt, you're from that stupid tribe, are you? Well, bring me the head of whoever did this!" And there's the problem. Even if you cannot tell the Caliph who committed the crime, the caliph can tell you "Fetch me the one who committed this crime". The only way to avoid this is if nobody knows who committed the crime. Then even if one (or ten) people confess under torture that it was them, there's no way to be sure which was the real one. So you need the conversation to continue like so: * Ug: As with your women, in public, we all wear identical clothing that covers our faces, and speak not. We take it further, too: we copy the mannerisms of one another. We exile from the tribe those who look too different. Only within the home do we have identities. I cannot tell you which of us did the deed. But then it inevitably all goes south: * Caliph: So you are all as one, any member of your tribe representing the whole tribe, speaking for the tribe, and replaceable by any other? * Ug: It is as you say, my Caliph. We are one. * Caliph: Then should I have your head, if it is the same as that of your brother? Would that be justice? * Ug: By the laws of my tribe, yes. I can't see a way of avoiding this ending, in a tribe where identity has been subsumed to this point. [Answer] I think a general solution is to have a system where there are no designed identification systems at all, and people are identified by a pronoun and context. This sounds rather unnecessarily difficult, but there are real-world examples. I went to a secondary school when I was younger and most of the time other teachers were referred to as 'Sir' or 'Miss'. When talking about other teachers we mostly referred to them by that, and when talking to pupils even teachers sometimes talked about other teachers using the words 'Sir' and 'Miss'. My dad was visiting the school that my younger sister was going to, and at the exact moment the headteacher said 'Yes, we've definitely integrated the Sir/Miss system fine, no problems at all,' a pupil in the background talking to a teacher said: 'Miss, Miss said she'd be with Miss but she wasn't.' and the teacher replied: 'Ah yes, she'll be with Miss in the canteen.' They understood each other perfectly fine. [Answer] Someone once told me about a culture (Navaho?) in which your name is practically never mentioned in your presence; if asked "who are you?" you'll reply, for example, "Broke Two Toes is my cousin" and keep listing relations (by blood or otherwise) until your interlocutor is satisfied that you've been narrowed down to one. You can have a different name in each village, and not know them all. [Answer] I don't think you're ever going to find a society where the concept of personal names doesn't exist - personal names are one of the very few true cultural universals, concepts that exist in every human society. A society that didn't have such names is almost unimaginable. HOWEVER... A society where all formal interactions are deliberately anonymised might be plausible. Let's suppose a culture where taking violent revenge on any tradesman who provided perceived substandard goods was not just accepted, but required; one could imagine that tradesmen might start anonymising themselves, so that one could never be certain *which* blacksmith made the horseshoe that broke. Alternatively, consider a culture in which a person taking on a particular role was considered to be personifying a (deity/spirit/djinn) that oversaw that role. They might wear formal robes and masks to help sell this idea, entirely subsuming their personal identity behind that of the god. Such a custom could expand to others, so that eventually all business was being conducted between anonymous masks. Personal names and identities would only be used in social or family settings. A crime committed by one of these masked individuals would have to be reported as "The blacksmith did it!" - but who's the blacksmith? How can you identify exactly which blacksmith it was, or even who is a blacksmith in their family group? It's not even any good to just go in and execute all the blacksmiths, because the person who was working as a smith on the day of the crime might not be doing that job today. [Answer] Have everyone use a new name every day. When questioned, one could only say "Joe Bloggs of May 1 did it". --- This would not preclude permanent records from existing for things like bank accounts by using a combination of name and date to identify the account holder (plus the usual private info like dob etc to verify). [Answer] Names are easier and therefore more plausible, but, in a culture where naming people "like things" is incredibly rude for some reason people may resort to replacing names with current locations? Whereby if the tribe couldn't see a person AND didn't know where they were they'd have no way to refer to them. You could refer to yourself as "me here"; Someone you're talking directly to as "You next to me" or "you in front" Someone in your immediate vicinity as "Him to my north west" Someone you just saw recently as "The lady in the garden"; Your deceased grandfather as "The man in the ground outside my house"; But when it comes to someone who you haven't seen for a while the best you'd be able to do would be something like "The one who was in the kitchen the last time I saw them" **Update: -** In the same "Names are rude" or whatever scenario, WITHOUT *replacing* names entirely, you could still achieve your objective by making names shared only with close relatives and partners, especially in a society where people value 'keeping themselves to themselves' and 'handling their own affairs' etc. Then, if someone asked about the 'who' in the 'who done it' and that 'who' had no close living relatives, no-one could say who it was (and they wouldn't say even if they did know the person's name). [Answer] You would need to break basically every rule of reality to pull this off. If identity has any value at all to these people, they will find ways to create identities. That's what humans do with language. You invent words when inventing words has value. So you need something extreme compelling people to not *want* to have identity. You want a social structure that has no concept of self at all. This is going to be radically unlike anything that has ever occurred in history. Want to sleep with your neighbor's wife? No problem. He doesn't have an identity, so he can't be mad. In fact, she doesn't have an identity, so you might not even be able to ask about it. In fact, you don't have an identity... One identity you will need is the identity of the tribe. Without that, you're certainly going to fall apart. Now I can't say this would work, because nothing could really do what you want, but the closest I can think of to a working solution is a revolving concept of identity. Identity is granted on a temporary basis while it is convenient, and then that identity vanishes back into the Tribe when it has outlived its usefulness. So your people might be able to say "The Senator did it!" where "Senator" is an identity, but they might have no concept of whether any given person was the Senator in question, because they have no concept of associating an identity with a person. Such a culture would almost certainly develop tremendously powerful possession like attributes. If each human body has no identity, but some roles can acquire an identity of their own, the next natural step is that an identity might "leap" from one person to another in attempt to avoid persecution. Your culture would certainly be steeped in what we would call pseudoscience with the expressed goal of making the tribe members weak to such possession. [Answer] I remember an Old Ayn Rand book called Anthem. In it, the use of personal names and even pronouns was taboo, and everything was referred to in collective terms. I, Me, My, and so on just wasn't allowed in the lexicon. It all became We, Us, and Our. In your society they could adhere to similar rules under the idea that the collective is far more important than the individual. The genesis of this might be the result of some sort of isolation and long term, existential threat. When asked whodunnit, the answer would always be "they did it", as the thought of personal identifiers would be somewhat alien. It would take something fairly radical to cause even a small group of humans to shed personal identity in the first place, but build it up over time, with tradition, and you might get something sustainable in relative isolation. Maybe you could have each community allow one individual to interact with the rest of the world, and that one individual would take a name. Make the interaction with the rest of the world be perceived as a bad or difficult duty. Necessary, but not something that people would seek for individual gain. The hardest thing is that you are making humans act in a way that is kind of contrary to millions of years of evolution. When you have an individual advantage, you get to pass along genes. That is a tough drive to overcome. Given the setting of around the 10th century Caliphate, it would have to be a small tribe on the very edge of the Caliphate or empire. The more remote, the better. A part of the problem is that the religious texts are going to be using personal pronouns and names. The history as taught by those key texts shapes a heck of a lot. Your isolated tribe is only going to pay lip service, if anything at all, to that dominant faith. They might say, God is Great and bow in the direction they believe Mecca is during prayer, but the rest is going to be so much drivel. [Answer] This is a hard one to reconcile without the eventual creation of names. It is almost irrational to me, assuming a societal existence. It seems inevitable that we would have names in some form. Assuming verbal communication. Otherwise we might expect *unique identifiers* which could be your particular smell, or more likely in modernity, the color choice and co-ordination of your clothing, hair, or head-wear, for example. A more advanced form of *tartan* which could not only signify which family you are from, but your position in the family (and whether or not you are single), etc. It would lead to ranks, colors, and stripes of the military. If it were just customary to conceal your name, or it was forbidden to speak any name, then it is my reckoning that people might be *serialized based on location of birth* or by trade, or something probably mundane - but this is kind of how names develop. [Answer] ## Complete anonymity. I'm reminded of the movie "A Scanner Darkly" where agents wear "scramble suits" to mask their identity. However even in that movie, agents had code names to identify one agent from another, and the anonymity was there to protect their "real" identity because they were undercover agents. You could take it a step further. Perhaps every member of the tribe wears the same clothing, the same mask, every day. It's impossible to tell anyone apart because they all look the same, perhaps even act the same. Or maybe there are different styles of dress and masks that are randomly distributed to the people every day to totally scramble any identifying features so that even a distinctive scuff of dirt on clothing can't be used to identify anyone. Maybe even: personalities or roles that revolve around the clothing, rather than the people wearing them. Did you get the "chieftan" robes this morning? Congrats, you're the chieftan. [Answer] ## Use only a few different names for everyone Instead of doing away with names altogether, just have a very limited list of surnames (if every male is named Mahmud, Hamud, Muhammad or Hammid - it'll be impossible to find the correct Mahmud iben Hammid...), and make it culturally unacceptable to use other names. As a real world example, the Luo tribes of Kenya and Tanzania traditionally used around 50 surnames, dictated by the time or circumstances of the birth (e.g. 'Odhiambo' means "Born in the afternoon")- see this [wiktionary appendix](https://en.wiktionary.org/wiki/Appendix:Luo_surnames) for the list. A Luo acquaintance once told me that all of his friends and family had only 4 different traditional names between them all (today most Luo people also have an additional "Christian" surname, so it's far less confusing). [Answer] Since you don't want them to be able to identify another for sure if they can't point with a finger at them this could be an approach: Let them only use pronouns, but replace them with the feeling/what he sees/what he thinks about the person he wants to name. Actually much like the Japanese -san -chan -kun etc. But don't use them in combination with a name. Without set rules anyone can find a way to give someone a temporary name. One day you might get called *unwashed dog* (while your mother, even with the same dirty look, could call you *light of life*), the other day after cleaning and making yourself nice the same person could call you *cute guy*, while yet another person could call you the *one I despise*. This gives a great way for human interaction, for people it will be easier to accept the emotion of others because how I call you is how I feel about you. Interaction gets "realer". On the other hand this would require people to not really care about how others perceive them or don't get hurt after hearing a "name" they don't like. [Answer] If your guys are really religious they could refer to themselves only as part of group. Like "We are X", so we could imagine a dialogue with a stranger: > > – Who did this? > > > – X did this > > > – Do you mean *you* did this? > > > – We are all X. X did this. > > > It would require some kind of sect though that would brainwash its newcomers (or just raise children in a special way). It might be not like they have no name, but more like each of them has same name which is also name of the group. But it solves the "cannot provide answer to 'who did that' question". Inside the group they could use 'you' if talking directly, or point a finger if talking about someone present. [Answer] **Internet-like** I would think about names on Internet - You know, that I am Gilhad and my reputation is (just now, just here) 221, with 1 silver and 4 bronze badges. This is not much, so I am now really known here, but anyway it is that I am not total newbie here and maybe you will remember me so. Maybe a year later my reputation will be much higher and I will have more badges and you will say "I got this idea from Gilhad. You know him? Does not talk many times, but usually has something to say." and others would or would not agree and they would know about me, my ideas and such. You can google me and find out more about "gilhad" and it would probably be me. But if you meet me on the street, you would not recognize me, until I, or someone else, will give it away. And it would be hard to prove whether that dog with the black left leg is "gilhad" or not. Anyway if I want to disappear, I can stop being "gilhad" any moment and create another nickname and go by it with new reputation, maybe even with a new approach to problems. (Actually I may do that already for years, who knows and who cares?) My ***true name*** is something totally different and many people, who know me as "gilhad", have never heard it and would not recognize me by it. Still, they consider me a friend, some of them met me in person on more occasion and that is enough for them. "gilhad" means something for them for sure. But for the Caliphat it has no real value. I play a lot of Role Playing Games and I change characters even in one game over time. Co-players usually refer to me by my character's name during the session and also in every day life at the era of that game campain, as some of those names are more catchy for them than plain old "gilhad", which they use to address me formally. So if there was some conspiracy against the Caliphat and some rebels were interrogated, they may (by their best knowledge) give me as "Monsieur Klobrc" as it is the only name they did hear in personal talking about me. And so the Caliphat would need to catch some members of my group to reveal, that "Monsieur Klobrc" is "gilhad". But even so, who is that "gilhad" anyway - there is more people who knows me as "gilhad" only, than who knows my ***official name*** (and of that a lot did not hear anything about "gilhad"). Still, nobody has a problem with it (except maybe the Caliphat). So using nicknames can be the answer to your question - of those, who should know, the nickname is good enought to describe and target person. But out of that group the nickname means nothing and one person may go under more nicknames at the same time, without problems. The only way the Caliphat can pin-point down is to force people to point fingers at those, who (they think) know me and are able to point their finger at me personally. But shouting loudly in the right places (or write on a wall or anything else) to tell "Monsieur Klobrc" that there is such and such problem would probably work in the way, that I would get aware about mentioned problem soon enough. --- Also, see at this very question - I bet there is a way less ***real names*** than nicknames and it still looks natural for all of us to the way, that nobody mentioned it here before. (As answer from gilhad to Mickey - the Caliphat has good luck find who asked and who answered. The community knows well, but cannot say it to you, oh mighty Calif, no matter what.) [Answer] It would take good memory, but people could be referred to by how long since the last encounter. "The man I am talking to", "The woman I just talked to", "The boy I taught last year". Everyone else is "One I have never met". [Answer] 1. I upvoted @Mormacil's answer, but let me give you an analogy that you may find useful. In some countries, you can refer to a building by a street address: 1854 Jackson Lane. You could find Jackson Lane and go in the correct direction and somewhere adjacent to 1853 and 1855 you'll find 1854. In Japan, this is not true. As I understand it, the buildings are numbered in the order they are built. In Central America this is even less true: you will be given directions like, "Go down the main road towards Guacamal, and 200 meters past the dairy, turn right. Then proceed to the park where the big tree used to be (before it burned down), and turn right." I think this could provide some inspiration for names for people. They could be names related to position/role/job (as in Mormacil's answer) or familial relationships, or shared incidents, as several other answers suggest. But I think that if you get your head around how street directions vary from place to place, it could help with your name issue. (In my mind, the key is that "names" are relative paths and if you encounter a problem anywhere along the path, you're stuck, but you may pull something else out of the analogy.) 2. I also think about some languages that have very nuanced words for relatives. For example, English has sister and brother to distinguish siblings by gender. Then step-sister to distinguish siblings by other parents. You can have a first cousin twice-removed, which is fairly specific but does not indicate gender. As I understand it, some languages have many specific words for various relatives rather than using a street-address-like "first cousin", "second cousin", etc. Perhaps these names could be very specific so they don't speak about "oldest brother" but have a specific word for that. And perhaps that word depends on the gender of the speaker. And perhaps that word depends on the relative social statuses of the speaker (see "honorific languages"). And perhaps the word depends on the person's zodiacal sign and the year in which they were born (as years are named in many cultures and viewed as influential). So there might be 144 different names for a particular relative, based on which month and which year they were born in. So the person being interviewed might well name the individual fairly specifically, but an outsider trying to figure out or to use the description might find it nearly impossible. For example, I think of U.S. servicemen who learn Japanese from Japanese girlfriends: the problem is male speakers and female speakers will use different words. So perhaps the investigator is male and the witness is female. Or maybe the investigator is a middle-aged, married male and the witness is a young, single female. If he tries to ask anyone about the relationship he's given, they will totally misunderstand him. Thus it's not that the witness can't *say*, but that the investigator can't *use* the "name". (Oh, and perhaps actual names are viewed as sacred and only immediate family members actually know your name. Or perhaps the opposite: human names are profane -- there is only One Name. Everyone else uses relationships.) And we're not even getting into multiple uses of relationship words. "Hey brother, can you spare a dime?" The person is not your brother in the genetic sense. Similarly, I had an "aunt" and "uncle" growing up who were simply friends of my parents, and I know people who talk about "cousins" who are not cousins in the general sense of the word. 3. Perhaps many titles are used in the language, but most people don't actually know what many of them mean. Perhaps I was told that this person is "my friend's oldest brother's butler's programmer cousin", and that's how I'd refer to this person in my conversation. You ask me what "programmer" (or "butler") means and I have to say I don't know. It's probably something the person does, but it could be other things. I know what a "smith" does and what my father the "cobbler" does, but... In fact, I may not know anyone except that particular person who knows what a "programmer" is. The investigator could wander around all day asking people to direct them to anyone who is a programmer, and no one actually knows. [Answer] You are trying to succeed in a very serious writer's challenge. You are making up a nation without one of the basic traits of intelligence... no, actually, without the basic trait of life. Animals of all kinds have a sense of identity or possession. Without it — well, you are inventing a society more alien than aliens in 99% of sci-fi stories. If language lacks the unique identifiers for people — it could mean only one thing. The intelligence that invented that language is basically and completely unable to discern other people. It is only "me" and "somebody" for that intelligence, and no other notion of man available. Seriously, the only reason ancient Inca did not have a word for "PC" is because they could not imagine one. Ancient Greeks could imagine robot even as they did not have any idea how to build one — they had words for "robot". Your tribesmen can't even imagine that people can be different. At first, it seems possible to imagine this, but the problem is in the details. For example, if a tribesman is sincerely unable to answer "who stole the horse" to Calif, this also implies that * Tribesman is unable to discern Calif from a kinsman and would not know how to treat them differently. * Tribesman is unable to recognize an act of stealing when he sees it. If he is unable to say who is who, he is unable to say whose item is this. Thus, he is unable to say if it is a legal owner or a thief is taking the item. May be tribesman can tell apart "mine" and "not mine" and can tell if the item is stolen from him. Or maybe he has no notion of "property" and "stealing" altogether. * This "tribe" does not live as tribe. They are not able to tell who is from the tribe, who is not. They may be able to discern this from some sort of clan markings, but even if a person dons those markings right in front of them — will they be able to understand it is a ruse? * They have no family. When woman has a baby, she is unable to recognize her baby from other babies. This most likely means they nurse all babies in a tribe together. * They can not be proper Muslims, because they can not understand what is the difference between the Prophet and simple man. As you see, they would be completely alien among any culture on Earth. If they were like this for the long time, they will have their own culture unlike anything on Earth, and you, as writer, would have to build every little fact of it from the ground up, and is not allowed to take *anything* from *any* known culture. If your tribe had become like this recently, they are in a dying state because their culture is not adapted to their abilities. Anyway, I can not imagine how they can have any sort of peaceful relation with "normal" people around them. Religious people would see them as abominations that should be killed on sight for the love of God (whatever God). They definitely would not attempt to talk with those tribes. [Answer] ## What about solipsism? Simple: The people are all living thinking there is only one consciousness that is imagining the others: everyone is I. If you ask someone: "Who did this?" you will get something like: "I did, but you know that since you are me. Silly me." These people would be very generous, but that doesn't mean they can't defend themselves (like you can have your leg cut if it get infected, they can accept that sometimes a part of themselves got cancerous and must be deleted). Here is an example of a casual conversation this tribe could have: A: My feet are hurting, why wouldn't I stop a bit? B: I thought I wasn't stopping before the next oasis. I must remember about the dangers of staying under the sun. A: Let's go, I can still walk after all. C (this one is traveling with the tribe but not an actual member): Guys, a weird thing has bitten me! Do you have a doctor? A (beginning a sort of chant): Am I able to heal that? B (repeating): Am I able to heal bites from this animal? All the tribe (chanting): Am I able to heal bites from this animal? D (coming from the other side of the caravan): Yes, I can. [Answer] Yes, reaching the explicit goal of "impossible for someone in the tribe to name someone when questioned at length about 'whodunnit'" is impossible. Even if you manage to invent some convoluted reason for tribe to not use names, nothing stops the questioner from simply labelling each and every tribesman himself and using those. Actually you don't even need names to point out a specific person (or *any* specific object for that matter). A simple "that guy over there" or "3rd person from the right" will work as well. Therefore no matter what excuse you invent for not using names, it won't be going to help you in any way. Even referring to themselves only as part of group won't work. "We all did X" is easily defeated by direct question to point to a limb that "did X (held dagger when X is murder, touched goods when X is stealing, etc)". And here's your *whodunnit*, directly connected to that limb. [Answer] What if I call someone: The one who lives in a house and have a plum tree in the front. Or *the one with a short leg*. Or *the one with a big forehead and a small mouth*. Or *the one with easy walking*. I mean some particularities, which for sure everyone presents and are decisive for that person. [Answer] **Pronouns for all!** First consider a conversation involving a small number of people, e.g. two people talking and the subject is a third person (male) and possibly a fourth person (female). Assuming both sides are aware of the context, this entire conversation can be carried out without names! We have *I*, *you*, *he* and *she*. Of course those pronouns will refer to completely different people in another conversation. Other languages have further pronouns which refer to seniority or familiarity (e.g. *vous* and *tu* in French). Now imagine the relatively small tribe have hundreds of pronouns in their language, referring to different aspects of people (e.g. their relationship with the person doing the talking, male or female, whether they are older or more senior than the speaker, whether they live near the speaker, etc.). It might seem to get very confusing, but the upshot might be that they can refer to almost anyone in the tribe with a combination of context and these pronouns and maybe a little clarification here and there ("No, I meant *he* with the moustache, not *he* who once ate the superhot chili"). But it works because the people of the tribe *know each other so well*. They rarely meet outsiders and so there is a very small range of pronouns to refer to one - maybe just one or two words. Now the Caliph comes along and asks "Who did this?" and the tribesman uses one of these pronouns to identify the guilty party, and as an outsider, the Caliph hasn't a clue who they are referring to. So the Caliph asks someone else, who uses a completely different pronoun. Now he is really confused. Of course, he could very easily gather everyone together and have someone point to the culprit or have the witness bring him to them - but that seems out of the scope of the question. [Answer] This being the Xth century, our Bedouin tribe must've read the Coran and, at least, knew about names, how they work, etc. So it's unlikely that they didn't use them ... if they weren't "haram", forbidden. A common theme in the Coran is that, to Allah, all Muslims are alike, no matter their wealth, their color, or their ethnicity. Only their deeds sets them apart. That's why, during the Hajj, all the pilgrims, rich and poor, Arabs and non-Arabs, wear identical white clothes; a symbolism for human-equality between all Muslims. **Unsurprisingly**, this idea of 'deeds-only' was pushed way too far by some Muslim cleric who declared all names haram. One must not have a name, any name. People in this cleric's tribe refer to each other exclusively using pronounces, and vague descriptors. Abdallah, the servant of Allah, is a good alternative too, specially when communicating with the external world for trade and such. It's a very popular name that's also frequently used à-la-John Doe. Amatollah is the female form―even though it's much less common. --- **This scenario avoids a major drawback with others' : shortcuts.** Over time, people would naturally form shortcuts, deliberately or not. What started as smith-by-trade would become, after repeated use and habit forming, Smith-by-name. But with our haram-naming tribe, the only habit that's formed is to avoid naming people. Even when asked by the Calif, one would never name a person. If that gets them killed, they'd be considered a martyr. [Answer] I'm terrible with remembering names, and my daughter (usually referred to in our house as 'little thing' as she was a small baby so everyone remarked 'She's such a little thing!') is no better. There are plenty of acquaintances I'd find it impossible to name. So the same person gets referred to by various means - my 'little thing' calls 'my brother's daughter' 'the little girl on holiday' (my brother's other children are boys, and we visited with them last summer). My wife is normal and uses her name. If I were to found a tribe, you might expect outsiders to find the lack of names a bit confusing, and whilst each person might use the same descriptions for others, different people would use different descriptions for the same person. Then add to that a language barrier - [Hungry hill](https://en.wikipedia.org/wiki/Hungry_Hill) was allegedly called because the local guide was getting hungry at that point and stopped cooperating with the English map makers, or [Welsh signs](http://news.bbc.co.uk/1/hi/7702913.stm) not translated, and you get an official setting off for Ms. Peth Bach or [Ned's wife in Gwybod](https://translate.google.co.uk/#auto/en/Nid%20wyf%20yn%20gwybod). [Answer] # This cannot be achieved, unless... > > This is a big Catch 22 every time I try to wrap my head about it. > > > Yeah no wonder, because rephrasing the question only slightly, what you have asked is a pure Eat-The-Whole-Cake-And-Keep-It question: * *I do not want people to be able to **identify** anyone within the tribe.* * *What can I use as **identity** for the tribesmen?* Hence **you cannot use anything as an identity because assigning [identity](https://en.wikipedia.org/wiki/Identity_(philosophy)) to someone makes someone identifiable**; that is the very purpose of identity. The big problem for you is of course that identity is next to inescapable; if you have seen a person, then you can identify them. Their very physical appearance is a form of identity. Your memory of them is a certificate of identity. So when the caliphate's agents puts a sword on your throat and tells you "tell us who did this or you will suffer for it"... then you may, quite urgently so even, feel compelled to go to the tribe with them and point that person out. So if you do not want anyone to be identified, you must make everyone in the tribe **un-identifiable**. This is next to impossible to do so you are bum out of luck. ...or are you? [](https://i.stack.imgur.com/ZlzcT.jpg) *Woman in Saudi Arabia wearing a [niqāb](https://en.wikipedia.org/wiki/Niq%C4%81b)* Image licence: CC BY 2.0, Walter Callens. [Source](http://www.flickr.com/photos/waltercallens/385807779/). ]

[Question] [ My world is basically the same as our own but with slightly more advanced cybernetics and virtual technology. Specifically, they have a technology to create true matrix level virtual worlds. The most popular of which is based on a fantasy RPG. Users connect their minds to the virtual reality and choose different classes for their avatars in this virtual world. As they play, they can unlock new skills, abilities, and ability levels. However, as amazing as this game is, it comes with side effects. Since the game is so real you can suffer from post-traumatic stress disorder (PTSD) from your gaming experience. You also feel the pain as if it were real. And most frightening of all is that the more you play, the higher is a risk of a coma or even a complete brain death, should your avatar experience death in the game. The chances of death in the game resulting in actual death increase with the time spent playing the game. Yet despite this, over 1/3 of the world population spends one day a week playing the game. 1/5 of the population spends 3 days a week playing. Assuming that these gamers are relatively sane why would they keep playing even knowing the risks? [Answer] ## People risk themselves all the time **Drugs** Plenty of people have at least tried drugs, some of which can kill, most of which have dubious sources...and yet the thrill, peer pressure and community are enough to make them ignore the more sobering facts. Perhaps these things do kill...but thats something that happens to other people, right? Much like with drugs perhaps the general consensus becomes that **those who do die just didn't know their limits**, that it stems from some fault with the person. It is easy, then, to **consider yourself** as much more **sensible** than that, the **danger is negligible if you're doing it right**. **Adrenaline junkies** Parachuting, Mountain climbing, base jumping...the list of things we do for 'fun' which could easily kill us is nearly endless. Perhaps it is the feeling that you're just **too bubble wrapped in the real world**. Your day to day life is so controlled that you couldn't risk it if you wanted to. Your game would be the perfect escape for this, to feel in control again. **Sky diving, for example, why is it a bigger thrill than if you were inside a plane? You're just safer and in less control in a plane.** Your game has taken away these safety measures and become the skydiving of games where all others games are like watching it all from a metal box. [Answer] Some thoughts ... * Maybe the real world ... sucks. It could be some kind of dystopic future where automation has destroyed most people's jobs (see Spinrad's "Little Heroes") and there's little opportunity or hope for the populace. *Why not* check out? * Maybe the virtual world is *really fun*. You have a gorgeous girlfriend there. You're buff there. You have friends there. Your "analog life" is only there to fund your online life. You make the "Achilles' Choice" to live fast and hard, and accept the risks. * Maybe it's not just a game. You "telecommute" into the virtual office, for a company which only exists in the virtual world. Your contract does state that you have to unplug and exercise so your analog-body doesn't melt into goo. [Answer] **The game is very addictive and rewards are very high** Games are very addictive. They are often specifically designed to provide immediate gratification. Your game can be especially good at this. Considering the described level of technology, it is very much possible that the developers managed to hijack [the brain reward system](https://www.neuroscientificallychallenged.com/blog/know-your-brain-reward-system) and gameplay [stimulates an unusually high release of dopamine](https://www.helpguide.org/harvard/how-addiction-hijacks-the-brain.htm). This would result in addiction similar to sexual addiction. The game-set can also inject substances mimicking brain neurotransmitters triggering dopamine release. That would be similar to opioid drug addiction ([opioid drugs](https://www.wikiwand.com/en/Opioid) are similar to endorphins in their structure). The majority of people are very easy to hook up on something. Some people do not get addicted (even to opioids) and we do not know exactly why, but they are a minority you can disregard. So, you can just say that the game is easily available and is very addictive. Availablity is a big factor. People need a chance to put their hands on the game if you want 1/3 of the population to play it. The rewards should be also quite high. Teenagers are happy to spend their time playing. Virtual perks and rewards are gratifying enough for them. However, adults need a bit more motivation. So, the game should offer something important enough that they skip their TV session (dining out/ fishing/ whatever) and play instead. Perhaps, something like a lottery with a giant prize could work to attract new users. The initial gameplay should be easy, safe, and enjoyable. People need to invest time and effort into the game but do not feel like they are taking a risk. However, over time they become attached and their ability to assess the real risks will decline. People tend to underestimate risks that are not well-understood/defined and/or do not threaten them immediately and directly. If your game keeps people comfortable and is not perceived as threatening, people would most likely ignore the information about possible health risks in the end-game. And for some people, higher stakes will make the game even more enjoyable: The adrenalin rush! [Answer] Don't confuse sanity for behaving rationally. Sanity is defined by the norm, not what is logical or sensible. Consider that people who honestly believe they are being visited by aliens are not considered to be fully sane, because few people share that belief and there is little evidence to support it. On the other hand, billions of people believe in a supernatural, undetectable and omnipotent being who manipulates their lives and the world around them, despite there being about as much evidence as there is for the aliens. Because such a belief is fairly common, it is considered sane despite being irrational. Therefore, there is no reason why sane people would not be willing to take this kind of risk if it was a social norm to do so. You might also compare it to gun ownership. Statistically, owning a gun in many countries only increases your risk of dying. But human beings don't think like that, they assume that the statistics are skewed by people of lower ability and that if they own a gun they will not have deadly accidents, will not one day feel suicidal and when drawing on an opponent will come out on top. Another example is gambling, where statistically most people lose money and the system is usually designed to ensure that even skilled players do so, but many people think they can beat the system anyway. Similarly, many people, particularly men, would likely look at a dangerous but rewarding game and think they could do better. [Answer] the best answer is the combine of many factor, like real life suck, the game is very addictive and have high reward, etc.. However, there's another factor that i haven't seen mention here: They have nothing else to do. If you have the technology to make such game, then i think you can also creat robot and A.I that will pretty much replace human in the workforce. You will have a huge population that clueless about what to do with their life at that point, people who dont have any goal to achieve everyday, any place to go at 8 AM, any thing to do after wake up.. these people will pretty much try anything that give them a sense of meaning, and thus, flock to your suicide game.. [Answer] # All your friends are there Humans are irreversibly social creatures and absolutely terrible with calculating risk. If you give them an opportunity to easily interact with other people, in a comfortable setting, they'll do it. Social platforms accrete users over time by slowly roping in non-users. The primary draw is "I'm on this cool thing, come and see", so they sign up. Eventually, the new thing stops being cool but provides enough convenient functionality and more importantly, good memories that people stay. Facebook is like this. Twitter is like this. Eve Online is like this. World of Warcraft, to varying degrees, is like this. Every single successful social platform and MMORPG has followed this pattern. If this game was built correctly, and it sounds like it was, then will offer something for practically everyone. Escapists get to leave reality for a while. Explorers get to find new cool things. Griefers, grief people. Achievers get shiny badges. Everyone from casual gamers to the most hardcore will find their old friends, make new friends and go on adventures that aren't possible in real life. # It'll happen to someone else News sources will not fail to report deaths resulting from dying in-game. Unless these become prevalent, say you have a 30% lifetime risk of dying while in this game, few will stop playing. If death is rare enough then players will rationalize playing by saying "Oh, other people die but that won't happen to me" and keep playing. They will further rationalize, "I don't play that much" or "I don't do that kind of thing". Whether or not this actually reduces the overall risk, the rationalization will be enough to ignore the risks and keep playing. Also, these deaths aren't gruesome, blood spattered murders. They're more akin to strokes. If they were gruesome deaths then the graphic nature might be enough to deter players. [Answer] **Inception theory** This issue is slightly addressed in the movie Inception. People come together to live in the dream world. As time is slower in the virtual world than actual world they can live longer in the virtual world even if they live shorter in the actual world. One conversation in movie goes like this > > -They come here everyday to sleep? > > > -No. They come to be woken up.The dream has become their reality.Who are you to say otherwise, huh? > > > So, people have accepted the virtuality as the reality. And go to actual work just for the sake of earning some money which is needed for sustaining their life. People have already given up their ambitions in real world as it would be comparatively difficult to achieve. Wherein, inside the game you can choose your avatar, their abilities, looks and life paths. You ask why? Why not? **Improved healthcare system** With improvement in the cybernetics scientists are able to find and isolate the cells causing cancer and heart failures. So average life expectancy of people is increased. Because of that population of earth is also increased and same is with competition in jobs. So rather than working through the tough competition against another human and robots people have started to engage themselves in the game. Now people even have started to get bored of this long life as they don't have many things to do. So they have accepted approach of YOLO (You only live once) in their life and live life to the extreme (even if it is in virtual world) they don't mind if their life is shortened by this. You ask why? YOLO. [Answer] **A real life example:** If you are older, you may remember the 70s. During this time TV in Europe was sponsored by the country, advertisement *during* movies and shows **was completely unknown**. Also game shows in general were hold to a highly ethical standard, just insulting or ridiculing participants was considered low and triggered enraged protests. I can also use always safely "he" because the idea that a woman would do this was unimaginable (you see the reason below). In this era Tom Toelle, a German filmmaker, made the ["Das Millionenspiel"](https://en.wikipedia.org/wiki/Das_Millionenspiel). [The movie can be watched here](https://www.youtube.com/watch?v=M4GeJHFElE0). It was meant as a scathing remark for the direction TV may be going. It was presented as a pseudo-show where a participant is hunted by a team of killers for one week. If he survives, he gets 1 Million D-Mark (Which is enough for a lifetime of safety in this time). If he loses, he loses his life. His killers get for every hunted down member a bounty, so they have an good incentive to find and kill him. To prevent the candidates from simply hiding in a lone spot, the participant must occur at control points at a given time if he does not want to lose his prize. The killer team are allowed to get hints from persons who know the location and do not want that the candidate succeed from pure spite. Also the moderator and all members behind the scenes are shown to be repugnant and remorseless assholes and are cheating/manipulating the hell out of the game. If you find this story remarkably close to ["The Prize of Peril" by Robert Sheckley](https://en.wikipedia.org/wiki/The_Prize_of_Peril), this is the reason the film was shown only one time because of copyright issues. For maximum effect the film was shown without warning, used a well-known moderator (Dieter Thomas Heck) during the time and interspersed the film with mock-documentaries and advertisements. The team was quite shocked that they did not only receive the storm of protest (which they anticipated and were glad to receive), **but also serious applications of becoming the participant or the hunters(!!)**. So, you do not need to fear that is unrealistic. People are prone to underestimate or even neglect personal risk, Russian men for example have a shortened lifetime of 14 (!) years compared to women because of all the unhealthy lifestyle (smoking, excessive drinking, risk activities). Even I don't have a car, but drive a motorcycle knowing well that my risk of dying in a crash increased approximately tenfold. [Answer] There is a real strong tendency for businesses to encourage repeat business and regular consumer activity even to the point of encouraging addiction. And a lot of science fiction has already been written about neuro-electric addiction or "wire-heads". If the neural interfaces to these games jolts the pleasure centers of the brain, then it will be tough for people not to keep coming back for more. B F Skinners rats were well documented to keep pushing the pleasure lever, while ignoring the food lever, until they starved to death. A lesser stimulus might just keep people coming back for more, whenever they can. [Answer] ## The game is still safer than real life. Background risk: We all experience a few micromorts(1 in 1000000 chance of death) of risk per day, if 2 billion people play the game for a day and 1000 players randomly die in the game and then die in real life the game remains **safer than real life**. Going Scuba diving costs 5 micromorts per dive. Base-jumping costs 430 micromorts per jump. Traveling 6 miles by motorbike or 10 miles by bicycle costs about 1 micromort. Those same people would have been out crossing roads, driving cars drinking real wine if they'd not been playing that day. The game is good, the game is very good and most players in the game don't spend their time fighting dragons, they spend their time in virtual mansions and playing virtual golf or crafting virtual goods. Even if you do die in the game it's not a certainty you'll die in real life, you might just wake up a few days later feeling crap. The people who actually go out and seek out dragons to slay are the people who'd be base-jumping in real life if they weren't playing the game. And they're still safer doing their thrill-seeking in the game. So even though every day hundreds or even thousands of people die playing the game, they're still safer than non players on those days. [Answer] Lio has mentioned the extremes but the average person doesn't throw themselves out of a plane or climb Everest. There is a classification of risky activities that covers things "normal" people do. ### Assumed risk activities These are basic day to day activities to many people, simple common things with no great aura of danger around them. Whether for fun, riding horses, swimming, indoor climbing, sailing, skiing, kayaking. Work related, climbing ladders, trees, buildings, and using heavy machinery and power tools. Or just the daily commute, cycling, riding a motorbike. We call them assumed risk because they seem routine but any of them *might* kill you on any given day, they could easily leave you with serious injuries if you make a mistake. Yet we (those of us who do such things) don't consider them particularly risky when due precautions are taken, and occasionally have to be reminded that these activities are actually dangerous. **Whether the reason is fun, convenience, efficiency or otherwise, humans take risks.** Perhaps the risk and reward are required to be equivalent, but consider the risk of death on the road compared to the benefit of spending an hour less commuting, yet this is the game I play every day. [Answer] Your game is not so different from what we already have in our life here: alcohol, cigarettes, driving fast cars, doing bungee jumping are just some of the activities which are known to increase the chances of death for the person engaged in them, yet people keep doing them! The answer to your question is pretty straightforward: adrenaline and/or endorphins. Once they get in your blood stream, you feel damn good. And you can't stop with them. [Answer] I would imagine a feasible answer could be based on the perceived risk, not the true risk of playing the game. The more you play the higher the chance of death. Ah ha, I say to my parents that warn me away from these games, I will only play one day a week. Perfectly safe. Risk of death is probably 1 in 10,000 safer than driving to work, playing a contact sport etc. No problem whatsoever. Ok so I'll play 2 days this week because I want to help John from work finish that quest. Really, what's one extra day going to do. Sure I said this last week because I wanted to finish levelling toolsmithing, but so what. Look I still have a solid 2 days a week where I don't even log onto the game. That's more than enough time for my brain to cool off or whatever, the adverts about it being dangerous are clearly way over the top, everyone else who does it is ok. I'm fine. My name is Thargold the Grey, I sleep in the **physical** realm to make sure my body and mind are sound, but that world doesn't matter to me any more. I spend every waking moment in the kingdom of good, I'm so powerful here the heathens of evil couldn't kill me even if they wanted to. There's literally no risk at all. Does anyone hear the sound of an army marching in the distance...? [Answer] **TL;DR**I'd recommend reading up on addiction and PTSD. Also consider how the Game itself will be able to meet the needs of many different kinds of players, and how in doing so would make them dependent on it. Also look into the current day anti-gaming hysteria, as much of your own story could be a direct contrast to it. Also, think Facebook. *Yeah, sorry. This is longer than I meant it to be.* **Intro:** We could already be in this world, depending on who you ask. Gaming is commonly pointed to as being the cause of many of the modern social ills, from the ["obesity epidemic"](http://www.post-gazette.com/news/health/2012/11/12/TV-video-games-linked-to-obesity/stories/201211120171) in modern countries to [social anxiety, depression, suicide](https://www.technollama.co.uk/does-playing-games-lead-to-depression-and-suicide), or even [violence](http://www.techaddiction.ca/violence-in-video-games.html) which could lead to an increase in [murder rates.](https://www.psychologytoday.com/blog/slightly-blighty/201508/do-violent-video-games-contribute-murder) Let's assume for the moment that it's true, what would make a gamer *want* to be a gamer? Addiction is the commonly-named devil. In today's world, I think it's the only one ever given. It's a good descriptor as it is frequently used by gamers to describe videogames (eg, [current-gen MOBA addiction](http://www.mmogames.com/gamearticles/moba-monday-mobas-addictive/)) while being vague enough to allow one to envision it into being as threatening as an unhealthy love of chocolate or as benign as daily meth use. It's also a great way to demonize something without bothering to try and understand what drives the addiction to begin with. So why would a gamer choose to play a game that can kill them? I could write a book on just this, but I'll cover what I consider hasn't been said yet. **Minimizing Cons:** Many intelligent people will accept more danger than they realize, either [through belief](https://www.psychologytoday.com/blog/science-choice/201504/what-is-confirmation-bias), [relying on bad information](https://www.business2community.com/big-data/bad-data-side-effects-01164045#pUuYxTQdIextzopI.97), or due to our in-built preference for [early gain over far-off consequences](https://www.nirandfar.com/2017/08/hyperbolic-discounting-why-you-make-terrible-life-choices.html). I'll give a few examples below. *Perceived Danger is less than Actual Danger* - The world is a messy place, filled with messy information. Some information is more correct, sure, but it's hard to say what is true. I see no reason to simplify this in a Sci-Fi world. *The actual danger could be unknown*, leaving many people guessing at what the cause of these new comas are. For example: the comas are linked to both Game play as well as energy drink consumption, is this an odd correlation or could it be the cause? Well, my friend has over 10,000 hours of Game play and hasn't experienced any problems, so it can't be the Game. Yo, did you hear that the pro player who live-stream comaed just broke up with his girlfriend an hour before? Just don't play on a bad day man. Wireless signal density in the lower metropolitan area may be linked to genetic damage and may be an indicator for those at risk. It's a calcium deficiency. WHAT ABOUT THE VACCINES?!? Truth be told, having a new epidemic creates a new marketable need. Think organic food and homeopathy; new products will spring up to offer solutions and answers on what the new problem might be. Some may be honest mistakes based on [anecdotal evidence](http://www.peggysuesurvived.com/alternative-cancer-therapies.html) and may even offer some benefits, while others will [outright lie](https://sciencebasedmedicine.org/ph-miracle-living-dr-robert-o-young-finally-arrested-but-will-it-stop-him/) or [use it to drive their own agenda](https://www.xojane.com/it-happened-to-me/narcanon-scientology). As long as it doesn't immediately threaten all living humans, society will be happy to argue, sensationalize, and make money off of it. No rush, especially if altering the Game would have a large impact on society. And it would. However there's also the possibility in which *the actual danger is known but hidden*, which leads us down the rabbit-hole. If the Game company has a good media and marketing group, they can [coerce public opinion](http://sethgodin.typepad.com/seths_blog/2006/04/ode_how_to_tell.html). Or maybe they can make the believers out to be the crazy ones, ostracizing the truth. Eg [the conspiracy is the cover up](https://skeptoid.com/episodes/4373). *Actual Danger also exists in the virtual tech* - It could be that the tech the new Internet runs on itself may cause the problem, the Game just increases the risk. This is like the difference between smoking a pack a day and a pack and a half a day. It's there, but if you know about the risks it may not seem as much of a problem. **The Benefits:** Due to having a third of the population playing the Game, it will be a primary force in the story's culture, especially if that third was isolated in a specific area (say, the developed world). As the *Game is Culture*, many will play it just to be part of the in crowd. The Game's *influence in Economy* will be large, and could be similar to how [Entropia Universe](https://www.entropiauniverse.com/) combines real money with virtual property, [Second Life](http://secondlife.com/) focuses on social groups and custom content, or be based on making transferable wealth through [inter-game cryptocurrencies](https://enjincoin.io/). Likewise checking the [current top PC games](https://newzoo.com/insights/rankings/top-20-core-pc-games/) shows that games focusing on quick slices of action (or rounds), creativity and world-building seem the most popular, especially when mechanics are fairly simple to start. However, games like [Eve Online](https://www.youtube.com/watch?v=KZQ4ejFq7BY) show that adding optional depth can lead to die-hard fans. All of this is based on the merits and technology behind the game, little to do with any dependency. Instead it fulfills the needs of the player to create, be noticed, hone their technique, and to encounter novel experiences. Basically fits with the [Bartle Taxonomy of Player Types](https://en.wikipedia.org/wiki/Bartle_taxonomy_of_player_types). To bring in the population and keep them playing, all you need is intertia and a low barrier to entry. Imagine if all you had to do to view Facebook was close your eyes. If the Game is tightly integrated with the virtual world, so that falling into it is as easy as changing a filter on your virtual HUD (think Augmented Virtuality sitting on top of plain old Augmented Reality), then habit will take players where they need to go. And the more virtual reality becomes the norm, the less likely you'd have to do real things, like drive to work. Important to note is that even in a relatively prosperous and safe nation, it may still be safer to go into a game that may kill you. Not only is it easier to go get drunk at a virtual pub than it is to go to a real life club, worry about fights, being hit by cars, passing out in the cold, muggings, ending up stranded with no cash, etc. But the likelihood of dying is probably low in many areas. And even if you die, so what you'll probably be fine in the morning. As for pain and PTSD; well we already live in a world where people are starting to feel [disconnected](https://www.forbes.com/sites/carolinebeaton/2017/02/09/why-millennials-are-lonely/#5fb7b5377c35) in real life, while gaming and online relationships can create [long-term friendships](http://www.theesa.com/article/video-games-help-make-lifelong-friendships/). Deep friendships are also built on [shared painful experiences](https://www.psychologicalscience.org/news/releases/shared-pain-brings-people-together.html), such as [war](http://observers.france24.com/en/20121018-videos-usa-army-soldiers-war-afghanistan-tread-fine-line-therapy-voyeurism). As the disconnect with the real world grows, virtual pain (not "real" but real enough) could make the virtual seem more like reality, while giving you a chance to become something else and find others that [can actually know you](https://en.wikipedia.org/wiki/Honne_and_tatemae). [Answer] If the risk of dying ingame is not as high as in Dark Souls and not loads of people you knew would die everyday, people would play it. Why wouldn't they? If the chance of dying is lower than the chance of dying from lung cancer from smoking for 20 years people will definitely do it, especially if it is not always the case you die in real life when you die ingame. People will think "It won't hit me." as they do with cigarettes. To summarize with everything other people said: * Fun to play * maybe addictive * adrenalin rush (a lot of people are into that. e.g. Bungee Jumping.) * escape from reality * feeling of accomplishment as you might be more successful in the ingame social world than your real life one * relatively low risk of dying, even if just perceived as low [Answer] The biggest problem with [Lio Elbammalf's answer](https://worldbuilding.stackexchange.com/a/97333/21658) is that drug users and adrenaline junkies are still a rather small group of people. While I am sure a lot of people drive their car too fast or have smoked a joint at least once in their life, I highly doubt a third of the population would go to such extremes. As such, we need more ways to achieve what we want. **Provide Extrernal Incentives** One of the biggest influences on our behaviour is the way our society works is what our peers think about us. Perhaps in your world a high level or otherwise powerful character is considered a much of a feat as an expensive car and a good job is in our real word. You could even go a step further of actively discriminating against people who don't play. You want your kid to go to a good school? Well, you better have a good enough reputation in the game. Even though people who don't play the game are the majority, the real wealth and power are among the players, and people *know* that! Make sure that the destinction between players and non-players is as unfair as possible, so that even "sane" people who would know not to risk their life would feel tempted. [Answer] As alluded too in other examples: **Addiction, adrenaline, community** **TL;DR:** There is a much advertised "opioid epidemic" going on in the US right now. What's causing it? People get prescribed pills for pain/anxiety/etc... then get hooked. Then progressively get worse... Add to that a neural enhanced adrenaline/dopamine enhanced experience... And then include your online "family"... **Addiction** People are, in vast numbers, getting addicted to opiods. What starts out as a prescription to alleviate pain - bad back, accident, torn muscles, etc... turn into something that can't be given up easily. What would start this? Much like prescription drugs are "gateway" drugs into other stuff... Farmville turns into clash of clans... Make these online games start out simple and "everyone uses this to relax after a long day". First you answer a few questions on Stack Overflow... next thing you know you're spending all day answering questions, get demoted at work, lose your job and yet you can't stop answering questions! WHY SE WHY!!! These addictions start out as "safe" doctor prescribed answers to pain, anxiety, stress, issues like bi-polar, etc... **Adrenaline** While it doesn't have to be exactly adrenaline... this game - when added to being "prescribed" as a relaxant - affects your brain. Life is boring. Works is boring. This game? OMG!!! exciting! Online gaming has some connections: At first, the "safe" n00bie levels are exciting. Exploring. Learning. Getting some levels. But at some point... it gets "normal". What's left? Higher level areas. PVP optional areas. PVP ONLY areas. Hardmode versions. Make a game like World of Warcraft or Eve that starts out with "safe n00b zones"... which progressively gets more complicated, more expansive and more... risky. Plug the game directly into the nervous system - Matrix Style - and you've got an adrenaline, dopamine delivery system that people... just... can't... put... down. **Community** Now you've got an addictive game... how do you make sure it STAYS addictive? Why has WoW been going strong as a leader for 15 years now? while other games have fallen to the wayside like abandoned dung heaps in the history bin? Community. "Online Family". I, personally, met my fiance on WoW. We've got life long friends through the game. People we've met and some we've never met. People that have been more influential in our lives than actual family. You go through the n00b levels together. Explore the expansions. Live through massive boss fights and overcome obstacles. Together. We are talking some Combat Unit level cohesion and comradery. Life long bonds that can't be broke easily. **again**... pair these three things together to make something addictive, exciting and an important part of one's life. [Answer] Maybe the people accept that death is inevitable and feel that death and risk of death should be faced with acceptance not with rejection? Instead of human life being sacred being interpreted as "stay alive and keep others alive", it would be interpreted as living a good life that ends in a good death. Instead of focussing on the length of life, they'd focus on the quality of life. Improved medical technology could mean people no longer worry about dying too soon. They would instead worry about living too long. Outstaying their welcome and staying alive beyond their own time. The music has become just noise with infantile lyrics about sex sung by someone who doesn't know how to sing. Politics is all about who shouts lies and insults loudest. The society accepts that death is a personal matter and that society has no right to stop people from making informed choices about their own life and death. Euthanasia and assisted suicide would presumably also be legal. This is actually rational and sane viewpoint. The obstacles are on the part of religious dogma. So you'd have to change religion from what it is currently, probably. You can do this indirectly by increasing the secularization and liberalization of society so that religion becomes more marginalized. Or you can directly alter the religions. The religions might simply have reconsidered what sanctity of life means. Or pre-determinism might have become dominant and the religious might simply believe that whether you die or not does not **really** depend on this game. It is a fixed part of Gods plan. So the one third playing the game would simply be the people who are **ready** to die and have decided to die **epic**, fighting monsters in a vibrant world of wonder as cool and powerful heroes. Sure beats jumping off a balcony or overdosing on pills. Probably beats growing old and infirm and passively waiting for death to finally come too. As long as it is your own choice this is entirely rational and even good choice. Your family and friends might be upset about you wanting to leave them behind, but there would be no real reason for society or law to object, if the religious issue has been dealt with. I think that in a society where death is accepted as inevitable and people want to end their lives with a good death, one third of population being ready to die is plausible, if the world is otherwise either safe or very stressful. It could of course be both. Some dystopias in fiction definitely combine "death is the only escape" with being good at keeping people alive. Additionally, if good death if not only acceptable, but desired, then it would also be acceptable for people to risk dying even before they are particularly ready to die. After all, if death is an accepted part of life, then risk of death should also be accepted as natural part of life. Risk of death in the game would be accepted as necessary for making it feel real. Indeed, the game would probably default to suppressing the knowledge that character death does not always result in player death while playing. Players simply could not remember that while playing. Instead they would play in certain knowledge that "death means death". [Answer] ## Time to learn something My whole premise revolves around the game speed. While these games would offer completely unique experiences we can integrate them into the real world fairly easily. This is a game/simulation so when people log in time can move at a different speed. This gives the player the feeling of a longer life and can learn more things. Whether what they learn are "soft skills" (how to manage/organize group events), a new language (I use Spanish more online than in my personal life), or facts (do you remember runescape willow trees?). [](https://i.stack.imgur.com/XmHvF.png) In a normal lifetime these skills take awhile to develop. In a simulation with accelerated speed (2x speed? 10x speed?) people who want to learn these skills put in a fraction of the amount of time. This would be especially important for slow developing adults (some forms of autism need more time to learn soft skills) or business skills like managing. ## Services A number of services are time intensive, being able to manipulate time would be a very nice ability to have for things like Therapy. Therapy costs as much as it does right now due to high demand and limited time in the day. If we make a 10x simulation a therapist can spend 6 real minutes with someone for 60 minutes of therapy. Other services would be things like reading. Ever want to read that whole book in a single night so you don't have to for a class/course? a 10x simulation would take care of that in no time. --- TLDR: given we can change the cycle time and the human brain can keep up with it, anyone who wants to learn anything would choose to log in and learn in accelerated speed. [Answer] "should your avatar experience death in the game". There it is. Perhaps most of the people playing this game do it in a way that's unlikely to actually get them killed in-game. Sure, the crazy people that head into dungeons are at risk, but there are thrill-seekers everywhere. Maybe there are a lot of people who enjoy playing the crafter side of the game, playing as merchants and whatnot. Perhaps there are techniques that people can use to make it really unlikely that they will die - hitting the logout button or the escape scroll when things get risky. The real question is, why would they build a game like this? What's the point? For the game designers, it should be *easy* to build a game where instead of experiencing "dying" (with the associated possibility of traumatic damage to the player), you experience "teleported to purgatory" (with no such possibility). It should be trivial to identify the sorts of effects that can bring about player death, and simply edit them out of the code. Why don't they do this? [Answer] Don't think about gaming, think about gambling. Gambling is pretty common, and lots of people do it in some form. They (consciously or otherwise) take a risk. Some do it because of the reward, but actually mostly it's just because risk taking is a rush in it's own right. I played EVE for a long time - it's a game where there's a lot of risk. Fully outfitted ships are a significant amount of in-game currency, and a lot of effort to replace. But fitting 'top tier' gives you a significant edge in combat. So people do it anyway, and there's a really huge adrenaline rush off victory - of facing that fear you're going to lose, and triumphing. And that rush correlates with how much you've got on the line - nothing really focuses your mind like knowing you're commanding a squadron of other players, and all of them have worked hard to bring 'good quality' ships to the fight. And if you screw up, and it's a total wipe - then you're talking hundreds of man hours of 'work' to get back to where you were. But you take that fleet into combat, give your opponents a pasting - and blow up *their* stuff - and you walk away exultant. The same rationale applies to people who play games in 'hardcore' mode - the ones where there's no savegames or rollbacks, and losing a character is 'game over'. It's more exciting and 'real' because there's a 'real loss'. So I can well imagine how that might extend to voluntary risk taking of potentially fatal risks - imagine being able to overdrive your character in game. When 'overdriving' you perform *much* better, so you're way less likely to lose... but if you do lose, then you're at risk of death. People *would* do that. They'd win, based on taking a risk; getting a reward (being able to dominate the game). And that goes double if there's some positive incentive to 'maintaining position' - in EVE, holding star systems directly correlates to getting good loot/items, and thus allows you to rebuild your 'high risk' stake more easily. (It's still effort, but it's not 10x the effort). Of course, you could make it 'real world' profitable too, and have in game currency possible to 'cash out' too. [Answer] Expanding on Daniels answer: Smoking is a very close equivalent to your game. It gives momentary satisfaction, and has little immediate side-effects, but the longer you do it the more serious your health risk becomes and thousands of people literally die from it every year. And yet, most smokers don't quit, and most of those who try to quit, fail. The simple answer is: Addiction. Your game is simply addictive. Games can be addictive, and something that directly interfaces with your brain has a shortcut - just have level ups directly trigger the pleasure/reward center in the brain and boom, that's exactly what the most addictive drugs are doing. Even though everyone knows the health dangers of smoking, one of the curious abilities our brain has is called *rationalisation* -- basically, your monkey brain makes a decision and then your "smart" brain comes up with justifications. You fell in love with that women because she's witty and beautiful, not because your hormones decided it was time to get down to business. You hate that guy because he is a corrupt criminal, not because he intimidates you and triggers your flight response. And smoking is bad the doctors say, but what do they know and your aunt smoked for all her life and she died 98 years old. So the game? Yeah, there are rumours of people dying, but firstly they are probably exaggerated, and secondly it only affects weak people. And also I can stop whenever I want, I just like it. Also I read on the Internet that you feel a tingling sensation behind your eyes when it's becoming too much, so when that happens, I'll just quit... [Answer] # Power. Fame. Money. Think about this: today, good videogame players are stars, earn a lot of money in sponsorships, play sold-out tournaments, have millions of fans. They even call games *[eSports](https://en.wikipedia.org/wiki/ESports)*! This is happening now, so there is no need to go very far in the future. [](https://i.stack.imgur.com/vNOQY.jpg) Also, **without the intention of entering politics, let me ask you a question:** why would people invade a country so that other people who stay at home can obtain the assets of the invaded country (oil, mining, whatever)? ? It is very likely that you will be killed or seriously injured, and you will not gain anything. Even returning home alive could be a horrible experience due to PTSD and [survivor's guilt](https://en.wikipedia.org/wiki/Survivor_guilt). **And again: this has been happening for centuries, nothing new.** **Do you want to talk about health?** It has been proven that playing games has some benefits, but the disadvantages are really huge for veteran players and, in general, for people who live online: the most common are joint pain, obesity, epilepsy and acceleration of vision loss. From the psychological side: alienation, confusion, loss of contact with reality and [in some extreme cases, suicides](http://www.dailymail.co.uk/news/article-4264838/Teenagers-committing-suicide-social-media-GAME.html) **Economic Angle?** People already spend thousands of dollars on games that are more limited than those that cost 50-60 dollars. I mean THOUSANDS. People who spend 10, 20 or 30K are not the norm, but they do exist. I mean ... university education, a home, a business, a future wasted... What do you think will happen to some of them if they realize what they did? Personally, I know a woman under heavy medication after she discovered that her son spent more than $3000 on games stealing their credit cards. A well-known case is [**Clash Royale**](https://clashroyale.com/): they are in a nothing disguised path to take the players to a level of abuse like never before seen. They even have their so-called "reactions" used to mock and abuse other players, and "offers" of 20 or 30 dollars for POSSIBILITIES (nothing real, only the possibility of achieving something slightly better). And Clash Royale has more than 100 million users completely willing to be abused. This is just an example of the level of abuse any regular Joe is willing to take for just a few minutes of fun. Remember how outrageous [The Truman Show](https://en.wikipedia.org/wiki/The_Truman_Show) was? Well... same thing was done thousands of times already and just became old. Bottom line is: most people don't care about the bad sides, [immersion is escaping](https://www.theatlantic.com/health/archive/2015/02/the-good-and-the-bad-of-escaping-to-virtual-reality/385134/), that's all it is. And you never die in virtual life. # In short... So, question is... **what would be so complex in your scenario?** It sounds more like more of the same. You can add some huge benefit as well and the reasoning would be more like "why NOT do it?": you have the **chances of benefits, entertainment, escaping from real life, a sense of community and belonging... and nobody will shoot you with a rocket launcher** [Answer] **1. Early adaptation** Maybe the entry-level age is very low. I could imagine that once this technology exists, schools might start using it for educational purposes: better to have a chemistry experiment explode in your child's face in the virtual reality than in the real world. Also, history would suddenly become interactive and more interesting, math equations and geometry could be represented in 3D, etc. the applications are limitless. Maybe this game is the next logical step. **2. Not much else to do** If this is the world of our future, maybe climate change and pollution have progressed to the level where it would be no longer healthy to spend our free time outdoors, and this virtual reality would provide the only way to "connect with nature" the way it used to be. **3. It may be lucrative** Very good players may get revenue from streaming their game - and those who "watch" not only watch it but experience it almost as if they were playing it. There could be other monetary possibilities in such a game, like the aforementioned virtual gambling establishments. [Answer] > > Yet despite this, over 1/3 of the world population spends one day a week playing the game. 1/5 of the population spends 3 days a week playing. > > > Actually, I would like to suggest that this ratio should probably be amended a bit. Unless the log-in log-out process to the VR environment is really cumbersome, or that the equipment is expensive and is usually shared, the figure seems to imply relatively tiny amount of users was playing it everyday, despite being insanely popular. In real world, over 1/3 population spend one day a week playing the game already mean almost entire developed world and significant amount of developing world users are using the VR product, yet for something this much popular, less than half of those people use it every days, it seems rather unlikely. As for why people do it despite the risk, just look at why so many people in the world are smoking and drinking alcohols which obviously increase death risk. For a VR world that would be this popular, it probably also have some attractive elements that would attract people into playing it. And then again, from experiences like smoking and drinking, the ratio of more active users or daily active user given in the question seems dis-proportionally low. [Answer] Due to governmental regulation of population numbers, children are no longer naturally conceived/raised, but rather cultivated and developed institutionally. Birth control is implanted at birth and gametes are harvested as part of regular mandatory care to maintain a controlled population level. Since people no longer raise their own children, one of the major incentives for reduced risk-taking (the strong innate desire to take care of your children, even at the expense of your own enjoyment) is gone. Further, some of the more cynical folks quietly speculate that the Genomic Planning Commission actually favors the genes for addiction, thrill-seeking and risk-taking behavior, both to provide another outlet for controlling population levels and to help keep people distracted and docile in the 'real world', to reduce peace-keeping costs. One wild conspiracy theory even suggests that the increased difficulty spike of the recent expansion pack was actually designed that way as a response to the recent inadvertent over-production event. [Answer] I can easily see a world where most of life's hard issues are taken care of. There's very little toil, everything is perfectly well-balanced, the world is tame and sterile... and hugely stifling. People go to these inner-dimensions to find a world with untamed lands waiting to be conquered. They go there to discover and claim something new. They go to feel involved and alive, because the world they leave behind is all so perfectly crafted that it's become dull. The real world's civilization has an underlying affliction. Crime is gone, conflict is gone, but so has compassion, so has greatness. All answers have been solved, there is no more mystery, there is no more drive, there is only apathy and a slow lingering death without the ability to leave even a single mark on this "perfect" world. [Answer] This isn't even hypothetical. People *are* getting killed daily in traffic as a consequence of immersing themselves in their smartphone. Why would they do that? The risk is well-known. The reward is small. "It would not happen to me" is the main reason. Denial. Denial actually drives so much of human behavior that it isn't funny. I don't see that you'd need any special explanation for your scenario. It certainly does not make less sense than a whole lot of things happening all the time. [Answer] ### Because the risk is very small, and on top of the incredible adventures the game offers, there is an incredible reward to claim. Events that are very unlikely almost always happen to other people: why would it happen to you if you're careful? Besides, the game is very fun, and you have a chance of getting something that will change your life : winning the game and making your character virtually un-killable, become very wealthy, something like that. For some, it's a game. For others, it's a necessity to win because of the reward. [Answer] Playing causes adiction, like nicotine. The game owners and the goverment know it, but the economic benefits are too great to simply lose them. People think that they really like to play, but in reality they suffer when they are not playing. ]

[Question] [ **Can there be a planet that space missions can take off from, but never land back?** It is easy to imagine that thicker atmosphere, large amounts of space debris or higher gravity could entirely stop space missions. But I'm thinking of a case where space missions could be developed, but by necessity they would always have to be one way trips. Constraints: * Planet should be able to support life that is similar to Earth. * Locally evolved civilization should be able to construct rockets that can take off from the planet with enough payload to carry living beings and life support. * It should be significantly more difficult to land back - hundreds of years difference in technological level needed. * Some form of communication (such as radio) should be possible between surface and space. [Answer] ## It's suffering from massive Kessler Syndrome The problem with this planet is, that there are only two very small zones along the poles where you don't get hit by anything when you launch. You need to launch pretty straight up above the debris cloud, and only then burn sideways. The cost of launching on this absolutely worst of all paths is super high, but the only way to even get into space without a collision. However, trying to return means you have a much flatter trajectory and need to pass through the zone of debris - and that means you are guaranteed to get hit due to the density of debris. [Answer] ## Ancient planetary defense system. The planet is in a star system with lots of asteroids. Those usually would make the planet uninhabitable. But millions of years ago the planet was colonized by a species of precursor aliens. The aliens installed a fully automatic planetary defense system which destroys anything on a trajectory heading for the surface. Mostly to protect it from asteroid impacts, but probably also to defend the planet against other spacefaring civilizations. This made the planet habitable and allowed the aliens to terraform the planet and create an ecosystem. However, the alien civilization isn't there anymore. Circumstances that are not relevant here either killed them or caused them to abandon the planet. But although the precursor aliens are gone, they left the stable ecosystem and the automated defense system behind. Over the past millions of years, intelligent life evolved, created a civilization and discovered spaceflight. After all that time, the defense system is still working and protects them from asteroid impacts (and occasional visitors from other spacefaring alien species). Unfortunately the system doesn't recognize the primitive vessels launched from the planet as friendly. It lets them launch, but it doesn't let them get back down. The ancient aliens might certainly have known a way to tell the system to not shoot down their own crafts, but that knowledge was lost to time. So anything that tries to return from orbit gets shot down by the defense system. Why don't the current inhabitants try to get the defense system under their own control? The answer is that they can't. Their technological level is still far too low to understand how the system actually works. Perhaps they could destroy the system or parts of it permanently. But then they would also compromise their defense against asteroids and risk getting wiped out by the next bigger rock that comes around. So until they have the technology to provide asteroid defense themselves, that's not an option. The precursor artifacts could also be of cultural or religious significance for their society, making it politically impossible to get rid of them. They are, after all, *literally* a gift from their creators that protects them from harm. That's far more substantial than what other religions have to work with. [Answer] ## The planet has no atmosphere. In a pure oxygen environment, humans can survive pressures [as low as ~2PSI](https://biology.stackexchange.com/a/40505). The people on your planet can survive in underground pockets of gas, like we have [here on earth](https://en.wikipedia.org/wiki/National_Helium_Reserve). Unfortunately this has big ramifications for your spaceships. We use the atmosphere to our advantage during re-entry. Spaceships have massive horizontal velocities during orbit, something on the order of 8 km/s, and *all* of that velocity has to be removed before landing. Current spacecraft always use drag in the upper atmosphere to slow them down; and I'm not talking about parachutes. Simply ramming into the atmosphere generates tons of heat, enough to burn up most meteors. That's all the kinetic energy being converted into heat! Without the atmosphere, though, the only way to lose horizontal velocities is to turn on those rocket engines again and propel yourself in the opposite direction. This takes nearly as much rocket fuel as it did to get into orbit! Our best existing spaceships had a payload capacity that's [about 6%](https://en.wikipedia.org/wiki/Payload_fraction#Examples) of the total weight of the spacecraft. The fuel can easily be [over 80%](https://en.wikipedia.org/wiki/Propellant_mass_fraction#Significance) of the mass. So while obtaining orbit on your planet will be comparable to what we have today (easier in fact, because you don't have pesky air resistance or anything to deal with), landing would be pretty much impossible with anything conceivable made from today's technology. Due to the [tyranny of the rocket equation](https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation#Applicability), you need more rocket fuel to launch your fuel for landing (and you need to bring more fuel for that fuel, and so on, and so on), you would need incredibly efficient rocket engines that can take far more than twice as much fuel to orbit as needed while maintaining a reasonable payload fraction. Maybe some futuristic [high-power ion-engines](https://en.wikipedia.org/wiki/NEXT_(ion_thruster)). [Answer] The atmosphere contains a chemical that eats away the outer layers of the rockets upon reentry, when atmospheric compression turns the gas into a plasma. The problem doesn't happen on lift off because the velocity are lower, and shielding the rocket to withstand the reentry can only be done with materials which make the rocket to heavy to reach space, until a few hundred years of material science development find the compound which is both light and sturdy for that application. [Answer] Other than an *alien ex machina* type of answer, like [Philipp](https://worldbuilding.stackexchange.com/a/237733) answered, I can't think of any pure astrophysical reasons. However, there there could be other reasons preventing them from returning. **Contagion Reason** For the first 3 successful missions to the moon, astronauts had to quarantine for [21 days](https://en.wikipedia.org/wiki/Mobile_quarantine_facility). After Apollo 14, NASA realised that there was no reason to quarantine. But what if there was a reason, for example, near your planet there is space dust that is so harmful, that the worlds governments forbid any return missions? Then astronauts who leave, can never return. There is no reason to worry about the poisonous space dust naturally entering Earth, it gets neutralised when it burn and breaks up during entry. But that process would kill all of the astronauts on board, if a spaceship tried that. Nowadays, with all of our modern medicine, there are (typically island) countries that have no rabies. In order to keep it that way, if you want to bring your dog with you, [some places](https://petraveller.com.au/blog/quarantine-rules-for-international-pet-travel-to-switzerland) require up to 6 months of quarantine. If whatever space contagion could only be discovered by dissecting the dead body, then why would anyone want to return? They would have to be killed and examined right away. **Preparing the body for space is a one way process** [Liquid breathing](https://en.wikipedia.org/wiki/Liquid_breathing) is a process that involves filling the lung with a liquid that has a lot of oxygen inside. Surprisingly, mammals can actually survive using this. There are many scientifically, militarily, and medically ways that liquid breathing would be beneficial. But it doesn't exists outside of laboratory experiments. That is because after the lungs are filled with the liquid, it can't be reliably dried to be able to breath air afterwards. You can bet there is lots of money up for the grabs, for whoever can develop a way for liquid breathing to be viable. Yet with today's technology, that doesn't exist. What if going to space involved a one way body transformation? Then the moment you return, you would die. Maybe there is a lot of radiation, and you can do some skin transformation to survive that radiation. But then when you return, and there is not so much surrounding radiation, you would die of reverse- radiation poisoning. Or maybe when entering space and you experience 0 gravity, your bones get extremely fragile. In 0G space that is not a problem, but the moment you return you would be crushed under your own weight and die. [Answer] **This is a LOT harder than you might think** I was having fun with the idea of a naturally combustible gas, maybe methane, occurring in low enough quantities in the atmosphere to allow the evolution of life but high enough quantities that, during re-entry, it would ignite. Clever technology (like really long bell housings) could conceivable allow for thrust while allowing the exhaust to cool so the atmosphere doesn't ignite on launch. But the lengthy re-entry process just dooms the planet. Then I read @Rafael's answer (which I upvoted) and realized that the problem is easily, if not cheaply, circumvented. Just slow down, ease through the atmospheric boundary, and pop chutes. **The only idea I can think of comes from an episode of Star Trek Voyager** The episode in question is "[Blink of an Eye](https://en.wikipedia.org/wiki/Blink_of_an_Eye_(Star_Trek:_Voyager))." The gist of the episode is this: something is causing a time dilation field between the planet and the ship in orbit. Hours on *Voyager* are centuries on the planet. The planet evolves civilization from primitive humanoids to an advanced species that develops a way to visit *Voyager.* The episode uses a technobabble cause for the time dilation: a tachyon field. But a better solution comes from the movie "[Interstellar](https://en.wikipedia.org/wiki/Interstellar_(film))." > > The *Endurance* passes through the wormhole into another galaxy with a planetary system orbiting a supermassive black hole called Gargantua. The crew intends to investigate three planets, each previously explored by NASA volunteers, who shared positive reports for habitability. The first planet is an aqua planet with massive tidal waves and no dry land. Doyle drowns after failing to get into the probe and getting knocked off by one of the waves, and Amelia and Cooper fly back to the Endurance, only to find that decades have passed due to the time slippage caused by the planet's proximity to Gargantua. Romilly, having remained onboard, has aged 23 years. Cooper replays messages from Earth, learning that Murph is now his age and has become a scientist working with Brand. > > > **Time Dilation Prohibits a Practical Return** In other words, there's a scientific basis for the kind of problem that really would make it impossible to return. The planet orbits close enough to a black hole that the simple procedure of entering orbit experiences massive time dilation. One thing the movie doesn't go into is that while the ship is on the far side of the planet compared to Gargantua (e.g., the planet is between the ship and the black hole), time on the planet moves much more slowly than on the ship. *But when the ship orbits around to be between the planet and the black hole), time on the planet would move faster than on the ship.* One might conclude that orbiting the planet once would average out the time dilation and, therefore, allow a re-entry in sync with the time experienced on the planet. I don't have the equations to prove that, and I suspect it's incorrect. If I recall my astronomy correctly (I might not, it's been a honking long time), gravity is not linear with distance. It's logrithmic. That means the time dilation when the ship is between the planet and the black hole is ***worse*** than the dilation experienced when the planet is between the black hole and the ship. While this solution may not guarantee the inability to return (or, more precisely, the meaninglessness of returning), it goes a long way toward meeting you needs in a suspension-of-disbelief manner. [Answer] The planet has a very treacherous surface (steep cliffs, shallow waters dotted with jagged rocks, marshes, etc) which have only sparsely been made survivable by humans at a great cost and are merely connected to each other via a network of narrow roads and tunnels. This setting would enable civilization to arise, the roads could be used by travelers and merchants on foot or with carts - later by vehicles with internal combustion engines and locomotives. Space-capable rockets could be built from the resources available, but unless ~10 meter CEP precise landing capabilities are developed, no landing is safe enough to attempt. Crashing down on boulders, sinking in swamps, breaking up on rocks or drowning in perpertually stormy seas is all but guaranteed when landing outside man-made territories - and any "fortunate" landing on the tiny, painfully expensively prepared safe areas would result in huge damages to infrastructure and human life already present there. And thus no landing capabilities are developed at all. [Answer] ## They figured out rockets before we did The idea behind a rocket is not difficult. You need fuel, an oxidizer, and a way of controlling the burn. Perhaps some iron aged alchemist figured out kerosine rocket fuel and maybe they have a slightly lower gravity than we do making getting to space with an imperfect fuel much more doable. So, your Leonardo de Vince, Archimedes, or Pakal like guy figures out rocket fuel, and starts launching stuff into space, but his understanding of aerodynamics and material science is still way too primitive to figure out how to make a re-entry vehicle because he cant figure out why things burn up on re-entry or how to make them heat resistant enough to survive. Maybe they blame the burn up on the wrath of God, so they assume there is no scientific problem to be solved. [](https://i.stack.imgur.com/vdkRP.jpg) So instead of making the problem of re-entry harder than it is for us, you make the problem of getting to space easy enough that your civilization needs to wait hundreds of years to catch up with the 20th century science that made 2 way travel possible. [Answer] Philosophically, that's easy - like [Heraclitus' river](https://en.wikipedia.org/wiki/Heraclitus#Flux_and_unity_of_opposites), the planet continuously changes, so you can *never* go back to the *same* planet you lifted off from. Unless time on it stops as soon as you leave. But that's not what you meant, I suppose. So. For a *single* flight (like the Apollo missions), it is doable - have a deep enough gravity well that no significant payload can escape the planet's gravity unless they exhaust the fuel needed for the reentry brake. This way, also, atmosphere density increases fast enough that aerobraking from the Karman height to the ground would result in a meteoric burn. But if the above is not doable, or potentially infinite fuel resources are somehow available in orbit, so that you can always support a Space Shuttle-style reentry, then you need a planet you *can't land on*, ever. Hiding the surface wouldn't work - radar, parachutes and helicopter-like propellers would allow landing anyway. So, we need to disrupt a very large, even armored landing capsule that could split open and release a helicopter at a suitable altitude, capable of hovering and choosing the landing zone with ease; or prevent that helicopter from hovering, or at least from landing without crashing. The only way I can think of is violent, continuous cyclonic *storms* over the whole planet. Like Jupiter, but *worse*. You can stay safe on the ground (maybe in a deep depression) as long as you like, and wait for some brief respite, and launch *just then*, in the ten or fifteen minutes' of relative calm in the eye of a storm. Let's imagine there is on average at most only *one* such period, in any one given area, every two or three days. When leaving, that's easy: you prep for launch, and wait. And wait. And wait. When you're sure you can, you launch - and you need about three minutes to rise to safety. But when coming back, once you've committed to reentry, you do not know whether the safe area will be or even whether there will be one. Chances of hitting the right five-minute window in three days, if the weather is truly unpredictable, are less than 0.2%. Even aborting the landing and retrying if things look ugly won't increase that very much. And landing in the middle of a storm means crashing almost surely. You cannot hover at high altitude (also, it would be useless), you cannot use parachutes - they might even be worse - and the landing vessel cannot fly in the weather. Given those conditions, you simply cannot land. Of course, the plausibility of such a hellhole of a planet is debatable, to say the least. [Answer] **Planet inside a (Kerr-)Nordströn Black Hole** Charged black holes have 'two' event horizons, both of them being before the sigularity. Thus, when tou cross the second you are inside the black hole but with the singularity spatially away from you (spacelike distance) not in your future. This means that you could theoretically enter the black hole and go about your life inside it (i.e. you '''could''' have a functional solar system inside). Now, the important part. When you are inside you can cross again the second event horizon that you crossed, which would actually lead outside, making you go outside the black hole but in a different universe (don't quote me on this). The reason being, from the inside they are white holes, effectively. Charged solutions are not actually of physical interest, though, because the charge would in reality equalize quickly with all the matter orbiting the black hole, closing the Cauchy horizon. The stability of the system is concerning. Inside the black hole you could also find the naked singularity, which I don't know how anyone would regard in a novel, but, hey. It's not extremely believable, but not wholly unphysical either... **i.e. white holes might be your best bet.** [Answer] **Freakishly tall mountain above the winds.** [](https://i.stack.imgur.com/i8QzS.png) <https://www.reddit.com/r/NoMansSkyTheGame/comments/mbqibg/this_is_the_highest_mountain_ive_ever_seen_in_nms/> This is where they launch from. It is up above most of the atmosphere. Wind speeds are high but the air is so thin that the wind is less able to tear things to shreds. Shredwinds is how it is lower down until you get below the surface, which is where your people live. If you could land right on top of this mountain you would be ok. You could go home thru the tunnels, the same way you got up there. If you miss and run into the storms below, you and your ship will be torn to shreds. [Answer] Many little planets A three body system is chaotic, a 20 body system is pure chaos. Once you take off the only thing to do is thrust and get out of there ASAP. Returning home is a suicide mission, you don't know what is going to hit you from where and setting a course to your home planet becomes an impossible task as you don't have a clue where it'll be in the next day or so [Answer] An underwater civilization that's evolved on an airless moon orbiting a gas giant, with ocean beneath the frozen surface, like Ganymede or Europa, but bigger, with an earth equivalent surface gravity, but a tenuous atmosphere due to the temperature. Once they breach the ice and get the idea to start launching satellites, they will have great difficulty getting them to return with negligible atmosphere to use for breaking plus most of the reasons for returning things are returning living people, who on earth can land in the ocean/taiga and wait to be picked up, even if off course, while for them the surface would be a deadlier environment than space. [Answer] **Rapidly evolving pathogens** If the planet has really rapidly evolving viruses and bacteria, then population would evolve equally rapidly evolving immune system. But if you were to leave the planet for a months long trip, your immune system wouldn't get regularly updated, the pathogens upon your return would be too different to recognise and thus lethal. This solution would need a planet to be on a smaller size, as otherwise even traveling on it would be dangerous. Or it should be really windy. It has to have a mechanism for whole population to be exposed to similar pathogens everywhere in small time windows. [Answer] **The planet has catastrophic weather almost perpetually, except for a day or two every ~100 years** Even at our own level of technology, we have [pretty stringent requirements](https://www.nasa.gov/sites/default/files/atoms/files/falcon9_crewdragon_launch_weather_criteria_fact_sheet.pdf) for good weather in order to conduct a launch. Suppose your hypothetical planet has horrendous weather, at least in the upper atmosphere if not on the ground, that makes launches doomed to failure a majority of the time. Due to weather patterns and seasonal changes and planetary influence and other hand waving, the weather on your planet is only safe for launches for a short window every ~100 years. Maybe it is predictable and scientists can plan for the big day, but maybe it's not and they have to keep everything ready to go at a moment's notice. After the window closes, the weather prevents any hope of landing, at least until some future advanced tech can protect their ships. Assuming the people of your planet have a lifespan less than the frequency of these rare good launch/landing days, that's effectively a one-way trip. [Answer] The planet spins rapidly combined with very low gravity. On lift off, it slings you off of the surface, facilitating easy access to space. On re-entry there are two options, either hit it face on or try to catch it on the side. In case 1 it would be like trying to jump from a moving truck, no way you could land safely. In case 2 youd skip off like a rock skipping over water as gravity would be too weak to catch you. I'm not doing the math, but I suspect a large asteroid might match the criteria. The required spin could be the result of a collision with another asteroid. [Answer] # Extremely Dangerous Megafauna Perhaps your planet has skies littered with ~~Dragons~~ Sky Lizards whose domain covers the entire planet, that are extremely territorial. They are vicious and hardy creatures, that can and will easily decimate anything encroaching into its territory. By necessity outgoing rockets are moving far too fast for them to be intercepted. Rockets coming in for landing though? Either slow enough they're lizard food, or fast enough they're pancake. [Answer] How about this: **High gravity planet.** It supports life and all that, just not necessarily human-friendly. The natives are short and squat but they have figured out how to get into space through fairly conventional means. The ships that get launched from here have to be very strong. Lots of structural reinforcement. All this is unnecessary in space, though, and just adds to the cost of any maneuvers or any other travel they want to do. So one of the launch stages actually jettisons the main hull, revealing a far lighter, thinner internal structure that is fine for space but absolutely cannot land. (There could be emergency landings via parachute but the vehicle destroys itself on touchdown because it can no longer support its own weight.) So you can, maybe, if they included the emergency parachutes, "get back down" but "landing" is not an option, in the sense of ending up with an intact ship. And if there's no parachutes, you're not getting back down at all. (Perhaps the lighter module actually does not include the heat pads necessary for re-entry at all. They can get you up, but ditching all the weight means you can't come back down.) [Answer] # Edge of a black hole Your planet is very close to the photonsphere of an ultramassive black hole. Were it a stellar black hole you and the planet would be spaghettified, but tidal forces are smaller for the bigger holes. Due to conservation of momentum, if you take off either you or the planet will cross the event horizon (unless you do it from the poles, which might be prohibitively expensive). In either case that will be your last contact with the planet. [Answer] # Travelers from the planet have access to 'resources' that inbound travelers do not Perhaps the planet is very unpredictable due to its gravitational pull, or perhaps the inhabitants have shot so much junk into space that it is very difficult to find a way through. Either way, plotting a course is very difficult and perhaps the trash is even organized in a pattern that going out is generally easier than going back in. Fortunately you are able to overcome this with heavy calculations just before and during the launch, but this is only possible with **vast computational resources** which you have on the planet but not on your spaceship. Secondly you may need to observe the situation with **very accurate sensors** from the perspective of the launch. Something that obviously would only exist planet side. Lastly you may need a **stable&adjustable base** to even adjust the approach angle in the final seconds of the launch countdown. In short, there may be all kind of resources needed that are available planetside, but would be very hard to make available in the middle of space. [Answer] **Option 1** #### Physiology The planet has a strong gravity, more than double than Earth gravity. Not only reaching space from there is extremely expensive, but the aliens adapted to such gravity had to develop some clever tricks to adapt themselves to the loss of gravity. Trouble is that those tricks are not reversible. Those who reach the outer space are not able to go back without suffering some mortal physical damage. Since this is the heaviest of the planets that developed some life forms, it is too dangerous even for the inhabitants of all the other known planets. **Option 2** #### The magnetic cloud A cloud of ionised gas surrounds the planed. It scatters the light and creates constants magnetic storms that affect all the electronic equipment on board, any spaceship or missile passing through is blinded for a while. It may be safe to leave because going towards outer space the likelihood of bumping into something is small. But it makes it impossible to calculate a safe return route. [Answer] Astronauts lose muscle-mass every day while they are in a no/low-gravity environment. Only with a strict training regime during their stay they are able keep this process in check a bit. However even with such a training regime they are not able to walk or even stand after returning to earth. Full adaption to earth-level gravity can take up to a few months. Perhaps creatures living on a planet with a higher gravity than earth will never be able to adapt again after a few months in a no/low-gravity environment. [](https://i.stack.imgur.com/pxaXL.jpg) [Answer] # Severe Weather [](https://i.stack.imgur.com/ulXM9.jpg) Like, hurricane-severe. A dramatic axial tilt and short year gives your planet harsh, extreme, quickly changing seasons. That paired with the continental geography and atmospheric conditions cause **near-constant** gale force winds, monsoon rains, or [hail the size of minivans](https://www.youtube.com/watch?v=SldtLuz9Ur4). Don't forget lightning. There are very few times a year when the weather is tame enough to launch, and the most advanced weather tracking technology can only predict those days a few days out. There is no way of knowing in advance when or where it would be safe to land. **More importantly,** the lack of clear days to launch severely limits the frequency of shuttle tests and the knowledge they bring. Recovery of wrecked test craft for postmortem analysis is nigh impossible. Thus, what might take Earth a few years of progress would cost your civilization several decades. [Answer] You can't have such a planet naturally. If the planetary physics allows take off, it allows return. If you make it like in your question, a planet you can take off from and you can never return to -- face it, you're going to look a manic divorcee. ; ) [Answer] I propose a very simple solution: just have the planet be orbiting its sun very quickly. It's hard to land there because it's hard to hit a fast-moving target, especially when you have to arrive at the same velocity as the planet in order to not crash into it. But leaving the planet isn't any more difficult than usual, because "at rest" the rocket already has the same velocity as the planet does. [Answer] **Deliberately imposed restricions** The planet is under the yoke of the Galactic Empire. The Empire doesn't allow its subjects to get too uppity with their own spaceflight. Return trips are forbidden. ]

[Question] [ The goblins in my world are classical fantasy goblins. They aren't too smart, have primitive technology, live in tribes, and use tamed boars, wolves, and other wild animals. They usually have a boss, who runs the show because he is so nasty, convincing, strong or intelligent that the others respect him. The goblins raid or to extort income from nearby communities. They like to consider themselves great rulers. However, I **don't want them to build big and complex empires**. Nothing more complex or closer to a state than their extortion scheme territory. Additionally, they are supposed to be extremely unreliable allies, whether they forge an alliance with their kin or other races. Additionally, their **tribes** are supposed to remain small, **never bigger than 500 goblins**. The best explanation I could come up with is based on [**Dunbar's Number**](https://en.wikipedia.org/wiki/Dunbar%27s_number). For them it is **larger, the 500 goblins** per tribe I mentioned, but they are **unable to trust someone who they don't know personally**. They can develop trust in new people, but they tend to act paranoid and violent around those who they don't consider members of their tribe. Is this a good and believable way to achieve my goal here? Are there alternative/better approaches? [Answer] **Dunbar's Number is believable** I believe that Dunbar's Number is a very believable approach although it needs a slight twist. Think about Goblin (or any other) society as a connected graph of who-knows-who. There is a vertex for each member of the society and there is an edge between vertices if and only if the two members know each other. Then, the Dunbar's number, let it be $k$, is the upper limit on edges that originate in a vertex. Assume that this limit is saturated and each member knows exactly $k$ other (the graph is $k$-regular). It turns out that the expected distance between two arbitrary vertices in the graph is a $\Omega(\log\_k N)$ (see [1](https://math.stackexchange.com/questions/1944552/bounding-the-expected-distance-from-two-arbitrary-nodes-in-a-k-regular-graph)) where $N$ is the size of the graph (the number of members of the society). That notation means "at least". Solving the equation $x = \log\_k N = \frac{\log N}{\log k}$ where $x$ is the bound on distance for $N$ (see [2](https://www.wolframalpha.com/input/?i=Solve+for+N%2C++x+%3D+log+N+%2F+log+k)) gives $N = k ^ x$ (unsurprisingly :-P). Now let's think about how to interpret this. The Dunbar's number $k$ is clear, that's how many meaningful societal connections can a member maintain (or rather an upper bound on it but you can assume Goblins are close to it since this should happen in densely packed, nomadic and warrior societies). The distance $x$ can be thought of in terms of cohesion of the society. More developed societies form more abstract hierarchies and concepts of inter-personal relations. When the size of society grows beyond acceptable interpersonal distance, the society splits. I would guess that Goblins would not trust anyone more distant than a friend-of-a-friend whereas you are pretty much willing to trust me that I will not kill you even though we do not have any friends in common that would vouch for me. Now, assuming that Goblins are much more primitive than people, let's say they have Dunbar's number $k = 25$. (Or, actually, they need not necessarily be that more primitive, this number might grow super-linear or whatever, check Dunbar :-) The upper limit on Goblin society with $k = 25$ that operates on the friend-of-a-friend basis is: $$ N = k^x = 25^2 = 625 $$ Pretty close to your $500$. Remember that these are all upper limits; not every Goblin has all $25$ friends and it is not all perfect such that there is always a friend in common. I am sure you could come up in your settings with something like $25$ being slightly larger than average band of Goblins that sets for raids together. Or, if you want, the other solution is e.g. $k = 8$ and distance $3$ for $8^3 = 512$ with smaller units (families?) of goblins and slightly more complicated societal structure (what about families keeping together on maternal lines through mothers and grandmothers of a clan?), also $5^4 = 625$, just larger the distance the harder it will be to saturate that upper bound. Just if you are curious, for people it gives: * distance 2: $150^2 = 22\,500$ * distance 3: $150^3 = 3\,375\,000$ Hope I did not mess this up at some point. --- [Answer] **They Lack Sophisticated Agriculture** Goblins spend a lot of time raiding and extorting villages because they are always on the edge of starvation. Hunter-gatherer populations are never very large: the absolute largest were the indigenous tribes of northwestern North America, who had villages of up to 400 due to the abundance of the salmon runs. The Plains Nations who hunted buffalo from horseback had bands that varied in size, but never got particularly large (For reference, 2,000 Lakota Warriors was considered a massive number at Little Bighorn). So your goblins are essentially hunter-gatherers, maybe primitive horticulturalists who are just scraping by and must work hard to sustain themselves because they have been pushed into the least productive land and to gain a large population is an unobtainable dream [Answer] Because they don't want to turn into a dragon. Dragons are created when a group of about 800+ goblins get together in a single community. After a few years of that, something happens, and all the goblins die, except for the one that turns into a dragon, absorbing the memories and knowledge of the entire community in the process. Little is known about why this happens, but the goblins have figured out that 500 members is safe. The only groups that get bigger are the ones trying to turn into a dragon, and they don't stick around. [Answer] **The more crowded it is, the more goblins run amok.** <https://en.wikipedia.org/wiki/Running_amok> > > In a typical case of running amok, an individual (often male), having > shown no previous sign of anger or any inclination to violence, will > acquire a weapon (traditionally a sword or dagger, but currently any > of a variety of weapons) and in a sudden frenzy, will attempt to kill > or seriously injure anyone he encounters and himself.[10] Amok > typically takes place in a well populated or crowded area. > > > Culture bound syndromes of sudden unprovoked murderous craziness are found in other cultures - the original "wendigo" might have been something like this. Current American society offers another painful example. Goblins have this tendency and the more of them there are the greater the tendency. In big groups you can pretty much count on one or more goblins going into a crazed fury from which there is no return. No-one likes that. It makes it hard to get things done. The goblins avoid bunching up. I like this too because it offers more narrative grist for the mill: as opposed to boring Malthusian principles, spectacular and bloody consequences when there are too many goblins in one place. [Answer] From personal experience, I can tell you that goblins are fairly moralistic creatures, and their societies are governed not be a central authority, but by patterns of social rewards and punishment that emerge based on the all-important trade-off between the egalitarianism and meritocracy. Unfortunately, the system is imperfect. For starters, if the tribe gets too big, the goblins lose track of whose-who and the process of altruistic punishment is consequently frustrated by issues of imperfect information. Nepotism and familial favoritism can also sometimes undermine the system, leading to unjustifiable distributions of privilege and social standing which ultimately harm the tribe. Since smaller tribes tend to be more cohesive and less prone to the petty squabbling engendered by bonds of kinship and loyalty, this too creates pressure for smaller tribes. Although goblins are typically peace-loving, the process by which a tribe fractures in two is fairly conflict ridden, and all-out war between the two fractures is not wholly unheard of. The tales of the fierceness of goblin warriors are not exaggerated; when the lives of your loved ones themselves are at stake, there can simply be no compromise, in peace or in war. [Answer] A reasonable explanation could be that tribes larger than 500 would be too hard to self govern, or be ruled by a single ruler. Self governing tribes without a ruler could fall apart like you describe, when the members don't know and can't trust one another. The way how could be as described below. For tribes ruled by a single ruler, this would cause internal strive when a younger ruler with different ideology pops up and gathers a following. They could question the older ruler and spike a civil war. They could either kill the opposition or be wiped out, significantly reducing the overall population. If you don't like the violent option, they could instead split off from the tribe and form their own. The rate at which this occurs would increase significantly the larger the tribe, setting a feeble balance of around 500 members. [Answer] Goblins only respect strength. A goblin captain can command about twenty ordinary soldiers, each of whom he has personally beaten in a fight, and who knows him well enough to know he could do it again. A goblin chief can command twenty captains the same way. You can't have a third level, because goblins don't get that tough. This allows 421 adult goblins, who will typically have about 79 children with them. The idea of legitimate authority by appointment, election, ancestry or wisdom just *doesn't fit* in their minds. [Answer] logistics and **sewage** * Your goblins are unable to scale up their economy/food production, they can't produce enough food(goblins are usually depicted as hunter/gatherers and not farmers) and goods to support a large number goblins * They they live in tight, cramped spaces and don't know not to shit in their drinking water and have rampant diseases culling their numbers, this kept happening in real life until people [(**john snow**)](https://en.wikipedia.org/wiki/John_Snow) figured out that feces in the water is a great way to kill off your population with cholera and started building modernized sewage system, your goblins are not aware of sanitation. * Sanitation in general is a very limiting factor on population growth, the larger the population living in poor sanitary conditions the larger the chance for a plague outbreak and goblins are not immune to disease [Answer] **Goblins are *incredibly* social.** Goblins adore interacting with other goblins. The more goblins there are the more goblins they want to meet and talk to and hang out with. Eventually it gets to the point where a goblin's day is entirely taken up by social interactions with other goblins. They don't have any time for any other... activities. They're too busy partying to get busy and make little goblins. [Answer] **Goblin disputes (which are common) are solved by the chief favoring his relatives.** If a goblin isn't one of the chief's relatives then he's better off helping to create a new tribe. At much more than 500, there are too many non-relatives who would benefit by a change in leadership. This can be the tribe splitting or the chief being overthrown (i.e. a civil war). [Answer] All of my goblin knowledge from DMing the ["We Be Goblins" Pathfinder campaign](http://my.weasy.net/4051.pdf) tells me that there are a few reasons as to why their populace might be limited, but here's my top 3 theories: 1. Goblins are **highly superstitious**. These superstitions result in a variety of things, such as persecuting any goblin found to be writing, using writing, or in any way trying to learn. Often times, this will involve killing (usually violently) a lot of goblins as part of a judicial system. Because of their superstitions, there might be a reason why a certain goblin population refuses to go over 500 goblins, maybe because they think 500 (or some number below that) is unlucky, so they will send other goblins away or sacrifice them so that they don't reach that. This works as well as a theological reason (i.e. Their God doesn't like 500 goblins all together.) 2. Goblins kill each other, *kind of a lot*. Goblins are inherently evil creatures and have no semblance of morality, especially when it comes to claiming valuable objects from other goblins. It's only every so often a goblin tribe will find something valuable and go to war in order to take it, culling their numbers in the process. 3. Because of their incredible ability to be **obnoxious**, **dangerous** and **war-faring**, many other civilizations, especially humans, take notice of an exceptionally large goblin hoard, and commit goblin-genocide. Some combination of all three of these factors is almost definitely a possibility. [Answer] **The more goblins, the more ways the loot will have to be split.** You have said your goblins survive by extorting their nearby neighbors. They do not provide for themselves. If there are more goblins in the camp, they will need to split whatever resources they split more ways. Many reasons could contribute to it never getting greater than 500: The leader wants more loot for him/herself. The more minions the less the leader gets to take home. The rest of the camp/tribe wants more for theirselves. The more tribemembers the less loot for each individual! [Answer] Isnt a simple answer "they do get larger, but then something happens that will split the tribes"? Lets say you get bigger than 500 members and now have to raid, pillage and extort for those extra members, which no part of the lands they live in can sustain. This can have varied effects. The tribe could start starving causing members to drop until it is sustainable again (similar to how nature does it with apex predators), or the tribe is forced to attack more lethal targets like walled cities directly to get what they need, losing more members until they are at 500 again, or the scarcity of loot and food causes discontent and a portion of the tribe will assemble around a new leader who will either instigate a bloody fight for dominance or simply leave the tribe with promises of better loot and food. Even if the land can sustain it such a society could be large enough to cause a second cunning, vicious or whatever leader to stand up and either fight or peel off a portion of the tribe to start a new one. [Answer] The goblins reproductive system are modeled after ants, they have a queen who gives birth to all the goblins and none of the others do so. Untill. . . The colony reaches the size of 500 individuals (this seems a bit tiny in my opinion) when this population is reached all the resulting goblins instead get a new queen, and they go off to found a new colony. ]

[Question] [ If an island in a sub-tropical region were to be unreachable because of natural phenomena, what could those phenomena be? The people trying to reach said island have 17th century seafaring technologies. [Answer] An island that is entirely surrounded by an undersea methane gas fissure that is constantly active would be inaccessible by any kind of ship even with modern seafaring technology. The only way to reach such an island would be by air (which your world doesn't have). Methane gas has the very real-world property that it reduces the buoyancy of a water causing any boat passing over a gas fissure to capsize and sink. Such fissures do exist naturally on the Earth. In fact, methane fissures are one of the more plausible explanations for the Bermuda Triangle (even though the Bermuda Triangle is myth; ships are no more likely to sink there than anywhere else). **Update:** If you're looking for a weather-related phenomenon, think of a permanent hurricane that encircles the island at all times. Jupiter's Red Spot is an example of a hurricane that has been spinning for eons. It's not hard to imagine something like that existing on a habitable planet. If the island were in the eye of such a hurricane, the winds there would be calm and the environment peaceful. None of the inhabitants there (if there are any) would know of the world beyond the great storm, and no outside vessel would survive the trip through it. [Answer] **Reefs**. [](https://i.stack.imgur.com/yz0y0.jpg) *Public Domain, USGov-NOAA, 2005-07-25* They are and were a very dangerous obstruction for ships if they only leave very shallow water for passage. Because the ground climbs very steep, it causes massive breakers, destroying any ship stranded on the reef and making a passage per boat very dangerous. ADDITION: In fact, there is a reason why most of the exploring of uncharted lands occurs during the 18th century. Only precise navigation allow the creation of maps which give location of reefs for further exploring and that was not possible until the [longitude problem was solved.](https://en.wikipedia.org/wiki/Longitude_rewards). James Cook had access to the newly available lunar distance method and later copies of John Harrisons H4 chronometer. MAKING IT MORE DANGEROUS AND IMPENETRABLE: Put the island in the subtropic southern pacific. There both [trade winds](https://en.wikipedia.org/wiki/Trade_winds) and the [South Equatorial current](https://en.wikipedia.org/wiki/South_Equatorial_Current) are running in the same direction. Fully-rigged sailships like in the 17th century *can* run close-hauled (zig-zagging in direction of the wind), but not very good. So if the island is a far away from ports in the west (logistics), it is nearly impossible to reach from the western side. On the eastern side build reefs/shallows which are formed like a elongated horseshoe. Large reefs like that reveal themselves through the continous braking of waves so the sailors will be alarmed in time, but the ship is trapped in lee shore position: *Both* wind and current are moving it against the reef which is a death trap. Only agile ships like schooners will be able to escape the trap. [Answer] Consider [Rockall](https://en.wikipedia.org/wiki/Rockall). [](https://i.stack.imgur.com/NAmI0.jpg) Source: [Wikipedia](https://en.wikipedia.org/wiki/Rockall). Rockall is a barren island that is approximately equidistant between Ireland, Scotland, and Iceland, temperate, but with no natural harbor or even an obvious place that one can land without ramming into a cliff face. Wikipedia, citing Fisher, James (1957). Rockall. The Country Book Club. pp. 23–35., states that the first known visit to Rockall was in 1810. [Answer] Rockall is a good idea but lets go even farther and add some nasty vulcanism: You have an island that has cliff faces except in one area. You can pass through a narrow, turning area and reach a calm body of water within. Volcanic gases are bubbling up in the lake. Normally it is in a delicate balance with the CO2 saturated water staying trapped in the depths. It doesn't take much to upset the balance, though--say, a ship's anchor dropping into it. The ship sails in, drops anchor, the CO2 rises and kills everyone with no apparent cause of death. It won't take much for the people around to leave the killer island well alone. (Without an understanding of the situation they won't realize that after it strikes the threat is gone for some time.) [Answer] **Doldrums**, **Trade Winds**, **Gyres**, and optionally: **Perpetual Overcast** and **Military Mandates**. Start off by having your island located in the [doldrums](https://en.wikipedia.org/wiki/Doldrums); anywhere between 5°N and 5°S. Next, make the topography of your island so that whenever the trade winds do kick up, all the air at the surface flows away from the island. I'm no meteorologist but I think if you made Death Valley (which is below sea level) into an island (and perhaps surrounded it by mountains), that would condense the moisture out of the passing air and continually feed these winds. Or all of the above, vice versa. See also, [ocean gyre](https://en.wikipedia.org/wiki/Ocean_gyre). For instance, the [Sargasso Sea](https://en.wikipedia.org/wiki/Sargasso_Sea), which is the home of the Bermuda Triangle and the real reason why the area is so treacherous to *sailing* vessels. [](https://i.stack.imgur.com/5SGYl.jpg) If you really want to screw with the navigator, make your planet perpetually cloud covered. That will make using sextants difficult and navigating by the stars impossible. Couple all of that with a mandate that under no circumstances should any naval vessel sail into these waters, and until someone eccentric enough and with deep enough pockets charters a 'scientific' expedition, your mystery island will remain completely undiscovered. *Yar. There be dragons.* [Answer] The only thing that keeps people away now is radioactivity. In the 17th century this was not something they knew about. But they would simply get sick and die terribly if they tried to stay there for any length of time, *especially* if they collected the strange glowing rocks. So why would short-lived (geologically speaking) isotopes be around? For a first idea, consider the [natural fission reactor](https://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor). How about a meteorite? A chunk from a newer patch of dust, only recently enriched by a supernova, sent planitismals scattering. Or, you might start with natural uranium or thorium ore, but provide a unique way to **concentrate daughter elements** to dangerous levels. People are experimenting with using microbes to mine, and metal deposits have been caused by such microbes. So maybe something evolves that uses uranium and thus concentrates it. This also causes high mutation rates, so you see other microbes and eventually complex life that makes use of all the available daugher elements. This has the further benefit of making all the life on the island “mosterous”, decended from extremophiles that live deep in the Earth and hot springs. And of course it’s all highly toxic and radioactive: **even the pollen** will be inhaled and cause bleeding tumors. Any crew that comes up to the island for a few hours, even if they *don't* send a shore party to get fresh water and food (as is SOP) will be too infirm to work the ship within 2 months and dead in 6. Normally any ship will take on water, meat, and fruits and vegetables — this will kill them within days. [Answer] [](https://i.stack.imgur.com/Uq6FJ.png) It could be closed off on all sides such as [this](https://bulbapedia.bulbagarden.net/wiki/Sootopolis_City) example from Pokemon. This is a [giant volcanic crater](https://en.wikipedia.org/wiki/Volcanic_crater), the only way to get in there (in this case) is by diving underwater. While diving is certainly something that most anyone could do, finding an entrance wouldn't necessarily be easy (the first people to discover it would have likely done so by luck). [Answer] ## Voracious wood boring fauna [](https://i.stack.imgur.com/GdiIR.jpg) Make the [shipworms](http://news.nationalgeographic.com/2017/04/shipworm-giant-oceans-rare-bacteria/) very large and very hungry, and no ship will come anywhere close to the island and tell the story until a century later when they figure out [copper sheathing](https://en.wikipedia.org/wiki/Copper_sheathing). [Answer] Perhaps a volcanic eruption or a extra terrestrial impact created a crater with several concentric ring walls. The outermost ring wall looks like a very large island with steep cliffs rising out of the sea all around. Trying to land on the cliff side is very dangerous. If someone manages to land and climb up to the top of the cliffs they will see the top of the ring wall is rather thin and bare and treeless. On the inner side are more cliffs falling down to into the sea, connected by underwater passages, or maybe a freshwater lake formed by rainwater. And maybe from the top they can see all the way to the next inner ring wall, or maybe it is beyond the horizon. So there is no gap in the outer ring wall, no way to sail a ship through it, no trees to build a boat or a raft, and it would be be very hard to haul a boat up and then lower it into the inner body of water to explore it. Thus the outer ring wall will be mapped. But nobody knows how many inner ring walls there are and if there is a large island in the center. Does that make it isolated enough for 17th century technology? Possibly someone made up a myth that there is a central island that is a paradise or loaded with gold or something, and thus the protagonists foolishly believe the myth and seek to reach the central island without any proof there actually is one or what it may be like. [Answer] To elaborate on Z.Schroeder’s remark about [Henders Island](https://en.wikipedia.org/wiki/Fragment_(novel)), a very complete plot outline is given on Wikipedia. The island is populated by viscous *fast* monsters that have remained isolated because they cannot tolerate salt water. The island is remote, in the South Pacific, “about 1,400 miles south-southeast of Pitcairn Island.” It’s at a latitude where ships don’t like to travel, so the shipping lanes miss it. > > “The island is only about two miles wide,” Glyn said, encouraged. He read from cue cards Nell had prepared for him. “Since it is located below the fortieth parallel, a treacherous zone mariners call the ‘Roaring Forties,’ shipping lanes have bypassed it for the last two centuries. We are now headed for what could well be the most geographically remote piece of land on the Planet Earth. This empty patch of ocean is the size of the continental United States, and what we know about it is about equivalent to what can be seen of the United States from its interstate highway system. That’s how sparsely traversed this part of the world remains to this day. And the seafloor here is less mapped than the surface of Mars!” > Glyn got an appreciative murmur out of the crowd and he charged on. > “There are only a few reports of anyone sighting this island, and only one report of anyone actually landing on it, recorded in 1791 by Ambrose Spencer Henders, Captain of the H.M.S. Retribution.” > > > The 1791 voyage that did stop there found a butte sticking out of the water with no landing, as Robert Columbia notes in his answer. This includes lack of a reachable anchorage for the ship anywhere around the island. Note that in this story, only one crewman was killed. The monsters only attacked the shore party, and the ship, several hundred yards off, was safe. The captain chose not to report the attack but indicate that it’s not worth visiting. So, it *is* approachable, but nobody bothered going there. An ocean vessel could keep station without anchoring and send a launch. They could bring ropes, ladders, etc. to get up onto the land (but then be killed). But even without monsters, his explaination as to why nobody *did* go there (even though they *could*) does seems to hold up through the age of sail. * location away from shipping routes * documented as being worthless to voyagers * not near anything [Answer] An island with no natural harbors, with steep cliffs all around (such as Rockall in a previous answer), in choppy waters and with at least seasonal bad weather, should do the trick, at least statistically. There's no place that can be one-hundred-percent-guaranteed unreachable but there are many places that most people don't consider it worthwhile enough going to great trouble trying to reach in the first place. If your island has no safe place to land a boat, and the weather around it is usually bad, and the island is away from the main seagoing routes (so that getting there takes a lot of time), and there's nothing there of great value (that you know), then only very determined people will even thinking of trying. That in itself will also contribute to the island's legend of inaccessibility. [Answer] # **Basically something that kills off people** **or atleast deters them from going there** Here are some scenarios... * Strong gale winds and repeated cyclones regularly occur in a ring-like arrangement around the island causing attempts by explorers to prove fatal, discouraging others from trying. * Floating sea weed surrounding the island releases [*enter some hormonal drug-ish something*], causing sailors to be very aggressive. This leads to massacres aboard the ship, while the lone massacre-er starves to death as the weed entangles the ship's rudder. * Jagged rocky structures surround the island, both above and below water, severely damaging ships, while row-boats are not enough for the rest of the journey. Your imagination limits you in these setups. [Answer] Put your island near the poles. This works on two levels: one it's too cold to approach, and two it's too close to the poles for magnetic-based navigation. In fact, Captain Cook didn't cross the Antarctic circle until the 1770's, which is later than the time period you're discussing. [Antarctic Timeline of Discovery](http://www.south-pole.com/p0000052.htm) Depending on how big your island is, the harder it'll be to get there; an island only a few hundred meters across placed right at the very poles might never be discovered, especially if there's no other land masses within the Arctic/Antarctic circle for any explorers to desire to go there (from the above link, most of the early Antarctic exploration was due to hunting seals etc.) It would be much later before steamships with ice-breaking prows would be able to get close enough through the surrounding ice to deploy ground teams (dog sleds, etc.) So: 1) Difficult to navigate to even within a few hundred kilometers of the island; compasses don't work, cloud cover for most of the year so astrogation doesn't work. 2) No need to go that far south to begin with as there's no indication there's resources there worth exploring. [Answer] Snakes can cause problems for colonizers. As [mentioned here:](https://en.wikipedia.org/wiki/Ilha_da_Queimada_Grande) > > A lighthouse was constructed in 1909 to steer ships away from the island, operated by a single family. The family was found dead in the 1920s, having died from attacks by golden lanceheads that had entered the residence.[5] The lighthouse is now automated.[6][7] Due to the number of snakes and toxicity of their venom, the Brazilian Navy took action and closed the island to the public. > > > [Answer] There is a difference between unreachable and uninhabitable. Johnson/Nikamuoro Island, where Amelia Earhart probably met her end, is reachable, but in a tropical climate with no fresh water, it is uninhabitable for any length of time. Bikini Atoll is reachable, but is still too radioactive to remain for long. Rockall Island is reachable, but there is no practical reason to want to land there, aside from the difficulty in actually getting ashore. For an island to be unreachable, with 17th century sailing methods, and for that island to be located in the subtropics, which counts out extreme cold in the polar regions preventing it from being reached with 17th century technology, it would have to be a combination of the island itself being uncharted and thus unknown (a lot of the oceans were uncharted in the 17th century), and protected with either doldrums (no wind) or prevailing winds not being favorable for discovering the island. Or maybe Jacob told John Locke to move the island again... [Answer] Just to build on some of the excellent suggestions here already (particularly the reference to the Sargasso Sea) ... I think one could really push one's creative license to describe an island that is formed from the volcanic pumice ejected from a globally-sized geo-kinetic cataclysm (see Deccan Traps). The volcanic pumice is buoyant and naturally floats (silicon dioxide mostly)... and given a mid-ocean gyre such as the previously mentioned Sargasso Sea, one could have an island that is rotationally bound and agglomerates much in the same way that planets form from proto-planetary disks, or similarly the ocean garbage patches currently found in several oceanic locations of our own world. Sufficient geologic time and a few thousand fertilizing seabirds could instantiate a biome on this floating mass of pumice. The ocean gyre adds climate-change possibilities on human time-scales as the surface current and trade-winds slowly but surely rotate the pumice-island from the sub-tropics to the sub-arctic and back again on regular and predictable cycles. For a 17th century mariner, this moving target would be the equivalent of Terra Incognita, a rum-induced mirage, or similar, yet it can be habitable and perpetual… and intriguingly predictable. [Answer] 1. The island is surrounded by sharp rocks, the area is shallow, and/or strong currents smash the ships into the rocks. 2. The island is encircled by a lava, wood ships touches it, starts a fire. The burning ship has to retreat or everyone is killed by the lava or ship fire. Even if there was a natural underground thermal vent and water temps were 140F, the crew would be in a wooden oven(ship). Leave or bake to death, even 120F might be problematic. [Answer] Its just really far away from anywhere worthwhile going. The [Easter Island](https://en.wikipedia.org/wiki/Easter_Island) was discovered by a European in 1722 after someone spotted it by accident in 1687. So, had it been somewhat smaller (as is your island) and also typically rainy there (lots of clouds), no one will have plausibly have found it. [Answer] * The island is surrounded by a waterfall - the sea water goes to the abyss. * The island is surrounded by extremely turbulent water, with whirls. * The island is surrounded by extremely hot, boiling water. * Extremely dangerous animals occupy the waters around the island, for instance those who prey on ships and their crews. * The island is surrounded by artificial anti-ship traps and hedgehogs installed in the ancient times. [Answer] Both of the following would be unreachable: 1. An island which is the top of an erupting volcano 2. An island which is an active geiser w/ boiling water flowing over a narrow and jagged rim Add earthquakes, tsunamis, and lightning storms if you want (and get yourself an overkill) [Answer] The idea isn't fully fleshed out, but... imagine an island with ring mountains with unscaleable cliffs. There is a sea current that runs around this tear drop shaped island. It has a saltwater river exiting on the leeward side of the island. This river is fed by an underwater intake that funnels water from the current, like a ramjet. Leaving the island would be easy. Fishing with nets in the flow provides for the inhabitants. The cliffs would have the added issue of extreme smoothing and polishing by sand blasting provided by the current. There would be no anchor point for a ship and smaller crafts would be pushed along by a current that got stronger as you approached the island due to a venturi effect. ]

[Question] [ I guess making a tower out of ivory would make little to no practical sense as opposed to making a tower out of wood, stone, concrete, or other materials. I suppose building a literal ivory tower would be immensely costly and, if the world elephant population was not go extinct, would possibly have to be an endavor spanning a few generations. Still, such a tower would be awesome as per the rule of cool. A dominating empire, or kindgom, during its glory days, could build such a tower for its capital city's academic community, just to show off to other countries in the region: hey guys, look, we are the superpower here, we're so damn rich we could afford it, our humanities and science is so magnificent that it really fits for our leading academia to be located in this kind of facility, we are the alpha apes on this continent! (Dazzling with glamor is known in the real world, look at Dubai for example) However... Is it feasible at all? Can we, realistically, get enough ivory for such a tower? Can we get enough ivory without driving the world elephant population to extinction? Is ivory solid enough to support a large tower? Are the costs sky-high realistic or sky-high unrealistic? ANd if at all possible, no cheating please. Ivory tower is ivory tower, not concrete / stone / metal / whatever tower with ivory embelishments. What is not a window should be made of ivory. Time setting? I suppose that paradoxically it doesn't matter now, as the answers would be the same for ancient Rome and today... but if I'm wrong, what is the minimal technological advancement setting that could support such a tower? [Answer] The critical property for building a tower out of ivory (or any other material, for that matter) is its compressive strength. Strength data for ivory is surprisingly hard to find, and the few references I could find are for the tensile strength, not the compressive strength. Using human dentin as a proxy for elephant ivory, we can estimate the compressive strength at around [300 MPa](https://www.ncbi.nlm.nih.gov/pubmed/8272502). This is comparable to mild steel ([250 MPa](https://en.wikipedia.org/wiki/A36_steel)), and superior to common tower-building materials such as [brick, concrete, and granite](https://www.engineeringtoolbox.com/compression-tension-strength-d_1352.html) (80 MPa, 43 MPa, and 130 MPa respectively). From an engineering standpoint, it looks like ivory would do just fine as a construction material. Getting enough ivory to build a tower is a different matter. A pair of elephant tusks can get you perhaps [100 kg of ivory](https://en.wikipedia.org/wiki/Elephant#Tusks). If you're lucky, you can turn that into 30 or so bricks. Even a small tower, 3 meters across and 10 meters high, requires around 700 elephants for the outer walls alone, not counting any floors or interior partitions. [Answer] It's definitely possible in certain fantasy settings, some of which would even allow the tower to be carved from a single tusk. [](https://i.stack.imgur.com/XugFH.jpg) [Answer] The building itself is doable. Ivory is what teeth are made of, and they are *made* for compressive strength. You might need some architectural adjustments for load-bearing structures, to compensate for ivory's [poor tensile strength](https://link.springer.com/article/10.1007%2FBF01730290). The tower is going to look decidedly romanesque, with barrel vaults and small windows. But, given the sheer *amount* of ivory required, you're right that this is a multi-generation (multi-century, even) endeavour whatever you do. And, clearly, hunting elephants is never going to work. So it would make a lot of sense to breed elephants for large tusks (currently, the opposite is happening, with good results - tusk size [and even occurrence](http://www.independent.co.uk/news/elephants-africa-tusks-ivory-poaching-born-without-a7440706.html) is esteemed to have decreased as much as 40% in the last centuries). You want to breed them for size, growth speed and structural strength. It turns out that zoo elephants fare poorly in that respect ("stress, lack of exercise and overweight" being blamed for that). Actually, taking the long view, it turns out that you want the elephants (especially the males) to [live a long life](https://www.tandfonline.com/doi/pdf/10.1080/00445096.1970.11447388) with the less possible need for defending against predators, digging in hard and rocky terrain for water and/or roots, and battling for territory. Older elephants are the most productive source for the best ivory. Economically, you need to do the exact opposite of what ivory hunters do. You really don't want a small market with huge prices. What you do then is create and maintain the largest possible reserve for elephants to roam free in, and encourage the best specimens to breed; but apparently this is what they already tend to do, so you just need to *leave them alone* and let them do the work. # Graveyards When elephants grow old, their molar teeth become less and less functional and their dietary habits change. In the end, they'll become hermit elephants and roam less and less far from the area where easily chewed food can be obtained, and in that area they will eventually die. By carefully landscaping and maintaining the grass varieties throughout the reserve, you can establish areas especially suited for elder bulls, which will therefore become ["elephants' graveyards"](https://en.wikipedia.org/wiki/Elephants%27_graveyard). Once the elephant population is large enough, monitoring these comparatively small areas should guarantee a steady supply of the best possible ivory. [Answer] I'm guessing you'd consider this cheating, but seriously: what's wrong with an **ivory facade**? It's pretty common for the core of a building to be constructed with one material, but the exterior facade gives it the appearance that it was constructed with something else. A good modern example is [brick veneer over a wood and plaster structure](https://vintagerevivals.com/2015/03/installing-brick-veneer-inside-your-home). [](https://i.stack.imgur.com/5s4E4.jpg) Assuming sufficient supply in your world, you could cover every exterior and interior surface of your ivory tower with ivory to give it the appearance that it was used as a construction material, while the load-bearing elements use a more appropriate (and cheaper) construction material for your world. This would absolutely satisfy your goal of using this massive ivory display as a demonstration of wealth while still making the existence of the tower feasible. EDIT: Another really good example is modern skyscrapers. Obviously the exterior glass is not load bearing, but if you showed someone a skyscraper who completely lacked the context for what they were looking at, they'd think the building was made out of glass. But really what's going on is that the weight of the building is carried by a core structure, and the exterior glass is supported by each floor. [](https://i.stack.imgur.com/OZtY3.jpg) I'm fairly confident that a "glass skyscraper" is basically a direct analogue to your "ivory tower". You could choose to explain the core structure architecture, or handwave away architectural technology as a protected trade secret or even ["lost technology of the ancients"](http://tvtropes.org/pmwiki/pmwiki.php/Main/LostTechnology) kind of thing. You could use the [Ogier](http://wot.wikia.com/wiki/Ogier) race from the Wheel Of Time as a kind of backstory template. [Answer] What do you mean `if at all possible, no cheating please.` So let me bend the rules... Others have addressed the building of a tower with this material. If you have sufficient technology, you could just 3d print ivory. We are already experimenting with this (well not for ivory) it's called 3D bioprinting <https://en.wikipedia.org/wiki/3D_bioprinting> > > Three dimensional (3D) bioprinting is the utilization of 3D printing and 3D printing–like techniques to combine cells, growth factors, and biomaterials to fabricate biomedical parts that maximally imitate natural tissue characteristics. > > > So with enough sophistication, you could bio print as much ivory as you need. You could also bio print it in larger sheets more suitable for facing a building. I would go with a facade of ivory, with a traditional structure underneath. If ivory is susceptible to the environment, you could coat it in something that is not. This could easily done as part of the printing process. For all intents and purposes it would be natural ivory, does it matter if it's taken from an animal or grown in a vat? So to speak. For time setting: I would say it would have to be post-modern. For one the building practices of the modern age, has allowed us to bring together different materials. Materials that on there own you cant build from, but when combined make nice structures. Think of wall board, and 2x4's individually they are not so nice. A house would be pretty boring with just 2x4s and wall board is not really structural, it can t support another story on it's own. In the same regard is modern buildings with things like marble facades or glass and so on. We literally have countless materials we can use now. Throughout most of human history you had, wood, stone, earth (bricks, mud) and maybe plaster. The other reason is sourcing the material, I think getting natural ivory is going to be quite difficult. You could hand wave something in, like some graveyard of mastodons. Some large animal with a large amount of ivory. Magic, or something else. So given that, you might as well use technology, it's no less plausible then any other means. I think you will be hard pressed without some amount of hand waving to rationalize that amount of natural animal material. [Answer] Ivory is not a suitable building material, as it is a substance that will degrade quickly and heavily over time from exposure to the elements. From [Wikipedia](https://en.wikipedia.org/wiki/Conservation_and_restoration_of_ivory_objects#Deterioration): > > Ivory is hygroscopic and anisotropic, tending to shrink, swell, crack, split, and/or warp on exposure to extremes or fluctuations in relative humidity and temperature, It is subject to photolytic color change. Its organic compounds decompose by hydrolysis with prolonged exposure to water, while its inorganic compounds are attacked by acids. Deteriorated ivory is porous, brittle, and prone to impact damage and delamination. Many conservation problems are caused by previous conservation treatments such as incompatible and degraded coatings, adhesives, and attempts at reconstruction. > > > Check out the article for more information. [Answer] Theoretically, one could raise these animals in captivity and slaughter them for their tusks, while preserving the skin/etc; for other uses-- Keep in mind that elephants aren't the only animal that produces ivory. (Walruses, Hippos, even a couple types of birds, I believe.) It isn't impossible, but would likely be a very drawn out process and kill alot of animals. Tusks do not grow back, so once harvested you've put the animal in a very bad position. Good question! [Answer] I'd stick together a few wonderful answers from here: * A single tusk is about 100 kg * You can *unroll* dentine or even grid it into a powder and add glue. So, I assume that all 100 kg of ivory go into the building * Ivory is more or less as good for construction as steel * We might still end with steel-ivory complexes for the core, but I disregard it here * Eiffel tower weights around 8,000 tons, Empire State Building is estimated at 364,000 tons without inhabitants. (Per <http://stupidquestionarchives.blogspot.de/2008/03/empire-state-building-weight.html>) So, a very crude computation says than we'd need 40,000 elephants for ivory Eiffel tower and 1,820,000 elephants for ivory Empire State Building. This is using two tusks from an elephant, notice that females have smaller/different tusks and we do not put all other teeth in the grinder. > > Between 1980 and 1990 the population of African elephants was more > than halved, from 1.3 million to around 600,000 > > > <https://en.wikipedia.org/wiki/African_elephant> > > In 2003, the wild population was estimated at between 41,410 and 52,345 individuals. > > > <https://en.wikipedia.org/wiki/Asian_elephant> So, taking a local African empire (Zulu?), building an ivory Eiffel tower seems doable (even if a moral no-go), an ivory skyscraper would require harvesting mammoth tusks, discovering elephant graveyards, or an extensive breeding program. [Answer] Very large elephants are the answer. The tusks would be strong enough to build a modest tower. In some parts of the world you can see structures made out of whale bones, after all. Genetically engineered, really big elephants. Preferably hairy. Maybe they could shed their tusks at intervals, like some deer do. Maybe there is some barren, cold part of your fantasy world where giant hairy mammoths could roam at will, maybe accompanied by mammoth-herders. They would of course be revered as gods, complete with human sacrifice and festivals. [Answer] *A previous version of this answer had some language and insinuations that were abrasive and my intentions were not clear. I apologize for that, particularly to the OP, as well as to all the users at large as I do value my inclusion in this community. I have re-written the answer as follows...* Let me come at this from another angle: If the character who is ordering the tower to be built is a tyrant, then yes, an ivory tower is feasible. It would take a tyrannical type personality to even want an ivory tower and it would take a tyrant to kill all the elephants required to build anything that could be considered a tower. That is just my opinion, but I believe it to be true. Truly rich and powerful people just don't do that sort of thing or else Jeff Besos, Warren Buffet, and Bill Gates would have ivory towers. So if your character is a tyrant he can send out all his minions to kill all the elephants they can find and bring back their tusks. Then he'd have his slaves (a tyrant would have those too) build the thing for him. Now I imagine that he'd need to have built a structure of some kind first (wooden, brick, etc.) to put the ivory on. Ivory itself wouldn't be the building material. Not good for that. There are some carvings made of the stuff, but not huge structures. So some of your needs might not be met - He probably would drive the local elephant population to extinction, and depending on how arrogant this tyrant is he might want a really big tower, so he might send his minions all over the world for even more ivory, thus widening the influence of how wiped out the elephants could be. And the tower would not be 100% ivory. It needs an initial structure to hang the ivory on, as ivory itself its not a great building material. This answer assumes modern day technology where we don't have magical or sci-fi means of "creating" ivory, and it also assumes the "cool" factor (from the OP's question) that would come with having real ivory as opposed to an artificial or manufactured version of it. [Answer] The problem with your question is that elephants are not merely part of a ecosystem to be managed or a resource to be managed. Just as members of the species *Homo sapiens* hope that objective extraterrestrial observers would consider them to be semi or even fully intelligent beings and thus worthy of being considered people with rights, there are many other species on Earth that might be considered semi or even fully intelligent beings by objective extraterrestrial observers, beings that might deserve some or all of the rights belonging to people. Until and unless society can be absolutely certain that such beings are not intelligent beings, it is safer to act as if we were certain they are intelligent beings and punish killing them as if it were an act of murder. Because if we do so needlessly, the bad results will be a lot smaller than if we need to do so and don't. And the three surviving species of elephants are among the species of close to human intelligence that should be treated like people. So if you are writing a fantasy story, you might have a scene where Emperor Ru-thlyss XIII is attending the laying the foundation stone for his pet project, a literal ivory tower for his university. And suddenly a space time vortex appears and out pour men and armored elephants who scatter the crowd, slaughter the bodyguards, and capture Emperor Ru-thlyss. Ru-thlyss is told that in the distant future wizards (in his ivory tower, ironically) discovered that elephants are people and learned how to communicate with them. Because elephants still remember the great ivory hunt that decimated them in the time of Ru-thlyss, human and elephant wizards discovered a way to travel back in time to stop Ru-thlyss and his great ivory hunt. So now they have taken over the Imperial government and will decree the death penalty for any person who dares to kill an elephant or make any object out of ivory. Ex-Emperor Ru-thlyss will be the first person tortured to death under the new law. All teeth are made of ivory, and in the world today, if you are thinking of a contemporary story, many millions of persons are born every year and many millions of children a few years old lose their baby teeth. In some societies it is common for children to be paid for their baby teeth by the "tooth fairy", and of course a wealthy enough government could buy all the baby teeth in the world. And of course many millions of people die every year and a wealthy enough government could pay to harvest the teeth of many of them. Millions of farm animals are slaughtered every year and I am sure that bones and teeth are harvested and put to some economic use. A wealthy government could buy millions of teeth per year. Walrus ivory was an important historical alternate source of ivory. The government could try capturing, breeding, and raising Walruses in ever increasing numbers for their tusks. in a fantasy world, wizards could use spells to track all the tusks and all the teeth of all the elephants in the world. Whenever a tooth fell out of an elephant's mouth, or was swallowed and excreted, or a tusk broke off, or an elephant died, wizards would be magically alerted to the location and use spells to obtain the ivory. Maybe the wizards could also use magic to gather no longer needed teeth from sperm whales. And in a science fictional setting perhaps technology could do most of what I imagined spells doing. Tiny robot "insects" could fly into elephants mouths and attach tiny trackers to teeth and tusks, for example. A fantasy story could have wizards seek out elephant graveyards where elephants go to die, loaded with the ivory of elephant generations. And there is prehistoric ivory dug up from dead mammoths in northern lands. Genetic engineering could probably be used to make millions of farm animals grow long tusks out of their mouths and other body parts. Ancient Greeks made often gigantic chryselephantine statues of gods, with wooden frames and thin gold sheets molded into clothing and thin ivory sheets molded to form the flesh. It is claimed that the Greek sculptors had techniques to soften ivory tusks and unroll the concentric layers they were composed of to get thin sheets of ivory much wider than the thicknesses of the tusks. They would mold the ivory sheets onto molds to give it shape before the ivory stiffened. Since ivory is a rare material, and since the ivory tower will be more impressive the more floor space it has, it should be as close to spherical as it can, because a sphere encloses the most volume for the least amount of expensive ivory cladding - I have grave doubts about the structural strength of ivory. Thus I can imagine an ivory clad building shaped like a hemisphere 500 feet wide and 250 feet high. Of course that might not be towering enough to be an ivory tower. Or the tower might be a cylinder 500 hundred feet tall and 250 feet high topped by a dome 500 feet wide and 250 feet tall. Or the cylinder could be 500 feet wide and 500 feet tall, with a 250 foot high dome on top. Or the cylinder could be 500 feet wide and 750 feet tall, with a 250 foot high dome on top. Maybe the tower could have a cylinder 250 feet wide and 250 feet tall, supporting a three quarters dome 500 feet wide and 375 feet tall for a total height of 625 feet tall. Or for a more tower like form the the tower could be a cylinder 100 feet in diameter by 1,000 feet tall. I have to say that whenever I think of an ivory tower I picture a marble tower, to be precise, the Leaning Tower of Pisa as it would have looked if it never leaned. <https://commons.wikimedia.org/wiki/File:Leaning_Tower_of_Pisa_(April_2012).jpg>[1](https://commons.wikimedia.org/wiki/File:Leaning_Tower_of_Pisa_(April_2012).jpg) <http://www.theflairsophy.com/2017/10/the-leaning-tower-of-pisa-italy.html>[2](http://www.theflairsophy.com/2017/10/the-leaning-tower-of-pisa-italy.html) Ivory consists mostly of dentin. It should be possible to synthisize dentin, and if can be synthisized it can be done on a massive industrial scale. > > Dentin rates approximately 3 on the Mohs scale of mineral hardness.[3](https://en.wikipedia.org/wiki/Dentin) > > > <https://en.wikipedia.org/wiki/Dentin>[3](https://en.wikipedia.org/wiki/Dentin) And dentist study the properties of human dentin in a tooth environment. But I am not sure where to find the properties of dentin as a construction material. You should assume that ivory and dentin is only useful as a cladding material and not as a structural material. And to prevent weathering and pollution problems the ivory should be encased in a clear transparent material that protects it from such effects. ]

[Question] [ A popular story line is that some rapidly spreading plague kills 95% of the human population. That's 7,125,000,000 decomposing bodies that have to be dealt with **quickly** before flies and bacteria spread "normal" disease to the remaining 375,000,000 (hungry, traumatized, disorganized) people. The Black Death took 7 years to kill about 50% of Europe. That gave time to dig mass burial pits. This, though, is at a whole different — and seemingly impossible — scale. (Note: The plague has two weeks of symptomless infectious stage, and then a rapid (few days) death.) [Answer] # Meta-logistics for the author The problem that you — as the author — have is this: how do you kill off 95% of the world's population by means of a plague, without having the corpses cause so much health problems that you drag down the remaining 5% too? The answer is: **you do not**. It is not credible to kill 19 in 20 people and then have the remainders live happily ever after. So instead you kill off, say, 65% of the world's population with the plague, and the remaining 30% you want to get rid off will be from secondary effects caused by rotting corpses everywhere, mass starvation, breakdown of sanitation and medicine, loss of heating / cooling, loss of fresh water, environmental disasters and so on. Adjust these numbers as you see fit and that seems credible. The point is that you include the secondary effects from the blight into your count and then make that combined count end up on 95%. [Answer] # Leave Them The logistics of collecting the remains to cremate them would be overwhelming - by the time so few people got to even a small percentage, the rest would be quickly decomposing, making collection next to impossible. The rest of mankind would most probably be concentrating more on survival than disposing of the dead. The only real course of action I think is to retreat to a safe area and let nature do the work of disposing of the remains. Grind the bones down at a suitable time - you're going to need that fertiliser... [Answer] I agree with all of the other answers. I suppose it depends on how quickly people are dying: * If people are dying slowly enough that survivors can burn them, that would be ideal. One helpful factor here is that every person that dies leaves behind a certain amount of burnable materials -- clothing, bedding, chairs, houses, cars, etc. So, if survivors can stay safe while collecting bodies and fuel for cremation, that would be ideal. Perhaps bodies should be loaded into cars, then set the cars on fire. It would be a very toxic, smoky environment, but it could be a last resort cremation solution if clean burning fuel can't be gathered fast enough. People should be very careful, though, to make sure any fires are easily contained, since there will be no fire department to put out the fire if it spreads out of control. Perhaps large parking lots could provide a relatively safe burning station where embers won't easily fly to nearby burnables. Weather will be an important factor here in making sure the fires don't spread--excessively dry areas will require extra caution, while rainy areas can prevent easy cremation. * If people are dying too quickly to be burned, then [decomposition becomes a major factor:](http://www.enkivillage.com/how-long-does-it-take-for-a-body-to-decompose.html) [](https://i.stack.imgur.com/e5rK4.jpg) People would need to move a safe distance away during this time and wait for full decomposition. After a year has passed, much of the decomposition will be complete, particularly if bodies have been left outside. Survivors should then be cautious when reentering sealed environments (buildings, cars, etc.) because incomplete decomposition might leave disease vectors. [Answer] Given the massive scale of the death and lack of people remaining, the consensus answers are let the bodies decompose while you move to a safe area. This is indeed the correct answer, unless there is some compelling reason that the bodies need to be disposed of right away. If we assume the human remains are still a disease vector (the killer bacteria remain viable even in decomposing flesh), then disposal by fire is probably the best way to deal with this. For the most part, we can assume people will not simply drop dead in the street at random, but have been infected and are dying in their homes or hospitals as the disease symptoms weaken them and confine them to bed. Assuming the time of year is right (high summer is ideal), the survivors could attempt to commit the largest acts of arson in history and torch residential neighbourhoods and hospitals, ensuring the bodies contained within the houses and buildings will be consumed in the fire. The two huge problems with this are building codes, which make burning modern buildings difficult, and control. Modern buildings are generally designed in such a way as to minimize the ability of fire to destroy them. In modern steel and concrete construction (office buildings, apartment blocks, hospitals, factories etc.) the danger isn't the structure catching fire, but the internal fittings like furniture, carpets and so on. Deaths in these fires is often due to smoke inhalation rather than burning, so unless circumstances are ideal, torching an apartment tower and ensuring the bodies are consumed will be far more difficult than just showing up with a deck of matches and a can of gasoline. The second issue is you might actually be *too* successful. If the fires begin to converge, or there is a huge source of fire to keep the conditions in the city ideal for burning (recently the Canadian city of Fort McMurray was consumed in a firestorm, but the city was essentially surrounded by a massive forest fire raining burning embers on the city and knocking out power and emergency services), then anything you might want to salvage from the city will also be destroyed. This is a consideration even if you are just looking at neighbourhoods, burning a house down might spread to engulf the local supermarket, eliminating a source of stored canned goods and light duty equipment that would be useful to you. However even expedient arson might not provide the solution. Human tissue is full of water, and it takes [a lot of energy to completely burn a human](https://www.quora.com/How-much-energy-is-required-for-a-human-cremation?share=1) (roughly 100 kilojoules simply to vaporize the water, before combustion takes place). A burning building isn't a controlled environment, and ensuring you have enough heat sustained for the right amount of time on the bodies is problematic. The worst case scenario is you burned down the city, destroyed your source of supplies and still didn't dispose of the bodies. Far better to just move far away into the countryside and wait for nature to take its course. [Answer] I'm assuming you don't want to have 7 billion bodies rotting all over your world and this is the reason for your question. A couple of options: 1. Bodies are left to decay on their own except in the area the survivors are living in/around - survivors will clean out living spaces for themselves for obvious reasons 2. If you kill the population off slower, people will have time to get to a hospital and/or get put into quarantine zones - bodies will pile up in fewer, smaller areas and people will flee some areas both of which will leave huge swaths of land unpopulated (clean of bodies) 3. You could have the disease itself speed up the decaying process to eliminate the bodies faster - the disease could liquefy a body in days 4. Or you could also have mother nature speed up the decaying process by a sudden explosion in the rat population (rats could be immune to the disease) Adjust your initial kill rate of 95% or survivors would either have to be immune to the disease itself or the disease doesn't survive in the bodies. [Answer] Assuming this is modern-day Earth, you're ignoring a multitude of different cultural and religious burial practices. Even if you somehow managed to impose a directive on the entire world, people in many regions would simply refuse to comply because they have specific rites that "need" to be performed when someone dies. I'll give just one example. A partial reason for the Ebola outbreak in western Africa 2 years ago is because local death rituals necessitated fully washing the body of the deceased. This, of course, made spread of the virus very easy. Even when people were educated about it, they insisted on performing their rites according to custom. I don't have all of the answers to give you, but if you're going to write a "realistic" story, you might consider investigating this angle. [Answer] I think the biological mass of 7 billion people is actually reasonably small (all things considered). Assuming they're just corpses (and not roaming zombies), the survivors can probably all easily find areas entirely uncontaminated by the decomposition of the dead. Think about it - how far do you have to drive (bike, run) to get to an area where you have a few square miles of land that has no people on it (answer - even in the U.S. not very far - Australia? Africa? South America?... other than the very densely populated areas, it's MOSTLY empty space). [Answer] I'd imagine that a zone would be created where the survivors would live, including an exclusion zone. The best way to get rid of the bodies would probably be cremation. Slowly as more area is needed remains can be removed from other areas, although if they wait long enough earths natural mechanics will also dispose of the problem. Survivors would need to make sure their water table doesn't become affected though. [Answer] I'd suggest fire pits. Fast and possible. Yes, most move away from the smoke and the populated areas, and make sure there are no bodies there. Burying them without chemicals or coffins could indeed make the water bad. [Answer] Survivors would leave the population centers behind and let nature take its course. Scavengers could take care of the corpses in a couple years. No centralized disposal effort would be sufficient given the numbers of dead relative to the number of survivors. The most efficient way I can think of is heavy earth-moving equipment, mass graves and lye, but that might not be sufficient past the small town scale. [Answer] # The most efficient way won't be done. The most efficient way to manage this is to find a region that had a relatively low pre-plague population density and that has the elements necessary to rebuild your population. Good farmland, access to clean water, etc. Move all of your survivors there, clean up what bodies are onsite, and move on with life. By the time your population has recovered to a point that they need to expand, they can do so relatively easily into neighboring spaces, etc. By the time they reach a high-population-density area like a pre-fall city, natural decay will have solved the worst of your problems. But that's a best case scenario that doesn't take into account the logistics or psychology/sociology of relocating all survivors in the midst of the most horrific possible event ever in human history. # Instead, you have chaos. TL;DR: welcome to every post-apocalypse world found in history. Some areas will have clumps of survivors. Maybe they work together and clear their immediate surroundings. Maybe they work separately and achieve the same goal. Or maybe they are too busy fighting for survival to do anything but clear the home they occupy. Your best-case scenario is that people gravitate towards small towns, work out their differences with regards to self-governance, and eventually settle into a pattern where they form clean-up crews that go house-to-house, disposing of bodies and spoiled foods, releasing any surviving pets trapped inside, turning off breakers, etc., so that the houses can be occupied later, when population expands due to "immigration" or birth rates. If electricity can be restored to the town, they'd want to leave it shut off for each neighborhood until that neighborhood had been swept by clean-up crews, so ovens aren't left on or other electrical fire hazards don't destroy the town. (See [Stephen King's The Stand](https://en.wikipedia.org/wiki/The_Stand) for a fairly good representation of this model.) [Answer] Your question suggests the need for the 5% to clear up the 95% ... but why bother? There are other things on your mind - food, water and security being the obvious. All you need enough space to be able to survive a month or so (time shamlessly taken from the other answers); but you don't need to clear everything up. If for example London falls - you're not going to go to london and try to clean up all the bodies there, you're going to move out into a town at best where you have a few hundred corpses to clear rather than thousands. This wouldn't even require any thought by someone in living at the time, because the question "How do I survive" does not have "dispose of every body" as an answer; thus would not even be considered as a task for completion. [Answer] How you would get rid of the bodies would depend on your local environment and the rate at which they appear. Any disease that first causes sickness, gradually weakening the affected over a day or more would cause the sick to congregate at medical facilities, and as soon as these overfill, at home. Its not realistic to assume all 95% who will eventually die will be dying over the course of a few days, more likely it will spread out over weeks, if not month. Even highly contagious diseases do not infect everyone on first exposure. Take the outbreaks of mostly harmless flu as an example, it usually lasts month, even in highly populated areas. This means the majority of bodies will be immediately discovered, and as soon as the scale of the pandemic becomes obvious, authorities will work to deal with it. As the pandemic progresses, more and more people will die at home (medical facilities become overrun on the first few days). Even if 2-5% of the initial population would die per day, collecting the dead bodies (especially under martial law) is relatively manageable logistically. All you need is a truck and some people to go around a neighborhood to collect the dead. Most likely these will be accompanied by armed soldiers and not delivering dead bodies will be dealt with as a crime under martial law. Once collected, the bodies can be disposed of by any means locally available: by burining in waste disposal facilities, mass graves or even by dumping in landfills. While 7 billion sounds much, in terms of weight and volume its not so much compared to the amount of waste we have to manage annually anyway. Its just a very busy year for the garbage movers. At some point, when the death toll has climbed high enough, civilization will break down and organized disposal of the dead would come to a halt. Its hard to imagine at which percentage this would happen exactly, from a standpoint of pure work force, there is no reason why this couldn't work even until only the 5% ultimately surviving would remain. But realistically it would break down at some point, psychological effects of mass death on this scale are hard to imagine. I'd say the amount of bodies isn't the major problem, the main problem is maintaining order and organization. As soon as the society falls back to savagery things really go downhill. The best chance of survival then is in rural areas, there are fewer people to begin with and more resources (food, water). Considering that there will have been a phase where the dead have been disposed of orderly, there wouldn't be too many corpses to deal with in rural areas. [Answer] No one plauge kills all 95% of the population at the same time... It takes a while for the plague to be recognized, then to spread and finally burn out. You assume "rapidly spreading", which is very vague, but even so it may take months to get there.. So if you want to do it fast, go for "bio attack", with as many "Patients Zero" in as many international transportation hubs as possible. But it will still take weeks. Then there's the question of which season - warm months will increase both decomposition and removal of bodies by pests. Civilization does not break suddenly, too. Initially there will be services to take care of the bodies - NYC has approx 0.002% death rate daily... It's quite possible to increase it by order of magnitude before healthcare/sanitation is overwhelmed after few weeks. So that's 0.5-1% right there taken care from start, more depending on various factors. It's quite a lot, actually. Then society collapses, mass panic, evacuation jammed roads etc. In big cities rats, flying rats and other bugs take care of quite a lot of bodies rather fast. WOn't help survivors there - they will suffer secondary effect of that in all forms, i.e. rapidly spreading flesh-eating bacteria, all kinds of worms and insects feeding and reproducing at phenomenal rate. Most of the survivors will be in rural and/or remote areas. So not much bodies to start with. Distance from cities will also prevent diseases to spread there. I'd say you have to work some more on initial conditions of your Apocalypse... [Answer] Even if deaths occur in a short period of time, it's not an overwhelming logistic problem if people remaining alive (and healthy) want to dispose the corpses. A 95% death rate means that each survivor has to deal with 19 corpses, and that doesn't seem an impossible task, even if a sizeable part of the survivors can't do it (elderly people, children and so). Furthermore, in such a sudden crisis, survivors are likely to be able to use excavators or other equipment to bury or cremate corpses. The main problem would be to coordinate survivors for burial. In a 40 people village it's easy for the 2 survivors to agree to do the task of disposing the 38 remaining corpses, but if most of the 100.000 survivors of a 2.000.000 inhabitants city keep waiting for someone else to do the task of burying the 1.900.000 corpses, nobody will do and the survivors will need to flee the city. [Answer] In [Sugar Scars](http://www.goodreads.com/book/show/26095435-sugar-scars) by Travis Norwood this problem was solved by government deception. The government informed people that the virus was spread through air, and the only way to avoid infection was to seal your house with duct tape and stay indoors for a month. Thus, all the bodies are conveniently contained within sealed boxes. The lie is also believable enough that not many people need to know the truth. You only need to cope with the bodies if you want to salvage resources from homes. Presumably you would prefer to take supplies from shops and workplaces. [Answer] Just start making mass graves as soon as a noticeable amount of people died from it, say 10 to 15 percent. Or just start pouring them in the canyons spread around the world. As for the spreading to the living, well, start enslaving the already sick, unless they find a cure. [Answer] ### If your goal is to get rid of the bodies for story purposes let the diease do it for you. This is a little convient for pure chance but there are several plant diseases which basicly liquify the plant fairly quickly. So you might be able to tailor your disease or a secondary infection to *help* clean up your cadaver problem. I will add references if I find some [Answer] Have your disease affect the minds of the dying: like lemmings they will flock to water (rivers and beaches) and die in it (drown). Problem 'solved'. ]

[Question] [ What shape of ship would be optimized for space combat in the context of a future space navy? What advantages and disadvantages would the shape you have chosen have and why is it the best for future space warfare? Space warfare will be in a close to hard science scenario. Space is a 3D environment where no stealth is possible because since space is cold, the tiniest amount of heat would radiate like a beacon. Most combat would be based on bringing your weapons to bear on the enemy as fast as possible, maneuvering as fast as possible or simply having redundant systems and long range firepower capability. Assume technology has advanced 500 to 1000 years from the modern day. There is limited FTL, low intensity artificial gravity, and most weapons would be relativistic direct fire or guided. [Answer] **Cigar-shaped.** Space is a 3D environment, and attacks can come from any direction. This suggests that a sphere might be the best shape, with weapons mounted across its surface, but that would both be inefficient (most weapons could not come to bear upon a single target), and present a large target. A cigar-shaped object would allow weapons to target in all directions, particularly if turret-mounted, while vasty increasing the number that could bear on a single target and presenting a minimal cross section. Of course, this assumes direct line-of-sight style weapons. If space combat is based on missiles, and these are fired at extreme distances, the most effective shape will probably be the one that can hold the most missiles, so we're back to a sphere again (missiles could be fired from any 'side' of a sphere, and be guided to the target). Space combat might also be based on passive engagement - laying of 'mines' of some kind along desired (e.g. economical, efficient) routes. In this case, either technology - mine detectors/eliminators - will render the shape of the spacecraft moot, or, if we assume that these mines are difficult to detect/remove, then a cigar-shaped ship, propelled lengthways, would present a very limited cross section and so miss most mines (at least relative to other shapes). The 'nose' of such a ship might even be purely armour / disposable, to negate the impacts with mines that it doesn't miss. [Answer] You have FTL and gravity control. Between the two, physics is completely different. But I can try. First, energy. If we assume a 1% per year growth rate, 1000 years from now we have a 20000x higher energy budget (E4.5). We are currently a K-type 0.7 civilization; they would be a K-type 1.15 civilization. A K-type 1.15 civilization has no sigificant portion of its economy on planets unless it is a gas giant; their energy budget is 30x larger than what an Earth-sized planet can radiate without boiling its oceans. If we assume a 3% growth rate, they are a K-type 1.9 civilization (ie, within rounding error of 2). This has either swallowed an entire star in energy-consuming structures, or have lower density (say ringworld size) structures over a good chunk of the local galaxy. If we assume a 5% growth rate, they are a K-type 2.8 civilization (ie, within rounding error of 3). This civilization has swallowed every star in a galaxy in dyson-sphere like structures or found more efficient ways to use the energy of a star and are using it. --- Gravity manipulation and FTL mean they have access to ways of manipulating the universe that are as alien to us as self flying jet planes are to a hunter gatherer society. By occam's razor they are related: this civilization can manipulate the fabric of space time to cause it to bend in strange ways. Together with the above energy budget, chemistry based matter as we know it is going to be as modern a material as bone is to us. You would no more build a tank out of carved mammoth bones than they would generate a space ship out of metal alloys. Sure, it is elegant and beautiful and it is amazing what primitive people can pull off with such limited tools. But for serious engineering? --- Finally, information. Human ability to process information has been growing at as exponential and as steady a rate as our ability to process energy. Arguably they are tied, as what we call energy is really energy arranged in a highly usable way, which is a question of entropy, which is information. We have every reason to believe that we are close to being able to emulate a human intelligence. We have been able to emulate increasingly complex networks of nerves and replicate the behavior of relatively simple organisms. Barring a surprise (like, for example, [we encode memories and information in DNA](https://www.theatlantic.com/science/archive/2018/01/brain-cells-can-share-information-using-a-gene-that-came-from-viruses/550403/)), scaling up to a human is a matter of marginal technical improvements in remote sensing and computing. Even if we assume that making smarter than humans turns out to be hard, creating artificial human-scale intelligence isn't far off on the scales we are talking about. As humans are shockingly horribly suited to the environment of space, initial intelligent exportation will be with such beings, and such beings will out-compete water-bag humans at living in space. The bandwidth to communicate a mind state from one location to another isn't going to be that high (again, assuming continued scaling of current technology). So warfare is going to involve intelligent munitions on suicde missions with backups and indoctrination that their sacrifice is worth it for their highly related "left behind" copies. Life support won't be a question; just maintaining a computational platform. Hardening these against electrical weapons is going to be easier than keeping a biosphere around. --- So, we are talking non-matter based distributed networks of the descendents of uploaded minds piloting exotic high-energy weapons. Nothing is going to resemble a WW1 battleship or WW2 aircraft carrier. Those where designed based on the energy budgets and situations of a gravity-locked biological life form using 20th century technology, not a space-based intelligence using 30th century technology. If there are civilizations using space battle ships that fire relativistic projectiles and guided missiles, they'll be the equivalent of US white supremists stockpiling assault rifles for the coming civil war. History has passed them by. [Answer] I think a more important factor than the shape of any individual ship is the relationship of ships in the fleet to each-other. A primary challenge of war craft in space would be that, due to inertia, the path of a ship would be easily predictable by the enemy (just goes in a straight line at constant velocity). Hence, it can easily shoot a missile from a long distance away and guarantee it will hit. This could be somewhat avoided by the ship accelerating or decelerating, but this is costly--not only does it use up energy to expel a projectile, but it also means that the ship has to part with some mass each time it does this. A better solution to this challenge would be to have the ships connected to each-other by elastic strings. For simplicity, let us say that there are 2 ships rotating around a center of mass, which are prevented from flying off in different directions by an elastic string. The ships can communicate to each other to pull on or to slack out the string during battle, in some sequence that is indecipherable to the enemy ships. This will change the rotational acceleration of the ships, making it very hard for the enemy to predict where each ship will be in the future. Furthermore, all mass remains in the system and, assuming there is a good way to recollect energy when the rope is slacked out, it uses relatively little energy. On the ships themselves, this would simply be perceived by small variations in the apparent gravity on the ships (higher apparent gravity when the elastic string is pulled, lower when it is released). This could be compensated by, for instance, adjusting the small level of artificial gravity. [Answer] Depending on what offensive and defensive technology is used in your universe, different shapes would have different benefits. Relevant factors are: * **Minimize or maximize surface area to volume ratio**: A smaller surface/volume ratio allows you to add thicker armor to your ship without adding more mass to it. On the other hand, if waste heat is a problem in your universe, you might want to maximize surface area in order to improve cooling through radiation. * **Minimize or maximize profile, in one, two or three dimensions**: A small profile makes you harder to hit and allows you to use even more armor for less mass in that particular direction. But on the other hand, you also have less space for placing your own weapons. You also need to keep the enemie's maneuvering capabilities in mind. If they can outmaneuver you or attack from multiple angles at once, you might not be able to show them your "best side" at all times. If you require solar power, then you need a large surface area in at least one direction. * **Structural integrity**: If you take hits, you want to avoid breaking apart. * **Engineering concerns**: Your ship design might be heavily influenced by a primary system which requires a certain shape. If one specific component (propulsion, weapon, etc.) is the main contributor to the volume of your ship, then that component's ideal shape will be a major influence on your overall design. ## Spherical [](https://i.stack.imgur.com/XFnE4.png) The best way to concentrate all your mass in the least amount of space and under the minimal amount of surface area. If armor technology is relevant in your universe and if your enemies are fast but have trouble aiming, then you want a sphere. They won't find your weak side, because all your sides are the same. But keep in mind that if the enemy *does* land a good hit with a penetrating weapon which can pierce through your whole ship, they will do the maximum amount of damage to your internal systems. Also, with such little surface area, getting rid of waste heat could become a [problem](http://starwars.wikia.com/wiki/Thermal_exhaust_port). ## Long [](https://i.stack.imgur.com/GSJza.jpg) The shape you imagine when you imagine a space *ship*. When you can manage to always point the bow towards the attacker, you have a very tiny profile. Adding some thick armor to the bow gets you a lot of resilience for very little mass. But even if the enemy manages to flank you, you still show comparably little profile. And you still got a good surface/volume ratio. A structural weakness is that a powerful hit from the side might easily cut your ship in half, which will likely disable it completely. If your design is dominated by systems which are long and thin (like linear accelerator weaponry or certain propulsion technologies) then this shape will be the most natural one. ## Flat [](https://i.stack.imgur.com/VqbkE.jpg) The classic UFO shape is very flexible when it comes to profile. Depending on situation you can minimize it by showing the edge to the enemy or you can maximize it by showing them your face. A direct hit on your face will easily pierce it, but the damage will be localized. If you have lots of redundancies in your primary systems, it will take several hits to take you down. Hits from the edge will easily miss and will only damage the outer sections. If the enemy can outmaneuver you that they can face your edge if they want to **and** has a weapon which is capable of piercing your ship edgewise **and** is accurate enough to do so... well, then you are pretty screwed no matter what shape your ship has. ## Filigree [](https://i.stack.imgur.com/0ZBlY.jpg) If you need to maximize surface area for some reason, then this is the shape to go. But keep in mind that it will likely be very fragile. A fractal shape could also be useful if you want to maximize the occupied volume of your ship. The enemy might be able to hit you, but they will have trouble doing any actual damage, because there is just *so much* ship to hit. [Answer] Ship combat is about much firepower you can effectively bring to bear on your opponent while reducing your own exposure to their weapons. Basing this on the known factors of ship to ship warfare during the age of empires, it's all about how many guns you have. That requires you to have a shape that maximises the surface area to give you enough space to mount all those weapons. The sphere is well known to minimise the surface area to volume ratio, what we need is the opposite, we need to maximise the surface area to volume ratio. This will reduce the mass while allowing us to mount more guns. I was going to suggest [Gabriel's Horn](https://en.wikipedia.org/wiki/Gabriel's_Horn), but it is a rather impractical shape to build. So I shall instead suggest a [Menger Sponge](https://en.wikipedia.org/wiki/Menger_sponge) [](https://i.stack.imgur.com/iqKBA.jpg) This gives a considerably larger surface area for your mass so you can mount more guns, and allow you to launch indirect firing weapons such as missiles and fighter craft from protected internal openings. Any resemblance to a Borg cube is entirely co-incidental. You will be assimilated. [Answer] Obviously this is a subject of substantial debate, and there isn't really one "right" answer. But I would like to make some additional points not mentioned in the other answers here. Fundamentally, this question depends on two things: * What is your state-of-the-art in weapons and propulsion technology, and; * What kind of combat do you want? As an avid player of space RTS games, a designer of combat ships in Newtonian physics simulators, and an aerospace engineer for the US Navy, my philosophy on starship combat is to avoid close-in engagements at all costs. In my experience, if you get close enough to your enemy for a slug fest, you're *both* going to come away in bad shape. And spaceships are inherently bad combat platforms for a lot of reasons: * It's very difficult to maneuver in space, and the more massive your ship, the harder and more expensive it becomes * By their very nature, guidance and propulsion systems cannot be shielded from damage and will be the first things you'd lose in a fight * Unless you're using some kind of reactionless drive, every engine and thruster on your ship will present a large, soft target * For every action (fire a gun, take a hit) there is an equal and opposite reaction (you get pushed away, undesired rotation, harmful vibrations or accelerations, etc.) * A solid object about the size of a BB traveling at orbital speeds can [make a hole several inches wide and deep](https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20120002584.pdf) * Holes in your spaceship are generally worse than for any other vehicle (even submarines) unless your ship is unmanned I much prefer long-range engagements, preferably with the advantage of surprise. It's much safer for you, and you're much more likely to win. For this approach to work, agility and stealth are your major design drivers. If, however, you want epic close-quarters slugfests, your architecture will need to be fundamentally different. Speed and agility will still be essential, but you'll trade stealth for heavy armor and layered weapons. Keep in mind that providing lots of surface area to mount lots of guns is **not** the best strategy! More surface area means more mass, and more area for the enemy to hit. Complex shapes are hard to build, harder to repair, and very bad for attitude control systems in space due to irregular CG, resonance frequencies, flexibility in the structure, and weird effects from battle damage. Less is more in this scenario: you want just enough weapons to kill your opponent, and just enough area/mass/systems to support them, no more. Space them out so that one good shot by your opponent won't knock out multiple weapons or vital systems at once. Redundancy will be particularly vital in a close-quarters battle, because you *will* take lots of damage, and armor alone won't protect you. If you have your eye on CQB, do you envision frontal assaults or classic broadsides? Frontal assaults would compel a wide, flat ship with most of its weapons on the front for maximum damage output. Broadsides would emphasize symmetry about the long axis with mirrored weapons on either side. Perfectly symmetric ships are not a great idea here because of the amount of duplication. For example, take a sphere: the weapons on the rear are useless if confronting an adversary at the front, and all they're doing is slowing you down. Engines on the sides or front are dead weight and added vulnerability unless they're actively being used. If you favor long-range combat, do you want conventional or directed-energy weapons? Torpedoes have great damage ouput, but suffer from limited speed, maneuverability, and vulnerability to countermeasures. Lasers would be superior with near-instantaneous damage on target, are scalable to whatever your power source can handle, and impossible to effectively counter, but have relatively low damage output. (And no, you can't just coat your ship in mirrors -space is dirty, and those mirrors won't stay clean enough to protect you from a big laser.) Will your ship be fighting alone, or with support? Combat support or logistics? A ship with combat support won't need as many weapons or firing arcs, because it'll have buddies which can fill the gaps. A ship with logistics support (think [oilers in the US Navy](https://en.wikipedia.org/wiki/Replenishment_oiler)) won't need lots of onboard fuel, munitions, or maybe even crew spaces, so it can be smaller and lighter than a lone-wolf ship. Finally, stealth isn't as impossible as you might think. Space is *vast*, and finding one little glowing pip of thermal energy in a sea of stars is no easy task. Take [this interstellar asteroid](https://www.sciencedaily.com/releases/2018/03/180319120111.htm) which passed through our system just a few months ago: we didn't see it until it had already passed and was on its way out. If you place your heat-rejecting components and radiators in one protected spot on your ship and cover the rest with thermal coatings, you'll look just like the background. Lastly, I'd suggest you look closely at modern naval warfare and ship design, because although it's (mostly) 2-dimensional, it really is a good analog for space combat considerations. [Answer] It depends on your science. The most likely is that they will look very similar to modern rockets and spaceships - basically like a tower. There are solid, basic engineering reasons for those designs that aren't going to change easily. There are a bunch of little reasons. Heat dissipation is likely important and is harder the more spherical you get. Efficiency of design - only having one engine (or bank of engines), power flowing along one direction, etc. Having a variable cross-section might be important - the ability to point your "nose" into enemy fire to reduce the chance that relativistic weapons hit you. But all of those are relatively minor. The biggest reason is structural. A tower-type design means that thrust is 1) always primarily in one direction, and 2) the materials of your ship are aligned with that thrust. A sphere or cube would need to be massively over-engineered, in comparison. You might be able to do a sphere with engines all along one hemisphere, but that doesn't scale as well as you try to make the ships bigger. You can solve this by adding more power and AG, but that means more heat, and that's not easy to get rid of. Additionally, there's no such thing as a free lunch. That power your spherical ship is using on AG could be put to better use in a tower-based ship. Because of the extra engineering, it also means that you can build more tower ships for each sphere, even given the same materials. Even if spheres are better 1 to 1, that's not going to be the case - someone who sticks with tower ships will end up with a tonnage advantage, even if everything else is equal. To get away from tower ships you need some sort of overriding reason to build a less efficient ship. It could be a requirement of your FTL engines, or even your normal-space engines if you get creative enough. But basic technology advancements aren't likely to take us away from a tower/cigar design. [Answer] The "Children of a Dead Earth" video game has basically solved this for hard science. This [link](https://childrenofadeadearth.wordpress.com/) backs up most of the science behind the game. Basically Kerbal Space Program with guns and missiles, his cone shaped armored warships are probably the closest to potential reality given that he has virtually no hand-waved science so the ships and weapons have to actually work. [](https://i.stack.imgur.com/tRJ4J.png) You can see the sloped armor to deflect impacts from ahead while allowing sensors and weapons to fire ahead as well. Engines are at the rear where the nozzles are protected, since without controlled thrust you are adrift. [](https://i.stack.imgur.com/c4QGG.png) The interior is mostly fuel/remass tanks, coolant so radiators can be stowed if necessary while in combat, and the crew living module. The layout is like a very narrow tower rather than a horizontal hallway since under thrust "down" will be towards the engines. [](https://i.stack.imgur.com/NNQeD.png) Obviously the aesthetics are lacking compared to the aerodynamic ships in media, and civilian, non-combat ships would look quite different (more like lollipops with a bulbous habitation module with internal rotation or a ring so the ship can be spun for gravity when not under thrust and a long column of tanks and radiators with an engine at the rear). You can go to [Atomic Rockets](http://www.projectrho.com/public_html/rocket/) if you want to read up on all sorts of very realistic, practical ship designs. Essentially, your engines determine the ship shape. Here are some examples (all shamelessly lifted from Atomic Rockets). First is a classic Heinlein torchship, basically a sphere with a fusion rocket at the end. [](https://i.stack.imgur.com/Umt8q.jpg) Very practical, but probably not what a dedicated combat vessel would look like since it offers a huge profile in every direction. But great for optimizing internal volume and keeping everything away from that super radioactive drive. A more aerodynamic version with some concession to atmospheric stability. [](https://i.stack.imgur.com/PINTM.jpg) Finally, a more likely shape, which is the lollipop design from Attack Vector:Tactical where the engine is as far from the people as possible. [](https://i.stack.imgur.com/mq8T8.jpg) The spikes on the rear are radiators for the engines, designed to stay in their own shadow to limit the neutron damage. Again, high performance engines have HUGE radiation emissions, so there are a lot of design constraints. The ship also has to support itself when under thrust, so everything tends to be stacked over the engine which reduces the total weight of the superstructure (towing a ship is even more weight reducing since pulling requires less strength in support structure than pushing) like the Avatar movie Venture Star [](https://i.stack.imgur.com/lsIRv.jpg) Where the big thing to the left is the engine that tows the smaller cargo/crew module to the right. But having your engines up front probably isn't the best for combat, so we are back to the CoaDE cone shape which offers some protection to the engines. If you sort of handwave away the radiation from the engine, you can get stuff like the Rocinate from "The Expanse" [](https://i.stack.imgur.com/iWd8Q.jpg) which has an engine with less shielding for the crew, some aerodynamic atmospheric capability, the tower design, sloped armor, and quite frankly, a more pleasing aesthetic appearance than the CoaDE cones. Even with FTL (how exactly does that work? Wormholes, warp drive, jump gates, etc) the "real space" combat would still dictate the cone shape, unless you are using some sort of magic engine that doesn't require remass and doesn't emit lots of nasty radiation/toxic byproducts you don't want washing all over your ship and living areas. Most sci-fi ships have MASSIVE engines, but almost no fuel! This is the opposite to reality. Limited artificial gravity could limit the need for ships to spin when not under thrust, but what does "low intensity" mean? It is weak, only in parts of the ship? Because while under thrust there will definitely be a pull opposite the direction of thrust, so either you are counteracting that so you can have a horizontal "ocean liner in spaaace" layout or just compensating for not having thrust during the long periods of weightless drifting between destinations (unless you have something like the Epstein drive in "The Expanse" series, which can thrust almost indefinitely on very little remass). Relativistic weapons means either lasers, which diffuse at relatively short ranges AND generate as much heat in your ship as they do on the target ship, or super rail guns which still deliver as much kinetic energy to your ship as the target (but hopefully you have recoil compensators to spread it out). Point being, a near light speed kinetic impact will destroy ANY ship, no matter how armored, so no point in armor in that case (rather better to let the projectile zip right through your ship). But you have to decide on how heat will be handled (since almost no modern sci-fi media depicts radiators they just ignore it), do you have some sort of energy/gravity shield, and how do ships maneuver in real space (i.e. how hot [radioactive] are their engines and how much remass/fuel do they need to carry). This will dictate a lot of the practical ship design. Is there an aerodynamic re-entry requirement? If so, then a streamlined hull is necessary. Otherwise you can have almost any shape you want, just realize that it all has to be supported while under thrust, unless your antigravity can compensate. [Answer] Given there is no stealth in space and you can aim and fire at long distances, there are a few different ways you can go. 1. If weapons are relatively short ranged. If ships weapons are relatively low powered, then the issue might be to be able to manoeuvre when in relatively close proximity (relative may still mean hundreds of kilometres away). The "[Star Fury](https://www.youtube.com/watch?v=nanfQ0mviaU)" fighter of the TV series [Babylon 5](http://tvtropes.org/pmwiki/pmwiki.php/Series/BabylonFive) provides a possible answer. The ship's reaction motors are mounted at the ends of the long booms, providing a great deal of leverage to move the ship about all three axes. If you watch carefully, the ship can be orientated to point in any direction to track, acquire and fire on any target, but may continue on the same orbital path, unless the engines fire long enough to impart a change in velocity different from the initial path. While never actually mentioned in the show, the rectangular booms housing the engines could serve as heat exchangers or radiators as well. [](https://i.stack.imgur.com/hfnfn.jpg) *The adaptable Starfury design* This design can scale very well, with the caveat that larger ships will tend to turn more slowly since they have greater mass, thus more inertia to overcome before pointing the main battery at the target. 2. Space combat takes place at long ranges (10's of thousands of kilometres).This isn't the sort of space battle seen in movies (evidently inspired by the age of sail wooden ships pounding each other with muzzle loading cannons). Ships are far enough away the are not visible to all but the most powerful sensors, and except for laser weapons, there is significant time between shots being fired (out of electromagnetic [railguns](https://infogalactic.com/info/Railgun) or [coilguns](https://infogalactic.com/info/Coilgun)) or missiles arriving on target. While turreted battleships might seem to be the solution, the sheer length of electromagnetic weapons firing at orbital or interplanetary velocity precludes this. Instead, the ship might resemble a sea urchin, with long spines corresponding to rail or coilgun barrels extending in all directions. When targets are detected, the appropriate barrels are energized and fired. Either fine control can be applied directly to each barrel (say a small 2 degree of freedom ball mount) or the ship itself makes fine control movements. After the long journey, the projectiles might also have small rocket motors to make final adjustments to strike the target as well. Like a real sea urchin, this ship could also be "grounded" on a small asteroid and still present a bristling array of weapons. [](https://i.stack.imgur.com/p8Ysh.jpg) *Sea urchin based coilgun ships would resemble this* If missiles are the primary weapons system, they will be quite large. The New Horizons spaceship took only 9 hours to cross the distance between the Earth and the Moon, but it was launched on an Atlas rocket derived from an early Cold War ICBM [](https://i.stack.imgur.com/Elk2V.jpg) *If this is your anti ship missile, your launch platform is going to be huge* This suggests that a similar dynamic will be in play, the ship will essentially be a mobile ICBM field, and the final product may resemble "corncob", with each "kernel" being the cover of a launch tube. [](https://i.stack.imgur.com/p2OcF.jpg) *Not so tasty when it's shooting at you* 3. Ultra long range weapons (out to one light second). Since the space environment allows you to build huge structures in zero gravity, there are few limits as to what you can actually build. The Atomic Rockets "[Conventional weapons](http://www.projectrho.com/public_html/rocket/spacegunconvent.php)" page has a long section on lasers, and the ultimate laser weapon is an X-Ray FEL driven by an electron beam accelerator a *kilometer* in diameter. At one light second (300,000km, slightly less than the distance between the Earth and the Moon), it has enough power to slice through metal, ceramic and carbon fibre in *milliseconds*. The one light second rule is rather arbitrary, based on the notion that you want no more than two seconds to elapse between the time you fire the beam and the time you see the results of the shot. At one light minute, it is still powerful enough to melt materials, and is a dangerous radiation source to unshielded sensors (or people) a *light hour* away. [](https://i.stack.imgur.com/UbNU4.jpg) *The Ravening Beam of Death (RBoD) X-ray laser* At that point, the shape of the ship is largely irrelevant, since you can be theoretically slice an enemy ship into small pieces from incredible distances. The RBoD will be an unlovely assembly of girders, power modules and radiators. It will likely be surrounded by a cloud of small drones with provide sensor data, giving a finely detailed 3D view of the surrounding volume of space. [Answer] When you consider The Kzinti Lesson (the more efficient a reaction drive is, the better a weapon it makes). Any civilization that can produce the energy to travel between worlds can also produce a weapon that can turn pretty much any solid matter into plasma making armor irrelevant. This means the quality of your ship's defence is exactly proportional to its ability to avoid damage altogether. If we assume two ships have good enough of sensors to see and target each other at any given range, damage avoidance becomes a function of how narrow your profile is vs your maximum acceleration in relationship to that axis. For example, if your ship has a 10x10 unit front profile, and you can accelerate 10 units in any direction in the time it take an enemy missile to compensate to hit you, that means through randomizing your strafing acceleration, an enemy missile has a 1:2 chance to predict your X profile and a 1:2 chance to predict your Y profile for a total chance to hit of 1:4. If you extrude that ship's profile to be 1x100 units (same area but thinned out), then an enemy missile has a 1:20 chance to predict your profile on the X axis and a 1:1 chance to predict your profile on the Y increasing your overall chance to evade a shot 5 times over the squared out ship. Logically, the more you can stringify your ship, the more effective that randomized strafe can be to reduce your odds of being hit, but you you can only min-max you ship's thinness to a point before you risk it breaking under its own inertia. Also, when a stringified ship does get hit, it is cut completely in half separating vital systems from one another. Since a stringified ship is so fragile, this means an enemy ship can just compensate for your evasiveness by firing a lot of weaker shots instead of one big ship vaporizing one. **The Solution: A Spherical Hex Lattice** [](https://i.stack.imgur.com/vZJvl.png) By modifying these principles and turning your ship to a spherical lattice, you maximize how "thin" you can make any one surface of your ship while also maximizing its overall structural integrity. It also breaks up lines along any single vector so a targeting system can't take one cardigan component for granted like it can with the stringified ship. Even if you fire a bunch of shots into the "hitbox" of the ship, 99% of them will just pass harmlessly through the lattice without hitting anything at all. It will also propagate damage way less than a solid design. If a weapon designed to vaporize an equally massive solid ship scores a lucky hit, it will only vaporize a few nodes, while leaving most of the ship in-tact. With each node containing systems that can't just be cut off in bulk like on a stringified ship. Firing at it is a lot like trying to kill a swarm of bees with a handgun. However, it does have 1 advantage over a swarm which is that certain systems don't need to be in every node. In a swarm of smaller ships, each ship needs thrusters, senors, weapons, computers, etc. which all need to be miniaturized enough to fit on each swarm ship and powerful enough to target larger ships at range. This means most of the mass of your swarm is just expensive, redundant support systems whereas a larger ship might have less redundancy but more powerful systems. In a lattice ship, the engineers control the level of redundancy; so, you might have 30 nodes allocated to propulsion, 20 to weapons, 6 to sensors, etc. This way you get all of the advantages of integrated systems you see on a big ship with all of the difficulty to fully wipe out like a swarm *(Note: This idea is an adaptation of the "spaghetti" ship exploit from the MMO spaceship building game, Starmade, which demonstrated that such ships could take on "traditional" ship designs of similar tech 50 times their mass and win. This game also demonstrated that high density spherical/cubic ships performed the worst out of any ship design shapes because they are easier to hit from all directions, and always have plenty of vital systems to punch through no matter what damage propagation profile your weapons have.)* [Answer] If you’ve ever read Arthur C. Clarke’s “Hide and Seek,” you know how important it is to be able to maneuver. A ship with spherical symmetry, and especially with vectored thrust, can turn on a dime. If you need more surface area rather than less (which I imagine is more likely to be because of heat dissipation when you only have radiation, not convection, to remove heat than to have more space to stick weapons), you could make the sphere a hollow lattice, maybe with some internal struts. The engineering of different spaceship components might give you more interesting shapes. If you need to generate a shield in the form of an ellipsoid, you want two separated foci for it, so maybe you have a beam with those on either end. Maybe the engines have to be kept apart from the crew. Maybe spikes radiate excess heat. Something like that is what retroactively explained the iconic shape of the *USS Enterprise* and why other ships in the same universe have the same recognizable style based on it. If the spaceships need to enter atmosphere, it makes sense for them to be aerodynamic. If they need a bay or a hangar, that changes the design. [Answer] I think that the shape is basically irrilevant, but you should add some details about the technology level (Is there FTL ? What weapons ? Artificial gravity ? Are there something like an actual fighters ? ) True, space is a 3D environment, but at the same time you can deploy your fleet in a 3D formation. Making an analogy with the current fleets, the attack can arrive from every direction (let's forget the submarine for now) and you deploy the ships to cover this (roughly in a circualr shape). There is no reason why in space you cannot do something along the same logic: the attack can arrive from every direction, so you deploy your ships in a sphere (or cilindrical) shape, with the advandage that, without a strong gravitational force given by the Earth, every ship can aim its weapon towards the outside of the sphere and be oriented accordingly so that it need to cover only its top. Assuming this, the shape of the ship became pratically irrilevant and you can use whatever shape make sense or is more efficient for the ship type, but you don't need some particularly exotic shape. Bonus point, you still operate a ship where, from a human point of view, there is a top and a bottom, which is the natural situation for the crew. [Answer] **Disk or Saucer Shaped** Probably with a structure like several movable concentric rings joined together to form a saucer shaped ship. *The outer larger rings are to be joined edgewise with the next smaller ring inside them* It is quite efficient for a Space Battleship- * It has the benefit of 2 large surface area faces, providing room for a large number of retractable turret based weaponry. * The shape provides the maximum maneuvrability ,after the sphere, for 3 dimensional space travel. Multitude of small engines along the rim, for quick burst of speed, and a main engine near the centre for long travel. The movable concentric ring design allows the main engine to be fixed in place. The easy movement would lead to greater rates of evasion or escape. * The ability to move in any direction in a plane in an instant, gives it the advantage of unpredictability, with no chance of path prediction attacks. * Concentric ring design allows the turret basea weaponry to be aimed and oriented in a large number of ways, leading to higher flexibility in combat, and significantly higher accuracy. The rings could be aligned to increase or decrease the rate of fire by allowing or not allowing the inner ring turrets to get a line of fire on the target. The angle of the ship, with respect to the plane of the assailant, could regulate the rate of fire by allowing more turrets to fire simultaneously. * The shape itself is very hard to hit when seen edgewise. With all the turrets retractable, the ship basically becomes a line in space from the side, and the damage dealt to the ship ( if any) would be minimal due to the direction of the attack. Adding armour to the ship only along the rim would add minimal bulk and make the ship practicality impenetrable from the edge, giving an insurmountable tactical advantage. So all in all the concentric saucer is a very balanced shape of ship to have. It boasts the title of the shape most difficult to hit (after the rod shape) and the highest concentration of fire (after the sphere). Its maneuvrability is second only to to the sphere but with the distinction of having significantly less mass, causing less fuel consumption. Overall, it appears to be the best shape for a space Battleship [Answer] There is no reason to assume that space ships will look anything like ships at all. The shape of a ship is driven by environmental constraints - water most importantly. The desire to keep it out, the need to cut through it efficiently. In space, none of that is true. The ISS is probably a much better model of a future space ship than all the SciFi movies. Even your average oil platform is closer than the Enterprise or the Death Star. Especially a war ship is quite likely to be made up of frames and struts and a lot of its enclosed area will actually just be the empty space between the structural components. This way, any individual part can be hit, destroyed or discarded as necessary without impacting the stability of the structure. The need for an actually enclosed area, with atmosphere and (preferably) gravity, would be a tiny part of the whole thing. The crew quarters and control areas. Want to repair the laser array? Don a space suit. A war ship would be built with redundancy in mind, so it can sustain a couple hits without losing vital parts. It would try to put the hottest parts (engines, some weapon systems) at the edges so an enemy targetting them doesn't hit the control or central parts. Must-read: <http://www.projectrho.com/public_html/rocket/> It's a massive website, but it tackles all of these questions in as much detail as you can stand. Don't write SciFi without reading Atomic Rocket first. ;-) [Answer] One that looks exactly like an asteroid? To expand slightly: Any spaceship that looks like a spaceship and is detectable will be space dust in the first few hours of a space war. The most effective spaceship has these characteristics: * Does not look like a spaceship * Does not emit anything detectable * Does not move in a way unlike other space objects * Has weapons that cannot be tracked back to the spaceship So, a hollowed-out asteroid, with nukes that drift at low speed in a random direction for a few hours before firing, using fake "outgassings" or EMP propulsion for movement, staffed by a computer. <https://en.wikipedia.org/wiki/Electromagnetic_propulsion> [Answer] As a aerospace engineer, here are my thoughts on this question: In space (unlike in a planet's atmosphere), there is nothing comparable to air resistance. So protuberances, booms, antennae, photovoltaic arrays (a.k.a., solar panels), etc., don't have any negative effects on a spacecraft's ability to travel through space. Therefore, spacecraft can be virtually any shape. All spacecraft need to be built as light-weight as possible, because the more massive the spacecraft, the bigger the 'engines' would need to be, which would require more 'fuel' (whatever type of fuel it might use). In fact, the energy required to accelerate a mass can specifically be calculated using Einstein's General Theory of Relativity -- as velocity gets closer to the speed of light, mass goes to infinity, and the energy needed to accelerate that mass also goes to infinity. Now you might say then that the mass is irrelevant, but that would be a mistake -- any 'work-arounds' that allow for FTL travel do not negate fundamental laws of Physics, and wouldn't apply to sublight speeds. So the design of the spacecraft's structure would have to be light-weight, which would make any protuberances, booms, antennae, PV arrays, etc. rather flexible. However, a vehicle with FTL capabilities would also experience tremendous rates of acceleration, or at least would experience considerable gradients of acceleration, when jumping to FTL speeds, or even at sub-light speeds. In other words, different parts of the spacecraft would be accelerated differently. Think of it as the equivalent of your head snapping back when you slam on the gas pedal in your car. These acceleration gradients would make it undesirable to have any long flexible structures sticking out of the main body of the spacecraft, since they could more easily break off. Also, from a structural efficiency standpoint -- getting the most volume for the least mass -- a sphere would be the best choice. So the closest to a sphere that you could keep the spacecraft, the better from the basis of minimizing mass. Also, it would minimize the cross-sectional area in all directions, making the ship a smaller target. Another consideration is that *the crew compartment (and anything else where the crew needs to access from inside the ship)* is essentially a pressure vessel -- normal atmospheric pressure internally, and zero pressure outside. In order to withstand the pressure differential and not create unnecessary stress concentrations in the hull, a sphere or cylinder (with rounded ends, like a SCUBA tank, Propane tank, etc.) would also be the most desirable. But you're talking about a war ship, meaning it will be equipped with weapons to fend off enemy ships. In order to be effective in a combat situation, the gun emplacements need a wide range of motion to have as wide a field of fire as possible. Think about the turrets of a castle or other fortification (e.g., Fort Ticonderoga), of the shape & location of the gun turrets on a B-29 or the tail gunner of a B-52 -- they stick out to create as wide a field of view as possible. So IMHO, I think a sphere with gun turrets that stick out (a shape something like "Bumble Balls") would be the most effective. Alternatively, a cube with the turrets at the corners could also work pretty well. [Answer] Frankly, it's easy to be caught up in the "configure my weapons" issue and forget the "physics of reality" issue. If you have the tech to fight a serious battle, then the only shape you'll be using is a sphere. Remember, unless you're going to stand-too (hard to do in space!) and lob stuff at each other, you're going to need to turn. The early U.S. space program used a very short cylinder, but it was short enough to manipulate with four evenly-spaced thrusters. If you're big enough to handle munitions, you don't have that privilege anymore. Physics will force you to efficiency. So, a sphere with (ignoring strength) six thruster emplacements and a single engine set pushing it forward. Weapons bristling in all directions so that you minimize the need to spin, pivot, and turn — because that all takes time (unless you have some Clarkean Magic to absorb inertial energy...). This solution has other benefits, it's least likely to break in half, least likely to have chunks (like corners) blown off, most likely to have an evenly dispersed magnetic shield (magnetics like spheres, think "planet"), and least likely to be snuck up on (no corners, angles, or shapes to look around, just "out" from the center). It also has the cool ability to gently spin during an attack to bring more weapons to bear "broadside." Try that with another shape! [Answer] Shape is irrelevant unless said ship enters atmosphere. The best design is a mobile factory that pumps out drones. The capital ship hides while the drones fight it out. Considered a ship is full of people and life support equipment, you really don't want people shooting at you if you can help it. [Answer] The ship and warfare are designed within your world and therefore it must obey the rules you created. * Where the ship take its power from and how? * Where are the ships supposed to maneuvre and how? * What are the systems it is carrying? * What weapons it is using and what weapons it is exposed to? * What defences the ship have? * What is the ship's estimated survival time within the battle? * What is the technological evolution of the spacecrafts? * Are you building a world for a book (series), computer game, RPG sessions? Do you expect to need a photodocumentation of your ships? All points above limit the ship design to a degree regardless it is personal or cargo carrier, civillian or military. Now, you have a set of possible shapes. For military uses there are two types of equipment: Fighter and Support. * Fighter is designed to be as lethal as possible and as tough as possible. The actual design differs from the means how the figther strikes (Death Star-like range attack, X-wing dogfight) and how much it is affordable and expendable to the fleet. * Support is optimised to carry/provide as much as possible. Again, the actual purpose of the vessel defines the actual design. Last but not least, if you need a graphics for a cover, illustrations, game visuals and "the community", the good-guys' ships must look sharp and sexy and the bad-guys' appropriately badass. [Answer] I'd have to say long rod/cigar shape for flexibility. What I haven't seen mentioned--it would pivot better than any other shape, allowing you to get any part (Except the dead center) out of the way of an incoming attack almost instantly. With a little extra fuel you could pivot on a point besides the center. Note that this pivot can take place in any axis. Longest distance of acceleration for cheap guns like rail guns where you are just flinging inert matter. This can also be used to drive the ship (Accelerating hydrogen, for instance, to near the speed of light would be a great drive). Large surface area for mounting external "smart" weapons like rockets. Smallest profile if the combat is one on one since you can point right at your enemy and he would have to hit you head-on. Also smallest profile in flight so you are less likely to hit space junk--only one small end section of the ship needs to be hardened against abrasion from interstellar hydrogen/micro meteors. Could spin for gravity if you like when outside of combat. Inside combat I think the spinning for gravity would negate nearly every combat advantage though--but the change might make for some interesting story devices. [Answer] ## The shape best suited to secure your faction's strategic objectives. The other posters have provided an excellent scientific foundation for your designs, but consider alloying it with your navy's strategic goals. Weapon design tends to follow the mission objective, whether that be the seizure of a valuable resources, suppression of opposing forces, or the destruction of strategic assets. ### What shape of ship would be optimized for space combat in the context of a future space navy? First, disregard the notion that the Millennium Falcon could survive a high speed flight through the interior of an Imperial Star Destroyer. Or a Death Star. (I don't see any flaps!) [](https://i.stack.imgur.com/214jS.jpg) *Atmospheric Re-entry* --- As [Ian Kemp](https://worldbuilding.stackexchange.com/a/107922/49132) and [Rob Watts](https://worldbuilding.stackexchange.com/a/107906/49132) pointed out, spacefaring vessels don't like air. If your navy's in the business of subjugating planetary colonists, then the engineering department would temper the abstract geometries of its products with some aerodynamic capabilities. This gives you the artistic license to design different classes of vessels with each suited to the task for which it was built. Most importantly, this creates an asymmetric combat environment in which a purpose-built atmospheric fighter in it's own territory will be able to [outmaneuver](https://www.history.com/this-day-in-history/spanish-armada-defeated) an unwelcome interplanetary visitor with ease. The same goes goes for combat against "amphibious" (transatmospheric) spacecraft, though the advantage would be less pronounced. > > 1588: Spanish Armada Defeated > > > The Spanish ships were slower and less well armed than their English counterparts, but they planned to force boarding actions if the English offered battle, and the superior Spanish infantry would undoubtedly prevail. > > > Motherships might be look like this: [](https://i.stack.imgur.com/qpjDf.jpg) While transatmospheric varieties will start to look like space shuttles and planes will look like planes (albeit optimized for atmospheric specifics like air density). *Construction and Resupplying* --- Getting fuel and repair materials into space isn't easy, so maybe the most effective unit would be the one that sacrifices some combat effectiveness for the ability to be replenished at any outpost. Many battles have been lost by generals who [neglected their supply lines.](https://dailyhistory.org/Why_was_Rommel_defeated_at_El_Alamein%3F) > > Why was Rommel defeated at El Alamein? > > > The Allies were close to their supply bases in Egypt and the Axis forces supply lines had become stretched in contrast. > > > ### What advantages and disadvantages would the shape you have chosen have and why is it the best for future space warfare? **Motherships** would be flimsy "bags of air" that warehouse supplies for refitting smaller craft. **Security craft** are usually cheap, sturdy, and fuel efficient for running patrols (e.g. cop cars). I'd go with a universal frame that can be fit with modular components that can be replaced as they break or the objective changes. Vessels that **assault asteroid** colonies might be tough little spike potatoes with omnidirectional maneuvering. **Space station assault craft** would be quick transporters with a variety of docking ports and a few forced entry options that won't cause decompression. A tube covered in ports seems likely. *Additional Considerations* --- > > Space warfare will be in a close to hard science scenario...no stealth is possible because since space is cold, the tiniest amount of heat would radiate like a beacon... > combat would be based on bringing your weapons to bear on the enemy as fast as possible...most weapons would be relativistic direct fire or guided... > > > You just described a video game called Elite: Dangerous, which focuses heavily on delivering a hard science experience. Check out the interviews of David Braben, who can go on for hours about transatmospheric flight and [combat in gas giants](https://www.youtube.com/watch?time_continue=55&v=ypIq3fg9nMM). --- [Answer] The ship would have: * A large circle facing the attacker with small holes for the guns to fire through. * Behind the circle a set of guns, sensors, engines, and the cockpit all a long way from each other able to move around when needed. The circle would be big enough so that your cockpit weapons and engines can be hidden from view behind it. The circle would allow your critical systems to be hidden from the enemy sensors while still firing. An enemy would in effect have to play battleships to destroy your crafts critical systems, methodically working through every part of the circle where your systems could be hidden. [Answer] There was a big discussion on the [Aurora forum](http://aurora2.pentarch.org/index.php) a few years ago about realistic space combat. Here are some takeaways from that: Except for knife fighting ranges you need seeking weapons (missiles). The reason is that detection ranges are very long due to the limitations of stealth in space. The reason is that you cannot target the ship. Light speed communication and detection means that you are seeing where the ship was. Also your weapon takes time to arrive. Lasers travel at c. Most anything else travels significantly slower. You have to target the probability bubble of where that ship might be when your beam/projectile/etc. arrives. The probability bubble gets bigger with the combination of acceleration available to the ship and the combined travel time of the detection radiation and the weapon's travel speed. You can shrink the probability bubble two ways: better processing power to rule out unlikely outcomes faster than the bubble grows due to the time of calculating that and giving up damage to attack an area. Missiles shrink that bubble by course correcting as they travel. Missiles can be better than fighters because they can apply more acceleration to "dodging" (making their probability bubble bigger) on approach since humans tend to squish if you get too energetic. Also, missiles don't mind going on a one way mission. Some are actually eager for it: "Bomb #2, get back in your bay." That leads to a doctrine of missile vs anti-missile weapons with variations. Anti-missiles can be either small missiles or direct fire weapons. So the strategies are: 1. **Long range missile slugging match:** Throw out as many missiles as you can as fast as you can since any ship you eliminate is one less ship firing on you and less defensive firepower. The side that runs out of ships, assault missiles or defensive missiles first loses. Variations revolve around different mixes of offensive and defensive output and a decision between mass devoted to launchers vs mass devoted to missile storage. 2. **Turtle with a knife:** Have enough speed, defensive firepower, armor and shields (if they are a thing in your universe) to wade through the missile storm to get into knife fighting range. 3. **Combination fleet:** A usually non-optimal combination of the two. Also note that I mentioned that there are limitation on stealth; not that it was impossible. The more efficient your systems are ad doing what they need to do, the less heat you will radiate. Also, you can concentrate some of the radiated heat away from your target (if you know where that target is). Also, ship stealth is helped by the fact that space is big and there is a lot in it. Detection capabilities (a combination of receivers and computing power) determine how bright relative to a distant star a ship has to appear to be spotted in a short time. That will determine how far away the ship will be before you spot it. Shape can help with the cross section but you have to give up storage volume to do that. You also have to decide between storage and launchers. Given the distances involved, you can likely put most of your launchers on one side of the ship or you can spin she ship. That is a factor of other world considerations. [Answer] **The only thing that would matter** is the moment of inertia tensor. (Which physicists and engineers often just call the "moment" usually.) <https://en.wikipedia.org/wiki/Moment_of_inertia> There's no other consideration, at all: since there is no air resistance. (It's surprising nobody else has pointed this out.) Note the excellent example animated-gif **of four rolling objects** on that wikipedia page. Depending on your desired strategic approach, your engineers would create objects with different moments of inertia. (Each would have **different advantages** - consider an ice skater pulling in her arms during a spin.) In space nobody can hear you scream, there is no surface effect physics, no viscosity physics (aerodynamics, etc) - but there is your moment tensor. Which changes everything and is the "whole" design. --- BTW note that ***even more-so***, if you have "inertia control" (just as in Star Trek and most scifi ships) - then, the design of moment of inertia is all-important. Indeed: just one example, you could have a ship that deliberately is long and slender with **huge weights concentrated on each end**... Then by using your "inertia dampers" ***on just one end*** you could create astoundingly fast (sci-fi) combat movements - spins, "dodges", and so on. [Answer] We can't really give any clear answers to this because of the first rules of warfare: 1. Build your tools in the best way to deal with the environment you will fight in. 2. The enemy is part of the environment you will fight in. The correct shape for warfare is *always* completely and utterly dependent on what you need to do with it, and that includes surviving enemy attacks. So what sorts of attacks are they using? If they have laser based attacks, ships which can maintain integrity while rolling (like cigar or spherical ships) will have a huge advantage by making it difficult or even impossible to target a single point for a long period of time. If they have kinetic weapons, shapes which are effective at taking hits from kinetic weapons would be valuable. I could see a structure which is little more than a thin shell with the actual body of the craft inside on mobile girders. If you can't see where the "heart" is, it's hard to hit it, so all of your hits on such a craft become glancing blows. If they are using nuclear weapons, then it might become effective to use a spider like structure. Have a large number of dumb objects spread far enough apart to make it hard to hit all of them with a nuclear strike. Even the mighty Tsar bomba was not lethal at 45km. Put wires between them, and your spider can flit along them to escape any particular attack. This would force them to fire quite a large number of weapons at you to trap the spider -- and hopefully you're shooting back at the same time. Likewise, your environment includes FTL. What does that do to to your design. One of the comments on another answer pointed out that there's an in-world explanation in Star Trek that the ships are all smooth and curved to cut down on warp drag. If your FTL works like Star Trek's does, you may need to take that into consideration. [Answer] To borrow from a comment I left elsewhere, you really have to look at exactly hat the characteristics of your ships propulsion are in order to know what the best shape is: You have limited FTL and limited Artificial gravity. The implicatons of having those depend on how good they are, as limited AG could go right out to inertial damping, which means your turn characteristics could be significantly different. Are you using reaction drives for sublight thrust/manouver, or are they reactionless? Again, a factor. The timescale involved puts us into and beyond Trek era, where we have inertial damping, force fields to help with structural integrity (all based on the same space-bending effects that make FTL travel possible) and spaceship hull designs that, out of universe, are desgined on aesthetics and looking good on camera, but in universe, are based on warp field physics so are more efficient than a flying brick (see also the Borg, who are supposed to be so good at warp physics that they can make their non-aesthetic flying bricks travel faster than everyone elses anyway.) Arguably, your technology level and the underlying nature of it will inform your ship design as much as your tactics. [Answer] The shape of a ship is determined as much by other factors as by optimal fighting capability. Manoeuvrability is important; your ship needs engines and thrusters and whatever else in order to be able to simply get from one place to another. It also likely needs some way for crew to embark/disembark: airlocks, docking ports, escape craft, etc. These requirement will all have more effect on the final shape of the design than its offensive or defensive capabilities. To be sure, for a warship, shape is important. But it is not the first factor driving the design. [Answer] **SPEED** In space, I don't think *shape* matters at all. I think its all about *speed*. Imagine a ship that is faster in every way to all the ships around it, flies faster, shoots faster, and computes faster with onboard super (quantum?) computers. In short, you couldn't shoot it down because its faster than your ship and faster than anything that you can shoot at it. But it could still blow the heck out of yours because it shoots faster too. Whenever I see a movie where aliens attack Earth (Independence Day) and alien fighters shoot it out with human jets (Independence Day) it always seems like the two types of craft are on equal or close to equal footing (Independence Day). NONSENSE! The alien ships would run circles around ours. With their greater tech they would totally obliterate our jet fighters and not even take one loss. It would be a total and complete slaughter! No offense to any fighter pilots. And its not because of the shape. Its because of the speed. So all things being equal, except for the speed, the much faster ship would absolutely win. **Better yet**, imagine a ship that could teleport? One second its there, it shoots the snot out of you, and then poof, before you even know it laser blasts are rocking your ship and you never even saw your enemy. Whichever side achieves either or both of these technologies first will have the upper hand as long as the other side doesn't achieve the same or equivalent tech. Even force shields wouldn't help because those can only take so much damage before they go down too. Sooner or later speed wins. **And if you really want to go way out**... how about a ship that is made out of energy? Or a ship that can "phase through" objects? Or a ship whose body resides in an alternate dimension?! You cant hit it, but it can hit you, regardless of shape. Those are more hand wavey, but we've all seen worse in sci-fi. Don't just think outside of the box... forget there's a box altogether! [Answer] I think it all boils down to how realistic do you want to emulate real physics. No matter the shape of the ship, if you want to be able turn and fight is not simple at all. For instance, your ship is travelling along at 0.2c at heading 180.0 and you've done a pass-by shot at your enemy, even if you rotated your ship to keep the primary weapons on the enemy, you are pretty much on the same heading of 180.0, and you will need a tremendous amount of energy to change your course to come around for another pass, and you can only expel so much thrust to do so or you'll smear all life on the bulkheads... unless you have inertia dampers. So to have combat, your pretty much have to slow down to a point that it becomes a slug fest, or it becomes an orbital conflict and you can use the planets gravity and atmosphere to bring your ship around. Other than that, it long range weapons that accelerate very rapidly at first, then use cold rcs systems to align on target so detection is darn near impossible. Watching a ship on TV turn like an airplane is not even close to reality. Just saying. Frit [Answer] **Any shape that can hold your FTL drive.** If your FTL technology allows ships to accelerate faster than light in realspace and not by taking a shortcut through some other dimension (hyperspace, thirdspace, the Warp etc.) then any FTL-capable ship - literally every one - is a potential weapon of mass destruction on a hereby unprecedented scale. Take, for example, the Space Shuttle orbiter. Assume we've replaced the Space Shuttle Main Engine assembly with FTL drives and filled it with ballast to increase its mass to its maximum takeoff weight of 109000 kilograms for a higher impact energy. Assuming a velocity of 1 *C* (which is great for a weapon but still not that useful for interstellar travel), it would impart over a million megatonnes of impact energy on a target. That's enough to crack a planet in half. Your space war would be a cold war, as literally anyone with minimal FTL capability could reduce a planet to a debris field orbiting a star. The very threat of it would be enough either bring someone to the negotiating table or cause your civilisation to be annihilated in a "get them before they get us" scenario. ]

[Question] [ So, just to clarify, you needn't worry about vague rules - this question is relevant to my own fantasy universe. In this such universe, magic is not a separate energy, it is the ability to control energy (heat, light, electricity etc) much in the same way as the Inheritance Cycle series tackles it, if you're familiar with it. The manipulation is also pretty similar, as words and gestures must be bound to the action to cause the effect (usually), the spell is not as simple as 'fireball' either, it is an explained process - for instance: gather heat in fixed place (to create fireball), sustain flame, move flame this way (shoot the fireball). Unlike the Inheritance series however, the magic is not bound to one language, there are multiple, the words simply help structure the spell in a human brain, and having 'magic languages' separate from communicative language prevents unfortunate accidents. While most spells will be uttered or shaped with gestures, some larger or more complex spells would take too much time to be viable in battle, so a way to speed up the process is to pre-write the spell with runes. Once the rune is inscribed, and the power source of the spell specified, the rune's spell can be activated with as little as a single word. As I was designing a weapon for one of the main characters I realised quite an important flaw in the runes, since they are written (and probably glowing when activated as-per rule of cool), anyone who can read the language would instantly know what spell the object is capable of casting and be able to counter/negate it. Obviously, fantasy and rule of cool dictate the runes should remain exposed, but logic would have them covered. **What reason would there be to have them exposed?** I wonder why this question hasn't come up in any other fantasy series. Side note: If you could, adding *how* the runes are hidden would be great too, if your answer is in favour of hiding them of course. Edit: While it isn't final, I'll add some extra info to clarify a few things - As I have it now, magic just needs to be bound to something, and you need the intent to use magic, then the spell can work. When casting in the mind, the electrical signals in your brain provide the physical binding, gestures and words otherwise provide such bindings. These things are temporary, while a rune is less so, once the spell is bound to the words made by the runes, it can be cast again by anyone who knows the activation sequence. This part could change if need be. P.S. I'm unfamiliar with the fantasy-related tags - I usually ask about sci-fi - so if you know of other relevant tags please add them. [Answer] I say leave them out in the open. If a guy has a sword in his hand I can guess what that can do. Just like I can guess what a device might do if I can read the runes. If I am an expert I might be able to watch how the bearer of sword or staff moves and judge even further how dangerous he is. > > ... anyone who can read the language would instantly know what spell the object is capable of casting and be able to counter/negate it. > > > Great idea! By the time you are close enough to read a person's device you are at close quarters and already at risk from the device. Trying to pre-empt the action on those circumstances requires quick thought. Having a character realize what might happen in the few seconds before it does happen offers lots of narrative possibility. A mage might counter attack by triggering the enemies magic early. There might be someone magic literate but who cannot work magic. Can she pre-empt / block / duck the magic attack using mundane means? I cannot work magic but I am an artist and good sketcher. I sketch the symbols I saw on a device on a big stick then use it to bluff my way thru the magic literate. You have opened the door here to lots of fun. March on thru! [Answer] If I may add an option from the modern world: **Use encryption!** Here's how: 1. Have a single decryption rune on the hilt or pendant or something. Be sure to use a strong algorithm. 2. Select a good password and keep it secure. It could be spoken or engraved really small on a secret ring or something, OTP style. 3. Encrypt your runes. This might take a while without a computer, but is still possible, though tedious. Make it part of their training, or let them use an encryption rune to do it or something. 4. Engrave encrypted runes on blade. (Looks like rune nonsense to anyone else) 5. At run-time (during a fight) use your secret password to obtain the original runes (pword combined with rune specifier required ). Would be useful if you could think this part so your enemies don't hear it. (Arguable doesn't matter as you'll kill them, or they'll kill you) **Why it works:** The only unencrypted rune is the decryption rune. Even if they could decrypt runes while in a fight, Kirchoff's Principle ensures that it is useless without the password. Your runes still look cool, while giving away no info. And they are also secure from any other attacks, like secretly looking under the covers when you're not around. All you need be concerned about is a brute force attack, and that could take millions of years, even with a modern computer, so is not feasible. This may be seen as an interesting way to both hide the runes, and not hide the runes. [Answer] **What could prevent hiding of runes?** * They require open space. It may be drawing mana that exists only in the air, receiving blessing from astral beings, or needs space to vent waste energy and heat of. Having some extra material between them and open air would weaken them. * They are 'bound to an item' in a way, that requires them to be cast on finished item. If the item undergoes modifications, this bond weakens. * Runes require maintenance. If they are hidden, you must first uncover them, requiring more complex structure of the tool. * They are cool looking! They are pride. And they are the selling point of magical items when sold! * It is considered a taboo and very bad luck if someone hides his runes. * Creator didn't considered a need for hiding the runes at the time of item creation **Then, how could you hide the runes if you really needed to?** * Maybe, there are certain materials, than can visually hide the runes without giving out negative effects. * Maybe, there are spells or tricks that can suppress unwanted side effects, like dim the glow. * There are ways, how to modify existing runes without changing their effect, but to make them practically un-readable. Or masked behind other 'dummy' runes. * Proxy runes? Having your complex spell running somewhere else, in a big altar or something, while the item itself is just 'receiver' of the final effect. [Answer] ## Because it doesn't matter that they're exposed Different authors deal with this in different ways. Some have the rune patterns extremely complex and the activation rune/sequence relatively simple so that reading the runes doesn't gain you anything in a short time because it's not cut and dry until the pattern is read and understood. Others take the assumption that if you're creating a fireball or another simple spell, them reading it isn't going to gain them anything because they can typically easily counter it normally. Also, sometimes you want to use them being able to read the runes/figure out the pattern as a plot driver and I can name a couple of books where that was the case such as escaping a rune prison, learning different abilities that are tied to completely different runes, etc. My point being that unless it's a trap, you're not going to have time to read them unless they're static and if this is during a battle, it's likely not going to be static. As well, just because you know what runes they have, doesn't mean you know what they're going to use next especially if the activation is not the same as the original spell. It also depends on how long specific spells take to activate in your world and even if they know what's coming, they might not be fast enough to counter that spell unless they also have a rune specified for that purpose and unless they read the other's runes ahead of time, they likely wouldn't be prepared for that anyways without chanting some long complex spell. [Answer] The thing about magic is that it's usually somewhat dangerous. In the real world, when an animal is somewhat dangerous, it tends not to hide that fact. Poisonous animals are brightly colored so that you know not to eat them. The same generally goes for venomous animals; they may be able to kill their foes, but they don't want to fight to the death in order to find out. Similarly, in human society, we put warning labels on things so that people don't hurt themselves. In terms of security, sometimes just letting people know you have it is enough to deter them from trying to take anything from you. That's why home security systems come with signs you can put on your lawn, so thieves will think twice before breaking through your window or pointing a gun at you. Just because they'll get caught doesn't mean you want them to try to break in anyway. I think this can apply to runes as well. A runed item is going to be dangerous to your allies, and if your enemies don't know about it they won't be afraid to attack you. If people see your runes and back off, that's an easy victory, and everybody gets to go home unscathed. Plus, consider this: the more runes you openly display, the more unexpected it'll be when you use an object with hidden runes. [Answer] Have you considered that if the runes were hidden, you might simply grab the wrong sword? Imagine attacking a super powerful demon and... oh wait, this is my normal sword not my Holy Sword of Holiness. Guess I should label these in the future. [Answer] So I can think of a few ways that runes could be left in plain sight and have their purpose hidden, or where having them visible is actually important: **They don't work if you cant see them.** So having the magic language independent has some interesting implications. There are lots of computer programming languages, and they each have an interpreter to get them into something that is understandable by the computer. So I write a simple function in Java, or Python, or C#, and they all look different, but once compiled the computer processes the instructions as 1's and 0's. So in your world the compiler/interpreter to get it to a universal low level language is the human brain. The spell, whether spoken, written, or action, doesn't do anything on it's own, it just gets the signals in the brain into the right configuration and that is the "machine language" that the universe actually executes. So someone pulls out the scroll with the runes, looks at it, and speaks the activation phrase, but it's his mind that is subliminally processing it into machine code and executing it. If they can't see the scroll then the rune program can't be imprinted and compiled. They don't even have to be able to read the runes to make it work. How often have you seen a phrase like "the runes were hard to focus on, seeming to twist and writhe under my gaze." That effect could be caused by the viewers brain being twisted to the right configuration to run the spell, assuming you know the activation word to complete it. That doesn't mean that they runes have to be visible to everyone. You could for instance put them inside of a folder, or a book, so that they can be closed up and out of sight when not needed. **"Written in an unknown language"** So since magic is language independent, it seems reasonable that each wizard could create their own rune system that is for them alone, and so anyone else that sees them will just see weird shapes and squiggles, and not actually be able to read what they do. A wizard who is also a linguist might be able to figure it out given enough time and examples, and maybe a Rosetta Stone, but to anyone else it just wouldn't mean anything. And it wouldn't matter so long as they work. **"I looked upon it, and despaired"** You might want them visible as a means of intimidation. "Oh crap, is that a level 4 plague of lice Armageddon spell? We don't have anything that can counter that. We'd all die from scratching our own heads clean off. It might be time to sue for peace." [Answer] Consider a basic spell for a sword. Runes of Enduring Sharpness. These have to be engraved on the blade, there's no point having them anywhere else, you don't want a sharp hilt or a sharp scabbard, you want a sharp blade. The same would be true for any blade effect, firey, icy or whatever you so choose. You could consider manufactured spells for ordinary people the same way. Your big thug of a hero wants to be able to throw fireballs. He's not overly bright, nor is he able to pull out a scroll and read it in the middle of a fight (reading is not his strong point anyway). Inscribe the runes on his blade and tell him to point the sword where he wants the fireball to go and to say the magic word. The runes are both the source and the controller for the fireball which then comes out of his sword. [Answer] I think that a better question to ask yourself would be "How do I have my characters cover/hide their runes logically". Say we are talking about your sword. The runes are going to be etched onto the blade, or the hilt most likely. How exactly would you not have them exposed? They would have to be etched onto the blade after it was made. One reason why they would need to be exposed could be that if they were covered or hidden, they wouldn't' be able to draw out the power source they were looking for. They would need exposure to be able to suck in the heat or the air or whatever. One thing you might consider, and I think this happens often in fantasy, is that the runs ARE hidden or invisible until activated. Once activated they simply flash and draw power, then fade. In the heat of battle nobody is going to have time to look at them and read the spell. And in the case of your blade, if it shot fireballs, and they did read it and use it, they would simply shoot a fireball at themselves I would think. In the case of runes hidden on a doorway or something else, they wouldn't be visible until the person knowing the spell came by and used them. One would assume he'd be by himself or with a trust worthy person in such a situation. [Answer] If a rune's power is not infinite, the process of drawing power through the rune could erase it from the material when it 'expires'. Not only is a rune inscribed on something like a sword going to be hard to conceal, but if you want to be able to reapply the rune you can't bury it in the middle of the material. Alternatively, or in addition, since the rune is essentially acting as the spellcaster, the effect will emanate from the rune itself. Hiding a small magical protection rune on the rear of a shield won't do much good, it needs to be large and inscribed on the enemy-facing surface to be effective. For the same reason, a tiny rune on the pommel of a sword won't give the blade the desired effect; it needs to run the length of the blade itself. This could also mean that an object with multiple effects might have superposed runes, since they all need to occupy the same space to be effective. Anyone with a basic understanding of the rune symbolism can figure out a simple one-rune device and employ a counter (provided they have enough time), but figuring out the individual components of a multiple-rune symbol could be more difficult. And if you see a guy coming at you, carrying a sword that looks like a mass of entangled lines, it's probably time to start running. [Answer] Short Answer: Magic Runes generate heat and corrosion when activated. I find adding some physics to magic makes the world much more interesting. Follow Brandon Sanderson's Law of Magic: [First Law](http://brandonsanderson.com/sandersons-first-law/): > > An author’s ability to solve conflict with magic is DIRECTLY PROPORTIONAL to how well the reader understands said magic. > > > [Second Law](http://coppermind.net/wiki/Sanderson%27s_Laws_of_Magic#Sanderson.27s_Second_Law): > > The limitations of a magic system are more interesting than its capabilities. What the magic can't do is more interesting than what it can. > > > Rune magic is interesting in that it's often associated with using particular magic materials. There's an artistry and difficulty to create these runes in the first place. There's also often a magic languages or specific set of magic shapes like circles of power. So tie that all together with the physics of how these runes actually behave. For my setting, (I'm a GM) I said that the reason that people use certain materials is that channeling magic through runes damaged the object channeling them. Runes would only work as long as they held their shape. Writing a rune on a piece of paper would likely generate so much heat that the the paper would be destroyed before the spell completed. Etching runes into steel swords was a viable option because steel could withstand the heat shock, but it would rust over time. Taking care of your magical weapon actually required physical maintenance. Even better, make a magical object out of gold, which can handle heat well and is immune to corrosion. Gold then becomes the preferred metal for magic runes, and can be inlaid in strong metals. Stone also works for rituals, but once the corrosion blurs out a rune etched in stone, it's hard to repair. Having a clear set of physical consequences allows you to think through trade-offs in character. "Why not put the runes inside the hilt?" What is the handle made out of, because that things going to get hot. "Why do scrolls require nice parchment and expensive inks?" Because the materials need to be flexible but last long enough for the spell to complete. Using this reasoning, you can build a whole world from it. Personal items with hidden runes would need to include gold threading and corrosion resistant materials. That makes maintenance more difficult. They could hide runes, but most of the time it's more practical to have them out in the open. [Answer] In order to preserve the Rule of Cool, and to also riff on other answers about runes having to be exposed in order to draw energy, have your combat magi also be like martial artists. Runes are exposed and flash during casting, and **might** broadcast the intent to a possible counter, but the superior mage depends on timing and movement in order to best an opponent. Even novice martial artists learn to watch opponents and can see a punch or kick coming before it lands. They just aren't able to do much about it at first. As they grow in skill they are able to counter, deflect, and avoid blows. Even at the highest levels, sometimes a simple punch or kick gets through, so long as it is properly timed. Even if the language of magic is not really standardized maybe some of the side effects give clues about a spell...Red for heat, blue for water, white for air, green for earth (thereby expanding on the rule of cool). Then have Magi infuse a focus object or objects with a variety of attacks and counters and the greatest portion of skill then gets down to who can sling a cone of ice, raise a shield, and follow with a fireball in rapid succession. Or maybe have your magic follow existing martial arts. One Mage trained in Wing Chun Abra would throw a volley of very fast, but less powerful spells against a wizard who is partial to a Northern Shaolin Kadabara style which relies on strong, linear attacks. There is all kinds of fun to be had here. I want to see what you come up with [Answer] Whenever the rule of cool gets in your way, double down. Make it even cooler. My favorite approach to problems like these is to make the problem dynamic: what if the runes changed in response to the wearer? Quite often humans don't know what they want, so its reasonable that some of the structures we create in our brain to cast spells have a little ambiguity to them. A skilled practitioner can use this ambiguity like a paradox or a zen koan to expose truths inside their own mind. Like a Ouija board, the flickering shapes may reflect the subconscious truths that the practitioner does not consciously admit. Or it could be summoning a demon... one never can quite tell. In either case, this would give your magic system a solid root into the world of psychics and fortune telling, which is always a good fun place to explore. Engraved on a sword, they may act somewhat differently. These runes may be designed to focus the intent of the human holding them within the confines of the particular runes inscribed. These runes may be swirling with intensity, changing shapes depending on what the wielder's subconscious is thinking and how pure their intent is. This has the effect of obscuring the "correct" meaning of the runes from any prying eyes unless the wielder is permitting the "correct" energy to come forth from them. You no longer have to fear your opponent reading your weapon. You could think of these pairs of runes like [homographs](https://en.wikipedia.org/wiki/Homograph). The word "bear" could mean to carry a load, or it could be a furry mammal. It's not clear outside of the context. When you hold the sword, your subconscious reveals the proper meaning of the symbol by making it glow in one way or another. The easiest approach to this would be to carve two runes on top of each other, but to make sure that only one can fully glow at any one time. This has countless fun tributaries you can explore. Perhaps the process of engraving the runes can impart a preference as to which swirling runes are easiest to select. Perhaps one set of runes engraved one way highlights a glowing "kal vas flam" trio of glowing runes which is ready to unleash a fireball while the same cold runes engraved in a different way (perhaps a different stroke order) is easier to cause to glow with the glyphs for "vas rel por," a teleportation tool. With the runes extinguished, or glowing with response to an unfocused mind, it may be impossible to tell which glyph is actually there. If you consider that runes may have more than one meaning, it gets even more fun. Perhaps you have a staff that's been engraved to glow with the runes "vas rel por," but you have enough raw skill, you may be able to convince the staff to instead glow the portions of the runes responsible for "kal vas flam." Suddenly a staff that everyone through could only do teleportation is now a powerful weapon in the hands of an expert mage. It would be very reasonable to have swords engraved with multiple spells to suit the wearer's needs. The next layer of cool up from that would be glowing patterns that are "hard" to make occur. The king might have a sword passed down from generation to generation, and each king learns the secret of how to make it shine with the king's spell. This would serve as a rapid way to identify a one true king! Abbeys may have weapons locked away where only the senior monks know the secret for unleashing its true potential. Finally, it explains why runes are visible: many reasons. The king has his visible because its a proclamation to the world. The Abbey may keep weapons whose runs are visible because they are excellent training tools for the monks to teach newcomers how to channel the energy correctly. A skilled assassin may choose to hide the runes, manipulating them through sheer feel, but a less skilled one may choose to reveal them just to make sure the proper runes are activated before issuing the spell. Finally, with all of these reasons to have runes be visible, there would be a social force encouraging it: anyone hiding runes would be seen as a shady character (possibly an assassin!). Good true righteous fighters would not be afraid to show their runes, so anyone who hides them is clearly shady. A [closing story](http://languagelog.ldc.upenn.edu/nll/?p=4230), from Japan, showing just how much fun having runes with multiple meanings can be: > > My wife had an English teacher in Kobe long ago who always signed for things at the post office. No matter how many times he went there, the regular clerk always asked him first to use a seal. He always politely said he had none, whereupon the clerk then—and only then—let him sign. > > > This went on for years. Eventually, he went to a shop and had a large square seal carved with the characters 馬鹿 *baka* (idiot, fool). The next time he went to the post office, the old ritual ensued. "Don’t you have a seal?" the clerk asked. The teacher quickly produced his new chop, loudly stamped a large and bold 馬鹿 in the required spot, and thrust the paper before the clerk’s eyes. > > > The stunned clerk, getting the message but rather at a loss for a snappy face-saving riposte, stammered out, "A! A! Umashika-san desu ka" (Omigosh! That’s Mr. Horse-and-deer, of course!) Saved by multivalent kanji readings! > > > [Answer] Runes are required to be visible because they are required to be accessible in order to be read and used. A runed stone of fireball in your pocket isn't going go off if you accidentally say the wrong word. Or, as a more extreme example, the 19 identical runed stones in your backpack aren't going to go off when you activate the 20th stone held in your hand. To activate the runes of awesomeness on your sword will require that you read, and possibly touch, the runes to bring them to life. However, the runes may not be glowing until they are activated. Prior to glowing it may not be visible from any real distance, especially if it is being violently swung at the observer's head. Additionally, there is one example in fiction of a dwarf carefully carving runes into his masterwork. This is from *The Crystal Shard*. > > Bruenor needed no model for the first carvings; they were symbols etched into his heart and soul. Solemnly, he inscribed the hammer and anvil of Moradin the Soulforger on the side of one of the warhammer's heads, and the crossed axes of Clanggedon, the dwarven God of Battle, across from the first on the side of the other head. Then he took the silver scroll tube and gently removed its diamond cap. He sighed in relief when he saw that the parchment inside had survived the decades. Wiping the oily sweat from his hands, he removed the scroll and slowly unrolled it, laying it on the flat of the anvil. At first, the page seemed blank, but gradually the rays of the full moon coaxed its symbols, the secret runes of power, to appear. > These were Bruenor's heritage, and though he had never seen them before, their arcane lines and curves seemed comfortably familiar to him. His hand steady with confidence, the dwarf placed the silver chisel between the symbols he had inscribed of the two gods and began etching the secret runes onto the warhammer. He felt their magic transferring through him from the parchment to the weapon and watched in amazement as each one disappeared from the scroll after he had inscribed it onto the mithril. Time had no meaning to him now as he fell deeply into the trance of his work, but when he had completed the runes, he noticed that the moon had passed its peak and was on the wane. > The first real test of the dwarf's expertise came when he overlaid the rune carvings with the gem inside the mountain symbol of Dumathoin, the Keeper of Secrets. The lines of the god's symbol aligned perfectly with those of the runes, obscuring the secret tracings of power. > > > [Answer] > > Unlike the Inheritance series however, the magic is not bound to one language, there are multiple, **the words simply help structure the spell in a human brain**, > > > Therein lies the answer. "When a tree falls in the forest and noone is there to hear it, it makes no sound" applies to your magic system. It's not confined to runes, either. Why would a sorcerer speak the words of a spell, exposing himself to counterspells, when he can just think them? The words must be spoken out loud, to be heard by ears and to take form in minds (even if not everyone understands the words) before they can, through their effect on minds, affect reality. Just so, the runes must be exposed. They don't have to be deliberately read and interpreted or even noticed by anyone, but they DO need to be exposed where people can see them in principle. [Answer] > > [...] the spell is not as simple as 'fireball' either, it is an explained process - for instance: gather heat in fixed place (to create fireball), sustain flame, move flame this way (shoot the fireball). Unlike the Inheritance series however, the magic is not bound to one language [...] > > > I think this is already a good excuse to leave them exposed. The actual spell won't have your parentheses in there to explain it so it won't necessarily be obvious what the spell is going to do. The fact that they can be written in different languages makes them even more inscrutable. Determining at a glance what someone's spell (program) is going to do without actually casting (executing) it would take a great deal of skill. Spells could even be crafted to be misleading, such as a clever spell disguised as a common fireball spell. Another thing, hiding the runes only solves part of the problem. If the object is stolen by an enemy, the enemy can take it back to their lab and put a great deal of time into reverse engineering it. Hidden runes don't help with this part. Groups of wizards would put many years into developing obfuscation techniques and secret languages. Hidden runes to such people would be a sign of weakness. [Answer] An alternative reason that I don't think I've seen mentioned here is to hide the trees amongst the forest. Lets say that you want them exposed for rule of cool, and you have an in universe reason for them needing to be displayed, maybe they need to be in contact with the magic in order to shape it. If you want to stop people from being able to easily decipher it at a glance then put dummy runes on it too. For example maybe the runes for extreme heat are written on there as the main offensive choice, but these are hidden in a sea of other carved runes that might not even do anything of note, but they do assist in stopping the enemy from knowing which runes to read and which to be wary of. In a fight there probably isn't enough time to read the whole set and figure out which might be the dangerous ones too. [Answer] Ever heard the saying "Out of sight, out of mind"? If the purpose of the runes is to > > simply help structure the spell in a human brain > > > and that having it written out > > prevents unfortunate accidents > > > Having it written somewhere that you cannot see it, is going to provide significantly less mental focus and safety. This is probably only slightly less risky than just doing it all in your head. If you are worried about someone else interpreting your runes then use a cipher that is only meaningful to the caster. It doesn't even have to be a complex cipher. After all, how long does your opponent really have to figure it out before you are done casting? Or write your runes on 2 (or more) separate items that you only assemble at the moment you are going to cast. So there is no time for someone else to read and comprehend the whole thing. [Answer] An option used by some characters in my shared world: Make the runes very difficult to read because of the way they are drawn One of the way used, for example, was to hide rune in clothes by using slight tint or pattern alteration, or even changing the shape of the fabric to trace the rune. This character, an anthropomorphic wolf, ended up drawing "invisible" runes on his own body by changing the thickness of his fur on the pattern of the runes. Other options to do this: use the grain of wood, brushing of metal or other slight pattern to draw the rune, in order to keep it hidden. However, this solution is not much help if the rune start glowing when activated, but at least it provides some element of surprise before the spell is cast. [Answer] What if magic has to obey some of the laws of thermodynamics? Enchanted items, like real-world machines, will then usually produce an quantity of heat related to the amount of work they do. A simple spell that moves a lot of energy, or a very complex spell that moves a trillion tiny bits of energy in different ways, will produce a lot of heat. Perhaps very low-level enchanted items do not require special cooling and can be easily concealed. Mid-level enchanted items rely on air-cooling to stop their runes from melting off, so it is common for magic items to have exposed runes. And high-level items have magically powered water-cooling channels, often with an exposed air-cooled rune or two on the water pump or on any other minor subsystems that use less power than the primary spell. [Answer] You can decide that only the holder of the item can make the runes react to the words, implying a biological link that seems scientifically hard to imagine, but we're talking magic. We can invent a rule like this as long as we're consistent. You can decide that some sort of ritual must take place to bind item and owner and therefore only he/she can work the magic, but everyone can see them. You can decide that only the owner/holder can read the words, which appear as gibberish to others. You can decide the words can only be read in certain circumstances, like under a full moon, and the wielder did this to learn the words, which are visible to everyone else but gibberish to everyone, including him, except that he already knows what it says. That can set up a cool scenario where on every full moon, people are trying to hide their items. Imagine someone purposely setting up a battle during full moon and suddenly during the fight, everyone can control other people's items - but only when the cloud cover parts. [Answer] If you already have magic, why not just have a spell of Rune Hiding? It can be a rune too. If everyone always have a big blatant Rune Of Rune Hiding on every weapon, armor, shield, ect, it doesn't give a lot of information. And it can even be used as a basic strategy. Even if there's actually no other runes on your sword, inscribe a Rune of Rune Hiding and now everyone will be wary of it. You can even go one step further and hide mundane runes to fool a spell of magic detect. While the enemy mage is busy trying to analyse your sword to see which runes you're hiding, your sword only really has an harmless rune of make-a-duck-sound hidden by the rune of rune hiding. Hell you can even manufacture objects with fake runes (stamped/painted/engraved/ect). Anyone without magic abilities couldn't tell the difference. [Answer] Consider the entries of the [IOCCC](http://www.ioccc.org/years.html "International Obfuscated C Code Contest") (the files that end in .c). They appear to be complete gibberish, perhaps ascii art. Many are, but they are also valid C programs. If you do not understand C they appear as nonsense. Know that they look like nonsense to me too unless I carefully take them apart. See the [spoiler version](http://www.ioccc.org/years-spoiler.html "IOCCC winning entries with spoilers") for a short description of what each does. Maybe magic is like that. Similar effects look different when a different mages craft them, and similar appearing runes may have subtle differences that give very different outputs. This is caused by either incidental differences in style or by deliberate obfuscation. Well crafted runes advertise their function to the lay person by taking the shape of something familiar, but there is no relation to the outer outline and the true function. This gives you "revealing runes is mostly harmless" but does not give you "runes must be exposed to function". [Answer] The rune could be like a mnemonic device. Perhaps to a wizard, the sight of the rune triggers the full memory of the details of corresponding spell, much like the opening chord of your favorite song triggers the memory of the whole song. Something like this is used in the magic system in the Dresden Files. [Answer] Some explanations to leave the runes exposed: 1.) Power demonstration: Soldiers marching with weapons having glowing runes on them can fill the hearts of the enemy and the peasants with fear and submission. 2.) Status symbol: Having powerful runes on your armor and weapons might be a symbol of your wealth, privileged status, or runecarving skills. 3.) Chivalry: The ethics of some faction may require their members to play with open cards, and view weapons with concealed runes as low-down and dishonest. They can use overkill curses to punish those, who dare to use such unholy weapons. 4.) Law: Just like the law makes difference between the open and concealed carry of firearms, or require toys to be distinguishable from real weapons, the law in particularly civilized and lawful countries may require all magic tools to have visible signs of their capabilities. 5.) Fast use: If someone is wielding his weapon speedily, its almost impossible to read the runes, even if they are exposed, glowing, and written in a standard language. The enemy would only see light stripes, not letters and symbols. [Answer] I am probably super late by now, but you could make the realization that their runes are exposed to the enemies a part of the plot (maybe during a war someone took advantage of it). After that they start hiding their runes. However people don't like them as much because they don't look cool, so they start inscribing light runes that are connected to the main rune, and their only purpose is to give off light and look cool on the outside of the weapon. People could then customize their weapons by choosing the color of the light rune. If the enemies also do this to their weapons, you could choose to make the light runes a weakness to give you the upper bound. You could say that the main runes would slightly affect the light given by the light runes, and that really experienced mages would be able tell part of the main rune (e.g "It will create fire, but that's all I know"). [Answer] Seeing the runes could be part of aiding the weilder's focus - much like seeing the letters C, A, T can bring the image of the animal to mind, seeing the runes helps bring the image of the magic to mind. Along the same vein, perhaps your runes have specific meaning to the user - the opponent can see that the sword is enchanted, but they mean nothing to them (much like reading a different language.) Covering the runes becomes unnecessary, or at least offers insufficient benefit to make it generally worthwhile. [Answer] I think you already have a fine answer in your post. > > Once the rune is inscribed, and the **power source of the spell specified**, the rune's spell can be activated with as little as a single word > > > With this you can use natural energy as a reason for both hiding and showing your runes. Lets say you add runes that are hidden, you need to ether define a internal power source or use small amounts of the radiant energy (heat, light, etc.). If you do use radiant heat energy it forces the spell to be endothermic reaction limiting you in both power and options. However if you want the powerful exothermic reactions (flame, bright light, etc.) you will need to use a powerful energy source (large, hard to carry, expensive, etc.) or a powerful external source (sun, rotation of the planet, etc.) [Answer] That would be simple. The runes that are showing are no more than a small bit of the runes for the spell that are simply designed to throw people off and make them guess something else. In the Inheritance Cycle, it is mentioned that a skilled magician could say "Water" and get a gemstone. And with runes, you can probably do even more. What is to say that the rune saying "Fire" that is exposed is not actually part of a spell to focus sunlight onto your head until you burn like a bug under a magnifying glass, or that the rune saying "Death" won't just paralyze your sword arm when activated? And since this could clearly happen, eventually people will just learn to stop trusting any reading of the runes. That, or they might be a spell that, each time it is casted, it rearranges the runes to do something else useful (like [Malbolge](https://en.wikipedia.org/wiki/Malbolge) code) so that no one actually knows what it is about to do. [Answer] ### Runes may not do need to be visible even if they aren't covered In the Skulduggery Pleasant series there is a character called China Sorrows. She's a rune mage. Her runes are only visible if she press the rune with its counterpart (when she uses it) and than it's too late. ]

[Question] [ I've seen the discussion on how bipedal mechs are inferior to treaded and wheeled vehicles in almost every way. However, all of these questions appear to be related to *bipedal* mechs. I'm wondering if spider mechs have any advantages over the aforementioned normal vehicles. For those of you wondering, a spider mecha is one that is very low to the ground and has four or more legs. I'd imagine these would be far more practical than bipedal mecha, as these are lower, probably faster, and more agile than bipeds. But what about advantages over normal wheeled and treaded vehicles that fill the same combat role (armor, specifically tanks). Do they have any advantages, or once again are boring normal tanks better than mechs? [Answer] Okay, so a did a bunch of research into legged robots for my thesis and they aren't going to replace armored vehicles any time soon. The most basic reason, they aren't as efficient in doing what armored or wheeled vehicles are specialized in. They are also very complicated to program, since you have 4/6/8 or more legs which all need to interact versus 2 treads, or some wheels which only really move in 2/4 directions. Legged Vehicles are all terrain vehicles. They can walk over rocks, climb mountains, jump up buildings, jump over gaps, lower and raise their bodies, kick stuff and anything else you could imagine a robot doing. This is 100% more flexible than any wheeled vehicle, because a legged robot could be designed to do all this with just their legs. Your not going to see a tank ducking down or jumping over a gap, it's just going to steam roll over whatever there is in its way. So legged robots are extremely flexible in their movements. The problem is, that if you want to compete with tanks you need to be able to do something a tank can't do, and do it more efficiently and cheaper. Fundamentally, a 4 legged robot is going to need roughly 12 motors as well as a generator and fuel to run it and that is a lot of weight to carry. It can't move as efficiently as a tank over flat ground because it has to lift its legs and body weight, while a tank just rolls around and has to defeat friction, not gravity. Next if you want more firepower, you need to carry it around with you, so you run into the same problem as before. More weight, means larger motors, which decreases efficiency. So in the end, a legged mech won't actually replace the role of a tank. Even bipedal robots won't replace the role of a tank, because a tank is good at its role. What you will see, is the use of smaller sized legged robots like boston dynamics Big Dog which will assist soldiers. Its small enough that it's motors won't over burden it. It maintains its flexibility of movement because now its human size, so it can avoid debris and jump around if it needs to without knocking down buildings. It can have a gun mounted on it to fight infantry or carry supplies for soldiers, or scout ahead over rough terrain. There are even smaller ones, like remote controlled car small, which gives you even greater flexibility. They can search through small gaps, cling onto piping and climb around, stalk people, or perform search and rescue. Like having an actual remote control spider. So back to your question. Legged mechs advantage is their flexible movements. They won't replace a tank, because a tank can already cover 80-90% of the situations a legged mech would be better in, but a tank would still end up cheaper, more efficient and less prone to breaking (There are a lot more moving parts in a legged mech). [Answer] > > Do they have any advantages, or once again are boring normal tanks better than mechs? > > > Existing vehicles are still better than spider mechs. The reason is *ground pressure*. Note how much contact this tank has with the ground, dispersing the weight so that it doesn't sink. Compare that with the GITS spider tank. One's going to sink in the mud, and the other isn't. Of course, you might say that the spider tank would work better on streets or roads, but wait until the road gets wet. That think has the traction of a peeled banana... <https://images.fineartamerica.com/images-medium-large/7-m1-abrams-tank-at-camp-warhorse-terry-moore.jpg> [](https://i.stack.imgur.com/hGbFZ.jpg) <https://orig00.deviantart.net/90fe/f/2011/019/2/3/23f524f5775765bc02a156e47afbc3b7-d2pg54g.jpg> [](https://i.stack.imgur.com/rZkKn.jpg) [Answer] They would fulfill a role, but only in extreme terrain. > > "but ground pressure!" > > > It's called "designing things". You don't design legs like animators and model creators do, you design them to specifications. For example you could design legs that have large surface area's extending below the center of the spider Mech, this already gives you larger surface area's than current tanks can have. (imagine an "L" shape for a leg with the L pointing to the Mech center so it doesn't take extra space). Another method which I'm favoring is to use tent-peg like idea's. Similar to a tent-peg it greatly increases the grip on the ground allowing it to climb across extreme terrain a tank wouldn't dream off. UNLIKE A TENT-PEG because somehow someone is going to envision a spider-mech with tent-pegs for legs, the legs would use conical shaped ends. The legs compact the earth as they enter the ground, the conical shape quickly increases the surface-area and also sends forces sideways besides downwards to relieve the amount of pressure the ground below needs. The legs could even have a series of cones at the ends extending towards the center of the spider-mech (again with an L shape) to spread out the surface area it stands on even more without losing its grip ability. I did a back-of-the-envelope calculation for an 8-legged spider-mech using excavator arms for legs. If the excavator arms are 1/4rth the size of current excavator arms and 1/4rth the strength then you could build a 120 ton spider-mech (and excavator arms probably use the usual 20% safety margin for maximum forces it can take so it can handle even more under stress). If you keep it at around 80 tons it can lose 4 legs and still keep going. > > "but legs are easily destroyed!" > > > Actually a lot harder than most people expect. Are you really going to fire at a target that constantly accelerates and decelerates and presents a small target? Of course not! You'll fire at where the legs meet the chassis, which puts it in between a tank and a wheeled vehicle in terms of vulnerability. A wheeled vehicle can lose several wheels and still be fairly operational. A tank loses a track and it's a stationary turret/artillery food. A spider-mech would take longer to disable than a tank but have worse consequences for being disabled. > > "legs take up a lot of weight, you can carry less stuff!" > > > Tracks weigh tons more than wheels but they carry more weight. Legs would have similar properties plus extras. Legs would allow for a far higher recoil compensation than tracks or wheels. This means spider-mechs would be able to carry larger weapons for lower weight class vehicles. > > "its harder to stabilize!" > > > Wheeled/tracked vehicles go over every bit of terrain, which makes them less easily stabilized. A walker, once the tech is there to keep it balanced, would be far more stable. The end result: spider-mechs wouldn't replace tanks, but there's tons of terrain where tanks are far too limited. History surrounding the alpine troops show that movement through extreme terrain can give you unparalleled advantages in engaging tanks moving through limited area's, or engaging the supply routes or bypassing enemy forces and striking at construction or forward bases. Edit: disadvantages of legs would of course include slower max speed (but probably higher than most think), more fuel consumption (although like tracks this could equalize on rough terrain), higher & longer maintenance costs and tougher battlefield repairs. This is practically the same list as between tracked vs wheeled vehicles. Tracks haven't edged out wheeled vehicles and wheels haven't edged out tracks because they both have their uses. Spider legs would also fit on that scale and have its uses, but as its own category rather than a replacement of legs or wheels. Edit 2, limitations to tracks: While many people focus on the disadvantages of legs, tracks also have disadvantages. People will be quick to point out that tracks have lower ground pressure even than a human standing on his feet. What they fail to realize is that this is a requirement for tracked vehicles. When turning the entire track slides across the ground. The higher the pressure, the harder it becomes to steer and the more likely you are to rip up the ground and damage the tracks. The longer you make a tank the more this problem will arise. But make the tracks too short and it becomes unstable while turning. The ratio as I've heard it is 1.5/1.8 to 1 for length vs width for the tank to remain both stable and not have trouble steering/breaking the tracks. This, much like all the disadvantages legs have, means that a tank is in actuality limited in size, weight and capabilities similar to a legged vehicle (the actual limits imposed aren't similar ofcourse). [Answer] In addition to other points mentioned in other answers, I'd add these points : > > I'd imagine these would be far more practical than bipedal mecha, as these are lower, probably faster, and more agile than bipeds. > > > No, they'd be less practical for maintenance reasons. Every leg introduces at least 3 or more complex and critical joint assemblies and every one of those is a potential point of failure. > > But what about advantages over normal wheeled and treaded vehicles that fill the same combat role (armor, specifically tanks). Do they have any advantages, or once again are boring normal tanks better than mechs? > > > Again think in terms of vulnerability and exposure of critical components combined with maintenance and wear and tear issues. Tanks are tricky to fix in the field, especially on an active battlefield, but they're easy-peasy compared with a legged vehicle. The legs require hydraulics to replace muscles. That adds another huge vulnerability. A hit that doesn't actually destroy anything can still be sufficient to make the operation of the locomotive system impossible. There's a potential problem with the locomotion being an extremely uncomfortable ride. Likewise targeting systems. Modern tanks have targeting systems that maintain the gun stability while moving and hence allow accurate firing while moving at full speed over uneven terrain. This would be an order of magnitude harder to arrange with a walking vehicle as the motions are not as easily compensated for. This is very important as the primary function of a tank is to plonk an armored mobile and stable gun platform on the battlefield. The capability of the gun is of primary concern. Firing first and accurately is one of the first survival rules for armored vehicles as it's almost always possible for the enemy on a modern battlefield to destroy or disable an AFV. I'm skeptical that such a system could be as efficient as a normal tracked system. Every movement requires the lifting and adjustment of every part of the entire set of leg assemblies. That's a lot of work, most of it not doing useful work (i.e. not directed where you want it). [Answer] Since everyone's missing the question entirely and talking about the disadvantages, The Key advantages I can immediately think of: **Height** Assuming you're not talking a crawling mech (see the real-world logging mech) Then most sci-fi walkers show a much taller aspect than most real world vehicles. That height is a point of vulnerability, it reduces opportunities to go Hull-Down under enemy fire, however at the same time, it presents a couple major advantages. First and foremost, it's always easier to kill someone down-hill from you, the height means that you can fire explosive shells down. Against a conventional tank this translates to being able to fire directly at the top armor of the vehicle, instead of being forced to strike its sturdiest front-plating. Secondly, an ability to flex the legs in a sort of "craning the neck" to see over obstacles without exposing the whole vehicle, being physically more flexible always presents options. **Extremes of mobility** The biggest advantage of the spider-leg configuration is that it actively can hook into rough terrain and pull the machine over obstacles rather than require ground-friction like a tank. The spider-tank can crawl over steep hills and clamber over ruined buildings and obstacles to attack from an unexpected quarter. **Redundant components** Legs on a walker are very very segmented. The usual complaint about them is that they'll be high-maintenance, but that doesn't mean they have to result in downtime. Simply detach the leg entirely and replace with a factory-fresh replacement in half an hour or less. You could certainly never do this with a tank. Fictional example: see the early parts of the film Chappie, where they maintain the drone robots by this exact methodology. Additionally, beyond the basic four legs, a hexapod or even arachnid configuration would provide multiple redundancy, able to lose anywhere up to half its limbs and keep moving. Meanwhile a tank would be instantly immobilised by a single equivalent hit. **Shock and awesome** Things with too many legs, making loud servo-whines and behaving like giant animals hit a lot of Fight-or-flight buttons. If you want to intimidate, there's nothing like the looming presence of a mech. A tank simply cannot compete on this front, and Shock & Awe should never ever be discounted. [Answer] Tanks are heavy. Really heavy. You may think that your groceries take some lifting, but that's nothing compared to a tank. The M1A2 is listed as having a weight of 65 metric tons. In order to distribute that much weight over soft ground without sinking, all except the lightest tanks are supported on tracks that spread that weight out over a very large surface area. Take a look at a picture of a tank. Look at how much area its tracks cover - let's call it a third of its width and as long as the hull. (Yes, I'm approximating.) So for a tank 8m long by 3m wide, the tracks are distributing the weight over 8 square metres. Now imagine your spider tank of equivalent weight - in order to not sink, its weight must be distributed over "feet" that take up that much area. At all times. So let's say you have a six legged tank and two legs (one each side) are being lifted up at any moment as it "steps" forward, it means that the four remaining feet must be supporting the entire weight of the tank. This means that each "foot" must have a surface area of 2 square metres. Visualise this and you will see that your spider tank is wearing clown shoes! Then you need to add legs, and armour on those legs (since they are outside the hull and not protected by it) and a much more complicated drive system than a tracked tank's (which is quite complicated enough), all of which adds more weight so you need bigger feet to distribute that weight and legs and - forget it. A legged *tank* is not viable *on earth* any more than a man-sized spider is, and for much the same reasons relating to squared/cubed ratios. Low gravity worlds with very rugged terrain might make such vehicles feasible, but that's a separate question. [Answer] Quad or more legged mechs could be used to climb up terrain that is difficult for normal or heavy off road vehicles, specially if carrying a large artillery gun or cannon. Weakness is that once a leg is shot off, speed and mobility will be reduced increasingly by the number of legs destroyed. As another option, you could have wheels attached to the legs so they gain the same speed and mobility as wheeled tanks and these can switch out to climbing legs so that they can embed themselves much better in mountain or cliff-sides. Think along the lines of climbing axes or spikes. Also if say a quad legged mech gets one or two legs destroyed, they can theoretically still move about with the wheels attached to their legs and if you are up to it, maybe put in some wheels on the under-carriage. This way you get the best of both worlds? [Answer] JPL has been developing a 4-legged wheel-footed mecha called ATHLETE for lunar (or other extraterrestrial) astronaut support for some time: [JPL Robotics](https://www-robotics.jpl.nasa.gov/systems/system.cfm?System=11) And based on their brief, the wheel on side limb apporach allows for mission flexibility - as in there can be end-of-limb attachments in their scenario for sapping, and other tasks - and that applies to this OP's question also - for tanks to be useful motorized trenchers ATM, they require basically a backhoe attachment or in fact to be armoured bulldozers - the legged mecha could fulfill a large part of that role with a low weight attachment onto the existing limbs. *"...The All-Terrain Hex-Limbed Extra-Terrestrial Explorer (ATHLETE) vehicle concept is based on six 6 DoF (Degrees-of-Freedom) limbs, each with a 1 DoF wheel attached..."* Nasa & JPL are also working on a smaller unit, for very rough terrain on satellites or smaller planetoids (Europa and other targets) called LEMUR: [LEMUR article](https://www.smithsonianmag.com/science-nature/new-generation-interplanetary-rovers-crawling-toward-stars-180962625/) *"...The robot’s four limbs are fitted with interchangeable circular “feet,” which can be swapped out for attachments with different functions, Swiss Army knife-style, to help it traverse a variety of surfaces. Rock-climbing feet feature a series of tiny, razor-sharp steel hooks, known as microspines, to grip the rough surfaces of rocks firmly enough for one foot to hold the entire robot’s weight. For smooth surfaces, such as the outer hulls of space stations or satellites, LEMUR adheres itself with gecko-like sticky feet..."* So - to recap what we can garner from these two brief articles: 1) Multi-limbed, articulated robotic locomotion is non-problematic, and is actively being solved and approached now as a *solution*, not an exotic imagining. 2) Maneuvering and multi-functional advantages of said systems over wheeled locomotion on severely fractural terrain is considered a *critical operational advantage* - directly analogous to a strategic advantage in military applications. 3) Weight to power, power density over time, repairability and redundancy on these systems are solid enough that competent, studious, well-funded folks are *seriously* considering ***relying*** on them for missions without any possibility of local fallback positions, and in conditions where these systems will be light-minutes of communications away: either they have a great deal of confidence in the mechanics, or the redundancy, or the repairability and control systems. From this we can comfortably posit that the primary solid argument advanced against this locomotion concept is that of the difficulties in armouring the drive systems against weaponsfire, explosives and so on. My counter would be: mech carries two field-replaceable full limbs, plus two more additional "feet", as they are the most likely to be damaged in the course of regular ops, minus all the armour. Operator can then decide in situ whether operational tempo and conditions warrant field-stripping of armour from damage limb(s) during replacement, or if simple replace-and-run is called for. Said replacement full limbs would be carried pre-combined, back to back, as linear battering ram. Similarly, the two replacement feet would be preconfigured with trenching attachment and hoist attachment, to allow for easy field use of such attachments, and easy stripping of those from replacement feet should exigencies arise. That's my 15 cents. [Answer] One advantage of "spider tanks" that hasn't been mentioned is the potential for additional angle of elevation of the main gun, which would be useful in urban warfare. All tank weapons have fairly limited max elevations (20 degrees for the Abrams according to a quick google search). In most operations, this is not a problem, but in urban warfare, it means that a tank cannot fire at anything above the second or third story of a building (depending on how far away it is). Assuming that a "spider tank" can independently move each leg, it could raise up the front of the vehicle while lowering the rear, granting additional elevation to the gun and increasing its threat area. [Answer] **Spider mechs excel in steep high-mountain terrain where tanks are completely useless**. Even if a slope is less inclined than the maximum slope (which is normally something like 60% which is still only 30 degrees), a standard tank would be stopped by the extremely rocky ground. A spider mech has no problems with ground pressure because the terrain is solid ground. It can apply a pincer movement with two sharp legs holding the mech securely in place, so even vertical or overhanging walls with ice on it can be climbed. It can principially also jump over or traverse steep crevices. 6 or 8 legs also makes it extremely improbable that a mech will fall when 2 legs are breaking through a hidden crevice. Still the mech should be as light and sturdy as possible to maximize climbing and traversing ability. This rules out big cannons, so a spider mech will likely only have machine guns and anti-tank rocket launchers, it will avoid to get in a direct fight. It will use surprise and its ability to retreat in impenetrable terrain as main tactic, needless to say that helicopters and ground support planes will be the archenemy of a spider mech. [Answer] **Legs are good for one thing: agility** Have you ever watched [two boxers fight](https://youtu.be/457ezBDaRUY?t=30s)? I mean *really* watched what they were doing? Credit to everything on the human body, but it could be said that boxing is about your *legs.* They're used to: * Keep your balance * Shift your weight for leverage and strength * Move you deftly out of harm's way or into a superior position in almost any direction. So your spider mech has an advantage over wheeled or (worse) tread tanks in that it can better keep its balance, hop out of harm's way, perhaps even right itself when knocked over (if they're designed well). Have you ever tried to tip an Abrams back on its treads? I haven't, but I bet it takes more than a couple of big Tongans to do it. **At literally everything else, legs stink** *I'm assuming we're comparing apples to apples by talking about manned mechs. The arguments for drones are very, very different because you can make the mech (comparatively) very, very small. Wheels/treads are great when there's enough weight to keep them solidly in touch with the ground. They're less valuable when the object being moved is very light.* (1) Let's add some armor to that boxer. And a big ol' gun. Let's let him look a bit like the [combat dudes from StarCraft](https://i.pinimg.com/originals/7b/89/32/7b893257011b71bf56ce20e7954eca24.jpg).1 Suddenly you're having to add all kinds of mechanical enhancement to the armor — and you'd think you're doing that to enhance the combat abilities of the wearer, but you're spending most of the energy *just moving the armor.* In the same way that most of your gasoline is being used to move the car... *not you.* So, the more armor you add to the mech, the less valuable the legs become because adding enhancement to overcome the weight is seriously a losing battle. As armor increases, the mechanics to move the armor increases, the fuel needed to power the mechanics increases, all of which adds stress to complicated joints... and all you really wanted to do was kick the other guy's butt.2 *Armor almost always succumbs to armament. You don't see plate mail anymore because rifles pack enough punch at enough distance that you might as well be standing there begging them to shoot you ... which is what you'd actually be doing.* (2) Now let's add tree roots, bushes, things that are easily squashed and driven over with wheels and treads but are an amazing hang-up for legs. The issue isn't tripping, the issue is the inability to move a hung-up leg forward, which means you're a sitting duck.3 (3) And your center of gravity, which is high for anything with legs but low for (almost anything) with wheels or treads (monster trucks violate this rule... but that's outside the scope of your question). A high center of gravity means it's easier to make the unit unbalanced, tip it over, or control it with trip wires (see my last point). It also raises the unit unecessarily high off the ground, making it an easier target. (4) Then think about *speed.* This is where legs really, really stink. It doesn't matter how much you enhance joints, wheels and treads can always out run legs. (5) Finally, add to this the increased complexity of affecting knees, ankles, hips, rotor cuffs, tendons, muscles, and a whole lot more. There's an engineering axiom that, frankly, should be considered a *Universal Law.* **KISS: Keep it simple, stupid!** Those cool mechs, gundam, and all other things robotic used to fight Godzilla and who knows what else from the 8th Dimension and Beyond are just that... cool... and absolutely useless. Complicated design and automation that can only be driven by an operator with a PhD in physics costing bazillions of dollars and it's all wasted [by a single shot](https://www.youtube.com/watch?v=TKR_wUyx1hI&feature=youtu.be&t=18s) from some crazy dude with a big ol' gun that cost pennies on the dollar to build compared to your mech and that can be [aimed and fired by a 10-year-old](https://i.pinimg.com/736x/48/13/29/481329672fb2c5f899fb9cada75e42df--afghanistan-war-great-photographers.jpg) hiding behind a rock. So, looks cool in anime, but in real life the cost-to-value ratio is way, way, way in favor of wheels and treads. If you really want mechs in your story, you need to do what all previous authors have done... you need to *declare it to be so* and move on with the story, because you'll never be able to justify the tech. --- 1 *Which, if you think about it, is so unbelievably unrealistic that it makes angels weep. Think about how far you'd have to dislocate your sholders to get them into the arms, etc. But, it's a heckuva game to play, so no complaints. Nosireebob.* 2 *An astute observer might claim that the same is true for wheeled vehicles and tanks. That's true, but not to the degree of moving joints. It's relatively easy to increase engine size to turn a more heavily loaded axel compared to all that needs to be done to move 2–3 joints. If the problem increases geometrically for tanks, it increases exponentially for mecha.* 3 *If you don't believe me, the next time you get your foot stuck in some brambles stop and* really think *about what your brain can do with your foot pretty much unconsiously — you twist them, rotate them, tip and tilt them... and still you occasionally get your feet stuck. What the human brain can do with a foot is almost as breathtaking as the enormous effort it takes us to simulate it artificially — and we still can't build a robot that does it as well.* [Answer] The first thing that springs to mind is the likelihood of mechanical failure. Essentially you increase the chance of mechanical problems or failure in direct relation to the number of parts involved. While tanks are capable of traversing terrain that wheeled vehicles find difficult, when moving on roads the vibration will shake parts loose. To the point that regular vehicles carrying troops will be employed to follow up the tanks to pick up anything falling off the tanks. WW2 tanks would often be abandoned by their crews not because they were destroyed or damaged but because of mechanical issues. The other consideration is fragility. If you have a multipedal system it will fail if one of the legs is destroyed, therefor they need protection. One way to do this is to make them smaller to be harder to hit, the other way is to add armour, or in other words sacrifice mobility or speed [Answer] Note: the question doesn't specify a "tech level", so I'm going to assume a near future setting where the required tech (power supply, actuators, stabilization) has matured a bit. ### Ability to utilize cover Currently, tanks require relatively specific terrain conditions to make good use of cover while still being able to fire, and take time to get into those positions. Gun depression, for example, is one limiting factor. A vehicle capable of varying its height and leaning in all directions can effectively adjust its silhouette to whatever cover is available, "peek" over or around it just enough to fire and quickly shift back. ### Modularity and active defenses The tank evolved around the necessity to carry as much armor as possible around a gun large enough to penetrate the opponent's armor, and it's pretty well optimized for that purpose. However, with the (foreseeable) introduction of faster and smarter drones, missiles, point defenses, directed energy weapons and sophisticated electronic warfare, having the heaviest armor might not be the ideal defensive strategy anymore. A less compact, but more modular design that offers faster heat dissipation and greater arcs of effect for multiple, coordinated point defenses might stand a better chance against this range of threats. This does not necessarily mean legs, but a "spider-like" design would fit the requirements pretty well. Note also that part of the reason that current tanks need to be compact is that they (still) require a crew of roughly 3-6 people. People are fragile, need room to move and air to breathe and don't react well to shock or fluctuating temperatures. If you can replace (most of) them with machines, you gain a lot of freedom in how you shape your vehicles. ### A more stable firing platform Assuming a mature and field-tested control software, the range of motion of multiple legs and their ability to, effectively, act as springs should allow a vehicle to better compensate for recoil, the vehicle's own movement and extreme firing angles, improving accuracy in less than ideal conditions. [Answer] > > "Tanks don't go in forests. Forests have trees in them." - Col. Mercier > > > A legged spider tank unlike a similarly sized conventional tank would be able to pivot its self on it's side or back to squeeze through gaps in trees or alleyways, edge across narrow paths on mountain sides. I can easily see legged vehicles with this ability being dominant in forests or urban sprawl where they are the only armour available. [Answer] I presume you already know the works of boston dynamics, espicially the [LS3](https://en.wikipedia.org/wiki/Legged_Squad_Support_System)? The Article list a number of disadvantages as to why the LS3 is currently not useful for field service, but most of it could potentially be mitigated with future technology - The main critique was AFAIK noise and maintenance. In theory these could be scaled up and mounted with weaponry to fill a similar role as for example the [German Wisel](https://en.wikipedia.org/wiki/Wiesel_AWC). They would be lacking Armour, but could be hard to hit. Imagine trying to aim at [something like this](https://www.youtube.com/watch?v=_luhn7TLfWU) with your 120 mm main gun from your conventional tank. They could also cross terrain that wheel/chain vehicle cant. So a viable future scenario could be "spider" bots as autonomous guerrilla force against conventional tanks. Here it would be an advantage that such a unit could potentially be built much cheaper than the MBT it destroys and thus would be kind of disposable --- Edit: Example calculation as thought experiment (with today's technology): Nation A fields 10 M1 Abrams tanks, costing is $4.3 million each Nation B has devoped some intelligent software, and fields * modified camera drones for ~12k * equipped with one rpg7 equivalent ~2k * a Pickup-truck as launch vehicle ~50k. A whole system of one truck with 10 attack drones would cost less than 200k. Nation B could send a **swarm** of over **200** autonomous **drones** like a swarm of bees to kill off the **10 Abrams**, and still save over 90% of the military budget! Imagine what those rocket-bearing robo-dogs could do once they can be produced with economics of scale... [Answer] Now what should be noted before I provide my answer is this, it matters where your fighting because every planet is different. So on earth the simple answer is no, the dust isn't a serious problem and the only advantage a walker would have is the ability to climb up a wall or cliff-face which is a very niche application. I don't have the ability to go into the reasons it wouldn't work here but I will say that I asked questions relating to this but for the moon, they are [Would walkers work on airless worlds?](https://worldbuilding.stackexchange.com/questions/106667/would-walkers-work-on-airless-worlds) and [Would tanks or small walkers be better for Lunar militaries?](https://worldbuilding.stackexchange.com/questions/106757/would-tanks-or-small-walkers-be-better-for-lunar-militaries). hope they help. [Answer] Note that below I use the term 'walker' instead of 'spider tank'. This is really just personal preference, since the two terms mean essentially the same thing in modern times. ### Terrain: Tracked vehicles are very good at handling certain types of terrain. In particular, for a tracked vehicle to be effective, the terrain has to fit a couple of constraints: * It can't be particularly steep. Most AFV's that use tracks are heavy enough proportionate to the traction provided by the tracks that they can't handle steep grades (I don't know about modern stuff like the Leopard 2 or the M1A1 Abrams, but a lot of older tanks couldn't handle more than about a 20-30% grade). * It needs to not be jagged. Rocky beaches are bad for tracks. So are [dragon's teeth](https://en.wikipedia.org/wiki/Dragon%27s_teeth_(fortification)). * While it can be somewhat soft, it still has to provide decent traction. Sand is usually fine, provided you aren't going up steep dunes. Mud is usually fine, provided it's not too deep. Snow, unless it's very hard packed, is typically not (most tanks can handle snow up to a certain depth, below that, the snow will get into the gun, the engine intakes, and the cabin vents, and cause issues). Note that this is very design dependent, some old tanks (such as the Porsche Tiger) were notorious for digging into mud as often as crossing it. * Water may or may not be an issue. Most modern tanks can ford rivers fine, provided the other constraints are met, but that was not always the case, and the vehicle needs to be designed for it. * Certain types of fortification are problematic (the aforementioned dragon's teeth, as well as things like [Czech hedgehogs](https://en.wikipedia.org/wiki/Czech_hedgehog)). Now, of these constraints, the first one is essentially a non-issue for a properly designed walker (if you make the feet right, you can climb vertical surfaces). The second is not as much of an issue for a walker as a treaded vehicle. Soft ground *might* be an issue for a walker, depending on the design. Tanks handle it fine because they spread their weight well, there's no reason a walker can't do likewise, see for example water striders (they use other tricks in addition to spreading their weight, but the general principle is the same). However, even without spreading the weight of the vehicle, it *still* may not be an issue, if you can pull the legs out easily, you can just let them sink and be fine, or you can create something very light that can move very fast across soft ground (and therefore the feet don't have time to sink). Water may or may not be an issue for a walker, it's really design dependent, though I would envision that less work needs to be done to let a walker ford a river than a tank. As far as fortifications, a line of dragon's teeth would have to be *very* wide and very narrowly spaced to stop a well designed walker, and would as a result probably be impassable to infantry as well. Czech hedgehogs might be a bit more of an issue, but probably not as much as they were for tanks. So, overall, while a walker may not do as well in certain types of terrain as a tank, it would probably do better in types of terrain tanks have more issues with. ### Maintainence So, hydraulics are horrible for maintenance in a combat zone. One well placed bullet will render them inoperable in such a way that they can't be reliably repaired in the field. Their only real advantages are weight to power ratio (which is insanely good compared to other options), and the fact that they can be trivially made to lock into position when unpowered. Pneumatics are a bit better for maintenance (you can patch the hose, and then just pressurize the system with a portable compressor), but are still easy to damage and trivial to cripple. There are three alternative options to hydraulics and pneumatics: * Rotary servos, one (or more) per joint. This is immediately out, it's too hard to replace them, and it's difficult to make them fail-safe. * Ball screws or lead screws. They're reliable, insanely durable (most designs can tolerate a lot of damage before they completely stop working), and can be easily adapted to fail safely (that is, have the leg lock into position instead of collapsing). * Linear servos. Not as durable as ball screws, but they're a lot easier to replace, and are also very easy to make fail safely. Beyond that, just make sure you have more than one actuator per joint. That allows you to lock the working ones in place to safely replace a failed one. ### Defenses A walker is harder to defend from counter-battery fire and anti-tank fire than a tank. The joints pretty much need to be at least partly exposed, and unless you're using rotary motors in each joint, so does whatever actually moves the legs. Height is also an issue (though, unlike a tank, a walker could be made to be variable height). Being higher up makes you an easier target (though it can also make it harder for enemies to take cover from you). On the other side of things, mines may not be as much of an issue for a walker as they are for a tank. If a tank runs over a mine, it's usually either done for, or at least completely stuck there. If a walker steps on a mine, it can just adjust it's stance to compensate for the damaged leg and foot. Of course, this won't work reliably more than once or twice, but it's still enough for the walker to relocate to somewhere better defended for the crew to repair it. ### TL;DR Walkers would probably work, but not in the same roles that tanks do. I can easily envision them being used as armored recon vehicles in particularly difficult terrain that is uncrossable by conventional wheeled tracked vehicles, but I don't think it's reasonable to assume they would be the primary form of armored infantry. Regardless, it depends entirely on their design. They almost certainly won't look like anything you've seen in movies or other media, considering that those are almost always designed to allow for good storytelling (classic example, the AT-AT's used by the Galactic Empire in Star Wars episode 5 are pretty much worthless from any realistic military perspective, they have no fail safes to keep them from falling over if the controls are damaged, and they're trivial to trip). [Answer] It all depends on the circumstances, wheels are better than tracks when you're driving on concrete and asphalt as they enable you to reach higher speeds more efficiently and give you more traction when cornering. On the other hand a multi-legged design would probably be slower than a tracked vehicle but it could handle the especially rough and/or soft terrain that tracked vehicles traditionally struggle with. If your combat vehicle is being deployed to a highly developed area with reliable road quality having wheels is advantageous, if it's being deployed to a place that has been shelled or is simply undeveloped natural terrain a tracked vehicle would be more reliable. A multi-legged combat vehicle would be even more reliable and could operate in terrain that precludes wheeled and tracked vehicles, but it would only be advantageous in those circumstances. [Answer] I'm going to go ahead and base my answer around what we see in the Ghost in the Shell universe, where spider tanks are plentiful. I know this is `science-based`, so take this with a grain of salt. **1) They are not as big as actual tanks** I'd wager the main spider tank from GITS isn't actually as big as as a proper tank. It also seems to be equipped with less firepower - miniguns and some rockets. This leads me to believe these are designed for something else than a typical tank. **2-1) Urban warfare** Because they are smaller, spider tanks are probably more suited for urban warfare where you want to avoid damage to the infrastructure. The spider tanks in GITS can also be quite mobile, as they have wheels on each leg, allowing them to use roads at high speeds. **2-2) Combat inside buildings** Given the smaller frame and higher agility in an urban setting, spider tanks can enter and fight inside buildings (again, avoiding the potential damage driving a tank inside would cause). **3) Storage and transport** I'd imagine a spider tank can be "stowed away", making it take far less space than an actual tank. This means they can be hidden from sight in strategic places to defend critical points. Still taking GITS as an example, there are cases where spider-tanks are used as defences on ships at sea as well (albeit that one seems like a stretch). **4) Specialistic equipment** This is mimicking point 1 a bit, but I'd wager that given the tech needed to construct a spider tank, they aren't meant to replace actual tanks in a full out war, rather they are strategically deployed to perform certain tasks. Think sabotage, hacking, relays, strategic defences (remember these can be stowed away and / or transported with more ease). [Answer] You're posting in world-building, so I'm assuming your interest isn't replacing all tanks in your world with spider-tanks, but enough to get a good story? As others have commented, the increased complexity of multipedal tanks will make them less efficient, due to the added weight of the mechanisms. Programming the legs should be fairly trivial. Ignore 4-legged tanks; go for 6 or 8 legs. They provide much superior balance and 8 legs provides significant redundancy. If you're looking near-future, you could extrapolate some development of actuators like muscle wire or EAPs to provide motive force, instead of hydraulics. However, you're probably going to be looking at a lighter armoured spider-tank compared to a main battle tank. But who cares? We're fighting in places where main battle tanks just can't function. One other potential benefit of legged tanks is that potentially they could *dodge* incoming attacks, by shifting their bodies, much faster than a tracked vehicle could. This would provide significant protection, as voiding attacks will always be better than relying on armour. So you need a scenario where tracked tanks are particularly ineffective. You're likely looking at mountainous terrain, or potentially a post-urban terrain – particularly if the buildings are heavily engineered rather than light residential buildings one can drive through with a tracked tank. The issue is that in most of these scenarios, a helicopter is likely to out-perform a tank, and is readily available and tested. So add in ground forces with guided RPGs or similar designed to take down choppers. One other scenario springs to mind: Common spider-tank designs in manga put wheels at the end of the legs for road use. Interestingly, this could allow better on-road performance than a tracked vehicle (tracks are notoriously bad for roads, which is why the army always transports tanks on flatbeds not driving them), but better off-road performance than a wheeled combat vehicle. This could be ideal for a mixed urban environment where you don't want to cause massive damage to infrastructure by ripping up roads with tank tracks, but you need to cross rubble, climb stairs, get past bollards, etc. [Answer] I would imagine that spider mechs would enjoy benefits over tanks in aquatic/amphibious or zero gravity/very low gravity. traversing liquids (eg water) could be acomplished by raising the feet above and out of the water and then propelling forward, negating the resistance of the body of water or even being more of stealth as it could pierce the water surface with minimal disturbance (especially with care to ease into the initial dip of the foot to avoid a "plunk" sound as for space/zero gravity, the legs could double as directional thrusters or to improve grip around the surface it is traversing (like how your fingers reach around a tennis ball or inflated balloon the size of a watermellon. [Answer] Can the question be reworded to "Can spider-mecha replace conventional tanks" or "Can spider-mecha effectively destroy conventional tanks"? There is a plenty of answers why the first option is not plausible. On the other hand, if you want to design tank-slayer you are focusing on tank's weknesses and anticipating their strengths. Tanks are big, heavy, slow, noisy and deal heavy damage per shot. Therefore the counter must be agile enough to escape tank's guns and deal focused damage to the critical parts. Tanks are useless in deep mud and on very steep hills. Make the spiders light enough not to get stuck and able to climb. A small fast unarmed mecha that can resemble in a form of [czech hedgehog](https://en.wikipedia.org/wiki/Czech_hedgehog) can be effective agains moving tanks imobilising them long enough to be easy target to other weapons of your choice. Small mecha carying a landmine and placing it at the right spot and running away can be effective too. A swarm attack of small and agile spiders against tanks are effective because tanks cannot fire at all of them at the same time. [Answer] So. Tanks are built for a specific battlefield role. Optimized for it. While we call it a 'Spider Tank', it may not necessarily fill that precise role. As noted in other answers, a legged vehicle has certain advantaged over a tracked one: Mobility and resilience. Mobility, in the sense of being able to climb over things, like parked cars. Resilience, in the capacity lose multiple legs, without being disabled. It might be better to think of spider tanks as an 'armored car' capable of moving through a gridlocked street, than as a tank. They only need to be sufficiently armored to survive small arms fire. [Answer] 1. **Mobility** A walking transport's mobility is far beyond anything that normal tank can dream of. Walkers are able to move through any kind of terrain (which can cause troubles to normal vehicles) and even extremly tilted surfaces. Can a normal tank climb a 90 degrees oriented wall? The spider tank can! 2. **Endurance** A car with one lost wheel becomes nearly immobile (not taking into account the art of driving cars on 2 wheels). A tank with one lost track turns into a gun with pretty thin armor for an immobile fortification. At the same time a spider tank with its one lost leg can perform without much difficulties (of course, every leg should be independent, otherwise it will totally restrict any further movement). At max it can lose all but 3 of its legs (to maintain balance) to keep moving. 3. **Control** A car is driven most simply: press the pedal and turn the rudder. A tank requires a bit more advanced skill to keep both tracks coordinated. A walker requires a very complex coordination system that allows all its legs to have the job done, and with every additional leg beyond first 2 the complexity increases considerably. 4. **Costs** * The more complex the vehicle is, the more money is required to build such a thing. Spider tanks should be really expensive toys * The more complex the vehicle is, the more parts there are to break. You definetly dont want a weapon that spends more time in workshop fixing itself than on a battlefield fighting * How much time and money does it cost to train a tank operation team? Multiply these numbers times and times to imagine what you should spend on a spider tank operation team. [Answer] These days, if you want a robot to move around and be "flexible" (this rules out bipeds because like us humans they tend to fall over), there are three options: Wheels, tracks, and spiderish things (there may be more, but these three are the most commonly seen ones). Tracks (tanks) are good for traversing rough terrain, but not very flexible. A spider-mech would excel in "tight environments", where a tank might be defeated because of turning radius or something similar. Aside from that, there aren't that many advantages. Spider-mechs are (presumably) more lightly armored because putting too much armor on them removes their flexibility. There is one significant disadvantage of a spider-mech or any type of mech against a tank: the joints. You can't have that much armor over a joint, or else the whole purpose of the joint is gone. You would have to have the armor *on* the joint. If you put too much armor on the joint, you would get these unwieldy legs. Conclusion (TLDR): Spider-mechs would kind of work but not really. [Answer] **Advantages of Spider Mechs Over Tanks** 1: Look cool That's it. They're more expensive, more complicated and more easily damaged. When you can have a dozen tanks for the cost of one mech, tanks win every battle. Quote by Joseph Stalin: “Quantity has a quality all its own.” ]

[Question] [ Humanity is immortal. You can backup your mind, you can choose your body, biological or robotic, in any shape or form. In a universe like that, there is any motivation for racism to still exist? [Answer] ## Yes, sadly but for a good reason Racism is a sub-type of in-group bias, where a person will favor someone mentally labeled as "in my group" over someone "out of my group". Other examples of this type of bias show up in politics, text editor choice, religion, sports team preference and most any other instance where some characteristic can define a group. The reason we humans have in-group bias is because those with this bias are more fit than those who don't (over the lifetime of the species. Recognition of racism as a harmful thing is a relatively new thing, just the past few centuries or so). Humans are social animals, so the groups we belong to dictate our survivability. A group that concentrates it's time and attention on itself, will naturally do better than a group that dilutes its limited resources on other individuals/groups. Consider the difference in how bad you feel about something bad happening to another human who is a great distance away and far from your internal in-group definition compared to a bad thing happening to someone of your race and socio-economic standing in your town. Proximity and same-ness dictate a lot of your emotional response. The only thing that stops racism is cultural training. It takes effort to overcome those biases and behave differently. Perhaps, over time this will happen, but a magical post-scarcity, post-mortality, post-cis human world won't automatically fix this bias. [Answer] # Yes, there will be As long as there is free thought, there exists the ability to prejudice against others. Racism is defined as abuse toward a particular race and culture, so if the culture still exists, there will be people to oppose it. [Answer] A culture is not a race, you can't be racist against an idea. With the option to choose any body of your liking, it would be hard to see how people would still hold beliefs about a certain look giving people certain inherent traits. Especially if it's such an established part of society that anyone can have access to, I don't see why anyone would care. Depending on how available the procedure is, people could change bodies, sex, gender, species like we change clothes, and people would think nothing of it. That being said, depending on how your society is built, if a certain appearance was tied to a culture (People of culture A are typically green, people of culture B are typically blue) then there could definitely be prejudice between the two. This could even include sub cultures using body modifications as statements. Many today (or at least some years back) would judge one for wearing black clothes, piercings, dyed hair etc. In a similar way, people belonging to a sub culture could adopt certain body traits to show that they belong to that group. Perhaps the future punks will have long ears and sharp teeth. Others would then be likely to be judgemental towards people with those traits. Though this would still not be traditional racism, just like today it is not racist to judge someone based on what they wear. Today we deem it racist to judge a person for a look they were born with and had no control over. If changing your appearance is as easy as it is to change clothes, is it still a race in the traditional sense? Prejudice yes, but I still would not call that racism. Another route you could go down would be that different bodies are of lower or higher quality, and cheaper or more expensive respectively. An expensive body would last longer, be stronger, maybe smarter or even robotic. This would provide a clear indication of what 'class' you belong to, and allow people to easily judge you based on your looks. It would more or less be out of a persons control what body they could be reborn into. It would be more like classism than racism, but at least you can argue that the way you were (re)born is something that can be judged. [Answer] **Depends** An important concept here is [cultural racism](https://en.wikipedia.org/wiki/Cultural_racism), basically the belief that an 'other culture' is essentially and unchangeable different in a specific way: > > After WWII, as the idea of different biological races became controversial, the term culture received increased significance in racist reasoning. Scientists usually talk about so called "Culture racism". Instead of starting from biology, culture is used to explain how people are and what they do. Culture is seen as something solid and unchangeable. The rhetoric and the purpose of the division is the same as when talking about biological races though. Stereotypical notions about the cultures of ethnic groups as essentially different and incompatible with the (for example) Swedish culture lies as a foundation of cultural racism. Cultures are seen as unchangeable and very "deciding" for a person's characteristics. > > > This has largely replaced discredited biological racism. The function is the same, though: Justifying existing social hierarchies. If we are actually not all equal it's ok that we don't live under equal conditions. So, in your transhumanist future, exist there any power difference, privileges between sentients? If so those in a better position (relative to anyone) will look for a way to justify this, maybe an updated form of cultural racism, maybe they'll invent 'cognitive types' or something else. The important point for this something else that it attaches to a person or a group an \*unchangable' characteristicum that will justify their lower status. If, on the other hand, in your transhumanist future, there's little privilege to defend, such an updated racism will have less foothold. [Answer] If we're talking of racism specifically and not simply prejudice, then understanding what might happen in this transhumanist future requires an appreciation of where racism originated. It's been mentioned that people are naturally distrusting of those outside of their comfort zone; their in-group. This relates to the [Dunbar number](https://en.wikipedia.org/wiki/Dunbar%27s_number), or the average number of meaningful personal relationships a primate species is capable of (thus group sizes and potential for empathy) based on their brain size. That's a fairly hard rule, but it doesn't mean it will translate into institutional racism. The racism we see today is based upon specific social developments. Firstly, the domination of the world by European-American Imperialism, which in large part relied upon the [transatlantic slave trade](https://en.wikipedia.org/wiki/Atlantic_slave_trade), which led to [pseudo-scientific ideas](https://en.wikipedia.org/wiki/Scientific_racism) for why this had happened, which, unsurprisingly, offered convenient explanation for the imperial powers. Of course Africans are slaves because they're not really human, and so it's fine to enslave them because they can't do any better. This intellectual framework relied upon an understanding of feudalism. In the old world society was stratified into (generally speaking) nobles, merchants, and peasants. Slavery was not an alien concept in this context since peasants were often legally tied to their land, and thus owned by their lord. Serfdom was an even nastier sort of system; the serf one rung below a peasant and one rung above a slave on the social ladder. This social system was transplanted to the Americas by the colonial powers. Old world divisions dissolved and were reformed along racial lines to reflect the new power dynamics. [In Spain's empire Iberians were at the top, Amerindians in the middle, and Africans at the bottom](https://en.wikipedia.org/wiki/Casta). This division became law... but over time it became awkward to the point of absurdity. What happens when an Iberian has a child with an Amerindian? Well, obviously they form a new caste which sits between the two. And then, what of when their children are from union with other castes? As you can imagine, after a few generations it became almost unenforceable because at first glance it was now impossible to tell which group one belonged to. Little surprise that this system crashed and burned by the time of Simon Bolivar's revolutionary wars. The racism we see today is a legacy of those times and a continuation of those beliefs. So, how would transhumanism change this? One potential is that it makes it much easier for people to empathise with out-groups, because of body swapping they can be black for a week, and thus see how they are treated differently. In theory this should lead to a severe drop in racism. Perhaps the state could mandate that in order to reduce prejudice, during their teenage years children have their bodies swapped a few times for a few months at a go, ensuring that as a result of them existing as a few different genders, sexualities, and ethnicities, they are trained to have greater empathy, as natural out-groups become part of their individual identity. However, it depends on how fairly the gains of this transhumanist future have been shared. It'd be quite easy to imagine the technology is priced out of the market for the most people, ensuring a social decay back to God-kings of old. Only now they actually are immortal demi-Gods of sorts. The richest can afford super GM bodies and live forever. The poor? Well they're not much worth keeping alive for that long, are they? Prejudices in that case would carry on because the social circumstances don't change. Similarly in a future where there's major wars between different ethnic factions there would be a lot of hurt and anger on both sides. You've also got to consider that even if we can change our bodies to any sort of shape... would we want to? Would it be allowed? [Self-expression isn't a value which has universal appeal](https://en.wikipedia.org/wiki/Inglehart%E2%80%93Welzel_cultural_map_of_the_world). Most of the world's societies are guided by conformity and tradition. In that case, even if let's say, space North Korea, has its citizens granted immortality, why would they be given a body that was not what is deemed absolutely Korean? Either the culture or the state dictates what is acceptable, and if neither approve of self expression people will neither want nor be allowed to defy tradition. Therefore whoever looks like an outsider won't be considered a full member of the group. An even nastier idea is perhaps that the state or culture encourage racist beliefs as part of their judicial system, and punish people by giving them the body of a group the people have been taught to dislike. Then we don't so much have a meme which associates, say, black people with crime; but rather makes a causal relationship between the two. You are white or black or whatever, because you are a convict. [Answer] When we look at evolution we often discover that doing something the way we always did have been the key to survival. Because hey it worked so far right? So every time something new is introduced to the reptilian brain, a certain kind of suspicious arise. The same kind of suspicion starts when your boss tells you to work in another way, it is the reptilian mind, it is also the reptilian mind that make you go back to the old routines, even though your intelligent brain tells you it is more efficient the other way. Now when you see something or someone that looks different the reptilian mind is also there, the brain at the first stage register the change. The first iteration it might not even be a someone it registers just that the grass field looks different than before, then second iteration it registers what is the change, and this is just comparison, does it look like me or not. If it does the brain don't put as much work in to it, but if it don't it starts to register, is it a rolling bolder, a charging bear, pouncing tiger or a person that looks different. Now the reptilian brain teaches the brain what to be aware of to survive. To make it to the fittest part. It might not just be racism. A person's skin color. (Outsiders might be marauders coming to burn the village and kill us) It can also be towards persons with baggy jeans and hoodies, in case a person had a previous experience with people with those significant symbols. The brain thinks in symbols, so it is important to remember that one can even experience a cautious nature towards a certain person based on walk, talk, clothes, would it be baggy jeans or a police uniform. This is where racism originates from, a combination of the nature of the reptilian brain and what you teaches it. If you teaches the brain to be warm and welcoming towards everyone, if you talk to people of many cultures, you teach the primitive brain that other people are ok. In-fact you don't even need to wait for an immortal human with cyber brain, you can start today! [Answer] > > In a universe like that, there is any motivation for racism to still exist? > > > Fundamentally, racism exists because of differences between people. It happens that it involves discrimination or negativity based on a specific identifier. Race is an obvious and external difference currently and as such is often the precipitator for this discrimination. Humans like feeling part of a group. Unless in your future society this social aspect of humankind is gone, it is likely that: * Humans will group themselves based on some commonality (family, occupation, gender, shape, whatever) * Humans will then differentiate themselves based on this commonality It is entirely likely and possible that humans will take those new differences and effectively create new forms of discrimination/racism. Whether those are explicitly *racism* is up for debate, you might not have "racism" on a technicality, but the underlying motivation and premise will surely still exist. [Answer] I think strictly defined racism will fade. It might take a while, but as visual racial characteristics disappear and time passes, people will find other reasons to discriminate. *Cultural* Racism will be with us as long as we will have cultures. The idea of "Us vs. Them" is very strongly embedded in the human psyche and will probably be so forever. There will probably be more movement between cultures when people no longer carry their ancestry on their skin. This will probably stop discrimination from becoming *too* bad, as people will simply desert to other cultures. Except for a few fanatics. See that guy over there? He is the last remaining plaid-skin! What a criminal disregard of the Monochrome Law! Consider this: You have not been promoted, but that other guy is. Which explanation are you most likely to believe: * The other guy is better than you. * The blue-skinned boss is promoting blue-skinned people. We Greens have to stick together to fight Blue-skins racism! In times of plenty, everybody are friends and nobody is discriminated against. Not much, anyway. In times of scarce, people start looking for scapegoats, and it is always "Them". "They" are taking all our jobs. "They" are getting all the good asteroids, leaving just the gravel to "Us". Unfortunately, something is always scarce, and "plenty" is always relative. It doesn't matter that you have a spaceship if your neighbor has **two**. How did he get so rich? Must be nepotism... [Answer] # Yes! Simple answer but people find reason to be racist, for example they will be racist vs people because they choose a white body e.g. how stupid they are. It is like Apple and Samsung even if we can choose the people still hate each other on stupid small things. People could hate on other people depending on where you were born. Here in China we have the best bodies and stuff like that. Also culture and religion form hate and racism. [Answer] Transhumanism will provide the ability to create not just new races, but entire new species of humanity (descendants of humans who are unable to reproduce with traditional humans without the assistance of technology). Development of these new species will be driven by cultural values. In fact, people with strongly held ideologies (religious zealots, fanatical communists, etc.) will seek to encode these ideologies into their offspring. If a subculture values obedience to elders, they will encode obedience into the genome of their offspring. If a subculture values pacifism, they will remove the ability to experience rage from their offspring. Clearly, these new races and species will have very strong fundamental disagreements about a wide variety of core beliefs. [Answer] Yes, racism will persist. Even though we all merge into one race - same skin shade, same shape, same hair, same crotch/infant-feeding equipment, same abilities... There will persist the reason to hate "the other group (race)": straights vs. LGBT; men vs. women. **Unite!** Ok, we are all the same, we are all hermaprodites. All exactly the very same... There is still reason to hate "the other group(race)": Age; Older hate the younger because, well, they are younger, healthier, full of ambitions,... Youngsters hate elders because they won't let them do what they wanna do,... **Unite!!** Ok, the "science&technology" vanished aging, health differences and there are three states of human being: *infant-adults* totally isolated from the others, grown, AI-educated. *Adults* moving freely. New adults are indistinguishable from the ones who just moved from another place. Their death is driven only by probability. *Dead ones*. But there is still a reason why to hate"the other race": North-comers vs. South-comers. **Unite!!!** Ok, S&T guys took over the Earth and Moon kinetics, so the Earth rotates randomly, so does the Moon. There is no North, South, east or West. The surface is terraformed so every cubicle has the equal sea-to-soil ratio, they are exactly the same. But there is another reason to hate "the other race": Religion. The catholics hate protestants, Westboro baptist church hates everybody else, All hates atheists. **Unite!!!!** Ok, there is one and only one religion (no religion is religion too), right? Satisfied? But there is another... Aw, c'mon! ...reason to hate "the other race": Habits. [Big-end hate the small-ends](https://en.wikipedia.org/wiki/Lilliput_and_Blefuscu), Cat-lovers have dog-lovers,... **Unite!!!!?** Ok, people are exactly the same, there is absolutely no difference between two people right? NO DIFFERENCE, guaranteed. But do they have free will? Are they people, actually? Darn, only two stones cannot be racist, because they do not think at all. But there is [The First Sirian Bank](https://en.wikipedia.org/wiki/The_Dark_Side_of_the_Sun), you know. I wish I have [never ever asked](https://youtu.be/FfIILqRSMzw?t=2803)... (I wish there were translation, but you don't actually need to hear what they speak, her faces are well descriptive...) [Answer] Just go on the internet and see, we always find reasons to hate eachother like * the shows we watch * the music we listen * the way we dress * the people we vote for * the imaginary invisible borders we were born in * cat vs dog * thor vs loki * iphone vs android [Answer] A semantic quibble: several of these answers say "yes" (which is ridiculous) but then go on to explain that they actually mean "not per se, but new bigotries/factionalism would take its place" (which unfortunately I believe). This is a sci-fi pet peeve of mine. If you want to write dystopian scifi, write dystopian scifi. But don't give me a utopian transcendent race and then tell me "but they still believe the racial gobbledy-gook that was invented in England in the 16th century to justify replacing the banned indentured servitude market with an African slave market. Oh and everyone still conforms to 1950's gender norms. And the Foundation will still run on nuclear power." Hopefully we'll have evolved beyond our baser instincts toward factionalism, but at the very least I am certain the factions won't be "blue skins" vs "red skins." Instead, I think it would be between the "baselines" (those who stick to the level humans had naturally evolved to at the time this transfer-to-a-new-body singularity happened, basically using the new technology as a rejuvination or back-up safety system [more "facelift" than "breast augmentation" you might say]) and those who don't. [Answer] Discrimination is human nature, its how we differentiate one thing from another. In fact, I'll go as far as saying that differentiation is a base constituting common human analysis done by a thinking mind. There will always be a "sought after" human body / enhancement. Something that'll set it apart. People who don't have it hate the ones who do and scream, "My Privilege!!". People who do have it cry, "Damn Plebians!!" Some human characteristics are just more perfect and fine than others. It gives rise to the human need to always have that perfection in no matter what they do. Sometimes this need is even seen in pretty [mundane things](http://www.lenna.org/full/l_hires.jpg). So coming back to the point, human beings , as they say, will always find a way. Here's a small [thesis](https://i.stack.imgur.com/a5bcH.jpg) on human nature. Its pretty crude but it gets the point across. Its not easily understood, but it delves pretty deep into the workings of the gritty societal structure that is and constitutes being human. ]

[Question] [ The world I'm building would be based on a new planet discovered and colonized by modern humans (us, essentially). But then some disaster or another happens, and the end result is that all contact with Earth and other humans is lost, and only a few hundreds to a few thousands people remain on the new planet. All or most of the technology is lost, but they're otherwise safe and in good health. After a period of adaptation they start to settle here, have children, and so on. Now, my thought is that after a few centuries or millennia, descendants of the earth people would have either forgotten altogether about Earth, or only deformed myths and legends would remain. **But is that accurate?** Wouldn't the survivors write down accounts of Earth and the modern world, and endeavor to keep the memory alive? Or is it realistic to think that after hundreds of generations and all the sorts of disaster, strife, political changes and warfare that could have occurred, historical records would have been lost or destroyed? [Answer] There's a reason we use archaeology to reconstruct what happened in the past. Written records are powerful when they exist, but they're also fragile. It takes relatively little damage for a document written on paper to become illegible; stone lasts longer, depending on the environment, but it's so laborious to carve that you'd only keep your most important records engraved in stone. In a survival situation, you have much more important things to do than record the name and location of your homeworld. Unless your people maintain an industrial civilisation, and are able to devote extensive resources to recording their past and preserving those records, it's perfectly feasible for knowledge of the past to be lost. [Answer] It's possible, but it requires a trip through illiterate barbarity lasting centuries. This means that they cannot forget only about Earth: they need to forget everything, writing, math, engineering, science. For all practical purposes they will be an independent civilization, having to re-invent almost everything from scratch. The ancient Egyptians wrote all sorts of things on papyrus and carved very many inscriptions on stones, some of which are breath-takingly huge. Nevertheless, by the 8th century (the time of Charlemagne and [Harun Al-Rashid](https://en.wikipedia.org/wiki/Harun_al-Rashid)), about 1100 years after the [Greek conquest of Egypt](https://en.wikipedia.org/wiki/Ptolemaic_Kingdom) their descendants had completely forgotten everything about the glory and the power of Ancient Egypt; they could not read the inscriptions, they had no idea who had built the mighty pyramids and the abandoned temples; not one single name of a pharaoh survived. [Answer] **Ancient records without evidence are treated as myth** Imagine we have ancient records handed down from two thousand years ago stating that humans arrived on Earth from this ancient, beautiful paradise filled with fantastic creatures and places we've never seen. Nowhere can you find any evidence for this place. Would you believe it? **Digital records might last a long time, but digital standards are fleeting** How long will the original records last in a readable format? Not long, I'd think. Some people will try and preserve the old records but, over time, they'll get lost and mixed up with fictional sources. I don't think that you can rely on data getting passed on readable and unaltered for a long time. [Answer] We didn't forget about Rome or the Fertile Crescent, but we largely forgot about Africa. The dividing line is essentially when we started having cities to live in and keeping history in some form. What this tells us is so long as an they live in a city and keep a history of some sort they'll remember Earth in some way. Maybe they won't know it as Earth or think its real after a few generations, but it will turn up as a common myth with a derivitive names that can be tracked back to Earth or Home or Sol... It would be a celestial place or a place across the sea, based on the flair of the person telling the stories. If civilization breaks down any further Earth might be lost, but it is very unlikely because even then the survivors would always be talking about how Earth is going to save us and it would be passed down as Earth is a god or redeemer or christlike figure that would get passed down without effort. Asteroids might even come to be called "earthships" because so many would look up and ask that question and people would say something like they bring great hope, but leave in sadness. [Answer] I certainly think this is possible. It entirely depends on how bad things become and the situation of the colony throughout the generations. There was parallel I was thinking after reading Orwell's 1984 (no spoilers here). One string of events I can imagine: * Elites gain control over everything after brutal war. A strict totalitarian regime. * People forget how to read/write in whole. Perhaps 10-20% literal, mainly by Elites and their lackies. * Science is forsaken for dogma to maintain power over the common man * Plague happens and it happens only the common man's genome was diverse enough to remain intact. This could be the recipe for Earth to be lost to legendary stories and Sol may just be another star in a constellation. [Answer] # No. These humans are clever. When populating a new corner of the universe, one's origins become extremely important. Firstly, these marooned humans arrived with a full body of knowledge. Chances are, amongst them, lie; scientists, historians, mathematicians, astronomers, etc. One of the first jobs to take care of, post disaster, would be to work out planet Earth's time - relevant to their local. Additionally, what area of the night-sky does planet Earth reside? They'll need to record this. Let's assume all monitoring equipment was destroyed in the disaster. Perhaps their spaceships, in which they lived, were lost - including all of their technology within. Naturally, these humans would start to build structures from scratch. First homes, next schools - dedicated to passing on crucial information. Frameworks would reinforce peaceful upkeep within society. Many lessons from back home would apply here. Although, they'll need to be wise when it comes to preserving their roots. Sure, most of their tech was wiped out in the catastrophe. But how about their personal belongings? Were individuals left with; id cards, passports, photos from planet Earth? Perhaps fossilised life within key-rings, unique to Earth and used as a reminder of back home. A central museum would be a great location to store these kinds of items. Evidence is the most important value these humans hold. They'll decide to apply rationality to their existence wherever they see fit. One of their most crucial segments of evidence can actually be found within them. Their genetic code. **There are no signs of human evolution on this strange, yet habitable, planet.** [Answer] Yes, and it doesn't even take that much of a disaster. Take the best case scenario - a computer virus wipes out all preexisting records, but technology otherwise continues to work. Everybody immediately writes down what they can remember. The colony has been established for a while, so none of the colonists are former starship crew. Nobody knows how a warp drive works beyond crude analogies like "a chariot pulled across the sky by a captive star". Nobody needs to know the precise location of Earth. Ordinary people might point out a particular star to their kids, but that doesn't happen if it is only visible from the other side of the planet. None of the colonists have any personal experience of earth, just the very brief overview they got in school, which doesn't go into any depth and probably misrepresents the facts anyway. Maybe Earth was a dystopian hellhole that the colonists were escaping, maybe it was a paradise with a duty to colonize the galaxy. Hardly any of them bothered to look up actual facts. There's probably also a conspiracy theorist or two who believe that Earth never existed despite all evidence to the contrary. But that evidence is gone, and all these people have equal power to record their version of history. Then a few hundred years down the line someone connects a description of Earth as paradise with a guy in the same set of records talking about the afterlife as paradise, and you have solid evidence that the whole lot is just a religious myth. [Answer] Werrf Makes a valid point that if they lose most technology or it appears that they are struggling to survive rather than living comfortably and just lost their walkie-talkies, they will be less likely to be focused on preserving something like we are from earth and more concerned about how do we live. OP said that the remaining humans survived a disaster of some form. It can be implied that some or maybe even many humans were killed as he states remaining humans AFTER the disaster event, and he stated that it destroyed most of their technology, and killed off communication. That said though, this doesn't mean after a millennia++ of time, the civilization wouldn't have created their own technology and through that dug up their past. Whether or not paper documents or other stored data would be A) preserved, and B) functional to the new technology is another story. Before I continue, I would like to point out that I am bringing up ideas that have been tossed around and being used for the sake of an applicable argument and may not reflect personal belief. We question whether something like the pyramids were really created by the Egyptians because of the advanced level of thinking or other historical civilizations. There are groups of people that say, these ancient cities are just too advanced for their time, some "outside" influence had to play a factor. What if we on earth might be living the situation you described but lack the technology to really dig deeper into the past yet? It is entirely possible that even if the stories are recorded, and physical evidence is presented (say a part of a ship with the letters "EARTH" has been found) due to it being discovered thousands of years later, it is possible that the researchers who dug it up attributed the myths and legends of Earth to this sign. They may interpret this finding to someone who saw an ancient sign and wanted to write up a story about where they came from. So, is it POSSIBLE for them to forget they are from Earth? my answer is yes. Just depends on where you want to take the story and how you present the sequence of events from them losing contact to modern day. [Answer] It is somewhat off topic but just to make a point, in Arabic language the word for human "insaan" comes from the root word meaning "to forget". Human beings over time forget everything. Something can only be preserved if it is passed from one generation to another without being corrupted which is not trivial. [Answer] I think that through oral tradition, legends and stories about sol and the Earth would still exist. At some point the legends might be so distorted and far from reality that you might consider that it s equivalent to having forgotten about Earth. But I m pretty sure that stories about the first group of men and women, coming from the stars will somehow survive. Some people will say that it s a myth, some people will still believe those legends. [Answer] Your question implies that the tech level never falls. **WHERE THE COMMUNICATION IS CUT OFF MATTERS** The disaster that cuts off communication can be on Earth, not on Planet X. In fact, I would make that so, because if the disaster happens on Planet X's end, there will be impetus to rebuild those lines of communication. Should it happen on Planet X, you'll have to have a reason for them not to rebuild. On Earth, it might not be a priority-- but for the colonists, it would be--this is where they are from, and for Earthers, it might be a big resource sink when they have enough problems to deal with at home. It might not even be any kind of disaster on either end, but rather that one of the relays in space needed to communicate had a malfunction or was hit by an asteroid or space debris--and it's too far for either planet to replace or repair. **ALL IT TAKES IS ONE WORLDWIDE REGIME** Lots of answers on here talk about how you'd need a Dark Age in which knowledge is lost, but that's not actually necessary. Things that happened 2,000 years ago become more lore than fact. They might know their ancestors came from elsewhere, but might not know much about Earth. Also, lots of this depends on societal structure. Were these people more concerned with building their own history and leaving earth behind? Could there be an age in history where this was true? After all, they were abandoned by Earth. Just one hundred year period of "book burning" could reduce the likelihood of Earth knowledge. If people are angry about Earth "abandoning" them, that is, no longer communicating, the people on Planet X may, in a generation, want to destroy all remnants of Earth. The regime might see Earth as the source of all societal ills, and want to build a new utopia, which they may believe can only be done by erasing all notions of the Earth that they came from. Furthermore, because this society could have been founded WITH the idea that they would be building a better world, so there could already be a faction which will eagerly use the communication cut off as an excuse not to look back. There may be some that reverently keep evidence of Earth-That-Was, but the majority can forget. [Answer] Yes, they will forget, unless they have a reason to remember. Read: **religion**. In their answers, [aember](https://worldbuilding.stackexchange.com/a/68341/3106) and [fred](https://worldbuilding.stackexchange.com/a/68327/3106) touched on this, but I would like to elaborate: The assumptions in your question are largely correct. The descendants have enough to handle themselves and after a few generations they have no specific reason to maintain memories about Earth. Look at it this way: who will remember you in 100 years time? (sorry) However, *stories* about Earth will last longer than actual memories. They will distort and may turn into legends. And legends persist: they appeal to people for emotional/moral reasons. Religion is only a small step further, it is after all largely stories with morals. Just look at our own history to see how often religious stories have been used to maintain the power status of an elite. I'm not saying a religion *will* develop embedding Earth stories, but it is a possible scenario, assuming 'human nature' does not change substantially. (BTW This later question [How long would it take for a real event to turn into a myth?](https://worldbuilding.stackexchange.com/questions/69640/how-long-would-it-take-for-a-real-event-to-turn-into-a-myth) is a nice follow-up if you follow this train of thought) [Answer] Whether that can happen or not is going depend heavily on what happens after they leave earth. If they in the process cut off all contact with the mother, eventually memories of earth will fade and turn into mythology. If they leave earth under some religious or political pressure to leave, they may well start out thinking of earth as an evil, corrupt, place with everything children are taught being shaped by that vision. If they maintain contact with earth, diplomatic relations, trade, travel back and forth, memories will be retained much longer and more accurate (though they probably still will turn towards some kind of rose coloured glass image of a far more perfect and desirable place than it really is). [Answer] There's a book by a Spanish author (Jordi Sierra i Fabra) titled "A place called earth" that addresses a similar scenario: during the investigation of the "death" of a robot a human stumbles across the re-discovery of planet Earth which the civilization had long forgotten. It's actually a trilogy. It doesn't seem to be published in English though. [Answer] I guess it depends exactly what you mean by "forget". My own family immigrated from Europe to America just 4 generations ago (in the 1870's). I know this from oral and written history, but it is not really relevant to my every-day life. In other words, I'm aware of it, but I don't think about it unless I'm with relatives and the conversation turns toward that topic. Essentially, I've "forgotten" about my family origins in that sense. However, as a matter of historicity, the written documents will likely stay in my family in perpetuity. Every generation seems to have at least one member who is interested in genealogy. I think it would likely be similar in your fictional group. Most people would get on with their day-to-day lives, not really caring about Earth anymore. But the history buffs in the group would keep the memory alive, and probably ensure that it be taught to children after schools get established. I think comparisons to Earth's ancient history are not really applicable, because we're better at keeping records now than we were thousands of years ago. In short, people will remember it the same way we remember things like the American Revolution today. [Answer] A lot has been said already. One interesting example from Fiction is missing however. **SPOILER ALERT!** In the later books of Asimov's Foundation Saga, it is rediscovered that Humanity comes from earth, a couple millenia back. In the Series, Earth is nearly completely forgotten - no mention is made before those last books. And that is without any sudden catastrophe, Earth just became uninhabitable. So yes, it can be expected that Earth would be forgotten or just end up as a very arcane Myth. [Answer] Yes they will and it will not take long. Only the first generation would remember earth from their own memories. Everyone that is born after the disaster will have to relay on what they said or whatever information is recorded. After (or before) the death of the last some from earth. The leaders of the colony will carry on their earth given mission and society. Those not in power but wanting to be will insinuate that the leaders are lying and the data is wrong. If the manage to take power the record will change. Even if they don't they could destroy some recorded data. Even with modern computer more times information is copied more corrupt it becomes. So record data is not reliable. Oral history is even worse. Could we forget about Earth though? Yes why not. Look how quickly children of emigrates change and forget their home country ways. If their was not communication between UK and us. Would today's USA people speak of coming from UK? [Answer] It also depends on whether the remaining humans (after the catastrophe that led to the communication loss) WANT to remember the original Earth. In Marion Zimmer Bradleys "Darkover" series, the remaining humans decided to destroy the remains of their ship and all information on it, as to not create a "temple" of sorts, where everything that they lost is stored (e.g. information, that is of no use on the new planet). Since it was obvious, that there was no chance of returning or re-establishing contact within the next generations, they wanted a fresh start with a society, which would not always look back to what they could not have. [Answer] Stories that are retold time and time again evolve, which can be seen even with simple things that are written down, such as prayers. So Earth wouldn't be exactly forgotten, but over time the story would change so much that it may be hard to recognize it's the same story. For example it may become a myth about a realm of the gods which sent some gods to create humans on the new planet. Which might later change to a single god that created the planet and then the humans. That is unless a written record is preserved (e.g. bible), knowledge of the written record is culturally relevant (e.g. bible), and people are still able to correctly interpret the language and cultural background from the time the record was written (no example exists, sorry). [Answer] If information about Earth is passed down by word of mouth, it will only be possible to pass on information that is understood by the population. So the basic idea of "we came from a place called Earth that circled another star" might survive, but stories of what Earth was like will doubtless be heavily corrupted into stories that align with the current culture. An example of this process can be seen in the "[cargo cults](https://en.wikipedia.org/wiki/Cargo_cult)" in the Pacific. Native islanders saw westerners with seemingly inexhaustible goods ("cargo"), and tried to fit what they saw into their own cultural framework. The result was a complex mix of observed facts and local beliefs, with several common tropes appearing in different cults. These included using western rituals and symbols, such as military parades, crosses, and replicas of technological artefacts made of local materials. Some cults included a belief that westerners had stolen the cargo and hence that the right actions would lead to its return. So in this scenario we would expect to see Earth become a mythical place of flying wizards who could shoot deadly lightning bolts from their hands and conjour up wealth by incantations. This myth would become incorporated into religious practices, with religious tropes such as millenarianism and judgement of dead souls being cast into this framework. Religious and political leaders will attempt to claim the support of Earth, and promise that the riches and powers of Earth will be available to themselves and their followers. Any surviving artefacts will attain religious relic status, and there will no doubt be a brisk trade in fakes. [Answer] As many have said, a lot depends on your definition of "forgetting". Since a lot has been said i will focus on a single aspect: Information without context is meaningless. Your survivors will have at least a basic understanding about the importance of record-keeping for future generations, so it seems safe to assume that they will write things down. As soon as ever possible, people will start educating children, because they know about the value of education. They will also teach history. But all this is just information, with a marginal context at best. We know a lot about ancient egypt, don't we? The guys who built those pointy skyscrapers in the desert? With the funny gods? What was it like to be egyptian 5000 years ago? Let's try something simpler. Do you remember what life was like before the internet? There's a bunch of people on here who cannot, because they weren't born then. What was it like to be a woman 100 years ago? You had basically no rights. First, you were de-facto-property of your father (not your parents, mind you), then you married, and became the de-facto-property of your husband. Rape was not really a crime, especially when you were raped by your husband: he had the right to do that! Voting? Don't be silly! Having a bank account? As a woman? You must be kidding! And don't get me started on contraceptives, family planning or such. You would give birth to many children, on average one per year, but the majority of them will die after a few weeks. Hygiene was only just being invented, so those women who had very progressive doctors and midwifes had an above average chance to survive childbirth. Antibiotics were only just becoming a thing, but obviously not for the common people. Oh, and the toilet was most likely a wooden outhouse in the backyard, while water was fetched from the well. By the way, your life expectancy was somewhere between 40 and 50 years, which was a great progress already. Around the year 1600 A.D the average life expectancy was 20 years (but to be fair, since most people didn't live to have their first birthday celebrated, that alters statistics a bit). To get to the point: Although we have enormous data available about the time 100 years ago, we have no idea what it was like to live at the time. And we cannot even begin to understand what life was like 2000 years ago. So, if by "forgetting" you mean "not knowing anything about it", i guess the answer is no. But if you mean having some idea about what living on earth was like, i am sure this will be forgotten. And it would be even without any catastrophe. ]

[Question] [ **This question asks for hard science.** All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See [the tag description](/tags/hard-science/info) for more information. I've got a lunar colony that struggles to obtain resources, so they're looking for ways to launch satellites into orbit without using up a bunch of rocket fuel. One plucky engineer has suggested that [trebuchets](https://en.wikipedia.org/wiki/Trebuchet) are the way to go, pointing out that the lack of a lunar atmosphere and the reduced gravity are clear advantages that make it possible on Luna. We've got plenty of materials, but nothing from the future. Our satellites are ~1 kg and have withstood all forces we've been able to apply to them so far. **Given current technology, could a trebuchet be used to launch a satellite into orbit around the Moon?** I've tagged this question `hard-science` but am open to some theoretical/unsupported conjecture. [Answer] **No.** No matter how much velocity you can give your satellite, its trajectory will either contain the point it was launched from or not be a closed curve. *an object is in orbit if it returns to its previous position in phase space (assuming we are talking about a close orbit).* if we assume the trebuchet to be the only source of speed, then it means the moment the projectile leaves the device it must already be in orbit, implying the same projectile will impact the machine after exactly 1 orbit. (give a look at [Newton's cannonball](https://en.wikipedia.org/wiki/Newton%27s_cannonball) for reference) So your satellite will either fly away or hit the ground. You can provide most of the velocity with the trebuchet but your satellite needs at least some other source of thrust to correct the orbital trajectory. Other issues make a trebuchet a poor choice to send a satellite into an orbit. They are powered by gravity, something there ain't much of on the moon (see L.Dutch [answer](https://worldbuilding.stackexchange.com/a/111212/40076) for that). Trebuchet have a tendency to impress an angular momentum to the projectile something that is undesirable for something that isn't spherical and has active components inside, not to mention it is all energy removed from the velocity you want to deliver to the satellite. Finally, the trebuchet deliver the energy mechanically so if we assume that your machine can deliver orbital speed to the projectile, we must also assume some part of it will accelerate to the same speed and therefore be subject to a lot of stress. Ultimately, you need to correct all of these problems, and while this might be possible the trebuchet is ultimately a poor choice especially when compared to simpler, cheaper and more effective alternatives like a coilgun/mass driver. [Answer] # It is possible...eventually To be clear @SilverCookie's answer is correct. In simple Kepler mechanics, when you give a single delta-v to an object there are two 'orbital' possibilities: the orbit returns to where it started, or it is not a closed orbit and your trebuchet payload is above escape velocity. However, in this specific case, it is very possible for an object to reach lunar escape velocity (2.38 km/s) without getting anywhere close to escape velocity relative to Earth (11.2 km/s). Here is where we have the possibility to establish an orbit with various interactions of our payload with the Earth and the moon. A trebuchet launch at greater than escape velocity relative to the moon will have at least two vector components relative to Earth: the 2.38 km/s velocity in the direction of the launch ($v\_l$), and a ~1.02 km/s velocity in the direction of the moon's motion ($v\_m$). The approximation is due to the fact that the moon itself has variable velocity as it pursues its elliptical orbit, in the range (0.970, 1.08) km/s. The final launch velocity $v$, dependent on angle between moon's motion and launch ($\theta$) would be (from the [Law of Cosines](https://en.wikipedia.org/wiki/Law_of_cosines)): $$ v = \sqrt{v\_l^2 + v\_m^2 + 2v\_l v\_m \cos\theta}$$ The codomain of this function, given the values above, is (1.36, 3.40) km/s. The minimum and maximum are found with launch angles of $\pi$ (directly away from the moon's motion for the minimum) and 0 (directly in line with the moon's motion for maximum). Note that this all involves only orbits in a 2-D plane. The launch angle will in turn be the orbital angle of the object; so long as its orbit is prograde (in the same direction of the moon). If the launch angle is retrograde, you subtract $pi$. If the maximum speed is chosen, the angle is 0, which is the angle at perihelion. If the minimum speed is selected, launch angle is $pi$, but the orbit is retrograde so orbital angle is again 0; the object is still at perihelion. The angular velocity of the launched object is $$\omega = \frac{v\cos(\theta)}{r}$$ The minimum possible angular velocity is 0, the max is $8.85\times10^{-6}$. Now we can use [Kepler's equations](https://en.wikipedia.org/wiki/Kepler%27s_laws_of_planetary_motion) to get some ideas of how to get back into a lunar orbit using the Earth. # Use the Earth's atmosphere to drop your velocity. Since we have seen that it is possible to have zero angular velocity relative to the Earth, then there must be possible launch trajectories that intercept the Earth. If so, then it is possible to get one that brushes the Earth's atmosphere. Use the Earth's atmosphere over a series of orbits to bleed off kinetic energy from our launched object. Once the object has lost enough energy, its velocity at the distance of the moon's orbit will be reduced to below the Moon' escape velocity. If the object then approaches within the Moon's Hill Sphere (about 60,000 km), it will start orbiting the Moon instead of the Earth. Mission accomplished. I will admit that there is probably a lot of trial and error and lost payloads involved, but it is *possible* and that's all that matters. [Answer] The average orbital velocity around a body of mass m at a distance r from its center (assuming the mass of the satellite is small with respect to the other body) is given by $$v\_0 = \sqrt{\frac{mG}{r}}$$ Assuming you want to fly few meters above the surface you need to have a velocity of $1678\:\mathrm{\tfrac{m}s}$. This corresponds to $1.4\:\mathrm{MJ}$ of kinetic energy for $1\:\mathrm{kg}$ of mass. Since a trebuchet works using gravity, you will need to have that much potential energy stored into the counterweight. This gives you the constrain of having a mass $M$ placed at height H in the moon gravity $g\_\mathrm{m}$ so that $$HM = \frac{E\_K}{g\_\mathrm{m}} = 868530\:\mathrm{m\cdot kg}$$ Assuming your trebuchet has a counterweight moving $10\:\mathrm{m}$ vertically it means you need a mass of $86853\:\mathrm{kg}$ as counterweight. Using lunar rocks as ballast this requires a cube with $7\:\mathrm{m}$ side (credits at Daniel for the hint. (Math corrected.)), and its center of mass will be located at its center, $3.5\:\mathrm{m}$ above the bottom. The counterweight CoM will have then to swing from $+13.5\:\mathrm{m}$ to $+3.5\:\mathrm{m}$, which is the realm of possibility. To be sure that the orbit of your satellite will not intersect any other point of the Moon, you are limited to place your trebuchet on the top of the highest lunar mountain, which according to Wikipedia is [Mons Hadley](https://en.wikipedia.org/wiki/Mons_Hadley). From there any plausible length of the trebuchet arm will be enough to fly above the peaks, including your trebuchet (unless you want to play catch and release with your satellite). Nevertheless such a low orbit will be highly sensitive to deviation induced by minimum variation of local gravity or drag by solar wind, and thus unlikely to be stable on the long term. [Answer] [As Silvercookies said](https://worldbuilding.stackexchange.com/a/111217/9852), a (closed) Kepler orbit that starts at the surface will always intersect the surface again. However, that's really irrelevant here, because Kepler orbits are an idealisation. They give a good approximation when you're orbiting a dominantly heavy object with good spherical symmetry (making it equivalent to a point mass). This is well fulfilled for the sun, which is why the planets have very Keplerian orbits. It is also fulfilled pretty well for the gas giants. For anything else in the solar system, you don't actually get such orbits. The Earth-Moon and Pluto-Charon systems *seem* Keplerian, but that's just because they're two-body systems with no significant near other influence: this results in both bodies Kepler-orbiting their shared barycenter. But this doesn't work if there are more than two masses at work. So, as [kingledion remarked](https://worldbuilding.stackexchange.com/a/111266/9852), you can basically just use the Earth to leave a Moon-tangent orbit. But it's not at all necessary to resort to aerobraking at the atmosphere here – it's sufficient to trebuchet into an orbit that gets close enough to Earth to be a bit disturbed by it. <http://nbviewer.jupyter.org/gist/leftaroundabout/3955d27877e19be39d0f61fdafce069e> [](https://i.stack.imgur.com/Nkrge.gif) Conretely, you need to launch from the far side of the moon, with a bit of extra velocity in direction of the moon orbit. Seen from the moon, this orbit will look thus: [](https://i.stack.imgur.com/ymyT5.gif) Note that such an orbit isn't really stable – it may eventually crash. But that's the case even if you stay so close to the moon that the Earth's influence doesn't interfere, because the moon isn't completely homogeneous! So: for a stable controlled long-term orbit, you'll need thrusters either way. But for quick experimental satellites, launching from the surface is not problem at all. [Answer] No. While it's possible to throw something into orbit (but you still need something to circularize it with), a trebuchet isn't capable of doing it. You're going to need a ridiculously heavy counterweight and a ridiculously long arm--and your arm is going to snap when you try it. You need 1730 m/s to reach low orbit. That's 176 g-seconds (1g for one second.) Let's be pretty brutal and figure you launch at 10g (plus the lunar gravity.) You need to boost for 17.6 seconds to accomplish this. You moved 15km while doing this. (And reality is even worse--since you're not moving in a straight line you're actually experiencing more than 10g of acceleration.) You want to eject horizontal, without a gargantuan hole you can't start below the horizon. Thus you have 90 degrees of motion. Your trebuchet arm must be 9.5km long. Out of what do you plan to build the arm that will stand up to the strain? I'm not up to calculating what it would take to keep the arm from snapping but my gut says it's going to be huge--which means it has a huge amount of momentum. Your counterweight has to be big enough to accelerate this whole thing. What's it's support cable made out of? Note that the lower the acceleration of the cargo the worse the numbers become. Rather than a trebuchet, what you want is a linear motor. Think of a maglev train, except it just keeps accelerating. The train itself is build so it won't fly off the tracks when it's weight goes negative. It accelerates to the right speed and releases the spacecraft, which is now in an orbit with a periapsis at zero and will have to circularize when it gets up there. (Note that this scales pretty well. Limiting yourself to 5g but with a track wrapped all the way around the lunar equator you can eject anywhere from a sun-grazing orbit to a bit over solar escape.) [Answer] The two existing answers address difficulties in converting the energy imparted to the satellite by the trebuchet into an orbit. You have limited resources, but don't clarify what resource are available. You need also consider that a trebuchet stores potential energy generated by humans over a long period of time and releases it in short period of time. > > Counterweight trebuchets are powered by gravity; potential energy is stored by slowly raising an extremely heavy weight box (typically filled with stones, sand, or lead) attached by a hinged connection to the shorter end of the beam, and releasing it on command. Traction trebuchets are **human powered**; on command, men pull ropes attached to the shorter end of the trebuchet beam. The difficulties of coordinating the pull of many men together repeatedly and predictably makes counterweight trebuchets preferable for the larger machines > > > [Source](https://en.wikipedia.org/wiki/Trebuchet#Basic_design) The humans will need to be fueled by organics (*food*) & Oxygen and will require significant people hours of time to store that energy. You would likely get better results with the same volume of organics and less people hours, by converting the organics directly into combustible fuels. The only real advantage the trebuchet would provide is allowing the oxygen & carbon to remain on/in the lunar colony. Organics used on moon to store energy in the trebuchet would be converted to Carbon Dioxide in the closed lunar environment (presumably) and be available to convert back to pure Oxygen and Carbon. Organics used direct propellants (rockets) would either be used in space and lost or would need to be fired in a way that they could be recovered inside the closed system. [Answer] I’m seeing your giant trebuchets modified with mangonel or scorpions to fire the satellite away from hte moon when the long arm of the trebuchet has provided them with their initial velocity tangential to the moon’s orbit. Which ever form of torsion catapult adorns the tip of the trebuchet, they fire radially along the axis of the arm. The release point is selected to maximize the gravity boost from both the moon’s and earth’s orbits. ]

[Question] [ Earth, far future: We built multi generation ship which can get 20 000 people to another solar system in next 20 generations (600 years) For scope of this question assume that ship itself is well built and it will indeed be able to carry people and material to its destination and technology wise, the mission will be success. But what about the people? Some of the things about multi generational ships were talked in separate questions, but one I believe was not: **What cultural norms would be best to follow on multi generational ship regarding marriages and love?** Questions to be attacked: * How should we treat marriages and love, given the fact that we do not want to cripple during the flight? * Should we force anyone into having kids, even when they might not want to have any? (Again, we kinda need diversity in DNA after 20 generations) * On above: Should we ban gay people and asexual people? Personally I have an idea that best would be to create religious cult and let only those people in the ship as generation 1. Is there better idea how to tackle behavior on relatively closed area? [Answer] A few little lies never hurt anyone, right? The problem of love and marriage falls into a major problem (DNA variety) and a bunch of minor problems (not so many fish in the sea). Surprisingly, the Major problem is far easier to fix than the minor, and it actually fixes a lot of the minor problems in the process. # Gene Banks The main reason why love and marriage is such a problem on a multi-generational ship is that letting anyone procreate with whoever they want risks narrowing the gene-pool, and you can't have a big (living) Gene Pool because there's limited space on board. Well, what if the gene pool doesn't have to be alive? It would be far easier/smaller/more effective to keep a massive sperm/egg bank. Cryopreservation of sperm is cheap(er) in space — you'd need radiation shielding and some way of dealing with any close fly-by's of heat sources you have to do, but it would still be vastly cheaper and easier than on earth — and apparently frozen sperm has [no expiration date](http://health.howstuffworks.com/pregnancy-and-parenting/pregnancy/fertility/sperm-bank3.htm). All humans are sterilised at the earliest opportunity. In the case of females, all the eggs they will ever create are present before they're even born, so they can be... harvested (just to make this seem more evil than it is), and added to the bank. Then when two adults love each other very much and want a child, the computer determines the optimal pairing from the bank and bingo. ## Why Would This Work? * Genetic diversity would be even easier — you wouldn't be limited to just the best genetic match between similarly aged members of the crew, you could choose the *best possible combination of egg and sperm from a sample of the entire human race* (or close enough, I'm imagining there would be a space limitation). * No requirement to have children — One of the big issues with the "must make the right people mate" method is that it means that certain people are **forced** into having children. If the DNA of the child is independent of the parents, there is no longer this requirement. * Parental love — because the child still comes from the womb, maternal/paternal instinct would be as strong as ever. You can teach that this is perfectly normal and it wouldn't even be strange if white parents "gave birth" to a black child, that's just the way it is. I think this is preferable to test tube babies (though that would be possible), because the family unit is still an important concept, and it will be needed at the other end of the journey. ## Options For those of you worried about sterilisation from birth in case of a bank accident that destroyed the gene stocks, clearly you would keep backup storage in different sites. In case of catastrophic loss of the entire system, I would argue that a tin can floating through a vacuum has bigger problems to worry about, but there have been recent advances in reversible vasectomies, including [this novel approach](http://www.iflscience.com/health-and-medicine/sperm-blocking-implant-could-be-latest-male-contraceptive) which is literally a switch that can be turned on and off (though it takes a while to turn the tap off again after). If you're worried that this will be a temptation, let only the chief medical officer know about it, though the less secrets on a boat the better. Going the technological route again, include a failsafe in the landing mechanism - if at any point the system in control of landing loses contact with the procreation systems for an extended period of time, it could trigger the reenabling of the reproductive system if the switches are fitted with some sort of RF trigger. # The Minor Problems This ultimately boils down to "Not so many fish in the sea". 20,000 people is the size of a medium sized town. Given this small sample space, there will be a limited amount of people of a specific type of personality, so unless genetics and personality prediction comes on massively before this ship sets off, it is likely that every now and then there will be a mismatch between the amount of people attracted to a specific personality and the amount of people currently on board with that personality. This I fear is unavoidable, and dealing with heartbreak and loss is where the family unit will come in. There are of course a number of other aspects which are solved by the Gene Bank approach: * Free love — Anyone can love anyone they want, even their sibling they want to. All the social taboos that arose out of the need for genetic diversity are no longer valid. * Non-heterosexuality is fine — because noone is *required* to have children, all forms of sexuality are fine, so long as enough people are still happy to parent children. Make test tube babies (The spaceship form of Adoption) socially acceptable, and it makes that even easier. * Racism basically disappears — because you have no idea what your child is going to be like, and because families can be made up of radically different genes, it destroys the segregation that allows racism to form. You would still get sex-related crime due to jealousy, probably, but this would allow for a much more liberal society than otherwise. Through sterilisation you have made it physically impossible for anyone to break the rules, but have provided a system whereby everyone still gets to experience everything you go through having a child. Yes, you can argue that people would like to raise a child of their own genes, but that's your society talking. It's not something that is strong enough to rebel over (and I'm saying that as a parent). It's a far far easier mentality to change than arranged marriages! Ultimately, it's not even one you have to lie about. When people learn about biology and DNA, they can be told about why the process is necessary. They can be told about the Gene pool, how we all share genes and how "There's a little bit of all of us in everyone else on board". This will help engender an overall feeling of community. If I haven't considered anything, let me know and I'll see whether I can fit it in! [Answer] > > We built multi generation ship which can get 20 000 people to another solar system in next 20 generations (600 years) > > > Good news! You've got significantly1 more than a [minimum viable population](https://en.wikipedia.org/wiki/Minimum_viable_population)! What does this mean? You have enough people that genetic variety will not be a significant issue unless something kills off more than half of your population. What constraints do we still have? Obviously, the ship isn't going to get any bigger, so there's a hard limit to how big the population can get. Also, you don't want the population to drop, so you've got to replace everyone that dies. Something else to consider is complexity—the more complex the system, the more likely it will be to degenerate, especially over the course of 600 years. You shouldn't rely on computers to manage the complexity for you because there's always the chance that a hard disk will fail and lose important information you need. So what you need is something simple but effective that people can keep track of. ## The plan: The standard expectation is heterosexual monogamy—people are allowed to marry who they want to and have two children together. It is also expected that there will sometimes be non-standard situations. The most common will be couples who cannot have children, including both homosexual couples and infertile couples. Whenever that happens, a deficit of children will be noted, and couples can apply to have an extra child to fill that deficit. As such, it will be possible for a couple to have three (and rarely four) children. Multiple births (twins, triplets, etc.) can have the opposite effect—a surplus will be noted, and the next time a deficit is noted it will be automatically cancelled out by the existing surplus. The ship should be kept at 90–95% capacity to allow for surplus supplies to be collected and to handle temporary surpluses in children. This child count can also be used as a tool to encourage fidelity and family stability. In the case of divorce, the child count will be split between the two parents. If they get divorced before having children, there is no penalty. If they have one or two children, then each adult has a child count of one half or one and in a subsequent marriage to a previously-unmarried person they would only be able to have one additional child. In the case of a divorce with cause (abusive spouse, for example), the at-fault spouse could receive the full child count while the other spouse gets custody. If this occurs with two children, then the at-fault spouse incurs a child surplus. It is also possible to have an imbalance of men and women. A surplus of women is a minor problem—polygyny (one man having multiple wives) can solve this without causing any confusion about parentage of children. This would only be permitted when there is a surplus of women, and the surplus women (wow, that sounds terrible. They'd have a much more polite term) might be encouraged to join childless couples. In these cases, the families would be permitted a number of children equal to the number of adults. A surplus of men is a bigger problem. Letting a woman have two husbands makes it hard to tell who the father of a child is. Unfortunately, the natural ratio of men to women is a little unbalanced in favor of additional men ([somewhere around 1.05:1](https://en.wikipedia.org/wiki/Human_sex_ratio)). This means that minor measures should be taken to counter this. For example, I'd suggest that dangerous tasks should be assigned to men. With these standards, it should be pretty easy for everyone to keep track of their genealogy to at least their great-grandparents. This makes it easy to make marriage to close-relations taboo; marriage between siblings or cousins will be forbidden, and marriage between second cousins would be discouraged (though not forbidden). 1. A minimum viable population is somewhere around four thousand individuals. That is level at which a wild population can survive *without human intervention*. In other words, without planning. As long as you're above that level, you're good to go. If you fall below that level, you'll need to start taking measures to encourage genetic diversity. With a comprehension breeding program, you could survive falling down to a couple hundred people. [Answer] Trying to engineer the culture of a generation ship (or a space colony or even an Earthy city or university campus) could backfire wildly if it is too far from the "norms" of the founding society. An ship crewed by Indians or Chinese will not work too well if they are expected to follow *Western* cultural norms, nor should you expect a ship with a largely American contingent to be receptive to living under a Confucian social structure in a Chinese ship. So the social and cultural norms of the launching society will most likely be in effect on board. Since one of the issues to address is genetic variability, some current social norms will carry over well (most Western cultures discourage marriage between first cousins, for example), and Americans, with their notions of physical and social mobility, will probably keep the DNA pool well stirred without much further prompting. Establishing a religious or quasi religious cult to ensure the goals of the ships launch crew are maintained over time is more problematic. It is possible to create extremely static cultures (Ancient Egyptian culture lasted for 3000 years with change happening at glacial speed), but the people raised in these cultures will probably lack initiative and flexibility to deal with shipboard emergencies or the changing conditions once they reach the target star. Indeed it seems almost impossible to avoid social, cultural or even linguistic drift, especially over extended periods of time. Shakespearian English was spoken only 500 years ago, yet is virtually incomprehensible to the modern English speaker, to give an example, and you can also look at the social and political structures of late Tudor England, or the sorts of sports and games popular then compared to now to see just how much change is really possible in that time. The best way to ensure transmission of ideas over the long term might be to "encode" them into legends and children's stories. People learn things on their mother's knee which can stay with them for life, and be transmitted to the next generation. Sometimes the meaning is lost over the years ("Ring around the Rosy" is a song about the Black Death, for example), and sometimes the culture refuses to let go of the past (when I was deployed in former Yugoslavia, the Serbians told us stories of the Battle of Kosovo Polje in such vivid detail that it could have taken place in the 1990's. It happened in *1389*!), so this is a plan with a mixed chance of success. The only real way to ensure the passage of the founder's intent *is to have the founders themselves arrive*; either the ship is a giant freezer carrying frozen colonists, or the colonists are carried in vitro and "birthed" on arrival to be taught the Founder's intentions, of the ship moves at close to the speed of light, so very little time passes on board compared to the outside frame of reference. [Answer] I don't think there is a problem. Through most of mankind's history we lived in much smaller communities. The typical hunter/gatherer tribe is 150 people, and they may meet with up to 10 or 20 other tribes to exchange marriage partners giving a total community size of no more than 3000. In fact until the 19 century 20000 people would be a large city. So let people marry as they please. If you're still worried about genetic variety you could have the sperm/ova bank mentioned earlier, and encourage each couple to have one child from there. That should give plenty of genetic variety without getting heavy handed about it. [Answer] I think the best solution is probably to detach "relationships", "procreation", "child-bearing", and "child-rearing" as much as possible. [Lois McMaster Bujold's *Vorkosigan* novels](https://en.wikipedia.org/wiki/Vorkosigan_Saga) have the technology of artificial wombs, which allows the work of carrying children to term to be delegated to machines. This frees women from an obligation while improving safety as well. It would be possible to mandate that everyone donate sperm and eggs — genetic diversity is a valuable communal resource — while not actually forcing anyone to do the particular work of child-rearing. There's no need to impose restrictions on anyone's sexuality then. It's also important to think of how the colonists would be aware both of the *mission*, and of the environment of the colony ship. Everyone on board would be an extreme environmentalist by Earth standards: every resource is finite and limited, nothing can be thrown away, any damage to the spaceship is a threat to all aboard, and the crew *know* that it is their responsibility to look after it for future generations. In that kind of environment, some form of commune structure would probably thrive. Childrearing would be shared. "It takes a spaceship to raise a child". Relationships among the adults would be entirely flexible so long as they weren't harmful to the social order. So Mormon-style polygamy would not be allowed but Heinlein-style probably would. [Answer] Just enforce a maternal equivalent of the draft to your female passengers. At the onset of their physical maturity, all male passengers will contribute to a sperm bank; and through artificial insemination, all newly mature female passengers will make a withdrawal. A computer will play match maker so that genetic diversity can be maximized. After that first child is born, their mother is free to have additional children if they choose, conceiving them either artificially or naturally. Bisexual and/or mono-sexual dating, co-habitation and marriage would all continue at the participants' discretion; and all eligible females would be single-mothers, so there would be no social stigma involved. To balance the tables, all male passengers would be required to spend nine months doing community service in the human-waste processing plant, and/or outside the ship's hull. Also, all jobs involving exposure to radiation would be reserved to male passengers who have already contributed to the bank. [Answer] Because it's a relatively small group of people, you'll want to have some system to rule out accidental incest. Iceland is currently doing that now, and they have over 300,000 people. You may want to get rid of love as an aspect in marriage and family planning, going back to Victorian-style cultures. Remember, that is a relatively new development... Romeo & Juliet was originally written as a satire of the terrible things that happen if you follow your heart rather than marrying who your family wants you to marry (Spoiler: you're going to die) and only recently (last 80 years) have we started reading it as "look at this tale of love breaking down walls" which was not the original point. If this is reinforced strictly on the first several generations, this system WILL break down over the 600 year period. You'll want to build whatever anti-incest system SEPARATE from the rigid family/marriage structure so that will remain independent and required, while the social norms change over time. [Answer] This issue has already been explored in surprising detail in Robert A. Heinlein's *The Moon Is A Harsh Mistress* (which is excellent in a lot of dimensions). In this case, the "ship" is actually the moon, but it's probably worth reading the story so that you can see what has already been explored in this idea space. It is also touched upon in Neal Stephenson's *Seveneves* (which I am still reading...also great so far). Stephenson clearly did his homework, so I think it's worth reading for the science (whereas, Heinlein focuses on the sociological aspects). [Answer] If you only make small changes to current society, people might want to fall back to different patterns that they remember or read about somewhere. Establishing a social system that stays stable for 20 generations in a row is rare. You can get rid of that if you simply get rid of the males, which mandates a drastically different system. Use sperm banks, pre-filtered for X chromosome only. Establish pregnancy at specific ages like we have school at specific ages in today's societies. Some current societies have one or more years mandatory military service at around 20, or mandate working in a factory for several months before university. There's some way to bend the rules in all these cases so the same should apply to pregnancies — just make it so there's an expectation to get pregnant at a certain age, and some economic drawbacks if you refuse. If you only have females they only need to have one child on average instead of 2 (plus/minus early deaths, twins, women who really want a second pregnancy, women who are infertile, women who want to opt out, etc), which also might make things easier. This setup allows the population to make lots of changes on their own over the generations, but self preservation mandates that certain constraints are upheld, such as population control. But honestly, for a 600 year journey **I'd use several smaller ships** with different social systems on each, and hope no more than half of them die from technical failures. Only 100 fertile women and a well stocked sperm bank are enough to make a viable population, so even a single ship surviving will be good enough. [Answer] Love and marriage would continue to function based on your pre-ship cultural norms, but the children you raise might not be yours. **Psychological Health** Psychological health is *really* important when you’re in a metal tub flying through space. It’s so important that deep psychological studies are being done merely on the approximately 500 day round trip to Mars. A generation ship is an entirely different level of magnitude, which ups the stakes quite a bit. You really don’t want the first generation to mutiny or dissolve fifty years in and you definitely don’t want a random late generation to do it. Love is a very fundamental human emotion and one on which quite a bit of chaos can be sewn when not respected. As a result, you really do not want to interfere with a person’s ability to love or marry whomever they choose. The core problem that raises this question is genetic diversity. In such a small population over a long period of time you want to truly maximize it, and it’s clear that traditional means of free marriage are not constructed to support that. However, there is a solution: artificial insemination or in vitro fertilization. **Carefully Planned Children** Birth control would be heavily encouraged if not mandatory for couples. A genetic database would allow couples to match based on the desired genetic diversity, but this would not be required. Births and pregnancies would be heavily planned with both limits and quotas (with special exemptions as necessary). If you're a couple that is properly genetically diverse, you may be allowed the privilege of having children naturally. For everyone else, the woman would be required to have some percentage (if not one hundred percent) of her children with the genetic material of someone else on board. The man would, likewise, be required to contribute his elsewhere on the ship. In spite of this, the couple would be expected to raise the resulting children as their own. **Accidental Pregnancies** These would happen, but hopefully infrequently enough that they could be handled on a case by case basis with the child coming to term. It’s possible that these children would be excluded from the collective pool of genetic material in the future. [Answer] I think a 'religious cult' would be a dangerous way to go. Not the least of which you would have to start 'indoctrinating' the passengers before you even put them on the ship. Religions change and mutate, and even more they fracture and split. When you put in place a religion to 'keep people happy and focused on a goal' you have built in a flaw that could jeopardize the whole mission. While religion beliefs have a purpose, creating the mission to be the purpose will eventually cause distension on the best way to fulfill that purpose. And once you put faith behind it, then decisions will become matters of doctrine and purity of purpose, not what might be the safest or best way to accomplish the goals. Or even if the original goals turn out to be impossible, what are reasonable alternatives? Using religion in the way you are suggesting will quite likely cripple scientific decisions that make sense at the time. With around 20,000 people most people would be able to do what they want, within reason. I think there would be some gene tests so that there are people that 'shouldn't' be paired (like you immediate family) only it would be a little wider spread. Why prevent homosexual relationships? They have been around forever and will pop up even if there aren't any in the beginning. If they want kids they can have kids, if not don't. Since there will be population limits as to how many can live on the ship at any one time, who can have children and when will need to be controlled. Someone of course would have to monitor this, to make sure that an even distribution of genes continues and mixes. But if a homosexual woman wants children the genes could come from a man not interested in raising any. The point is, while someone needs to keep good records (and using paternal DNA for each child) there should be enough mixing with 20,000 people that there shouldn't need to be much direction from above. Having kids might become more of an artificial insemination process, you can love who ever you like, but your children are from the community and for the community so it's your responsibility to have the best one for everyone (meaning it might not even have your dna) [Answer] Your population size seems acceptable. I've read somewhere (can't find the reference now though) that the genetic variability between relatives that are removed further than first cousins is not more problematic than in the general population. (Eurocentric, but I suppose that the specific population could be taken into account, since it is said (again, no reference) that there may be more genetic variation in a single African village than across the whole of Europe.) Cousin marriages have been quite common in history in Europe and the Middle East, and still seem to be in certain parts of the world. Since your ship's population is the size of a medium sized town, I am for interest's sake suggesting a different approach to most of the other posters: instead of inventing all sorts of sci-fi interventions, why not go the opposite direction and organise a conservative society similar to an era when a town of that size would be the norm? That would be the starting parameters for the environment (meaning the darwinistic term), but it probably would adapt (through natural selection) over the course of its journey. (When arriving at the destination, the environment would of course change again, where a new course of adaption would be needed.) One problem that you mention is the whole love/offspring thing. A slight adaption to current western culture, just moving a little bit back in history, might be to have parents arrange marriages. While this has a negative connotation in modern western culture, it does not need to have, if parents have the well being of both their offspring as well as their society at heart. It is not too long ago that this was acceptable even in some western cultures, and history has shown that the modern invention of marrying due to some not-quite-mature adult's youthful feeling of infatuation does not necessarily result in better choices, more stable families and thus more a stable society. (A computer *could* provide input as to the expected genetic desirability of the offspring, but I think this is not really necessary.) In any case, a society with such "conservative" norms may help in keeping the gene pool healthy (if the norm is to have children, and people that may otherwise be inept at obtaining a mate or too selfish to find one, are "nudged" into the right direction.) The other problem would be to keep the population size as big as allowed by resources (to ensure maximum variability) but no bigger. This would probably by regulated by the already well-known "procreation license" system. I see that this will create, over time, an "offspring economy", where the permission to procreate may be linked to money (or some other value), either negative or positive (because it also costs resources to rear that child). Then again, it seems that one of the ship society's main purposes would be provide enough resources so that each child may reach adulthood, so the cost of childrearing may be taken away from the individual and become society's problem in a very socialist way. It needs to be pointed out that from a genetic PoV (and maybe others) one child would not be exactly equivalent in value to another: if variability is of high importance, a person's (genetic) value decreases with each sibling he/she gets. I would argue that it would be most desirable to maintain the largest amount of genetic variability on ship until it reaches it's destination, where the most desirable traits for that environment are then to be allowed to be selected by natural selection. The on-ship population should not be allowed to homogenise. If people are from different races, it may be a good idea to keep it that way. There should be high-IQ and low-IQ people. Technical people, artists, dreamers, warriors, acrobats, thinkers, talkers, listeners ... The mechanics are of course all interesting, but what's even more interesting in my mind is the human factor behind it. You could have the same mechanics, and have a very authoritarian or a very liberal society, a society where off-norm is very negatively "frowned upon" or one where the norm is encouraged in a very loving way.... and all might have vastly different outcomes. Since social aspects are as much environment as the tech is. It's of course a thought experiment - as worldbuilding should be - but I guess if one writes a new scifi novel, going contrary to the beaten path might bring some interesting results. [Answer] 20 000 people is easily enough genetic diversity. Just make it so that people are not allowed to marry cousins, which I believe is already the case. So you don't have to do anything special to take care of inbreeding. The main issue is keeping up the size of the population, you could introduce laws where people are not allowed to have more than 3 children, and if there aren't enough children then introduce incentives, like better food or living quarters for people who have children [Answer] Firstly, you have to choose your 20,000 people. People that are already married are unlikely to wish to join the ship unless their partners are also allowed to join. People with world views that don’t much how the ship is going to operate are also unlikely to join. This is very important, that if you wish to have a good mix of genes you need people from different countries to join. **Therefore is it possible to have a single system of “partner choose”**? I assuming you are choosing the 20,000 people base on the skills they have, therefore they will be mostly of “post education” age maybe a lot older. **But…** You need to have a mix of ages joining the ship; otherwise they will all become old within a few years of each other. There could also be issue with them all having children within a few years of each other. So I expect that you will need some people that are over the child baring age, or to set out with a lot less people then you have space for. I also expect you need children to be joining the ship with their parents, so that you don’t have a gap of 18 years before the first set of new “trainees” start work. You don’t want people in the same job beading with each other too much, otherwise you will get lots of autism with “thinkers” breading with each other. Therefore the method of choosing partners must not just be based on who someone works with. Given partners will want to be of about the same age, and you will have an age profile from 0 to about 80 once you have been going for a generation. Assuming 3 years between partner ages, there are only 20,000÷80 × 3 ÷ 2 =372 people that each person can choose between as their partners. So it is very possible to have a system when someone meats with every possible partner. **Everyone would have gone to the same school as their partner!** As it is already clear that peoples parents will be of different races and hence have different “world view”, the next generation will have a mix of world view from the parents. This will reduce the choose of partners evens more, as someone is most likely to choose a partner with their own worldview. [Answer] As others have noted, the problem is more likely to be too many children than not enough. I suspect a generation ship would have to put limits on how many children couples could have rather than trying to force them to have more children. I suppose this could be a problem if the initial crew was made up entirely of infertile people, hermits, and homosexuals. Or more realistically, if there were enough such people in any given generation along the way that population fell. But unless something about the nature of life on the ship makes people not want to have children or incapable of having children, there would likely be enough people who want to have ten children to make up for those who have none. Trying to create unusual cultural norms for such a ship faces one tough problem: Presumably once the ship has been on its way for a couple of months, it has traveled beyond the reach of anyone back on Earth. If you had ships that could flit back and forth across the light years in a few hours or days, you wouldn't need a generation ship, you'd just send people in these FTL ships. So you can make up all the rules you like for how these people are supposed to behave, but once they're beyond your reach, they can freely chuck the rules and do whatever they want, and there's absolutely nothing you can do about it. Even if you picked the initial crew to be people who agree to this unusual society that you think is a good idea, the next generation is going to rebel against it, or at least question it. That's what teenagers do. The idea that you are going to raise children in a carefully controlled environment so that they completely, slavishly follow everything their parents teach them is a pipe dream. People have been trying to do that for thousands of years, and it's never worked. (Every now and then I hear people who have just had their first child talk about how they are going to raise this child to follow in their footsteps and uphold all their best ideals — whether that means being tolerant and open-minded or working tirelessly to stamp out all the inferior races or whatever — and I can only smile and say, yeah, good luck to you. That's not how it works.) Maybe, possibly, you could indoctrinate the original crew with brainwashing techniques and drugs and high-tech mind control, and then they do the same to their children, generation after generation. But would a crew of such doped-up robots really be the kind of elite you need to successfully complete such a dangerous and complex mission? And even if it worked, it would take only one generation, anywhere in the 600 year voyage, to say, No, we're not going to do this to our children, and the whole plan falls apart. (There might be a science fiction story there, about a few who decide not to brainwash their children, and now there are two factions on the ship, the brainwashed and the not-brainwashed, who struggle for control.) If your ship was really big enough for 20,000 people, I don't think there'd be a lot of trouble with maintaining genetic diversity and allowing people to choose mates in the traditional way. If the crew was much smaller, if it was only a few hundred, I can see there being an issue that if, say, Al and Betty are the only people on board with a certain gene, that if they marry each other you risk losing that gene, and so they must be forced to marry other people. The smaller the crew the more you'd have to work to insure initial genetic diversity. You don't want everyone on board to be, say, white Anglo-Saxons descended from people who lived in or near London. You want to make sure you have some whites, some blacks, some Hispanics, some Asians, some tall people, some short people, some artistic people, some detail-oriented people, some big-picture people, etc. A society advanced enough to launch such a ship is probably advanced enough to be able to do genetic tests to be sure that there is sufficient genetic diversity. If the "first draft" crew, perhaps selected for specific job skills, is missing some genes, that they could say, Hey, we need some people with gene A17G4, which controls predisposition to growing bananas, or whatever. [Answer] 20000 people is a huge population on a generation ship. With careful breeding 200 people have enough genetic diversity to support 80 generations (~2000 years) without running into problems. With 20000 people, you'll have no problems, so I wouldn't worry about it. As I Stanley said, you could also include more genetic samples in the form of sperm easily enough. Not eggs though, as I believe those have a frozen shelf life of 20 years with current technology. Your biggest problem is space and resources. While population will fluctuate, the ship won't be getting any bigger, as there aren't really any resources to add on with in interstellar space. You'd probably want a 2 child limit, with additional child bearing privileges given out through a lottery or something to make up for accidental losses over time and to make up for people that can't/wont have children. A population spike would be a bad thing unless you're anticipating losses in the near future. I wouldn't bother with a cult, as that could lead to other problems. You could get the result you want by just drilling the rules into everyone, and starting young with new generations, so that when they are of age the idea of only being allowed 2 kids won't be questioned. Another benefit of the birth lottery is so that people have hope. That way it's not the leaders of the ship telling you that you can't have that baby, its just luck not going your way this time. Maybe next time though! Another thought is that there will be people that just don't want kids. These people might not make the best parents if they are forced, so allow them to give/sell their privilege away to someone that really wants it. [Answer] I adore these thoughts and images, thank you all. To begin,we will need the first set of parents to be the healthiest, and the most straight, and all 'good scouts' type of people you can get. This is to give the next two generations the very best chance of being healthy. Then, when these first parents have kids, the recessive genes, and just chance, will start showing up, and you will start to see certain conditions, and every different type of human you can possibly get. To prepare for this, you also need some old people. Not just for their experience, but when they get sick, and die, the doctors on the ship will be able learn, and observe, and experience, what to do with illness, and what to do when a patient dies. Imagine if you filled the ship with 100 'perfect' couples.... 40 years later you will get a sick child, and the doctors won't have a clue of what to do. Each ship will need enough people, ages 45-70, getting on board, so there will be a good flow of sicknesses and death. (And maybe they can teach the youngsters on board some other ideas, along the way.) --- And as for quantity? I think the optimum number for a ship would be 3000-9000 people, with space to grow to 5000-12000 people. Instill a fear of sibling and first cousin marriage, and then after that just let people choose their own spouses. ( And there was a great idea earlier, not just one ship, but a dozen ships.) And the idea of needing to decide what to do about consanguinity? Or people choosing not to breed? Or homosexuality? Forget about it, once they launch, each ship is on it's own, and should be able to decide how they will handle with social differences. ]

[Question] [ There are a lot of great questions about [What would happen if the internet failed semi-permanently](https://worldbuilding.stackexchange.com/questions/20578/20-years-into-the-future-what-would-happen-if-the-internet-failed-semi-permane) and [What would happen if electricity stopped working](https://worldbuilding.stackexchange.com/questions/33826/what-would-happen-if-electricity-stopped-working). As we all know, Google has a great impact on the internet. I'm not only talking about the search engine, Google offers a lot of other services and a lot of computers already depend on Google being alive to work properly, to name one of them: Google's nameservers available under the IP addresses `8.8.8.8` and `8.8.4.4`. There are probably even more services, which are used by servers all around the world. So the question is: If Google suddenly disappeared, every server owned by Google shuts down, how big would the impact be on the internet? Would the internet collapse completely as there is just too much which is dependent on Google's services? [Answer] The impact on the *Internet* would likely be **minimal.** Now, don't get me wrong. There would be **widespread disruption of service to a lot of people who use Google's services.** But the Internet is designed in such a way that the existence of any one node or any one link isn't critical to the network itself. In the modern Internet (as opposed to the original DARPA design) there certainly *are* nodes that are central to the network, but in terms of the network, Google is more of a leaf node than a central node as they *do not provide physical connectivity* to any significant number of Internet users. They are (a large set of) end-points, not transit nodes. [Google Fiber](https://en.wikipedia.org/wiki/Google_Fiber) has on the order of a few hundred thousand users in a small handful of areas; that service disappearing would be an annoyance to those few hundred thousand households who would consequently lose access to the Internet, but would be insignificant to the Internet as a whole. The first thing that lots of people would notice is probably that **anyone who uses Google's DNS infrastructure would find themselves unable to resolve any host names.** That's easy to fix: just change back to whatever resolving DNS servers your ISP provides. Takes the tech-savvy person maybe a minute or two once they realize what's happening, but their first reaction would probably be to write it off as a connectivity glitch, not Google disappearing. For the less tech-savvy people, the ISP support departments might be overwhelmed with calls about why everything just stopped working, but it isn't a difficult fix. Once the ISP's support department realizes that Google's DNS servers are having problems (even if they don't know yet what those problems are), they can have their technicians set up a web page, accessible by IP address, explaining what's going on and how to fix it, and place a recorded message to the effect of "if Internet stopped working for you and restarting your computer does not help, then try entering the address [203.0.113.1](https://www.rfc-editor.org/rfc/rfc5737) into your web browser and follow the instructions there, then call again if doing so does not resolve your problems" early in the call loop, well before the call reaches a human being. (That won't be useful information to everyone, even everyone who has that specific problem, but it will help some, cutting down on the flood of support calls.) Second, **anyone who uses Google's services (search engine, e-mail, etc.) would find themselves unable to access those services.** The search engine is probably the easiest to resolve; just use [another one](https://en.wikipedia.org/wiki/List_of_search_engines). (That Wikipedia article took me about 30 seconds to find, and no, I didn't use Google -- or any other search engine, for that matter -- to find it; just Wikipedia's own search feature.) With how many people store things exclusively in the cloud on other peoples' computers, there would be widespread grumbling in large parts of the world about lost data. Such lost data, if no backups exist, may lead to problems or even bankruptcy for some companies, but [that's a problem of having no backups](https://superuser.com/a/374561/53590), not of Google disappearing. **But neither of those are critical to *the network "Internet" itself*.** Your bank's web site will almost certainly keep working just fine. Your local newspaper might be relying on Google infrastructure for their web site, but large national newspapers should be able to quickly get back online if they don't stay online. Content (except that stored on Google's servers) won't suddenly disappear, but it might take some fiddling to establish alternative ways of accessing it (see point on Google's DNS servers above). Stack Exchange would very likely remain online but with reduced functionality as each page gets some Javascript from Google's servers; people should still be able to ask [whether unicorns will survive racing through a line of infantry](https://worldbuilding.stackexchange.com/q/4764/29), and read-only access to the important content will work perfectly (I know this because I run NoScript and sometimes forget to turn on Javascript from Google's servers when visiting Stack Exchange...). [Answer] Yes, Google is big and provides a lot of services. But it's not like they're the only ones out there providing these services. If Google suddenly and mysteriously evaporated tomorrow, millions of people would be inconvienced for weeks. Then people would switch to other providers offering comparable services. I don't know of any service that is offerred ONLY by Google, but if there is something, and people care, someone would come along to offer a comparable service. Bing and other search engines would take up the slack on search engine business. There are hosts of email providers and DNS providers, losing Google would be a drop in the bucket. I don't know an existing alternative to the Google App Store, but if there isn't one, somebody would build one in a hurry. Etc. I'd guess that within 6 months or so there'd be little noticable remaining effect. People who had valuable data on Google servers that was lost would be harest hit. They might take considerable time to recover. I suppose some businesses that had critical data stored on Google and no backups anywhere else could be ruined. In real life it's hard to imagine Google simply disappearing over night. If they started losing money it would likely be months or years before they actually went bankrupt. Or whatever scenario you're supposing, people would likely have time to adapt, so when they finally did close up shop, it would be a minor disruption for the few who had failed to prepare. Their servers and software and buildings wouldn't just evaporate: other companies would buy them up. It's like when US Airways went bankrupt, their planes and pilots and so on didn't all disappear, they were absorbed by other airlines. People who had tickets were inconvenienced, but that's about as far as it went. It's not like it led to an end to all air travel. Big companies go out of business all the time. It's tough on the employees and investors, but the rest of the world goes on with little notice. [Answer] If Google were to disappear then the other search engines would all have an opportunity to become the new Google, it's likely that eventually one of them would win, be it Bing, Yahoo, or Duckduckgo. It's very likely that the winner would probably be more nefarious and less fair about their search engine results as well, because Google do tend to be quite unbiased and equal opportunity. As for the ramifications of all of Google's servers disappearing, I'm sure a fair few people would be very upset about losing their sites and their online documents (I know my company would lose a lot), but it would be quickly replaced by the next best thing. In conclusion: Google going down would mess up the internet for a few days for the average person, whereas the issues could be potentially lethal for a lot of companies that rely heavily on search engines. [Answer] ## Essentially nothing. In fact, Google has **[already disappeared](https://en.wikipedia.org/wiki/Websites_blocked_in_mainland_China)** for almost 20% of the world's population. All of Google's (including Android) services are completely blocked in China, along with Facebook and a number of other highly popular Western web services. While technologically competent tourists are able to use SSH and VPNs to bypass such blocks while there, overcoming these blocks, a fluorishing local internet ecosystem has sprung up to cater for the [niche](https://en.wikipedia.org/wiki/Ecological_niche) of services provided by Google and Facebook. These, in addition to the competitors of Google in the Western world, can also take its place easily. Such websites include [Baidu](https://en.wikipedia.org/wiki/Baidu) (China's number one search engine), [WeChat/Weixin](https://en.wikipedia.org/wiki/WeChat) (China's Facebook equivalent) can all take over the parts of Google that are already in use. While the transition may take a few days to complete, it is unlikely that any significant lasting effects will occur as users transition to alternative services. In fact, it is possible that overseas equivalents will evolve and take over Google's niche faster than their Western competitors, due to the fact that the necessary infrastructure is already fully in place and running. For example, Youtube receives web traffic that is orders of magnitude higher than any of its Western competitors, and Google has an immense amount of network infrastructure in place to support that traffic. It would probably take weeks to months for competitors such as Vimeo (which has [less than 3%](http://blog.capterra.com/youtube-vs-vimeo/) of Google's userbase) to expand their infrastructure to handle the hordes of cat video watchers, while overseas competitors such as [Youku from China](https://en.wikipedia.org/wiki/Youku) (~50% of Google's userbase) or [NicoNico](https://en.wikipedia.org/wiki/Niconico) (Japan) will likely have infrastructure better equipped to handle the massive influx of users. [Answer] Google is HUGE, and provides many services, but the Internet was designed during the Cold War to survive a nuclear Armageddon. It would still be there, but with a significant reduction in cat videos et al. via YouTube. (Along with all other services that Google provides.) Secondarily and tertiary effects would have major effects in the business sector, so there would be significant economic disruption. Local governments and academic institutions which use Google as an email and storage service would suffer, many documents would be lost and communication would effectively be disabled until they switched too other services or provided it themselves like in the old days. There would be mass emotional distress, and fear. Android phones wouldn't be much better than dumb phones, with most services disabled and no more updates. To some, it might seem like the world ended. Then everyone would buy iPhones and use Bing, and be okay. Of course, if you bring Google Fiber into the picture, that's a different matter. It **is** the Internet for some. And that depends on how closely integrated/dependent Google's services is with its hardware. And how proprietary its hardware is. If it's hardware is fully independent and standardized, it will simply be absorbed into the Internet. All other outcomes depend on how many trained personell remain who are specialized in Google's tech, and the depth of integration services (including Google's private services only they know about) have with hardware. The less independent, the more Google Fiber comes crashing down. So the Internet via Google Fiber would end in that case in areas only serviced by Google Fiber. (None of those exist, yet.) And yet, another provider would just run a line out there. Hopefully the cellular networks aren't plugged solely into Google Fiber in that case! [Answer] You have to realize that Google as a cloud service provider is relatively modest. Modest in the sense they are still top 5, but that in this particular area Amazon is dominating real hard with about a third of the world's market share. [](https://i.stack.imgur.com/92rP6.jpg) Amazon has clients such as NASA, Netflix or the freaking CIA. Losing Amazon would have a much more substantial impact that losing Google. The biggest impact the disappearance of Google would probably be purely economical. On the stock market first, Alphabet's market cap is (currently) 492.02 billion USD, which is about the GDP of Sweden, i.e. loads of money to have disappeared suddenly. Alphabet (which is Google's parent company in case you didn't know) also owns venture capital funds invested in various company. The disappearance of that would hit companies funded by Alphabet pretty hard. Beyond that, any service is replaceable. Consumers would likely only lose data, which is kind of a bummer but not the end of the world (and a valuable life lesson about the volatility of The Cloud™ and how local saves are important). Companies relying on Google/Alphabet services would lose vasts amount of money and those unable to find an alternative quickly would fold. The Internet itself would shrug it off and find another video streaming service where to downvote Call of Duty trailers. [Answer] For the internet as an infrastructure nothing would change at all. For the community called Internet(s) only minor changes would happen. * Youngsters wouldn't understand UTFG prompt, something like "dial" word for the phones nowadays; * Youtubers would lose their "jobs" and start the real ones; * Android phones would become scrap or Canonical/Mozzilla would ressurect their Ubuntu/Firefox over Android projects; * Zounds of Ultimate compilations of anything would disappear, thus procrastination would become harder, for a while; * People will start using dedicated tools instead of one G-stuff; * many StackExchange users would lose their reps and badges because htey would need to create brand new accounts; * People relying on google only will learn the words "Diversification (of risks)" the hard, painfull and expensive way. And for the world and reality? Some people would commit suicide, some would die of laugh. The others would get used to the change. [Answer] There would be chaos for a while at least. It's actually part of an experiment that I've been working on to see how it affects me personally. A number of very large and critical pieces of infrastructure rely on google's datacentres such as the UK Tax service [HMRC](http://www.theregister.co.uk/2015/06/05/hmrc_is_going_google/) and there are probably parallels in most countries, so basic things won't happen. In the USA they have [Google apps for Government](https://www.google.com/work/apps/government/). Killing that stuff off is going to have a huge effect on people who don't even own a computer or smartphone... Even as a normal user, one can easily choose not to use google search & mail but their hold on the internet as we use it daily is deeply insidious. Take googleapis, googlefonts - those are not sites we normally visit directly, but block them at your firewall and you'll soon know about it. a number of third-party sites will just point-blank refuse to work properly. Then you get into the included content (google maps, embedded youtube videos which carry things like user training.) If you want to experiment then you can obtain a list of google IP ranges and just block them at the firewall. I'll give you 10 minutes of trying to get a normal day's surfing done before you have to undo them. [Answer] Interestingly, there was a video posted by Tom Scott recently about what might happen if someone in Google disabled passwords on all accounts one day, and what would happen to the rest of the internet if Google dropped off the net due to something like that. Spoiler, in a few hours the whole internet falls over. But then not long after everyone goes back to business as usual. <https://www.youtube.com/watch?v=y4GB_NDU43Q&feature=youtu.be> [Answer] As other answers have said, Google going away will ahve almost no impact on the Internet. It will have a very large impact on the Internet services people commonly use. Other answers have already covered the big pieces, but one aspect that's been missed in a lot of the answers is the less-visible infrastructure services Google supplies. Most will be only a temporary disruption, but many mean a large and permanent loss of data. ### [Google Sign-In](https://developers.google.com/identity/sign-in/web/) You can log into many sites using your Google account. Suddenly, you can't. Recovery of that account will be almost impossible because your [[email protected]](/cdn-cgi/l/email-protection) is also gone. This also effects many Android and iOS apps and many devices. ### [Hosted Javascript Libraries](https://developers.google.com/speed/libraries/) Google hosts a lot of popular Javascript libraries like jQuery and AngularJS which web sites directly link to. When Google disappears, all those web sites will stop working or work at greatly reduced functionality. Fortunately, this is easy enough to fix by replacing the link with another library host, or your own local copy. A few days of web spread chaos on the web while this gets fixed, but it's a trivial fix. ### Maps Many sites and applications rely on Google Maps. For some it's non-critical functionality ("directions to my restaurant"). For others it's critical. There are plenty of other map services out there, but with different APIs. Changing the code to use them is fairly easy, but not trivial. ### YouTube disappears On the one hand it is a temporary disruption as there are plenty of other video services out there. More importantly is the loss of all the videos only on YouTube. The loss of artistic and cultural content will be very large. ### [Chrome Browser](https://en.wikipedia.org/wiki/Google_Chrome) Google's browser has about half the market share on all platforms, including smartphones. With Google gone, it will no longer be updated making it vulnerable to security problems in the short term. While large portions of the browser are Open Source, much of it is not. A significant effort would have to be made to reconstruct the original code, and rebuild a development team. However, there's a question of whether that would be legal. Fortunately, there are other browsers to step in and take Chrome's place. ### Google Contacts, Drive, Docs, and Keep There are other services which provide a similar product, but like with YouTube, all your documents in Contacts, Drive, Docs, and Keep are now gone. If you didn't have them locally mirrored, they're lost forever. Everything from slide shows to budgets are gone. ### Android Many people have stated that Android phones will become scrap. I don't believe this is true. All the basic functionality will still work: voice calls and text messages. All apps which have locally cached content should still work: contacts, calendar, even maps if you turn on local caching. Non-Google apps will continue to work fine... assuming they don't rely on Google Sign-In or Google APIs. Alternative Android stores already exist. Android users and app providers can switch to using them. Critical apps like Maps, Contacts, and Calendar will have to be updated or replaced to use working APIs. Android itself, like Chrome, is *mostly* Open Source. But there's critical pieces which are not. However, there are already Open Source versions of Android ready to go, such as [CyanogenMod](https://en.wikipedia.org/wiki/CyanogenMod). ### Google Voice Anyone using Google Voice probably just lost their ability to make and receive calls and texts, since that is all routed through Google. They also lost all their text and voice mail archives probably forever. Fortunately, [they should be able to transfer their number to a new provider](https://support.google.com/voice/answer/1316844?hl=en). It might take some time if Google truly disappeared to get the number unlocked. [Answer] Not much to add but Google ads bring a lot of revenue to small businesses. people study how to make their site appear higher in the search results of google on certain topics. There are companies that have staff just doing that. The process is called Search Engine Optimization (**SEO**) and although the title seems generic, many of these "practices" are concentric to how google gives your page to a user. Other search engines may use the information provided by SEO in a very different way. It may take weeks to train staff to rethink their optimizations. There are still many places today that don't have access to internet. many people who do, use cellphones likely for BBM/whatsapp as their primarily internet usage. **Interesting Fact** [This](http://beta2.statssa.gov.za/publications/P0318/P03182015.pdf) document on pages 56 & 57 show that in South Africa in 2015 only 10% of people use internet at home or even have access to it there and another ~50% or so have access by other locations (work /school/ university) So I say some places will be hit harder than others but a sudden disappearance of google will only cause a temporary hurdle to many people/industries. (Although I also think some people would give up using the internet XD) ]

[Question] [ This magical library is old as the history of magic itself, storing scrolls and tomes of all† spells ever devised by powerful wizards and apprentice mages alike. The scrolls are ready to be activated at once, and may be used as a trap. They cannot, however, be activated by the library itself at a whim. **However, this ancient library has no external sensor.** It is able to detect presence within its rooms, but has no knowledge beyond if the presence is magical or not (to differentiate between animal and human, mage or just commoner with no magic). **The shelves and all parts of the library are its body, but cannot be moved.** It knows and feels 'pain' if any part is destroyed. Scrolls and tomes are not included in its body, though. This library is at a secret location in a desert. Anyone can come in to learn spells within, and many an adventurer has done so, including a few commoners who accidentally stumbled upon it while wandering in the desert. **Anyone will have no memory of the library once they leave,** but the knowledge and items gained therein will remain with them. Because of this, the place has become a vague legend. A band of raiders now is trying to raid the library, in hope of gaining the rare and forbidden spells contained within it. These raiders consist of thieves, mercenaries, and mages; as many as 10 people. **How could this sentient library defend itself against these raiders?** ## Additional background: 1. Anyone can learn magic as long as they are capable of understanding the working of the spell. 2. Anyone has affinity to magic just as like smart people understand physics or chemistry. 3. No mana needed to activate a spell. 4. Summoned creatures are both 'permanent' and 'borrowed' from other dimension, including Necromancy. 5. Scrolls can be activated without knowing the innerworking of the spell. 6. The library is sentient and intelligent, and can communicate telepathically (one-directional via concepts and images, not your daily usual conversation) 7. This library has benevolent nature. 8. This is the first time someone send a coordinated raid against the library. --- **†** all spells that are documented and presented within the library. If a necromancer creates a new forbidden spell, and no one knows about it, how it works, and no one brings the knowledge to the library, then it is not archived within the library. [Answer] It sounds to me like the only proper *faculties* your library has are the following: 1. Sensation - it can feel it's own body; corollary, it can feel pain if it's body is harmed; additionally, it can detect the presence of any interloper, though it has no mechanism for identifying them specifically, it can gauge an entity's general level of magicallity. 2. Sentience - it can think, furthermore, it has had a great deal of time to do so. 3. Communication - it can relate to other minds by projection of thoughts via the medium of images and sensations. Your library has rather limited options for *self* defense. It cannot cast spells, as it has no mechanism to learn them (the last man on earth has all the time in the world to read, but broke his glasses?). It cannot manipulate its own structure (thereby trapping, discombobulating, or otherwise interfering with an interloper). It cannot even properly track cause-and-effect, as it has no mechanism for linking any sort of pain it feels to the presence of a particular outsider. In your example, say there are 10 people in a room, and the library experiences the pain of a bookshelf being broken. Did one of the interlopers cause this pain? If so, which one? How would it discover this? It couldn't even ask, because its telepathy only allows the projection (and not the receiving) of thoughts. Your library *needs* guardians. Of course, according to your proposed caveats, the library has no means of creating these guardians itself; the most likely explanation to my thinking is that the library has requested such patronage from among its visitors. Perhaps an order of magical monks or bookish scholars now maintains permanent residence therein, or perhaps a single powerful magician calls the library home. Another possibility is that a number of individuals maintain regular custodianship of the library. A select number of wizards, for instance, might take shifts dropping in to place and restore wards, maintenance automagical guardians and servitors, mend books, clean, etc. Such guardianship would not be hard to establish, the library would simply need to communicate to a trusted visitor (perhaps recognized by his magical signature) that it required such guardianship. A final possibility - the library is telepathic - is telepathy common in your world? Can the magically skilled learn it easily, or at all? If not, it could be extremely disconcerting to even powerful magicians to have their minds invaded, and they would likely have little defense against it. If the library could overwhelm a person's mind with sufficiently strong and malicious communication, it could - perhaps - render them catatonic, overwhelm them with intense fear or anxiety, induce any number of debilitating conditions of the psyche, or even lead them astray and into dangerous encounters. [Answer] Since the library can manipulate memory by making people forget itself, I would just use that. Make people forget any plans the library (or whoever set the protection spell) does not approve of before they can get in. Works best with a second defense that makes it difficult to find the library without the memory magic being activated. A magical gate that activates only for people whose minds have been sanitized at a location revealed by the mind magic. So your thieves would totally forget their plans of plunder before they ever got inside. This could be an active block so that even if the thieves read their own written notes of the plunder plans once inside they won't be able to really comprehend them while inside. The thoughts will simply be erased from their working memory before they can fully process them. Same would apply to all defensive magic that could block the mind magic. The library could even be little less benevolent and more predatory than you describe. It could add memories of people wanting to bring it new spells. And convince people that they have a deep conviction not remove any originals from the library collection, only copies they themselves have made while in the library. [Answer] Why exactly do our bad guys need to raid anything? Surely they're free to go in, learn and/or copy whatever they will and head off with their knowledge intact? Regardless, it seems likely that their goal would be to steal physical items. Maybe they're lazy and don't want to put in the work to actually learn or copy their spells or maybe there's also physical artifacts of power in the library too. So how do we prevent that? Well magic obviously, but what kind?. # No Library card, no borrowing! One suggestion would be warding magics on the exit that prevent you from removing physical items that belong to the library, be they books, scrolls or something else. You try to walk out the door with my priceless tome? It simply disappears from your bag and is magically returned to the appropriate shelf position, ready for the next sage / mage / random commoner to peruse. This could also double as a maintenance / shelf stacking task so that the library doesn't need any physical servants to go around tidying up after people who are too lazy to put their books back where they found them. The book has been sitting on a desk for an hour? It automatically magics it's way back to the appropriate shelf. The best part of this is that the memory manipulation makes it super mysterious. Raiders go in, pack their bags and walk out with a dozen priceless books then they get outside and they just don't have them. This leaves them wondering whether they ever actually tried to steal them in the first place because they don't remember their time in the library. Nobody can even work out why the place is impossible to loot! Plus it's a handy plot hook when someone works out how the wards work and tries to break them? # Physical defense? Magically returning books are great and all, but that doesn't stop someone having a tantrum and breaking things in the library, causing it pain and suffering and requiring repairs. The Library needs some sort of physical guardian to prevent this. Magically animated golems seem like a good option. These could be completely autonomous so that the library doesn't need to consciously control them, rather like an immune system. They tidy up, repair damage, do maintenance and deal with pesky viruses (or raiders) all without the library needing to have any input. [Answer] Actually, **who cares about defending anything**? Nothing in the question says that the library can't have "regenerative" properties. It's already somewhat alive, so it can probably completely "heal" itself, replacing missing scrolls with copies and repairing any shelves, walls, ceilings, etc. Since triggered by damage, the "healing" can be done by "spells used as a trap", so it's involuntary (like in humans) and doesn't need any conscious act from anyone sentient. The library could be built with a [healing factor](https://en.wikipedia.org/wiki/Wolverine_(character)#Healing_and_defensive_powers) so great that it could regenerate itself from a single sliver of its shelves (no mana is needed, helpers can be temporarily summoned, so really, are there any limits?) In this case, it probably will **welcome** raiders, not stop them, so any garbage from breaking things will stick to their clothes, and then will get carried away by the raiders. And then new clones of the library will grow in other places all over the world, **spreading the knowledge**. Thus fullfilling the purpose of the library better. [Answer] I own a beautiful rare book on fireworks. It should be titled "Explosives for Idiots, a Guide to Extraordinary Displays of Self Harm." Recipes include "Not smoke, but Brain Destroying Mercury Vapor", "Really Real Blinding Heat", "Intensely Vibration Sensitive Explosives", "Super Sticky Sweat Triggered Igniters that Produce Poison Gas" and "Put All That Stuff in a Rocket, What Could Go Wrong?" I paraphrase. I am trained as a chemist, and would recommend the book but for the spectacular deaths and injuries doing so might cause some idiot somewhere. A library filled with similar "magic" tomes would not need much defending. [Answer] The library is guarded by a great and terrible monster, a dragon with tough, leathery hide like book bindings. Its wings are scrawled all over with chaotic markings in the shape of letters from every known script. Its teeth are thin as sheets of paper, but stronger than steel. Its presence is truly fearsome, as it projects a magical aura causing all around to fall silent. It is ordinarily a docile, harmless beast, but woe betide any who causes harm or offense to the library, for the Bookwyrm will hunt them down! [Answer] Is the library "anyone"? If so, it can learn spells. **A lot** of spells. **Do not mess with a sentient library.** Especially, do not mess with a sentient library **that has a sense of humor**. On the most basic level: Dispel magic until there is no more magic detected and then Baleful Polymorph bad actors into bats or something else that eats moths. If you want to be kind, give the bats unique markings and then list them in a log book. That way the librarians can question them and, maybe, end their sentence. If polymorph doesn't work, disintegrate after disintegrate will solve the problem. I few gust of winds will clean that man right out of my stacks. [Answer] # There is nothing physical to take There aren't really any physical scrolls, just magic the library itself has to present the image of such scrolls. When a raider "takes" a scroll outside the library, the magic is dispelled, and the raider has a handful of nothing. In contrast, a scholar would bring blank scrolls and ink into the library. A physical transcription of the scroll image (possibly "automated" by casting another spell) can be removed just fine. There could also be some magic that automatically reads all spell scrolls brought into the library (analogous to the way that any books found on ships at Alexandria were copied for the Library there). This could cause maintenance problems with duplicates, but a magical "source code repository" system could dedupe the spells, and even track multiple variations of spells with minor differences. [Answer] A powerful defender. A library with the attributes you describe would be a natural stronghold for a powerful mage or cleric. Access to all those spells would eliminate the need to travel to find new spells and items. Occasional visitors who conveniently lose all memory of the location once they leave would be a good source of whatever the defender needs. Additionally, an ally like this who has a scrying stone or other means to communicate with the outside would be an invaluable resource to help the library defend itself. If a symbiotic relationship can be established with a friendly ally, that would be great for the library. On the other hand, if this defender is evil and devotes him/herself to attacking and looting all visitors to the library, that could provide even more plot fodder for the adventuring party seeking the library. Along the same lines, if this raiding party does contain mages of a scholarly bent, one of those may see the advantage of making the library his home and decide to stay here, perhaps betraying his comrades in the process, to become that defender. Depending on how deep you want to get into this idea, it's entirely possible the library could become home to a school of magic, as well. The synergies involved in this would be similar to the other options above. [Answer] # Baiting The library could try to ascertain the intentions of newcomers by placing more or less obvious hints pointing to a supposedly "forbidden" section, containing unimaginably valuable and dangerous magics. The library could also emphasize them with telepathic communication. This could prove useful, as those with malevolent intentions (and an utter lack of common sense, since they're trying to raid a legendary magical library) would much more likely be drawn to items out of their depth. The actual bait section need not be anything more than an area filled with gibberish books to confound even the brightest of mages, since bright and driven individuals are often given to find patterns where there are none. Other, fancier, means could involve combinations of direct teleportation out of the library, destruction of magical items, induced insanity, disfigurement etc. Just to give some ideas. [Answer] Are you familiar with Discworld's L-space? In that case it is just a side effect of the accumulation of magic, but in your case it can very well be a sentient choice. Navigating the depths of the library can become impossible, even with people taking conventional precautions like making a map or leaving a trail. If what you want to protect from is just looting/taking specific things away, then raiders can be locked in until they give up their loot, or even forever if need be. Or they can be led to some dangerous specimens stored within the library. And protecting from destruction or "cutting a way out" can be achieved just by having dangerous results from destroying magical items such as books and scrolls. The walls, floor and shelves need not physically move, and you can still give it unconventional, even varying space (or spacetime) geometry. Or you can achieve that unnavigability by affecting the minds of the people inside it, since you already have it erasing their memories at the exit. Though if you go that route, you might as well make it affect their intentions and actions directly. [almost off-topic: experience getting lost in L-space first-hand in the [Discworld MUD game](http://discworld.starturtle.net)] [Answer] Use the telepathy as psychological warfare? Implant flashes of thought, ideas, imagination seeds in the minds of the raiders, causing them to turn on each other. Another idea would just be weaponized communication. Loud, bright, otherwise overwhelming sensations blowing someones mind apart whenever they look at a specific door, or in a direction away from where the library wants them to go. The sound could be used to cover up groups calling to each other, etc etc Theres also the possibility of other people who just happen to be studying there at the time of the attack. [Answer] We can use three options to make our library from sentient to sentinel. Illusion, destruction, restoration. First one up is illusion. The library will have a prototype of itself conjured as an illusion. People stumbling upon it will be tested for their intentions here. If they are hooligans or have malevolent intent, the library will be sealed away from them. Otherwise, they will get into the true library seamlessly. Destruction. There will be a gauntlet leading up to the library. And the library will be full of traps. Any violation of 'rules' will trigger traps. So much for being a benevolent library. Restoration. At the very sensation of being intruded, the library will cocoon itself into a protective shell, which will be virtually impervious to any magical/physical damage. [Answer] One possibility is for the library to have some sort of detection system for knowing whether one's intentions are good or bad (you said it is telepathic and intelligent) and then flood trespassers minds with horrible images and therefor traumatizing him. :) [Answer] I would suggest a different tangent. Rather than defending itself, it would instead proactively bribe people with valuable knowledge to recover stuff. Raiders steal it's books - library then offers an arcane academy access to to make copies of some scrolls that they REALLY REALLY want. But first - they need to go find the raiders, recover the books and ... discourage repeat performances. Maybe better yet - it 'encourages' them to prevent it in future, because it would be a shame if the arcane lore of a hostile nation advanced a few hundred years overnight, now wouldn't it? [Answer] What would happen to a primitive man blundering into an electricity sub-station? Especially an avaricious one attracted to shiny copper thingummies? I wonder whether the library needs to defend itself, given its contents. OK, so the scrolls would also need to be somewhat sentient. But even the most primitive life will defend itself against destruction to the best of its ability, and will interpret an attempt to drag it away from its home as an attack on its life. I'd expect a hostile visitor to meet his end attempting to read or steal a potent scroll, and discovering too late that the scroll is reading him and stealing his mind as he does so. Indeed, some of the less pleasant scrolls may have this attitude even towards humble students. The library may actually offer advice about the correct degree of mental humility and the shelves where only the most potent of mages should attempt to browse. Or, if it feels threatened, to lie. [Answer] From your description, the only possible weapon in the library's arsenal is telepathic communication. It cannot move the shelves or the books, so physically hurling either towards intruders isn't an option. The consciousness of the library is essentially a brain in a jar - something that can feel & think, but not physically interact with the world. And affecting memory only seems to occur upon the person leaving the library, so that's not really an effective weapon while they're still IN the library. Now, that being said, the telepathic communication alone - even just in the form of images & concepts - can be used to distract & confuse interlopers. While intruders are reading the books and attempting to learn spells, the library can make them see the wrong words, or visualize the wrong images. Thus the very mind of the intruders themselves becomes the weapon. Perhaps the entire library is under an enchantment - the same enchantment that gives it life - that would make the books turn to ash if they leave the library. It could even be the same enchantment that makes them forget about the library, and that would tie everything together as well as giving the library a defense mechanism external to itself. Also, if this is for a novel or story, you may want to explain WHY the library needs to defend itself. If the books themselves are not part of its "body", then would it necessarily care if someone takes a book? If so, why? Does it feel possessive of the books? Greedy, even? Otherwise, it would only care if someone were to harm the library itself, the shelves, etc. [Answer] The library has had thousands (perhaps 10s of thousands) of years to practice sneaky tricks on invaders. Mostly it has learned to manipulate raiders desires and ideas to a very fine-tuned degree. How? When a raid occurs, it acts as though it is a passive reference system leading raiders to the most powerful spells, while in reality it leads them to dangerous spells. It could also feed paranoia in the raiders so they end up killing each other while trying to protect the secrets of the library for themselves and not the others in the group. Imagine a sort of group descent into madness induced by subtle nudges by the library telepathic suggestions, and perhaps the spells it tricks them into invoking. Perhaps over the aeons it has also manipulated previous visitors to create more direct defences. Imagine a more benevolent mage living there for many years. The library feeding him ideas that raiders might come and attack, so he gradually uses the spells in the library to create elaborate defences. [Answer] ## Let the library rearrange its own shelves. Not all magical books are safe to handle raiders suddenly find themselves surrounded by the equivalent of the Necronomicon, where death is best outcome they can hope for. try to steal and expect to be lost in the halls for the rest of your life. [Answer] If you really think it needs to defend itself, it could easily do so. **Using telepathy** By using its telepathy, it can introduce images into the minds of any looters. If the looters don't understand what's going on, it might scare them and even make them go insane. Even if they do understand, it might still work. Some of the lesser (or everbody even) gifted might be persuaded that the images represent real events; the memory of one of the other members of the group stealing from you or trying to harm you in any way may be just enough to make those suspetible to the suggestion assault those who aren't, forcing the group to dismiss itself. **Using scrolls** Simply activate the ***kill all people*** scroll. [Answer] # The library doesn't exist I've my idea reading the [@Monty Harder](https://worldbuilding.stackexchange.com/a/74302/35041) answer. Instead of only the books been a proyection -so you can't steal them-, all the library is one. There is an special and ancient spell casted a long time ago in the middle of the desert, **the spell is the library itself**. When someone reach to that location they are induced into a illusion and they see "the library", but they aren't there really, so you can't destroy it or steal it (you still are able to make a transcription of a book). Even, if people is making trouble (like attack another people or *try* to destroy the library), it's able to defend itself making illusions on the people. It can make people see nightmares to scare them, or simply make an illusion when the mercenary archived to destroy the library or steal all the books, and when they get out of the desert, they discover that all was an illusion. # The library is able to rebuild The library was build with two spells. * **Reconstruction:** This spell self repair the library when it's damaged (turn off fires, reorganise books, rebuild wall, etc). * **Conservation:** This spell desintegrate all the matter (even book) stolen from the library in order to archive the conservation of mass and energy of the reconstruction spell. # The library is in a pocket world To enter into the library you have to travel across a portal. The library is in a pocket world and was casted with some kind of time loop spell or conservation mass spell that protects it. * **Time loop:** The library is always in a time loop, if you break it, you have only to wait for the end of this iteration in order to loop again, and each time it make a loop, all the library is restored to it initial form. If you stole something, when the library reach to the next loop the stolen things will dissappear (and re-appear in the library). * **Conservation mass:** Inside the pocket dimention there is a conservation of mass, the library can't loss mass. You know how works a teleporter? It save the pattern of the item, turn the into into raw energy (90 petajoules per grame) and rebuild it using the pattern an the energy. Well, the library do something similar, it has an stored pattern, and the pocket world can loss energy or mass, for each grame of stolen thing you have to left a grame, or simply the portal won't work, then, all the matter inside library is turn into energy and rebuild again using the saved patters. The library has just regenerate completely. # The library is in another dimention This is quite similar to the first title, but instead of been an illusion it is in another dimention, and there is a passive spell in the area to see that dimention. Because it's another dimention you can't touch them (or steal), so all there aren't books (you can't change of page), there are a lot of pergamines already opened and floating in the walls. ]

[Question] [ One thing that necessarily happens on a generation ship is that people die of old age. Now that poses a tension: On one hand, you need to handle the dead with dignity. On the other hand, you probably cannot afford losing the materials the dead are composed of. So in short: How would a generation ship responsibly handle the dead? [Answer] To complement @*Ville Niemi*'s suggestion *Thermal hydrolysis*, there is already an equivalent in the context of death customs. It's called [Alkaline hydrolysis](http://en.wikipedia.org/wiki/Alkaline_hydrolysis_%28death_custom%29). Although alkaline hydrolysis is rather controversial in that it "does not show sufficient respect for the teaching of the intrinsic dignity of the human body" as the New York State Catholic Conference put it – link in wikipedia – whether it is acceptable or not depends largely on your culture. --- Note there are also [alternatives to burial](http://en.wikipedia.org/wiki/Burial#Alternatives_to_burial), e.g. "The Yanomami have the practice of cremating the remains and then eating the ashes with banana paste." **However**, this so called *Endocannibalism* can – in it's traditional form – *transmit* the incurable degenerative neurological disorder termed *Kuru* **if** your population contains infected individuals. Regarding prions the CDC states [on cremation](http://www.cdc.gov/ncidod/dvrd/cjd/funeral_directors.htm) > > [...] cremated remains can be considered sterile, as the infectious agent does not survive incineration-range temperatures. > > > and [on alkaline hydrolysis](http://www.cdc.gov/biosafety/publications/bmbl5/BMBL5_sect_VIII_h.pdf) > > The alkaline hydrolysis process, using a pressurized vessel that exposes > the carcass or tissues to 1 N NaOH or KOH heated to 150°C, can be used as > an alternative to incineration for the disposal of carcasses and tissue. > > > The > process has been shown to completely inactive TSEs (301v agent used) when > used for the recommended period > > > --- @user3082: Thanks for your contribution. I edited my answer according to your objection. [Answer] Soylent Green are people. It's the new recycling. On a more serious level, I'd suggest looking into what are now known as woodland burials. The body returns to the forest as nutrients. You could do the same in the biosphere pod. One variation of the woodland burial involves freeze drying people in liquid nitrogen then breaking the frozen remains up into little chunks that are a lot more biodigestible. [Answer] **Organ transplants and Cannibalism** Humans are resources, they have: * Body parts that can be transplanted into other people * Bones that can be used as material for art and other practical purposes * Meat that can be cooked and eaten * Hair that can be woven into clothes, fabric, and wigs * A hefty water content * Skin for leather Once organs are harvested, the remaining biomass can be pumped dry of water, solid mass like bones then taken out, skin removed, and the rest used as fertiliser. Anything not used there and then can be stored for future use. There's also a multitude of other things to be done: * Medical and scientific research * Medical and scientific education * Power generation ( plasma incineration ) * Livestock feed [Answer] [Thermal hydrolysis](http://en.wikipedia.org/wiki/Thermal_hydrolysis) combined with a bioreactor of some kind. Turns organic waste and dead bodies to fertilizer and nutrients. There probably would be separate systems for managing sewage and the dead, though. This would not really be that different from cremation, but should waste less energy. The methane generated by the bioreactor could be used to power the hydrolysis producing carbon dioxide and water. Which together with the fertilizer produced would maintain food production. [Answer] Dignity is a society-invented concept. In one society, it's dignified to bury a corpse under ground in a designated [graveyard](http://en.wikipedia.org/wiki/Cemetery). In other, it's dignified to leave the corpse in high ground to have vultures eat it, called [sky burial](http://en.wikipedia.org/wiki/Sky_burial). Yet another used [small ships or boats](http://en.wikipedia.org/wiki/Ship_burial) to dispose of the body with honors. Ferengi from Star Trek [broke the body in collectible pieces](http://en.memory-alpha.org/wiki/Ferengi_death_ritual) to be sold as "last profit". Very dignifying procedure - for a profit-centered society. A space-faring society would inevitably work out their own ways, and it will be those ways they'll see as "dignified". Most likely consider our own ceremonies shocking, despicable, barbaric and wasteful. Bottom line: make it any way you see fit. It's not for our society to judge it. [Answer] Approximately the same way we do it here: Composting, by way of burial. Depending on the time frame and capacity, it might be necessary to carefully manage the compost pile. We might have to give up on embalming and persistent spacious coffins, and put in the dirt microbes that will digest humans quickly. Bones might need special handling. But if the capacity is high enough and the time frame is long enough, the need for careful management could be minimal. [Answer] **Depending on how the ship's engines run, one could use the concept of the fusion torch**. Essentially, the body is fed into the ship's reactor (or whatever else powers it, provided that its energy output is similar or greater). The conflagration blasts it into its component atoms, which can then be collected and sorted by a device akin to a mass spectrometer. Once you have these stores of raw elemental material, you can use them as you would any other store of that same material: it is, in many ways, the ultimate form of recycling. Research on the fusion torch didn't work out so well on Earth, but for something like a generation ship it could be ideal. There is no sanitation risk, because any pathogens on the body are blasted just as the body is. There is very little wasted matter, because every component of the body can be recycled in this way. There is very little wasted energy, beyond what is necessary for the ship to run, because you already needed to run the engines (or at least a power plant), and the sorter can also be used to recycle other matter. **In a spiritual sense, this need not be much different from how things are done now**. Many religions include a concept of "returning the body to the Earth" in a symbolic sense. The process I outline above returns the body to the ship, both symbolically and, to a degree, literally. [Answer] ## Cremation Cremation. The body is converted into Carbon dioxide and water vapour, which rejoin the atmosphere, plus carbon ash mixed with a few other nutrients which can be sprinkled on the soil and will fertilise the plants. Nothing is lost. You will presumably have machinery in place to balance the levels of carbon dioxide and oxygen if your vegetation isn't up to the job. ## Expect about 1.1kg per hour Assuming a population of 10,000 and an average lifespan of 80 years, you can expect one death every 2.9 days or so. An average North American adult human is 80kg. That's 1.1kg per hour, most of which will be water. This is a very moderate amount of carbon dioxide for a good size biosphere to soak up. [Answer] I can see a few methods: **1. Cremation** This is already a popular method of dealing with your body when you've passed on (at least here in the UK). A furnace doesn't take up much space, and especially on a ship where you have huge amounts of power, it certainly won't take up much of it. You *could* then drop the ashes out into space - [one astronomer is doing this with Pluto](http://www.dailymail.co.uk/sciencetech/article-2906946/The-man-PLUTO-New-Horizon-probe-mission-dwarf-planet-carrying-astronomer-Clyde-Tombaugh-s-ashes.html) - but you have to decide whether that's ethical or not: is it polluting the Universe? **2. Cryogenic freezing** [We do already have the technology](http://en.wikipedia.org/wiki/Cryopreservation) to do this one. When someone dies, you can give them a coffin, a funeral, and then put the coffin in a cryogenic freezing unit until you get to your destination. The big disadvantage of this is that it does take up a **lot** of space - with that many people on board, you're going to need a big room to keep all these dead people in. And of course, it'll be a lot of work to get them all off the ship when you get to your chosen planet. **3. Sanitary Vacuum Disposal System** Also known as "throwing bodies out into space", this method is the simplest: after the funeral, you stick the body in an airlock and open the outside, thus letting them fly off into space. This might actually appeal to some people because of the almost romantic ideology that your dead relatives are out there somewhere, watching over you - in this case they really are out there. However, this does again have the problem of are you polluting space? [Answer] While I side with @RoboKaren (my version is a woodchipper in the forest), and I like the other unique answer, @VilleNiemi - I might be persuaded to argue with @TonyEnnis. Depending on the length, and losses (and surplus material) available on your ship/trip, it might be possible to save some parts of people for burial on the destination planet. I'd think it'd be something like 'save the skull' or 'save a bone chip', while recycling the rest. But, only if the biosphere doesn't need the materials. I anticipate that any generation ship is going to have losses; guy who suicides out the airlock. Guy in the collection/maintenance probe whose fuel tank exploded and jettisoned him into deep space... Etc. [Answer] Hugh Howey's "[Silo Series](http://en.wikipedia.org/wiki/Silo_%28series%29)" touches on your exact problem. The inhabitants bury the dead in the growing levels and the bodies decompose and are used for food crop growing. It even mentions how there is a different smell in the growing levels compared to the rest of the habitat. Social conditioning over a couple of generations could make it so that people honour the food grown, literally, by their forebears which has the added benefit of stigmatising food waste on a generation ship. [Answer] Begin Flowchart: Step 1: Did the deceased die of natural causes: Yes - Step 2, No - Step 4 Step 2: Does the deceased have any healthy organs that the organ bank is missing: Yes, remove and store - Step 3, No - Step 4 Step 3: Are there enough bodies in storage for medical training: Yes, store body - End, No - Step 4 Step 4: Reclaim water Step 5: Reclaim bone - for use in fertiliser Step 6: Cremate and process remains, remove carbon, phosphorus, remaining calcium, iron, potassium, sulfur, sodium, copper, selenium and magnesium Step 7: Inject remainder into space/intern/return to family End [Answer] They'd probably have a ceremony, similar to a funeral today. The funeral ceremony would depend on where the generation ship originated, as each culture of Earth seems to have their own traditions. The ceremony could begin with kind words, or shooting a flaming arrow, placing coins on eyelids, or letting them sail with the river. Whatever does happen will be performed by a close loved one. The family of the deceased need to grieve but still get a sense of closure. As long as the body isn't ripped apart in a chamber in front of everyone, there is a lot of inspiration with Earth's cultures as to how to handle this. [Answer] I recently read [Artur C. Clarke](http://en.wikipedia.org/wiki/Arthur_C._Clarke)'s *[2001: A Space Odyssey](http://en.wikipedia.org/wiki/2001:_A_Space_Odyssey_(novel))*. (*Forgive me if my knowledge of the story differs from the movie; I haven't watched it yet*) At one point in the book, when Hal kills the three hibernating astronauts, the surviving crew-member (Dave Bowman) wraps their bodies in white, and sends them out of the airlock to make their own travels through space. I kinda thought that this was the space version of [burial at sea](http://en.wikipedia.org/wiki/Burial_at_sea) (*out of necessity, not due to preference*). Admittedly, the craft that he was in was *not* a generation ship, but I thought that this incident might help explain some of the questions at hand vis a vis the question on ships -- assuming there's nowhere to place the body, and nothing to do with it (*either truthfully, as in the case of Dave Bowman; or because of "dignity" issues*), then perhaps this might serve as a model for the procedure on generation ships. [Answer] I believe that in a large enough spaceship, there is no reason the same "services" being provided on earth could not be provided in space. This takes care of the different "dignified" methods of handling the dead. Where the difference comes, is in the handling of the bodies **after** the ceremonies. If the body is to be buried and maintained buried for say 100 years, there should be a cemetery to accomplish this. After the 100 years any remains are exhumed and used as fertilizer or burned in the reactor. If the body is to be cremated, then it is burned in the reactor. If body parts are donated (to be reused), obviously, they are removed from the bodies prior to either of the two previous procedures. [Answer] As in most of the answers I believe it all comes down to culture. I think a good analogue of this is within the Frank Herbert's Dune Universe. On Dune (A mostly barren desert planet with very limited water resources) the native inhabitants [Freemen](https://en.wikipedia.org/wiki/Fremen#Collection) recycle and reuse all water including capturing exhaled breath, bodily waste and even the processing of corpses. Such is the value of water, that spitting is considered a very high form of respect (An activity usually frowned upon in other cultures). I believe the key sentiment in the processing corpeses is that the dead are dead and require their water (or other consitutants) less than the living. To Quote: > > “We will treat your comrade with the same reverence we treat our own,” > the Fremen said. “This is the bond of water. We know the rites. A > man’s flesh is his own; the water belongs to the tribe.” > > > The other half of the solution is that in a ship that travels for generations with a small group of people with presumably little outside contact it becomes much easier for social norms to be transformed over time. ]

[Question] [ In my RPG campaign setting the orcs are tougher than most other races. In hard times they can eat wood (small bushes and fresh pieces of trees). In really hard times they can eat healthy soil and survive enough to continue their march/siege, but they don't like it. How do I begin to explain this process? While I could hand-wave it away with the word "magic," I'd like to have at least a believable starting point [Answer] Starting from the ground up: how much caloric energy even exists in the things orcs eat? Energy metabolism for aerobes involves combining oxidizable with oxygen - in essence burning them. One can burn things in a bomb calorimeter to see what the caloric value is. I looked up caloric values for fats, ethanol, protein and conventional carbohydrates (e.g. wheat flour); then wood and leaves, then various soils. from <https://en.wikipedia.org/wiki/Food_energy> > > Fats and ethanol have the greatest amount of food energy per gram, 37 > and 29 kJ/g **(8.8 and 6.9 kcal/g)**, respectively. Proteins and most > carbohydrates have about 17 kJ/g (4 kcal/g). > > > from [source](http://onlinelibrary.wiley.com/store/10.2307/1936045/asset/ecy1971525923.pdf;jsessionid=02541A2796915DCB72C43370AD40463A.f01t04?v=1&t=j63170ts&s=b22ce8be822742a3691c3c871563ea673a269be3) [](https://i.stack.imgur.com/otALf.jpg) from [Caloric values of organic matter in woodland, swamp, and lake soils](https://www.jstor.org/stable/1932684?seq=1#page_scan_tab_contents) > > Caloric values of organic matter in woodland, swamp, and aquatic soils (± standard deviation of the mean) > $$ > \begin{array}{c|cc} \text{Soil Type} & \text{Kcal/g > ash-free > dry wt} & \text{Ignition > loss% > dry wt} \\ > \hline > \text{11 woodland humus layers} & 5.04±0.04 & 57 .5±5.7\\ > \text{20 swamp soils} & 4.87±0.04 & 77 .3±1.5\\ > \text{9 lake and pond muds} & 5.24±0.05 & 59.3 ±3.6 \\ > \end{array} > $$ > > > So: for a fire, carbs, proteins, wood, leaves and soils all have comparable energy value - 4 to 5 kcal/g. I was surprised to read it for soil. Why can't you make a fire from dirt, then? Maybe my efforts have used dirt with too much sand or clay; the authors of the soil article specify that this is topsoil rich in organic matter, not deeper mineral soils. Then why can humans eat corn but not wood? The calories in wood, tree leaves and soil are mostly as cellulose: the evolutionary masterwork of the plants. It is made of sugar and very much a carbohydrate, as energy dense as starch, but very difficult to digest. To digest it one must have commensal bacterial to do the job. These live in the specialized gut organ called the rumen in ruminants (like cows), also in the less specialized digestive tracts of pandas, and in the cecum (part of the colon) of rabbits. The problem rabbits have is that the cecum comes after the small intestine, and the small intestine is where nutrients are absorbed from broken down food. What good is it for your bacteria to break down cellulose into sugar if you can't soak up some of the sugar because you are about to poop it out? The rabbit solution: refection. Eat the poop. That poop is full of microbes breaking down the cellulose. Give them a while and that poop is full of nutritious sugars. Back in it goes to absorbed the second time around. from <http://www.columbia.edu/itc/cerc/danoff-burg/invasion_bio/inv_spp_summ/Oryctolagus_cuniculus.htm> > > European rabbits are ravenous eaters and indulge in a diverse diet of > grasses, roots, tree bark, leaves, grains, fruit, seeds, and buds. > Since this diet is low in nutritional value and high in > difficult-to-digest materials, they are known to reingest their feces > to obtain extra nutritional value from the food the second time > around. > > > Your orcs are set up the same way. They can extract energy value from twigs, leaves and soils by letting their colonic commensal bacteria break it down, then re-eating the product. This also explains why they don't like it. [Answer] It is possible, because it is real. See documentary video "Haitians eat dirt cookies to survive" <https://youtu.be/s3337cj4sJQ> Also, in Vietnam (use google translate to read): <http://news.zing.vn/nuong-dat-de-an-o-vinh-phuc-post396355.html> [Answer] Loam (consists of sand clay, silt and any organic and water mixed in) contains vegetation that is breaking down. Often forest floors have layers of leaves lost each year. The carbohydrates that make a leave structure will give on energy when oxidized. Same as other food. They can also eat live roots, shoots, grubs, worms, bacteria, slugs. Fungi are usually present as single cells even if they do not show a cap above ground. It is likely that sand and clay cause constipation. Compost piles can have many of the possible nutrients that are in loam. Smashing everything and manufacturing a large pile of rot seams appropriate behavior for orcs. You could have a preferred fungus that the orc bands carry with them. The fungus will have the enzymes that convert chewed beta cellulose (wood) into simple sugars. [Answer] You could take a slightly different approach, if your Orcs are green you could make the argument that they are able to perform limited photosynthesis in their skin, eating the dirt gives them the nutrients they need to perform photosynthesis which they don't usually get from their usual diet of meat and more meat. ]

[Question] [ Assuming we had a non-spherical asteroid that doesn't have a magnetic "north", how would the inhabitants define areas on the asteroid? How would they explain to a visitor to go to a very specific spot to retrieve or leave something besides "head over the hill sunward for 50 km" [Answer] My suggestion would be that you select a point on the asteroid to act as a pole. Perhaps the point of first landing? Then, using that point and asteroid's centre of gravity as references, you can map spherical coordinates. [Answer] Whoever is going to be on that asteroid will necessarily used radio communication to keep in contact with the rest of the crew. To ensure communication a network of antennas has to be established, since a single antenna could at best serve half of the asteroid. Each position can then be simply referred to the distance from the (closest) antennas. [Answer] I'd maybe consider using the axis of rotation - it would be a very rare asteroid that isn't rotating somehow. Imagine sticking a skewer through the asteroid along the axis. That would give you a top and bottom, and then you can use spinwise and counter-spinwise (or something similar). Obviously only works if you have an asteroid that is rotating nicely, something that is rotating a bit more chaotically might be more of an issue. If it's not rotating at all, or is spinning chaotically then Arkenstein XII's answer is definitely the way to go. [Answer] I would suggest that they use a GeoHash which subdivides the asteroid into a hierarchical grid that can be navigated based on any desired granularity <https://en.wikipedia.org/wiki/Geohash> The origin point of the geohash should be the starting outpost location and this would provide a mostly sequential means of describing location where "most" objects that are physically close to each other, share similar geohash values. NOTE: there are some minor cases where the hash of nearby locations will not be similar, but for most things it should be good enough. Also NOTE: Geohash is a competing system of location to What3Words which is used here in Ireland and which produces non-sequential descriptors for location. This makes it impossible to know if two locations are close to each other just based on their 3 words which is why I would recommend using Geohash instead. [Answer] Depending on the length of your characters' stay on the asteroid (is it a mining operation, or are we setting up a habitat?), I'd say just establish a series of beacons that your personal navigation system can triangulate with. If it's longer-term, you have to set up magnetic shielding against the worst bits of solar rays anyway, so you might as well use that system and have a magnetic north as your standard. An alternative to either of those would be to use the rotation of the asteroid as your north/south, and set up from there. If it's not spinning, this obviously wouldn't work, but it's worth bearing in mind. There are lots of ways to do it, but if this is a corporate thing, then they'd be likely to do whatever is easiest. That would be the triangulation beacon system, which they'd need for comms on a large, dense body anyway, and it would work regardless of why the asteroid is being navigated. It could be standard procedure. [Answer] **Use Peaks and Valleys, and polar coordinates** In the old days, prior to GPS, cartography and mapping were major and necessary fields of study. Obviously without a magnetic pole you would be unable to create universal direction, but you could still create a 'map' by using surveying techniques found mainly in triangulation of mountain peaks. Basically, you identify the highest point in a field of view, triangulate this with others to determine its distance and height, allowing you to build up an accurate map of peaks. As it is an asteroid, it has a centre of mass, and should be relatively easy to determine which peak is the highest - this would be your reference point. The second tallest peak would be your reference base line, from which you could measure polar coordinates in a consistent anticlockwise direction from centre of gravity (z-axis) for all peaks thereon. Often, when exploring Australia, Charles Sturt would have to 'artificially' create mini-piles of rocks to serve as references to determine coordinates. If your asteroid is flat, this could be used to create artificial reference points too. Edit: To clarify the process: As an example triangulation was used to map completely the Rocky Mountains in Colorado: [](https://i.stack.imgur.com/PSCVi.jpg) By using mountain peaks between 3 points, distances can be determined very accurately. Identify 2 peaks from one peak, measure the angle, then move to an alternate peak to measure the new angle between the first peaks. By plotting this on a map, you can use this to determine way finding, distance measures and reference points without necessarily relating to latitude / longitude. (It was also possible to use this technique without a compass). Another example, giving each 'triangle' an identification in the Equadorian mountains: [](https://i.stack.imgur.com/AcWoN.jpg) By coding each triangulation, you can use this to describe locations. Pinpointing coordinates can be accomplished by mapping over a grid (polar or rectilinear) if necessary, perhaps based on the two tallest peaks as the origin. This is a very flexible system, and was used in the 'old days' in particular when mapping difficult terrain, and is very accurate. [Answer] You have to remember that even on Earth, apart from the poles and equator, the coordinate system is arbitrary. Greenwich isn't even a particularly important location in the grand scheme of things, apart from hosting the Royal Observatory that's used to define the 0 meridian. The problem is the minimum number of points you need to define a coordinate system relative to a body. On a cube we conventionally select a vertex at one corner and three dimensions from that point. On a planet you take the axis of rotation to define the equator, and an arbitrary point on the surface to define a 0 meridian, everything is then defined relative to the equator, the 0 meridian, and the direction of rotation. Asteroids are irregular. If it's tumbling then you could take the longest axis instead of the axis of rotation and the point of landing as 0 meridian, it could then be modelled as rotating around that axis, even if the axis itself is not stable. If it's spinning then you have poles and the landing point can be the 0 meridian. If you haven't landed on it yet then any arbitrary distinctive point can act as 0 meridian. [Answer] Let me start by clearing one thing - **poles are not defined by magnetic field**. Poles are defined by **axis of rotation**. Magnetic poles are somewhat independent from geographic poles and are only used as handy approximation, especially when you can't get a hold of more accurate measurement e.g of sun and stars, when the sky is clouded. <https://en.wikipedia.org/wiki/Poles_of_astronomical_bodies> As for your actual question - it depends on what you mean by **large** asteroid. Really big ones (bigger than 400km diameter) end up being nearly spherical due to their own gravity, we recently decided to call them **dwarf planets**. All dwarf planets rotate mostly regularly so you don't need to invent any new system, just choose a prime meridian, maybe a place of first landing, or the highest mountain, and you're good. <https://en.wikipedia.org/wiki/Dwarf_planet> Smaller, irregular asteroids, may not map nicely, especially if their rotation is very irregular, but you can still define the main axis by calculating mass distribution, choose the axis that gives **maximum moment of intertia**, which for regular bodies overlaps with axis of rotation, choose prime meridian (same as above), and you're good. <https://en.wikipedia.org/wiki/Moment_of_inertia> For very small asteroids, don't bother with Earth-like coordinates. If your total area is comparable with big cities like London, Moscow or Paris, do something similar. Define "districts" and "neighbourhoods" with memorable names. Place couple of beacons and plaques to make it clear which is where. Everybody will learn them after living there for couple of weeks. In **conclusion**. For any reasonably spherelike object you can define a **North Pole**, where the major axis crosses the surface, choose an arbitrary **Prime Meridian** and plot an Earth-like **grid** of coordinates by simply projecting an imagined sphere on the actual surface. The asteroid doesn't even have to be very regular. These basic rules will work for all kind of potato shapes, as long as it has mostly positive surface curvature, which will always be the case except for **very small** asteroids. For those, you don't need a grid because the very small area and irregularity allows you to name all sectors unambiguously and just use those names. [Answer] You can use the same coordinate system for celestial navigation (latitude and longitude) used by Terran mariners. What you need is : an almanac, a watch, a device for measuring the angle of the stars relative to some average horizon, and a map. ## Almanac The basic concept of celestial navigation is this : imagine several easily-recognizable stars. Next, imagine that you could draw a line from each of these stars that would pass through the center of whatever you are standing on. This line will touch the ground at one (only one) location. An almanac records these stars and the location (in latitude and longitude) of the point on the surface where the imaginary line from the star touches the ground. ## Watch and Calendar And, this spot will move as the object rotates around it's own axis (days); but will only move a little with the seasons. ## Measurement Device (Sextant) When you are standing on the spot where this imaginary line from your easily-recognizable star intersects the ground, that star will be directly overhead. ## Map Likely, you are not standing on one of these spots at any particular time. The angular measurement times the average radius of the asteroid provides you with the approximate circular (radial) distance between that point and where you are. Measure multiple stars to determine where these circles overlap on a map. That is your (approximate) location [Answer] Maybe the easiest way would be to add a number of beacons and then just run bearings off, or between, them. Possibly designate one, or a few, as Prime(s), analogous to magnetic poles, and relate the bearings of the others to them. There are a number of navigation systems that use, or have used, fixed beacons to determine locations with varying degrees of accuracy depending on range from the beacons. [Answer] The center of mass would be the origin, all other coordinates (x, y, and z ~ latitude, longitude, elevation) would be pulled off that. You would orient and find the location of the CoM by triangulation of the stars as it rotates, with repeated measurements over time and in different places on the surface of the rock. [Answer] 1. [](https://i.stack.imgur.com/4wId4.jpg) You can apply a graph to your asteroid and find the distances of each point. From one another with this equation. AB^2=(Bx-Ax)^2+(By-Ay)^2…………………^2=squared If you make the same graph on four sided sections of asteroid you will have a rough grid. Next 2. [](https://i.stack.imgur.com/bHBgJ.png) This is a better way to make a three dimensional coordinate site system labeling each point from the center as a distance with the equation: The root of [(x2-x1)+(y2-y1)+(z2-z1)] where each point is a labeled coordinate at the surface of the asteroid. Next 3. [](https://i.stack.imgur.com/sbvf4.gif) Use a circle grid to plot points from center with meters or kilometers or centimeters. [](https://i.stack.imgur.com/5V38C.jpg) Then you find the angle degree of the point with this type of equation. Remember your circle grid always has a 90 degree angle already. [](https://i.stack.imgur.com/RV8G7.jpg) One can also find angle this way [](https://i.stack.imgur.com/fdBcP.jpg) Now apply the equation. X^2 + y^2=(r cos @)^2. + (r sin @)^2 Where @ is a Greek representational letter for degrees or radians. And this gives a unique coordinate for any point and it’s distamce from center of asteroid. You can put a stake or pin at any point and create a grid by stretching a bright colored string from one to the other. And use these shapes to find area. Next 4. Another way is calculus if the asteroid is spinning you can find sections of surface area as zones of the asteroid. [](https://i.stack.imgur.com/W2y38.gif) And use integration. [](https://i.stack.imgur.com/4hS86.png) For this you need the radius or diameter at each given integrated section. It if one can imagine a large amount of sections and each having a sub measure of length sections to each sliced section it also makes a grid. There are few more possibilities and I will add if asked. This is a rough idea and I am a little rusty and just woke up. Will edit later. I had a better presentation but the pictures would not copy here. [Answer] To elaborate on and combine a few other answers, consider that the Earth's magnetic north is not in a constant position, so it is not the factor in how lat/long coordinates are determined. Rather it is the axis of rotation as has been pointed out by others. The equator is determined by being the great circle (circle which circumscribes the geoid of the planet), upon which twice per year (on the equinoxes) the sun travels exactly 180 degrees from horizon to horizon in a perpendicular fashion. Leap years are a thing because there is a slight difference in the time it takes for the earth to complete a single orbit of the sun vs. the period in which two equinoxes occur. In your case a similar equator could be determined by observing the relationship between the body which the astroid orbits vs any 'wobble' along its axis of rotation (although this may take longer than a single 'year' or orbital period about the body.) The 2 points at which any two lines that are perpendicular to that equator intersect are its 'poles'. Lines which then intersect at a 90 degree angle at the poles can be used as meridians, the points at which those meridians intersect the equator are effectively arbitrary (the prime meridian is Euro-centric due to the fact that European cartographers defined it, not for any special geometric reason.) The last step is then determined by math which describes projecting the surface of the asteroid to the abstract sphere that these lines define, surveying specific landmarks (natural or artificially placed) to act as well-known points which can be surveyed against as a reference system for any other point on the surface, allowing you to triangulate coordinates. These landmarks need to be offset along either the x or y axis from one another. On a personal note I am also a fan of the answer which mentions 'geohashing' for modern cartographical applications. I have worked on an abstract specification known as 'Discrete Global Grid Systems' with the Open Geospatial Consortium which is conceptually similar and I'd encourage you to look into it if this sort of thing interests you. Its basis divides the sphere defined by an equator and meridians into a grid of triangles which is then projected to the surface of the body. Ironically, this is shown in the illustration of the robot in the left sidebar of this site. However your question specifically mentions coordinates, which a hashed addressing system does not provide. [Answer] Yes, you can. Cover the asteroid with a triangular grid of points and measure their relative locations, making the coordinate system you want to locate yourself within. You need it fine enough that you can see the three nearest points wherever you are. Trivially, if you make it fine enough, just knowing which triangle you are in is accurate enough, but we assume the triangles are not that small. [](https://i.stack.imgur.com/I9aj1.png) We know points $A,B,C$ and distances $a,b,c$ from the map. We want to locate $D$ by measuring the angles $ADB, BDC, CDA$ Using the measured angle $ADB$ we know from the inscribed angle theorem that $D$ is on a circle centered at $E$ on the bisector of $AB$. If angle $ADB$ is greater than $\frac \pi 2$ the center of the circle is outside the triangle and located so the angle subtended by $AB$ is $2\pi-2ADB$. If angle $ADB$ is less than $\frac \pi 2$ the center is inside the triangle and the angle subtended by $AB$ is $2ADB$. We can construct two of these circles based on different sides of triangle $ABC$, find the intersection, and that is point $D$. In the diagram, $E$ is the center of the circle that $D$ is on. We assume $ADB \gt \frac \pi 2$. That will be true for at least two sides of the triangle. Given the coordinates of $A,B$, we find $F$ as the midpoint of $AB$. Then $AEF=\pi-ADB$ and $EF=\frac 12AB\tan (\pi-ADB)$. $D$ is on the circle with center $E$ and radius $AE$. Do the same for another side, find the intersection, and you are done. [Answer] The asteroid would be mapped before anybody ever landed on it, rotation, procession etc would not, I think, be used due to the relative impact on these things from habitation and industry. <https://dawn.jpl.nasa.gov/multimedia/images/image-detail.html?id=PIA17480> It doesn't seem logical either to adopt magnetic polar attributes, as these are un-managed variables. As with L Dutch & G.B. Robinson's answers, triangulation to communication antenna and 'relative stationary' satellites would be most useful, reliable & probably become ubiquitous. It's not like asteroid dwellers would be without electronic devices at any time, as their lives would depend on them. 3d mapping is not really any more complex, tho we would probably expect long term residents to develop abbreviations and colloquial terms as references [Answer] Expanding a bit on LDutch's answer and MttJocy's comment on it. Take a page from pre-GPS aerial and nautical navigation systems. Aviation commonly uses (fading as GPS is taking over, but still present) the VOR system and ADFs to figure positions and navigate. Essentially the various beacons all broadcast at a different frequency, with a directional pulse that varies in phase with the base signal. By calculating the phase difference between the primary and secondary phases your ADF provides your bearing from the station. Getting a bearing from two different stations gives you a very precise location. There are also some things that can be done in terms of phasing and signal strength to give an approximate distance from a single station, allowing for a rough position fix off of a single signal, but I am not aware of it being done in practice as the two bearing option is much more reliable. The major drawback for this system as currently implemented, and your intended use is that it is line of site and relatively short range (~200 miles). If you are too far from a station, or a pesky mountain (or the horizon of your asteroid) happens to be between you and it, you are not going to be able to pick up the signals. Meaning this system is not commonly used for surface travel. The LORAN system was developed in WW2 and used until fairly recently for nautical navigation. It again works by using a series of fixed position transmitters, but in this case they come in paired units. Each member of the pairing is separated by a known distance, and they pulse out synchronized signals. The receiver compares the time difference in receiving the two pulses and from that difference you can plot a line of your relative distance from the two. Grab readings from an alternate pair to plot your location. The major advantage this system has over the other is range (~1500 miles) and being much less sensitive to LoS issues, though it is also somewhat less accurate. With the sensitivity and precision of modern electronics, it is conceivable that someone could build a 3+ point LORAN system and pinpoint their location pretty accurately off of one reading, the challenge being keeping the signals synchronized across the additional broadcast stations. Now the range and LOS issues are primarily a function of the frequencies that are used in broadcasting the signals. So you could theoretically implement a VOR system in the frequency bands used by LORAN and have better performance in that respect, but it will also change the timing and phase calculations for determining direction. These would be engineering problems and may impact how quickly and reliably you could find you position. (Way too long since I studies this stuff to remember that level of detail) Once the beacon network is established your coordinates become a range and bearing to a convenient beacon. "10 klicks from beacon XYZ bearing 175". Note, I would advise against trying to establish a GPS network around an asteroid. That system is dependent on known orbits & timing for the satellites, and I suspect it would be very difficult to maintain such with the irregular shape and weak gravity of an asteroid. [Answer] TL;DR: Two spikes, a ruler and a protractor There is no perfect solution, just as there is no perfect solution for Earth. Witness differing data (as plural of datum, in which a datum is the basis of a specific system of reference). Here is a document describing conversion between two equally acceptable systems of datum: <https://www.ngs.noaa.gov/CORS/Articles/WGS84NAD83.pdf> Here's a short snippet from that paper which goes to the heart of this difference: > > First of all, one should understand that the 3-D Cartesian frames to > which the coordinates of the NAD83 and WGS84 refer are not identical. > Their origin, axes orientation in space, and the unit of scale > differ. Why? Simply, because the definitions of these two frames are > based on different sets of observations, processing algorithms, and > perhaps, geodetic assumptions. > > > So there is no one right answer for difficult surfaces -- we can't even get it settled rigorously for our relatively simple surface here on Earth. We simply agree which set of imperfections to try to work around. YET there must still be many more wrong answers than right answers. Here's my **proposed less-wrong answer**, which is similar to many answers provided here, but perhaps more complete: Select a **north pole** and drive a real or imaginary spike into it. Select an arbitrary **prime meridien** and drive another spike in where that intersects your **chosen equator**. We are unlikely to have a handy set of facts to support definitions like "equidistant at all longitude", so a naturally defined equator may not be available. Likewise, if the thing does not rotate appreciably, or if that rotation is perturbed or wholly inconsistent with an intuitional model of where poles and an equator "should" be, we can still get by with nothing more than our two chosen points -- a north pole, and a 0-0 point (corresponding to 0-0 in the Gulf of Guinea, check it out). With these two points we can always measure two facts: * angle of rotation about the north pole from the prime meridien * distance from the north pole as the space crow flies These are not perfect, but can be agreed upon and figured by independent observers. Any radio distancing scheme could also be based upon these two points to yield the same two facts about position. This would also support map projection such as we are familiar with, including all of the existing shortcomings. [Answer] Assuming a sufficiently advanced society, what about artificial poles, magnetic or otherwise? [Answer] **A map with landmarks** The asteroid would be mapped out and photographed to generate a 3d model with landmarks Like a pirate's map, directions would be given from the nearest landmark. [Answer] Mobile network sensors. The OP clearly states that there are inhabitants. I'm going to make a leap of faith assuming that all the areas of interest have at least some inhabitant, or have had some visitor. Local linear embedding has been used to reconstruct global maps from pairwise local distances. All you need is to equip the locals with peer-to-peer devices, measure the ping time, and resolve the local linear embedding problem, et voila: the map is ready. Bonus points, as long as the inhabitants don't move simultaneously in the same direction or according to some linear transformation, you can recompute their position over time and map unexplored areas of the asteroid. Note that, as long as you can track changes in the pairwise distances between inhabitants, then you can define an "absolute" map, i.e. One where the thing you called North remains in the same place relative to the asteroid. Any new inhabitant's location can be easily located on the map again by local linear embedding, or by trilateration from existing inhabitants. References: <http://www.cs.toronto.edu/~fritz/absps/globalcoord.pdf> <http://www.pnas.org/content/early/2008/07/07/0709842104.abstract> Etc... [Answer] Assuming the asteroid is only inhabited by scientists exploring the asteroid, you could use 3D coordinates in some reference frame of the asteroid. This will work regardless of what shape it is, even if the shape changes. ]

[Question] [ Anybody who has consumed a space opera movie, tv show, or video games knows that energy weapons go **[pew-pew](https://www.youtube.com/watch?v=ss1nFJC197M)**. I however want to do something more creative for my setting, and with truth being stranger than fiction I thought to that reality might provide a better answer than anything that I could just make up. So I ask what sort of sounds would accompany the firing of an energy weapon? In particular weapons that produce energy/plasma bolts. The closest phenomenon to that classic space-opera trope is [ball lightning](https://en.wikipedia.org/wiki/Ball_lightning), so I imagine that they might sound a little thunder & lightning. The weapons that I plan on using in my setting are closest to being plasma weapons, that fire the space opera standard glowing blob of light. [Answer] In space, no-one (else) can really *hear* your weapon fire, unless their ship's sensors can detect the weapon firing (by its electromagnetic signature) and provide an artificial audible feedback. This could be anything from "Pew" or "Zap" or "crack" to "Energy weapons fire detected bearing...". In an atmosphere, the audible signature of the weapon depends on the power of the weapon. Where the power of an energy weapon is high enough to ionise the air it passes through, the cessation of the beam results in the low-pressure ionised path it carved in the atmosphere collapsing with a crack or a bang, the loudness increasing and the pitch decreasing with the diameter of the ionised path. [Dye-lasers](https://en.wikipedia.org/wiki/Dye_laser) in an atmosphere typically make a distinctive crack or bang with each pulse. The weapon itself may be entirely silent, or it may make a quiet, high-pitched whine similar to the charging capacitors in a camera flash. Indeed, many solid rod lasers are pumped using flash tubes, so this high-energy capacitor whine would be entirely in-character. It is possible that a weapon might whine quietly, the pitch increasing as charge accumulates, holding at a high pitch when full charge is reached and maintained, followed by a crack as the weapon is fired and a quiet, low, rising tone as the weapon charges again. [Answer] A laser weapon fired in the atmosphere will essentially create a crack of thunder as the beam heats the air in its path. The sudden expansion of the air will create a low pressure channel, which will be rapidly refilled (creating the thunder sound effect) when the beam no longer fills the channel. Since "real" laser weapons will most likely be pulse beam weapons to minimize atmospheric effects and to pack as much energy into a short a time frame as possible (to defeat enemy countermeasures and ensure that each strike on target delivers as much damage as possible), then strangely the effect of a military laser weapon firing will be somewhat like being downrange of a machine gun. Many years ago, a common training event was going to the "crack-thump" range. The trainees would be in protected space like a bunker or battle trench, and bursts of machine gun fire would be delivered overhead. The student would hear a "crack-thump" sound, with the "crack" being the bullet passing overhead, while the "thump" was the actual sound of the shot being fired. Since the bullet moves at supersonic velocity, the crack of the sonic boom arrives long before the sound of the shot, so by carefully listening, the distance to the enemy weapon can be estimated (the greater the separation between the crack and thump, the farther away the enemy weapon is). So there will be a "snapping" or "cracking" sound as the beam passes through the atmosphere, with the rate being determined by the pulse rate of the weapon (probably more than 100rounds per minute, but maybe not as fast as a mini gun, due to other considerations). The sound at the target will be determined by things like what the target material is, how the material is affected by the beam and even if the material is under stress (if it breaks because of the energy delivered by the beam, then you might get anything from a "twang" like a guitar string snapping to the shattering of ceramics). Spallation effects (bits of material tearing off from the far side of the impact) will also have a sound of its own and change the sound of the overall target (imagine beating on the outside of a metal garbage can and each time you hit it, the sides of the garbage can are thinner). The sounds at the weapon itself will vary, depending on "how" the laser is driven and used, but certainly there will be sounds from the generator, voltage and electrical handling systems (which convert electrical energy into the short impulses needed to drive solid state lasers), sounds from the optical train (the mirror's servomechanisms for pointing and tracking, and other sounds if it is an adaptive "rubber" mirror being flexed rapidly to overcome atmospheric activity), and most importantly, the sounds of the cooling system. Most lasers are horribly inefficient in converting electrical energy into laser light, so a 100Kw battle laser might have up to 20% efficiency and 5X that amount of energy being dissipated as waste heat. Even a Free Electron Laser (FEL) has a theoretical efficiency of @ 65%, so large radiators or heat sinks are a must. (*Edit: I somehow managed to get the efficiency and waste heat mixed up when writing the answer. corrected now*). [Answer] I pulled aside an old friend of mine who has a PhD in this stuff. He promptly explained that a laser this powerful will typically produce a phenomenon called [self-focusing](https://en.wikipedia.org/wiki/Self-focusing). ## Self-Focusing This is both good and bad. It's good because the intensity of the beam at the focus grows until something gets in the way and stops it. It's bad because the location of the focus is not easy to control. Typically, you get the focus only a short distance away from your optics. When you're trying to use a flashlight of doom against your foes, having a range of inches isn't desirable. ## Pulsed vs. Continuous High-powered lasers are always pulsed. You want to cram as much energy into the target in as small a time as possible. It also has the benefit of helping to bypass any countermeasures you may find. Pulse periods are short. Very, *very* short. Down around the dozens of [*femtoseconds*](https://encrypted.google.com/#q=femtosecond). Assuming you have adequate cooling and an ample supply of power, you can fire many hundreds of pulses per second. ## Theory vs. Practice In practice, your self-focus will be in the air, where it gets so hot that it turns a small volume of air to plasma. Plasma sounds like a great thing to have, but in photonics it's not. Plasma *loves* absorbing laser light - which it then radiates with a [blackbody curve](https://en.wikipedia.org/wiki/Black-body_radiation). The combination of blackbody radiation, and rapidly heated air does one thing - scatters and defocuses the beam. Your high-powered energy weapon has become a very expensive, very complicated torch. Each laser pulse will make a tiny explosion at the focus as it re-heats the air/plasma. Firing thousands of pulses per second will create a tone equal to the rate of pulses. If you're privileged enough to be at a university with a photonics laboratory, you can witness all of this yourself. <https://www.youtube.com/watch?v=_AfRc4gLwI8> <https://www.youtube.com/watch?v=jBjqT3AQkH0> [Answer] This topic was a favourite amongst "fellow Nerds" at Be'er Shiva University, in Israel, many years ago. It was agreed almost universally that a laser-type or maser-type "weapon" would produce an audible "Bang," like our contemporary projectile weapons. **A VERY audible "bang," by all estimates.** Admittedly the photon ***behaves*** as though it is "massless," but remember elementary Physics: **\*Photons/light behave as BOTH a wave**, **AND** **a particle.** Photons or microwave energy at sufficient amplitude to serve as a weapon would obliterate everything in the beam's path. At the literal "speed of light." The virtually-instant obliteration of all air molecules along the beam path would produce the same sound as a lightning bolt produces, passing between clouds or clouds and the ground: A really big "Bang." The impingement of the energy-beam upon the target would initiate the obliteration of the target's structure at the site of the impingement. As a so-called "weapon-grade" beam-weapon would have to produce very rapid vaporization of the material of the target for it to be effective, there would be a definite audible "signature" to the impingement: The "Bang" of destruction. This noise would be augmented by the out-rushing of ionized vapors consisting of partly-combusted elements of the target's construction or makeup at very high velocity--- at what amounts to an "explosive velocity." Liberation of gasses---ionized or not---from an explosion-site produces a "Bang." At the moment the beam broke through the "skin" or "armor" of the target there would be a very rapid in-rushing of super-heated ionized particles and associated vapors that would serve to flash-consume any atmosphere or vapors within the target as well as flash-ignite any combustible materials (plastics, fuels, explosives, flesh, etc.) within the target. This very rapid combustion of the contents of the target would constitute an "explosive event," resulting in a "Bang." When the beam is discontinued, the ambient atmosphere would rush back to occupy the void created by the annihilation of the atmosphere by the activation of the beam. Air rushing back into a void or area of extreme-low-pressure produces a "Bang." An energy-weapon would, evidently, produce an audible noise similar to an explosion ***At Every Phase Of Its Operation.*** In all practical respects, these "reports" would probably overlap a bit, unless the beam impinged upon a very, very hard---or thick---target, which had slowed down the penetration of the beam into the core. Then, there might be multiple distinct explosive noises: The first "Bang" would herald the firing of the weapon, and the second (or secondary) "Bang" would be the destruction of the target's contents. This would be much like the sequence of "reports" when a direct-fire artillery-piece is fired at a tank--- one report at the moment of discharge of the weapon, and a later report when the target was destroyed. There doesn't seem to be any way around the ***at least theoretical*** production of "gun-like discharge sounds" during the deployment of an energy weapon such as a very powerful laser or maser. [Answer] If the shot is supersonic and mass-less (laser or energy), then no sound would be made by the projectile. If the shot is supersonic and has mass, then the projectile will break the sound barrier at some point (likely immediately upon emission) and be deafening. Addendums: * The weapon may make a noise separate from the projectile (a reaction, explosion, or discharging battery). * The impact may cause a noise (super-heating flesh, rapidly melting metal, good old fashioned explosions). * Burning the air as the projectile (or laser) passes may cause a variety of effects, from nothing, to a slight sizzling noise, to an explosion, depending on how reactive the environment is. ]

[Question] [ We've all played fantasy RTS (real-time strategy) games, like WarCraft or DOTA, where you're in a battle and you need to spend gold to upgrade. Maybe you're buying troops or gear or whatever. But if the orcs are smashing down the walls of your castle, why do you need to pay 600 gold to train a footman? It's not like you're conscripting him to go off and die in some pointless war for magic crystals - you're conscripting him to go stop the orcs trying to ransack his home. The driver behind this is I'm making a game and the mechanics work quite well. But in flavor, the bad guys are beating down at the last bastion of hope for the good guys. Luckily, you'll come in and save the day. But it uses gold as a resource, and that just seems tacky to me. It works well enough, but I just can't see why gold matters so much! So, why should gold matter so much? And is there a drag and drop replacement I can use instead of gold? [Answer] From a world building perspective, consider what, in fiction, limits the size of your army and what it can do. Maybe your city, being under siege, is starving. Then 'Food' might be your resource - to keep warriors strong and fighting fit, you need to feed them. Otherwise their muscles will waste away and they'll be useless in a fight. But you're just fine for swords - your people will exceed their capacity to feed their soldiers before they run out of swords. Similarly you can use something more abstract - your people are on the ropes, so maybe 'Hope' is in short supply. You need to give your soldiers the hope that they can still win, so they have the strength to get up in the morning and face death rather than curl up and go quietly. To answer the posed question, gold is important to most armies because it's what limits the strength of the army: with gold, you can buy weapons, you can hire soldiers, you can pay for supplies. But when you're fighting for your very existence, then it's other things that limit you: it doesn't matter how many swords you have if you can't feed the arms to swing them, or give those arms the hope to inspire them. [Answer] **There is always a cost involved with each individual person (or unit) in an army regardless of the situation.** Most RTS games dramatically speed up and simplify certain aspects of army raising and management. No real life soldier is trained on a time scale of seconds. Equipment doesn’t craft itself. Ammo and food needs replenishment over time. All of these things combine into a total cost for that soldier over the time that he serves, and most games choose to consolidate it into one or two resources. Gold (or your equivalent currency) often makes the most sense since every component of the total cost described above can be bought or paid for. When the castle is surrounded and it’s life or death, those costs don’t disappear. Gold may seem to be less compelling, but that’s not necessarily the case. If a real society is placed in this circumstance, you don’t have everyone just throw down for the greater good. Some people might attempt to flee, no matter how unlikely success is. Some would want to be with their families in the end or die on their own terms. Some might still push for peace. When your army needs reinforcement to defend the walls, how are you going to incentivize the blacksmith to keep crafting gear? Who’s going to pay for the bread the new soldiers will need to eat? How will you convince the poor peasants to actually take this dangerous job? Gold is not worthless in this situation -- after all, everyone wants to live, in which case they can spend it. However, if gold still seems too far fetched to you, consider the alternative. Instead of incentivizing you must use the only other options you have available: fear and force. Your blacksmiths produce at spear point and the peasants either join the ranks or hang in the town square. Food for the army is simply requisitioned, leaving others less to eat. This behavior has consequences though, and might lead to serious unrest or revolt. So, in a sense, you can think of that as an alternative currency. If you’re not paying for a soldier with gold, you’re paying for them with the stability of whatever societal order you have left. [Answer] The short answer is that you're right; gold doesn't really matter in situations of life and death, but what the gold *represents* does. The study of economics is the study of production. Money (in this case as represented by gold) is really just a measuring stick; a way to consistently quantify the relative value of (say) a platter of sandwiches (20 gold) and a new car (20k gold). The last thing you want with orcs beating down your door is untrained, undisciplined 'soldiers' standing there on the other side of the door with a pike thrust in their hand and a photo of an orc waved in their face being told 'kill anything that comes through that looks like that'. Such a force can never hold. What you want is a 'trained and disciplined force', that knows how to follow orders, knows which end of the pike to use on the orc, what the enemy looks like and which doesn't lose its collective head in the face of danger. That takes time, training, materials (food for your army, smiths and armourers turning out weapons, etc. The army has to be fed; the armourers need to be fed; the metal for the pikes and armour has to be mined by people who need to be fed. That means that the farmers have to work their hearts out to feed all these people *before* the orcs get here. All that production is going to the common good of the city state but each person's relative contribution is measured through them being paid. Without money, there's no justification for a farmer producing more food than he or his family needs, beyond trading for other items he may need like ploughs. Smiths won't produce ploughs unless he can trade them for food, coal and the other things *he* needs. Who would bother with being a professional soldier if there's no living in it? Gold (or more generally money) gives any economy a way of determining the relative value of each person's contribution in a way that can be tweaked by the government. Got an orc invasion imminent? Recruit more soldiers by paying more. Smiths and metal ore go up in value and taxes have to rise. In times of relative peace, you disband the army so that the prosperity of the nation is poured back into civil asset production. Your soldier at the gate isn't being paid 600 Gold to stand there, it's costing your city state 600 Gold to train and support him in standing there, pretty much as AlexP states in his comment. [Answer] Indeed, it seems a bit stupid to have your castle being attacked and you, the all-mighty King, not being able to pick some commoners, train them and throw them into battle just because you don't have some coins with you atm. The training, weapons and food for those commoners *do* have some cost, though. It is not like you could make new swords out of thin air, and bread out of dirt (unless you actually could, but that is not the point). However, **nobody said that you have to pay that cost upfront**. I mean... You're under attack, ffs. Just fight and solve the damn situation, and we'll talk about costs and settle payments later. So what I'm saying is: **implement banks and a loan system**. Have your Kings be able to declare a *State of Siege* when under attack, which enables them to postpone payment of all war-related costs until after the battle is finished. Add some interest in there to make players think twice. You could even make the rates higher or lower depending on the player's victory/defeat ratio (a stronger, battle-winning King is more likely to get loans from banks than a King who is prone to have many losses), or some other kind of "trust factor". Don't overdo it, though, since that is not the point of your game, but it could be a nice feature. [Answer] My favorite example of something like this is from one of the best (IMO) turn-based strategy games of antiquity, [*Lords of the Realm*](http://store.steampowered.com/app/397350/Lords_of_the_Realm_II/) (specifically the second one, which had the smoothest mechanics). Some more modern games have implemented something similar, but I've never seen it totally duplicated for whatever reason. The game is a medieval kingdom-building game with economics, politics, trade, and of course, war. **When you raise an army you have two options: Draw from the local population, or hire mercenaries** (assuming any are nearby). Raising the army from the locals decreases your population by an equivalent amount, **which impacts your ability to staff resource-gathering or production roles**. **It also, depending on how many troops you raise versus the total population (and some other factors), affects morale**. Got 10k citizens and you want to raise a 1k-strong army? Not a big deal, as long as your population is already reasonably happy. Got 5k citizens and want to raise 1k troops? Get ready for some serious unrest, not to mention a huge hit to your economy. What's great about this system is how it adds a realistic complexity to your planning and response. You can have all the gold you want but it doesn't matter if your citizens hate you for conscripting half of their family. On the other hand, during a siege, they'll be much more willing to fight for their survival. You also have to consider equipment. **You can't just force-manufacture 1k swords, you have to have them already when you raise an army or else everyone will just be fighting with farming implements**. Also a freshly-raised army is going to be inexperienced no matter what, so unless you attach them to a veteran unit or experienced mercenaries, they're going to fight like the n00bs they are. # The bottom line: Raising troops doesn't need to require gold. It needs available manpower, and any equipment you want them to use, and it can impact happiness and productivity. [Answer] The combatants might need to import weapons, skilled labor or other resources from foreigners who demand payment in gold. This often happened historically. Another justification would be if gold is itself a raw material for magic or alchemy. If someone isn’t invested in winning at all costs, and the underdog is probably going to get defeated and wiped out, then asking them for cash payment in advance is just common sense: when they lose, they won’t be able to pay you back. You’re right that short-term profiteering off a life-or-death struggle doesn’t make a lot of sense. Compare the way the US traded with the Allies before 1917 to how it traded with them before December 7, 1941. It switched from Cash-and-Carry to Lend-Lease precisely because it wasn’t going to let Britain run out of supplies even if it had run out of gold to pay for them. The lore of these games does, you’re right, often ask us to believe that this battle is an all-important matter of life and death or that absolutely everyone has chosen a side and gone all-in. But if people aren’t willing to build stuff for the Good King’s army on credit, or just do whatever they can to save their own skins and let that be their reward, they don’t act as if they see it that way. [Answer] The answer to your question is that "gold" is just a game-mechanics that serves to limit a players recruiting, upgrading and other options. It is named "gold" because we are accustomed to a system where money is the center of economics, so it appeals to the familiar. You can use other restrictions, if you want. Many games use time as a restriction - there is no "gold" cost, but it simply takes time to train a soldier or build a house. There is also nothing wrong with thinking that in a desperate situation, other game mechanics can apply, for example to give both players the thrill of a desperate last-ditch defense attempt. I included such a game-mechanic into my old browser game BattleMaster, where a city under pressure can recruit citizen militia. Something you would not normally do (bad combat values, reduction of population, etc.) but in an emergency it might save the day. So if you as a game designer think that under specific circumstances, the normal rules should be replaced with other rules, go ahead, design it, test it and use it. [Answer] The other posts cover why gold is so important so I'm going to list some stuff about resources in RTS games. **Firstly** there is always more than 1 resource in a game. Your standard gold resource is just a much better representation of all the different components you would actually need, but there are usually support resources like wood/stone/metal which are used to help created Tiered units. E.g. you might be able to make a catapult with wood, but a Tank with metal. You will want to limit your self to about 3-4 resources for a RTS. Having too many resources usually results in a more complicated learning curve and is much harder to balance out the effectiveness of each resource. Less resources makes balancing the early and late unit/building tiers hard as there are very few resources to stop you from rushing to an overpowered tier. The one resource all RTS games have appears to be population. Basically a Unit cap and not really a resource. So this leaves you with 2-3 Resources you can have. This is when you can focus on replacing gold or making it more realistic. **Realism** Gold and support resources like wood/stone/metal. The gold has different meanings depending on what you build. For structures, it represents the labor cost, with wood/stone/metal representing the buildings materials. For Units, it represents the overall cost, with wood/stone cost for weapon/armor building, training equipment and so on. You don't need to use wood/stone/metal, you could replace it with magical powder, crystals, gas, the hearts of demons if you feel like it. **Fantasy** Replace your gold with a magical materials which can be gathered. For example Crystals. These could be used to magically create your units, or build their equipment/weapons which might work better with the feel you want. Of course you will want to throw in a 2nd or 3rd support resource for building advanced units. Maybe something like a Grimoire? or Gold as a support resource and not the main one. The Biggest issue is the resources need to be tied into the world you are building and have some importance or significance. You wouldn't use gold if your world uses gems as currency and they would use Crystals as a main resource if it was extremely rare and difficult to obtain. There is nothing wrong with being Tacky, many RTS games use a similar set of resources and this lends a sense of familiarity and allows you to focus on the more interesting and differentiating aspects like the Game play, Units and map design. [Answer] You are right, it is one of the areas which requires a suspension of disbelief. Civilization actually had a really nice alternative, the ability to draft units from cities. This was a unit which appeared and could be used immediately. It was a weaker unit, due to the lack of training. There was also a negative impact to the city, it varied between versions but essentially the loss of a population point and a period of unhappiness. I could see a similar mechanism working for an RTS, sacrifice a farm to get ten stick wielding peasants. The sacrifice would be great enough to make it a manoeuvre of last resort, mostly delaying the inevitable but may be useful against a zerg rush like situation. [Answer] What if your currency is instead a power source for a device that speeds up time to train them? Maybe the wizard performing this service can just teleport cross country and so he cares little about your town and is just there to make a fast buck. Then the only resources involved is whatever is actually needed to train someone such as food or metal for armor. Gold is merely the wizards charge. Naturally he has orc customers so he wont let you cheat. Plus it explains why metal and food dont matter. Part of the charge is for increased food production so really all you need is gold for the wizard and any people in the town who are especially greedy. Honestly though I agree that in a life or death situation charging like that for a service is a bad idea and if anything the blacksmith should be payed later after the battle ends. Especially if there isnt enough gold to pay them. [Answer] It's simply an abstraction. 600 gold to train a footman is meaningless. In reality you'll need food, equipment, and time to train a footman (plus people to turn from peasants into troops). Now you can abstract some of those away in the form of "gold buys food" and "gold buys equipment" so you only need gold and time - you've replaced all the complexity of a real world economy with something a lot simpler. Now it might be that time is also ignored for games like these, where players want instant gratification, but usually there is a time cost to training troops before they pop out the barracks. In cases like you describe, where you think you should be able to conscript all available force to the battle as partially-trained troops, its simply that the game doesn't cater for it. Troops here will not necessarily be individuals but units, if instead of "footman" the game had "light infantry" you'd get the idea, but they call the battle units by arbitrary names. As a result, you could assume that all available peasants were already involved in the battle and already catered for as part of the defending castle defences. So really that's all it is, making something complex into something simple as the focus of the game is not economic management but simple troop deployment and battle. If you want a more complex economic game, there are plenty out there that require you to build supply and production chains (and TBH they're a lot more fun than mine-train-bash games). [Answer] Money is crystallized sweat. Money is a way to represent previous hard work. But the conversion of money to goods can be fairly fast, but the conversion to skills or services takes time. This is a fundamental flaw in the game mechanics. I ran into this in an online game, Elvenar. To explore a province cost gold. But to go there didn't. To my thinking, the costs of mounting a defence or an expedition occur before the event. So your beseiged castle: * When you think that the enemy is coming for you you spend gold to recruit fit locals to come and fight for you. * You spend gold to pay the blacksmiths to beat plough shares back into swords (or billhook blades. * You spend gold to buy food to feed your new army. * You spend gold to clean out the water cisterns and get them topped up. * you spend gold to stock firewood to heat the oil caldrons. * Once they are at your gates, gold diminishes in value except for bribing the enemy to go away, or buying the secret entrance to the tunnel to the crypt. This is one thing that games don't do well: Things take time. E.g. If I send an expedition to explore a province, it would make more sense, as king, if I send out a given size force with instructions as to how to act in terms of fighting or negotiating. Presumably I've learned how the local Black Hats act by being an expedition force commander previously. Sometimes I never hear from them again. Sometimes they come back with a new treaty. Sometimes only one comes back, wounded. I may send them out with gold or with trade goods. They may come back with different goods, no gold, no horses....Anyway, I send the force out, but nothing happens days of game time, minutes of clock time. Meanwhile those soldiers are not available to mount my ramparts. The costs for mounting such a force should happen at the outset. You should already have a surplus of 50 horses for the trip. Of course to have 50 horses you've been buying or growing food for them. And for every 8 horses you have a stable lad that shovels manure, etc. He has to be paid, or at least clothed, housed and fed. If you don't have horses on hand, you have to buy them from a horse trader. If you have a habit of not buying from traders as they pass thorugh then traders don't come by very often. Anyway, your objection to gold in this context is well founded, but reveals a fundamental flaw in the game play: The lack of long term consequences of actions; the need to plan ahead. [Answer] Gold is money. Money is fungible. Resources other than gold can be exchanged for gold (or vice versa). So you don't actually need gold. You need: 1. Iron ore. 2. Other ore to mix with the iron to make alloys. 3. Coal to burn and smelt the ore into metal or to shape the metal. 4. Water/oil/whatever to quench the metal. 5. Stone to sharpen the weapons or round off the armor. 6. Leather and cloth to put under the armor, as metal chafes. 7. Labor to do the smelting, shaping, quenching, and sharpening or rounding. In addition to all that, the soldier previously supported a family. Now you have to do that. Now in your game, you are playing the lord (or mayor or whatever leader). The lord does not make each of these decisions directly. The lord delegates. When the lord delegates, the lord transfers resources to the delegee to handle things. For simplicity's sake, this is tracked as gold. Using gold as the single resource means that you don't have to spend all your time making decisions about things like building weapons or gathering food. You delegated those tasks. Too many weapons and not enough food? Your delegees trade resources until that works. Note that no matter how complex you make the system, with multiple resources, etc., it still won't match reality. In a real world, you would immediately have all the conscripts. There would be no way that you could add more (short of waiting for children to grow up). In reality, the time to collect and spend resources is long before the actual conflict. In reality, your decision is going to be more like the Civilization 5 game. You can have an individual working on food or participating in the military or doing scientific research or collecting scrap metal to make into weapons or armor. Except that it's worse. Some people are going to be useless at one or more of those tasks. Sending Ben the Blacksmith, who has a limp, out to collect scrap metal is not going to be nearly as effective as having him work in the smithy. It just takes too long for him to get around. And he has difficulty picking up things on the ground, as he can't squat down with his bad leg. For game purposes, we ignore such details. Not just money, but labor and materials are fungible. This has some basis in reality. One economist described the process of buying cars via international trade as planting car seeds in Iowa. In reality, these were corn seeds, which grew, were harvested, and shipped overseas for money. The money was then used to buy cars from Japan or South Korea. Similarly, you could have Ben making trade goods at his forge. You trade those to merchants for food and trade the food to local children who pick up scrap metal for you. This is very much like having Ben pick up scrap metal but more efficient. And again, we can measure this simply in the gold value of Ben's trade goods. In game terms, do you want to make each and every decision like that manually? Realize that most of the decisions are the same. Yes child, I'll give you food for scrap metal. Yes child, I'll give you food for scrap metal. Yes... And there are many decisions. Where'd you get the food? Also, what is food? Is it an apple? A pear? A loaf of bread? A wheel of cheese? So the decisions can be many, quite similar, and yet subtly different. [Answer] Because gold is the original form of currency, which is essential to trading. Gold was a valuable metal in pre-industrial times, because it is impervious to natural corrosion, and it is one of the first metals that a human could work with. It is also fairly easy to determine the purity of gold, with what was available to pre-industrial civilizations. The trader carries a flat black stone, called a touchstone, that they have made a mark on with gold of known good purity. When someone offers them something that looks like gold (might be fool's gold), they scratch it on the rock next to the known good gold mark, and look at the color. If the color matches, the gold is good. If it doesn't match, the gold being offered isn't actually gold. Early civilizations could quickly ascertain that what was said to be gold, actually was gold, without needing a modern laboratory. Gold marked the first move away from a pure barter society, where you traded what you had, for what you wanted... assuming you could find someone who wanted what you had, and had what you wanted, which could be fairly rare. With gold, you traded your goods for gold, and then you could use that gold to buy just about anything... without having to search for someone who wanted what you had to trade. The invention of currency and general acceptance of gold as currency marked a huge increase in early civilization's commerce. That is why gold is considered valuable in general, because most people think it's worth a lot. I would assume that in fantasy games, that same basic principle applies. If you're in need of chain mail, but the armorer isn't interested in that fancy potion you have, but the potion dealer down the street is, and is willing to pay you gold for it... you can take that gold to the armorer and get your chain mail. ]

[Question] [ **Scenario:** Deadly virus wiped out 80 - 90% world population and it did it pretty quickly (in 2 months) Although it is plausible that among these 10 - 20% of survivors will be people who actually know how to run nuclear power plant, it's safe to assume that they will have different tasks to solve now. Now, I did read several apocalypse scenario questions here. And it seems that it is wide consensus, that should the nuclear power plants remain unattended for longer period of time, they will simply overheat and cause major damage to their surroundings. I know that power plants are mainly run by computers. Also, the nuclear power plants have several backup power on and off-site to provide emergency power to help cool down. So, **In case of no natural disaster, will unattended nuclear power plant cause any damage to its surroundings?** Please try validate your claims by references. [Answer] # **No**, *probably*. Here's why: Nuclear power plants will be unlikely to go into a meltdown scenario in the event of operators' absence. After several days, most will shut themselves down if they have not received maintenance. However it is plausible that a lack of operators combined with some hitherto undiagnosed problem with the cooling cycle or systems could begin a series of events that lead to a meltdown. Nuclear power plants are already some of the most failure-redundant systems we have. Such events as mass strikes, earthquakes, power surges are all planned for as a matter of course. A properly-designed nuclear plant would be much less likely to explode without human contact than some other things in cities such as * Gas works * Coal/Gas power plants * Sewage treatment centers * Oil refineries Even if there is a runaway heating without humans present, there are several redundant cooling systems that can replace each other. Computers can dump the control rods if a large meltdown starts to occur, and even if the core burns though the container, it will be caught in a '[core-catcher](https://en.wikipedia.org/wiki/Core_catcher)'—a structure designed to stop radiation from escaping in the event of an accident. However, in the unlikely case that damage *does* occur, what can we expect? Well. A nuclear reactor will not go off like an atomic bomb, because the fuel is not in a pressure container. The most likely scenario is that a runaway reaction would cause the fuel to melt through the bottom of its container like a thermite charge, and drop onto the floor slowly sizzling away down into the concrete below. large fires would be set in the immediate vicinity by the intense heat, and localised explosions would throw radioactive debris around, which could be moved several hundred kilometers by the winds to affect a long but thin area with radioactivity. However, this would mostly be unnoticeable apart from in the nearest few km. # Source(s) * Book: *The world without us* ISBN-10: 0753513579 * <https://en.wikipedia.org/wiki/Core_catcher> [Answer] Short-term, it's probably safer if they *don't* shutdown. When the generator no longer produces electric power, the cooling of the residual nuclear reactions depends on power coming from the grid - if the grid is down, the cooling fails and when the backup generators run out of fuel, you may get a steam explosion. This doesn't necessarily mean a release of radiation, and it *definitely* doesn't mean a nuclear explosion (that's just popular pseudoscience - nuclear power plants simply can't "go nuke"). However, in your scenario, most people are already dead. That means that even for those places that will get affected by a radiation release, the remaining people are going to have plenty of space to live on. Don't forget that the more area you "poison", the lower the radioactivity at any given place - worst case scenario, the site of the plant itself and its nearby surroundings might be dangerous, but most land already has plenty of natural sources of radioactivity that are stronger. Just avoid possibly contaminated water (which may be tricky, since you need a lot of water to run a power plant, so they tend to be close to big-ish rivers), and you'll be mostly fine. Life is actually quite resistant to radioactivity - you may get an overall increase in occurence of cancer and similar issues for a while, but nothing too major. I mean, we're talking relatively to 80-90% people outright dying basically overnight - you should really concern yourself with *all the dead bodies everywhere*, rather than a bit of nuclear fallout, maybe. But let me stress again that there's *not* going to be a nuclear explosion. There will be very little to no *direct* damage to the surroundings. All we're talking about here is a (potential) release of radiation and radioactive substances. It's actually very hard to make a nuclear bomb - and nuclear power plant designers have pretty much the opposite design goals. [Answer] The short of it, **YES**. Both the radiation and poisonousness of the materials encased in these facilities will long survive their containers and especially the cooling systems. Today maintenance is a big cost factor sometimes requiring these facilities to shut-down for a while. If you dive into incidence records even so there are many many small problems per year. Left unattended either in a 'safe' state or not will make for a poisoned area later on always. I expect few real blow-ups. I expect all of them to poison both the immediate environment and pretty far downwind and downstream while the containment structure degrades much much faster than the important nuclear degradation times, both for power plants and weapon systems. Not to forget an entire ubiquitous industry carrying poisonous corrosive substances in truly BIG containers. Examples? Cooling system problems caused both Three Mile Island and Chernobyl. Achilles heel, as heat will keep coming and to stop it from building you need the facility in working order. Fukushima is another example of the bad stuff surviving where the structure goes down. (Luckily) no examples of long unattended facilities. Yet. Better carry a good, up-to-date map. References: <https://en.wikipedia.org/wiki/List_of_nuclear_power_accidents_by_country> <https://en.wikipedia.org/wiki/Three_Mile_Island_accident> <http://www.nei.org/master-document-folder/backgrounders/fact-sheets/chernobyl-accident-and-its-consequences> <https://en.wikipedia.org/wiki/Fukushima_Daiichi_nuclear_disaster> <https://en.wikipedia.org/wiki/Kyshtym_disaster> <http://www.forbes.com/sites/realspin/2014/02/27/the-dangerous-degradation-of-the-u-s-nuclear-arsenal/#3cc993be2104> [Answer] Short-term will be fine if the automatic shutdown systems work. The very long-term is more of a problem. The reactors will have the usual pre-reprocessing mix of fuel and toxic waste products, wrapped in zirconium tubes, inside a steel vessel filled with coolant (usually water), in a steel and concrete structure. All those materials are durable, but they are not *forever*. The weather always wins in the end, possibly hundreds of years in the future. And when it does things will start to leak slowly into the water table. This is why waste reprocessing plans include treatments like "vitrification": enclosing it in glass. Because it remains potentially dangerous for tens of thousands of years. The design of the [Waste Isolation Pilot Plant](https://en.wikipedia.org/wiki/Waste_Isolation_Pilot_Plant) is interesting here, especially their PDF on how to design warning signs to last a hundred centuries: <http://www.wipp.energy.gov/picsprog/articles/wipp%20exhibit%20message%20to%2012,000%20a_d.htm> [Answer] In short: **no**. EDIT 2: And the reason for this is how you phrase the question: "should the nuclear power plants remain unattended for longer period of time, they will simply overheat and **cause major damage to their surroundings**". That(!) — the boldfaced part — does not happen, even in the very unlikely case of meltdowns. Not even in the worst case scenario of Chernobyl did we see that. Chernobyl is currently an unintentional wildlife preserve. Nature and wildlife are doing just fine, save for one part, known as the "Red Forest" where the fallout was so heavy it actually killed the vegetation. That however is a shining exception to the rule. The **rest** of the area — and Fukushima even more so — remain undamaged. Then we can start to ponder what "damaged" actually means. "Damaged" as in "destroyed", "disfigured", "dysfunctional" or "disturbed"... no, that does not happen. But "damaged" as in "uninhabitable" or "economically unusable", that is different matter since humans are quick to abandon such areas. However even with that definition you are going to have much bigger problems elsewhere. Chemical plants, refineries, oil wells, waste facilities and waste dumps, and — which is particularly alarming — dams of all sorts.... [hydro power dams](http://www.nytimes.com/2016/01/11/world/middleeast/neglect-may-do-what-isis-didnt-breach-iraqi-dam.html?_r=0), [tailings dams](https://en.wikipedia.org/wiki/Tailings), [coal ash dams](https://en.wikipedia.org/wiki/Kingston_Fossil_Plant_coal_fly_ash_slurry_spill) and water regulation dams in particular. And the breakdown of clean water and sewage facilities is going to take a much higher toll on us. And this is still while assuming that catastrophic failures **do** happen at under-staffed/abandoned nuclear power plants... a scenario which I am about to explain why it is not very likely at all. The long answer: A nuclear power-plant can be shut down in seconds. Literally so. The issue then is [residual decay and the heat that creates](https://en.wikipedia.org/wiki/Decay_heat). And here is where it gets a bit curious and most people misunderstand. Used nuclear fuel is not in a steady state where it remains at the same, let us call it "danger level", all the time and then - after a set time - *click*, it is suddenly turned off and stops being dangerous. Anti-nuclear campaigners aside, this is not how it works. Spent nuclear fuel starts off at **insanely** dangerous when you have just closed the reactor, to "worrisome" within a week, "handle with care" within a year, to "let's wrap this up and put it away" within 50 years... and then the rest of the time is pretty much just us being unnecessarily paranoid. Spent nuclear fuel is like the embers of a recently extinguished campfire. At the beginning everything is crazy hot. But the hotter something is, the faster it cools off. So in the beginning, the activity of the fuel is intense. But the isotopes that cause this intense heat decay the fastest and therefore disappear quickly. The more time passes, only the less and less intense isotopes remain. A quote from Blade Runner captures the essence of this: *"The light that burns twice as bright burns half as long"* The critical time where you need to keep actively cooling the fuel elements — in order that the residual heat will not melt them — is about one week. After that you need to keep them soaked but they will not boil away the water. Within a month you can open up the reactor, take out the fuel elements and put them in [the storage pool](https://en.wikipedia.org/wiki/Spent_fuel_pool). Natural circulation is more than enough to keep the fuel elements nice and snug and safe to be around, as long as you top up the pool. Not because the water keeps them from melting but because [water is an excellent radiation shield](https://what-if.xkcd.com/29/). So with your scenario of 2 months until the apocalypse **and** 10-20% of the population remaning, nuclear power plants will have plenty of time to safe their fuel. If the worse comes to happen and some plants are left without the resources to safe them this thoroughly, they only need to keep the pumps going for a week, then leave it filled with water. The reactor pressure vessel and the containment will handle the rest. In the long run we are then left with sites of spent fuel elements in pools, dry storage on the surface or in reactor vessels. Does that present radiation hazards? Not really no. Sure there may be some local contamination from damaged fuel elements, but unless someone deliberately goes in there and starts lifting elements out of the pools and try to break them, the **fuel cladding**, the pools, the reactor vessels and containment buildings will keep the nasties — I-131, Cs-137 and Sr-90 in particular — inside. That is after all why they are there. Sure... the "Irradiated Wasteland" trope is very popular and an effective plot generator. But if you are going for "reality check" here, then it will not happen with your scenario. If you desperately want to use it, the downfall will have to be much faster. And — again — then your problems will be much larger elsewhere. EDIT: In a pre-Fukushima scenario, then the disaster scenario where nuclear plants blow up left and right **might** have been slightly credible. Post-Fukushima however it becomes outright nonsense. Not only has Fukushima set the baseline for what a nuclear plant must be able to handle — a sudden and catastrophic loss of both cooling and emergency cooling — but other measures to mitigate the damage done by a meltdown have also been put into effect. Two of them are especially noteworthy... * **Hydrogen re-combiners**. Noted already during the Three Mile Island accident, accumulation of hydrogen in the containment is a major issue. That may end up exploding, as it did(!) during both TMI and Fukushima. The solution to this is to install passive hydrogen re-combiners. These are catalyzers in the ceiling that makes hydrogen combine with oxygen — in a non-explosive manner — and become water again. * **Release filters/scrubber**s. The other issue identified by TMI was the need to be able to vent containments in a controlled manner. This is actually rather simple to achieve, using scrubber pools and stone filters, which can absorb up to 99.9% of the substances of most concern. Some counties had already after TMI started employing these countermeasures. Here is an example from Sweden, the Barsebäck Nuclear Power Plant. The cylindrical structure to the left of the two reactor blocks is [the release filter, known as FILTRA](http://www.ans.org/pubs/journals/nt/a_33639). [](https://i.stack.imgur.com/4g4qK.jpg) So — again — the issue will not be with nuclear power plants because they are, compared to the rest of our civilization, ridiculously well prepared for disaster compared to some other problem areas. A final note: as someone both invested in the debate on nuclear power **and** nuclear technology in fiction, I personally feel that it is long past due that we got over tripe such as The China Syndrome, or the TV series "24"... *"Eeep! Terrorists stole the McGuffin that controls all our nuclear power-plants and caused all 104 of them to start melting down, and we can't stop it unless we get the thingie back! Oh noes!! It happened in a few sites, and everyone around them are now **dead!!!"*** ...because this trope is as silly and unrealistic as to assume a light drizzle over New York causes the city to disappear under six feet of water within a few hours. Nuclear tech in fiction has been assigned magical properties of the blackest sort for the past 60 years, and it is time we got over it and stopped using nuclear as a lazy plot-generating device in apocalyptic/dystopian fiction. [Answer] **Yes, they will** The critical event is loss of electrical power. After this event, diesel generators will start up (hopefully! there were examples of failure ...) and an automatic shutdown will be performed. However: The ongoing nuclear decay in the fuel will demand further cooling. The diesel for the generators is limited (typically, for one day of operation). When the generators stop because of lack of fuel the nuclear power station will start to destroy itself. Fukushima is an example of exactly this scenario: Power outage, diesel generators destroyed by the tsunami, self-destruction of the nuclear power plants. The human operator teams present at the site weren't able to stop it, because they could not restore the cooling in time. [Answer] # Yes, the landscape is scattered with nuclear debris. Most nuclear power plant designs will fail spectacularly with long lasting effect on the surrounding area. ***The notion that nuclear reactors can run for extended periods of time without human intervention is simply not founded in reality***. Keeping a nuclear reaction from becoming ***[critical](https://en.wikipedia.org/wiki/Critical_mass)*** is a feat within itself. It's balancing act of maintaining a state that is less than critical. It will fail within a few months to a few years working under the assumption that it is not getting it's cooling water replenished which is entirely plausible. Most [nuclear power plants](https://en.wikipedia.org/wiki/List_of_nuclear_reactors#United_States) in the United States require are [light water reactors](https://en.wikipedia.org/wiki/Light-water_reactor) or [pressurized water reactors](https://en.wikipedia.org/wiki/Pressurized_water_reactor) and require the circulation of water in order to stay within a 'steady state' of operational limits. The two failure scenarios that come into play under an unattended state both involve overheating and a change of state to critical. Other incidents occur on the timeline to critical such as hydrogen explosions but these events are essentially ancillary and aren't central to root cause. # Background There are two types of nuclear reactors that can suffer from water related failure. * BWR - [Boiling Water Reactor](https://en.wikipedia.org/wiki/Boiling_water_reactor) * PWR - [Pressurized Water Reactor](https://en.wikipedia.org/wiki/Pressurized_water_reactor) **Failure Scenario - Lack of Water** Both water cooled reactor types suffer cataclysmic failure due to a lack of water. Some reactors can be more robust than others depending on the design. Many reactors derive their cooling water directly from their environment using ocean, lake or river water. These reactors are prone to having their water intake ducts clogged with debris thereby restricting the flow of cooling water to their segregated cooling systems. A lack of human intervention in these reactor types can lead to failure. Cooling towers are used with reactors that are not in close proximity to ocean, river and lake water. [Palo Verde Nuclear Power Plant](https://en.wikipedia.org/wiki/Palo_Verde_Nuclear_Generating_Station) in Arizona is one such example as was [Three Mile Island](https://en.wikipedia.org/wiki/Three_Mile_Island:_A_Nuclear_Crisis_in_Historical_Perspective). In the event of an overheating reactor in the United States the ***[Federal Government only requires a 30 day supply of cooling water](http://www.ucsusa.org/clean_energy/our-energy-choices/energy-and-water-use/water-energy-electricity-nuclear.html).*** This cooling water, called a UHS (Ultimate Heat Sink) is a finite source and dissipates over time due to a number of reasons including evaporation, steam release and lack of re-circulation of primary cooling circuits due to radiation (the water for cooling is used one time only, in some cases, due to the amount of radiation contamination of the water) As the water supply for cooling dwindles and water pressure decreases enough for flow rates to diminish beyond preset thresholds, the reactor undergoes an automatic shutdown called a [SCRAM](https://en.wikipedia.org/wiki/Scram). A SCRAM event does not require electricity. Neutron absorbing [control rods](https://en.wikipedia.org/wiki/Control_rod) are held in place by electromagnets above the fissile pile and upon loss of electricity the electromagnets lose their magnetism and the rods are dropped into place bringing fission to a near halt in the core. These systems are automated and do not require human intervention, however, the continued [decay heat](https://en.wikipedia.org/wiki/Decay_heat) of the fissile material continues to create issues with cooling and with a finite water supply, eventually, the reaction pile becomes exposed to air which cannot cool the fissile rods due to simple lack of density. At this point water changes it's state to a gas and becomes steam. The heat increases further and more steam and pressure buildup in the chamber. Water becomes superheated and takes on properties and attributes more akin to an organic solvent. The pressure is so high within the chamber that it eventually prevents the water from boiling. This [superheated water](https://en.wikipedia.org/wiki/Superheated_water)'s hydrogen bonds are eventually broken and the chamber becomes filled with superheated highly pressurized hydrogen which eventually explodes due to combustion or the failure of the [reactor pressure vessel](https://en.wikipedia.org/wiki/Reactor_pressure_vessel) to contain the extremely high pressures. This failure has been made famous by the [hydrogen explosion](https://www.youtube.com/watch?v=JMaEjEWL6PU&ebc=ANyPxKph6UUphWug4RTYsumv0wCh_XloJRss4UsMQZ2UdhEW5Mx3y5EVRe9YjBy_ztCTgDfKFoh5) at the [Fukushima Daiichi reactor containment vessels](https://en.wikipedia.org/wiki/Fukushima_Daiichi_nuclear_disaster) in Japan due to the tsunami which did not damage the reactors, it damaged generators that prevented the circulation of water for the cooling systems. The loss of integrity to the reaction chamber is the penultimate step to the catastrophe, all systems are essentially destroyed and now the fissile material can become molten and eventually melt through any concrete casements that require cooling features in order to prevent the molten nuclear pile from actually melting through it. Once this molten pile of nuclear material hit's moisture an explosion can occur sending nuclear debris into the atmosphere and contaminating the surround landscape with fallout. Mind you, this isn't a nuclear explosion it's just an explosion....but you see what the problem is here, it's called a [meltdown](http://http:/https://en.wikipedia.org/wiki/Nuclear_meltdown). **Conclusion** Water inlets that use water from the environment (rivers, lakes, oceans) for secondary cooling systems require regular maintenance to prevent debris from clogging their inlets. US located closed loop cooling reactors require only 30 days of backup cooling water. Manual events such as steam or pressure release to prevent containment vessel explosions won't be occurring. There are disaster prevention events that require human intervention. See this [IAEA root cause analysis document](http://www-pub.iaea.org/MTCD/Publications/PDF/TE-1756_web.pdf) and salivate over it's plethora of manual events and whether staff followed procedure and a logical decision tree before, during and after a disaster. I will close this scenario with, ***there's nuclear waste all over the place.*** **Other Failure Scenarios** There are hundreds of nuclear reactors across the world. [Educational and research reactors](https://en.wikipedia.org/wiki/Research_reactor) are sprinkled across the topography of nations. Some are mercury and graphite cooled. Others use molten salts and even molten sodium. Fast reactors requires considerable human intervention and are used primarily in naval ship propulsion and in some cases the production of electricity in Russia. There are a plethora of scenarios where these reactor types can go bad in their own [unique](http://40.media.tumblr.com/tumblr_lnpzrhkZzq1qfvq9bo1_1280.jpg) and beautiful ways. All in all in this scenario that I put forth is feared. There are many other failure points that I have failed to mention. The list is too long and nuanced. With the framework you have presented. [**Here is the official US Government Nuclear Reactor Regulation Response Plan to Pandemic**](http://pbadupws.nrc.gov/docs/ML0812/ML081210310.pdf) Notice the emphasis on staff and staff skills and manning the facility to prevent failure. With all the dead engineers it will be difficult to staff these facilities, chaos will ensue attempting to man the reactors as they slowly begin to fail one by one. So to answer your question again. # Yes, the landscape is scattered with nuclear debris. [Answer] Damage, yes. Major damage, no. We already have a perfect example of what will happen: Fukushima. That happened because the reactor was tripped and not getting any power to deal with the residual heat of the nuclear fuel. The computer should be able to keep things running until something goes outside acceptable operating parameters. (This will inevitably happen as the fuel gets too contaminated with decay products even if nothing actually breaks.) The first reactors to fail will be ok--they will continue to draw power from the grid for cooling. Eventually, however, too many will fail. One of the things that will cause a trip is the lack of two separate sources of power. As too many plants on the grid fail this will eventually cause a cascade that takes down every remaining nuclear plant. They'll fall back to local generators to keep the fuel cool--but eventually those run out of fuel. The rods boil their storage dry and you get a mess. In practice the failure will happen pretty quickly as many of the external sources of power they rely on are fossil fueled--and those will shut down pretty quickly due to a lack of fuel. All the safety improvements are based on buying enough time for the emergency crews to put things back together properly--if the emergency crews aren't coming they'll eventually fail. [Answer] Some misconceptions here. Most reactors would scram (automatic shutdown). But scram is not a fail safe. It's merely one safety measure. It's assumed humans step in and do the rest. The reason for this is time. It takes months if not years to bring a reactor that has been running back to a safe temperature. It's a full time management process, not a light bulb. That won't happen in a catastrophic situation so the core will start to heat up. Meltdown and breach of containment will occur within days followed by massive release of radiation. Some people talk about radiation like you can escape it being say 100kms away. No you can't. One reactor can spread deadly radiation over an enormous area. That's just one reactor! Seriously if people really knew how dangerous these things were there would be riots in the streets. [Answer] The containment will be breached within hours, not hundreds of years. The decay heat will melt through the containment like it's butter. The containment is designed to contain the core under circumstances where it's being cooled. Nothing can contain that heat without active cooling. It's laughable what is being suggested here. ]

[Question] [ Any spaceship over several hundred tons is an extremely dangerous weapon in the wrong hands, particularly if it's intended for reentry. Made mostly of metal and possibly shaped to be able to breach an atmosphere without trapping enough air and generating enough friction to destroy itself, it'd be at least dangerous as the worst asteroids that have hit the Earth were it sent plummeting into the surface at full burn. Not only that, but it may well be able to hold its own against an armed assault - it doesn't have to be functional or even in one piece to not destroy a town. Even if it is vaporized or broken up, coming straight down in a planned route, the fireball or resulting explosion would as devastating (if not more) than an atomic bomb. Clearly, any commercial space-faring civilization has the capacity for one lunatic to try and wipe out as many people as they can with their own death. How would a planet protect itself against such a malicious threat? [Answer] The answer to that is pretty much the same as "What prevents someone from deliberately flying an airliner full of passengers into a skyscraper?" today. It *has* happened. There may be safeguards and lots of them, but there is a possibility that they will be circumvented. Given that it is possible but unlikely that a deliberate collision could occur, the most obvious is that commercial spacecraft would be designed to simply not allow a planetary collision without overriding all sorts of things, at which point they would be designed to broadcast a warning (that the ship itself would be programmed to ignore) that the ship's safeguards had been overridden and it was on a planetary collision course. If you knew about that, you could override that too, but I don't expect that it would be made common knowledge. Planetary traffic control would constantly be checking that it had control (i.e. direct automated control, not just telling the human pilot "Do this") of nearby ships, and if any didn't acknowledge control (i.e. make the exact course change requested by traffic control computers), it would be flagged as out of control to planetary defense. If it was on a collision course, a warning would be issued - if there was time - otherwise it would simply be destroyed. Better a whole lot of small objects entering a planetary atmosphere than one large one. Even if it is full of passengers, it is better that they all die than an Extinction-Level-Event occur on the planet. [Answer] Short answer: have the author/GM deliberately design the world so that the threat isn't a serious one. Long answer: The devil is in the details. There are essentially three broad categories of safeguard available, the effectiveness of which vary heavily depending on exactly how your world is set up. Unless you tweak the parameters very carefully, they're all likely to have fairly major implications for what your world ends up looking like. For a lot of standard Sci-Fi worlds - ones with widespread public ownership of starships, FTL travel using highly efficient engines, effective energy shields, and significant technological capabilities available on the black market - the answer essentially boils down to "you can't". An incoming ship is too fast and too durable to stop in time, and the government doesn't have the ability to prevent a psychopath from taking full control of a ship in the first place. ## 1) Preventing psychopaths from gaining control of the ship in the first place. There are two halves to this, which would almost certainly be used in concert. First is making sure that they never get behind the helm of the ships at all. Starship pilot licenses could be heavily regulated, including mandatory psychological testing (probably at regular intervals). Similarly, the ownership and sale of all starships could be regulated, with all spacecraft either directly government-owned, or owned by people who have been thoroughly checked out and determined not to be a threat to public safety. Second is making sure that if a sick bastard does manage to get ahold of a ship, they can't crash it into anything valuable. Biometric scanners that only unlock the controls for authorized users are one possible tool. Other options are hard-wired safety systems that won't allow the ship to travel above a certain speed within a certain distance from planets, and remote overrides to allow traffic control to take command of any ship that enters their sphere of control. The effectiveness of these is strongly dependant on how good computer/electronic security is in your world - if criminals have the skills and resources to effectively hack and/or hotwire such systems, then other precautions will be necessary. ## 2) Intercepting the ship short of its target This one depends heavily on the performance characteristics of your ships and sensor networks. A successful response requires both that the defenders detect the incoming ship early enough to respond, and that they have assets in place that can intercept the ship once they do detect it. Orbital defense platforms are an option but might find it difficult to prevent debris showers from hitting the planet even if they destroy the ship. More likely this would need warships held on permanent alert (if the threat is serious enough, specially-designed interceptors would probably make up a significant fraction of the world's military forces). Long-range, high-resolution sensor equipment is essential here, and faster-than-light sensor capabilities are highly recommended. In particular, a ship traveling at close to or above light-speed is effectively *impossible* to intercept without FTL sensors - your first 'warning' arrives at the same time as the incoming ship. Effective long-range weaponry helps the defenders - without it, they need an actual physical interception with another ship, and that could be difficult. Effective ship defenses help the attacker, as does any mechanism (artificial gravity, force fields, inertial sumps...) that will prevent a ship from being physically deflected from its course by an outside force. High maximum speeds are more useful for the attacker: they increase damage potential, decrease the time the defenders have available to respond and make the ship a more difficult target to intercept. High ship acceleration rates favour the defender - or rather, low accelerations favour the attacker (as long as ship operation ranges are significantly higher than maximum sensor ranges). The attacker can spend as long as they like accelerating, while the defenders are scrambling to intercept a ship that is likely already at full speed. ## 3) Ensuring that there aren't any targets If neither of the above is feasible, the only remaining option is to ensure that there's nothing available that a suicide run can destroy. Burying everything below the surface of the planet is one option, but only works against relatively slow starships - at sufficiently high speeds, you just can't bury things deep *enough*. Otherwise, the remaining option is to abandon planets completely. Move everything vital onto self-propelled space stations, and keep them moving in a random pattern to prevent an attacker from being able to predict where they'll be accurately enough to hit them. [Answer] Apart from the comparison to the airliner scenario in Monty Wild’s answer, it might be worth checking out the safeguards we have against somebody launching a nuclear weapon into an inhabited area, since that would be comprably desastrous *and* has not happened for a long time. That is, if you can get reliable information about this at all. I think among the important points will be: * Have more than one sick bastard be required, i.e., spacecrafts are designed such that steering them requires more than one human *by design.* (Moreover to avoid people planning to collaborate on this, assign people to missions randomly and never let people work together who know each other.) * Take maximum action long before any imminent danger. In case of a spaceship, do not only intiate a preinstalled self-destruct or similar when the ship *is* on a collision course and short before coliding, but when it takes the first steps to do so, i.e., deactivating the autopilot within a certain distance to earth, taking a collision course while being lightyears away or even entering the solar system with a large ship (which may be unfeasible though). Clearly forbid doing anything like this, so that nobody can complain about being blown into pieces. * Inherently delay all actions taken to create time for countermeasures. [Answer] The solution is have the spacecraft are flown by Artificial intelligence- it could even be a cooperative or a background operation where people appear to fly them but its simply impossible to actively crash the spacecraft to cause mass-damage. Most of our spacecraft are quite automated however the abilities of AI now are not utilised to their limits. A combination of expert system and 3D control and analytics program. The speeds of spacecraft are insane- humans would find it difficult to manage directly anyway. Pilots of aircraft can only manage their planes to avoid collision by having designated separations- only really possible in sonic and subsonic speeds. Control gets more and more difficult the faster you go. [Answer] Not a complete solution, but hiding entire planets could be a mitigating strategy. Imagine aliens greeting us tomorrow with the polite version of "here's what we consider our territory, here are the acceptable means of trade and communication, and any attempts of locating our home planet whithin that territory would be considered an act of war. No offence intended, it's just that your society occasionally produces murderous psycopaths, so it would be dangerous if you knew it" Many common faster-than-light-travel tropes, e.g. warp drives and wormholes, have the ship just dissappear from normal space than re-appear at the destination, either instantly or some time later. It's not much of a stretch to make it hard to track, especially if you do without the traditional special effect of having the ship sharply accelerate in a particular direction just before dissappearing. As for the radio bubble, it only travels at light-speed, and would not exist for planets settled after more effective communications are discovered, may be only a thin shell for other planets. It's not the be-all and end-all of planetary security, but it would be a nice addition if no definite solution is available. [Answer] I think some kind of active countermeasure would be used - missiles armed with advanced expanding foam canisters that adhere to the ship and expand into something like the Mars lander 'air bags' (it wouldn't prevent the impact, just mitigate it). Similarly other missiles could attach directly to the hull and deploy wind breakers to slow the ship down. Such crash landing systems may be built into the ship itself and activated by the navigation computer in the event of a collision being imminent, the firing of retro thrusters would also be a standard countermeasure. Edit: High speed automated drones could attach to the hull and fire their own thrusters to slow/redirect the ship to a less populated area. [Answer] Like the roman army always kept at a safe distance to the Capital Rome behind the river Rubicon (if my memory serves). And violation to that rule considered active treason without further investigation. Establish a perimeter that no trespasser allowed inside that zone (friend or foe or any celestial body) by destroying them by any means possible. Yes you may start interstellar war by destroying a massive alien ship just came by to say hi. But it's a part of the deal. [Answer] The most effective way would be to have no such dangerous spaceships. Either have no spaceships that are dangerous, or have many design features on the spaceships, and safeguards and precautions such that it would take a lot for someone to use a spaceship as a missile. Another very good countermeasure would be to have a very healthy society, which detects and heals psychopaths very readily. This would also have many other great benefits, and is a great idea overall. Another good countermeasure is to have and require entire crews of healthy people to control a ship. Another is to have technological countermeasures that can detect, divert, disable or destroy such a ship. Depending on the technology available, this might or might not be difficult. [Answer] In hard science fiction, interstellar travel is on the order of a type 2 civilization. And even then, you are sending star wisps, who self-manufacture a civilization at the target, not people. If you have a planet-bound civilization with a few billion people, heat dissipation limits the energy budget of the land-locked to only a few orders of magnitude higher than our current energy requirements. "Cheap" interplanetary travel requires a lot more energy than that. So for a mostly planet-bound civilization, only the rich can travel from planet to planet. Non-planet based civilization are either slow moving and self-contained, or energy-rich like the inter-planetary civilizations (able to import goods from the bottom of the gravity well, be it whatever). While a ship may move extremely fast, it won't change course extremely fast. So your best bet in such a civilization would be to thrust as far as you can outside the solar system, then adjust course on the way back to hit a target (coming in a high velocity). This won't be cheap energy-budget wise. This all assumes we are still mostly flesh and bone. If we have uploaded, the physical world could be beyond most of our permission levels. The few interacting with it and controlling high KE spaceships would be heavily audited for safety. If we go soft sci-fi and start adding near-light sub-light drives that accelerate at 100s of Gs, such a ship very quickly starts having the energy budget equivalent of a Type 1 or 2 civilization all by itself. Living on a planet when you have Type 1/2 civilization energy budgets owned by a few people (a ship) seems relatively ridiculous: the heat dissipation problems alone will make anyone in the planet's atmosphere a pauper. If we add in warp drive/jump drive and shields and the like, the game changes. One of the reasons why you cannot defend against weapons in a high energy civilization is that chemical bonds are already relatively weak compared to the energy budget of our weapons: shields can change that rule. You could just shield the planet. The energy budget of a single ship would be dwarfed by a sufficiently advanced soft sci-fi planet's energy budget of non-paupers (the heat problem handled by more hand-wavium, like really tall and hot "shield-material" radiators). The ship would bounce off mostly harmlessly. If shields don't exist, then a ridiculously huge perimeter defence that knocks incoming attacks off course could work, that perimeter getting larger as civilization energy budgets climb (as they also have to defend against relativistic KE attacks from other civilizations, or large parts of their own). Within the perimeter, you are not allowed unless you are run by the planet's trusted "ferry boat"ers. To visit Earth, please park at 3 light years at one of the designated docking stations, and get on board a locally controlled "ferry boat". Finally, there is no guarantee that any of this would work. For the longest time, attacks were balanced against armor. In the nuclear age, there are no defensive materials that can stand up to a thermonuclear bomb. We don't have weapons that can intercept an ICBM effectively (even a nuclear interceptor). Such a situation could exist. In that case, you'd no more give a private individual a spaceship than today someone is allowed to run a nuclear reactor in their back shed and have hobby h-bomb in the basement. [Answer] By the time such advanced technology is available, I would think all sorts of other advanced tech is around to deal with these issues. Especially since essentially these spaceships behave like asteroids, which we're trying to deal with as is. First thing that comes to mind from most sci-fi worlds is using a shield. Especially the kind as used on Dune, where the shield blocks fast moving objects. If you surround a planet with such a shield, any kind of suicide run would end with the ship smashing into the planetary shield if it comes in too fast, but regular landing ships can come in regardless. Slower ships that try to accelerate inside the shields would deal considerably less damage or might even be shot to scrap before they manage to speed up if detected. [Answer] A partial solution: Multiple types of ships. The big starships that could produce an extinction event are not allowed within a considerable range of a planet--say, a light-hour or even more. Furthermore, anything that's going to bust that zone in the next 24 hours is promptly destroyed. The defense missiles are large kinetic impactors--most of the plasma produced won't hit the planet at all. Interstellar traffic arrives at a station in the outer part of the star system. Traffic then transfers to shuttles that take it to the general vicinity of the planet where it is transferred yet again to smaller, lower performance craft for the final approach. The basic idea is to keep everything far enough away that the system defenses can take it out if need be. Alternately, use warp drives for your starships--you move space, not the ship. It doesn't need a drive capable of planet-killing speeds. [Answer] **Send up a rag tag team of NASA funded deep sea drillers** Cue Aerosmith. A team of highly trained and equally psychotic unlikely heroes are sent up in a pair of space shuttles to drill a hole into the hull of the spaceship and deposit a nuclear warhead under the armor plating. Hilarity ensues. [Answer] I'm not sure that stopping the ship would be that difficult (depending on total size) - consider the Columbia disaster. Getting a spacecraft to *survive* re-entry is very difficult, so hitting it with a reasonable-sized missile is going to cause very serious problems for the craft. With a large ship there will likely still be bits that reach the surface, but much smaller and with very little accuracy. As long as it's detected at long range and hit well before it begins re-entry, the casualties should be fairly light. [Answer] Automate ships. Just like we have autonomonous cars nowadays, all spaceships should be autonomous. You tell them where to go, and they will maneuver there on their own. This is the most ideal way to do thins anyway, since a computer is much better at figuring out the best paths and times to accelerate in order to get the most delta-v out of your fuel. Also ensure that ships follow the three laws of robotics. If anyone tries to fly a ship that allows direct human control - brand them as terrorists and blow them out of the skies. This way, all your psycho can do is ask the ship - nicely - to go to some town or city, and the ship will go there and land gently. If they do want to blow something on the planet with the ship, they will need to hack into the planet's transport infrastructure in the first place. Given a sci-fi scenario, if they are able to do that, they are able to do much worse stuff (i.e.: remotely comandeering nukes), so a rogue ship would be the lesser of your worries. [Answer] Usual formula to prevent ships from escaping (wich can hold true in the scenario proposed) is to use a tractor beam to stop the ship mid-space and force it to dock into another ship. [Answer] For objects the diameter of what we usually conceive as a spaceship (say, something the size of an aircraft carrier, end on) above about 100-1000 km/s very little of its energy will transfer either to the atmosphere or the crust unless it breaks up or spreads out in some way. This can be understood in terms of the Bragg curve for absorbing energy from heavy ions. A possible mitigation is to enclose the ship in a shield or design them not to break up. A strategy for the terrorist is to strike a glancing blow rather than straight down, to maximize energy transfer and breakup. Even at .9c, the Lorentz gamma is only 2.3 (<http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/ltrans.html> will calculate them for you). The classical KE is 9x9=81 times greater x 2.3 = 186 times the energy of .1 c. Or about 200 million times the energy of the actual Pioneer 10. This is still not enough unless the spacecraft is way more than 500 kg, which of course I assume. The problem is capturing the energy. I work in the field of radiation effects of high energy particles in semiconductors. Most high energy particles have very little to no effect. You have to slow them down so that they are basically stopping in the thin layer of silicon to capture much energy. This is called the Bragg peak, and you can google it. So the earth and its atmosphere are like that. The atmosphere will catch and stop ordinary meteoroids. Their energy winds up as a bit of heat and light and a sonic boom. It can be destructive near the ground as in Tunguska. The dinosaur event was captured in the crust because its size and frontal area were such that it stopped there, maximizing destruction on the surface of the earth, throwing up debris, etc. A faster asteroid of the same size would possibly destabilize the earth by interacting with the core. But in this case, the spaceship is far smaller. We just have it going very fast. So it is not going to transfer much energy to the atmosphere. Its time there is too short. You won't "see" it streaking across the sky, it is moving ten thousand times faster than a typical meteor. It'll just punch a hole about its own size in the crust and deposit its energy gradually along its track through the interior of the planet. It will deposit most of its energy right at the end as it stops, just like the heavy ions produced by cyclotrons. If it stops in the core, or anywhere very deep, we'll register a few seismic waves and that's about it. So I take back what I said about it automatically being an extinction event. It might not even be possible to achieve with "ordinary" size spacecraft because at worst they'd just make an ugly explosion as they rip out the other side. If going fast enough, they'd make a clean hole on both sides and impart relatively little of their energy to the earth, even though their energy is enormous. The hole would fill up with magma which would cool, and unless the crust is already thin there with magma close to the surface, it would not give any trouble. It would take a large diameter starship or a very clever terrorist. Now, there is some rationale for very large starships, essentially hollowed out asteroids or minor planetoids. These would shield occupants from cosmic rays and any debris they encountered, which will be a serious problem otherwise. Once you are effectively using stars to accelerate the things, it matters little if it is a couple orders of magnitude bigger than the kinds of ships we sail on the ocean. In fact in the 1960s DOD had a plan to send a nuke-propelled town sitting on bedrock on a planetary tour, so ships that size have already been conceived and we have the physics to propel them if we are willing to use it. If such a thing hit the earth at a relativistic speed, it would be catastrophic. Perhaps not of the order of the event that created the moon, because a town is still not so large, but it'd make a very big hole in the crust and almost certainly knock the planet off its axis. --- Here is an unrelated analysis inspired by Scott Downey's post "I think some kind of active countermeasure would be used ..." I would have commented, but apparently being a new member I have not the privilege. This has been looked at for asteroid defense, and you can google that subject. Just blowing up an object still leaves a debris cloud proceeding along approximately the same trajectory, which can be a great deal more dangerous in this case because it spreads the energy over a larger area, helping it to stop (like the Bragg curve) in the crust or atmosphere and do the most damage. Generally, explosions (despite the movie) are the least favored asteroid defense. You have to deflect the thing, preferably without breaking it up into scattershot. Since asteroids are relatively slow, you can do things like fly along beside it and use the spacecraft's gravity to nudge it off course. Using an array of mirrors to focus sunlight and create a little thrust stream of vaporized material to deflect it has also been proposed. For a faster spaceship, a much more energetic version of either of these would be needed, such as a tractor beam to drag it quickly off course, or fusion lasers to create the surface vapors, but being careful not to break it into pieces. So, I guess you guys can fashion a pretty wide variety of conditions and related stories by re-sizing the ship. I look forward to reading them! [Answer] Harpoon parachute missiles. It's a harpoon with an explosive hook. On impact, the harpoon uses the explosive to permanently weld into the skin of the aircraft - the same explosion deploys a parachute. Then quantity. Have fully automatic harpoon launchers and simply have fighter jets assault a large aircraft with these harpoons parachutes. After several thousand, there should be enough parachutes that gunfire could not mitigate the drag of a million mini parachutes. ]

[Question] [ Suppose we have a civilisation which is made up of many creatures sharing a single hive mind. Each creature can see, hear and remember what each other member of the species (or possibly hive) has seen heard and experienced, they think and make decisions as one. Range limits are acceptable. They are not using magic, this is a purely biological trait, it's also safe to assume there are no physical nerves between each member of the collective. Could a species evolve this way, if so how would the mechanism work? [Answer] **The Problem:** Telepathy is defined as "Transfer of information on thoughts or feelings between individuals by means other than the five classical senses". That leaves some form of communication not detectable by human senses, though not necessarily some form of communication not detectable by human technology. The question also specifies *evolution* of such an ability, so this would imply that it is of biological, not technological origin. Since such tropes as "psionic radiation" or "mental waves" that can be transmitted from one human to another have been not been shown to be anything more than fairy tales by science, we cannot presuppose that they exist for another species. **Possibilities** However, this leaves quite a large range of possibilities for communication that is not detectable by human senses. The electromagnetic spectrum covers a wide range of frequencies, most of which (with the notable exception of the visual spectrum) is not detectable by human senses. Detectable by human instruments, perhaps (I'll discuss that "perhaps" later), but detection by human instruments isn't the definition. There is also the possibility of sonic communication using frequencies not audible to humans, manipulation of magnetic fields, and emission of pheromones not detectable by human olfaction. So, there are possibilities for "undetectable" communication. **Process of Elimination** If a species is to communicate memories, thoughts and sensory data at a rate that allows them to think and make decisions in a corporate manner, then whatever form of communication they use is going to require a very high bandwidth. This means that whatever form of communication they use is going to have to be high frequency, as studies in data transmission have shown that the higher the frequency of the carrier, the more data it is able to encode per unit time. This then immediately eliminates pheromones (which are inherently slow) and low frequency sound. There are still a lot of possibilities remaining. Another characteristic of Telepathy is that it is long ranged. When we consider sonic communication, we find that low frequency sounds travel much further than high frequencies, however we have ruled out low frequency sound as having too low a bandwidth, so this effectively rules out sound almost entirely. When we examine the electromagnetic spectrum, we find that the highest frequencies (above the ultraviolet end of the visible spectrum) are blocked by an atmosphere similar to our own (but they may not be in another atmosphere), as is most of the infrared part of the spectrum, and some (but by no means all) of the frequencies in the infrared and microwave parts of the spectrum. Lower frequency microwaves and higher frequency radio waves are long-ranged in a terrestrial-type atmosphere, though long-wave radio is not. So, the best candidate for high speed data transmission is microwave radiation. This leaves the question of how a life-form might go about generating such radiation. The following is educated speculation. **Evolutionary Prerequisites** The highest likelihood for "telepathy" is in a species that is able to precipitate a variety of metals in a variety of forms. (This also requires an environment high in metals.) If such a species was using metal to enhance its neural transmission rates (electrical transmission is vastly faster than human nerves' sodium-gate depolarization system), which is in itself a highly advantageous strategy in evolutionary terms, it is likely that creatures using metal as a nerve conduction rate booster would have found that unshielded nerves would cause radiation detectable not only within a creature's own body, but in other creatures too. As faster nerve conduction is too great an advantage to give up, shielding would have evolved, most likely by running nerves through the centers of metal bones. However, the possibilities of transmission and detection of EM radiation means that not all metal nerves would have evolved to be completely shielded, some could be partially shielded and be used to detect EM radiation, while with higher voltages (as demonstrated by the electric eel), other neuron-evolved organs could generate EM radiation of reasonable power. **Bandwidth** We then get to the point of bandwidth. EM radiation emission may well have begun at lower radio frequencies, but it is entirely possible that mechanisms could have evolved to increase the frequency of emitted radiation. Since a system of this type could have practically each neuron driving an EM transmitter of a different frequency, high bandwidth can be achieved by rapid changes in signal amplitude and frequency that is allowed by using high-frequency EM radiation, and also by multiplexing - using many frequencies simultaneously. This could allow an evolved bandwidth many times greater than our own Wi-Fi communication, which would also be somewhat directional. Another argument for higher radio frequencies and microwaves is that smaller antennas are required. Since all this bandwidth is relatively easily achieved in evolutionary terms - simply by duplicating the relevant organs - there is no reason why the beings would not evolve to make use of this bandwidth. Since the highest intelligences of species on earth are found in those creatures with an active social life (and this ability makes for a great social life), the evolution of intelligence is pretty much a given. **Bandwidth comparison** If we consider the data bandwidth of the human voice (not the bitrate required to duplicate the sounds accurately, but the actual volume of data it conveys), humans may be able to achieve a data rate of perhaps a few hundred bytes per second at most, including the emotional sideband on top of the raw data. Our hypothetical telepathic aliens could achieve a data bandwidth in the order of tens to hundreds of megabytes per second. Our telepathic aliens would need very fast brains to process all of this data, but fortunately since they incorporate metal in their neural structures, this is somewhat easier to achieve. The main bottleneck would be chemical neurotransmitters - if they used them. Fortunately, there are other possibilities for cell-to-cell communication. One possibility is an electrical connection, the other is a mechanical connection. Either of these are equally possible, and neither provides particular advantages over the other. **Effects** Given all this data bandwidth and a brain capable of processing it, it is entirely possible that each of these beings could communicate highly detailed messages - certainly including thoughts, memories, queries and answers - with a number of its fellows. Considering that much of their brains would be involved in running and interpreting the "telepathic" communication, they may not have all that much capacity remaining for actual original thought, so on an individual basis they may not be much more intelligent than a human, quite possibly somewhat less so, however they do not really need to be any more intelligent on an individual basis given that when they have a problem that they need to solve and cannot do so on their own in a reasonable time, all they have to do is ask a few friends and share the load of considering all the options. Considering the range of microwave communication, these friends need not even be within visible range, they could be hundreds of kilometers away. Sharing of memories would happen almost automatically as individuals added them as context to the problems they are asking for help with, and the advantage of shared experiences cannot be underestimated. **Detectability** As for detectability by human technology, an evolved pattern of communication over multiplexed amplitude *and* frequency modulated radio and microwave bands could certainly be *detected*, but it would most likely be fantastically difficult to *interpret*, and to the uneducated and unsuspecting observer (who is most likely detecting "interference" on only one frequency at a time) would find it hard to distinguish from noise. Anyone ever actually listened to a 56k modem on their phone line? It sounds a lot like static. It would require extensive computer support and years of work to even begin to interpret communication like this. **Social Organization** Since higher frequency microwaves (that can carry more data) are attenuated by the atmosphere more than lower frequency emissions, these beings would be able to communicate faster with nearer compatriots than more distant ones, and this would give them the tendency to form regionally-restricted social groups rather than a single global society. **Appearance** As to what these beings may look like, I imagine them with mobile structures that would look a little like short, thick tentacles that house the microwave transmitters and receivers. They would also be very likely to have inhumanly fast reaction times given the speed of their nerves that is necessary for their mode of communication. They would most likely be able to see some frequency of visible light and be able to hear, but the limits of their vocal communication - if they were capable of that at all - may be some sort of sound that communicates little more than a threat, warning or submission to other species that do not share their mode of communication. I leave the rest to your imaginations. [Answer] I'm sure this won't be as hard science as one might be expecting but the questions certainly made me think. Of course the first order of business would be some form of what we currently call telepathy. At first blush this seems truly of the science fiction realm. However, we have electronic equipment that can talk to each other with energy waves. Though it is also true that humans do the same thing, we just use sound waves instead of electromagnetic waves. Currently telepathy is a kind of magic where thoughts in one head are transferred to another. We do that all the time with the slow analogue transfer of verbal communication which isn't error proof. ## Current Science There are studies of [reading brain activity](http://www.scientificamerican.com/article/mind-reading-technology-speeds-ahead/) with head sensors for a whole host of different tasks, from making bionic limbs for amputees, to game interactivity. There have already been privacy concerns for different brain reading technologies. They are each having different levels of success. I also found they are working with different technology to [Hack the brain](https://www.yahoo.com/tech/brain-hacking-is-having-incredible-effects-and-its-94844111639.html), the study was finding ways to help people learn faster and improve cognition. Now once we have computers that can read and write to the brain coupled with wireless technology we might become 'telepathic' in a couple decades. ## Hive Mind I would think communicating with a very high bandwidth would be the primary goal of 'hive mind telepathy'. So for a hive mind, all the members are going to be 'broadcasting' all the time, so there would be a low 'hum' at all times (like a beehive) and any could 'channel surf' through the different channels. As such each individual would be able to repeat or rebroadcast what they are seeing from someone else etc. For this to be a biological solution, some kind of data rich em wave would have to be generated. The biggest difference between speech and telepathy is the volume and accuracy of the data being transferred between individuals. [Answer] Additional to bowlturner Answer: **Pheromones and hormones could establish a Hive mind communication.** When you build up some feelings your mind sets your body in the mood by giving hormones your the blood, so the Organs know "now is feelings time!" and stop with their normal work. When your Body is the "Hive" with the Organs as the slaves to that "Hive" you could easily see the Hormones as one kind of communication beside the nerve system. The Wikipedia [article](http://en.wikipedia.org/wiki/Ant#Communication) for ants says: > > Ants communicate with each other using pheromones, sounds, and touch. > > > Your creatures could all send the pheromones over their lungs to the atmosphere. Only creatures not on a connected location or in range would be separated from the mind. **Special Organs that are sensitive to highly swinging sound levels** Additional to the answer with the hormones, if you don't like to put Hormones in your atmosphere. Let them develop a internal organ that works like an ear but in higher frequencies. The organ gives than the hormones to the body and also amplify the sound it becomes to it surroundings. So in the middle of a crowd you would have much more hormones than in your home but still enough to be connected to other creatures. ALSO this version of Hive mind could be broadcast by sound systems. Example for "Organs" that make Hive minds possible by the [Borg](http://en.wikipedia.org/wiki/Borg_%28Star_Trek%29#Borg_Collective) > > The collective is broadcast over a subspace domain similar to that used by the transporter. > > > In one Particular episode of Voyager you can see Seven of nines Brain, and the subspace device the hive mind uses. [Answer] Information is encoded in the connections between neurons. It can also be encoded in alternative ways, as a sort of floppy disk or pendrive, like proteine chains. Suppose that a species has the ability of encoding an individual's brain info into proteine chains, and decoding received proteine chains into neuronal connections. In this way, physical contact between individuals can transfer any information between them, effectively making them share all experiences and knowledge. In this way, an isolated individual has all the knowledge of the last time it was at the hive or contacted such another individual, but not any info after that. Transfer is not instantaneous like telephaty, and then if one of these individuals finds a soldiers outpost and is killed by the space marines or whatever, the colony (the hive) will not have the information. This makes the point for the characters to kill every species individual that can have seen or heard them. This knowledge sharing mechanism does not implicate any intelligence. Information is simply shared, and it may be the amount of shared knowledge what makes sense of each knowledge piece, or the summed up intelligence of each tiny individual, or some sort of queen or braineds subspecie. [Answer] To answer your question, we need to find a way or ways for individuals to quickly and accurately share information. In insect species we see several means of communication. Dancing/movements: bees communicate with one another through intricate movements. Since you will likely want to communicate more detailed information quicker than bees do, you could have specialized appendages that signal other creatures at the speed of light. You could skip the middleman and just have creatures that can emit specific wavelengths of light that they can precisely see and understand. This would travel at the speed of light but break on line of sight. You can alternatively use sound. To communicate so much information your creatures would probably emit a constantly modulating drone and have extraordinary hearing that can differentiate the sounds coming out. This method would be slower than light but can bend around obstacles, making it potentially more reliable around rough terrain. Other posters have gone in depth on various means of telepathy, but I would like to mention [electroreception](http://en.wikipedia.org/wiki/Electroreception). This is present in sharks, bees and some other animals. It allows these creatures to sense changes in electricity, another way to transmit information. Nerves are electrical impulses. Perhaps your creatures are so sensitive and their nerves unique enough that they can read nerve pulses right out of each others heads and communicate that way. [Answer] > > this is a purely biological trait, it's also safe to assume there are > no physical nerves between each member of the collective. > > > Just to open up the possibilities, why do we need nerves? What do they do? Nerves transmit information from one place in a body to another. Outside of the brain itself, that is their primary job. So what's so special about nerves? Not much, other than they have good bandwidth and are remarkably hard to hijack to force a body to do something it didn't want to do. All you need to do is focus on the traits you need: * Good latency * High bandwidth * Hard to hijack Now, for your requirements: > > Each creature can see, hear and remember what each other member of the > species (or possibly hive) has seen heard and experienced, they think > and make decisions as one. > > > Many of these requirements can be extrapolated from things humans do today! Most visualizations of a hive mind assume "can see and hear what each other member of the species has seen or heard" means something along the likes of a movie being downloaded. The bandwidth of this is highly unrealistic, and would quickly limit the growth of a hive mind. But consider "Big Data," the art of processing data like what Google has to deal with. In there, you don't transmit all of the data to everyone (that would be petabytes of data). Instead, you send out small programs to all of the nodes to analyze the data, and report back a succinct message with results. I would expect this to be a more realistic biological hive mind. This also suggests that not ever member of the collective has access to 100% of the mind's experiences instantaneously. There would be a time delay as the Big Data style command propagates through the hive. Their culture would adapt to this. We can also look at the military. The military has devised low bandwidth hand signals to accomplish great levels of communication with low risks of their communication being hijacked. They also have drum-corps, which require synchronized stepping so exacting that it is hard to think of them as 100 individuals. Better to think of them as 1 corps. Finally, consider professional dancing. When we see an astonishing performance by a duo, it's often exclaimed that "they looked like one fluid body." This suggests that we have, with touch, already gotten close to the "many bodies - one mind" ideal of a hive mind. Happy world building!. [Answer] A hive mind may require the assistance of the environment it evolved on: an atmosphere or a planet surface that is highly conducive for sound or for electrical signals would make it possible for individuals to relay data into it and have it quickly propagate to all the other members. Evolving to perceive these messages in a parallel manner, via multiple, external dendrite-like structures would make it possible for members of the species to act as if the planet itself were part of their own body. Just as we humans perceive nervous signals from our extremities as instantaneous, even if they do take a few milliseconds to reach our brains and be processed into sensations, so would members of this species evolve to perceive even distant signals as part of a continuous present perception. [Answer] Technically hive-mind implies two things: Very high bandwidth ranged communication channel The channel use is automated with information flowing from node to node automatically. Neither of these is particularly implausible or even difficult. The difficult part would be an environment where that level of processing power would be useful. It is commonly thought that the nodes in the hivemind can be "dumb", but actually this doesn't make sense. A high bandwidth communication channel would require a highly developed brain anyway. So there would need to be some intrinsic value in the information channel itself. Maybe a need to very rapidly react as a group to changes in environment could explain this? A social insect could evolve faster and faster communications as the scale and speed of required responses increases. Most likely mechanism for such use would be sound. An array of resonators with different frequencies with modulated amplitude? Such resonators would probably naturally resonate with other nearby resonators and if they evolved from an automated warning mechanism they'd be directly linked to the nervous system. With the communication channel relatively fast in relation to individual brain power this would create a semi-plausible path to hive-mind. And acoustic resonators could evolve into microwave resonators allowing greater range and bandwidth. There would also need to be some reason not to use the chemical systems real-world insects actually use. Maybe the situations would change so fast that the persistence of the chemical markers would become a handicap? ]

[Question] [ What would a planet's rings look like from the surface of that planet? Would the rings be perceived to be stationary or move across the sky, and would the alignment of the rings relative to the axis of rotation affect this? [Answer] Very cool, I'm sure. Roy Prol put together a fantastic animation describing what a Saturn-like ring system would look like from the surface of the Earth: [**What Earth Would Look Like With Rings Like Saturn**](https://www.youtube.com/watch?v=hoz5Q2rGQtQ) Essentially, the rings would most likely be aligned with the planet's equator running from east to west. When viewing the rings directly from the equator, you would be seeing them perfectly edge on, appearing as an impossibly thin, bright white line running directly overhead from horizon to horizon.   But as you move farther from the equator, the rings would appear wider and wider and closer to the horizon. In the northern and southern latitudes, you would be able to make out the individual ring patterns, but the rings themselves would not appear to move to the naked eye. You're looking at billions of particles ranging from maybe a few meters across down to micrometers in size viewed from thousands of kilometers away. The surface of the rings would look like a translucent band of light made up of a pattern of concentric rings vaguely similar to the rings you see on a record album. It would put on a fantastic light show as the sun or moon moved behind the rings shimmering in varying intensities of light as the density changes from ring to ring, all while we enjoy seasonal periods in its shadow. In an Earth-like system, the pattern most likely would not be quite as complex as those seen on Saturn because we have fewer natural satellites (one moon) which causes many of those patterns. But you would likely see a few "ripples" in the ring system as the gravitational resonances of the moon and other objects in the solar system would seem to bend small regions of the rings into wave-like patterns. As you approach the twilight hours around sunrise and sunset, a portion of the brightly lit band would abruptly break off into pale shadow as part of the arc passes out of the sunlight into the the shadow of the planet. The early night and pre-morning hours would be brighter than what we have now as portions of the brightly lit ring would remain in the sky long after sunset, and appear again well before sunrise. But throughout the night you would always be able to see the rings, as they would be illuminated by the moon, internal reflections and atmospheric effects reflected from the planet. Of course, this all assumes the planet is rotating in roughly the same plane as the solar system. Planets can be tidally locked and not rotate at all (relative to the sun). And if we were talking about a planet with its axis tilted nearly perpendicular to its sun (like Uranus), you could end up with a situation where the rings were constantly illuminated, and the normal transition of "day and night" might not apply. [Answer] I had one major addition, related to seasons and tilt, that seems to have been (partially) overlooked: The rings (assuming equatorially bound rings and a planet with an axial tilt) can shadow themselves. They have a 'top' and 'bottom' (or north and south if that makes more sense to you), and the star(sun) will only shine directly on one side at a time, and the intensity will change, depending on the season. So an observer in the northern hemisphere, during a summer day, would see the complete ring, at its most reflective (but due to daylight washing it out, it would not seem to be the "brightest"), that same observer, late that night, would see the (apparent) brightest rings of the year, but with the shadow of the planet falling on them, so they would not appear 'complete' but would have the dark gap mentioned by the answer selected by the OP. BUT The same observer, in the same location, on a winter day, would not see the rings themselves, directly, but might see only their silhouette (like a ring eclipse), or possibly a strip of sky darker than the rest, depending on if they were directly in the shadow that the ring, or on the edge of the shadow, or not near the shadow. And at night in winter, they would see nothing of the ring at all, other than the black strip of missing stars. From the spring equinox, the rings would slowly brighten until the summer solstice, and then start to fade again until the autumn equinox when their brightness is reduced to its lowest point, where it will remain until spring. ]

[Question] [ In a Middle Earth type world, there exists a magical map. It has the property that anything that happens to the map also happens in the real world. The map can be 'zoomed' in or out to get the right level of detail. The **best** resolution would be as shown in the following map. You can see the scale in the bottom right under the coat of arms. There is a black and white line the total length of which is marked as 200 yards. [](https://i.stack.imgur.com/RR5Kd.png) **The obvious problem** Given that changes to the map affect the world it represents, the owner could in theory cause instantaneous catastrophic effects by tearing the map in half or scribbling all over it. I'd like to be able to change the course of rivers, or make bridges collapse in a natural-seeming way. However I don't want to simply draw a mountain and have it suddenly appear out of nowhere. **Question** What rules can I make in order for the map only to cause changes that seem natural and possible to the inhabitants of the land and that happen at a reasonable scale and in a reasonable space of time? I don't want the owner to have to be an expert artist or map-maker. [Answer] Anything that happens to the map happens to the real world... eventually. Changes to the map simply put the world on the path to reach that change, and naturally the more impressive/far-reaching changes take longer to finish. * Draw a new patch of green behind your house, and spend the next few minutes wondering how you never noticed that big tree in your backyard. * Draw a line of grey circles across a river, and the water level will soon drop just enough to expose a series of stones to let you hop across. * Draw a fine villa on the edge of town, and magically the paperwork for it is approved and the builders are paid for. Construction should be finished by the end of the year. * Draw a new river and over the next few months a series of severe rainstorms or a newly constructed dam will cause a lake to overflow, creating the river. * Draw a new island in the middle of a bay, and feel the first few earthquakes caused by the new volcano [that will soon form your island](http://www.surtsey.is/pp_ens/gen_3.htm). * Rip the paper in half, and a large asteroid is set on a millennia-long collision course with the world. So, if someone wants to cause a major catastrophe or otherwise significant change to the world it's unlikely that they live long enough to see it happen, and gives plenty of time for the change to be corrected by someone who wants to preserve the world. [Answer] The map and the world are magically linked to each other. Much like a rubber band, whenever they are pulled apart, the potential (magical) energy tries to force them back together. However, both the map and the world can shift back towards their initial positions. This is partially how the map stays true to the erosion, volcanoes, tectonic shifts that have taken place since the initial creation of the map. Most owners don't properly recognize the power of the map initially. They try to draw a bridge, and after a few minutes, most of the drawing disappears, so they correctly determine the map is magical, but figure it's just an accurate representation of the world at the moment. However, if they look closely, they might see a couple rocks near either side of the riverbed. If you continued drawing the bridge over and over, eventually, the world would concede to the map, and your bridge has formed. Occasionally, the world is less resistant to change -- perhaps there is a heavy storm already coming towards the area before you draw a river. It was going to travel another mile or two, but hey, this is just a lot less energy than resisting the magical potential of the map. The storm erupts, erodes a canal, and a fraction of a flash flood later, you have your river. A particularly persistent user could, in fact, make a mountain. If they drew the mountain every night before bed, after a couple years, they might have a hill, and after several decades, The Englishman Who Went Up a Hill But Came Down a Mountain may concede. [Answer] **The correct tools for the correct job** In order to have something done on the map, it has to be done *correctly* - That is, things like notations and such won't show up, because they're not meant to be part of the map itself. Instead, you have to have the correct inks, the correct pens, etc. And not only that, but you have to draw it correctly. You can't just mark an 'X' over a bridge and then the bridge disappears. You have to *remove* the bridge by painting over it. The skill of the user determines how obvious it is that this map was used. When removing said bridge, if you draw the shoreline *almost* right, in the real world, it'll be obvious. The shore will suddenly, and very *cleanly*, move. Someone who knows about the map would be able to pick up on something like this. Similarly, even though the map is magical and causes changes, those changes aren't held together by magic. An impossibly tall cliff simply won't work. I also like the concept of things happening somewhat slowly. You draw a mountain, and there won't suddenly be thousands of cubic kilometers of dirt. It'll shove itself upward over the course of some arbitrary time period. As far as doing something like tearing it in half, or holes? The map simply doesn't do anything to those areas. They can't be updated - you would have to move where you're viewing. [Answer] ## The map has its own goals, and will reject any changes that conflict with them > > Mr. Padfoot would like to register his astonishment that an idiot like you was ever put in charge of this map. > > > This map was created for the purpose of saving the local beaver population. As such, any changes that might endanger the beavers are summarily rejected. This means that things like bridge collapses or new stands of trees are generally allowed. A river adjustment is usually fine, unless the adjustment would leave a beaver dam high and dry. Sudden mountains cause all sorts of ripples throughout the ecosystem - and big changes are rarely good for the thriving populations currently living in balance. Even if the mountain *would* benefit the beavers in the grand scheme of things, the map's ability to predict the outcome of its changes is finite, and it will reject things whose effects are too complicated for it to fully comprehend. And surprise catastrophes are right out. Of course, the map wasn't *labeled* with any of this information, so it's not at all obvious that the sticking point as to what works and what doesn't is the *beavers*. --- Obviously, beaver protection is just an example. Choose your own obscure set of dictates for the map to follow. [Answer] # Add a user interface Just like I can't erase a program from Windows by rubbing an actual eraser against the screen, so too will the map answer only to commands it understands. A drag and drop interface would be nice. Otherwise make it require some special ink or pen to operate it. These can be enchanted so that you can draw a decent river on the map even if you can't draw stick figures by yourself. Tearing the map into pieces will not tear the land, it will just destroy a really useful magical device. [Answer] The effort you have to put into altering the map is directly proportional to the effort it would take to apply that change to the reality. To give you an example, removing part of a forest will be easier than deviating a river which will be easier than rising a mountain range. If you don't have the right amount of force or stamina you simply cannot even think of performing certain tasks. Side effect: forget about folding the map, unless you are a tectonic plaque. [Answer] **The maps scale also applies to time**, or at least the changes do, so at 1:25000 resolution a change that takes 1 minute to draw takes ~17 days to complete in the world. Redraw the river and the river will spend the next 17 days shifting position. That also gives you 17 days to fix it. This also means the more you zoom out the longer changes take. If the **changes take the path of least resistance**, that is they change the world in the way that requires the least energy to achieve the results most changes will look completely natural. Buildings building themselves will never look natural. **As an additional measure changes on the map have to be changed with the right tools, ink** (perhaps even special inks), spill a glass of water on the map and nothing happens, until the water starts to bleed the ink. This almost has to be true otherwise your townsfolk will see a giant pen changing their world. You could place further limits by having the map only able to change things that are in its map key, you can move the river because water is in the key, you can't set the town on fire because there is no fire in the key. tearing the map will simply destroy the map and have no effect on the world. **The map needs to be intact to function**. [Answer] As my 6 year old son observed, all magic systems are about manipulation of energy. The map acts as a user interface for managing the energy to alter the landscape, but there is a finite amount of energy available to work with. What is the energy source? Does it draw on the energy of the "earth"? The energy of the user? Or some other energy source like a trapped demon? It takes energy to manipulate large amounts of energy. If the map directs say the entire energy of the world, it uses energy from another more manageable source to direct it. Does it draw from the map's user? In that case the possible changes would be in proportion to the energy that can be provided by the user. If the user requests a change that is beyond the available energy limits, then the map either rejects the request and returns to whatever state it was in before the request, or it attempts to fulfill the request and self corrects to match what really happened afterwards. If the map sets of something bigger than what was intended, it also self corrects afterwards. [Answer] **Change the past, instead of the future** I'll offer a slightly different take: instead of having modifications to the map change the *future* of the landscape, have it change the *past* of the landscape. The map is essentially a time travel (or, if you prefer, a timeline-jumping) device. Take a blue paint and draw a new river? You look up and it's always been there. Pour green ink all over an existing town? Look up and the town is gone. It might have been built a mile upriver, or a thousand yards to the north, or perhaps it used to exist in this spot but a violent uprising occurred in *this* town instead of a different one, and it no longer exists. Nobody but you is ever surprised by any of your changes, because to everyone else, it has always been this way. The user of the map is cautious because small-scale changes generally "work out", but the larger the change the less predictable. The map *allows* you to wipe out the entire United States of America by painting it over with a freezing ice storm, but once you're done you have no idea whether the pilgrims landed in Brazil instead, whether America is populated by a huge tribe of technologically advanced Eskimos, whether the ice storm in America has affected the Sahara desert in unexpected ways, etc. Frustratingly, the map is surprisingly resilient to changes you'd *think* would change the course of history (somehow, things just seem to end up the same no matter what you do...) EDIT: I'll add from a mechanics perspective: a useful physical experience for the map would be painting on it with inks/brushes, but the map slowly "fades" your changes into its own style. You don't have to be a master artist to use it, as whatever you do will end up looking like it should; but, a better artist is able to make more specific and more predictable changes to the landscape. [Answer] Place a limitation on the map that you cannot add lines, only move them. The map then non-destructively moves the other terrain features to accommodate your change. The objects flow with the earth as if they were floating in water. Thus you grab a river and drag it to a new position. Other items, houses, roads, trees, etc. move out of the way to make room for the new location of the river. A person in a house that is being moved may or may not feel the gentle movement but they will see the shifting occurring. [Answer] The general idea of making magic less powerful is to make it expensive to use. Perhaps changing the course of a river requires the presence of a dozen powerful mages. But powerful mages are rare, live scattered over the world, and charge hefty fees for their presence. Collapse a bridge? The caster collapses as well, making him/her extremely vulnerable, perhaps permanently loosing a spell or two in the process. Creating a mounting requires sacrificing your first born, meaning it can only be done once in a lifetime; casters without a child will not be able to create mountains. [Answer] The original creator of the map was not actually trying to make a map that affected the world. Rather, they wanted to instead make a world within a map. Unfortunately because this would allow for violations of the laws of thermodynamics (which obviously still applies in a magical world, right?) the spell only succeeded in making a map that affected the world. They wanted to create an interface that made sense for such a world. Therefore because they thought it would be fun for the locals to toy around with they made the map have a limit on changes as something a human could feasibly do within their entire lifetime, per day per person. We will also ignore engineering requirement. The assumption here is that if a person assembled such a structure by just grabbing the materials readily available and assembling the object that they could perform that work in their lifetime. Perhaps it can be quantified as total energy needed to move all those materials but I'm not in the mood for intense physics calculations so I'm not going to try and attach a value to that. So suppose someone wants to demolish that village. Sure, they can. But literally all they can do is tear down the buildings and maybe bust the well apart as that is something a person could do with their physical ability within a few weeks time. Building a mountain though? That's going to take way longer than a lifetime if you are artificially building it. Now of course if you get 1000 people together and they each pass the map around then maybe you will get your mountain. However, I think that is a fair and unavoidable compromise. Having a large community work towards such a massive goal by using this isn't exactly unfair. After all if an army used magic to outright destroy an enemy kingdom by all at once launching fireballs across the country side and destroying villages that would not be as overpowered as one sorcerer casting a spell and the entire kingdom sinking into the Earth as the entirety of the land turned to ocean. The results are mostly the same but it sounds less unrealistic when you need more people to do it. Ripping the map in half won't do anything meaningful though. Just as with a map in real life the area that map represents shrinks by ripping it, so to does your map. Suppose I ripped that example map in half. Now the left half contains one half of the river and the other contains the other half. Each half can only directly affect that one region. It's not going to destroy the world. It's just a map. However, while we are on the subject of destroying planets via magical maps... Besides, considering the Earth is non-euclidean and the map is flat ripping the map in half under your original claim that it could destroy things would actually be more likely to not actually cause the problems you think it would anyways. I'm going to come back to this later but I think that if we assume that the spherical surface of the Earth's is being mapped to a flat surface and then we bend or rip that surface to change it that the corresponding change to the sphere might actually result in something much more exotic than a physical change to the Earth's shape. If we also factor in the curvature of spacetime formed by the Earth then the actual result might be a temporal shifting rather than a physical shifting. This is just hypothetical though and I'd have to *really* think hard about this. Basically the problem is that we aren't ripping a globe in half and getting two hemispheres we are ripping a map in half along a line such that things are still connected deep underground and possibly around the sides of the map and then potentially folding it. But because we are working with a spherical surface projected to a flat surface there are actions for which the spherical surface *lack an equivalent*. Hence why I suspect that if the distortion of the map distorted actual space that it would half to distort time as well by folding and ripping because that might be the only way for the math to work out. I suspect that areas that weren't ripped that are then laid together in different ways and folded might also result in a worm hole like effect, but that's also just a symptom of messing with spacetime arbitrarily. To elaborate further, poke a hole in the map. Poke another hole in the map. Let's assume the map can be folded or bent with no problems for now. Now join the two poked in holes. If the map can at least repair itself the result will first be vacuous emptiness forming. I don't even know what that would mean, but it sounds bad. Then all of a sudden a wormhole would open from that location on the planet to the other location. Everything around that area will also stretch inward which also will look very strange. Obviously the way to prevent this is to just assume damage to the map is damage only to the artifact not to all of space. In conclusion, considering the distortion from euclidean to spherical geometry it might be that the map cannot do it anyways in that form as a change on that scale of the map would be incompatible with the actual real world counterpart (the globe) as the transformation from one to other is simply impossible. There will always be a distance or trajectory distortion (or both). One way to resolve that might be to make the map affect time when messing on that scale, but I think the easier explanation is that the map simply can't look at things that large. Similarly limiting it to the amount of work a person can do in their entire lifetime makes it an easy metric for various users. It's easy for a random adventurer to see "oh I can only do as much as could have done if I lived out my entire life right now" (given instruction) then for them to understand what "1000000 joules of energy spent on moving materials" means. It's also easier for a reader to comprehend. [Answer] You require a special pen, which requires special ink, of which there is a limited supply to hand. Getting more special ink is either impossible (it came from a meteorite?), or really slow (perhaps it depends on some bugs that only eat a certain plant which flowers only on blue moons in the summer snow or something that suits your world) Diluting the special ink or cutting it with normal ink means the effects on the map are less predictable or don't have staying power (they revert) or simply don't work at all, wasting the special ink. Climax modifier, someone spills ink on the map and "stuff" happens then the map is cleaned somehow leaving traces of change. --- The map also uses energy, somewhat like a cellphone, the more the display is on/moved the faster it uses the "charge" and it can only regain its reserves by sunlight/full-moonlight/something. Perhaps more distance or more zoom uses the charge faster ? This would require the user to keep the map for times it is needed, not just idle GoogleMaps browsing like we've all done. [Answer] The map itself is not 'magical' per se but is rather attuned or responsive to magic. To nonmagical beings with no magical augments of any kind, the map is just a map. But apply a minor spell and things start to get... interesting. Your average bumbling spellslinger can scribble the thing black, and the result of their artistic exertions might be a faint Grey fog upon the land. Punching a hole through the paper might so much as open a molehill in someone's front lawn. But the great sorcerers covet such a map, for bound to their already awesome power, the land is utterly beholden to their will. A clever stroke of the pen and grand kingdoms are rent asunder, suddenly embroiled in political upheaval and strife -- but the user is for a time clouded in mind, divided from his senses. A well placed ember scorching the page grows an insidious mountain of smoke and flame, and the mage is racked with burning agony of body and soul. And an accidental tear may cause the world itself to shatter -- and with it, the very soul of the careless wielder. Thus the magic itself becomes its own limitation -- for it is said that magic always comes with a cost! [Answer] ## The map is not literal First of all, I'd make this map indestructible. It certainly can be damaged - but exclusively by magical means, like rituals, that would eventually guarantee that it will eventually "heal". Then, I'd say that only a specific kind of magic ink can be used to draw in this map. Either this or make it so that changes to the map can only be done during a given ritual. Anything else, like a pencil or regular ink won`t work (maybe the ink and the graphite just fade, eventually). This magical map works by projecting the idea of the drawer in the terrain - but it won't always work exactly as it's supposed to. For simple things like drawing a tree, it might work perfectly. But when a greater change is done, the effects on the terrain start to get more and more unpredictable. So if you draw a tree in the middle of a square, the ink will slowly spread, over the course of days, months, years - decades or centuries even - and slowly change its form and colours to start becoming a tree. It will, most times, be the tree the drawer thought of. But sometimes, the tree might end up becoming a different tree (which is of little consequence). This way you don't really need a person that knows how to draw, since the map kind of "scans" the drawer's idea from his mind. Just imagine how silly your map would be when found by your heroes, after 3000 years of people drawing shitty sticks and weird shapes in it. You might also adapt this to fit the extreme versions of what can be done to the map. If you burn it, maybe a great fire strikes the affected area. The burn stain would also change, just like the magic ink, and eventually portrait the destroyed area. The same can be said of tearing the map. Maybe it glues itself back together while portraying the huge canyon formed after the greatest earthquake ever registered. These unorthodox ways of using the map could be even more unpredictable. We'd all assume that burning the map would mean a great fire. But why couldn't the affected area just become a huge tar pit or a swamp over hundreds of years? - a drastic change to a biome. This factor of randomness could be a way to ensure that the map is not a weapon of mass destruction - at least not that easily. Remember that: These more agressive ways of shaping the map must also be done under a ritual, to explain why it heals itself even if heavily damaged (it's a magical map, dude :P) [Answer] # The map must be "Animated" over time": In my concept, **to enact a change, you would set the map backwards and/or forwards in time, select an interval, and draw the each change at each time interval.** * **Making changes requires energy, or effort of some sort**, on the part of the person making the changes, and so in any given moment of time they can only change a certain amount at a given scale. * **The shorter the time-frame acted on, and/or larger the scale, ths more energy/effort required up to some finite maximum.** + To make a river change at a certain scale, they might dial the time on the map backwards 10 years, and make slight changes, every year 10 times, or 12 times a year, 120 times. * **The map chooses how to get from A to B between intervals on the drawn on section.** + Draw a ladder on a building appearing in an hour from now, and some work-men come by and put up a ladder to clean the building's windows, then wonder off to take lunch. + Change the course of a river over 10 years at one year intervals, and perhaps most years the map chooses to have annual flooding and some minor rock-falls affect the changes. * **The Map decides how these changes affect (if at all) the area outside of that space drawn on (although ymmv).** + Make the course of a river change 1 hour from now, and a massive earth-quake occurs somewhere else in the map causing massive destruction that was unplanned for and perhaps unwanted. + eg. If you redraw a section of the river such that it will follow a new Course, and do it on a very section of the map, you can only redraw the end point and the topological change, the map is going to redraw the river's flow through the land outside that section with increasingly unpredictable consequences as the further upstream and more dramatic the change is drawn. + If you survey the area beforehand with map in hand, and put in sufficient effort to predict how the change would affect things (especially if you choose to move forward in time) the more predictable the surrounding changes will be. * **Changes that Happen over time give people that amount of time to react to it** + Dial the map back 100 years into the past, and make the river change course to empty into a basin with a town. The town was moved, or damned the water so that it swill flows similarly to how you drew it but perhaps not how you expected it. Or a few houses from a settlement for 2 houses 100 years ago exist as ruins, and a city is on a nearby hill with all the same people in it, or 50 years ago the whole town was flooded and its houses are all underwater, but some/all of the descendants and brand new people live in a city up the hill. + If the user wants to change the course of a river to flood a town, it could be done instantly with an earthquake (that is what changed the mighty Mississippi in a single hour!) But it would require the max energy that an instant change allows on a very small scale, so they would need to zoom in on a small area, and re-draw that area so the down-river portion of the river is shown pointing else-where, with a change in elevation to keep it from heading back fo the original course directly. + Make the course of a river change 1 hour from now, and a massive earth-quake occurs somewhere else in the map and changes the elevation of the area causing a wall of water to sweep through the town. Then, the map/physics/rng/gm will have to determine the rest of the course of the river. * **Changes are accepted as natural for those who have no "True Sight™"** + If a change is made everyone sees it as always having been that way except those who have a special true sight ability. + This ability is permanently conferred to those who have been in possession of the map while changes that were planed occur, or who have learned what it does and been preset for someone else demonstrating it. * **Physically cutting the map or ripping it up usually won't cause an effect**: + The map is "mapped" to the world, but does not join the world, instead it only acts on the world. + In certain circumstances, however you could reposition the map through cutting and mending the map, so long as all lines on mended edges match up without notation, or the notations are erased and redrawn as necessary. + To this end the User can detect, and create "Portals" or "Wormholes". While touching one side of the map to the other does nothing, a person could create a connection between places by only mending one edge of the map, joining areas far separated without moving where they physically are. + This would also allow the user to discover secret portals that other magical users created that exist, because, although they don't have the map, essentially they are doing the same thing, and at least the map will represent this when at a correct scale to be able to do so. [Answer] # does the interface have to be traditional? imagine you have the wielder of the map (now cartographer) sit cross legged with the map in front of him. His eyes close, and in his vision the space warps, as it dose when a star fighter in star wars goes into hyperspace. He looks at his hand and it is translucent. Then he turns around and sees his body. In modern times it is in what would be called a vegetative state, as its spirit has left it. he then pictures moving down, and sees his mom making dinner. Enshrouding her is a spirit identical to her body. her lips are moving, but he cant hear her. He has known of the power of the map for countless years, yet now its his. He goes to the park and finds a oak sapling. he knows he can effect terrain and time. he tries time on the sapling,k and it quickly becomes an old tree. as he floats home he starts to feel fatigue, so he goes to a fountain and finds himself five years older [Answer] have the map only command the water in the river. You erase a bridge and the river attacks the foundations. you change the path and the river bursts its banks. I'm envisioning processes that take weeks to years to complete. [Answer] Changes to the map occur instantly, but only in the owner's head. However (for instance) if the owner removes an existing bridge and then tries to walk across it, he drowns. Altering the map changes nothing in the real world. The map was created by a mage with a peculiar sense of humor. The mage originally arranged for the map to be found by an enemy, since mages are not allowed to use magic on each other. The map becomes in effect a third party and after a time the enemy kills himself with his changes to the map. The map is indestructible and continues to provide the creator mage with endless amusements. [Answer] The map and the world are linked because they are the same. They map is 100% accurate at the detail it shows. (In fact, that is probably what made it so hard to form, and why it took countless centuries of trial and error, even with all the magic available.) Now that it's formed, there is some leeway, but no one wants to test how much. No one knows how far you can take it before the connection breaks. And no one knows if breaking the connection will be a clean break or cause a catastrophe. So you must make a small change, and then wait for it to take effect, as it take some time. Then when the map is accurate again, you make another small change, and so on. Those trained to watch over the map and use it when needed are of course very careful. But even the villain(s) going after the map would never think to push it too hard, because of what might happen. Of course, maybe there is some villain who has the hurbis to think they can keep it all together no matter what, or who doesn't care what happens to the world. [Answer] *Map of Manipulation* # Skill requirement: (bonus modifier to your roll when using skill: * Geology : +8 * Lore : +2 * Oceanography : +4 * Cartography : +10 * Astrophysics : +20\* Users who are *'uneducated'* automatically critically fail and cause random severe weather. \* consult your DM [Answer] Don't forget that a map is merely a *two*-dimensional representation of a *three*-dimensional world. You necessarily lose some information when encoding reality onto a map. Therefore, adding something to the map does not provide enough information to completely and perfectly describe a change to the three-dimensional world. In your particular case, your magic map has the responsibility of filling in the missing pieces. For example, let's say you find a large, wide-open prairie and draw a tall brown mesa in the middle of it. Creating a tall mesa in the middle of the prairie would of course be the intended result. You head out to the prairie but...it's still perfectly flat. What happened? You survey the area from the air and notice that patches of vegetation have died back, revealing the rocky ground underneath. When viewed from an altitude, these dark-colored rocky patches form the shape of the mesa symbol that you drew on the map. Your magic map simply took your input and came up with the simplest, lowest-energy solution that would result in a map that looked like the one that you drew (similar to how a polynomial equation in mathematics can have multiple, equally-valid solutions). Because of this behavior, it's extremely difficult to make large-scale changes like adding or removing land-forms. Enough detail is left up to interpretation that the results of attempting something like that are difficult to predict, and are rarely close to what you intended. Moving existing things is a different story. The bridge icon on your map was created by the map itself. Therefore, the map already knows everything about the 3D structure of the bridge. Taking that *existing* map marker and relocating it downstream a bit would have the effect that you expect. As far as something like tearing the map goes, that wouldn't result in catastrophic changes at all. Tearing the map didn't actually *change* it. The information encoded on the map is exactly the same, now it's just in two pieces and a whole lot harder to use. [Answer] This is a specific set of rules known about the map, the shady merchant wrote this down from a series of notes from its previous owner. 1. The map is indeed very special, is not just like ordinary paper map as it is indestructible (at least so far everything that has been done to it never even scratch its surface, be it fire, water, dagger, even magic itself, somehow this map looks like predates magic, or even human?). 2. It has been known that the map have something like zoom ability, but the truth is the map just always shows its owner the area of their own range of vision. This mean, this map is quite useless to show you a road to another city. So many people before just throw this map, unknown of its full potential. 3. This zoom ability therefore also affect the map's power to change the earth. As when you are in a narrow alley, most likely what you can do is just remove obstacles ahead of you or put a big boulder to block your chasers. But when you are at the top of the mountain, there's quite much interesting things that you can do with it. 4. The map come with also indestructible pen, neglecting its indestructible trait, the pen is also very special as it is ink-less, nor it will work with any type of ink. 5. What the pen can do is simply manipulate what's already there on the map, like smudging on the land and sea. It may be boring, but in the hands of creative mind bearer, this is more than enough to act gods. 6. Swipe a shoreline to a nearby island, you got a natural bridge and receding shoreline on the left and right part of the bridge. Move a scoop of land from a nearby river, you alter it. 7. Beginners may think this map is lame. But with just those features known previous owner who is also a seafarer has been created a new sea from a dessert, the other previous owner even has a legend that with this map he can change climate, another one destroy a kingdom overnight, but the darkest tale is human has stole this map from titans, and somehow erase them from history with it paving a habitable world for us, but unhabitable for the Titan and god knows what else. [Answer] The simplest answer here that is not overpowered is that the person who wishes to enact a change must paint or draw on it the thing they want to change, then the map makes the change happen if and only if the change is something of an acceptable level of change. As you say in your example, ripping the map is catastrophic. So, if someone rips the map, the map rejects this change and the two pieces just zip back together as soon as they hit the ground. If you erase a city off the face of the map, the map just decides not to do it, and the paint or X drawn on it just flakes off. If you draw a cage around someone then it works, appearing around the person - assuming that the person doesn't move into the edge before you complete the drawing. In that case the drawing flakes away. You could even go as far as having the map be somewhat sentient like a living planet scenario. If you draw a dam bursting above a valley with a village in it, the map finds your change to be abhorrent and never accepts your changes again [Answer] Drawing symbols on the map with a pen or brush is only a physical representation of what you are actually doing - embedding your will into the map. The changes that occur in the real world are reflective of what your were willing to happen at the time you drew it, which has no relationship on how well you can draw. If accidental things happen to the map, these obviously were not intended and therefore the world is not affected by them. This would also mean the person modifying the map could be hiding their intention by drawing something different from what they were 'willing' to happen, confusing anyone who looked at the map until the change occured in the real world. ]

[Question] [ **This question asks for hard science.** All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See [the tag description](/tags/hard-science/info) for more information. What's the easiest way for your stereotypical aliens to destroy civilization from orbit? I'm taking "destroy civilization" to mean the destruction of all large-scale forms of governance, but bonus points for extinction. Criteria: Either cheapest or least energy consumption. The aliens have access to anything that's roughly possible for a Kardashev II civilization. The aliens use a magic-plot-teleporty device to get here, but everything else should be as hard-science as possible. [Answer] As Samuel states, throwing a big rock at the earth will certainly end civilization....and everything else too. Short of interplanetary rock throwing contests, the easiest way to end civilization is to nuke each and every major metropolitan area. They're easy to find, just look for the big shiny lights on the planet surface. [](https://i.stack.imgur.com/FBnbi.jpg) If these areas go away then civilization ends. Banking no longer works, government no longer works, transportation systems no longer work (or heavily degraded), and worst of all the Internet will get really really slow. You can't get paid because the bank that handled your paycheck isn't working and that's because the people who handle your paycheck can't get to work. How long would you last if suddenly ATMs and credit cards stopped working? What if your phone no longer routes calls or text messages don't go through? Would you panic? Even if the attacks happened at night when most people are at home, only [2.6% of the work force](https://globalworkplaceanalytics.com/telecommuting-statistics) actually works from home with any regularity which means that 97.4% of have to show up for work. (Admittedly the stats are US-centric but I believe are broadly applicable to any First World economy.) In [Central Europe during the Great Depression](https://en.wikipedia.org/wiki/Great_Depression_in_Central_Europe), unemployment peaked at 20% and output dropped by 40%. Unemployment hit 70% in some areas of the UK. In this situation, unemployment is at best 50%. Nuclear attacks on every major metropolitan area have resulted in an unemployment rate at least double, double(!) the Great Depression. It took a world war to get out of the Great Depression but this time, there is no untouched infrastructure to help bootstrap the process. Couple this loss of employment with 50% global casualties as [54% of humanity lives in cities](https://www.un.org/en/development/desa/news/population/world-urbanization-prospects-2014.html) and the world as we know it has pretty much stopped. It's not quite a Stone Age civilization reset but definitely back to the Iron Age. From "[Effects of Nuclear War](https://atomicarchive.com/resources/documents/pdfs/7906.pdf)" by the US Office of Technology Assessment: > > Most economic damage would occur from lost production...The major damage to the economy, however, would result from deaths and long-lasting injuries (to consumers and producers), and personaI tragedies and other traumas making people less able to work. The magnitude of economic loss could be expected to vary with the number of deaths. The attack would cause considerable economic disruption in the uncontaminated area. > Facilities there would *need to produce a vastly different mix of goods and cope with the absence of goods that normally come from contaminated areas.* Until people acted as if they believed the war was over, it could prove difficult to organize production in the uncontaminated areas. *Uncertainties about the legal and financial arrangements that support production (money, contracts, credit, etc.)* following a nuclear attack might impede production in the uncontaminated areas. Public disorder could also impede production. The changes and uncertainties would cause some economic disruption; however, the greater effort put forth would probably more than compensate for it. > > > *Emphasis mine.* Basically, questions about who gets paid for what, by who, and by what mechanism would cause a drastic reduction in economic output. Every dot on the map below is gone. How well is civilization going to work when those are all gone? [](https://i.stack.imgur.com/xrrze.jpg) (source: [citylab.com](https://cdn.citylab.com/media/img/citylab/legacy/2013/06/25/globalcitiesmap1web.jpg)) Oddly, in this scenario, North Korea might end up doing pretty well but only because they don't have anything to begin with. [Answer] Moving asteroids? Antimatter? Relativistic shells? Surely you jest! That's not energy efficient. **The most efficient way is to beat mankind with their own weapons.** Hack into the President's Red Telephone, or NORAD, or some silo in the Midwest and let the nukes go ballistic. Wait for counterstrike and mushroom clouds to settle. For extra effect, release viruses and spray whatever nerve gas is still in their B and C arsenals. Done. That advanced civilization would only need to listen in to our military radio communications for a while, use their massively parallel quantum computer to break humankind's most advanced encryption algorithms (their NSA is beyond what you can imagine) and radio down the launch sequence codes. This is wonderfully efficient because the ICBM target coordinates are *specifically selected to cause maximum damage or disruption* by our finest military intelligence. The aliens wouldn't have to scratch their tentacles just where to point their beams of death. The same argument also applies to B and C weaponry: specifically designed to wreak maximum havoc on human physiology. Why abduct humans and study their weaknesses when they already have incorporated all that knowledge in their weapons of mass destruction^W^W^Wself-defense tactics? Total energy consumption: a few Joules for carefully modulated electromagnetic waves. [Answer] **Hit the planet with an asteroid.** Guide a 100 km wide asteroid at the planet at around 10 km/second and there will be a global extinction event. Anything [larger than 3 km can cause extinctions](http://specialpapers.gsapubs.org/content/247/223.abstract), so the 100 km figure is simply to make sure the job gets done right. [Answer] **An electromagnetic pulse (EMP).** We want to destroy civilization - not destroy the planet. It's evident the Aliens possess some pretty interesting tech, else how would they have got here? I'm pretty sure that the energy requirements for interstellar FTL are massively high - orders of magnitude greater than anything created or generated on earth. This means there is some advanced energy generation or storage at play. The Alien race would be able to potentially rapidly 'discharge' this energy into the ionosphere - instantly knocking out satellites - so there goes communication and GPS. Up the power and you have a full on [Geomagnetic\_storm](https://en.wikipedia.org/wiki/Geomagnetic_storm) - with all the devastation that this would cause: * Radiation sickness * Electrocutions * Complete power grid failure * Global communication outage * Devastating weather effects (Hurricanes, Typhoons) * increased tidal forces (Tsunami, Earthquakes) All of which would be impossible to fight against, and all the aliens need to do is observe, and increase the power as required. [Answer] Post a query to the human's most popular Q&A site, then wait for the humans to list all of their vulnerabilities and easy ways to kill themselves. Wait for long enough for the question to go quiet. Then choose the method with the most up-votes and see whether in fact your alien technology can implement it. If so, use that method. If not, continue down the list in up-vote order until you find one that you can implement. Best part? This will work for any form of life with a large data-centric society. [Answer] The absolutely most efficient way would be to land in contested territory somewhere, and claim that you want to give some superior weapons technology to the leading nation of the world. Then sit and watch how the nations destroy each other as they try to make sure they are the leading nation. It will help if you have defensive technologies that can shield you from nuclear blasts. [Answer] Since it is already for human grade technology a little hard to imagine bringing up all the energy needed to travel and do all the things, lets just add a little more and use ## relativistic projectiles These could also be a convenient way incorporated into the travel of these species. Adding enough energy to a flipper steel ball to make it travel at significant fractions of $c$ can deliver the amount of energy of a hundreds of megaton nuclear weapon, without the drawbacks of the massive fallout (there will be some, but it is likely much less than with conventional thermonuclear weapons). It will also be a convenient way to slow down when traveling. It is fair to assume that they travel at significant fractions of $c$ to actually get somewhere in time, so firing enough of these balls gradually at earth will slow their ship down, obliterate the earth (no need for aiming, no one will survive a steady stream of thousands of hundred megaton bombs arbitrarily scattered around the surface), and if timed correctly by the time they get into orbit, everything is ready for whatever they want to do. [Answer] Does blowing up the planet count? In that case I've always liked [Greg Bear](https://www.goodreads.com/author/show/16024.Greg_Bear)'s idea in [The Forge of God](https://www.goodreads.com/book/show/64732.The_Forge_of_God): > > Fire two pellets of neutronium (neutron star material) at the Earth, one made from neutrons, the other from antineutrons. Due to their density they won't collide with Earth, instead they'll fall straight through it as if the Earth didn't exist, orbiting around the Earth's centre of mass. The antineutronium pellet will spark a little, but it won't annihilate catastrophically. Until they meet at the centre of the Earth, and then: kablooey. > > > I don't know how scientifically accurate this is, but it sounds legit. If the alien civilisation's intent is to use the Earth for their own purposes then they might consider this slightly overkill... :) [Answer] # Enhanced global warming After reading interesting [Aracthor's answer](https://worldbuilding.stackexchange.com/a/22602/3002), I had the idea to do the opposite. Instead of hide the Sun, lets show more of it to Earth. You would need to put a bunch of giant mirrors and/or lenses in orbit on outerspace and keep them properly aligned to reflect and focus the sunlight to Earth. This is doable with some small robotic mirror-bearing or lense-bearing starships powered by solar power. With enough mirrors and/or lenses in orbit reflecting the Sun light direct to Earth the result would be that Earth temperatures would rise. With a reasonable area of mirrors you could get global warming, weather disruption and famines. With a much larger area, you could *venusform*\* Earth. \* I coined that verb as something similar to "terraforming", but instead of making something like Earth, it would be like Venus. [Answer] # Hide the sun. If you find a way to completely block the sunlight to shine on a planet, you can be sure every life form should disappear quickly. * Any kind of photosynthesis become impossible, so oxygen levels can now only go down, and every plant outside a laboratory shall die quickly. Then herbivorous animals would follow, then carnivorous ones. * Temperature shall become icy in some days. Except in very heated bunkers, everything would froze to death. So just prevent the planet from being shined for one week, and you would destroy any vegetable or animal life form on the surface. Even if there would be some survivors that would have hide in some shelters, you can let the sun out to watch them starve to death. [Answer] [Stolen shamelessly from one of my previous posts.](https://worldbuilding.stackexchange.com/questions/6515/what-could-humans-do-to-render-the-earth-uninhabitable/6549#6549) **If you absolutely, positively need to sterilize the surface, you must blast it from orbit. [It's the only way to be sure.](https://www.youtube.com/watch?v=aCbfMkh940Q)** The problem you'll quickly run into is that the Earth is big. You can crash 10km sized asteroids into it, and there'll still be some survivors to whine about the injustice of it all. Now, we wouldn't want that, would we? There are two surefire ways. ## 1. Antimatter Bombardment No, the only way to be sure is to be thorough. You'll need a fair bit of antimatter, um, let's see... 1 Mt is $4.1\times10^{15} J$ so the Tsar Bomba (in the tested config) at $42MT = 1.72 \times10^{17} J$ 2 kg of $E=mc^2 = 1.79 \times 10^{17} J$ So each 1 kg antimatter bomb (as it anihillates with 1kg ordinary matter) would have a blast similar to the [Tsar Bomba](http://en.wikipedia.org/wiki/Tsar_Bomba), the most powerful nuclear device ever detonated in the puny humans' history. That gives you a nice $1,200 km^2$ blast incineration area. Now, if we were sloppy, we would just pepper the land area of $148,300,000 km^2$, so about 1,236 MIEVs (Multiple Independently Targetable Entry Vehicles) with 100 1kg (+containment) warheads each would do. But that would miss all the boats, planes and submarines crowding their primitive buoyancy based transportation lanes. With [about 100,000 ships](http://unctad.org/en/docs/rmt2011_en.pdf) out there, that's a lot of survivors. $361,000,000 km^2$ to cover, you'd need another 3,009 MIEVs. You might still miss a submarine or two, but without space launch capabilities, zero industrial capacity, and an all-male crew, you're set anyway. Pro: Clean blasts, little of that nasty radioactive slag. Also, once in atmosphere, any attempt to shoot down will only damage the containment system and detonate the antimatter. Con: You need a lotta bombs. --- ## 2. A dozen or more relativistic ships. Thanks to our friends at [Wolfram Alpha](http://www.wolframalpha.com/input/?i=relativistic%20kinetic%20energy&a=*C.relativistic%20kinetic%20energy-_*Formula.dflt-&a=*FS-_**KineticEnergyRelativistic.K-.*KineticEnergyRelativistic.m-.*KineticEnergyRelativistic.v--&f3=3000t&f=KineticEnergyRelativistic.m_3000t&f4=0.25%20c&f=KineticEnergyRelativistic.v_0.25%20c), I don't even have to do the calculation myself. Take your standard light-crafts, a 3,000 ton craft, push them to a reasonable 0.25 c and crash them on opposite hemispheres (preferably from multiple directions, but you could also do several hours apart). Each will clock in at around $8.8\times10^{21}J$, or about 10,000 times those anti-matter firecrackers from earlier, or about the same as a 10 km asteroid impact. To be really sure, send a few dozen of these. Pro: Almost impossible to intercept once acceleration is complete. Con: Your reptilian colonists awaiting in orbit might themselves cook a bit from the impact gamma blasts. [Answer] **Meteor** Don't bother nuking major cities. [Nuke](http://arc.aiaa.org/doi/abs/10.2514/2.4814) space rocks [onto a collision course](http://www.esa.int/gsp/ACT/doc/MAD/pub/ACT-RPR-MAD-2005-OnTheDeflectionOfPotentiallyHazardousObjects.pdf). Use a few for a faster results! A small moon would be a great candidate! But that's pretty messy. And after all, as a stereotypical alien invader, you're looking to colonize. Are there any cleaner options? **Virus** You knew you had a reason for all those abductions and experiments. Upload a human population in your brand new quantum simulation program on your ship's super computer. Now [in supertime](http://www.simulation-argument.com/simulation.html), evolve a virus that is guaranteed to wipe out those pesky sapiens! You could start out with a particularly nasty strain of HIV. When you're ready just drop a pod into a major international city, don't want it to burn up in the atmosphere! **Self-replicating machines** You just realized that you are an advanced race, and biological warfare is a pretty low-blow. And you've been watching some DirectTV while in orbit and an old sci-fi flick with a big Austrian guy inspired a brilliant idea. Drop a single small [machine](http://www.niac.usra.edu/files/studies/final_report/737Lipson.pdf) loaded with instructions to mine up a bit of resources and complete, then replicate itself. Finding a location with a suitable amount of resources available your colony will be able to double itself in hours. Within 20 doublings (maybe a week or two) your army will consist of over a million robotic soldiers awaiting your command. And when they are finished with their eradication mission they can start the construction of your new palace. And to think it just cost you one 3d printing of some plans you found on the galaxy-wide-web. Just make sure they say catchy phrases when eliminating the targets, like "Hasta la vista, baby." **Terraform** All this time you've been absentmindedly setting the planet's forests and crops on [fire](http://www.au.af.mil/au/awc/awcgate/cst/occppr05.htm) with the ship's laser canon, just for fun, when it hits you! You've been getting ahead of yourself. The planet won't support your new family as is. Now you feel silly for entertaining all these ideas. The eradication will solve itself! You drop one *Ready-Made Multi-Purpose Automatic Self-Constructing Terraforming [Factory Seed](http://www.niac.usra.edu/files/studies/final_report/880Chirikjian.pdf) 2000* on the planet. Now you sit back and relax. The planet will be a nice and cool 98 centigrade with plenty of that life giving arsenic in the water in no time. *Note: While the tone of this comment is lighthearted, the science is serious. None of these things require the alien to have huge amounts of energy or resources before hand (like relativistic projectiles or antimatter/neutronium bombs). In addition it accounts for multiple different end scenarios (such as destroying the everything, or just the biology, or just one species). It also leaves room for multiple starting situations like a lack of suitable asteroids/comets, highly exploited or otherwise unavailable resources. It's impossible to say what the most efficient method would be for an unknown alien on an unknown planet wiping out an unknown civilization, but we can make some good guesses I think.* [Answer] ## Massive Solar-Storm How About I don't attack earth directly, but rather instigate the sun to fire a massive 24 hour long barrage of solar flares in earths direction. If the flares contain a massive amount of radiation they will kill almost all life by radiation poisoning, burn the face of the earth, and the electromagnetic disturbance will destroy most orbital and local electronics. After 24 hours the whole surface of earth was bathed in the storm and civilization will be wiped out. And they lived happily ever after. [Answer] Make a survey of the planetary surface and collect samples of the most potent types of virus affecting humans. Use your sophisticated biotechnology to engineer them to be more transmissible and more lethal. Release them into major urban areas. That will require no further action from you and will result in sufficient loss of life that civilisation will break down. There will be humans with sufficiently potent immune systems to survive, but very few of them and they will now be living in a perilous post-apocalyptic world. Your mothership landing will be the least of their worries. [Answer] Depends on which definition of "efficient" you're looking at. **Efficient: achieving maximum productivity with minimum wasted effort or expense.** If you're really shooting for minimum wasted effort or expense, couldn't you just do nothing and wait around? On a long enough timeline most all civilizations are ultimately doomed; the sun will super nova or burn out eventually, large asteroid strikes happen every so often, and so on... > > Criteria: Either cheapest or least energy consumption. > > > Patience doesn't cost much and requires very little, if any, energy. [Answer] Consume all the oxygen. Send down microbes, or chemicals that will react with oxygen, and let them absorb the atmosphere down to under 5% oxygen. There are a lot of consequences due to lack of oxygen well beyond being unable to breathe without aid. For bonus points, getting rid of CO2 would help significantly. It's a slow process, but it's very, very efficient in terms of cost. [](https://i.stack.imgur.com/Oz3oM.jpg) [Answer] # [Gamma-ray burst](https://en.wikipedia.org/wiki/Gamma-ray_burst) The solution would be to bombard Earth with gamma-rays. Normally a supernova in a nearby star would be able to do that, but since the aliens are much more near Earth and can focus their energy much better and in the most suitable part of the eletromagnetic spectrum, they won't need something as powerful as a supernova. Just a bunch of powerful gamma-ray lasers will do the work. What would happen exactly? Accordingly to [wikipedia](https://en.wikipedia.org/wiki/Gamma-ray_burst): > > The major [Ordovician–Silurian extinction events](https://en.wikipedia.org/wiki/Ordovician%E2%80%93Silurian_extinction_events) of 450 million years ago may have been caused by a GRB. The [late Ordovician](https://en.wikipedia.org/wiki/Late_Ordovician) species of [trilobite](https://en.wikipedia.org/wiki/Trilobite) that spent some of its life in the plankton layer near the ocean surface was much harder hit than deep-water dwellers, which tended to stay put within quite restricted areas. Usually it is the more widely spread species that fare better in extinction, and hence this unusual pattern could be explained by a GRB, which would probably devastate creatures living on land and near the ocean surface, but leave deep-sea creatures relatively unharmed. > > > > > [...] Gamma rays would not penetrate Earth's atmosphere to impact the surface directly, but they would chemically damage the [stratosphere](https://en.wikipedia.org/wiki/Stratosphere). > > > For example, if [WR 104](https://en.wikipedia.org/wiki/WR_104), at a distance of 8,000 light-years, were to hit Earth with a burst of 10 seconds duration, its gamma rays could deplete about 25 percent of the world's [ozone layer](https://en.wikipedia.org/wiki/Ozone_layer). This would result in [mass extinction](https://en.wikipedia.org/wiki/Mass_extinction), food chain depletion, and starvation. The side of Earth facing the GRB would receive potentially lethal [radiation exposure](https://en.wikipedia.org/wiki/Ionizing_radiation), which can cause radiation sickness in the short term, and, in the long term, results in serious impacts to life due to ozone layer depletion. > > > > > Longer-term, gamma ray energy may cause chemical reactions involving [oxygen](https://en.wikipedia.org/wiki/Oxygen) and [nitrogen](https://en.wikipedia.org/wiki/Nitrogen) [molecules](https://en.wikipedia.org/wiki/Molecules) which may create [nitrogen oxide](https://en.wikipedia.org/wiki/Nitrogen_oxide) then [nitrogen dioxide](https://en.wikipedia.org/wiki/Nitrogen_dioxide) gas, causing [photochemical smog](https://en.wikipedia.org/wiki/Photochemical_smog). The GRB may produce enough of the gas to cover the sky and darken it. Gas would prevent sunlight from reaching Earth's surface, producing a "cosmic winter" effect – a similar situation to an [impact winter](https://en.wikipedia.org/wiki/Impact_winter), but not caused by an impact. GRB-produced gas could also even further deplete the [ozone layer](https://en.wikipedia.org/wiki/Ozone_layer). > > > [Answer] I think to an extent, the only way to destroy civilization would be to make humans go extinct; people gravitate towards systems of government, even if only at a local level. At least one system would probably grow over time, so the only way to make sure it's completely gone would be to kill everyone. While you could do that with an asteroid, it would be extremely hard to actually change the trajectory of something that large, unless you're willing to do the calculations, tap it slightly and very precisely while it's far away (100's of years) from earth, and then just wait around for it to hit. A much faster, easier method would probably be to just nuke the place. If you don't have enough to hit everywhere, then probably just hitting the major centers of government, commerce, woods/trees, and agriculture, would be sufficient to end civilization in fairly short order. Just make sure that you destroy enough so that any survivors won't be able to find food, fresh water, and/or shelter, or maybe even heat or oxygen if you can set off enough firestorms and destroy enough forests. Clouds of smoke covering the whole world would deprive it of sunlight and heat, which in turn would greatly facilitate the cold death of the planet. Ain't it depressing that we're capable of doing all that right now. [Answer] Why destroy when you can enslave? Destroy 1 major city, televise it, jam all frequency, and say "Join us or you're next" [Answer] If we assume the aliens are travelling at relativistic velocity between the stars (no FTL), then they have several options: 1. Launch a probe at a high fraction of *c* at the Sun while beginning your braking manoeuvre. The impact on the Sun will trigger massive solar flares and other energy releasing events which will destroy virtually any space based technology that we currently have, and fry much of the electrical and electronic infrastructure of the Earth. The world's economy will crash, and in most of the advanced nations, where farming is highly mechanized, the number of farmers left will not be able to feed the local population (much less the global population), and mass starvation will take care of the bulk of the world's people. If diverting part of the US corn crop to make ethanol cold raise food prices to the point of causing riots in Mexico and other nations around the world due to price increases, imagine the effect of stopping ALL food exports. 2. If they are moving at a very high fraction of *c*, they might just "buzz" the planet. The Lorentz Transformation of a sufficiently massive spacecraft would be like moving a massive object through the solar system, potentially disrupting planetary orbits. The Earth could suffer disruptions ranging from massive earthquakes to being moved bodily from the habitable zone, depending on how the aliens times their pass and how "massive" their ship appears in our frame of reference. (If the movement brings Earth into "their" idea of the habitable zone, so much the better). In any event, the amount of inertia of the Earth will require a very huge amount of energy to disrupt, and this energy will be felt in the movement of crustal plates, oceans sloshing from their basins and massive magma chambers emptying. 3. Kill the Earth. If the Aliens don't particularly care about the Earth, they could just send a probe at a high fraction of *c* to strike the planet directly. At .99\*c\*, even a relatively small object will crack open the crust and expose the mantle (<http://what-if.xkcd.com/20/>). It might actually be more "efficient" to send a shower of objects timed to strike all areas of the Earth as it turns in its orbit over a 24hr period to sterilize the planet without cracking open the crust, but even the energy release at that point will probably boil the oceans. One could imagine a shower of marbles being dumped from a missile bus moving at .99\*c\* as the impactor, at that speed, the material hardly matters. One of the advantages for the aliens is that it will be virtually impossible for Earth to see the incoming projectile (regardless of the target) at high fractions of *c*, it is coming virtually behind its own light, if you do happen to see it, it will be "in the past", and you won't have much of an idea where it is now. Even with futuristic technologies, there does not seem to be any way to see or stop highly relativistic projectiles coming from space. [Answer] We, humanity, already have the technology to destroy ourselves. Why complicate it with antimatter or near-*c* moving objects? Ever seen *The Day the Earth Stood Still*? I see two options that are both cheap. One is relatively quick, the other is kind of slow: ## Irradiate the surface. Everything will die in about a month. Cheap, easy, and relatively quick. **How?** Nuclear detonation in the atmosphere in key locations should do the trick. Someone already suggested hacking into the already existing systems on Earth for launching nuclear weapons. That sounds like it would cost only a small team of nerds and a ton of red bull. Alternatively, Uranium and other radioactive elements are pretty easy to find in the cosmos, I'm sure. Mining operations are probably not even marginal in operations management for this alien race. **Problems** The planet's irradiated now. Unless you have some way to reverse it you won't be able to use it for a very long time. All surface life is dead, not just humans. **Pros** The infrastructure remains. Everything you ever wanted to know about humans is now enshrined in the remarkably undamaged ruins of its cities. ## Targeted Biological weapons This was already suggested, but a virus strain that specifically targets humans and spreads and kills quickly would work very well. **How?** A combination of illnesses, covering multiple contagion pathways, all released in multiple locations around the Earth. **Problems** Not as cheap as irradiation, and not as efficient. You would need time for research, probably years, to determine and develop the most effective pathogens. There would also be survivors, whether immune or unexposed, that you would have to dispatch manually. **Pros** This leaves the planet human-free and relatively unharmed. If you do it right, you will get well over 90% of all humanity and nearly 100% of those in the cities. All others get pretty excessive (i.e. wasteful). [Answer] A pretty efficient way to destroy the earth would be to use a high enough powered laser from space to melt through the Earth's crust at its weakest areas (such as supervolcano caldera) to cause a [volcanic winter](https://en.wikipedia.org/wiki/Volcanic_winter). The idea is similar to the other ideas of causing extinction mentioned here, such as nuclear winter and just outright blocking the sun, but i think this has the benefit of really requiring very little extra technology beyond our current capabilities. All it needs is a big enough laser, powerful enough to melt silicon and whatever else is in the crust, with big enough focusing lenses of a material that can withstand the intense energy. Outcome: These [statistics](https://en.wikipedia.org/wiki/Nuclear_winter#2007_study_on_global_nuclear_war) are simulated projections for nuclear winter but i think you could draw a pretty direct comparison. Not the fastest way to do it, but i think probably the cheapest and most energy efficient, as well as being technologically realistic. [Answer] **Negate or Warp the Earth's Magnetic Field** Either temporarily negating, or warping the magnetic field of the planet such that the sun facing side effective has little to no electromagnetic protection. The solar wind would wreak havoc on anything electrical or electronic and on anything on the surface containing DNA (i.e. people, plants, life in general.) Negation could be effected via phase cancellation, altering the shape of the field can be effected via the employ of extremely strong and large directable fields. Electromagnetic field manipulation on this scale would be especially feasible by a sufficiently advanced alien race capable of interstellar travel. I do not see anything that would preclude such a possibility as such massive fields would likely be used in shielding, containment, the actual method of interstellar travel via the manipulation of the actual physical "shape" of space surrounding the craft, possibly directed energy inter-vessel weaponry, and so on. They would certainly be capable of harvesting, harnessing and/or producing the requisite energy to do these things. It might even be likely that such a vessel would be powered by some kind of a contained/managed stellar, neutron star, or even a black hole based "power plant" or "engine." Perhaps even a complete and permanent collapse of the planet's electromagnetic field could be caused by focusing complex, directional and huge fields on the molten core of the planet thereby causing a cessation of its rotation therein! A few days of this would be sufficient to wipe out any real civilization, kill a large portion of life on the planet, trigger lots of mutations among the remaining life and make earth an all around fun place for the few politicians who hid themselves in bunkers--if they had the time/wherewithal to do so before being affected beyond survivability--as they emerge thinking they'll have something left to run... [Answer] Not a joke: **jam their smart phones.** * The population aged under 30 commits suicide for obvious reasons. * The world economy comes to a grinding halt since top managers are helpless. Not as sexy as that antimatter device, but sadly much more effective and energy saving. Who said aliens civilizations wouldn't care for *green conquer*? That's what Douglas Adams would have thought about :-) [Answer] I find it unbelievable that no-one has mentioned the single most efficient weapon for destroying civilization, at very low energy and economic cost. <https://en.wikipedia.org/wiki/Biological_warfare> a couple of quotes from the above wikipedia: > > Offensive biological warfare, including mass production, stockpiling and use of biological weapons, was outlawed by the 1972 Biological Weapons Convention (BWC). The rationale behind this treaty, which has been ratified or acceded to by 170 countries as of April 2013, is to prevent a biological attack which could conceivably result in large numbers of civilian casualties and cause severe disruption to economic and societal infrastructure. Many countries, including signatories of the BWC, currently pursue research into the defense or protection against BW, which is not prohibited by the BWC. > > > That is, we are talking about a weapon less legal than nukes. And here's why. > > It has been argued that rational people would never use biological weapons offensively. The argument is that biological weapons cannot be controlled: the weapon could backfire and harm the army on the offensive, perhaps having even worse effects than on the target. An agent like smallpox or other airborne viruses would almost certainly spread worldwide and ultimately infect the user's home country. However, this argument does not necessarily apply to bacteria... > > > Aliens would have an entirely different physiology and would almost certainly be immune to human viruses, which have specifically evolved to reproduce in a human cell. (On the other hand, simple bacteria and parasites might prove deadly to the aliens.) So if theres a wave of alien abductions, they're probably taking people to use a guinea pigs to breed and incubate the ultimate strain of smallpox. Although the disease has currently been eradicated, we shouldn't get complacent and stop vaccinating, because when aliens attack we're doomed. <https://en.wikipedia.org/wiki/Smallpox> <https://en.wikipedia.org/wiki/Smallpox_vaccine> Note that smallpox played a major role in the conquest of the Americas. The Europeans brought smallpox with them, and the natives, having had no contact with the disease, were decimated. (In return, it is believed the Native Americans probably gave the Europeans syphilis.) [Answer] Aliens should research our culture and gain knowledge of the planet, before they will destroy us. I believe from perspective of inhuman specie I would've destroy human kind with the most creative way as possible. If we can convince entire human race that after you die, you become into anything you wished. Christians will go to heaven and atheists will become gods of galaxies, muslims will travel to gardens of virgins and etc. Maybe we the aliens will pour some toxic delusional drug into the atmosphere. Make everyone trip into dreamworld of endless possibilities. Countless casualties by suicides. The ones that keep breathing on this planet only because of fear to die. Yeah orbital strike with enhanced LSD is my final answer. [Answer] Destroy the 3rd world countries and wait for civilization to collapse. Modern first-world countries depend on the third world countries for so many resources it would be difficult to function without them. After all, those countries supply large amounts of the resources necessary to build a F-16 or any other modern weapon. The destruction of the 3rd world countries could be carried out via a bioweapon or something else. This has the added benefit of minimizing damage to the planet. [Answer] Throw a tether from the Moon. OK:said like this, it need almost infinite strength. But if you make something that hung until the earth atmosphere, the aerodynamic drag will slowly slow then crash the Moon down. This still need a science-fictionish tensile strength, but the energetic cost can be very small. [Answer] A lot of people have been ignoring the energy-efficient aspect of the request. There's a lot of things that would work but use a huge amount of energy. The most efficient way to destroy civilization would be from the Kupier belt. Take something say 20 miles across and deorbit it. Gravity does most of the work. It's slow, though. [Answer] They could use their "magic-plot-teleporty device" to teleport a large chunk of the nearby star's core into the planet. That'll do it. ]

[Question] [ It is a common trope in sci-fi that engaging a vessel's faster-than-light travel requires performing some complicated mathematics that takes a non-trivial amount of time. I want to know to what extent this is even remotely plausible. In other words: what [time-complexity](https://en.wikipedia.org/wiki/Time_complexity#Polynomial_time) is *reasonably implicated* by any arbitrary form of FTL? After all, in my own (limited) experience, almost all calculations typically fall into one of two categories: 1. Any everyday computer can complete it in a fraction of a second. I think that's pretty much all of arithmetic, algebra, geometry, ballistics, and calculus. Effectively zero time. 2. No single computer has any realistic chance of performing the computation in less than several hours. E.g. video transcoding, defeating some forms of cryptography. For someone fleeing for their life, this is effectively "infinite time." Of course, I'm aware that there are problems that would take more time (and energy) to solve than exists in the universe. The obvious challenge here is that we don't have FTL, and I'm *not* going to describe a specific system and ask you to analyze it. What I propose instead is to enumerate some observable characteristics that are common to a variety of popular fictional FTL systems, and then to reason about their time complexity. --- First, let's talk about the observed characteristics of the FTL systems I have in mind. Whether you're talking about *Star Wars'* hyperdrive, or *Battlestar Galactica's* FTL, or probably any of a dozen less well-known variants, the calculation cannot be prepared in advance. It must be performed immediately prior to the FTL transit. Even without knowing the engineering particulars, there are a couple of obvious reasons why this might be the case: some of the terms in the equations depend on the point of departure, or are time-sensitive, i.e. if your destination is something in motion, like a planet or star, you can't calculate its position without also specifying a time. And so the most straightforward approach is to read the current values from the environment. Of course, this isn't why writers do it: they do it because it's a low-effort way to manufacture a ticking clock when you want suspense. But this is the putative justification, and indeed it sometimes gets mentioned by characters. Another thing that's almost universally true is that there is no complementary calculation for how to shut down the FTL; I don't think I've *ever* seen something like that. This is true whether the transit is instantaneous (as in *BSG*) or not (as in *SW*). And if there is any math that must be performed during the transit (e.g. in *Star Trek*, the computer monitors the warp field and propulsion system to make continuous adjustments), it doesn't impact departure or arrival in any way that we see. Also, I am talking about *the math only*. It's often the case that the FTL system must "warm up" (or "cool down" from the previous transit), and that takes time too, but these are always presented as orthogonal concerns. Presumably, the math can be performed whether or not the drives are ready; you could even do the math just for fun, and not actually execute the transit once you have the solution. I only care about the time required by the math. --- Second, let's talk about some constraints. It's obviously impossible to evaluate the time-complexity of a set of problems if I don't specify those problems. However, I think we can reasonably exclude a lot of territory. For one: while there may be a huge class of problems that are either literally unsolvable by computers (e.g. the halting problem), or not solvable within a useful time (e.g. cracking AES-256), it seems self-evident that nobody would actually put these systems into a multitude of vessels if it was reasonably likely that very many FTL transits would fail to compute within a reasonable timeframe. If we had a machine today that could take us to the stars at faster-than-light speed, but it had the same time complexity as cracking AES, we *might* actually build a few of them and turn them on, because even though the likelihood of near-term success is low, the potential payoff is enormous. But we wouldn't put one of those *in every single spaceship*. And nobody who is fleeing from combat would consider that device to be their best chance of escape; they probably wouldn't even turn it on. If the math for a jump isn't *known* to be "[in P](https://en.wikipedia.org/wiki/P_versus_NP_problem)," people wouldn't rely on FTL as primary transportation. Not even for shipping freight: > > "I'm hauling 20 tons of frozen bananas to Alpha Centauri. We could arrive any time between 5 minutes and 1053 years from now, so don't wait up." -- ≠P Space trucker > > > Thus, I think we can say with absolute certainty that the whole class of FTL drives relies on math that is *known* to be solvable in polynomial time. I think we can say more: it seems probable that the bulk of any computation will take place in the domain of navigation. So, I'd expect to see a lot of arithmetic and trigonometry. Possibly there might be some physics simulation, which I assume involves calculus. Perhaps some database access to help determine the positions of known, distant objects. The problem for me is that all of this falls into the category of "easily solvable in milliseconds on current-day hardware." And it's ludicrous to suppose that a civilization where FTL is commonplace would have worse computers than we do. Moreover, even if we're talking about computational expenses similar to video transcoding, which (depending on the input) can take hours, it's absurd to think that (1) the civilization wouldn't develop specialized hardware to solve those problems quickly, and (2) individual vessels wouldn't purchase whatever extra hardware is needed to further reduce the computation time to zero. We do transcoding in the cloud; Han Solo would buy 10 fancy graphics cards and a 64-core CPU, because the alternative is death or imprisonment if he can't bug-out at the drop of a hat. *Nobody* is going to fly around with the slow factory model of jump CPU if they can upgrade. And if "calculation" is an accurate description of what is being done, very significant upgrades will necessarily be possible. And let's be realistic: the FTL calculation is *not* going to include actually transcoding a video, because that is obviously irrelevant to travel. It's *not* going to use deliberately-expensive computation (like bcrypt), because nobody *wants* the FTL to take longer than necessary. So, it seems to me, by the light of my dim understanding of computation theory, coupled with reasonable expectations about pilot behavior, that any version of FTL that requires pre-departure math would necessarily lead to one of exactly two scenarios: 1. FTL is not solvable in polynomial time, is therefore not even remotely practical, and so would not be part of most vessels; or 2. FTL is solvable in polynomial time, vessels will optimize it to death, and so the oft-seen countdown has no basis I'm not well-versed in computation theory, and I'm sure there are people here with a better grasp of NP-completeness than I. And probably there are additional meta-mathematical domains that are relevant of which I'm not aware. --- So, what I'm asking for is: Within the boundaries of the observed FTL characteristics I've described, and without manufacturing some set of time-consuming handwavium computations -- that is, *without inventing a specific system*, what are the narrowest boundaries we can reasonably place on the amount of time it would take to calculate the endpoints of an FTL transit, and/or plot a course between them through spacetime? Put another way: can you identify any problem domain that would *necessarily* be part of the whole family of "math before jump" FTL, that has many problems which are not solvable in polynomial time, or which couldn't eventually be optimized down to <1 second? I take both of those questions to be formulations of the same concern, so answers must survive both. [Answer] An arbitrary example of a calculation with suitable complexity, that matches the complexity of a hyperdrive jump, which cannot be pre-calculated but which *can* be calculated and shared to multiple other people for immediate use: Pick your starting and ending coordinates: These coordinates are mapped on a multidimensional Fractal space. For simplicity of illustration here, I will display a 2-d image of a Mandelbrot fractal. Just to show the infinite complexity that fractals can have. Now calculate the *exact* line of equipotential between your starting point (which is fixed) and an acceptable ending point near where you want to exit. This calculation takes a long time, but reasonably predictable time for any given parameter of accuracy. [](https://i.stack.imgur.com/Z9TqS.png) Yes, that image is of ONE LINE around an equipotential of the Mandelbrot set. And no, zooming in does not simplify the line. It stays at that same complexity level at 10-x, 100000-x, or googol-x zoom. No, you cannot precalculate this, as the exact shape of the fractal will vary depending on current interstellar relative positions, energy densities, and gravitic events (like the "bounce too close to a supernova" that Han mentions). As conditions change, the fractal representation of the hyperspace manifold changes. But, once calculated for current conditions, start position and desired end position, the solution will remain valid unless conditions change. This allows you to share your calculation to your fleet, allowing coordinated movement. A planetary-scale computing complex might precalculate a few million possible variations of conditions, for a known set of start and end points in the very near future, allowing smaller ships without the needed computers to do a jump. But the number of precalculations would depend on the number of independent variables, which are likely to be *many*. This is an example of a very computationally intensive problem, that requires a reasonably consistent amount of time to calculate to a given precision level. And cannot practcally be precomputed and stored in a database. P.S. The OP's example of video transcoding is actually a pretty good example of a suitable problem! It is a huge, finite, and quite accurately time-predictable task which is utterly dependent on input data, parameters, and desired output. The reason it takes OP "hours", is because they have **chosen that as an acceptable trade-off point between quality and time**. The same task could be performed in seconds, for a very low-resolution version of the video, or decades, for an ludicrously ultra-high resolution video stream. [Answer] ## Simulation of the galaxy. When you're doing FTL jump, thanks to the lightspeed lag, you are always operating on the information about your target system that's outdated from years to decades and centuries. Normally a star would travel a cosmically insignificant distance in this time, but you don't want to pop up "somewhere in the general vicinity" of the star, you want to pop up inside the planetary system, or even right on a suitable orbit around a planet. So you need to predict the position of the destination right now based on this outdated information, and do it to a precision with an acceptable error margin of several thousands of kilometers. Considering the complexities of gravitational interactions in an n-body system, you need to model interactions of thousands to millions of objects, since the errors in calculations, however small they might be, can be enough to displace you millions of kilometers away from your destination, or if you had bad luck, put you *inside* of it. So you need to essentially simulate the movement of a small chunk of the Milky Way, along with every significant source of gravity in it interacting with every other source - like stars, planets and nebulae (hello fluid simulations). And to do that, you need to simulate backward the stars around you first, based on their distance to you and data from your observatory module, to find their needed *objective* positions at the start of the simulation. It sounds like "hours to days to complete on a mainframe computer" type of problem, but extrapolating this into future sounds like a worthy task for a futuristic navigation computer of a spaceship would think over for several minutes. You can't optimize this task, because any optimization would invoke simplifications and approximations, the very thing you don't want to have when calculating your arrival point and velocity. The "less you spend on calculations - the dirtier and more imprecise your arrival is" can even be a good plot point. [Answer] **Chess.** from <https://chess.stackexchange.com/questions/2422/database-of-every-possible-move-in-chess> > > I believe your question essentially boils down to the topic of whether > it is possible to completely "solve" chess. Wikipedia has an excellent > article on the topic which should give you a good overview. > > > To summarise, the number of possible game variations in chess is > estimated to be 10^120. This is a staggeringly huge number, for > comparison, consider that the number of atoms in the observable > universe is estimated to be around 10^80. In other words, if you were > using the entire observable universe as your hard drive, you'd still > need to store 10^40 combinations of chess games on each atom, in order > to simply store it all. Needless to say, this is so far beyond our > current and forseeable technologies that most people consider it to be > completely impossible. > > > Assume that modelling a hyperspace jump is like modelling a chess game except there are more pieces. Given the initial set up of the relevant universe, the computer runs multiple jumps which return different probabilities of success. Some clearly have a low chance of success. The computer continues to run simulated jumps until it arrives at one with an acceptable chance of success, "acceptable" probability being something determine by circumstances. One could improve the chance of success by opening up possible destinations - for example if you are fleeing, any open space is acceptable. If you want to jump to a precise location with a high chance of success, many simulations might be necessary. "Many" being 10^big. It can be done. It might be done pretty quick, with luck. Or not. [Answer] **Calculation times, in practice, are often more about Human patience than computer power** Calculations *can* take a long time. In solid state physics people are often forced to leave a supercomputer running for weeks to simulate a quantum system, sometimes months. This is all just number stuff, adding and multiplying - its just there is a lot of it to do. However, a crucial point is that these kinds of solid state physics simulations will *always* take weeks to months no matter how good our computers get. The simulation makes all kinds of approximations, you probably want a set of atoms that is "effectively infinite" but you probably only have 100 as more would slow things too much for your patience. If computers got better your patience would not change, so it would take the same time and you would have 200 atoms. Maybe there is a variable you keep fixed in all your calculations - but if the calcs ran 10 times faster you would sweep that variable to see how it changed things. **Jump times, in practice, are determined more by Human patience than computer power** Ok, but FTL navigation is different surely? Maybe in 2650AD an FTL jump takes an hour to calculate, but by 2670 the same calculation is down to 3 minutes. By 3000 AD its 2 seconds. The period in history where it falls in the middle seems likely to be short. Unless there is another variable, something like the number of atoms above. People's patience remains the same, so on average if 1 hour is the most anyone can possibly be bothered to wait for an FTL jump (people of the future are impatient) then as computers get better people will take more of the other thing. What is the other thing? Maybe its the size of your ship, bigger ship -> more complicated jump calculations. Then ship size and computer power scale together. Maybe the scaling is something else - perhaps each time a ship jumps it leaves ripples in the warp that make the maths harder for the other ships nearby. Suppose that if jumps take X seconds it is profitable to have more ships flying routes. More and more ships are flying until jumps take about X seconds on average and some kind of equilibrium is found. Then computers get better, but economics will ensure that any reduction in jump times will be short lived, as that extra capacity will be filled by more people jumping. (Traffic on real roads can follow a similar pattern.) [Answer] Okay. I have to choose my words carefully to stay off the timekeeper's radar. Also, just for starters, I can't share any of the formulae involved because they are based on 23rd century "true" math and wouldn't make any sense to your 21st century approximation of that higher nomenclature. What is referred to as a "calculation" in your current age fiction is actually a computationally-intensive exercise in real world prediction. The task boils down to grabbing several sequential snapshots of quantum-particle level sensor data and from them calculating where every part of every particle in your immediate trajectory will be at several distinct moments in the proximal future. The gravitational and --CENSORED-- contributions of every particle to the underlying space-time must be known before it happens, for every particle in an arch forward out to the distance needed for your engines to achieve FTL (warp) or FTL-INFINITE (jump) speed. The reason for this is simple, but non-obvious until you actually start approaching these speeds. I don't have time (or editorial freedom) to go into the details, but just assume that even subatomic particle impacts become significant at near-luminal speeds. So you are not waiting on your computer to figure out the course to your destination or some esoteric value which is needed to get universal permission to go real fast. You are waiting for your computer to find the possibly-nonexistent instance in time when the path ahead is navigable out to the distance needed to go super-luminal. A number of factors influence this computation and none of them are known up until the moment that the FTL calculation is requested. * You need to know how many sub-atomic particles are in your forward path which will determine how long it will take to determine where they all will be at every possible (yet to be determined) proximal future moment. * With that calculation estimation curve established, you can then determine the specific moment in future time for which your computer should start searching for a clear launch window. This is done by adding the estimated calculation time and the engine engagement statistics (start-delay, acceleration-curve and subluminal-threshold) to the current moment, then back-tracking to allow for your ship's captain's average response time in issuing the "engage" command. *(Damn Shatner for starting that wasteful two-syllable tradition. A simple "Go" would have saved millions of cpu cycles.)* * Once your computer has this all worked out, it then has to continue computing it going forward until your captain gets around to deciding to start the journey. Most of the work is already done by then, getting the whole predictive model in place and running the particle map consistently ahead of real time, but it must then be maintained, with new window moments being identified as needed until the captain is ready to go. These factors have an obvious ramification for would-be faster-than-light adventurers... * It works much better in deep vacuum, where the particle densities are lowest. Launch windows appear very regularly when there aren't trillions of participants in the "let's block the launch window" game. Consequently, launch windows among the inner planets are pretty rare. Too many miniscule planetary sheddings and solar discharges can really get in the way. Your best choice of departure points is out beyond the Oort cloud, but getting there in some systems can take a lifetime at sub-light. Okay. I have offered what I can. Hope it helps. Hope I haven't said too much. As a disclaimer, none of the ideas presented here are actual scientific theories proposed by actual scientists either living or yet to be born. This answer does not violate the prohibition against early release of future information as everything stated here is purely speculative and not to be confused with actual reality. Any similarities to actual discoveries, either current or upcoming, are purely circumstantial. Please don't delete my personal timeline. [Answer] 10 light years is about 58,786,253,700,000 miles. Assume you have to check the entire path for obstacles larger than a few metres across, as running into the hyperspace mass shadow of a 50 ton rock at multiples of the speed of light is going to jar the bolts loose, and then some! (We know from current-day experience that walking into a 40 gram bullet at a mere 1700 miles/hr is going to do some damage.) So multiply the resolution needed by a thousand or so. Then consider that the rocks and other hyperspatial anomalies are all moving in different directions at different speeds, were all measured with finite accuracy, and were probably last surveyed *years* ago. (As a rebel/smuggler, you want to stay off the busier and better-surveyed spacelanes with their ubiquitous Imperial police patrols.) And you also probably can't bend your trajectory too fast. (At least, not without finding your face pressed hard up against the cockpit window saying 'Gnnngh.') So let's say you have to do a database lookup for any 'starchart' records for cells along a line 58,786,253,700,000 miles long and broad enough to include any rocks moving in from neighbouring cells down to a resolution of a few metres, project the position of every obstacle found forward to the present time (with error bars!) check for intersections, try to tweak the trajectory to avoid any hits detected, check accelerations along the new course for passenger safety/engine feasibility, and then recheck the new trajectory for obstacles. And that's *without* even having to do it in ten dimensional hyperspace with exotic mathematics. The complexity of searching in three dimensions increases with the cube of the size of the region, the complexity in ten dimensions with the tenth power. So scale up by 10, and a 3D search expands by a factor of 1,000, and a 10D search expands by a factor of 10,000,000,000. If we estimate that a 10 light year jump calculation needs to take around 100 seconds to be practical, then we have to process each thousand miles of trajectory in about 1.7 nanoseconds. That's on the order of a few clock cycles on a current-day CPU. Space is big! [Answer] **This is a [Frame Challenge](https://worldbuilding.meta.stackexchange.com/q/7097/40609)** I've enjoyed reading the many answers, but they all have one overriding problem: you're asking us to explain using today's best-guess concerning technology how we could do something that won't matter for some time into the future. I therefore question the usefulness of the answers. * If you have the tech to fly FTL, you certainly have improved computational tech. Since we cannot but imagine the tech needed to fly FTL, it's reasonably true that we cannot but imagine the computational tech available to calculate navigation. * Since we know nothing about flying FTL in the real world (other than we believe it can't be done), we obviously know nothing about the navigational hazards of flying FTL. We can look at the gravity wells, etc., that we know about, but how valuable can that be to you? Before we learned how to fly, the hazards of flight were basically unknown to us. We learned what they were as we improved the technology. **But more to the point, what all those SciFi shows were really doing was stepping past a bit of window dressing to continue telling their story** Over the years I've noticed that there's a number of people who perceive "hard sci-fi" as something it really isn't. They think that "hard sci-fi" is a story that rigidly adheres to science. To that end, they look for rational, scientifically complete descriptions of fanciful, [Clarkean magic](https://en.wikipedia.org/wiki/Clarke%27s_three_laws). I ran a publishing house for about 10 years, and one of the things I learned during that time is that new authors often got hung up in details that didn't actually relate to their story. So, why do all those wonderful SciFi stories basically skip over the mathematics and computational reality of navigating FTL? *Because it's irrelevant.* With incredibly rare exceptions, all stories fall into one or more of the [seven basic plots](https://en.wikipedia.org/wiki/The_Seven_Basic_Plots). Science Fiction is nothing more than the window dressing used to tell a story. Let's face it, unless you're writing a textbook about the history of some aspect of science or your writing an article postulating the possible future developments of said aspect, what you're really doing is telling a proverbial boy-meets-girl story dressed in your favorite genre of choice. **And there's where Worldbuilding.SE becomes really valuable** What we do here is help you develop that "genre of choice" infrastructure for your story. And that's why I have to challenge the frame of your question. Because any explanation of how fast or slow, how efficiently or inefficiently, how practically or impractically FTL navigation can be computed is fundamentally irrelevant even if your story depends on the fact — because you're asking how fast something can be done so far in advance of when it would actually be needed to be done that the answer is meaningless, and it's probably meaningless to your story anyway. [Answer] I think the idea behind this question is being dismissed far too easily. For instance, this comment is almost an ad hominem attack: > > "After all, in my own (limited) experience, almost all calculations typically fall into one of two categories:"... sorry to inform you, but you are correct. No, not about the complexity of calculations, but about your ignorance thereof. – PcMan > > > And those answers that *have* been given seem to miss the point completely and talk about the complexity of the problem, which is *not* what the question is asking about. --- Consider an algorithm of complexity O(10n): [](https://i.stack.imgur.com/DPPH3.png) — [plot (10^n) - Wolfram|Alpha](https://www.wolframalpha.com/input/?i=plot+%2810%5En%29) Up to about n=6, it will finish relatively quickly; between 6 and 7.5 it will take increasingly longer, and beyond 7.5 it will take a ridiculously long time. (Note that "n" could represent a million data points, not necessarily a small integer.) The first part of the graph is approximately linear, while the later part of the graph is approximately infinite. The vast majority of inputs will be in either the first group or the last group: quick to solve or don't even bother trying. The [Travelling Salesman Problem](https://en.wikipedia.org/wiki/Travelling_salesman_problem) is a common example of something that in general takes impossibly long time to solve. But if it is restricted to small problems, there are algorithms that can solve it quickly. --- For any given navigation algorithm there will be some minimum number of required input values. It's rather obvious from the above graph that that a solution for any such algorithm will almost always be extremely quick or extremely slow. If it's in the quick category it can easily be sped up with extra hardware (e.g. if it normally takes an hour, then 100 processors could do it in 36 seconds). If it's in the slow category, there's nothing that can be done to make it work in a useful length of time. If there is a practical algorithm for FTL navigation, it would have to be in the quick category, or it wouldn't be practical to use. And I'd say it's almost certain that, as the OP conjectures, it could be made to finish as quickly as desired. --- In terms of fiction, the flat part could represent calculations of trips of less than 25,000 light-years between endpoints. A single jump across the galaxy would be prohibitive to calculate, but with at most 4 shorter jumps anywhere in the galaxy could be reached. And perhaps the flat part also requires that the endpoints be near a large mass, such as a star. If this factor is combined with the first limitation, despite being able to quickly jump around within the Milky Way, intergalactic travel would remain impossible. But wait, what if there are rogue burned-out suns, black holes, etc. floating in deep intergalactic space. Finding them could could provide a series of jumps that could lead to Andromeda. *Stepping Stones To The Stars*"? [Answer] **Fourier Transforms and Uncertainty Principle** Assuming you have to measure some spectral properties of the hyperspace medium to make your jump, you'd have to collect data for a certain amount of time to reach a certain accuracy about the current spectral composition. The longer you "listen", the more accurate your representation will be. In the easiest case, you'd have to determine only a single dominant local hyperspace frequency to sync your jump drive to it. If you sample the hyperspace amplitude for a short amount of time, your uncertainty about it's frequency will be quite large, potentially leading you to set the drive to a sufficiently different frequency to tear the ship apart. The longer you "listen", the safer it will be, and the more smoothly your hyperdrive will operate. You could choose to listen to the sound of hyperspace all the time, but if doing so comsumes some kind of resource (a large capacitor power drain, degradation of the expensive sensor, exposition to dangers or constant negative effects (gravitational fluctuations, hyperflares, the Warp, ...), ...), it would be necessary to only activate the jump preparation if you actually plan to jump soon. A more complex relationship between the spectral composition of hyperspace, the planned route and the drive parameters would also involve CPU power as a secondary aspect, and might allow a ship with good CPU/better software to jump *slightly* earlier (heuristically estimating some parameters with imperfect measurements, leading to similar safety after a shorter time), but that effect would likely be small. If the mismatch between drive frequency and hyperspace frequency (or a similar metric) caused significant stress to the hyperdrive and/or the ship, you'd get a practical behavior very similar to star wars hyperspace travel: Having to calculate some parameters before being able to jump without just blowing up your drive, more rapid jumps being more risky, and the inability to precompute jumps (changing conditions). **Is this a universal problem domain?** Almost. As long as the jump drive has some parameters that need to be changed depending on "weather" and as long as that "weather" has wave-like properties, there would be a certain minimum measuring time below which safe parameter estimation would not be possible. How long that time is depends on the inaccuracy sensitivity of your drive and the exact nature of that "weather", which ultimately depend on natural constants (+- some engineering factor, which would vanish as the technology matured). In some hypothetical universes that time might be measured in nanoseconds or galactic rotations, but it is entirely reasonable that it might fall in the "10 minutes until we can escape the pirates" range. The variation of that time across different levels of technology might be relatively complex, but (assuming simple relationships and technology somewhere near physical limits) you'd expect at most a 50% time reduction between a cutting-edge experimental military hyperdrive and an older, but technologically almost mature one. **Could there be a truly universal problem domain?** The only universal necessity of hyperspace-type travel (without any assumptions about its details) is knowing ones destination (in some specific mathmatical description, from direction to fractal parametrization). In principle, a drive could convert you to tachyonic matter traveling in a perfect-vaccuum hyperspace (and back), so at least in some cases knowing direction, distance and speed would be enough. In this case, traveling away from something would almost always be trivial (simply wait for an amount of time guaranteed to land you in interplanetary space, as opposed to inside the core of a star), while traveling close to a target would only need storable/pre-computable sensor data. In practice, it might be necessary to get traffic control information from the target, so hyperspace phone speed might be a limiting factor, but that doesn't apply to fleeing from pirates, so it seems like there are no completely universal problem domains limiting all conceivable forms of hyperspace travel to wait before jumping. [Answer] # It's not the crunching of the numbers, it's *getting them*. To be able to successfully engage a hyperspace jump, you need to know exactly where you are, how much energy is required to enter hyperspace, and how much energy is required to perform the jump. Requirement #1 is simply Galactic GPS, and anyway, a small error is tolerable. Requirement #3 is just having good maps and again a small error is tolerable. The problem is in requirement #2, which depends on the conditions of local space, and these condition vary *continuously*. All the almost infinite gravitational sources in the Galaxy are moving and rotating and sending off gravity waves, and the resulting *noise* is what prevents hyper-entry. To "open a portal" it is therefore necessary to know *exactly* the hyper-conditions of the local brane with a margin of a few seconds. And, to do this, you need to deploy (disposable) hyper-sensors and map a large enough spherical volume around the ship, and transmit this set of readings (through FTL) to the computer. Being transmitted FTL, these readings describe the "future" conditions from the point of view of the ship, and can be used to calculate the exact conditions at the future time of the scheduled jump. The accuracy of the readings is proportional to the time covered by the reading themselves, usually several seconds (or as many as you need). Since the *ship* and the sensors themselves influence the readings, and do so with their own gravity waves that travel at the speed of light, there is no way of reducing this "settle time". Usually, furthermore, a little more time is required to have a margin allowing FTL recovery of the sensors, which aren't cheap (you can cut that time by abandoning the sensors). In an extreme emergency, you can deploy the sensors nearer to the ship, and use shorter readings to calculate a *rough* estimate for the hyper-entry. The rougher the estimate, the higher the risk of a catastrophic entry, with the ship hypering as a discrete collection of chunks. [Answer] It's completely arbitrary and as an author/world-builder you can add whatever simplifications you like. I'm a technical developer with roughly engineering math education & a bit more interest. I think it's more useful to relate time complexity to factors that make your in-universe decision making interestingly variable. 1. Risk - probability of a successful jump. That implies you may be up against a culture that accepts a higher risk for strategic advantage, out of desperation or warrior culture. David Weber explores this with relation to wormhole transitions, in his Stars at war series, especially [Shiva option](https://en.wikipedia.org/wiki/The_Shiva_Option). 2. Accuracy - related to risk (you may end up in a star) but consider starting point/vector, ending & desired accuracy. You could build in an exponentially increasing requirement for accurate calculation up to a threshold where galactic movement limits it. You can blindly jump at almost any time (although gravity well restrictions are a common trope). 3. Physics of observation. This gets more to a realistic physics/maths limit. Assuming you have jumped into a system, you need to get light-speed limited information back on gravity bodies, other factors. Very old industrialised systems would have patterns of satellites feeding this info from closer range. Think of this like we can use localised GPS from ground transponders to supplement orbiting locations, for millimetre accuracy. [Answer] An analogy: As the hardware capabilities of computers improves, the software running on them grows more hungry for the increased capabilities. The operating system for the latest hardware will run much slower on older hardware. So people tend to get a few OS upgrades and then eventually see the need to update their hardware as well to keep it running smoothly. Likewise, given the latest hardware capabilities, navicomputer software developers write FTL calculation algorithms that max out processing capacity of the system to achieve the calculation within a reasonable amount of time (say, 30 seconds). Let's say this puts the chance of catastrophic failure in an FTL jump at, on average, 0.02%. A few years later, more advanced hardware is available, and the software devs now are able to refine and add additional features to their computation software which, while keeping the time-to-calculate within a reasonable number of seconds, bring the chance of failure down to an average of 0.0185%. This is a reasonable enough improvement in safety that over the next few years the adoption by ship owners of the newer hardware and software follows a standard S-curve (some early adopters, most middling, some late). Some cargo vessels may choose to upgrade the software only, and suffer an increase in calc time from 30s to 1.5 minutes. But the tradeoff seems worth it to some. Some smugglers keep running the older software, but upgrade the hardware so they can calculate jumps in only 24 seconds. Thus, the "optimize it to death" may well look like how hardware and software progress look to us, and produce similar results to what we see in the real world. It goes slowly over time, and often we marvel at what the techies can accomplish, while also lamenting "why is it so hard to just make X system do Y?". It's messy, but we can have nice things. (That is, nice things that still have some time cost, as opposed to the only options being things that are either near instantaneous or unusably slow.) [Answer] Several things come to mind 1. N-body problem. There is no good fast solution for it as of now, basically you need to simulate, which might be a very painful experience if your n is the whole galaxy. 2. If you are numerically solving the differential equations that describe both very small and fast objects (your FTL ship) and slow and large (the galaxy), a fun little problem can arise: <https://en.wikipedia.org/wiki/Stiff_equation>. Which makes it a real pain to solve fast. 3. Something very simple, like having to calculate elliptic integrals in large numbers and very precisely. Since everything moves more or less along ellipses according to the Kepler laws, I won't be surprised if an elliptic integral appears somewhere. And that is not even considering relativity, the quantum mechanics and all the FTL science. [Answer] Frameshift: Nothing in your problem statement precludes precalculating the answer. Ok, you need to know your jump point--but can you not simply go to the point you did your calculations for? To some extent you must do that anyway as I can't recall any of the major systems that require you to stop before making your jump. (Some books do, however--but those always involve transit over fixed links, you just need to approach the link carefully.) Thus we need to take a different approach: Consider what happens with the GPS system. It inherently takes at least 30 seconds to get a GPS fix because you must download the weather report which describes the propagation delays which are to be expected. Therefore: Hyperspace isn't flat, it has waves. Ideally, you download a report on the waves from navigation satellites which maintain updated reports out as far as one can jump, but hyper-capable ships also have a sensor that can gather the information, albeit with less precision. The on-board sensor is simply a point reading and can't actually see the waves, they can only be determined by seeing how the reading changes over time. (Picture a pole in the ocean with a float that goes up and down and you can only read where the float is.) Getting the wave state reasonably correct is vital as it bends your course as you enter hyperspace. (Picture what happens to a reflection in the water when there are ripples.) Thus normal shipping simply reads the navigation satellites and makes their jump. However, when you're trying to operate without the permission of the authorities (I can't think of a scene where hyperspace calculation time mattered that didn't involve illicit operations) this isn't an option, you have to make your own measurements--note that it's **not** actual CPU time involved and thus you can't speed it up by throwing a bigger CPU at it. Yes, you can make a hyper jump blind--but if you do so where you arrive is **wildly** unpredictable, you very well might wind up so far away from home you can't find your way back. [Answer] **The calculation can be polynomial, take time, and not be improvable** *Getting through space* To get through space you just need to calculate f(t), based on g(t), for the trip at various natural number values of t from 0 to N. The value N increases with distance. The local space folding energy at every value t is e(t). An incorrect answer with much energy leaves your ship ripped apart, too little and it collapses on itself. > > If g(t-1) > e(t) : g(t) = g(t-1)-e(t) > > > > > If g(t-1) < e(t) : g(t) = g(t-1)+e(t) > > > > > f(t) = g(t)+g(N) > > > Essentially there is the energy needed by the tunnel determined by the end point, and the energy needed due to local fluctuations. *limits of parallel computing* So computers could do this in parallel right? It is just adding. Well, since every answer depends on computing the last value before we know any answer we need to wait on that computation to get the answer. However, the branching behavior makes it impossible to calculate the last value in parallel. Now it doesn't mater how many cores you have, you can't compute this faster than O(N). *Making it take time* You are moving faster than light and the effect of space folding might be very strong. Maybe you only need to run this algorithm for every kilometer, or maybe it is every meter, or millimeter. The greater the required accuracy, the greater the maximum value of t over the same space. Even the fastest adders and comparers still take non-zero time to run. Once you make the smallest component moves at light speed and you can't speed up anything you will not be able to compute this faster. once it is discovered it might be in every ship, but it still takes the same amount of time. [Answer] **Aircraft flight planning takes time** What I suggest as a good analogy (and perhaps the source of the trope?) is flight planning for an aircraft. Pilots are required to familiarize themselves with a bunch of information that is both required by regulation and necessary for the safe operation of the aircraft. Depending on the type of flight (general aviation, airline operation, military) and other characteristics the details will vary. The FAA has an [Advisory Circular titled "Pilot's guide to a Preflight Briefing"](https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_91-92.pdf) that explains some of the information required and the process. The preflight planning process is not currently computationally limited, but instead is essentially data source and human limited. If you are planning a flight for a long distance your weather briefing has to include weather forecasts for many hours in advance along the whole route of flight. It also has to include state information (airport landing procedure availability, etc), for your destination and the whole route of flight. The planning includes winds, visibility, icing conditions, navigational equipment outages etc. A pilot needs to gather the appropriate information, decide a route, perhaps gather more information, then perhaps do some calculations. The calculations themselves are not computationally intensive (ie fuel to climb to a chosen altitude at the current aircraft weight, temperature and winds), and they could even be done with simulations fairly quickly. But, the process takes some time. Some of this source information, from a pilot perspective, comes from sources that are computationally intensive to generate. Weather simulations to generate forecasts are one of the historical and ongoing uses of supercomputers. Pilots will then update their flight planning as the flight progresses (ie winds are higher, so choose a different altitude etc). The autopilot on an airplane will adjust for some local information (a local updraft, so descend to desired altitude) but they need to have a current "understanding" of the environment. In some sci-fi while in hyperspace information is cut off, so it would not be possible to adjust for changes in gravity etc in real-time. Those flight details would have to be planned out beforehand. If the environment can change (stars move, planets move, solar storms, space stations move etc) then there is a lot of information that has to be gathered or simulated. If it is necessary to plan your way around hyperspace, it seems reasonable that it would be necessary for the pilot, and the onboard computer, to have a good data set to do that planning. Gathering that information and synthesizing a good plan would involve scans, simulations, and communications with other data sources. It seems very reasonable to me that a hyperspace jump is at least as complicated and a flight current flight plan, and would take a similar amount of time. [Answer] There are some great answers here, but here's another. An FTL calculation is like calculating the detail in a fractal, the more resolution you want in the fractal, the longer the calculation takes. With FTL a high resolution gives you a greater chance of making a successful jump. Space liners carrying many thousands of passengers will calculate jumps to 99.999% resolution, each 9 increases the likely hood of the ship arriving at the destination in one piece and not diffusely smeared across several light-years worth of vacuum. A scam artist who's shields are down and is about to be annihilated by a gangsters turbo-laser shot might take the risk and jump at 90% resolution (anything lower than 90% is certain death), opting for near certain death as opposed to *actual* certain death. The inputs for the calculation are distance, direction and the conditions of your local space eg. density of the vacuum and amount of vacuum energy (maybe the further one is away from a gravity well the easier it is to calculate). Readings are taken every x nano seconds and plugged into the fractal like calculation, it can take y actual seconds (or minutes/hours depending on what your plot demands) for the results to converge on a given value, i.e. the final result of z%. There are jump points and destinations where the local conditions are known to *always* calculate a jump with safety factor so high it's essentially 100%, these are well worn trade routes and hyper lanes. A smuggler on the run (carrying only a kid and an old guy), who values his skin might well risk Imperial turbo-lasers for another second or two to get his FTL calculation up above 98%. [Answer] There are a lot of physics-y problems that take a long time to compute, but not prohibitively long. In college, I worked as a programming assistant for computational chemistry research projects. These calculations often required several hours of computation, sometimes even overnight- and this is on systems in the neighborhood of 24 cores with 64GiB of memory. Now these run a lot faster on GPUs, but still, there are an enormous amount of expensive computations that go into this. Atoms and molecules are *really complicated* in how they interact and there aren't any closed forms of the equations that go into these calculations, so most of these use gradient descent iteration using compositions of gaussian functions to approximate electron orbital wave functions. Spacetime at the astronomical scale is about as complicated as the quantum world of atoms thanks to relativity and gravity. It's entirely plausible that the mathematics required to make a sufficiently precise hyperspace jump do not have a closed form and therefore require iterative approximation. On top of that, the calculations must account for hundreds to millions of celestial bodies (mostly planets, moons, and stars; however asteroids, satellites, and debris may need to be accounted for in some cases) near the jump destination because of how they warp spacetime with their gravitational fields. Right there, you have an iterative calculation built on a $O(n^2)$ calculation of complicated equations, which may be iterative themselves. Although you can probably parallelize all the celestial forces on GPU-like architecture, you are still bound by a sequential bottleneck on the iteration. On top of that, such calculations might involve a number of randomized guesses in order to avoid local optimums, meaning it may iterate on a few hundred guesses until it's *pretty sure* that the solution has been reached with sufficient precision. The end result is a hyperspace jump that takes several minutes to hours to calculate, depending on how many significant celestial bodies are involved and how many guesses it takes to reach the global optimum. On top of that, since the celestial bodies which affect the jump are always moving, these jumps *cannot* be pre-calculated. Additionally, the jumping spacecraft must account for its own position and momentum, so each spacecraft needs to do its own calculations. What's interesting is that you could conceivably take a "risky" jump before the calculations are completely ready, but this could potentially land you a few lightyears off course, where your STL impulse engines are useless. This is great for quick getaways, provided you have enough Hyperjump fuel for another properly-calculated jump after that, but this *isn't* going to cut it when pursuing another spacecraft. [Answer] ## FTL calculations involve a simulation, or a simple calculation. In Star Wars, you navigate by traveling down hyperspace lanes, dodging the mass shadows of heavy objects. It makes sense it would take an arbitrary amount of time to calculate stuff, because they need to map out a route through a complex environment. There's many possible solutions for how they could fly, and changing and complicated situations from moment to moment. In Battlestar Galactica, they don't have good computer. They have an old ship with old data, and the cylons are much better at jumping. It makes sense they would take ages to calculate jumps, because they lack super computers. When the rebel basestar offers to join them, their modifications they offer would massively improve their jumps. ## Some universes just have fast travel. Take Star Trek for example. They can just go to warp on a whim. This is because they don't need to calculate routes, they just fly through the universe in a subspace bubble. They can react to local threats on the fly. So, decide what sort of ftl your universe has- it might be a simulation, and so can have arbitrary complexity based on what you need to simulate (made easier by known routes, or better data) it could be a simple calculation fast computers could make easier, or it could be you just move fast through space and need no calculation time. [Answer] I was going to comment on n-body but see that Wotan has done so. Various people havecommented on predictions based on obstacles in or near the "flight path", but these would need a super-luminal pre-flight ability to detect. Instead posit that the ability to launch depends on the ability to calculate local n-body constraints out to a certain level of precision. * Objects like in-system planets or the local star have minimal effect die to inverse squared (or some other) law, and/or they are advance predictable. * Any local "ships" or bodies have greater effects and if their actions are not controllable, anything that deiates much from a gravity constrained curve or constant acceleration would need to be factored in at the time. * It could be found that very small particles (dust, gas clouds) at very close proximity have a significant effect and need to be included in the n-body calculation. None of the above depends on the type of FTL used - it is a calculation necssarey to determine the appropriate parameters for making the "jump to light speed". [Answer] **It is all about the insurance...** Calculating the flight-path involves a certain risk. In an infinite universe there are infinite flight-paths possible. The trick is to find those paths that get you from A to B and *don't get you (or others) killed.* Not getting killed is not guaranteed. (Solving that would be a NP problem.) The best you can do in reasonable computing time is to find a solution with acceptable risk. As computers get more powerful it becomes a trade-off: * Faster calculation with the same risk. * Same calculation time, but finding a solution with less risk. Insurance companies don't like risk for obvious reasons. It really hurts their bottom line if they have to pay life-insurance for half the population of a planet if some space-cowboy jumped his freighter to the planets surface in stead of to parking-orbit. (And don't even mention all the material damage.) However the Galaxies insurance companies are quite wealthy businesses which have enough political and economical influence to do something about that. They managed to push all inter-stellar governments into drawing legislation that mandates that any improvements into computing capability must be put towards making jumps safer by reducing the risk. And to make any navigation computer that doesn't play by these rules illegal in their jurisdiction. That still leaves some cowboys, at the fringes of the known Galaxy, without these safe-guards that can calculate less-safe jumps faster, but they don't matter much. They can't get insurance themselves anyway. And the insurance companies categorically refuse to pay out any damages when they cause damage. They simply state "That this accident could happen is due to unregulated navicomps being used. Your government should have enforced the rules. We are not liable. Talk to your government for compensation." [Answer] This answer is a slight alteration on [Nullius in Verba's answer](https://worldbuilding.stackexchange.com/a/206216). Assuming you have to check the entire flight path for objects greater than a few centimeters, there is a nontrivial integration time needed for a telescope (or other sensors) to be able to "see" all the objects along the trajectory. Note that this telescope would have to be many orders of magnitude more sensitive than our current telescopes to be able to accomplish the task in a reasonable amount of time. As other answers have said, it's not about crunching the data, it's about acquiring the data. [Answer] Polynomial time is fast in theory, but it depends on two things in practice: 1. The size of the input 2. The degree of the polynomial Both of these are things you have to play with to make this premise work. As to the size of the input, we'd really only need to consider anything of sizable gravitational impact. Every subatomic particle between here and there gets you rapidly into the realm of computationally impossible. Everything dwarf-planet and larger can get you a nice couple thousand objects for reasonable length jumps. Now all we need to hit the timings you're looking for is a high degree polynomial time algorithm. Let's take a real world potentially relevant algorithm: [Parzen Windowing](https://en.wikipedia.org/wiki/Kernel_density_estimation). This is trying to find clusters of points by summing probability distributions (such as gaussians) around each point and using hill-climbing to find the peaks. This could be relevant to hyperspace because you need to determine which physical bodies are linked in the hyperplane so that you can properly determine the distortion they will have on your journey through the void. Parzen Windowing is a polynomial time algorithm, but the degree of the polynomial scales with the dimensionality of your data. Depending on the implementation, the complexity can be one polynomial degree higher than your number of dimensions. So, trying to do Parzen Windowing on 3-dimensional data (objects in space), you've got yourself a quartic time algorithm, i.e. O(N4). This is going to be slow even for moderate values of N (like a few thousand). There are a lot of [shortcuts you can to do speed it up](https://www.cs.bham.ac.uk/%7Epxt/PAPERS/fast_pw.pdf) but all cause a loss of accuracy. The tradeoff between speed and accuracy is key and likely always present. Consider smaller objects and your result will be more accurate but N goes up. Use more approximation to reduce the polynomial complexity and your runtime goes down as does your accuracy. This is actually mentioned in a major Sci-Fi property: in Battlestar Galactica, Helena Cain performs a [blind jump](https://en.battlestarwikiclone.org/wiki/Blind_jump) (a dangerous FTL jump performed without pre-computation to random coordinates) to get out of a bad situation. Whether or not blind jumps are possible will depend on your FTL system. If it's about just computing space coordinates, jumping to a random location is [99.9999+% safe](https://en.wikipedia.org/wiki/Stellar_density). Han Solo doesn't even know what a parsec is, so why would you trust [his explanation about FTL](https://www.moviequotedb.com/movies/star-wars-episode-iv-a-new-hope/quote_29894.html)? The real risk of poorly computed FTL, especially if you are using some sort of space-tunneling mechanism, isn't getting there, it's getting back. If you end up somewhere totally outside of mapped space, you may have no way back as you need to know enough about the objects between your source and destination to plot it accurately. Now you have to get back before you run out of food/fuel. But even moderate inaccuracy can waste plenty of time and fuel trying to correct, especially if FTL jumps are fuel intensive (if it's not, just do a tiny FTL jump to correct). As a result, it would make sense for routine (i.e. non-emergency) jumps to involve a large degree of computation. This also may be more important when multiple ships are involved as you want them to get to the same destination. The result of all of this is the following: * Spend a bunch of time (several hours) calculating and you can end up within a few thousand kilometers of the target, but if you get unlucky, you could end up a million kilometers away (takes a few days at sublight speed to correct); more computation time can reduce this risk for correctness critical jumps, but spending a day of computation to save a small chance of several days of transit is only worth it for correctness critical jumps or for stations computing coordinates for common hyperspace routes. * Shave some time on your calculations (do them in 20 minutes) and you end up within an Astronomical unit of the target and need to spend some fuel (which is expensive) and maybe a few days at sublight speed or another FTL jump to correct. * Do rushed calculations (5 minutes) and you probably end up within a light year of the target and need another (presumably smaller but still expensive) FTL jump to get there. There's also a 1% risk you are lost forever in space and will run out of fuel before you reach civilization. * Blind jump (20 seconds to get to minimum viable coordinates). You end up somewhere; 10% chance you're lost forever in space and will run out of fuel before you reach civilization. Could specialized hardware improve on these numbers? Sure. Make that part of the plot. The Millenium Falcon is "better at hyperspace", and according to the movie "Solo", [it's because it has a better hyperspace computing device](https://starwars.fandom.com/wiki/L3-37#Uploaded_into_the_Millennium_Falcon) [spoiler alert]. [Answer] I’m a computer programmer, and it’s quite common to have processes that take from fractions of a second to hours. These aren’t a single equation, but a series of data looks ups and calculations on the result. Given that you are traveling in space, it’s likely that part of what you are going to be doing is developing a good model of your position and environment. A count-down is feasible as percent done background task, maybe not super accurate, but does it need to be? Or perhaps that could be a plot point, it gives 30seconds left and jumps early, says it’s done and then jumps 5 seconds later. [Answer] You can make the calculations take as long as you want by saying there is no exact "solution". Instead there is only an approximation that a pilot can deem "close enough." For example, it could be that the hyperjump solution must be arrived at by simulating the jump based upon known values (gravity strengths and distances, perhaps). The result would be the locations and probabilities where the ship might end up. Slightly altering the hyperdrive's inputs can yield wildly different results. (Inputs could include the mass of the ship, starting vectors, starting velocity, how much power is dumped into the hyperdrive, etc.) A bad solution could spray the ship all over a solar system. Or land it inside a star. Or yield a near-infinite number of places where the ship would end up, each with an approximate equal probability. [Answer] # Optimization in a Highly Nonlinear Space Optimization problems can take any amount of time, so they're an excellent tool to use here. The trick to optimization is that typically the actual problem is NP-hard, but it can be approximated using P algorithms. The more CPU time you're willing to spend, the closer the approximation gets to the ideal answer of the NP-hard problem. In many real life physics situations, a system can be described as a set of non-linear differential equations. Given a current state and a desired state, you can compute the optimal path. Given a sufficiently tortured set of dynamics equations, you may find that there are very thin paths with acceptable costs, surrounded by vast pits where the costs are completely unacceptable. Finding a solution for a path through such a system can be extremely expensive. They can also be very initial state dependent. Drawing from a real life project I worked on, you could have your FTL computers constantly calculating plans to get from point A to point B, where point A is somewhere nearby and point B is far away. When it's time to jump, you resolve the problem for your exact point A', seeded by your most recent plan. There are many optimizers which perform much better if given a nearby point. Also remember that a jump can be more than just one impulse. It can be an entire dynamic solution for the time the vessel is in hyperspace. Needless to say, this dramatically increases the state space for this optimization problem, increasing the difficulty as much as you like. [Answer] # The problem isn't calculation, but verifying that the path acknowledges that they've "saved" a timeslot to avoid traffic accidents. As a bit close to a frame challenge perhaps, but there may not be as much of a problem with the mathematical computation on the ship computer itself - figuring out how to make the jump safely with other ships also making jumps along the same path, and not colliding with them at FTL speeds is where the complexity gates the time needed to make an FTL jump. Admittedly, this is taking a bit of inspiration from [Guardians of the Galaxy Vol.2, another space story that used portal jumping to achieve "FTL" without necessarily just moving at faster than light speeds,](https://youtu.be/yAB8g7doLYQ?t=5) but the same basic principle could be applied to Star Wars style hyperdrives and their claim of not being as easy to just jump, and could explain why a Star Destroyer takes as long as the Millennium Falcon to make an FTL jump, and even with knowing where the destination using hyperspace tracking, they couldn't necessarily just get to a location before another ship in FTL. So, what the ship computer would be relying on isn't their computer, but their computer's ability to send a request to other relay computers and verify that they can make a jump to a location safely and use it to jump to another, potentially pre-mapped location, at a specific FTL speed (Say, 1.25c instead of 1.5c, or 2.5c, depending on what their ship can accelerate/decelerate to.). Said relays would likely have a ledger of public timings for ships to ensure that they don't conflict- possibly involving ship sizes so that they can know how much efficiency they can stick in with ships, and check if they can safely leave hyperspace without crashing into another ship that was leaving the same gate and slowing down first -, and confirm a specific timeslot or deny a specific timeslot requested of the ship that was attempting hyperspace travel. Admittedly, a portal/relay explanation does run pretty close to violating: > > Within the boundaries of the observed FTL characteristics I've described, and without manufacturing some set of time-consuming handwavium computations -- that is, without inventing a specific system > > > But these same calculations could still be applied to Star Wars style hyperspace jumps, especially as occasionally ships have, [in Star Wars, gone through hyperspace in formation](https://scifi.stackexchange.com/questions/106496/can-a-ship-in-hyperspace-see-other-ships). So at least some confirmation of when to enter and where to go in from and how to exit safely would have to be confirmed, as you wouldn't want to go faster than the ship directly in front of you, even if, hypothetically, your ship *could* go through FTL faster. That may require communication with other ships, however, and the relay/portal jumping system would allow a ship to not necessarily broadcast where they were going to enemy ships along the way, without also conflicting with them. It also allows for a possible example of a greater way to scale up the transactions necessary to allow for FTL allowing for variance in how long it takes for a ship to get to FTL... # The timeframe of calculating a safe travel timeframe and ensuring a lack of collisions might be effectively enforced by a ledger verification system like a Blockchain Ultimately, this relays would likely want to have a way of enforcing that nobody breaks the rules they've setup in terms of timeframes available and try to jump in when another ship is also taking the exact same space in FTL-capacity. Given that these relays are likely automated for their traffic levels and not resolved like [modern aircraft going over the North Atlantic](https://www.youtube.com/watch?v=vBgulDeV2RU), and the need to manage a lot more relays that possibly can be brought into the same connection, you'd want to represent the timeframes in a way that makes the most use of the time they have, leaving gaps for anyone making an impromptu jump and hopefully resolving their issue quicker. As a result, a variety of ship computers might be requested to perform actions, or a variety of relay specific computers might be required to do this instead, of a set of [blockchain related transactions](https://en.wikipedia.org/wiki/Blockchain) on the timeframe they're moving through, and which relays to move from once getting to the next one. The amount of blockchain transaction blocks needed to ensure a ledger is both up to date and accurate to prevent travel conflicts, could be what causes a significant amount of time - giving the shipboard computer possibly only as much as a router IP address way of indicating where they want to go, and letting the rest of the relay network determine how they actually get there. and when they'll arrive and depart each relay such that it is smoothly done. Or in short, hyperspace traffic is the cause of why it takes so long to calculate a route, given that you can't recalculate mid-travel at the FTL speeds involved. --- [Answer] ## A Topical Example Using the Einstein Field Equations (EFE) So, the [EFE](https://en.wikipedia.org/wiki/Einstein_field_equations) is $R\_{ab} - {1\over2}Rg\_{ab} = {{8 \pi G}\over c^4}T\_{ab}$ Looks pretty simple, doesn't it? But it isn't. $g\_{ab}$ is your starting point in this oversimplified nightmare. It is an expression of your co-ordinate system. It can be 3-dimensions of space + 1 of time (the usual 3+1 = 4D), something simpler, or (for computing higher dimensions (such as "hyperspace") more complex. $R\_{ab}$ is your second derivative of $g\_{ab}$, relative to evey element of $g\_{ab}$. So, this is $\delta x \delta t \delta t$, but it is also $\delta x \delta y \delta z$ and $\delta y \delta z \delta z$. All said, there are $N^3$ equations for any given $g\_{ab}$, where N is the number of dimensions (4 for 3D of space + 1 of time) = 64 equations. Many of these 64 equations are pre-dumped when doing this by hand, assuming certain values will be zero, constant, or duplicates of others. But we're trying to figure out how big the calculation can be, so let's not skip anything. R is a product of $R\_{ab}$, $T\_{ab}$ is your stress-energy tensor, and may be the space-warping ship engine output that you are trying to calculate, although other massive and energetic bodies are contributing to this stress-energy. G is assumed to be constant, but might not be. Once you have calculated this equation **for a single collection of points** you may then compute the geodesic (the basic equations of gravitational motion). Each equation has at least one "body" or "component" contributing terms to it (that's not entirely true, the zero-body solution is equal to zero, but that's not useful for anything). Each "component" may contribute as few as one terms (n = 1), or as many as n = $N^3$ ## Let's Scale This Up To Known Concerns If string theory is correct that there are 10 dimensions of space + 1 of time, and assuming for a your hyperspace calculation that you can neglect none of these. That's N = 11, $N^3$ = 1,331 equations of various properties that you are looking up in your almanac or sensor feeds before you can compute an engine burn. So, let's say you're jumping to orbit: * You need to worry about the sun, earth, and the moon (3 bodies) : you have $N^3 [3 n^3] = 3N^6$ (or 5.314 million) calculations that you will need to perform. But let's say solar wind is a big contribution to navigational error in hyperspace, and you need to re-calculate at say every thousand kilometers between here and the moon (400,000 kilometers away). You'll have about 2.1 billion calculations total. Not so bad for a modern computer. But let's say you're going from Earth to Mars : 3 more bodies to worry about (Mars and it's two moons), and 2.1 billion kilometers of distance at the closest approach between Earth and Mars (five times that at the greatest distance between Earth and Mars, which would pass through the paths of Venus and Mercury). $6N^6 \times 2.1$ million = 22 trillion calculations. Which would take 372 minutes on a modern 1 gigaHertz processor. Imagine the not-best-case approach to Mars past Venus and Mercury : $8N^6 \times 10$ million = 141 trillion calculations, taking 39 hours on a modern computer (you'd need a faster future-tech computer to do this kind of calculation on the fly). This might also explain why, in these sci-fi scenarios, hitting your destination accurately is usually something of a surprise : you are neglecting all sorts of things like space dust, smaller rocks, and other vessels, just to compute this thing in a timely manner. The calculation has a lot of error in it, because you are knowingly ignoring a lot of things that contribute to the answer, just so that you can get any answer at all in a timely fashion. It might also explain why, in some of the sci-fi scenarios that use this idea that "high precision" jumps (into a planet's atmosphere, for example, or "too close" to the planet at all) are considered by most professionals in-universe to be suicidal. It is. [Answer] ## FTL works like a transporter > > And let's be realistic: the FTL calculation is not going to include actually transcoding a video, because that is obviously irrelevant to travel. > > > Actually, transcoding could be exactly what your ship is doing! Normal matter is restricted by the speed of light; so, in order to exceed the speed of light, you may need to become something else entirely... So, what your ship does is it accounts for every atom on your ship and translates it into a data stream of FTL energy which then reassembles back into normal matter somewhere else much like a Star Trek style transporter. But before your ship can do this, it needs to scan its entire self and transcode that into an exact data stream. You can not pre-calculate this because the exact composition and layout of your ship and the things on it changes moment to moment as people walk around and do things. If you were to say for example scan your ship 3 weeks in advance, then all that cargo you picked up last week would disappear, and everyone would forget what they spent the last 3 weeks doing because you are basically "using an old save file". But to make matters worse, if you used a calculation that assumes something exists that is no longer there, then you will not have enough matter to fully translate into an FTL data stream; so, you might come out the other side missing something else that needed to be reassembled from the same mass; so, congratulations, you just topped off your fuel supply as per the old copy of your ship, but your data stream did not contain enough mass to reassemble the left half of your captain's body. So, it is not the flight path that takes a long time to calculate but the exact state of your ship at the moment of activating your jump drive. You take a "snap shot" of your ship very quickly, but then spend minutes or so transcoding that snapshot into a data stream. **So, how does this ensure the calculation takes a human scale amount of time?** [Ray Butterworth's Answer](https://worldbuilding.stackexchange.com/a/206273/57832) does a GREAT job of explaining why there is such a narrow window between a ridiculously long and short calculation when the calculations scale exponentially as per a traveling salesman or multi-body problem type problem. But transcoding follows a different set of rules. The actual math behind video transcoding is very simple to the point that a single operation can be measured in the billionths of a second, but it takes a long time anyway because the process contains trillions of operations that need to happen. Your transporter follows the same logic. You ship begins by taking a molecular snapshot of the whole ship... let's say we are looking at a 10,000 ton destroyer. If we assume an average molar mass of about 45 g/mol we can say that your ship contains about 1.34e32 molecules that that need to be converted into some manner of data-point. Using modern computers this would take a stupidly long time and need a computer much more massive than your ship itself, but we are not talking about modern computers. If your civilization has learned to pack data into the false vacuum of space or into the as of yet undiscovered sub-atomic particles that make up all other subatomic particles, then you may be able to store and process vast amounts of data in a single atom. Since the only thing your ship does at this scale is wardrive buffering, it means you can scan at the atomic scale and only loose your warp buffer when you jump. If we can assume these specialized warp buffer computers are about ~20 orders of magnitude better than what we have today, then running this transcoding operation would feel a lot like rendering a video file does to us. The reason this scales well for your setting is that its complexity has a linear relationship to the size of your ship. So the calculations for a 10,000 ton ship are only 5 times as complex as for a 2,000 ton ship. So, in this respect you can not just keep adding computers until the calculation becomes arbitrarily short, because the faster you want the transcoding to happen, the higher percentage of your ship you need to dedicate to computing power. So, while it is not exactly the same as transcoding video files, it will follow more or less the same principles. You just need to match your setting's computational technology to the general wait time your plot requires. ]

[Question] [ I'm creating a science fiction dystopian world that takes place about about 50 years in the future. One of the characters for this world is a member a highly sought-after group of mercenaries that I want to use a high-tech bow instead of guns. What explanation could I give for this? [Answer] Make gun detectors common. * [Sound detectors](https://en.wikipedia.org/wiki/Boomerang_(countermeasure)) calibrated for firearms. * Firearms [sniffer dogs](https://en.wikipedia.org/wiki/Detection_dog#Functions). * Gunpowder [detectors](https://en.wikipedia.org/wiki/Explosive_detection#Mechanical_scent_detection). If you assume that firearms remain common because of all their advantages, then bows could be an useful **niche** capabiliy. Archers infiltrate enemy lines, take sentries out, etc. Perhaps the *first* scout in a patrol carries a silent bow. The *second* scout carries a machine gun, in case a bow isn't enough. [Answer] ## Total State Gun/Gunpowder Control If it's a dystopia, and there are rebels, this infers that a totalitarian government is in place. Such a government would want the tightest control possible over anything that could be used to subvert or oust them. This can extend to guns, and the chemicals necessary to make gunpowder. As such, munitions would be a prohibitively expensive black market product, if available at all. Trading in munitions could carry a mandatory life sentence with hard labour. ## Cool as F\*\*k Bow Other people have given some really nice ideas already for this. If the bow is demonstrably cool and useful in a way that a gun isn't, readers won't have an impulse to ask "Why a bow?", it will be obvious. This means providing a motive for having the bow, rather than an excuse. [Answer] Actually this is not a fantasy situation. In fact some assassins in real world in today's times have been known to refrain from guns altogether and use crossbows for various tactical reasons. The reasons they gave in the documentary are: 1- Dogs and chemical detectors do a marvelous job of detecting bullet propulsion chemicals (aka gunpowder and guncotton). This means that sneaking in a gun to a high security building is extremely difficult. 2- It is quite easy to assemble the crossbow bolts/arrows by joining different parts (the head, the shaft and the tail/fletching) once you have the components smuggled in. The only thing which could look slightly suspicious are the pointed arrowheads. These too, could be smuggled in as part of some decoration scheme etc. 3- Crossbow components are very hard to detect for anyone who has been trained to look for components of firearms. Smuggling in different parts of the crossbow one at a time would be quite easy. And smuggling in parts of a manual bow is ridiculously easy. Smuggling in parts of a sniper rifle would be next to impossible. 4- Bows don't misfire or jam. 5- Bows (and crossbows) don't require silencers. They are quiet by default. 6- It is **much** easier and faster to assemble explosive arrows (arrows with explosive tips) than getting or making explosive bullets. 7- Assembling a manual bow (not a crossbow) is much faster and simpler process than assembling a rifle or smg. The conclusion is that while an assassin wielding a sniper rifle (or assault rifle) is much more *dangerous* than one using a bow, it is far *easier* to smuggle in, and operate with a bow and arrows in high security settings. [Answer] 50 Years in the future it might be possible to have advanced bows linked to goggles (or implants) that tell you where the arrow will hit (HUD style) even with ballistic shots. That way bows could be used to attack targets behind cover with a certain level of accuracy. In addition to that worn body-armor might be tough enough to prevent both sub-sonic ammo from firearms and arrows to kill with a single shot but arrows could be fitted with needle-points carrying fast acting nerve-poison to take out individuals. That way even a slight scratch would be enough. And the size of an arrow makes it easier to build stuff into the arrow as compared to a bullet. Be it explosives, electronics of some kind, burning agents, poison gas etc. [Answer] Perhaps widespread recognition of the dangers of having toddlers, suicidal people, mentally ill people, etc. having access to guns caused a few countries to adopt very strict Japan/U.K. class gun control laws with great positive outcomes and that led pretty much every civilized nation in the world to follow suit. Suppose that around the same time that international bans on trade in firearms to be aggressively enforced. Fifty years to achieve that would be similar to the time frame in which chemical weapons were banned in an effective way - not totally gone but much more rare in world warfare. Bow and arrow control would not be nearly so necessary, because bows and arrows are only highly lethal in the hands of skilled users as opposed to toddlers, drunks, mentally ill people, suicidal people, etc. They are also well suited to allowing loosely regulated hunting while not leading to overkill of wild prey species like deer. And, in the absence of guns, bows and arrows would gain comparative advantage relative to the alternatives. It is much easier to learn to use a club or knife or staff or spear than a bow. [Answer] Since you are only trying to justify the choice for an *individual*, you could use any number of reasons; they wouldn't even necessarily have to be entirely accurate/reasonable if the character was operating on bad information or superstition. For an entire group, you need a bit stronger and more reliable justification. Some ideas for an individual: * The character learned to use a bow quite well before encountering/using firearms (hunting or archery contests as a child, perhaps?) and preferred to continue with the knowledge/experience they had rather than attempt to learn a new skill (firearms) * The character has some strong aversion or even PTSD related to guns. For example: Batman (DC Comics), [MacGyver](https://en.wikipedia.org/wiki/Angus_MacGyver) (after a traumatic experience with them as a child). * Someone from the character's past made them promise never to use a gun for some reason (maybe that have aversions to it like in my previous point), and they intend to keep their word. The remaining reasons are a little more applicable to groups, should you need to justify the choice for more characters: * The characters value stealth, and silenced weapons are not readily available. Bows are quieter than firearms. * Arrows are much easier to retrieve after use than bullets. This provides two benefits that I can think of. 1. The arrow can potentially be reused 2. Bullets can be [traced back to the gun that fired them](https://www.scientificamerican.com/article/how-can-a-bullet-be-trace/), but collecting them after use may be difficult or impossible. Arrows probably aren't as traceable (depends how far you go with the "high tech" angle of the bow, perhaps), but are also easier to collect after use so that they don't remain to be traced. * Arrows can be arced over various structures and forms of cover. Bullets? Not so much. A high tech bow may even amplify this advantage through some sort of targeting assistance. [Answer] Fatal allergies to any (or all) of the substances forming gunpowder this includes potassium nitrate, sulfur, coal, and many more. Whenever you discharge a firearm there will always be some powder or smoke that gets on the shooter's hands, eyes, and skin. [Answer] Your question had somewhat created the illusion of someone of higher class, so with that assumption, the usage of a bow (no-matter the high-techness) could simply be due to family heritage and long used hunting tehcniques and tradtion passed down in the family. These types of things are especially common in higher class families as they often have a very well documented and proud family background. I hope my answer can be used in conjunction with other great answers here :) [Answer] Actually, many reasons but most of them also apply to other high tech weaponry (eg. gauss gun, rail gun...). The power of a gun is in fact hidden in the bullet. You can buy a bullet and discharge it even without a gun (bad idea though). There's a video of a [guy shooting shotgun slugs out of pipe](https://www.youtube.com/watch?v=7Va87gB_4AI). At 1:18 time of the video he hits a bottle over about 12 meters. That's pretty impressive for two pipes, isn't it? The point here is that if government REALLY was afraid of it's citizens, **it would control not (just) the guns, but the ammo**. In extreme case, any explosives would be zealously controlled since homemade bombs are popular within ranks of rebels. Additionally, it is not trivial to make ammo at home or in a forest. This brings me to the answer: **High tech bow's ammo is cheaper and easier to get than gun ammo.** Presumably they can shoot arrows from plastic and steel? Manufactoring arrows is simpler than manufactoring slugs. Arrows are reusable. Unlike with a gun and a bullet, **the energy of bow and arrow is packed in the bow and your arm** (and in your case some bow's power source).. [Answer] Depending on the type of dystopia, manufacturing might be disrupted to the point that bullets are simply no longer available. It takes a factory and a well-organized supply chain to mass-produce bullets. People would no doubt use guns for as long as possible after whatever event triggers the downfall of civilization. but eventually, bullets will become rare commodities, available only to groups that planned ahead, or that have a lot of power and influence. [Answer] Arrows (and knives) can pierce [bulletproof vests](https://en.wikipedia.org/wiki/Bulletproof_vest), which are typically not stab-resistant. See, e.g. [this](https://www.youtube.com/watch?v=u6Xrn5DNwCg) video. [Answer] There is an old war film on that subject: <https://www.youtube.com/watch?v=eOM4IQjQtM4> This question and answers also have excellent responses on the matter: <https://www.quora.com/Are-bows-used-by-any-modern-military-unit-in-combat> The main thing is that bows are quieter than guns. You can also theoretically make your own low quality arrows anywhere. One group of special forces learns to make their own bows and arrows from forage in the woods, the Taiwanese mountain company. Crossbows are much more common among special forces and riot police, but bows aren't theoretically a bad choice. The thing with spec ops is, you generally take out the target with the first shot, or the alarm will be sounded and you failed, so the greater rate of fire of the bow is less considerable due to that. If you could work out what explosive arrows were good for, you might be able to figure out a use based around that (haven't found information on that yet). You could consider a mixture of bows and crossbows. If the crossbow fails to take out the enemy, the bowman can unleash rapid fire. Another possibility if there is a technological reason for it. Like, armour that works similarly to earth, and is bullet resistant, and arrows with molecular blades that are good at dealing with the armour. Hope this was helpful, it is an interesting idea for a setting. [Answer] **Personal force fields** that deflect **high velocity projectiles** were the reason why, in *Stargate* season 1 episode 8 *The Nox*, the SG-1 team use a traditional bow and arrow: > > SG-1 plots to take Apophis down a second time, this time utilizing a flaw in Apophis' personal defense - a slow moving object, like a staff weapon or an arrow, passes through the field easily, while also deflecting faster-moving bullets and staff weapon blasts. > > > Source: [stargate.wikia](http://stargate.wikia.com/wiki/The_Nox) Building from this, if forcefield technology is common and can be exploited with low velocity weapons, then those weapons will develop into more specilised designs, e.g. arrows loaded with tranqulisers to subdue a target, bows that can be deconstructed and look like household items to smuggle them etc. [Answer] [The Trigger](https://en.wikipedia.org/wiki/The_Trigger), a novel by Arthur C. Clarke explored the implications of what would happen if gunpowder could be made to remotely detonate. In this case, conventional firearms are unusable, and are replaced by other weapons (which could include bows in your case). [Answer] Maybe bows are more common/accessible in the character's home setting?I imagine that one could ban or place controls on guns due to the ease of them being used indiscriminately or accidentally (how easy is it to shoot yourself with a bow and arrow?) Alternatively, the larger form factor of an arrow allows it to deliver payloads with larger mass, at least when compared to a bullet. For example, you can make arrows that deliver explosives, corrosives, poisons, or even electrical shocks. If you try that with bullets, you find that you have to fire more of them -- which may not be an option, depending on the situation. Additionally, the size of the payload and its concentration can be what makes it effective. Imagine firing multiple explosive bullets onto a surface. Multiple shots do not necessarily mean that they can overcome the intrinsic hardness of the material. But a larger single payload on an arrow will deliver a concentrated punch that can make it through. The trigger mechanism will need work though, and you have to consider that without proper construction the arrow would break from the act of firing it alone. [Answer] I used to play a Shadowrun character armed with bow and sword. During the course of playing, I discovered many advantages of bows. The most obvious is, of course, that they are silent. The second is that you can shoot in an arc, giving you the ability to hit targets that a gun couldn't reach. Once you begin to modify your arrows, it becomes really interesting. Since you are talking about a high-tech world, some ideas might work in your world as well. Combining explosive arrows with rangefinders allows you to program the explosion so that you can shoot above or past the enemy and the explosion happens next to him, above him or behind him, negating cover or front armor. You can attach light (carbon or nano material) ropes to arrows, to double as grappling hooks or to deliver electronic shocks / taser effects. Range and power of a good bow are comparable to most hand-held guns. And aside from full auto (which is spray-n-pray anyways) the rate of fire is not so bad. English longbow archers had to be able to get three arrows into the air before the first one hit the ground. [Answer] Guns are very loud. Even with silencers and subsonic ammo, they make a huge noise. In comparison, bows can be made completely silent. Just look at modern hunting bows. And while there are/have been some odd gun designs made specifically to be silent (more silent than the standard silencer+subsonic ammo setup), they are still not as quiet as bows and they are extremely limited in capabilities: usable only at very close/point blank ranges, bullets have very low power, cumbersome to use, etc. These guns are pretty much useless in general combat, and are/were used exclusively in very special circumstances, like cia/kgb/mi6/insert-secret-service-of-your-taste operations (usually assassinations at very close quarters). Another reason could be the scarcity of ammo. Making decent quality ammo in large numbers requires specialized factories with lots of rare, specialized (and expensive) equipment that's difficult (and expensive) to make. Acquiring the needed chemicals in large enough quantities for the production of gunpowder and primers can be very difficult. Making the guns is actually a lot easier than making the ammo they shoot (assuming modern ammo that we use today). [Answer] Just put your characters in a **world of ice**. Like a thick jungle with layers upon layers of spikes overhead, all made of brittle ice and ready to fall. Let's say that any **detonation** would break tons of ice above and around everyone, and crush everyone. I am not sure how scientifically accurate that physics rule would be, but in our world [sound can break glass](http://www.acoustics.salford.ac.uk/acoustics_info/glass/) and [big guns are used to trigger avalanches](https://www.youtube.com/watch?v=m42jaXAgOO0), so it is not such a stretch of imagination. In such a world, people would avoid using guns, for their own safety. [Answer] An automation dystopia. Over the next 30 years, an automation singuarity arrives. An exponentially increasing numbers of jobs are automated. The resources needed to feed and clothe and shelter a human become less efficient for almost any task than building a robot with substitute resources (ethanol farming instead of food) and using the robot's labor. A welfare state initially develops. The police and military are replaced with automated police drones, so lives are no longer endangered. Brutal wars occur. As the underclass of unemployables grows over time, they are demonized and their economic activity criminalized. Drone police are exceedingly efficient, and the underclass gains a huge percent of criminal records. Criminals cannot vote. Disenfranchised and demonized, the police get increasingly harsh. Atrocities performed by people tired of their family being killed by drones are used to justify more serious crackdowns. A civil war breaks out. The anti-automation forces lose. It isn't pretty. The underclass expands. Becoming indingent becomes grounds for losing the vote and full citizenship. That underclass is stripped of rights to use weapons. There are small armed drones that are all over the place. They hunt down and kill people who use firearms and explosives (both chamical and nuclear). This is done through visual, auditory, chemical and radiological scanning. These drones are part of the infrastructure that the rich caste has put in place to prevent revolution. They are also used to police neighboring rich people and prevent them from raising an army using such weapons and use it against each other. Only a small number of elite guard (nobles themselves, if lesser) are permitted such weapons under the treaty. Violence among the poor is an amusing sport for the rich, so whatever they do to each other isn't really the noble's problem. Nobles also engage in "peasant warfare", where you get your non-firearmed peasants to war with another noble's peasants, especially on small scales. Time-delayed video of such wars (filmed by said drones) are a valuable entertainment product. Meanwhile, military drones conquor and settle more territory in the remaining anti-automation states. Traditional national allies and enemies are mostly gone; ensuring no anti-automation revolutions occur is the unified work of the automation dystopia. Possibly there remains one or two nuclear-armed anti-automation states. They are surrounded and choked off. Anti-ballistic missile drones fly around the free states borders. It is uncertain if the free nuclear states full-scale nuclear bomb strikes would be able to get through, but as yet they have not been overrun directly. [Answer] Honor and code of chivalry. Like Samurai warriors in modern Japan, who refused to abandon their swords in favor of fire weapons. If your world has a chivalry order, or some fighters who follow a strict moral code, employing bows instead of guns could be part of that code. [Answer] If there is a shortage of nitrogen or the agricultural needs for nitrogen overwhelms the needs for guns, then you cannot product enough bullets so bows and arrows make more sense. You could change the chemistry of your world so nitrogen do not lead to explosions. [Answer] Fire arms usage began dominating the battlefield between the XVI and XVII th century (source: [wiki](https://en.wikipedia.org/wiki/Early_modern_warfare#Decline_of_plate_armour)). The main reason was that it was easier to train for muskeet than for arquebus (another reason was that muskeet were fairly inaccurate but capable of piercing through plate armour). To reverse this situation one of the following or a combination would be possible: 1) Battles relying mostly on guerrilla tactics rather than open field battles. * as mentionned above bow shoots are not as easy to locate 2) Bows being easier/ cheaper to use than guns * bows can be made easier and more balanced than guns which could prove to be in advantage if running / horse riding most of the time and shooting at short notice a need. * bows could be easier to recharge if the environment is mostly wooden (post apocalypse, cities being no go for germs / chemical / nuclear waste) 3) Bows requiring less training than guns * if the daily life is based around hunting with bows, more advanced skills / training around bow shooting would be available leading to natural preference for bow as a weapon [Answer] You could go the Green Arrow route. Maybe these arrows have some specialized technology that would be impossible to fit into a bullet. Incendiary arrows, smoke arrows, arrows with a small speaker to distract guards on a stealth mission, (boxing glove arrows,) but the one that I could see having a definite advantage over a sniper a mile away would be homing arrows. Tiny motors in the shaft control the arrow's fletching in mid-flight, and a forward-facing sensor allows it to identify and track the target it was pointing at when it was shot, even when the target moves around a corner. It could even have a small solid rocket motor at the tail to give it additional range. [Answer] This isn't necessarily Earth, right? How about vicious and hungry raptors which turn up immediately after any loud detonation, or any loud noise. [Answer] I would say there is about 4 reasons for choosing a bow over a sniper rifle (for comparison) 1. Stealth (Nearly no sound except the string and the impact of the arrowhead) 2. No flash. (Guns have a lot of excess gasses coming out of the barrel which makes them give a pretty distinctive flash and in a high security building you do not want that.) 3. Bows can be improvised. (You can ofcourse buy a bow somewhere but you can also make a pretty decent bow if you have a knife/something to carve out wood.) 4. Bows can be as expandable as you want. (Compound bows for example are more "assault" and heavy duty bows which can fire arrows which do the same or more damage than a handgun. There are also alot of options which you could make up yourself since hey. We're 50 years in the future.) 5. Different arrowheads, same bow (A bow can fire incendiary, explosive and in your book maybe even EMP arrows and this is only touching the surface. A rifle can also shoot most of these arrows in bulletform but it would be plainly annoying since a lot of the time you need to find a rifle which is compatible with said bullets.) [Answer] EMP arrows could be a good thing, guns could say have an electronic finger print lock (or DNA scanner) that makes it only work for its user/owner; Knocking out the computer would make the gun a paper wait. Guns could also be electronic, say laser/plasma a computer (or some other elecronics) is going to be needed for regulating the energy. Shafts of aluminum arrows are hollow, so imagine adding rocket ignition to the arrow. Rocket arrow more impact & greater range. Rocket engine could ignite 10-20 ft after leaving the bow. Also the bow could be reinforced and/or have a blade mounted to it top and/or bottom for hand to hand combat. With reinforcement could just be a bo(asian quarter staff)/walking stick blades hidden when bow is unstrung that is if you like the blade idea or no blades mounted and concept still works well. [Answer] Lots of good answers already. I won't repeat them, but I don't think this point has been made by anyone else: Using a bow makes things harder for the police forensics experts. * Ballistics: It will be harder for them to work out the trajectory of the shot than it would be for a gunshot. * A bullet can be linked definitively to the specific gun that fired it. It is impossible to do this with bows and arrows. I don't think either of these points is enough on their own to justify using a bow, but they certainly would help. [Answer] Arrows could be extremely compact, silent and accurate if fired as a rail-gun system using magnetic principles. [Answer] How about changing the laws of physics so that the speed of light is in the same ballpark as the speed of sound (hundreds or low thousands of meters per second)? That way, as you try to accelerate past the speed of an arrow, the energy requirements go up exponentially, making guns take *huge* amounts of energy to go even 10% faster than arrows. ]

[Question] [ Time traveler here, stranded in the year of 1019 AD, medieval ages. Location: europe. While I can still access and post on web forums because my temporal transmitter has a 1Ky range, I have a broken solenoid. Thing melted down and it is part of my flux capacitor. And as a security measure my ship locked down **and unaccessible** until I can fix the solenoid. Stupid military protocols. I am without access to any technology, just my portable temporal communicator (what you guys in the early XXI century would call a cellphone). I have to make do with tools and techniques from the locals. I need to create another bobbin and all I have is copper wire. Naked copper wire and I don't need to tell that it would short-circuit the solenoid. Is there any way I can insulate the wire to repair my solenoid bobbin? Many thanks. P.S.: Don't worry about paradoxes. Nobody will believe this post is from a real time traveler. [Answer] The practice in the first half of the 20th century was to wrap wire in cotton cloth, resulting in something like a shoelace[](https://i.stack.imgur.com/PyaZt.png) from <https://www.vycombe-arts.co.uk/onlineshop/prod_3699705-Double-Cotton-Covered-Copper-Wire-Reels.html> Alternately, pass your wire through wood resin, which will leave a fine insulating layer over your wire, good enough for low voltage work. The problem is that the resin will be sticky when wet and brittle when dry, so don't wind too tightly. [Answer] # Beeswax Expensive mind you, anything food related is, and you're cutting into the candle supplies of the wealthy, but beeswax is a good insulator, easy to work, and available in almost any historical period. Not suited for high temperature use. # Cloth Also available in almost any period, though harder to work with for these purposes most cloths are reasonable insulators. Less temperature sensitive. [Answer] I have done this. I have an interest in old technology and I recreate crystal radios, telegraphs and mechanical television. When winding the solenoid you can seperate the windings by winding thread of similar diameter alternately with the wire (I used waxed sailmakers' thread). Once you get to the end of the coil former wrap a layer of paper (I used wax paper) around the coil and begin laying again. For a solenoid this seperation should not cause a major issue as I'm guessing that you are using the solenoid as an electromagnet and not an inductor. If you are needing an inductor then you can use an online calculator to take into account the extra layering and the wider wire seperation. I would also recommend coating each layer in wax before starting the next layer to prevent the wire from moving when you hit 88mph. The extra wax will act as extra insulation when handling the required 1.2 GW to activate the flux capacitor. The wax also minimises the build up of copper oxides. [Answer] You have **copper** wire. You need a thin insulating layer so that one winding does not contact the adjacent winding. This is easy. Assuming you can produce the copper wire, you need to **oxidize it** in an acid solution. This will produce a green oxide layer which is insulating. Wind the green corroded wire with no overlap on each layer. Put a layer of silk or cotton or paper or fig leaf between the layers of wire. The adjacent turns have very low voltage between them, so the insulation can be very thin. Some of the oxide may come off, but unless it comes off adjacent surfaces there is no short. Copper oxide can be a semiconductor. (nb, I remember copper oxide rectifiers from my childhood.) The bandgap voltage is (from one source) 2-3 V, which for most frequencies and core materials is less than the turn-to-turn voltage. If you have a high frequency for this coil, the volts-per-turn could be high enough to cause some conduction through the copper oxide. For DC, it isn't an issue. Scrape off the green copper oxide insulation on the wire ends to make good, bright copper connections. If you want to impregnate the coil with wax, go ahead, but you are probably in a hurry to get home. For those wanting to learn more, [this](https://www.researchgate.net/post/Why_are_the_resistivity_of_Cu2O_and_CuO_so_different) is a place to start. It differentiates between cupric-oxide and cuprous-oxide, which have different properties. [This link](http://www.sciencemadness.org/talk/viewthread.php?tid=65952) discusses how to make copper wire into either oxide. Simply exposing the wire to hot sulfuric acid doesn't leave copper oxide leaves copper sulfate, not one of the copper oxides. Copper sulphate is a salt, and as a salt, it may tend to be conductive when moisturized. If you get out something more blue (copper sulphate) than green (copper oxides), you should dry it well to eliminate any moisture. When dry, the salt should be non-conductive enough. You only need to use it once. [Answer] [Lacquer](https://en.wikipedia.org/wiki/Lacquer) is an alternative. It comes in many thicknesses. It's not too expensive. It can be painted on then heat cured. There are many different types that can stand up to a variety of challenges such as wear, heat, cold, even limited bending. [Answer] # Enamel Thin copper wires--like those used in inductors, transformers, motors, etc.--are enamelled. This is known in the modern world as magnet wire. Surely, you would prefer enamelled wire for your solenoid bobbin. We know that enamelled objects existed as early as the 13th century BCE. [A concise history of enamel.](https://www.iom3.org/vitreous-enamellers-society/concise-history-enamel) [Answer] **Think Trees** Gutta Percha , Latex , and Amber are reasonable insulators. Wrap the wires in various tree saps, and dry the covering over fire. Don't dry all the way, nor burn it, or it becomes inflexible. When working on the electronics, use dry clean wooden tools to avoid sparks and conduction. [Answer] Paper? Paper may not have been invented (or be readily available) yet, but it can be made with available tools and materials. Paper is used as an insulator in our time, so could work for you too - it's a good insulator and it provides physical separation. It does require you keep it dry though - but you could coat your work in wax when finished if moisture is a problem. If you're using lots of current, you may need to consider cooling too (although less so than if you use wax as your insulator). [Answer] Not mentioned yet, but leather is also a good insulator. So there are plenty of options, most likely you'd want a combination of them for optimal effect of course, and to reduce the mess (resin gets sticky, so wrap the resin coated cable in cloth and wrap that in leather because the cloth is vulnerable to mechanical damage for example). [Answer] Mentioned before leather. Intestines (small-large) best leather for a wire coating. Already a tube just pull it tight and let it dry. Smaller animals smaller tube. [Answer] In addition to the great answers so far, wax in general is usually an insulator, so a nearby candle or rendered animal fat might do the trick. If you don't want to kill an animal, or can't find a candle, then you can use wool. Really any type of fur or silk would do, but wool is a decent insulator, and would almost certainly be available in medieval Europe. [Answer] I think you could use grape juice thickened with flour. Both materials should be available in a medieval context (and long before that). It dries to a rubbery texture and you could run the wire through a trough of it a few times to ensure full coverage. To get an idea of the finished appearance, consider Georgian [Churchkhela](https://en.wikipedia.org/wiki/Churchkhela). You would want it thinner, of course, and well dried to avoid excessive conductivity. [](https://i.stack.imgur.com/s2WBC.jpg) [Answer] ## Pitch and cloth or paper. the first widely used insulated wire was insulated with asphalt (pitch) soaked cloth. both materials are available in a medieval setting. pitch is widely used by shipbuilders and a dozen other trades and cloth is a bit expensive but not prohibitively so especially for how little you need. Cotton cloth is expensive but nearly and form of paper or thin cloth will work, even collecting worn rags will work as long as you wash them first. this is really just acting a a physical carrier/spacer to keep the pitch between the wire while you wind it tightly. pitch is sticky which you don't care about, if it picks up sand or grit it only becomes a better insulator, it is waterproof which is a bonus, and stays nice and flexible. if you try to ue it for years it will corrode the copper, but this is a fix to get you to someplace you can buy wire not a permanent fix. [Answer] ## Wax boil/VPI that solenoid Suppose you have a V volt solenoid with N coil windings laid out in L layers. In solenoid windings, you only have very low voltage between adjacent windings - just V/N. Thus, a simple varnish will suffice for wires in one layer. Between each layer, you have 2\*V/L voltage, and you can use wax-impregnated cloth between the layers, or mylar salvaged from the rebuild - this being more important on the end of the layer that doesn't cross over. If, at this point, you can build a nonferrous metal "can" to enclose the solenoid, that'd be great. That will help the solenoid stay solid with wax even if it gets hot enough to melt the wax. Now, get a vat of wax to 212 F, and dip the solenoid in it. Or if you've done the can thing, that can be the vat. This will boil all moisture out of the coil windings. If possible, draw a vacuum on the vat to force all the air and steam to vacate the coil windings. You could simply release the vacuum and wax *should* be driven into the voids left by the vacuum; however if you can pressurize the vat, that will help. Let it slowly cool down to let the wax freeze. Congratulations, you have just done VPI (Vacuum Pressure Impregnation) in 1019 A.D. Now the tricky part, remelt the wax *just* enough to get the part free of the wax, but not so much as to melt the wax out of the windings, which would undo our work! This is where that metal can would come in handy. Now, you should have done all this stuff with epoxy instead of wax, but you didn't want to bring any epoxy. "It's just a day trip" you said. ## Insulated boards Now, if you need objects insulated, get maple wood. It has the best insulating characteristics of any reasonably available wood. Mill the maple down to rough dimensions, and then stick it in the wax boil for a day or two. A vacuum cycle or two wouldn't go unappreciated. You are boiling all the moisture out of the maple and replacing it with wax. Same deal with letting it fully cool then reheating it just enough to get the wood out of the wax. This will cause dimensional changes in the wood, which is why we waxed it "rough" before we did our woodwork. Now, have your woodcarvers do their thing. Finally, give it one more night's boil-and-freeze to make sure wax fully penetrates all the freshly exposed wood surfaces. [Answer] Use varnish to coat the wire. You can get it from a cabinet maker. I've done this before and it works. [Answer] Why not just go down the modern route, and coat your drawn copper wire with [cresol](https://en.wikipedia.org/wiki/Cresol) lacquer, derived from [coal tar](https://en.wikipedia.org/wiki/Coal_tar) or [creosote](https://en.wikipedia.org/wiki/Creosote)? These substances are reasonably commonly available, and have been known for thousands of years, from the pre-Christian era. Having worked (albeit briefly) in quality control at a factory producing copper transformer wire - exactly the thing that the OP wants, I can state with some authority as to just how copper wire is coated today. A modern wire factory both draws the wire and coats it, though the process of drawing the wire may easily be separated from the process of coating it. In essence, the drawn wire is passed through a metal die with an opening slightly larger than the diameter of the wire. Just before the wire passes through the die, a liquid mixture of phenols and cresols (which is pretty much just filtered and fractionated coal-tar or creosote, diluted as necessary by [turpentine](https://en.wikipedia.org/wiki/Turpentine), which is itself a light phenol-like compound sourced from the Turpentine tree) is poured continually over the inwards-face of the die, and is spread along the length of the wire as it passes through the die (remember that the die has a greater diameter than the wire). On the reverse side of the die, the coating is still wet and sticky, however heat treatment (in a modern factory, achieved by passing the wire up and down through a tower kept at a high air temperature of around 70°C+ for several minutes) causes the lighter solvents to evaporate, leaving behind a dry, non-sticky, solid and flexible coating. Using higher temperatures to drive off the light solvents more rapidly is not advisable, since the boiling solvents cause pitting in the coating, effectively compromising the integrity of the insulation. All that remains after the coating has been applied and dried is to wind it onto a spool for storage before it is put to its final use. This coating, while ideal for its purpose and very easy to apply, does have its drawbacks. The chemicals involved are toxic respiratory irritants, and can cause severe bronchitis in some of those exposed to it. I can attest to this from personal experience: I turned out to be susceptible, and developed bronchitis within three days of exposure to this environment. However, on ceasing to be exposed, the condition clears up within a few days. This is probably a small price to pay to be able to produce the needed insulated transformer wire. [Answer] You can fabricate a crude form of cellulose acetate which is a form of thermoplastic. It can be created with cotton and other natural fibers and concentrated vinegar aka acetic acid. Both of these substances would be relatively easy to obtain. If the solenoid can be activated by mechanical means instead of electrical. That is moving the piston by another way to engage the contact. This is also an alternative to avoid having to rebuild the solenoid thereby avoiding the need for copper wire and an insulator. A little bit of creative engineering. [Answer] You need a MIX of solutions. Your solenoid needs to have many windings, which means multiple layers. Traditionally, wax-paper was used between layers, and I believe still is. The next insulator is *spacing*. On your innermost layer, use a slightly larger diameter wire, not for conductivity, but to set the spacing of all subsequent layers. Now they won't be touching. As you wind all layers above each other, they will naturally space apart to align with the layers above them, so the wires will not touch those laid next to them. To ensure this, paint a layer of laquer, paraffin wax or other insulant over each layer. This will also make the wax paper layer stick better, which will make winding the next layer of wire easier. This should allow a large number of very fine, tight windings. [Answer] Send me the technical details of your temporal communicator and I'll make one and relay your message for you to your original time and they can send a rescue party to you with a spare solenoid... and it doesn't matter to you if it takes me a few years to complete the build as you'll still be rescued shortly after you send me the details! Alternatively, you can make isinglass from fish swim bladders (after all, that's a waste product, no-one will mind if you collect some fish guts from a midden) and coat the wires in isinglass. It's a kind of fish-based gelatin and will make a nicely coating substance that when dry will be non conductive and flexible enough to wind the wire afterwards. For added electrical security, if you have space in your solenoid bobbin, before it's quite dry you can coat the isinglass with some finely ground quartz... or any other non conductive dust to give an extra layer of insulator to prevent shorting in the solenoid. Once wound and tested, coat the entire bobbin in melted beeswax to ensure it stays dry even if you run across an inter-temporal rainstorm [Answer] **Distilled water** is quite a good insulator, easy to produce with tools you probably already have, and readily-available in both liquid and solid phases. ]

[Question] [ Since it's that time of year again, we need to look further into Santa's delivery mechanisms. We've discovered over the years that Santa is breaking a few laws, ignoring minor matters like [IP laws](https://worldbuilding.stackexchange.com/questions/31987/how-does-santa-protect-himself-from-ip-lawsuits) and air traffic control. We have greater issues with him largely ignoring some of the [fundamental laws of physics](https://worldbuilding.stackexchange.com/questions/30978/anatomically-correct-santa). The sound you notice of Santa's arrival is a shuffling in the chimney and a faint HO HO HO, that means he'll have to stay below the speed of sound. He also needs to spend enough time in each house to drink a glass of sherry, eat a mince pie, and at about 1 house in 100, [get caught kissing mommy](https://www.youtube.com/watch?v=PITCmngiMfA) under the mistletoe. All without accelerating so fast up the chimney the g forces cause him to pass out. **All in all, how many Santas are required to complete the delivery round?** [Answer] **Quantum Theory to the Rescue** Santa is — of course — not breaking any physical laws. Bending a few maybe, but not breaking. As we all know quantum theory clearly states that the position of Santa is not known until it is measured. So Santa really is in easy reach of everywhere(!), all the time. OK, maybe not inside black holes or beyond the cosmic horizon, but easily everywhere on Earth. Santa simply gets to appear wherever a "measurement" of Santa is made. To measure Santa you require : * Milk, a glass of (or a cup if you cannot get a glass; it is the thought that counts) * Mince pie or cookie (or a tasty replacement if no MPie is available. Again, it is the thought that counts) * The all-important *letter to Santa*. Santa prefers letters in crayon but will take whatever the writer has to hand as long as it is not something nasty. Although early experimenters thought a chimney was required, the modern quantum interpretation of Santa clearly shows that Santa is not hampered (no pun intended) by walls or anything material in the way. This explains why (good) children inside apartments with no chimneys still get a visit from Santa. A Santa measurement typically results in mysterious consumption of the foodstuffs and (possibly, if you are good) that Santa may drop a present when he (or she, maybe the beard is a disguise?) is *passing through*. Santa interacts strangely with photons, so trying to see Santa can lead to erroneous measurements. For example, Santa can appear to be someone else. Scientists speculate that Santa has a device which creates some kind of cloaking field (something we now know is possible!) which can cause these effects. So whoever you think you see drinking the milk and eating those cookies is actually an illusion and it was Santa all along. Being good (all year!) significantly increases the probability of a successful outcome to the experiment. Being bad can have a very negative effect. So let us be good. All of this means that only one Santa is required to visit everywhere, although currently it is beyond our technical ability to be sure of the actual number. It may also be that Santas — like electrons — are indistinguishable so we could not tell individual Santas apart anyway; investigations are ongoing. [Answer] > > All in all, how many Santas are required to complete the delivery round? > > > To answer this **complex** question, we have to take into account the **roots** of the obviously false rumor that Santa in an **imaginary** creature, while we know he is **real**. We have also to consider that **square** minds do not meet Santa, at all. Whoever spread that rumor based it only on a single word he/she heard and, being unable to go further, went to the wrong conclusion. Based on the above, the number of Santas in the world is $1 \ + \ i$ [Answer] For the US, about 300,000. There are about [336,900](https://www.bls.gov/oes/2017/may/oes435052.htm) federal postal delivery workers in the US. Their job description is: "Sort mail for delivery. Deliver mail on established route by vehicle or on foot." They already use fairly optimized routes, so Santa will probably follow essentially the same routes/procedures (if a postal worker is on foot, probably it will be faster for Santa to be on foot, too, rather than trying to navigate with eight nine reindeer, no matter how tiny). Santa does have some advantages. 1) The sleigh does not get stuck in traffic, because it is flying. 2) Parking is no problem for Santa. 3) Santa does not have to sort, the elves do this. Also, Santa does not have to worry about hiring extra Santas to cover for sick leave/vacation/etc., so the total number can be lower. On the other hand, Santa must eat the cookies and drink the milk (in the US), and sometimes kiss Mommy. I'm going to say this pretty much cancels out all of the advantages. So we need ~300,000 Santas to cover the US. [Answer] Around 1000 for each region of your tradition. That amount is needed for conservative breeding and to keep from inbreeding. You need those Santas be able to consume sherry, minced pie or cookies and milk. Or to be able to control Krampuses. A little edit for different sense of humour folks. *Santus christmasus* is mammal well known for it's red fur and distinct call "Ho Ho Ho" that can be heard when *Santus* go for feeding. Their usual feeding time is during last week of December but due to global warming they can be spotted out as early as late November when they try to get some food from small children. There are few species of this mammal usually distinguished by their food habits. *Americanus jollyus* have a digestive tract able to digest lactose and large quantities of sugars while *Brittanius fatherus* is able to live on alcohol and potatoes. Often, but inaccurate, *Ded Moroz* is put in the same Genus but they only share same family. *santuses* are animals that live in strong and close symbiosis with humans relaying strongly on finding food in homes. As they are very social creatures they "trade" presents for food. Kind like crows. The amount of santas needed in certain region is based on the fact that we didn't noticed a large deviation in santas build or behaviours that would be the results of inbreeding. Rather fast accommodation to changing environment. [Answer] ## Only one Santa uses the S̶p̶e̶e̶d̶ *Santa* Force to accomplish all of this. Sure, it's a single *night* but he is effectively manipulating time as needed to accomplish everything. A single night for you or me could be an entire year for Santa. In fact, due to the nature of the Santa Force, he is able to travel so fast, he is arriving before leaving and doing other slightly irregular tasks. That also requires a bit of an irregular pattern on his behalf: * it is plain *odd* to go from house to house in sequence. We have many Christmas m̶o̶v̶i̶e̶s̶ documentaries showing that after he leaves a house, he takes off into the sky...instead of going to the next house over. This is because he needs to go elsewhere and then comes back to the same city/neighborhood later. For us, it could be about five minutes, but for him, it might be *days* which he spent going through different regions of the world one house at a time. * The Santa Force also allows him to enter "normal" timeflow just before getting to a house. That's why people can sometimes see him arrive and/or enter. As opposed to to detecting a sonic boom and a brief blur that probably sweeps away the insides of the house due to the speed with which it moves. * The Santa Force allows him to arrive at a new destination before he leaves another. Which is why he manages to go around the world - he's not just super fast in transit, then normal speed for the presents delivery, then super fast in transit. That way he still wouldn't have enough time. Instead, once Santa Leaves, he has already arrived at a new destination and delivering the presents there. The travel is to "catch up" with himself. Yes, that does make it seem like there are multiple Santas at work but the Santa Force actually allows a single person to exist at two places at the same time at once as long as the person is *supposed* to be there. So, instead of doing A -> travel to B -> B -> travel to C -> C you actually do A, B, C -> travel to B -> travel to C. * So now we can also see why Santa wouldn't go to each house in sequence. Having (*what looks like*) 20 Santas climbing into the chimneys of 20 houses on one street is a bit unsettling. Hence why instead Santa would go through 20 chimneys at the same time but they are *different cities*. Well, actually it's a lot more chimneys but I'm getting the idea across. He then ensures he doesn't arrive at the same place at the same time by jumping around the globe. * All this traveling, physical effort, maintaining the Santa Force, and not the least of which *route planning* is quite tiring. Hence why he needs the nourishment provided by the offerings of food and drink. [Answer] It's simply not possible for one guy unless he has supernatural abilities. But what if he enlists numerous look-a-likes? This will be hard to achieve. Ideally, the stereotype would be a Caucasian male around 60+ years old, with long white beard and sufficiently obese figure. If we can be less picky about the stereotype and perhaps allow fake beards and various figures, we get a much larger population of look-a-like candidates. Dropping the criteria that he is Caucasian and male would help even more. In addition, this would help to overcome local, cultural differences, making the look-a-like blend in better. But how to recruit enough numbers and also make them work for free over Christmas? To cover the whole part of the world that celebrates Christmas, we are talking of many millions of Santas! The wage cost would be astronomical. The idea I came up with is to enlist parents who have little children, then have the parents dress up as Santa, with fake beard and red clothes. Each such look-a-like Santa takes care of their own family, free of charge. This reduces logistics tremendously! Nobody has to travel around at all! This is much more environmentally-friendly than having reindeer sleighs travel all over the world. While they are certainly better for the environment than cars, we would need to grow massive amounts of [*Cladonia rangiferina*](https://en.wikipedia.org/wiki/Cladonia_rangiferina) for reindeer fuel and distribute it all over the world. At the expense of increased greenhouse gases. That without taking methane-based reindeer farts in account. The best is to skip the reindeer all together. So with volunteer parents dressing up as Santa, without sleighs and reindeers, we get the enormous benefit of having free, environmentally-friendly, localized Santas all over the world. The down side of this idea is that parents would have to lie to their children and pretend to be Santa. In addition, children are quite likely to recognize their own parents and see through the lie. In fact, I always thought Santa looked very much like my own dad... Oh. My. God. [Answer] There is only one Santa, but he's (massively) parallel, not sequential, and is therefore able to be in multiple places simultaneously. [Answer] # 13,194,445 There are over 7.6 billion people in the [world](http://www.worldometers.info/world-population/). Lets say on average each house has 4 people ([statistical data](http://www.un.org/en/development/desa/population/publications/pdf/ageing/household_size_and_composition_around_the_world_2017_data_booklet.pdf)). If Santa spends an average of 10 minutes in each home, and we figure time between homes to be negligible because he goes directly to the neighbors house, then there are about 13,194,445 Santas. * Houses = 7600000000/4 = 1900000000 * Minutes in a day = 24 \* 60 = 1440 * Houses per day = 1440/10 = 144 * Santas needed = 1900000000/144 = 13194445 [Answer] ``` Number of Santas = (Number of Households * Calories consumed at each household) ---------------------------------------------------------- Number of Calories a Santa needs ``` Google searching for "Calories in a mince pie" yields **289**, Sweet Sherry gives **68**, and a half glass of skim milk is around **60** Calories. We can leave out carrots for the Reindeer because Santa won't be eating those. Not all households will approve of - or be able to afford - alcohol, but we assume that all relevant households will offer something to Santa if they can, which is where the small glass of milk comes in; that gives a range 60 - 400 Calories which Santa is known to consume per household. Most of the world is poorer than the USA, but most people are kind, so err on the lower side but not right at the low end. Say 150 Calories consumed per household visit. The WikiPedia page "[List of countries by number of households](https://en.wikipedia.org/wiki/List_of_countries_by_number_of_households)" sums to **1,587,890,386**. Not all households have children, and [this perfectly servicable blog post](https://www.census.gov/library/stories/2017/08/more-adults-living-without-children.html) suggests that 20% of adults in the USA live alone (20% of household); 8% live with only a partner (each partner counted halves that number to 4% of households), round that to 25% and then handwave it to 15% globally because childbirth and population growth declines with the wealth of a country and globally it will be more households with children than the USA. Knock 15% off the household count Santa needs to visit, for "no children" as an estimate. 1.348 Billion. And not all children are good - but [Stephen Pinker](https://en.wikipedia.org/wiki/The_Better_Angels_of_Our_Nature) and [Hans Rosling](https://www.theguardian.com/world/commentisfree/2018/apr/11/good-news-at-last-the-world-isnt-as-horrific-as-you-think) have both argued that the world is a better place than media presents, including living conditions, treatment of children, and education. It seems that should translate to fewer life stressors, more coping strategies, and therefore better behaved children than in the past, so that won't change the number of households Santa visits in a significant way compared to the low precision of the estimate of childfree households, so no change to the numbers here. Without wishing to get too personal, Santa is a generously proportioned fellow - 300lbs if he's an ounce. But he neither turns morbidly obese nor stick thin year after year. And old enough to have a white beard, but not old enough to retire, puts him in his mid 60s, and nobody would dispute that he has a very active job. Assume he is an average height or slightly above and this [Calorie Calculator](https://www.calculator.net/calorie-calculator.html?ctype=standard&cage=62&csex=m&cheightfeet=5&cheightinch=10&cpound=300&cheightmeter=180&ckg=65&cactivity=1.9&cmop=0&coutunit=c&cformula=m&cfatpct=20&printit=0&x=115&y=18) says he should consume ~4,100 Calories per day to maintain weight. He could push that in a day - but not far enough to be ill, and mince pies are quite rich. Say 50% more. > > 1.348 Billion households \* 150 Calories / 6200 Calories in a day = **35 Million Santas** > > > 35 Million Santas is almost the population of Canada, and the world population is made up of almost 0.5% Santa. This may seem a surprisingly large number, but it is not far from agreement with @user3067860 who calculated 300,000 for the USA alone based on the postal service. We have a number 100x more than that, but there are almost 200x more countries than USA - many with less dense population centers and less well developed postal routes and more households. @takintoolong calculates 13 Million based on number of households, but assumes delivery can take 24 hours and @KerrAvon2055 comments a doubling or tripling of the numbers, which brings it into the same ballpark. --- It could be, of course, that the concept of "one Santa" and "multiple Santas" doesn't apply in the same way as to the rest of us. One Santa, multiple bodies. Many models for such an organism have been speculated about - technologically such as The Borg Hivemind or Peter F. Hamilton's "Multiple Person", biologically in reality with the mycorrhizal connections of "one fungus" underground, or theologically with the Christian Holy Trinity of one Deity and three instantiations. Perhaps Santa requires a new proposal of this kind? But, at least on Christmas Eve night, there are [enough Santas to sink a battleship](https://www.popularmechanics.com/military/navy-ships/a11006/xkcd-answers-how-many-issues-of-popular-mechanics-does-it-take-to-sink-a-battleship-17066130/). [Answer] There is one santa but for each person that comes on earth Santa has an algorithm that allows him to predict the outcome of the life of that person combined with its interaction with other people in order to know exactly how many people needs a gift and where and when to bring that gift. Also this algorithm works together with a special device which creates another him by using his own DNA to create another version of him in a similar way that Mitsuki from Boruto has been created. But this technology creates other santas fast. So Santa has been there the whole time with synthetic forms of himself with an algorithm matching the possibilities needed to satisfy all new humans born each day before Christmas. [Answer] ## Santa is the leader of an organization of elves, which all do the delivery An interesting explanation to how Santa Claus works can be seen in the 2011 film *Arthur Christmas*. While the film itself includes tons of scifi/fantasy elements, I think it accurately represents how many people need to be involved in such a large event as Christmas around the world. Santa, along with the elves, travel from city to city in a giant aircraft, where the elves simultaneously deliver all gifts on every house and building in the matter of seconds. Of course, each elf intentionally leaves some "evidence" by biting the cookies and drinking the milk, to keep the illusion of Santa. Now, for the actual time to travel, they have 26 hours to do their routine (if they truly do visit every place in the world, you have to consider time zones range from UTC-14 to UTC+12). And they don't have to do it exactly at midnight, or at a specific time, as long as the children are asleep. They have some margin to plan their route more efficiently (but I won't go into the details of the Travelling Salesman Problem). Additionally, aside from the elves doing the delivery, there are more elves monitoring everything at the North Pole, guaranteeing that every kid in the world receives their assigned gift, as well as checking which traditions to follow in every land they visit, and also making sure they go unnoticed (yes, this involves breaking the law). For the number itself of elves... It's not clear how many there are, but it's easy to estimate them in the thousands or tens of thousands. [Answer] The relatively more recently established *League of Extraordinary Santas* and the ancient *Order of Saint Nicholas* have a varying and undisclosed number of members. Having rescued a large number of pygmy tribes people (now know as the *Emancipated Little Folk*) sometime in the past had boosted their numbers even further than what some would estimate. Due to the secretive nature of all three groups, accurate numbers are impossible to estimate. ]

[Question] [ It's often remarked that voting with dollars — not literally, but through spending and the influence that comes with control of capital — is more ultimately influential than actual voting in a democracy. What if a society were to set up its electoral system to counteract that, where the poorest people's votes counted for more? In fact, to simplify things, what if only if people in the poorest class were *allowed* to vote? Presumably, people would select policies that are to their own benefit, but also include the possibility of rising out of the voting class. Or, would they? Imagine a country roughly like America today but with this system in place. Would it be significantly different? Or, imagine this system put into place in the 1890s as a result of a vastly more influential populist movement — how would it play out? Presume that directly buying votes is illegal and effectively enforced, as well as equivalent coercion. And since it's kind of boring if the equivalent of tax evasion makes the whole thing moot, let's take for granted some effective equation which considers income and capital and takes into account (uh, pun might be intended) all possible dodges. [Answer] Likely nothing would be different at all. Today, the poor substantially outweigh the rich, as such, the ultra-rich directly control less than 0.1% of the vote. The political power that the rich wield is due to the power they wield over the poor, mostly via control of education, the media, and popular culture. In America, at least, almost 15% of people live below the 'official' poverty line, which is about $22,000. (<https://en.wikipedia.org/wiki/Poverty_in_the_United_States>) The middle class is alarmingly small. Combined household income above 100K already puts a person in the 79th percentile. Almost 50% of American households bring in less than 50K per year. <https://en.wikipedia.org/wiki/Household_income_in_the_United_States> Basically, the 'poor' already control the vote. The rich, however, control (or at least educate, entertain, and influence) the poor. [Answer] If your theoretical society is otherwise identical to ours, the results would be catastrophic. --- A few reasons to back my statement: * Poor people are usually lesser educated, therefore more vulnerable with the means of populism and propaganda. It means most likely the worst candidate will win. * Poor people are easier to buy. Anyone who would want to win an election would just had to hand out a few dollars to those who live in poverty. * Poor people are usually lesser informed. Because the lack of sophisticated media and the long and countless work hours, poor people has a less extended horizon. They could elect terrible people not knowing about the stuff they are guilty in. * Since only poor people can vote, but because of the reasons listed above most likely the rich are being voted for, the first set of politicians would use their power to deprive anyone else of publicity to keep their power. * If poor people would be elected they would soon become rich and lose their contact with reality. * Poor people are more vulnerable to threats... if the factory owner - who himself can't vote - mentions there will be a staff reduction if XY wins, how many workers of that factory will vote on XY? --- **Edit:** Rereading my answer made me feel I has to state I'm neither a fascist, nor a sociodarwinist. I don't think there are no smart but poor people, but I think quality education cost a lot, and in many cases people in poverty can't even support their children to go through free education, so they will not have well-payed jobs, so most of the next generation remains poor and undereducated. [Answer] > > ...people would select policies that are to their own benefit... > > > Nailed it. If this system were applied to modern America, the low-income voters would likely be motivated to support policy that would provide for all their needs and allow them to live a comfortable life without actually being taken out of the "voting class." Think government-provided housing, food, clothing, transportation, luxuries, etc. for everyone who makes less than the "voting cut-off salary," whatever that may be. Anything to improve the lives of the "voting class" without actually restricting their ability to vote and continue to influence policy. Best-case scenario, we'd end up with something akin to ["Basic Income,"](http://www.basicincome.org/basic-income/) where the government automatically gives all citizens enough money to live off of for simply existing, (hopefully) encouraging and enabling them to follow their passions and dreams rather than chase the almighty dollar. Worst-case scenario, we might see a situation in which the country isn't able to support the economic cost of providing for the "voting class" in the ways it expects and votes for, eventually bankrupting the government. [Answer] Well, mostly likely that those that became rich enough to not vote would leave for another country that didn't take away their opinion. If only the poor could vote, then they would tend to vote for things that help them out. Any reasonably advanced country actually tries to do this anyway, help those down trodden. But if only the poorest could vote, likely the communist/socialist hell that some are claiming will happen if certain people get into power (here in the US) would happen. They would tax the rich down. This would help push them out of the country. The other way could be that the rich all try running for public offices to have a more direct hand in what gets put into law, and they and their friends give themselves loop holes, kind of like today... Money always talks. Disenfranchising one group to benefit another never really works, it just puts those who can't vote into the power of those who can. What you really need is a way to level out the influence of the money behind those votes. This might be by forcing ALL political money to go through some kind of filter, that tracks all political funds. As well as actual tracking of individual wealth of every politician. How much they are worth at the beginning of the year/term and how much they are worth at the end, and they have to show WHERE the difference came from. But since so many are getting away with accepting bribes in one form or another, why should they vote in such a law? [Answer] This ultimately depends on: * **The importance of voting**. The right to vote is not terribly important for an individual in a modern, highly-developed nation-state. How much would an individual be personally willing to give up in material well-being for Red to be in charge for another four years, as opposed to Blue? * **The rate at which voting power decreases with wealth.** For a logarithmic relationship, a millionaire has 1/6th the vote of a pauper, and twice the vote of a trillionaire. A linear relationship would have considerably different effects. That said, some effects might be: * **Switch to corporate ownership of assets** Instead of people buying their own house, they would simply register a corporation to purchase the house. The corporation doesn't lose any voting privileges, so it's no loss to it. * **Move to consumption and income over saving**. You say *wealth* is tied to reduced voting power, but not *spending power*. Instead of saving for retirement (where your nest egg reduces your voting privileges), you consume now. * **Capital flight** People would put their wealth in vessels out of the purview of the wealth test. You say that the policy is well-enforced, but you didn't say it was well-defined -- which is, of course, how systems are gamed. [Answer] If votes count in *exact* inverse proportion to each voter's wealth, the power will end up with a small elite who can afford good enough accountants to make their legal worth on election day come out as $0.01. The vote of a typical working loser who needs to hold enough cash to pay rent and buy groceries won't be worth diddly, and they might as well not bother. Bonus points if the typical working losers *think* they're in power anyway, because the exact math of weighing votes at each polling place is not made public (each voter's exact wealth is protected by privacy after all, right?) [Answer] Via La revolution ... welcome to the oligarchy! So only the poor can vote and the become very powerful, by creating a permanent ruling class. They pass a law that only people who can currently vote and their decedents can vote, a grandfather clause. Then they can give themselves power, wealth, and benefits, think the party elite in Soviet Russia. Edit: It would have to be a constitutional amendment in the US to prevent the supreme court from striking it down. It would still be possible with a majority of the population. This holds true for restricting voting to any minority(subgroup) of the county's population. By restricting voting rights to any minority group you change a democracy to an oligarchy. [Answer] I think the way to look at what will happen is to consider the incentives on an individual voter. Call him Fred. Like most people Fred votes according to his individual interest. He votes for a party that will give him more money. Many others vote likewise and that party wins. So Fred gets his money, rises above the threshold, and ceases to be a voter. He's definitely gained on the deal; getting richer at the cost of the loss of a mostly symbolic privilege only used occasionally and which made an infinitesimal difference to his circumstances or, indeed, to the result of the election. Therefore let us assume most people act in the same way as Fred did. Soon there aren't that many people still left in the voting class. Assuming as per the question that the system is administered without significant corruption, they cannot be bribed because any substantial bribe would self-defeatingly lift them out of the category of voters. (A factor that would help to keep the system honest would be that any increase in the wealth of a poor person is difficult to hide. Furthermore there are by now not very many electors left, so they can all be kept under scrutiny.) So the question becomes, what sort of people voluntarily stay in the voter class? Two groups, those who cannot rise out of it - sad cases unlikely to exercise their right to vote - and those who *choose* not to. The second group splits into two sub-groups: persons for whom civic duty outweighs the desire for material wealth and persons for whom civic duty outweighs the desire for material wealth and whose politics I don't like, i.e. mad fanatics. *If* it persisted, this system might result in some sort of "Rule of the Saints". Three of the many historical examples of rule by an austere and committed minority are (in increasing order of their rule's severity) [Edinburgh under the Covenanters](http://www.bbc.co.uk/programmes/p00505n4), [Khomeini's Iran](https://en.wikipedia.org/wiki/Guardianship_of_the_Islamic_Jurists), and the [Khmer Rouge](https://en.wikipedia.org/wiki/Khmer_Rouge#The_regime). But it tends not to persist. There is an alternative scenario. Going back to Fred, he votes for the party that promises him more money. As in the earlier version, that party gets in, but this time the party bosses are smarter and Fred is … not so smart. They arrange things so that Fred and people like him always think they are going to soon be given enough money to rise out of the voting class but somehow, for excellent reasons, it never seems to actually happen. Fred and his neighbours get benefits and promises just big enough to keep their hopes up, and to dissuade them, perhaps, from seeking to gain wealth by other than political means. They remain in a state of poverty and dependency comforted by the flattery of politicians when election time comes round. I shall refrain from citing real life examples of this system. [Answer] This would give the voters a great deal of incentive to understate their wealth. Perhaps they vote in something where government assistance does not count. This is actually how poverty is usually measured in the USA now, so it's not so far fetched. So the new rich would be the poor, who only receive government benefits. Their government benefits might be mansions, but they're government mansions so they don't count in wealth. Of course, with the poor running things that way, the middle class would become poorer and poorer, eventually joining the voting class. But no one could leave the voting class. So it would swell and swell. Eventually they wouldn't have enough workers. They'd have to draft workers from the voting class. They'd come up with some snappy slogan, like "From each according to ability, to each according to need!" That didn't seem to work out so well in the Soviet Union. [Answer] I've always dreamed of exactly the opposite system: your vote is proportional to your contribution to the government (i.e. the tax you paid minus the benefits you received since the last election). Granted that this is contrary to current opinion, but it has merits: 1. It is fair. In the true meaning of the word. 2. Many of the successful democracies of the past implicitly adopted this system. 3. We know it works because this is how we've been running companies for centuries (i.e. shares) and they clearly out competes the government. [Answer] This would put politicians in an interesting position. On the one hand, they would have to cater to the poor. But on the other hand, when they get elected, they need to make sure that their voters *stay* poor so they can vote them again, while also keeping them happy so they *want* to vote them again. The result would be that politicians would avoid the question of social inequality as much as they can. They would instead try to mobilize the voters with other topics which are highly emotional but have little impact on social standing. Party lines would likely follow ideologies and philosophies and less income classes. I could imagine that fundamentalist Christian parties could do quite well in this system because of the Christian idea of idealizing poverty. An interesting strategy to stay in power might be to create policies which make the voters of the governing party worse off economically so their voting power increases. [Answer] The government would collapse. Why? It would collapse either by becoming a tyranny or by losing all power. Law compliance must be largely voluntary for a government to work. If those who have the most to lose were least represented, they would have the least incentive to be in compliance. Attempting compliance through large-scale enforcement efforts would result in a tyranny. Allowing those with the most wealth to side-step the law would lead to the government getting charged absurd amounts of money even for the basic services because those running those services would be viewing the government as external predatory forces (which must be resisted). They would thus charge as much as possible because price is the cost of **getting** service (not to be confused with the cost of **providing** service). At the same time those with the most money would be doing everything possible to resist using that money to support functioning of the government (ie, looking for ways out of paying taxes). The central theme of Aristotle's "Politics" is that the government must not disenfranchise any of the socio-economic classes from power. And that the power must be proportional to the amount of influence. Aristotle had a lot of examples to draw on because he lived in the times of Greek city-states. And each city-state functioned autonomously (more or less). So he was able to observe a lot of patterns on which to draw his conclusions. ]

[Question] [ In the middle of the North Atlantic is a black, hexagonal spire. It's 1.5 kilometers wide at the base, tapering to a mere 100 meters wide at the top. It rises 20 kilometers above sea level, and an unknown distance down (anchoring it to the crust). It's made of a magically strong material, is perfectly rigid, and does not sway in the breeze. It extends perfectly perpendicular to the surface. I'm having trouble comprehending what this would look like to an observer on the ground, and so I have three main questions: * Would you be able to see the top on a clear day? * How far away would the structure be visible, and would it first stop being visible due to the horizon, or due to the atmosphere obscuring it? * Are there any other interesting, readily-apparent effects caused by this tower? I imagine that, if it's in the Northern hemisphere, it'll act like an enormous sundial, but that's all I can think of. Bonus question, but not required: Is there any known material that could even come close to withstanding the forces acting against a construction this large? [Answer] If you were at sea level (e.g. on a boat), the tower would disappear over the horizon at approximately 505km away. [](https://i.stack.imgur.com/9xXED.png) Horizon calculations are generally dealt with as simple right-angle triangles; a tower meets the horizon at $d = \sqrt{t^2 + 2rt}$, where $t$ is the tower height and $r$ is the radius of the earth. According to [this site](https://www.nde-ed.org/EducationResources/CommunityCollege/PenetrantTest/Introduction/visualacuity.htm), the visual acuity of the human eye is about 1/60 of a degree. That means at a distance of 500km you could distinguish something about 150m tall/wide or bigger. So you likely won't see the top of the tower (at 100m) at this distance. Working backwards, if the tower were a constant 100m wide it seems you would cease to be able to make it out at $d = x/(2\tan (1/120))$, which is 344km. The tower is actually tapered so it would likely be a bit further than that, but the maths gets more complicated. Let's say for now that **ignoring the atmosphere, the distance you could see the tower with the naked eye would be somewhere between 350km and 400km**. This also answers question one: yes, if you were underneath the tower you could see the top (20km away) if there was no atmospheric scattering. It's hard to find hard data, but [various sources](https://pumas.nasa.gov/files/03_25_96_1.pdf) suggest **the best-case distance when considering atmospheric scattering is perhaps about 160km**. This is sufficiently far that the difference between looking at the top of the tower and the part touching the horizon is negligible. At a distance of 160km, the bottom 2km of the tower would be below the horizon. At 20km, the top of the tower is in the mid-stratosphere, above cloud layer and in amongst the ozone layer. It definitely could be obscured by clouds, but if the sky was clear I don't think the atmosphere itself would be a problem. I'm struggling to find much data on that. It would possibly depend on the time of day and how well-lit the tower was. One thing that occurs to me though is that **there may be permanent cloud cover** (see next paragraph) which could mean the top of the tower is *never* visible from the ground. I imagine the temperature differential between the top and bottom of the tower might make for some interesting effects (condensation? Permanent cloud cover? Perhaps it could be used as some kind of heat engine?). Similarly, it might provide a useful nesting surface for sea birds, shade for fish etc. [Answer] Interesting side effect: Astronomers would *kill* for a tower like this. * Middle of the ocean is where you find lowest light pollution levels on Earth * 20km up the atmosphere is rather thin further making telescopes work better * The tower is absolutely rigid so long exposures can be done and stabilization is easy [Answer] There would be a lot of local climate effects caused by the tower. One of the most visually dramatic would be clouds. It would likely have a [cloud wake](https://en.wikipedia.org/wiki/Wake#Waves_by_density_differences,_like_a_water_surface), the most dramatic of which are Von Kármán Vortices.  [NASA Earth Observatory images by Joshua Stevens and Jesse Allen](https://earthobservatory.nasa.gov/images/90734/two-views-of-von-karman-vortices) Cloud wakes are caused in real life by islands, and your tower is comparable to an island at the base. [Answer] Clearly it's going to be visible from extreme distances. You can see the Shard in London, or the Burj Kalifa in Dubai long, long before you can see anything at ground level around them, and from some places you can see the tower appearing to rise out of nothingness. Obviously whenever there is a cloud base the top will disappear, as happens with many skyscrapers (eg the Shard) on a regular basis. Depending on the smoothness if its sides, it will become a habitat for assorted wildlife from weeds and shellfish upwards. It may acquire it's own ecosystem. Condensation from clouds etc running down the side might be a useful source of fresh water for birds or seafarers. It is unlikely to remain its original color for long and unless it si perfectly smooth plant life will get hold, birds will cling to it etc. It's a pretty decent-sized island, it just lacks horizontal surfaces until it has some growth. EDIT: At with some skyscrapers, you will get an interesting situation at sunset and dawn where the base of the tower is still it darkness but the upper section is illuminated by the sun. This tower will be an extreme case: depending on how well it reflects, it may look like a bright red star or second sun well above the horizon. [Answer] One thing that no one has yet picked up on is the requirement that the tower be **perfectly rigid**. Such a material is fantastical indeed because it has a very important property - it violates the theory of relativity. A perfectly rigid material must have an infinite speed of sound. If it did not, then it would take some time for the sound of a bird hitting the bottom to reach the top. In fact quite a bit of time, since it's 20km tall. Physically this would manifest as a compression of only part of the structure, which is by definition a violation of it being rigid - you cannot compress part of the structure and not others. So this thing would be very, very strange indeed. For one thing, any vibration of the object is automatically felt throughout the entire structure, immediately. You aren't allowed to say that it doesn't vibrate, because it's attached to the crust and the crust most definitely does, so **it would act as a microphone to the insides of the Earth**. There is another issue, though. I didn't say that the speed of sound was "very fast", I said it was infinite. This is beyond "faster than light" to literally "there is no finite number to describe it". As one consequence you could use it for time travel experiments, since objects further from the earth's surface experience different time dilation compare to objects at the top, albeit on the order of nanoseconds. [Answer] > > Would you be able to see the top on a clear day? > > > Sure. On a clear night we can see the ISS. > > How far away would the structure be visible, and would it first stop being visible due to the horizon, or due to the atmosphere obscuring it? > > > [K. Morgan already mathed this out.](https://worldbuilding.stackexchange.com/a/181530/21222) > > Are there any other interesting, readily-apparent effects caused by this tower? I imagine that, if it's in the Northern hemisphere, it'll act like an enormous sundial, but that's all I can think of. > > > Time dilation. Time will pass differently on the top and the bottom of the tower, due to relativity (the top has greater linear velocity than the bottom, considering Earth's rotation). This actually happens to everything, even our bodies, but on a structure that tall the effect would be easily measurable with modern clocks. > > Bonus question, but not required: Is there any known material that could even come close to withstanding the forces acting against a construction this large? > > > No. That's why mountains won't go higher than the Everest on Earth. Not even them withstand such forces easily. [Answer] > > Bonus question, but not required: Is there any known material that could even come close to withstanding the forces acting against a construction this large? > > > One important property here is *breaking length* (see <https://en.wikipedia.org/wiki/Specific_strength>), the distance after which a material will break under its own force of gravity. For steel this is under 7km, so it is unsuited for building such a tower. But there are a number of metal alloys (mostly aluminium and titanium) that have breaking length beyond 20km and many carbon composite materials have breaking lengths in the dozens of kilometers. You could build your spire out of these and they would at least withstand gravity. Harder to answer is how they'd have to be built to withstand the forces of wind and whether the continental plate below the tower can withstand its enormous weight. I fear that the mass of the spire will crush the rock its built on and cause it to start sinking. This is one of the factors that limits the height of mountains here on Earth, see this answer on earthscience.stackexchange: <https://earthscience.stackexchange.com/questions/9745/how-high-can-a-mountain-possibly-get>, which reasons that the maximal height of a mountain on Earth is roughly 10km. To counteract this, you'd need a *gigantic* base that spreads out under the spire's foot and distributes the force to the point the pressure is below the compressive strength of rock. [Answer] From even modest distances, it would appear to be slightly leaning away from the viewer. The difference in the directions of "vertical" at largish distances apart on the globe would be noticable to the unaided eye. [Answer] * The top would be a 100 m object at 20,000 m distance. That should make it difficult to observe many details from a ship near the base, or even to judge if there is a top or if that is a distorted perception. Take a broomstick and peer along the length, can you really tell if the other end is round or flat? * The horizon distance, as mentioned by James in his comment, is 500 km away. Take that broomstick again, glue a cent on top, and then observe it from 50 m away. Can you make the cent out? * Concerning haze, the Rafale fighter has an [optical sensor](https://en.wikipedia.org/wiki/Optronique_secteur_frontal) with 40 km identification range against other aircraft. So an instrument like that should be able to identify a fighter-sized object standing near the rim of the top, some 30-40 km from the base. At that angle, objects standing near the rim are visible. [Answer] > > Would you be able to see the top on a clear day? > > > The air pressure at a height of 20km is about 60mBar. Air pressure is proportional to the amount of air above it (because it's the weight of the air above that produces the pressure). An observer at sea level will need to look through the air below to the top of the spire, and see it behind a background of the air above the spire. This is a 94% to 6% ratio. **There is roughly 16 times more air between the top of the spire and the observer than there is behind the spire top**. Why is this important? Well, when you look at the sky, the blue stuff, that's the air. And if you look at 94% of air, that's almost the same as if you look at 100% of air. The spire is black, as is the space behind the atmosphere. The only visible contrast that the spire has, is those 6% of air behind it that scatter the sunlight. And you look at it through a layer of air that's about 16 times as bright as the background. **As such, you'll be able to see the spire all right. But the further up you follow its shape with your eyes, the fainter the black becomes until you can hardly make out a slight shadow in the blueness of the sky.** [Answer] Viewing distance: on a clear day it might be up to 150km away, especially the top part which is above most of the dirt and haze in the atmosphere. On normal days it will be rather 30km to 60km. The detail you can make out is directly depending on the lens size you are using. You cannot, under no circumstances see the Apollo landing sites on the moon with naked eyes. With a rather big telescope, you can. The size of the lens that you need is calculable. On a boat, with your eyes, you will have difficulties seeing the top. With a handheld telescope, it might still be difficult. At least it is principally possible. If your boat has an installed telescope with an electronic control for all the movement, it will become easy. You can't see from below if there is a platform or something else, because of your perspective. You can't even see what's on your neighbours flat roof if he has three or four stories. [Answer] ## It wouldn't look all that tall **Seriously!** If you visit Dubai and wander around and look at the Burj Khalifa building. Since it tapers and you have no frame of reference it looks maybe 2x times bigger than those around it. It is not until you are way out in the desert and you can see it beside the other 'normal' sized buildings around it that you see it is towers 6-8x times taller than anything else. Your structure would be similar only there are no other buildings around to gauge it by. So it would just look like a moderately tall spike shaped building in the distance. Perhaps with a little snow and ice shading near the top half. [Answer] **You'd only see the top on a very clear day** Take a look at where the top (20km) would sit in the stratosphere, in relation to **even the tallest clouds**: [](https://i.stack.imgur.com/qutWT.png) **Its way above the tops of thunder heads!** But don't worry, there will be **lots of clear days** here, because it's safe to say that this thing would act as a giant **grounding rod for any storm in the area**. It would probably de-ionize the air so much that thunderstorms wouldn't be able to occur anywhere for around 20km from the spire, and depending on the material, it could be so grounded that it literally saps all the particulates out of the air (making the tower very very dusty) and **preventing the formation of clouds**. So, any clouds that **do** form within 100km of the tower would eerily drift always to the tower (because of the negative ionic attraction), just to always wisp away and disappear within kilometers of the spire. Would make for a very good "north star" idea, but yknow, "north atlantic spire" instead of a star. Also look at where it exists in our atmosphere: [](https://i.stack.imgur.com/cShmp.png) [](https://i.stack.imgur.com/3TyAs.png) **More than half of this tower would be -55C !** The cold temperatures would propogate down the tower (assuming it's a good heat conductor) and cause condensation at lower levels (because the atlantic ocean air is very moist), so there would always be water trickling down the sides, starting at around 5km high. **It'd be a very cool waterfall in the middle of the atlantic.** **Given that the air here would be very clean/pure, that every day was nice and balmy, and that the tower itself was a source of pure water, it probably is a great place to live or even take a vacation.** **Can We Build It?** Unfortunately, no, with today's technology there is no way to make a tower that could be this tall. As an engineer, I could show the mathematics as to why we couldn't but I'll simplify it to this: Because the earth rotates, the bottom of the tower moves slower through space than the top of the tower. Thus, this is the same effect as placing a stick in the dirt, then grabbing the top and bending the stick. We don't have any materials in existance that are both **strong enough** to be built tall and **flexible enough** to withstand the forces of bending. ]

[Question] [ *This question is focused on what one man could do without the implicit resources on a larger scale.* The year is 1980. Paul is a 17-year-old farmer in Iowa, with nothing really to his name besides his pickup. Late one evening as he's driving down the road a Handwavium bolt of psionic energy hits him. The Handwavium bolt accomplishes the following: * Over the next 36 months his abilities will develop as listed: + He gains a 'genius level' intellect + He can think faster (complex though and simple reactions), and focus harder than the vast majority of people + He gains military knowledge on tactical, strategic, and logistic levels the envy of modern military commanders + He gains extensive knowledge of chemical, electromechanical, and computer engineering on the level of accomplished professionals in these fields (all limited to the technology and research in this era) + His body approaches (but doesn't reach) olympian levels at a variety of activities + His body overall is extraordinarily healthy * **Most importantly he gains a vision that, in exactly, to-the-day, 25 years from that night there will be an alien invasion** He knows few details about the invasion (he recalls a fleet of saucer UFOs, various machines landing on the surface of the planet, and humanoid aliens walking about), but he knows with absolute certainty that it's coming. Well, Paul knows he can't just walk to the police station and say that aliens are coming as he'd *rather* not be thrown in the looney bin. As he has no way he can think of of creating proof, he'll have to keep this all to himself. Paul wants to help the world to prepare for the invasion. Paul wants to **consider every possible option**--every possible path he could take--and figure out how best he can ready Earth for this invasion. The threat of extermination is so concerning to Paul, that Paul is willing to do **absolutely anything to accomplish these goals.** **The question is not about what character actions Paul might take, but what Paul can do given that he only has direct command over himself as a resource.** What is Paul's best plan forward? [Answer] There are a couple good answers already about how Paul can help the world prepare by sharing knowledge, or advancing technology. **But** if he is really prepared to consider any option, to take any action, there are at least a couple more options he should consider, whether or not he actually decides on using them. ## Take up Super-villainy Honestly, there is very little that pressurizes R&D and advances technology like a real, genuine, threat. While it is possible that he can take advantage of existing tensions to market his new & improved defense technology, it isn't guaranteed - especially if the discrepancy between the incoming aliens and Earth is significantly greater than the discrepancy between what a nation can do with what Paul-advanced tech is capable of, and what the *next most powerful* nation can come up with in the intervening time. It is quite possible - if one nation gets too far ahead, or if (kinda like nukes) the tech becomes sufficiently dangerous that no one wants to use it on *their own planet/people* - it can stall out with either that one nation suppressing others and not needing more or better weapons, or with a Mutually Assured Destruction pact, which prevents the tech from being used/developed more - potentially before it reaches the levels needed to defend against the aliens. So, Paul might consider becoming a super-villain. As an individual, he can **become** a threat, to his specified level, and and spark innovation that way. Better yet, if he plans well enough, he can unite the best minds into working together against *him*, instead of against each other - and he might make strategies that develop piecemeal the tech he wants (better targeting systems to foil this scheme, now tighter focus to fix that, and preventing this kind of target jamming, how to avoid overloads) which can happen to be pieced together into the super-effective weapons and systems needed when the aliens come (as targeted as he can make it), instead of being halted as not-needed, if it *was* not-needed against purely human threats. He might not decide that is the right path to take - if nothing else, it will make *his* life miserable, paint a target his family and hometown, and if he fails at all (is caught, is out-developed, is killed) he will fail *totally* since no one will believe him after he makes himself that level of threat (or nuisance). But if he's honestly willing to look at all the possibilities, he should at least plan it out and see how it stacks up against *other* plans, to see which offers the best chances. Of course, since part of this idea's problem is how it will ruin his own life and credibility, he might try a *related* solution instead. ## Make a Super-villain (hoax) Hey, if *he* doesn't want the job, why not give it to someone else - preferably someone entirely imaginary, since then they won't get out of control. Probably. Hopefully. Anyway, he will need to plan some kind of background story for this villain, including a pretend-goal, and some kinda logic for how his actions will serve that goal. He will need some remote disguise, so it isn't clear he's imaginary - maybe a robot, or a costume, some signature effect, a signed *note*, whatever works - so people will know who this is supposed to be. Also, he will need to pre-develop some fairly advanced tech (again, as close to the alien tactics as possible) so he can have a "head start" on the rest of the world, and be a viable enough threat to the rest of the world to get the weapons up to par. As a bonus, this way he can be on the side of angels as long as the hoax doesn't get revealed - collaborating with them, influencing the direction of their inventions (and using that knowledge to keep the Villain's threat relevant). And, if he develops counters and counter-counters at the same time, he can get into a technology race with *himself*, and "release" technology upgrades targeted towards fighting the aliens from both sides, with a bonus of whatever the other human weapons developers come up with to make it better. It is possible, if he manages the threat level vs actual damage well enough, and has a good enough rapport with people he has been collaborating with - he might be (kinda) listened to even if the hoax is discovered. If they believe he at least believes in that level of threat, if he has made the villain frightening but not directly caused that much damage (via "last minute saves" by himself or various deus-ex-machina)... they might be willing to develop the tech just in case, even if the hoax costs him their trust otherwise, and possibly his freedom and/or future. And wouldn't it be worth it, for the whole world? ## Make an Alien (hoax) Well, maybe he doesn't want to cause that much damage, even if it does get everyone working together and the right sorts of directions to nullify the threat. But, having already had the idea of a hoax - can he try a different one? Make up some "alien refugees" (or possibly just the one) - maybe they can even be "advanced warning" of the alien threat, having barely survived the same species' advances (and possibly "lost their own planet" in the bargain). This will be similar to the "super-villain hoax", since Paul will want to *avoid* any scientific experimentation (including simple bio-analysis) that can prove it's a hoax. On the other hand, any *actual* alien refugee would also want to avoid being experimented on, especially if they saw some of our storybooks and alien treatment in them, first. So, having the refugee(s) openly state their "reasons" for hiding will help. Gifts of advanced technology (developed by Paul, of course) can be given - preferably to multiple governments simultaneously, and with carefully leaked media exposure - along with the warning of the alien fleet, its estimated arrival timeline, and the potential fate of earth, based on the "fate" of the hoax-alien planet, if the alien fleet isn't resisted. Obviously, it's best if the technology was a boost in the right direction. Possibly the information is "fragmented" or partial, openly attributed to the hoax-aliens laws about advanced tech or limited by what they "could scavenge", or what "they" (Paul) thinks is safe to give humans, and which actually depends on what Paul can actually come up with and what time-frame he is willing to give to his own tech development vs the world's response time. Human scientists can go over the data and develop ways to fill the gaps on their own. He may want to stack the deck of his hoax with media exposure, his tech or robots or whatever proxies *publicly* offering help in disaster scenarios, using their "advanced tech" to give warnings or open aid, kinda working the superhero trope and giving concern about human reaction as a reason for not coming forward openly. As long as everything is done through proxies, it will be *hard* to prove it's a hoax - especially if the tech involved can really be developed by Paul. And this way it will be possible to openly warn the world about the alien threat - nobody will be surprised or doubt that space aliens believe in and/or know about a space alien fleet! Again, it is possible that if even if the hoax is discovered, he might be able to convince the discoverers that he has a genuine belief in the coming fleet - he has proven his intelligence with developing all that tech and the hoax itself, yeah? And at least in *this* hoax, Paul and his "refugees" have been helpful and not caused damage, not acted as a threat, gifted technology and weaponry (to multiple nations, no less). So they might continue developing the technology just in case it's true - or even let the hoax continue, with people not in the know innovating in the meantime, until the invasion happens (or doesn't), thinking they can decide what information to release then. ## Start a religion (hoax) Actually, if he's already figuring out what to do to make villain or alien hoaxes work, why not check into what it would take to make a religious and/or cult hoax? As a bonus, he can even do this openly after a reasonable set-up period. He needs s good understanding of religion, psychology, and cults - both sincere and scams - to make it work, but he's intelligent enough to figure something out. So, Paul has been *blessed*. Really, he has been - and he can prove it, with all his shiny gifts of physical, mental, and educational enhancements! Let him gain some money, build some influence, look at dominant religions and what suits his needs, and see if he can't build a cult out of it. He can (as in other approaches), develop advanced tech to make the cult dangerous, powerful, able to *meddle* according to their creed. He might not want to start with alien-fleet threats (unless he's *really* sure he can get enough believers) - but powerful, and armed, and willing to develop some dangerous technology will get attention. Depending on the substance of his cult-message, some of that advanced tech can be used to "make miracles" via robots, remote tech, all kinds of things. Otherwise, the ability to develop so easily can be, er, given the question maybe that should be "actually is" a gifted miracle in its own right - if and when he has enough people, enough influence, enough trust, to undergo whatever testing to prove his various blessings. He can, again, develop and give away technology to various nations or interests (in accordance to his stated creed). He can give warnings about a coming menace - especially once he's bought influence with his tech and has some followers, he might actually be listened to. He can inspire generous or beneficial actions in his followers, to gain influence - or ambiguous or dangerous actions, to create a threat to work against. Paul has to start small, and build a network of followers, a cache of technology, and some serious influence before he can come out and talk about the alien threat - but unlike some other methods, he *can* talk about it. He can claim his enhancements openly, give the real backstory - with a study of psychology and history, he can figure out how to persuade people quite well. And, he can use advanced tech to "fill in the gaps" of his cult's beliefs, creating miracles, goodwill, or "supernatural" threats to get people prepared for the alien invasion. ## or Just *buy* the technology! Paul, with his intelligence and insta-knowledge, can probably come up with some ways to get rich, *fast*. And between wealth and intelligence, he's going to get *influence*. Have him offer (conditional) grants in scientific fields he believes useful to R&D, have him invest in weapons companies, communications and jamming, anything that might help when the day-of comes. He can get pretty far capitalizing on just the human-level threats, between national interests - and get a good tech-boost out of it, especially if he invests himself and his intellect along with the money. The difference here is, as he is gaining influence and attention - he can quietly take carefully chosen people into his confidence about the reason why. Wealth and influence will shield him from a lot, obvious intelligence will shield him from some more of the consequences if someone doesn't believe him - not all of them, not by a long-shot, but enough he doesn't have to worry about being dragged off to the loony bin, and he can let people sniggering at him go. People buying the weapons systems won't really care if they're getting lasers instead of missiles *because* their backer believes in aliens, they will care that the lasers are powerful and precise and destructive enough to replace the missiles as the go-to weapon. And while he might be able to convince people along the way, enough to avoid leveling off of tech or de-prioritizing weapons R&D because they think the weapons they have are good enough - even if he can't convince them or doesn't try, he can plow cash into research piecemeal that happens to *work together* - this bit of software helps the target systems, that has to do with increasing power, that little thing helps efficiency - so that when it's time, the pieces just need to be assembled to get your weapons and systems designed to be effective against the alien tech. This is pretty much the same work Paul was doing in the last couple options - what tech, and what tweaks, will steer people in a direction effective against the alien fleet, and what human tech can be developed around or between these requirements. In this case, he just uses grants to buy the individual research pieces originally (which might not even look like anything dangerous till assembly-time), and only pitches the weaponization of the systems and parts once the background, theoretical research is done. **Again, some of these possibilities are more pleasant than others**. But if Paul is serious about the threat and his need to get people ready, he should at least consider them - even if he ends up not using them in favor of a different plan. [Answer] Assuming that the object is to protect earth, and not just hide away when the aliens come... # Join the Department of Extraterrestrial Defense The Department was founded in the sixties, at the same time as the project to create a psychic supersoldier using LSD. Currently it consists of one insane bearded guy, in the 22nd basement level of the Pentagon. However Paul the supergenius, right after he collects his advanced degrees, decides to join it, and singlehandedly rehabilitates it - not because anyone takes the threat seriously, but because the research he does turns out to have wonderful practical applications. Strangely it all seems to relate to some kind of defense against a hypothetical and unbelievable alien invasion, but the by-products are fantastic. Good research will attract more people, who want to join not because they think invasion is coming but because the work is exciting. Being such a genius he also manages to siphon off some of the research funding for building prototypes of the hardware that will be needed when the aliens come. Justified by the scientific and technical by-products of course. As well as, or instead of, the above... # Write books and movies about alien invasion Pure fiction, of course. Make them strangely specific about the threat and where it comes from. Include some 'hypothetical ideas' about how mankind might repel the invaders. Get people ready for the idea. [Answer] Stealing a little from @DJClayworth's answer, this answer is probably too self-insert-fan-fiction-y to make a good story, but it is exactly what I would do: # Tell Carl Sagan On September 28, 1980, PBS aired the first episode of Carl Sagan's *Cosmos*. It quickly became the most-watched American television program of all time for a decade until it was overtaken in 1990 by Ken Burns' *The Civil War.* After the completion of *Cosmos*, Carl Sagan wrote - and then published, in 1985 - *Contact*, a novel about first contact with an alien species. Sagan would be the perfect person to, erm, contact. Our hero - Paul - makes a visit to Ithaca, NY, to share his experience with Sagan, and, if nothing else, impress him with Paul's encyclopedic knowledge of science, technology, engineering, and so on. Paul backs up every assertion with precise mathematical proofs, and it becomes increasingly difficult to believe the 17-year old is - without any alien intervention - nothing more than a genius unmatched in human history and has spent his entire life researching cutting-edge science while finding enough time to perfect an Olympian physique. Sagan comes to trust Paul and helps him access the right people in the right places. Maybe they're even able to retrace his steps on that desolate Iowa road and uncover some evidence about the aliens, who they are, where they're from, and so on. Perhaps they can also diagnose the causes of changes in Paul's body to rule out other options. With enough evidence in tow, Carl Sagan helps Paul Protagonist get a hearing in front of the U.S. Congress on live television. Whether the government officials are convinced or not, the media suddenly informs the world that top, respected scientists - and an unprecedentedly brilliant Iowan teenager - are adamantly united in evidence of extraterrestrial activity and an imminent invasion threat. At that point, the fate of the world is largely out of Paul's hands. Even if he had taken the get-rich-and-powerful route as other answers here suggested, without the global support of all of humanity, there is very, very little he could do to stop such powerful aliens, even with a net worth of, say, $50 billion dollars (most of which would have to be tied up in assets to avoid taxation), let alone how much precious time it would take him to get there. [Answer] Since he got such an intelect as to become an *honoris causa* engineer and scientist in many different fields, he can use his free time and knowledge to design novel weapons for the military and fill in applications for patents. In time he'll be noticed by companies such as Lockheed Martin or its competitors. He's bound to have a good job, which will grant him access to their labs and a good networking with pros from the area and the Pentagon. He may just keep inventing better and better weapons without needing any better justification than fighting whatever enemy the USA are fighting at the moment - Hussein, Bin Laden etc. When the aliens come, everyone is just going to think "wow, we are so lucky to have had Paul designing all this stuff for us in the last couple decades!" [Answer] Getting people to believe in aliens has been pretty well played out. So don't try. Also the first round of the invasion going to go to the guys with the high ground, and it isn't us. So don't try too hard stopping the invasion. Sooner or later we'll have to take the fight to them, which probably means shipping a lot of stuff into space. It'd be nice if it was a lot cheaper to do that. (in progress --SpaceX) Our energy infrastructure is probably not going to out last very long, so it'd be nice if we had a huge number of really nice large batteries all over the place. (in progress --Tesla) It's be nice if everyone had radios and cameras so that anything anyone learns that might help can be shared with whole world rapidly. (check) What else might you need? Insurgency. If he goes this way he'll want money and the US political connections that brings. Let's assume he gets them, as I have no idea how to. How to make an effective insurgency? Have caches of secret weapons and/or the means to make them all over the place and plenty of fighting men ready to use them. How do you encourage that? (Since you really don't want to even indirectly be on the losing side of a war) Have a powerful government throw their weight around, but don't bother crushing non-active opposition. Maybe lots of talk about banning guns but have little effective enforcement. (check) Cause real insurgencies, this lets a lot of people on both sides learn the lessons in a way that will stick. Maybe invade some countries that can't fight pitched battles but have a good history of not being conquered. (check) Increase the numbers of combat ready people not in the military or at least on military bases. Maybe promote better armed and trained police forces or fluctuate the number of soldiers in the military. (check) Hmmm... I'm sure I should go outside, but not sure if need I need fresh air or tinfoil. [Answer] The current structures of power in the more advanced nations of the world are difficult to infiltrate quickly and a lot of the world is indoctrinated into notions like democracy or patriotism that are hard to turn around in even a timeframe of the likes of 25 years. No one person could unite the world through politics and I also doubt an Alexander the Great-type figure could unify and maintain that unification of the world through conquest. Paul's main way to power in the modern world is through corporations. Money talks and Paul is more than capable of starting up businesses and creating profitable ventures in a realm that nobody would question or be able to significantly oppose a rapid rise. Once his organization reaches international levels, he can dictate policy and use his influence to shape things in the direction he feels things need to go. As to the types of business his companies engage in, there's no reason that he can't acquire R&D and work on defense tech (also a good way to get in tight with various states). There's also opportunities to form private military companies that could be prepared to double as a defense force in 25 years. Given Paul is the adept person that he is, there's also no reason that he cannot secretly engage in some of the other activities mentioned by other answers. The right approach is to have many eggs in many baskets, so he shouldn't just start one cult, he should start many. Alien hoaxes would be a great way to galvanize defense spending that can be spent on his companies, while media influence could subtly prepare people for invasion. One of biggest opportunities others seem to have missed, however, is attempting to duplicate himself. If others were to have the same Handwavium experience, we can assume we would be creating instant allies with similar capabilities. Even without the vision, having more people on his level could do more to overcome the resource problem he has as one man. All that said, I don't think Paul's chances are all that good- we already have plenty of olympians and geniuses and excellent thinkers in our time and yet the world is in the state that it is. Paul's new capabilities alone will not be enough to make the difference he desires- when the aliens come, Paul is going to need some luck to turn things around. [Answer] Things you can do when you're absolutely certain about the future: Buy insurance. With enough money and a narrow enough definition you can get pretty good odds. Start a cult. You don't care about seeming nuts. You care about getting people to do things. Be careful to tease apart what you know and what you assume. UFO's, saucers, and humanoid aliens walking about are all that have been foretold. Not our extinction. It may be that what you really need to do is prevent earth becoming a tourist trap. [Answer] Paul's a genius and can work really hard. The first thing Paul needs to do is to get rich. Money is the lever that lets him do lots of things. He can work multiple jobs, use his knowledge of science and engineering to get several BS degrees in a short period of time, and then get a good job with a defense contractor or a think tank like RAND. This is 1980, the cold war is still on, there are plenty of opportunities for that. [Answer] ## Mechanical engineers build weapons, civil engineers build targets He doesn't actually need to convince people that aliens are coming, he just needs to convince them to buy the weapons and system he develops that just happen to capable of putting the planet on an even combat footing when the aliens come. Should anyone question why he happened to go into this particular career he can just laugh and say "because aliens". He may suffer a downside from his particular place of origin for saying this, but in most environments people will just take it as a joke and carry on. [Answer] # Get himself checked out for mental illness Very simply put: the smarter you are, the less you trust your senses and your own conclusions, especially if those conclusions are way out of the ordinary. So at some point, Paul will realize "This is just plain nuts... it does not make any sense at all". He will assume that it is possible he has gone absolutely bonkers. He suddenly thinks himself smarter, fitter, better than others... **and** he thinks the world is about to suffer some great disaster. First suspicion is that he has become like the loonies on The Crazy Part Of The Internet that babble about chem-trails, Moon landing hoaxes and that the president was behind 9/11. He knows he cannot trust his own senses, so he gets a second opinion, preferably at a place where they are used to dealing with loonies like this. That will then turn out that everyone seems to say "No, you are not crazy, you are in fact very healthy, and admirably clear in the noogin'". Ok then, that is that taken care of. He is at least not **completely** bonkers. ## ...then: find the evidence But there is still the fact about the impending invasion. How can he trust that knowledge? He cannot. He needs evidence. He knows — just like you did now — that unless he can come up with a really good piece of evidence, then he is just as likely to be delusional. Smart and athletic, but with with a screw loose. So that is when he starts looking for it. Where are the signs that are not just in his head? Where is the stuff that tells not just him but that others that something foul is afoot? Here is where you as the writer can take several paths of how much evidence he find. Everything from "none at all" to "undisputable and more solid than the ten commandments", and everything in between. What do **you** — the author — want to happen here? [Answer] **Tony Stark Mode** * Year 1 : Start a company in electronics & entertainment business. * Year 2-4 : Step up into weapons manufacturing. **Bruce Wane Mode** * Year 6 : Start ET Research & Try to get proof (10% of Profit). * Year 8 : Invest on share market (10% Profit). * Year 10 : Step up into future weapons research (50% of Profit). * Year 14 : Increase future weapons research into (75% of Profit). * Year 15 : Stop ET Research. * Year 18 : Stop share market investment. * Year 18 : Increase future weapons research into (95% of Profit). * Year 24 : Get ready for imminent attack. [Answer] If Paul in this story is an American and super intellegent... Why not run for President of the United States and fix the problem that way? [Answer] Well the first year should be spent by using his abundent knowledge, improving physique and sharp reactions to steal a large sum of money. Increasing his social network by interacting with intellectual and influential people. Consolidating his knowledge by writing the most comprehensive books ever written about those subjects. Then he should use some his money to gift those books to experts in those fields. While offering to sell that at reasonably low prices(because free things are unlikely to be good) to other people and instutes. This will hopefully increase the developement of knowledge in these fields and also increase your reputation. If he continues to know the new things those professionals find out, this could create a positive loop. The people of the planet are a resource that he shouldn't waste. At this point he should have grabbed the attention of a large number of influential people around the world. He could possibly be offered a number of goverment adviser positions from multiple countries. Hopefully he can cause many countries to be on more friendly terms with each other by using mutual benifits. He should also during this union creation mention that if an alien race invades in 20 or so (hopefully he can get to this point in less than 5 years) that he would lead the forces of all countries (which they should all agree to as it sounds lika a crazy joke). He should then advise those countries to focus on research into electronic communication and weaponry (especially anti-air), while giving them other ideas on where to focus research. Then he should research into theses areas himself, supervising and advising projects that pique his interest, while advising the countries in other sectors to try yo keep the union more harmonious. Hopefully he can pull in more countries before the attack. --- This type of stratergy would have alot of risk (as a lot of really talented people fall by people who are afraid of them climbing over there head and a multiple of other reasons), however with high risk comes with high reward as without the contribution of a majority he will be highly unlikely to repulse the alien race. This is in my opinion the best plan of action. Though it is hard to determine if he could do everthing in 25 years and if a genius level intelligence is enough, personally I call whoever can do all this a monster. [Answer] The big problem is getting people prepared to fight back (i.e., train them to be soldiers in the upcoming war) without telling them that they're training for this upcoming war. Training is hard, and takes a lot of dedication over a long period of time. How do you get a large segment of the population to dedicate large periods of time to this activity on a continuing basis for the next 25 years? Build a continuing series of viral video games. With the various types of expertise he's going to gain over the next 3 years, he will have the skills to create such a series of games that will train people in strategy and tactics, and use of appropriate weapons, without them realizing why they're doing it. As we've seen over and over, people will dedicate massive amounts of time to playing addictive games, and this can be maintained over long periods if you make the games intricate and engaging enough, and continually present players with new and novel challenges. You can also make ungodly amounts of money off the games, which you could use to design and build remotely-operated weapons systems (some of which you could sell to the military to gain even more money) that exactly mimic those in your video game, so that at the end of the remaining 22 years, you have an arsenal of weapons and a global army with over 20 years of experience in using them them against invading alien forces, without anyone ever knowing what you were doing. Sort of a spin on the Battle School from Ender's Game, except in this case no one would know that they were training to fight real aliens. [Answer] I would like to add to Megha answer. I don't think it is feasible to become a supervilain to trigger arm race between countries to defeat yourself. Pragmatic approach: Paul needs to go to country like Columbia or some war torn African country. Paul needs to make a lot of money with drugs/blood diamonds/etc and build his own private army. With money he can also build research facilities and then hire/kidnap other scientists to help with a weapons research. Threaten them to get him results (worked quite well in Soviet Union). Get some advanced weaponry researched. Buy/bribe/threaten/blackmail politicians in rich countries. Make legitimate weapon research facilities in those countries. Sell advanced weapons and technology to everybody so they have it and want more, keep the last generation for yourself to always have a carrot to sell and a stick to defend against nosy and greedy. When the time comes: Paul has improved weapons technology for the whole globe. Paul has an army with the most advanced weaponry available. Since Paul doesn't have to abide to norms of ethics he can try to create genetically modified super soldiers, he can brainwash them to make them puppets and sacrifice them in the initial wave of alien attack to give Earth governments more time to prepare for war. He can conquer a couple of nearby countries just before the invasion and conscript their populations (like literally all healthy enough men and women from 10 to 50 years old) to wage war against aliens. [Answer] **Star Wars** Initially, in 1980 he uses his newfound genius to blackmail his way into Reagan's sphere of influence. He then convinces Reagan to begin work on the "Star Wars" project. This project is visibly about defending from the Russian threat, but in reality is about ensuring that enough aeronautic military advancements are made to defend enough of the alien missile bombardment for our counterattack to begin. **The Internet** At the same time, using his newfound influence, the protagonist makes connections at DARPA and starts work on creating the distributed global communications network that we will use to coordinate our counterattack. contributing his work to others he creates Usenet and writes the Ethernet standard. He will later directly influence the creation of TCP/IP, SMTP and DNS, which ultimately become the backbone of the internet. **Gulf War** Forseeing the inevitability of the collapse of the Soviet Union, our protagonist realises that the US defence force is going to be the only well funded defence force in the world. Our protagonist convinces Bush Snr to go to war in the middle east, ensuring that the military has experience with waging war in a logistically challenging environment. Unfortunately the pressures of being at war grate on the US public who prematurely call for the end of the war and elect Clinton. Our protagonist is unable to convince Clinton to continue the war in the middle east. He is able to convince Clinton to maintain high levels of military expenditure. Much of it is into black projects that our protagonist has started - stealth planes/submarines, smart weapons, drone technology and AI work. With the fall of the Berlin wall, a mostly peaceful world, and the internet well and truly breaking out, our protagonist realises the need for more military spending. He also realises that more than just the USA needs to be armed. The whole world needs to be alert and battle ready. Realising that we have key weaknesses in our transportation and logistics infrastructure worldwide, our protagonist, through spies in Pakistan, convinces Bin Laden to mastermind the September 11 attack. **September 11** Our protagonist convinces Bush Jnr to go to war in Iraq and Afghanistan, sharpening and strengthening the US' defence forces. Trillions of dollars are spent on the war, most of which is used to fund more covert research projects. Our protagonist uses the Iraq war to convince a wave of instability in the middle east, which is used as a human laboratory for testing our worldwide resilience to invasion. Some of the newer technology is tested during this war. Here you could cut to the invasion. The US has record military spending which is being tested in Afghanistan and Iraq. However, if the invasion is postponed to modern days... **The 2010s** The internet is heavily upgraded worldwide and advanced viruses are introduced to devices worldwide to strengthen the world's immunity to cyber-attack. Our protagonist works closely with the development of Google and facebook. These companies are used as a front to gather the largest collection of data so as to identify alien spy threats and intrusion into our global internet. ISIS is the culmination of decades of work into creating cheap, decentralised military forces which will be effective at stopping the invasion. Work begins on preparing to implement ISIS-style military cells worldwide in the event that conventional defence forces are unable to repel the invasion. Then, in 2017, 37 years after his initial vision, the invasion begins... [Answer] The answer is already embedded in your question. Isn't it obvious? **Defect to the USSR** and work to ensure their stability until 2005. Okay, maybe that's not obvious... The best preparation for war is **Cold War**. There was no greater motivator for military technological advances in the past 50 years than the cold war itself. Outright war does more harm than good. Two superpowers with massive resources available to them are **already** doing all they can to develop weapons and defense technology. Other than what Paul can contribute personally, there's not much more he can do. The collapse of either superpower or outright war are the two scenarios that will hurt our ability to defend ourselves as a world. As we near 2005, he can work to increase communication and relations between the two powers or even escalate the conflict (though he risks one misunderstanding the aliens as a creation of their enemy). He can be working on scientific advances during this time, of course, but with the entire support of a superpower. **Doubters** * One may ask: why would the Russians believe him? Well, why did the USA welcome and support dozens of German and Russian scientists? What they had to offer was too tempting. * How does he know the USSR will be the one that needs help to survive until 2005? A fair objection. Paul's a genius though so I'm sure he can figure it out. Unless Paul can create technology so far advanced by himself that he doesn't need political help, this is the best way to ensure the planet is ready for a fight in 2005. [Answer] ## Artificial Intelligence Quickly make a lot of money - which shouldn't be hard given his genius. Then start a business devoted to artificial intelligence. Since the aliens aren't *super*-natural then anything they can do is physically possible - all we need to do is learn what is physically possible and do it. Even if he can't conceive of it the ASI can. The aliens will be no match for the offensive and defensive weapons the ASI and his team devise. [Answer] A deeply cynical answer. **Paul is the spearhead of the Alien's attack**. What they have implanted in his head is all sorts of things calculated to cause us to do damage to ourselves. After all, look at where endogenous paranoia and belief systems and technological advances so nearly landed us during the cold war. One way or another, if Paul fails to think hard and deep about who delivered that bolt of revelation to him, and with what intent, he will (with the best of intentions) cause our civilisation to destroy itself. And he won't. Self-doubt has been erased from his brain at the same time as the rest of the stuff was planted. Actually the aliens are not interested in attack. Rather they are scared that we might discover the secrets of superluminal travel and get out there and attack them. They need to knock our sudden technological advances of the last 100 years off the rails to give their human-domestication project time to succeed. If they merely wanted to destroy us they would just spark WW3. That's their plan B, but they have morals and are trying something less genocidal as plan A. We are still a few decades away from the big secrets. ]

[Question] [ There are shapeshifters who can perfectly replicate a person, and eat their brains to absorb all their memories. These shapeshifters are cunning and predatory, and so humans form extremely close knit societies to try and combat them. In these communities, nobody walks out alone, all movements are tracked, all doors are sealed at night. All travelers are shunned. They know that any of their family members might be replaced by indistinguishable shapeshifters, so they stay vigilant. But, occasionally, mistakes happen - some one wanders out alone, and people start to wonder if it's same person who returns. Let's say that a family member is suspected of being a shapeshifter. They look identical, and they have all the memories of the original. There is no physical means of proving the difference. However, the shapeshifter can only duplicate memories, and not personality. By nature, the creatures are inhuman with alien psychology. Questions such as "what would this person do?" can trip them up and cause them to give weird answers. These shapeshifters are intelligent though, and suspicious of tricks. These questions can't be obvious or else they'll try to deceive their way out. If asked "Do you like cats or dogs?", for example, the shapeshifter would then just look back at their hosts memories and reply "oh yes, I've always kept dogs as pets". But if the shapeshifter isn't consciously aware of the right answer, then he's more likely to trip up. Thus the questions have to be something about the original that even the original wasn't aware of. So... How would the community best try and interrogate a person suspected of being a shapeshifter? Are there any pyschological tests or profiling methods that they could use to identify a potential body double with all of the original memories? And, follow-up question, could an interrogation ever prove the negative - could they ever say with certainty that that person is definitely NOT a shapeshifter? Or would the lingering doubt hang over their heads forever? [Answer] This is similar to the problem of finding replicants in *blade runner*, so just apply the **voight kampff** test. the point is that you ask questions that that are supposed to evoke an emotional empathy response which your alien minded creatures don't have in the same way the humans have so it would be possible to notice. Another option, that is used today, is gait detection. Copying a persons walk is surprisingly hard and assuming your shapeshifters only have access to the conscious memories of a person they will have no way to know exactly how he walked as that is not something you think about [Answer] **Behavioral Biometrics** In short, muscle memory. There is a section of biometrics called behavioral biometrics, which is based on your actions being different from person to person, as opposed to simply having a different face or fingerprint. The actions are learned and depend on your physical body, but is otherwise largely muscle memory and not a conscious effort. For example, the way you type on a keyboard. The millisecond time between key-down and key-up, and between key-up and key-down again, is different enough between people that you can reliably distinguish between them. Even if you were told which key presses were too fast or too slow, it is really hard to change that with conscious effort. The real person is likely to "behave like themselves" a majority of the time, occasionally being off the normal, while an impostor is likely to only occasionally behave like the target. It works very well when combined with a password, but can also be done on a continuous basis. - Example implementation: Each citizen have a short passphrase that they use to identify themselves with. The phrase itself is long enough that you get sufficient keystrokes to reliably authenticate the person. If the people don't know about the biometrics aspect of it, they will only think of it as their secret passphrase. [Answer] **Piercings** Similar to one comment about microchipping your population. A lot of cultures have a practice of ritual body-piercing. This isn't something that can be replicated by shape-shifting flesh, or by stealing clothing. The mimic would have to deliberately produce piercing-holes, steal the jewelry, and then have to install it. To me, it appears that that level of control is too much for a simple mimic. For a bonus, place the piercing somewhere that a human can't reach, like the small of their back. The mimic then has to duplicate the holes and either (a) bend inhumanly to fit the stolen jewelry or (b) get another mimic to do it for them. Depending on whether the Mimics can produce holes in their flesh to match their victim's, the tells would be freshly pierced (angry red or swollen) holes and/or an outright lack of jewelry. Everyone in the community would have ritual jewelry like this, so the guards at the gates need only check that the person still has theirs. As a result, your citizens can be pretty confident about who is and isn't human. [Answer] # Rapid fire questions I assume the creatures still need time to recall something. Asking multiple questions very fast with little time to answer would most likely trip them up. Make it anything that the person *should* know but might need *any* time to recall for the non-person: > > What's your favourite colour? Why did you get married to Alex? Where did you play as a child? Where did you get that scar from? Where is the money I lent you? What soup did you bring to the family reunion 3 years ago? > > > It should be easy to come up a list of questions per person that would be easy to answer *for them* but not to somebody who needs to search through the person's memories. Just wait until the person is missing and *then* compile the questions, so an impostor can't anticipate them. This is likely going to trip up even normal humans, so you should tolerate *some* error. If they need time to think about a question or two instead of firing off the answer immediately, that's normal. But if they stop and think about each thing, then it's time stop asking and start axing. [Answer] **Brain Scans** Ask them questions about what their emotional response would be to hypothetical situations while they're in an MRI. e.g. "A person pushes you to the ground -- how do you react?". If the section of their brain associated with long-term memory lights up e.g. They are trying to retrieve a memory of a similar event from their human host to know how to answer the question then you've got a shape-shifter. If the emotional section of their brain lights up as they place themselves in that imaginary situation and imagine how they might react you've got a human. [Answer] ## Chess Or, any other similarly complex game such as Go, or card games. If it is traditional in your society to be wary of outsiders, it's not implausible for it to be customary to play chess to "check" that your opponent is still the same person. Your shapeshifter may understand the rules of chess, or go or tarot or whatever, and may recall what their "host" did previously, but unless they can recall memories more precisely than a human, they probably wouldn't be able to emulate their playstyle. I'm a big Magic: the Gathering player, and everyone knows that my favourite colour is blue. But they probably don't know that I am absoltuely unable to play an aggressive deck properly and feel most at home in a control deck with heavy spell manipulation and disruption. I'm pretty sure my closest friends would be able to notice that if someone was impersonating me. [Answer] I feel like the best way to catch people/shapeshifters out are unconscious habits, and ways of feeling/expressing yourself. Little tics of the face, twitches of the hand, and fidgety motions may be related to personality more than memory, so a shapeshifter might struggle to replicate those sorts of things. Abstract things like sense of humour are clearly harder to judge, but even if a shapeshifter remembers the things the human found funny, faking/reconstructing a laugh from memory is really difficult, and laughter is often impulsive, so a shapeshifter wouldn’t have time to race through memories and think “would this human laugh at this?” By the same argument, crying - most people can’t cry on demand, and an absence of tears from a normally weepy person may well be a signal of something being wrong. I recognise that emotional responses might not be the clearest/most empirical evidence of an alien invasion, but they might be the things that they simply cannot replicated convincingly. Also: do shapeshifters have better memories than their human hosts? Or do they only remember things as well as the humans they consume? There’s this classic sort of thing: “Oh, do you remember the time when we went to the park and we saw the escaped snake?” “Oh yeah, of course!” *scans brain: remembers host human doesn’t like snakes* “That was really scary!” “Aha! That never actually happened!” If a large enough/personally important enough group of people assert a thing that you feel like you should remember, you’re often tempted to go along with it and say you do. Only once you’ve agreed in order to fit in, it’s revealed that it never happened at all. I realise this is a bit ham-fisted, but humans aren’t great at remembering absolutely everything that ever happened to them, and shapeshifters might be just as anxious to fit in and act like they’re part of the community, so might go along with things that the crowd of humans test them with. (Of course, if these humans are trained to be entirely honest whether they remember things or not, the shapeshifters may well capitalise on that memory and behave the same way - so, emotional responses may be the better way to go.) [Answer] ## Have daily jam sessions together Playing musical instruments and/or singing is a good part muscle memory, something that a shapeshifter probably doesn't instantly get from inspecting a victim's memory. A sudden loss (or rarely, gain) of skill could be a good sign of infiltration. This is the same as Spokio's answer. But you can take it to the next level by having the community members have daily improvisational jam sessions in rotating company. People learn each other's habits and preferences and notice something is "off" when someone plays differently. Since people are not aware of their own preferences on the same level and don't play fixed pieces of music from memory, this is impossible for a shapeshifter to reproduce successfully with any consistency, even if they are so agile that they can pick up a new instrument and play it with skill. As an extra security level, community members are not allowed to discuss others' musical performances (or lack of it), so a potential victim does not have memories of what others noticed about their performance. Interrogation is just playing together and happens every day for every single member old enough to hold an instrument or sing. This is of course assuming that the shapeshifters can't reduce their size and mass to child size. Otherwise it wouldn't take long for the communities to die out... [Answer] **Tell the shapeshifter they have Alzheimer's and ask them to take a memory exam** Make it very clear how well they're expected to perform on the test. I.e, "at this stage, you should only be able to answer half these questions correctly. Anything better will be a miracle!" The shapeshifter will answer half correctly. The real article will answer all correctly. [Answer] I wish I could remember the title, but I read a short story a few years ago about a society with a similar problem. Aliens could infect humans by replacing their minds with their own, but keeping the human memories. The aliens were very logical and didn't do unnecessary actions. The humans had a secret test to identify them. They police would find some belongings of the suspected infiltrator, wrap them in bubble wrap, and put the wrapped items in a box. The suspected alien was required to unpack the box and examine each item. It the suspect popped any of the bubbles, they were human. For your story, find an action that the aliens won't do, and then give them an opportunity to do it. [Answer] **Tell them a Joke** You say - "Your momma's *so fat*, you'd need three shapeshifters to imitate her fat ass." Given that alien psychology is different, and further on the lookout for suspicious people, it wouldn't be able to relax or jibe back at you. A human on the other hand would laugh despite the very real possibility. [Answer] **Secret Handshakes.** having a very intricate, well practiced secret handshake with everyone in your community. While a shapeshifter may remember all the moves of the handshake, they will not have it practiced well enough to fluidly complete the handshake and will be easily noticed. [Answer] **Body Tissue or Blood** Maybe extract tissue or blood from the shapeshifter. This works under the assumption that the shape shifter cannot control the matter that leaves its body hence the blood might turn back into its original form over a period of time. The tissue attached to the body of the shape shifter stays in the new form maybe using the energy it receives from the body but if it is detached from the body it should run out of energy at some point and return to its original stable form like how a chameleon goes back to its original color after it dies. [Answer] **Perform a psychopath test** [This article](https://curiosity.com/topics/one-trait-separates-psychopaths-from-everyone-else-according-to-a-yale-study-curiosity/) details how psychopaths differ from normal people in terms of imaging what it's like to be in another person's shoes: > > ... [A] new study shows that there really is a difference between how > psychopathic brains and neurotypical brains process emotions, and it > might not be as easy as toggling your sympathy on and off. If > psychopaths know they're being asked to step into someone else's > shoes, they can do so as easily as anyone else. It's when they're > tested on their empathy without realizing it that they start to > differentiate themselves. > > > If you took the test, it would work like this. First, you see an image > of a room with an assortment of dots on the walls. In the middle of > the room is a person facing one of the walls. The researcher asks you, > "How many dots do you see?" If the person in the image can see the > same number of dots that you can, it takes about one second to answer > that question. But here's where it gets interesting. If the person in > the image can't see all of the dots (because some are on the opposite > wall, for example), it actually takes non-psychopaths about 100 > milliseconds longer to answer. The non-psychopath automatically places > themselves in the shoes of the person in the image and imagines how > many dots that person can see instead of simply answering how many > dots they themselves can see. But for a psychopath, the presence of > the person and the direction they're facing makes no difference at > all. > > > There you have it: Normal brains automatically place themselves in the > perspective of others, while psychopaths have to actually make an > effort to do so. > > > Your shape shifters should be unable to control the millisecond timing of their responses as they attempt to place themselves in the shoes of the other person. As a bonus your society gets to eliminate all of its psychopaths. [Answer] **Memes** In the proper sense, a Meme is a shared idea. A small community is full of in-jokes and subtle references to things that people have said or done in the past. A shared story that comes very naturally to people who lived it and grew up with it. That and a mix of things like rhyming slang (thinking of Cockneys here) and it's quite possible to hold a conversation using phrasing that only bears passing resemblance to english. If the person you're talking to doesn't have any idea what you're talking about, they're probably not part of your community. For a similar idea: Austin Powers featured a conversation between Austin and his dad in "English English", which was a blur of cockney and englishisms that requires subtitles for most people but technically was comprehensible if you come from the right background. The bystanders in the scene were predictably mystified. Of course, given the mimics can use the memories they've gleaned fast enough to have a conversation, they may well be able to cross-reference memories and infer the connections well enough to pass the test. [Answer] All depends on the specifics of your shapeshifter. So they have a sense of humour? Can they replicate empathy? Are they musical? Can they tell doggerel from poetry? Can they comprehend riddles? The test should be set to match their weakness. What sort of weird answers do they give to what sort of questions...? Also, what sort of IQ do they have? A simple IQ test might weed them out. Do they have the same weaknesses as what they are copying? I doubt it. If the original is colour blind, or hard of hearing, or tone deaf, or unable to taste parsley, they could be tested like that. Also, are they right/left handed or ambidextrous? Alternatively, use something like a fire test or ducking: if it kills them, they are declared human, if they survive they fail the test and are executed. Brutal, but it keeps the shapeshifters out. [Answer] If the technology level is high enough, a microchip in the brain could download a memory each night. That memory would last a day before it is replaced at night by a new one. Even if the shapeshifters could steal the chip (the chip could send an alert when disconnected or on death), missing an update would leave them with false memories or without the most recent one, a simple test asking about the most recent fake memories will reveal the infiltrated. For a less advanced setting, I think the best option would be asking for something that didn't happen, maybe even something that contradicts the original person memories. This can make them nervous , *did the person forget it before I ate it's brain?*, *am I being tested or is this just a confusion?*, *should I admit I don't remember it or do I play along?* It's reaction will probably differ enough from the original human's behavior to confirm suspicion. [Answer] **Graphology** We already have a solution for this in real life. Handwriting is something unique to each person. It is a product of "muscle memory" not conscious memory. And graphological analysis (also known as "handwriting analysys") is an established field with experts and systems of procedures. In fact, it's so effective that a person's signature is used as proof of agreement to a written document. It is a fast and effective test with little subjectivity or uncertainty. It works in any time frame... it was effectively invented by 1575, and today's machine learning algorithms makes it incredibly accurate. ]

[Question] [ Once you do the handwaving needed to explain a modern-day world with flight-capable dragons in it, how would said dragons interact with the bureaucracy surrounding flying in the modern world? What sort of pilot's license would they hold? Would they get certified as an aircraft of some sort (perhaps in the Experimental category)? How would they display their registration? What would a checkride look like for them? How would they handle getting a medical certificate? What would annual inspections look like? Update based on comments: think along the lines of a sentient dragon, with an average intelligence along the lines of the smarter end of humans, and the ability to speak and read English, although they may need a typist to handle writing/forms-filling. Keep also in mind that they'd be sharing airspace with human-built aircraft, as well as some infrastructure (I'd envision them as capable of STOL, but not quite VTOL -- but even helicopters need runways in certain cases). Also, I was thinking they'd vary in size, but be no larger than a widebody aircraft, with RJ or bizjet-sized dragons much more commonplace. They'd be capable of high altitudes, as I see it -- getting into Class A airspace wouldn't be terribly challenging for them. Flight speeds would be slow, though -- they are most clearly limited to subsonic speeds, and likely to spend much of their time at relatively slow airspeeds to keep energy expenditure down; they'd also be able to see and hear a jet coming in VFR conditions, but wake turbulence, especially for the combination of a smaller dragon hitting a bigger airplane's wake, would be a hazard to them still, and they'd be large enough to generate significant wake turbulence of their own. [Answer] ### Dragons would run the FAA One day, you're flapping along, torching pigeons, and those runty little ground creatures that taste good with ketchup start making an awful racket. "Must be that Henry Ford again," you think to yourself. Humans these days and their internal combustion engines. Something sounds different this time. You look around and do a double take when you realize that the humans have *learned to fly.* Obviously, they can't be allowed to do this willy-nilly, but you've rather come to like some of the humans, so torching the lot won't do. Plus, humans invented ice cream. Instead you call a council of world leaders to discuss when and how these new devices can be used. Obviously, they can't just fly everywhere, disturbing the peace. They'll have to fly in designated flight lanes, and report what times they'll be flying where, so any dragons that cross their path would have ample notice to watch out. Dragons, of course, will keep flying where they want like they always do. Why should it be any different? After all, they are *dragons*. They'll have an additional responsibility, though: reporting errant human pilots to the FAA for removal of their licenses, unless, of course, the reporting dragon is hungry at the time, which is why all planes will be required at all times to carry an ample supply of ketchup. [Answer] ## Depends on size and intelligence of dragons If **dragon is "animal"** (domesticated, hopefully) and their intelligence is like a horse or dog, we can treat them the same as "objects" because they can be set to fly only on command. Of course, in that case you should have somewhere "breeding" facilities where young dragons are trained (something like obedience training for help dogs) and such areas would be either "no fly zone" or "high altitude only zone" (assuming dragon flight capacity as normal propelled plane) If **dragon is intelligent as humans**, you have to treat them as "person" and give them some human dragon rights. The "training" would look more like school where elder dragons would train youngsters in common flying rules (look both sides before flying over burj khalifa tower!) and most likely, there would be "fly rules" which could differ country to country (fly on the left over Great Britain) If **dragon is small** to hold two people, you could treat rules for them as for Cessna planes and flying in low populated areas would be about the same as flying a small plane here. I am not aviation expert, but I think that flying (relatively) small dragon over Alaska would be easier than doing the same over New York city. The **bigger dragon** the bigger issue, and if you have *really big* dragons, I would assume you either drastically control the breeding of dragons or you allow dragons only to fly in low populated areas. As of the documents: * Flying a dragon can only do a trained human (as pilot). You can mount other people to dragon, but you have to provide them a proper seating. Dragons would be not used for "travel" rather for "adrenaline sports" * Only given breed of dragon, and well trained (or having proper school diploma, if dragon is intelligent) are allowed to high populated areas * Communication with towers would be done over in-helmet (of pilot) accessories, such helmet would probably have also "radar responder" mounted * If dragons are intelligent, then radar responding device and some means of in flight communication device is a must, if such dragon wants to fly inside high populated areas. [Answer] **There's a difference between a hunk of metal and a dragon.** We built planes because we can't fly naturally. Planes are big, cumbersome machines that don't work without someone controlling them. While someone still has to control a dragon, that someone can be the dragon itself. Dragons are built for flying. Their in-flight responses are much quicker because they get instantaneous feedback on their control inputs, so to speak. In an aeroplane, the plane provides the feedback but it is not linked to the pilot's brain and he won't immediately understand what to do - the information has to be read, understood, then interpreted according to the pilot's training. Dragons are born with the innate ability to *sense* changes and respond instinctively, as a natural response. For this reason, they do not need regulation **in flight**. They are able to fly as easily as we can walk and collisions with aeroplanes would be almost nonexistent because of their reactions. However, what we might want to do is talk to them about our own ground safety procedures. For example, the danger of close proximity to jet engines and the fact that having a dragon make its nest on 27L at Heathrow would actually be a rather serious problem for us. They might, perhaps, be persuaded to use alternative landing and nesting grounds. It's not so much about regulating dragons because they're dangerous in the air, but working together with them to make sure that their innocuous mistake doesn't cause major disruption for us. [Answer] One thing people aren't considering is how much faster planes will likely travel than dragons. Let's say Dragons fly, travelling, at an average speed of 120 mph, which is much faster than any land animal and much faster than any dragon in fiction. The recommended takeoff speed for large commercial airplanes is around 200 mph, and the flight speed is around 550 mph (according to Google), so while the dragons might be more maneuverable and hear them coming, they may or may not realize that they have to move out of the way to avoid being creamed before its much too late, which considering the speed difference is likely a few seconds. The good news is that dragons probably won't bother flying at 35000 ft, so they'll mostly just need to be restricted from flying within a few miles of major airports or military airfields. This of course assumes the dragons are intelligent and realize the danger to themselves, if not the humans may have to develop environmentally friendly ways of keeping them away from airports (dragon whistles?), or failing that just shoot them down if they get too close and hope the rest get the message. If they were more like wild animals though, they probably would be mostly scared off by the sound of jet engines like real birds. [Answer] I’d suggest backing up a step. Presumable, these dragons predate modern aviation, and have been using their instincts to avoid collisions for millennia before humans started flying. They’ve now got an older right to the airways, and historically, it is as well established as your right to walk down the street. So if you want to consider flight rights, paperwork, and insist they get licenses or fill out paperwork to travel, you have to consider the political system, and who’s in charge. **Are the dragons the poor underclass?** If so, they might have lost their rights to the airways when the wealthier, more powerful humans developed flight. Under this system, they might need licenses for most or all flights, or only be allowed to fly over the their own homes, or only at certain altitudes. Keep in mind that if a dragon doesn’t fly extensively while young and developing muscles, those muscles will be weak, and restrict the dragon’s ability for its whole life. Imaging a healthy human who always used a wheelchair instead of walking until they were 18. They wouldn’t be able to walk without serious physical therapy, and would always have more difficulty than someone who has walked since infancy. **Is everyone equal?** Perhaps look into restricted airspace for human use craft, which are far more likely to crash than the dragons. If dragons want to fly in these restricted corridors, they might need to show they can avoid collisions with the less flexible aircraft to get official permission, or it might be more like a kid learning to cross the road safely, where it is basically a judgment call, and learning the rules as to how to recognize a legal and/or safe crossing point. But airspace basically belongs to the dragons, not the humans. **Are the dragons in charge?** Either no humans fly, or they are extremely limited, and only allowed to fly limited, undesirable routes where they aren’t in the way of the dragons. Maybe only at times when most dragons are asleep. Although if your dragons use human-made aircraft for long-distance flights, who knows what might happen. **How would human aviation have been affected?** If they need to defer to dragons, they may use blimps and hot air balloons more than fixed wing, and aircraft speeds would be restricted. Also, if dragons rule the sky, maneuverability might be prized over speed and carrying capacity because if the dragons say no to anything likely to kill them, then big, fast airplanes that need a huge turning radius are less likely to be developed. [Answer] Because [this](https://worldbuilding.stackexchange.com/a/9038/2968) answer made me think about regulations for intelligent dragons: Why regulate their flying at all? They are naturally flying creatures, so they should naturally be able to avoid crashing into things and each other. If they agree to please not land on human houses that cannot hold their weight (a house breaking under a dragon sounds unsafe for a dragon, too, anyway), and not land on a busy street because they obstruct traffic, I don't see much reason for regulation. Most rules for air-traffic exists because pilots may be unable to see oncoming planes, or by the time they see them, have no chance of avoiding them. But for dragons, flying even in the most busy of airspaces should be more like walking along a very full sidewalk. The same way, a piloted, non-sentient dragon would be able to naturally avoid crashign into other dragons... don't see them as airplanes, but more as horses! Edit/Addendum: Also, a world that has dragons flying around anyway would most likely have a whole more landing-sites than just airports. Small enough dragons would most likely be able to land on the roofs of larger buildings. If the dragon is small enough and can climb, they may have landing-spots and the SIDES of buildings. Also, depending on the intelligence and training of the dragon, they can land, drop off passengers, and fly off somewhere to come back when called. [Answer] Supposing your dragons are intelligent, plentiful and long-established, they would have agreed a system of rules and flight corridors long ago, just as humans agree to drive on the right or left. At places where many flight paths meet they would have fixed rules about height and direction, maybe even markers on the ground. High mountain ranges might have a queueing area for getting through passes. On commonly flown long-distance routes they might have stopping areas for sleeping and eating - a herd of sheep for snacks? In dangerous places or stormy weather they might gather and form convoys. Would they migrate seasonally? Would they have weather forecasts? Would little dragons need to get a licence to be allowed to fly high or long-distance? So anyway, when your puny humans arrive or learn to fly, they would patch into the established dragon infrastructure. ]

[Question] [ [This answer](https://worldbuilding.stackexchange.com/questions/30933/infinite-tube-world?noredirect=1#comment82150_30933) and its follow-up discussion with the OP made me think, and boil it down to the essentials: We live in a universe that’s either infinite in spacial extent or unbounded, and wrap-around effects are neglected. That is, even if space is finite, no matter where you are you can still move in any direction: there is no border to experience *from the inside*. But what if there *was* a border? By that I mean a border that can be experienced *from the inside*. This is distinct from what a higher-dimensional map would show as topological features. For the purposes of science fiction that is at least intelligent if not truly “hard” to the degree of Greg Egan, what could the edge be like? On a macroscopic scale of gas and spaceships, it could be “a wall”. But for the laws of physics, gravity, light, etc. what would it be like? I can think of two general cases: an impassible boundary or *not*. Imagine an edge you could fall off! So, **what's at the end of the universe?** An earlier question [with the same sentiment](https://worldbuilding.stackexchange.com/questions/13416/if-universe-has-an-end-boundary-what-else-exists-after-the-boundary?rq=1) was closed as “too broad” but was actually poorly asked and was not given much thought by the OP. But to be clear (and not infinity broad), I’m considering what kinds of boundary or edge would be other-than-hopeless in an intelligent SF story. Our SF is rather mundane in this respect, with even Diskworld being “large” like ours. How this affects the people living near it is important for storytelling. If the astronomers pointed out that we lived near the edge, like how in our universe we point out the structure of filaments and voids, everything else just keeps happening. For such a feature to be meaningful to the story, the nature of it might be important to the people living there. So besides *what’s there*, I ask, *why do they care?*. See also [this hard-science question](https://worldbuilding.stackexchange.com/a/31292/885). --- When I posted this, I was thinking of large enclosing borders of space. But for cataloging and exploring the sci-fi possibilities of physics at a boundary, it generalizes to small inclusions as well. For a long time I’ve pondered a story where a small piece of the universe gets walled off, and I even [started writing a story](http://www.dlugosz.com/zeta/?p=421) but boxed myself in since I didn’t know what the people studying it would be finding! But there are really two cases when it comes to storytelling. If the border was truly up close so people could probe it and experiment hands-on, the low-level physics is detailed and interesting to the story (e.g. the superconductor of heat in Prof.⊕’s investigation) and *needs* to have detail that doesn’t [make a wreck of the fictional universe](http://www.imdb.com/title/tt1549572/). A boundary that is cosmological can be seen but never explored directly, as with distant galaxy clusters. It will interact with the nearby space though and will affect the detailed structure. People in the story might themselves wonder what happens if magnetic fields cross it, but can’t walk up to try. So some lack of detail is possible on the scientific end, but we say “so what?” What is it about the cosmology that relates to a story? Originally (as in earlier today, before I was reminded that *The Pearl* is really a kind of border too) I was thinking that FTL-type space exploration might interact with it, getting up close and bothering the explorers, or having something to do with how their FTL technology works. [Answer] A few possibilities (bearing in mind that you can choose whatever you like): ## A WALL An impenetrable barrier, absolutely unyielding. A supernova won't scratch it, a black hole can't eat it, it's just a wall. That doesn't fit your model of physics? Tough, tell it to the wall. It may be glassy smooth and frictionless, and either perfectly flat or infinitesimally concave. It may be rippled or craggy or fractal, with pine-tree protrusions the size of galactic superclusters, or maybe just little grape-sized bumps here and there. It may be static. It may evolve, with waves and whorls that creep along its surface as slowly as glaciers— or faster than light, that's allowed, since we can't alter or impede them. Get in their way and they'll crush you effortlessly. There could be discontiguous incursions, big blobs of wall-stuff that appear, grow, contort, shrink and vanish. It may be black. Perfectly black, absorbing photons (and perhaps other massless particles) and giving nothing back. It may be white, refracting incident particles at random angles with no change in energy. It may be a blackbody, featureless but glowing with heat at any temperature you like, from barely above absolute zero (absolute zero being the aforementioned *black*) to red-hot to sun-bright and beyond, but bear in mind that it's big and you probably don't want to roast the universe. It could give off any kind of radiation you can think of, even short-lived particles that exist nowhere else. It could be opaque but with colors, different in different places, fractal patterns, changing colors, opalescence, polarization, coherence, writing, anything you want. Note that with some of these variations it can be very difficult to judge your distance to the wall, so approach with caution. Whole races of superintelligent scientists could spend aeons studying some of these walls. Take some of these walls to extremes and you get: ## CHAOS Not the nice, predictable randomness of blackbody radiation, but a downright horrible region of flux and perversity. Its exact location is difficult — and dangerous — to measure. Approaching it is insane. Even looking at it can be bad for your health. Greg Bear's [*City at the End of Time*](https://en.wikipedia.org/wiki/City_at_the_End_of_Time) comes to mind. ## A MIRROR Flat and impenetrable, but a mirror. From a great distance you can see that the sky is symmetrical. If you approach with great care you can stare your "reflection" in the face, and touch its hand. It feels like a wall of glass, but whether it's just a shiny wall presenting a mirror image, or that really is another you — or even just *you* — is a matter of fierce debate among cosmologists and philosophers. ## A SINK Looks like a black wall, but it swallows matter too. Poke it with a stick, and you have half a stick. ## A GRAVITY SLOPE Looks black. Things that go that way accelerate, red-shift and disappear. You can venture that way and come back, if you have powerful thrusters. ## SPACE There's just… space. Black sky. You can throw a rock and watch it dwindle in the distance. No stars, no photons at all except from the rocks and space probes we've sent. You can travel out there as far and as fast as you like, and come back if you have enough fuel. In some ways this is the most haunting prospect of all. Let's go home… [Answer] The end of the universe would appear to be **a wall of randomized radiation and charged particles**. The universe is *literally* everything. So beyond that wall is nothingness. Visualizing nothingness is something that's hard for humans to do - in cinema and novels it's often portrayed as being grey/average, or incomprehensible. But we do have example of nothingness in reality. It's the space between a point and itself, between 1 and 1 or 0 and 0. If you could press two quarks directly together, what would be between them? Nothing. And that's how the edge of the universe works. Because beyond it is nothingness, that means each point of the boundary is simultaneously contiguous to *every other point on the boundary*. Effectively, the entire thing is a single point. Any matter or energy that exits it is randomly distributed and re-enters the universe somewhere else on the boundary. In general this makes it useless for travel, as most organisms cannot survive having their component particles redistributed amongst the entire universe. Note: the similarity of this answer to [Cosmic Background Radiation](https://en.wikipedia.org/wiki/Cosmic_background_radiation) is almost certainly just coincidence, as I don't believe this to be hard sci-fi at all. [Answer] # A white bubble Could be the inverse of the black hole — a white bubble. The black hole is something that has a gravity so strong that nothing can escape — Once something touch its event horizon, it will never go back. In the other hand, the white bubble has an **anti**-gravity so strong that nothing can reach it. If you send some light to the white bubble, the light will be deflected by anti-gravity-lensing back onto your universe. This way, the bubble wall is an impenetrable event horizon that confines everything inside your universe without allowing anything leave. So, in some sense, a white bubble is a black hole turned inside out. It could be arguably a black hole viewed from the inside, if you are somehow able to reject the mainstream theory that black holes are gravitational singularities and replace it with a theory that black holes are gravitational bubbles from which imprisoned objects can't leave and where spacetime distorts in a way that it can be measured larger in the inside than what it is in the outside. This way, black holes would be spherical one-way wormholes entrances viewed from outside and white bubbles would be spherical one-way wormholes exits viewed from inside. # White bubble evaporation Further, you might know that black holes are predicted to eventually evaporate. Viewed from the inside, this could be either the [Big Rip](https://en.wikipedia.org/wiki/Big_Rip) or the [Big Crunch](https://en.wikipedia.org/wiki/Big_Crunch). Also, the time when the black hole forms in the outer universe is when we get a [Big Bang](https://en.wikipedia.org/wiki/Big_Bang) in the inner universe. This also solves an interesting problem: mainstream physics don't explain clearly what would be the cause of the Big Bang, but a white bubble theory could. # Playing with anti-matter [It is unknown in physics if anti-matter has standard gravity or if it features anti-gravity](https://en.wikipedia.org/wiki/Gravitational_interaction_of_antimatter). Most mainstream physics predicts that it should feature standard gravity, but anti-matter featuring anti-gravity remains a viable possibility that can't be ruled out. If you join the concept of anti-matter anti-gravity and the white bubble wall concept, this makes anti-matter running away from black holes and accelerating towards the white bubble wall to never be seen again, which would explain why there are almost no observable anti-matter in our visible universe. Also, this makes the white bubble unavoidable to anti-matter near its edge while black holes would be unpenetrable for that. An "anti-black hole" and an "anti-white bubble" would be the opposite objects. Also, this makes the black hole and the anti-white bubble event horizons an one-way entrance to matter and an one-way exit to anti-matter, while the anti-black hole and the white-bubble would feature the opposite. To make the simetry not break for photons, you should need to propose the existence of anti-photons. Anti-photons would be undistinguishable to photons except for their behaviour on a gravitational field. Also, anti-photons would be as rare as anti-matter, which would explain why we didn't knew about them so far: can't be distinguished from ordinary photons if you don't have something to gravitationally lense them and they are far too few to be denounced by those gravitational lensing effects. # Note Of course, to be able to realize this theory, you would need to speculate a lot about unsolved cosmological problems proposing some not-mainstream solutions. However, since you are already proposing a big wall to your universe, I think that this is OK. [Answer] If you want it to be something less than mundane, why not give your universe a metric similar to that of the [Poincare disk](http://www.ms.uky.edu/~droyster/courses/spring08/math6118/Classnotes/Chapter09.pdf) representation of the hyperbolic plane? In other words, equip your universe with a metric of the form $$ds=\frac{2dr}{1-r^2}$$ where $r$ is the distance from the center of the circle in Euclidean space, and $s$ is the distance from the center of the circle in this hyperbolic space. This leads to the relationship $$s=2\tanh^{-1}\left(r\right)$$ where $\tanh^{-1}\left(\right)$ refers to the [inverse hyperbolic tangent function](https://en.wikipedia.org/wiki/Hyperbolic_function). The point if this is that as one moves farther and farther from the center, one gets closer and closer to the edge of the circle, but can never quite reach it. You can get arbitrarily close, but you must always be a finite distance from the edge. Your universe has a boundary, but you can never reach it. [Answer] I don't think any sort of "hard" wall would make sense without violating conservation of mass/energy/momentum but perhaps you could imagine the edge of the universe as a broad singularity, kind of like a black hole except instead of being a point we look down into it's a shell we look up out at. You could re-tell all the qualitative stories about falling into a conventional black hole (e.g. a traveller crossing the event horizon would appear to slow down and fade away) only in an inverted geometry. [Answer] So the theory of [Brane Cosmology](https://en.wikipedia.org/wiki/Brane_cosmology) suggests that we picture the universe like a bubble, with all of our spacetime as the skin of the bubble. One theory suggests that the big bang was two branes colliding and a new brane forming as our universe, like two bubbles bumping into each other and a third bubble forms. The "bubble" that makes our universe is expanding faster than the speed of light, making everything in the spacetime skin move farther apart. If there is an "edge" of the universe, it is moving away from you faster than you'd be able to see it, even if was a place you could teleport directly to. So instead imagine a static universe (brane) that isn't expanding, and it's touching other branes, so if you could see it from the outside (the bulk) it would look like soap suds. Each brane might have wildly different properties and laws of physics; instead of being a 3 dimensional space it might be 7 dimensional. [Dividing a circle might get you 4 instead of 3.1416](https://web.archive.org/web/20171224102633/http://mathforum.org/library/drmath/view/55021.html) in some weird non-euclidean geometry where [spacetime is not locally flat](https://math.stackexchange.com/a/1080093/170257). So if you were at an interface where two branes are touching, you might be able to look across and see wild things. A universe where time runs backwards to our frame of reference for instance. Time as a loop, endlessly repeating. Time only passes when things are in motion. The book [Einstein's Dreams](https://en.wikipedia.org/wiki/Einstein%27s_Dreams) has a lot of [examples of possibilities](http://www.public.asu.edu/%7Ejmlynch/273/EinsteinsDreams.htm) in the dimension of time. Other dimensions/forces could be affected equally. The boundary may be impenetrable except to light, or it may be possible to push through at high enough levels of energy. This should be done with caution since the physical and psychological effects caused by traveling to a universe with a different number of dimensions might not be compatible with life. [Answer] # undefined behavior Let's just say nobody knows what happens at the end of the world. At least that's the case in Minecraft: [](https://i.stack.imgur.com/Zt34k.jpg) Image taken from <http://minecraft-de.gamepedia.com/Datei:Ferne_L%C3%A4nder.png> The world in Minecraft is continuously generated as you explore it based on a seed value given to a pseudo random number generator. The thing is, if you walk in one direction for like a month (or just manipulate your position), you get to the edge of the world. And you experience a lot of weird effects: * The game hangs * A lot of calculations overflow * The generated terrain looks weird (because of the overflows) Edit: Well *what* is an overflow? The computer just strictly follows its algorithm and crunching numbers. When the numbers get bigger and you get closer to the "end" of the world the result of these calculations are to big to be able to hold in memory. Numbers in computer games have most of the time a fixed limit, depending on which size was chosen. The most common size is 32 bit and therefore the numbers that can be held are in the range of −2147483648 and +2147483647. *Note:* in recent versions of minecraft this has been fixed, but you can read more about it here: <http://minecraft.gamepedia.com/Far_Lands> [Answer] If I may take Dan Smolinske's answer and mutate it a bit, I'd like to suggest a living boundary. In this particular line of thinking, the universe itself is alive, like an overarching Gaia of galaxies or like the Dao. After all, this is World Building. Why not stretch ourselves with a more exotic universe? Boundaries are meant to be stretched! In doing so, I get to tie in a nice detail: while its fun to pay attention to the boundary itself, we often see echos and shimmers of that boundary when we look outwards, warning us of where those boundaries are. Curious that... there's no real reason for it, but yet everywhere we find danger, we find little warning signs like breadcrumbs. Surely those are important. --- This living entity clearly has boundaries exactly like those of Dan's world: anything outside of the boundaries is so utterly alien that we are simply incapable of predicting what happens to anything that crosses out into it, and we perceive nothing but randomness coming in. No information goes in, so thus no usable energy or matter. The difference here is that, unlike Dan's world, this edge is highly fluid, constantly changing as the cosmic Gaia shifts and shapes itself, responding to the alien forces around it that are beyond our comprehension. The boundary may be so steady that it appears exactly as Dan's world might, when things are going well for the Gaia, but may flex dramatically as the world outside it upsets its delicate balances. Of course, such a theory would be incomplete without some concept of what is going through the mind of such a Gaia beast. Otherwise the flight of fancy does little good. Consider our Gaia as not a massive mother of all, as we view her as from the inside, but as one small fragment of a much larger, more chaotic world than any of us have ever seen. Out there, somewhere is something far more insidious than mere randomness and noise: there is an intelligence which slashes at our beautiful Gaia. This Gaia knows that this force is the one that it had always feared. It's a force which is indistinguishable from randomness, but sinister in nature. Left unchecked, it would snarl its way in with apparent randomness until one swift moment where all apparent randomness would dissapear, and it would be in control. (why do you think science is so extremely sensitive to non-random factors in their nosie?) Our Gaia had determined a long time ago this was not a provably winnable fight. If she were to go toe to toe with this intelligence, it would slowly beat her, battle by battle, until nothing remained. So, in an act of great beauty, great will, and great desperation, she took on life. She permitted herself to have one kernel of unknown deep in her core -- no more would there be provably winnable fights and provably lost fights. Every fight would be an unknown from here on out. And so she guards us, nurturing us, allowing us to find the solution to the battle she could not provably win. Typically we are unaware of her guiding forces, except for the curious cosmic radiation surrounding us when we look outwards. It's only when the world outside shudders that we see any change. When the fight is going well, she lets us expand our boundaries outwards, gazing at the stars wondering what makes them all burn so bright. As she does, a little of the Other leaks in, and we see it in our wars and in our weapons. When it does, she draws back, taking the stars with her, pulling the Other away with her while we wrestle with the little bit that snuck by. Do the stars not feel further from us when we are at war, deep in the trenches? Surely we wrestle along side her. Even in the greatest darkness we see light, working with us to contain it. And this is how we see that this universe is different from that of a universe bounded by true randomness. In the careful ebb and flow of the boundary around us, we find more good than bad. We find a curious pattern to the noise that didn't show up before until we stopped and *really* listened. Then, we will be ready to announce to the extra-universe around us that we are ready to demonstrate the most powerful weapon our Gaia has ever devised: the ability not to overcome and devour the Other intelligence, but to merge with it until it cannot tell the difference between us and them, and we cannot tell the difference between them and us. It's certainly worked before, though the world is always at least twice as strange afterwards. One day, we will take control of war, take control of hate. We will decide it simply cannot be, and declare it gone. Only then may we rap on the perfectly random walls of the sky, just to hear, for the first time, a response to our call. What message do we send? That's for the future to decide, but I have my suspicions. It would be a claim to a birthright. A final message to our beloved Gaia that her careful protection of us has not been in vain. > > This is my home > > I'm coming home > > > [Answer] ## Consider the universe as an encapsulment Clearly, anything that we can observe is inside the universe. But what if the universe was something that kept us in place? Consider, a 1-Dimensional ant that you want to keep in place. The ant can move along only 1 axis at a time. You want a natural feel for the ant, to keep it as happy as possible. To do this, you employ a circle. [](https://i.stack.imgur.com/Cbdic.png) As in the picture, the ant can move in positive or negative direction, as much as it wants! How natural. The circle guides the ant (in other words, the ant is constrained to the circle), and to a surveyor (unbeknownst to the ant), the ant is always touching the circle, and is unable to perceive anything inside. To the ant, the universe is wrapped. What about a 2-Dimensional ant? An ant which can move in 2 directions instead of 1? There are 2 ways to encapsulate this ant! [](https://i.stack.imgur.com/e3kor.png)[](https://i.stack.imgur.com/VOqpq.png) The first method is un-natural. Your and comes to an untimely stop when it reaches the edge of the circle. The ant would be sad that it is contained, and realises the finiteness of it's universe. This ant, however, is free to move along its plane as it pleases. The second 'Natural' solution constrains the ant to a 3d plane (specifically, a sphere), and the ant will never be any the wiser to what it's world is. Likewise, for us 3-Dimensional beings, we could be trapped inside, and constrained to a 4-Dimensional, wrapped surface. We could also be inside of a 3 dimensional sphere, where there is a hard edge. Either way, what's on the outside of either of these is a mystery. [Answer] I once asked Brian Greene (physicist, Columbia U) this question. He was lecturing on his multiverse ideas inspired by the arbitrary values of things like the fine structure constant. He subscribes to a weak anthropic principle. I asked whether the intersection of two universes was possible and whether we would notice. At one level, the definition of "universe" is problematic because if there's something else, then we should change the definition of "universe". For this question to have any meaning, we have to define "universe" as the region where our laws of physics hold. Under his theory, from a math standpoint, yes, intersection is possible, and we would probably see it in the cosmic wave background data. We don't see anything anomalous in the big sky survey, so if it can happen, it hasn't happened yet. Since the two universes would be expanding into each other, we would see the effect as some sort of wavefront, probably ripples. Further reading on this topic leads me to believe that those ripples would be either bands of chaos or order, depending upon whether the intersection amplified or cancelled terms in various equations. Given the delicate balance of universal constants, any intersection would probably in my opinion have bands of nothingness where matter became unglued. Related note: Our universe appears to be bounded in at least one dimension, time, by the Bang on one end, beyond which physics ceases. We can use that boundary for theorizing what a boundary in other dimensions would look like. [Answer] There have been some amazing answers to this question, and it's a fun one to ponder, so I will take a stab at it. I like to try to relate science-fiction type environments to real-world constructs. I think they are easier to imagine, explain and dramatize in a story setting. With that in mind... I imagine this boundary would be very much like a seam, like what one might find when two different pieces of fabric are sewn together in a whip-stitch pattern. The "pieces of fabric" in this case would be our universe (identified via elements of our laws of physics), the fabric of another universe (identified by areas where the laws of physics go haywire because the other universe has a different set of laws), and bound by the following three "threads:" 1) Time 2) Space 3) Light. This is where things get a little bit creative, a little more fiction than science. Visually, this would appear like a corkscrew pattern running through a section of space where strands of pure light, pure space, and pure time were wrapping around, consistently digging into *something,* a void, as it were, where the laws of physics shift to reflect the neighboring universe. If you were to travel across this pattern, it might go something like this: 1st Stop: Pure light. Can't get right inside this area because it's devoid of space and time, and I need both to continue to exist, so I'll just hover above and try to take some readings from this section of reality. Maybe I can learn a thing or two about light that I don't already know. 2nd Stop: Pure space. Still can't get inside, because I need time to exist but nothing moves. Absolutely nothing. It is a solid brick of space- it's not a black hole, cause there's no gravity well, but reality there is infinitely dense. Let's ping off this section of reality and see what we find, shall we? 3rd Stop: Pure Time: Constant, frenzied frenetic fluctuation. Too chaotic; I'd be every when if I entered this string - simultaneously experiencing every moment of reality all at once. My head would explode. 4th Stop: Our universe - Typical laws of physics, everything is normal. Space, Time, and Light all co-mingle in a familiar harmony. I could hang out here all my life long if I have enough resources. 5th Stop: Pure Light again. 6th Stop: Pure Space again. 7th Stop: Pure Time again. 8th Stop: Oh, hey, light space and time are all re-combing in a new and unique way...Kinda cool. I can hang out here, learn a few things, though "here" feels fundamentally different from everywhere else. I'm a little thirsty, after all, this travel across the seam, so maybe a little water...and why is the water flowing *up* my throat? Definitely got to run some tests here to learn the new laws of physics. This pattern would continue to repeat ad infinitum. The picture below might help visualize what I'm describing. Only, in addition to the one yellow strand (light), it also has a blue (space) and a green one (time). [](https://i.stack.imgur.com/W9vmL.jpg) [Answer] Maybe you can adjust your notion of what is a "universe." Is a universe literally everything observable and not, or is it something else? **What if we defined the "universe" as everything affected by the same gravity well.** It might be interesting to have the boundary of the universe as a plane of zero thickness that light and matter can pass through but gravitational effects can not. This would allow you to discover the existence of the boundary, and have it be interactive in interesting ways. The fact that the boundary is there wouldn't be immediately obvious because you can still observe the other universe. This adds a discovery element to the story which is nice because the readers and the characters both go through the same enlightenment process together organically. I think that we can use this model to make some interesting stories by playing with that core concept. --- **Orbits between universes** Perhaps two stars are on opposite side of the boundary but the planets orbiting them have orbits that cross the boundary. This would lead to strange due to stars effectively playing catch with planets as the planets go in and out of their sphere of influence. Multiple confirmed observations of this "orbit" are made with telescopes which prompts multiple conflicting theories. Our heroes are sent on a science mission to figure out which theory is correct. --- **Different gravitational constants** Perhaps each universe has its own slightly different gravitational constant. This variance in gravitational constant affects chemistry/physics in subtle but fundamental ways. These changes could really be anything you want from causing people to go "space crazy" over time if sent to delta quadrant because some chemical in their brain becomes slightly toxic. Or the opposite happens and the body's repair/self healing faculties are improved so people return from delta quadrant healthier and apparently more youthful. Or maybe the ship starts going haywire and our heroes need to abort and return to their universe. The possibilities are truly endless. --- **Universe boundaries aren't static** Perviously I was assuming that the boundary was static. Gravitational force still can't cross the boundary but what if the location of the boundary moves steadily in one direction? Everyone knows that gas giant XYZ doesn't have any moons which is quite odd since the inner gas giants all have moons. Then one year someone notices a strange anomaly where a puff of its atmosphere retains its momentum, converts its angular velocity into a straight vector velocity, and drifts off into space. People dismiss this as experimental error. However next time the gas giant is in the same position a satellite retains its momentum, converts its angular velocity into a straight vector velocity, and drifts off into space. As it is flying away it sends proof back to the home world that a large portion of the gas giant's atmosphere is leaving too. Your heroes go to investigate, discover the boundary. Experiments over time show it is creeping toward their home world, and to their horror it seems to be accelerating.... [Answer] Since the universe is expanding quite fast, we wouldn't be at the boundary for a very long time. For a pre industrial civiliation, one side of the sky would probably always "look dark" while the other side has stars. For a space civilization, the boundary might move so fast that I would physically be impossible to "reach it" I m not a PhD in astrophysics but my understanding of the boundary of the universe is that it s not really like some sort of wall but rather abstract. The concept of space and time don't exist outside of it so I don't think we can really understand it with references to our normal world. [Answer] # the other end Something not discussed so far is that we don't know the [topology](https://en.wikipedia.org/wiki/Topology) of our universe. This and some other answers are listed in this [Wikipedia article](https://en.wikipedia.org/wiki/Shape_of_the_universe), although the concept of the topology is not much discussed. In short terms it could mean that we don't travel through space as straight as we think we do, but wander around in circles. So when we reach the end of the universe, we could just happen to come out at the other side. Like we don't move in the inside of a 3-dimensional sphere (as at least my instinctial understanding of the universe is), but on the border on a 4-dimensional sphere. An example may be given with a dimension less. Image a flatlander, who lives in a 2-dimensional universe. To his knowledge there was a big bang and light goes in all directions, so he would just assume that the universe is like the inside of a circle, expanding in all directions. But in fact he lives on the surface of a 3-dimensional sphere and if he could just travel it fast enough in one direction, he would be back where he started. But he can't because the sphere he is travelling on expands faster than he could ever move. [Answer] There will be void. Most sophisticated sensor arrays won't read any background noises. There'll be no stars, nothing, because there's literally no space. You can build your most powerful spaceship and head that direction at full speed, you will never reach it. Why? Because I think of it similar to the escape velocity you need to escape earth or the solar system but at a much larger, universal scale, you'd have to overcome the gravity of the universe to reach the void itself using up all the energy in the universe, which practically cannot happen. BR Alex [Answer] It would be easier for us to see the other Universe through the tourist binoculars. And for then to see us... [](https://i.stack.imgur.com/DzDEh.jpg) [](https://i.stack.imgur.com/j7Bdj.jpg) [](https://i.stack.imgur.com/lSyr8.jpg) [Answer] Another approach you could take that conforms to all known physics is to simply place your civilisation near the edge of the currently known universe (CKU). Remember that the CKU is expanding outwards from the big bang so its edge is simply how far it has reached at a given point in time. Astronomers in such a civilisation would look in one direction and see the core of the universe receding from them and in the other, nothing. Until one day, they notice a faint glimmer in the dark... ]

[Question] [ In my universe a 4th ***SPACIAL*** dimension exists around our 3 dimensions. I'm playing with ideas for a society that has access to a 4th spacial dimension and am currently thinking of what they would be able to construct. My thought process is this: Say you are a 3D being and have a square 2D hotel in a 2D universe. You are thinking of adding an expansion but all available room near your hotel is occupied. So you build a whole new hotel and push it up one foot on top of your original hotel and install a way for the 2D people to move up and down between hotels. To them it would seem like they hadn't moved at all in 2D space and the hotel just changed around them. **Is it possible for multiple 3D buildings to occupy the same location in 3D space but be "stacked" in the 4th dimension?** (Under the assumption a 4th spacial dimension exists around our 3D universe.) Edit: Added emphasis on **spacial** because too many people think I am asking about a temporal dimension. [Answer] ## Yes It isn't any different to occupants of a 2D world asking whether - if there were 3 dimensions - could we stack objects on top of each other in a third dimension? One thing to note, however, is that if the fourth spatial dimension exists then the buildings must have some size in the fourth dimension. As long as you space them accordingly along this spatial dimension - just as you would any of our three - then you can 'stack' the buildings in this way. [Answer] You are the master of your world, so yes. Some practical concerns: Your guests are only three-dimensional and would like to stay that way. How do you get them from one "hyperfloor" to the next? Well, you put them in a "hyperelevator" and move the whole room across. Peasy, easy. **Are there alternate Earths** under the other "hyperfloors"? You can answer that question both *yes* and *no* resulting in different problems. *Yes* can mean problems with the natives of those worlds. *No* means there is no gravity on those floors. And you will have to make things completely airtight, and either import or recycle oxygen. (Or both) A related question is what is the view from the windows is like. **What do you do about power failure and fire safety?** The "hyperelevators" are not running, the lights are off and the guests are panicking. Your move. You need "hyperstairs". They will probably not look like ordinary stairs. The most reasonable look is a corridor that somehow starts on one hyperfloor and ends on another. Actually, you probably want something like that for water, waste and electricity too. Just problematic is that power failure anyway? The "hyperstructure" of the hotel... is it something you build once and then it is stable, *or* is it something that is more like a force field that need continuous power to maintain? Your choice, but in the force field scenario you will need an UPS (Uninterruptible Power Supply) better than the Pentagon. I am talking Tesla Batteries *and* Diesel Generators *and* Cold Fusion Generators *and* exercise bikes with dynamos *and* ... Finally, for marketing reasons you really need to find better words than "hyperwhatever". [Answer] **Initially consider it as time.** There was a building before the one you're in and a building after it. All you need to be able to do is move between those buildings. **Consider a co-ordinate system x,y,z,t. x and y are the ground level, z vertical and t your 4th.** Just as you move between your building and the one next to it, which shares your x,z,t co-ordinates, by moving in y, you can move in your 4th dimension between the buildings sharing your x,y,z co-ordinates by moving in t. The only problem is moving in that 4th dimension when you only exist in 3. There can be an indefinite number of stacked Flatland planes of existence, none of them are aware of the others, none of them can interact with the others or pass between them. They exist only in x and y, they have no z and no understanding of z. **But** There's always a but. Your society has a 4th spacial dimension, so they'll use it as a matter of course. Flatland has no access to the 3rd dimension so you can stack Flatland planes without a second thought and with no issues. Your society is going to have buildings that already exist and have length in this 4th dimension, you can't just casually stack them like 2D worlds in 3D, you'll have to put them alongside each other. You'll also have to work out terminology and decide whether like left and right, you can just go that way or whether like up and down, it has a force and you need to have something to support you in "flight". Going back to the example of time as a 4th dimension, while we can't control our movement a building still has a length in time. A building may be 10metres x 5metres x 20metres x 100years, but they still exist and have a fixed length in that dimension. * Time has a "force", it always draws us forward (like gravity pulls us down) * We can't travel against the force without assistance (which we haven't developed yet) [Answer] Really it depends. Let's consider the fourth dimension to be a spatial dimension perpendicular to all other three spatial dimensions. The main problem will be this: does gravitation extend into or along that fourth spatial dimension? If gravitation is fourth dimension, and unless the stack of buildings isn't secured, the stacked buildings will fall down, in the direction of the fourth dimension, and crash into the buildings stacked in the other three spatial dimensions. This might look like the buildings in three dimensional space inexplicably undergoing massive damage and deformation, apparently without a cause (as the stacks of buildings falling down in four dimensions won't be observable in three dimensions). This suggests you should four dimensional gravitation out of it. In which case, stacking extra buildings in four dimensions may be fine. [Answer] A good use for 4D would be to house a 3D prison. In 4D space you can achieve a vantage point where you can see all 3D points simultaneously, with no occulusion from walls. Similar to how if you stand in 3D above a 2D sheet of paper you can see the whole thing, irregardless of how many lines are on the paper that would block the view of 2D beings on that paper. While a 3D being might not be able to achieve such a 4D vantage point, they might be able to create a camera of sorts that can. As for hotels, as hotel rooms are independent of one another (ie you don't need to see the contents of one from another) all you need in 3D space is reception, an elevator and a single hotel room. The button in the elevator room transfers the elevator to a different 4D plane to face a different room. In any 3D instance this makes your hotel very small, no need for separate floors, but it can support infinite rooms. I'm trying to figure out if the elevator room could simply rotate in 4D space to face different rooms instead of translating, might be safer or more energy efficient. [Answer] # No Unless you just handwave everything, there is no physical sense to viewing *any* spatial dimension "different" from any other, or to be able to travel "through" an additional dimension. *Flatland* is a great example. If you take a Flatland style piece of paper (2D) and a second piece of paper, and put them on top of each other, you do *not* get 3D space. Topological, you are still locally 2D with some weird effects like being able to "tunnel through" between the sheets of paper by making holes and glueing the edges together, or forming a donut out of a single sheet by glueing opposite edges, or being able to flip beings by glueing a band of paper in the Moebius configuration. You can do a little experiment: Take a sheet of paper (15x15cm in size) and draw a 10x10cm square on each with a pen. Make it one of those pens which "bleed through" the paper, and thin paper. So it seems like the drawing is really "inside" the paper, just like a Flatlander would be. Now stack many of them, until they build a 10cm high tower. You now have a 10cm high tower of 2D sheets, but what you do *not*, in no fashion whatsoever, have, is a 10x10x10cm 3D cube. Thinking the other way round, no 2D Flatlander could ever "lift off" its universe to travel through 3D space, in the same sense that you could never lift off a pencil drawing from its sheet of paper. The operation would just not be defined in any useful mathematical or physical sense. Our (real) 3D is fundamentally different from a hypothetical 2D stacked upon each other. Even if you take our greatest microscope, at no time does anything fundamentally behave in a 2D way. A more mathematical way to see how this does not make sense is to see that all dimensions (to be called dimensions in any way making physical sense) would have to be *continuous*. The stacking 3rd dimension would be discrete and thus people would probably not even call it "space". All of this scales up seamlessly to 4D. # Bending What you absolutely could do would be to *bend* 3D space in creative ways. This is 100% compatible with our real world, as far as we know. This is what happens in the Flatland example, of course - stacking two sheets of 2D paper on top and glueing them is just an easier to imagine way of having a single 2D space in the first place and bending that one into a stacked configuration. But you cannot have a (physically working) 4D space somehow "embedding" a 3D space and having meaningful travel for the 3D objects. # Multiverse Your stacking version could also just be a multiverse as we are thinking about today. Those are perfectly happy (and basically required to be) stacking/discrete. But don't call them 4D please, either. # But... ...you can also just forget everything above, you have artistic freedom. It would just grate hugely on everybody who has a passing intuition about these things, spoiling suspension of disbelief absolutely. The broad masses won't probably notice anything, I guess. ;) [Answer] As you said it can be visualized as going from a 2D world to a 3D world : everything needs a depth in the new dimension. To stay with the 2D/3D analogy, your squares have to become [cuboids](https://en.wikipedia.org/wiki/Cuboid). As you can stack many slim cuboids in a cube, you can stack many 3D hotels in a 4D hotel as long as they have a very limited depth in the 4th dimension. Note that one tricky thing is to help peoples turn along the new dimension in order to get from a 3D hotel to another... There is a game demonstrating the concept, [Miegakure](http://miegakure.com/), I believe their videos makes the possibilities quitte clear. [Answer] Imagine putting multiple flat squares on top of each other. You end up with multiple squares in the same 2D space by stacking them in the third dimension. What you are proposing is identical but going from the third to fourth dimension. The limitation you face is that perception or travel in a fourth spatial dimension is not currently possible. So, in answer to your question: is it geometrically possible? Yes. Is it physically useful? No. [Answer] I have a problem with the answer(s) in this question, even though being an answer I thought of aswell I'm no expert but quickly I think "yea! you can have a building in one spot, then another in the same spot but in a different time period, and have a 'transportation' device to move between them" Buut If we place a building in a spot, then by accessing the 4th dimension we put another building in the same spot but 5s later, what happens once the first object meets the other? Will they crash? An object will suddenly appear where the first was. You could have buildings be separate more time, like 50 years from one another, but still. I think eventually the buildings ahead of time would have to be destroyed before hand. Placing buildings in the past would cause the same issues. It wouldn't be handy to have whole buildings I guess but rather solo rooms, easily destroyed before the 'crash' ]

[Question] [ I'm not aware of any animals which have evolved projectile weapons that they fire. There are a number that spit venom but none that even throw rocks, let alone using projectiles. On the other hand though creatures that do so are a staple both of fantasy (e.g. Manticores) and sci-fi (e.g. Zerg). Is it even possible to evolve natural projectile weapons? What would need to change in order to allow creatures to do so? Would those constraints change depending on whether they used found ammunition (for example an appendage that works like a sling, the animal gathers rocks to use in the sling) or had to grow the ammunition. The sling at least has the advantage that it can evolve gradually out of a more usual grasping limb. Would it even be realistic for a creature to expend the time and energy required to grow a weapon (for example a spike) only to lose that investment after firing. [Answer] *(Okay, I should not start thinking about interesting subjects on a lazy Sunday morning. This post went waaay long so I'll just put my conclusions at the start as a summary. You can read the rest if you like. I'll have to proof read after letting it set for a time so sorry for the typos.)* ### Summary Kinetic projectiles are not favored evolutionarily because: 1. They require a lot of intermediate forms that in turn require a specific sequence of environmental conditions. Existing forms place developmental constraints on exact forms the projectile system can take. 2. When the individual runs out of projectiles, it's out of defense. It's like the military axiom that logistics trumps tactics because a gun is only a weapon if it has ammunition. An animal could invest a great deal of energy into a projectile weapon just to find itself defenseless or unable to hunt. (Note that carrying around a bunch of ammo also requires energy and imposes tradeoffs of mobility and increased likelihood of accidental injury. Just ask a modern soldier humping half an ammo dump around everyday.) 3. Muscle powered projectiles are not very effective. Human hunters using muscle power and natural materials like hardened wood, bone and even flint, wound animals many more times than they kill them outright. Most hunter-gathers who use kinetic projectiles wound an animal and then run the bleeding animal into the ground (humans can run farther than any other animal on earth.) The instant kill, the goal of all hunters, requires relatively high technology, usually metal, a great deal of skill and a dose of luck. It is unlikely an evolved system can duplicate that. 4. As species (A) evolves a projectile offense or defense, that creates selection pressures on species (B-Z) to evolve a counter. It's the "Red Queens" arm's race. Even if we image a plausible scenario for the evolution of a kinetic projectile, we would also have to image the countermeasure. At every intermediate form of the evolution of a projectile, a moderately effective counter-measure could kill the advantage of the proto-projectile system and eliminate the selection pressure that would have produced the projectile. 5. ***Kinetic projectiles would be very expensive to create and use.*** The projectiles are literally thrown away so all the energy that goes into their creation is lost. Every miss is a huge waste of resources for the animal. The payoff for projectiles would have to be enormous. I think (5) is the real deal breaker. A lot of organisms throw a lot of things at prey or predators but it's always something lightweight and innately disposable, e.g saliva, venom, musk (skunks), vomit (vultures), feces (monkeys, vultures and way to many others.) In none of these cases is the primary modality of the "projectile" its kinetic energy. Instead these are all chemical payloads that irritate, poison, entangle, or chemically burn (vulture vomit) and which were already something the organism benefits from getting rid of eventually. ### Details: Let's walk through several scenarios in the evolution of a plausible projectile systems for organisms. For brevity, let's just concentrate on issue (1): intermediate forms. Understanding intermediate forms is absolutely critical to understanding evolution, especially the evolution of specific attributes. We must always remember that all species have specific forms right here, right now because the environment right here, right now shapes them so. Evolution has no goals, no progress, no direction, no conception of the future. When looking at the evolution of any phenotype, we have to evaluate each step ***without hindsight***. Any phenotype we see ***in hindsight*** as leading to the phenotype was itself a fully functional (or side effect of a fully functional) attribute of the species at the time it first appeared. Remember, this not engineering. Species don't start with an end goal in mind and then slowly evolve solutions to that goal. Instead, environmental forces shape organism from moment to moment constantly. Species don't develop attributes because they will need them later. Darwin noted, "nature does not make leaps" meaning that the development of a new attribute requires an accumulation of smaller change termed "intermediate forms" e.g. birds just didn't one day suddenly spout wings. Feathers started as near microscopic fuzz used for insulation, and only slowly grew large enough for for other functions. Wings started out as grasping limbs that combined with feathers, broke falls. Controlling falls led to gliding. Evolving muscular and skeletal structure to add power to gliding led to flying. Each of those changes which ***in hindsight*** led to feathered flying birds, was an intermediate form. So, to understand why something did or did not evolve, we need to understand what intermediate forms would be required, which in return would require understanding environmental pressures that would create that intermediate form. (There are also developmental constraints. When the environment shapes a particular form that precludes others e.g. if the environment creates a heavy, armored creature like a turtle, that precludes the development of flight anytime soon because the advantages of mass and density are diametrically opposed the needs of flight; low-mass and low density.) We want to understand why no animal has evolved a primarily kinetic projectile weapon that shoots a dense, possibly sharp, projectile with enough momentum and accuracy to use practically for defense and hunting. Let's consider solely kinetic energy transfer weapons. Technological examples would be slung stones, arrows and bullets (but not poison darts, fire arrows or shells with explosive, chemical or biological payloads.) Such a system would require several subsystems, each a fully functional intermediate form, each of which would have to exist before the projectile system could be useful: 1. **Target acquisition and aiming:** The system must be able to identify targets, assess its motions and likely future positions, then translate all that to system specific information that will let it launch the projectile so that it will strike in a beneficial fashion. 2. **Energizing the projectile:** The system has to add energy to the projectile to make it move. It could do so with muscles, air, fluid, chemical reaction or even (lamely) gravity. 3. **A shaped projectile:** The point of the projectile in this system is to transmit kinetic energy destructively to the target. To do so, it must be some combination of sharp (wedged shaped), dense, and rigid. 4. **Predictable or guided flight:** The projectile has to strike the target in order to transmit its energy but it is by definition severed from the creature that launches it. Therefore the projectile must either have predictable flight characteristics, like an arrow or a bullet, or it must be guided, like a seeking missile. We'll stick with predictable flight. Each of these sub-systems must evolve as an intermediate form. **Target acquisition and aiming:** Target acquisition would seem to have an obvious intermediate form of any animal's senses and neurological systems, which identify either predators or prey and then calculate how to move the body in order to evade or intercept the target. But shooting a projectile is an entirely different calculation problem than moving the entire body. There would have to be an environmental pressure that would shape the system to predict were the target will be in the future but that the organism itself won't be. The easiest intermediate form that meets that criteria would be long limb, lets say a tail. Tails naturally evolve as clubs. The club starts out accidentally as just a tail striking a predator or prey in course of a contact fight. Environmental pressures to make all energy expenditures pay the highest dividend would lead to the evolution of a tail club that could strike intentionally and accurately. Some extant lizards use their tails quite accurately as whips, so this is plausible. The targeting system begins as a means of directing the end of the tail to strike the target. **Energizing the projectile:** If we start with a whip like tail, then the rapid motion of the tail can accelerate the projectile. Combined with the existing targeting for the tip of the tail, anything that flew off the end of the tail would automatically fly in the general direction of the target. **A shaped projectile:** Living systems are governed by their energy budgets. As dynamic systems, they exist in the flow of energy through them. Everything they do, even just laying there, requires energy flow. Growing a disposable body part is a non-trivial expense even though animals do it all the time e.g. shed skin, hair, feathers, claws etc. You can see how important this is by the way that herbivore mammals eat the after-birth or many predatory species eat children that die or that they can't feed. Forming a projectile will be a high energy endeavor because the projectile needs a specific combination of mass and form. Creating biological mass obviously takes energy but complex form also takes a lot of energy to create to the form's design. All that invested energy will then be thrown away. It's easy to see how animals evolve whips and clubs on tails because the energy invested in making the weapon remains in the body - but a projectile requires a considerable energy investment that will be literally thrown away. Fortunately we have previously existing systems to build on. Animal bodies are defined by the membranes that separate the inside from the outside. The outside facing layers of most animals (and all land and air animals) are dead tissues and sacrificial; e.g. skin cells, hair, scales, feathers, teeth, claws, shells etc. Our projectile can start out as dead sacrificial tissue; e.g. skin cells and teeth or extruded material; hair, claws, scales feathers, etc. The easiest would be some kind of hard spike. If we start with the whip tail lizard, we could imaging scales on the tail tip evolving sharp edges to abrade the target. There would be pressure to make them cut more, so the scales would grow larger and larger eventually looking like sharp edged segments. The scale at the tip would be the most energized and have the most striking surface so it be the largest and the need to transmit energy destructively in the most efficient means possible would shape into a wedge or blade like form. The lizard would have a series of large scales growing at the tip, when one was ripped off or destroyed, another would grow out in its place, Even being smaller and not at the tip, they would still form a cutting edge. Eventually, it would be shaped into something all dead scale like a rattlesnake's rattle. Up to this point we have a barbed whip with a disposable and replaceable barb. It works by accelerating a wedge shaped cutting scale to a high velocity so that the wedge shape (the sharp edge) concentrates all the barb's kinetic energy into a tiny area on the target so they it destroys the tissue at that point. This barbed tail works as a final form itself to accurately strike a target and injure it. **Guidance:** It's easy to see how a barb-scale could accidentally become a projectile. It's already evolved to be detachable and disposable so at the point of when the whip tail accelerates it to a high velocity and then snaps back, the barb-scale would experience significant stress at its attachment point. If the tail cracked back before actually hitting the target, the barb-scale could just pop off and go flying in the general direction of the target. However, it would unlikely to be at this point an effective projectile. 1. The barb-scale would have little mass. Being abradable and disposable, it would be fairly lightweight to conserve energy investment. Being attached to the tail, the mass of the tail would store the kinetic energy to be transmitted - not the barb-scale. When it detached it would rapidly loose energy by air resistance. 2. An anchored cutting edge is not a stabilized flight form. Consider how difficult it is to throw a knife. A knife is optimized to transmit energy while held in a hand, not flying through the air. A thrown knife takes the the form of dart or javelin but a flying form makes for poor cutting or stabbing form accelerated along the curving path of an arch. To evolve as an effective low-mass projectile, the barb-scale would need to evolve a dart or javelin shape *while still being used as an attached weapon.* The only reason to take that form would be if the barb-scale worked best as a puncturing weapon instead of a slashing one. But, that is a problem because the best form for an attacking puncturing weapon is a curve that follows the arch of travel of the limb that drives it; e.g. claws, fangs or pick-type metal weapons (for puncturing armor.) Any puncturing barb-scale would end up looking like a scorpion's stinger - which would have terrible flight characteristics. There just isn't an intermediate form that works well as an attached cutting or stabbing form that also flies in a predictable manner. Once a creature had evolved an efficient cutting/stabbing whip tail, it would be precluded from easily evolving a projectile. Surprise! Dead end. So, we need to find another projectile. Kinetic energy is about momentum. Momentum is velocity times mass. High velocity with low mass gives the same momentum as low-velocity and high mass. In addition, a sharp projectile uses the wedge shape to concentrate the kinetic energy of its momentum in a small area, making it more destructive. That in turns requires controlled flight to ensure that the edge of the wedge strikes first. But, if you go with high mass and low velocity, it becomes simpler. Enough mass hitting will transmit the energy regardless how it strikes. The obvious solution, with evolutionary precedent, is a massive ball on the end of the tail that works like a mace, a crude bludgeon. It could evolve from a scale built of very dense and close packed proteins (most scales have air pockets for insulation and weight saving, that's how feathers got started.) There is evolution precedence for such a system in [Ankylosaurus](http://en.wikipedia.org/wiki/Ankylosaurus) and [Doedicurus.](http://en.wikipedia.org/wiki/Doedicurus) If the mace tip is detachable, it could fly off target. All the systems elaborated for the barb-scale would still apply. It would be like fighting by throwing bowling balls. But, there are intermediate form problem. Even if evolved from a disposable scale, the dense heavy bludgeon would require a strong attachment point lest it fall off while being accelerated. If it does, it's probably not even directed at the target but flies off on a tangent like an axehead that pops off during the swing. It might even strike the animal itself. The strong attachment point precludes the easy evolution of the mass from bludgeon to projectile. Hmmmm, but lets not give up. The most effective bludgeon is a dead blow hammer. A dead blow uses impulse to transmit a great deal of force in a short time. It does so by having a movable element inside the hammer and space for it to move. Usually, this is lead weights in oil and an air pocket. In a normal hammer, the actual transmission of force is not instant but follows a somewhat bell shaped curve. This occurs because a real hammer is not an ideal rigid body and it flexes and compresses. Plus, the momentum of the back of the hammer takes time to transmit against the opposition force of object struck. In a dead blow hammer, the mass of the free-weight inside flies forward to hit the front of the hammer in a much shorter time. More importantly, the equal and opposite force from the struck object is transmitted along the exterior container more than to the free-weight. The result is a peak shaped force transmission curve. Since it is usually the peak force that does the work/damage, a dead blow hammer is more effective even with the same overall momentum. (Impact wrenches, impact hammers and impact drills work on the same principle.) So, lets imagine the evolution of a dead blow tail bludgeon. It would be easy to form if the bludgeon was made of layers of scales instead a single giant one. At first it would be like a clacker-rattle with only a slightly higher peak force but if it paid off, it would eventually form fairly large free-weights inside a relatively thin "hammer" shell. The real world precedent is a rattlesnake's rattle which is a thin shell of merged scales with a ball shaped detached scale inside. In a weapon, there would likely be several detached elements inside. Now we have a dead blow mace weapon. It would more effective in transmitting impact than just a solid mass. One problem it would have, however, is that that the detached elements would be abraded to dust inside the airspace. The solution would be to evolve an opening in the outer shell to allow the particles to escape. The most effective point for shaking out the dust would at the tip in line with the maximal point of acceleration when the tail was whipped at a target and then yanked back. Waste not, want not - so the free-weight scales would evolve to disintegrate into jagged small units that could serve as an irritating dust. Likely, the hole would evolve to be just under the size of the free-weight scales. Free-weights work best when symmetrical so if one broke or got worn small, best to get rid of it. Now the tail is not just a dead-blow bludgeon but also scatters irritating dust and shards. In some circumstances, like fending off small pack predators; throwing irritants over an area might be more effective that trying to smack one of the fast moving little buggers. Now the environment might favor tossing the free-weights out the hole, instead of using the bludgeon. When throwing something lightweight, launching velocity becomes more important so the squat heavy bludgeon-tail begins to evolve into a thin, long fast moving whip with a hollow end full of dust and shards. As the tail began to accelerate more and more, the heavier shards would begin to store useful amounts of kinetic energy and become projectiles. No longer facing abrasion by smacking inside the bludgeon shell, they could become strong and dense. As extrusions, scales naturally form an ellipsoid shape. Rattlesnake rattles start off as an irregular ellipsoid that gets worn into a sphere. But once its primary function becomes flying as a projectile, the projectile would work more effectively as an ellipsoid. Eventually the projectile scale would elongate into a more of a cylinder form. Anything on the back of the projectile-scale that produced drag, e.g. bumps, breakage, air pockets or strings of scale or other tissue, would cause it to orient back to front. This would create the intermediate form necessary to evolve a pointed tip. So, we end up with a critter with long muscular tail, with a hollow rattle like structure at the end. Inside, its "barrel" might resemble a hi-li racket (jai alai cesta). It would flick dense ellipsoid or even dart shaped projectiles at high speed fairly accurately. The projectiles would be relatively small and grown at a lower energy cost. But still, the core problems remain. Run out of projectiles, and the weapon is useless. It's nearly impossible to digest scale, hair or other disposable extrusions so it's unlikely a projectile throwing beast could ever recover the energy invested in making the projectile by eating it, assuming it could find it. All the energy that goes into the the projectile is always lost whether the projectile produces a desirable effect or not. To sum this up. Imagine if humans made arrow tips solely from a giant tooth we grew. How fast could we produce them? It would take weeks to grow an arrowhead sized tooth. Every shot would have a significant risk of breakage. In the time it took us to evolve the capacity to grow the arrowhead tooth, our prey would be evolving counter measures e.g. they can grow teeth or teeth like structures too. Just as metal can make swords or armor, teeth could be weapons or armor. What else could we do with all the energy we put into arrowhead teeth? If you look at the arms race in human technology, muscle powered projectile weapons, it's clear that they were not a dominating weapon. It was not until paired with chemical energy that they became dominate and even that might be temporary. The return of body armor is forcing a redesign of projectile weapons back to heavier forms. The ability to intercept even small projectiles in flight will lead to other changes. I think it's safe to say that biological kinetic projectiles would be hard to evolve and have little net payoff. > > I do wonder if the lizard tail might evolve to scavenge rocks to use > for ammunition as the next step though? > > > For a rock thrower, you have figure out intermediate forms that don't involve actually throwing the rocks as weapons. You have to figure out a reason to move the rocks just bit and then another to move them some more and so on to reach a high velocity movement. It might start by moving rocks accidentally with a whip tail which leads to some intentional movement to build a nest or uncover food. Optimization of moving rocks leads to a horizontal, blade like tail perhaps with a scoop at the end. It would still be used as a whip. At some point the use as a whip would accidentally overlap with moving rocks and a weapon would be born, assuming the coincidence happened often enough a selection pressure for using the rocks intentionally would build which would lead to the evolution of targeting systems. But rock ammo would be very limiting unless the entire species lived its entire evolutionary span in an area where there were abundant loose stones. I think that unlikely. It might evolve to carry stones but as noted above, humping ammo has a huge cost for something that might not ever be used, or used effectively, and rocks are heavy. I think projectile weapons require too much specialization, too much expenditure for too little return. If you look at most animal weapons systems such as claws, you see that they perform several non-weapon task as well. Claws, for example, are used for traction, grooming and marking in addition to being weapons. Those additional functions helped claws evolve in the first place (probably traction first) and they help defer the energy cost of the weapon aspect. I have a hard time coming up with any plausible secondary functions that would defer the cost of a projectile weapon system. [Answer] Well other primates (monkeys, apes, gorrillas) definately throw things. The opposable thumb that we share with them really is what makes throwing things efficient enough to use. Some [frogs have tongues](http://newswatch.nationalgeographic.com/2014/06/12/frogs-animals-weird-science-tongues-adhesive-science/) that they use as weapons to snag insects out of the air. The [procupine](http://en.wikipedia.org/wiki/Porcupine) has quills though it is more of a defensive weapon as the creatures are actually herbivores. How ever it is likely that the idea for the projectiles may have come from seeing a porcupine shake its body and release its quills. While they are not propelled out with sufficient speed to penetrate much if anything this may not be apparant to someone who just saw it happen a few times. There are a few specie of spider that can [shoot their webs](https://www.youtube.com/watch?v=RPwPN6Me1M0) and the [Bolas Spider uses this as a weapon](http://en.wikipedia.org/wiki/Bolas_spiders) by weighting one end and slinging it at its prey to entangle them. > > Would it even be realistic for a creature to expend the time and > energy required to grow a weapon (for example a spike) only to lose > that investment after firing. > > > Bees do this with their [stinger](http://en.wikipedia.org/wiki/Bee_sting) even though some species die after their first sting at least if the skin is strong enough to attach the barb. So yes there is precedence for creatures evolving a single use weapon. [Answer] In general there is not a lot of evolutionary incentive to have a natural projectile weapon. Once you've used it it isn't good for anything, you can't exactly pick it up and try again. It also means you don't have that weapon anymore for the second attack. On top of that you'd need to learn how to be accurate with it. Also how is it going to be projected? pneumatic? You have three basic choices, air, liquid or a whiplike motion from an appendage. Animals that grow their own defense like the [porcupine](http://en.wikipedia.org/wiki/Porcupine) cost them quite a bit to maintain, it takes a lot of energy to grow something physical. if you go to all the trouble to grow a nice long pointy weapon, or a large club ([Ankylosaurus](http://en.wikipedia.org/wiki/Ankylosaurus)) why throw it away? The primary need for a projectile defense (maybe offense?) would be to keep the target at a reasonable distance. The [skunk](http://en.wikipedia.org/wiki/Skunk) has a spray that can reach 10ft. the [spitting cobra](http://en.wikipedia.org/wiki/Spitting_cobra) is up to 6.5ft. As a cloud from the skunk, it is an area weapon, as a stream from the cobra, it can be adjusted while spitting. Also primates do throw things, rocks garbage feces etc. Did some more looking Here is a list of different kinds of [projectiles](http://en.wikipedia.org/wiki/Projectile_use_by_living_systems) used by animals. Apparently there are some tarantulas that can flick " fine hairs are barbed and designed to irritate and can be lethal to small animals such as rodents" There is also a whole bunch listed that use non-body part projectiles, sand, rocks etc. They also 'tethered projectiles' which are things like the tongues of frogs, sent out and brought back. It also has a couple plants listed where seed pods will explode. So while there are more examples than I had at first suspected, something like a Manticore that shoots poisoned spines is unlikely. [Answer] I'm a bit late to the game here, but I'm going to mention a few more real-life animals and their weaponry. We are in the middle of evolution, so some of these might be intermediate stages of just the sort of thing you are looking for. * Lizards consider the expense of growing back a tail worth survival, so don't automatically discount the possibility that evolution won't try a projectile (particularly if it's edible or filled with something that aids digestion). * Archer fish. They are incredibly accurate at comparatively long distances. * Chameleons. Just imagine a bony spike on the end of that tongue. And it's reusable. * Porcupines. How much more of a stretch would it be for them to evolve the muscle control to fire those quills? Other animals have the fine control but not the weapon, and a porcupine doesn't have to worry about running out of ammo. * Spiders have been mentioned. There are a few varieties that fire webbing, and when they are done, they eat it, so they get the calories back. Tarantulas do fire hairs at the eyes of aggressors, and what's more they have an irritating oil on them. * Bombardier beetles. They fire **boiling** acid at enemies. They get one shot, but they're willing to do it to survive. * Stinkbugs/skunks. Probably not what you are looking for. * Jellyfish. They do shoot poisoned projectiles for both attack and defense, though they lack the sensory organs to react before actually touching it. Some of them have injectors several meters long. Imagine if they had eyes. * Birds have been known to drop stones on crabs to break their shells. A bit of a stretch, but I wanted to be inclusive. * Trigger shrimp have the muscular/skeletal structure to fire projectiles, if only they had the armature. Still, they pack a wallop and move fast. Ditto preying mantis. * A horned lizard will shoot blood from its eyes. Ew. * Some mulberry bushes launch irritating pollen to discourage herbivores. * Squid. Aside from the well-known ink, there are some deep-dwelling squid that fire bioluminescence as a defense. They will sometimes 'paint' a target on their attacker, making him easy to see. That's about all I've got on the top of my head, aside from what's been mentioned already. Have fun! [Answer] Assumption: We are talking large scale animals here, comparable to human size. Bees and spiders would have vastly different physical reasons due to their small size and already do some minor projectiles, see [bowlturner's answer](https://worldbuilding.stackexchange.com/a/545/81). Animals are typically concerned about two things in situations where a projectile weapon would be used. Either the animal is hunting, or it is defending itself. How good would a projectile weapon work in these situations? Hunting: You miss and you starve. Especially if the creature had to grow the amunition, there is a potential for a lot of wasted energy in a failed hunt. Aiming is hard. It is mentally intense and requires good vision, fine motor control, and the ability to adjust for wind and elevation. It would be extremely unlikely to evolve all of these skills in parallel. Additionally, even if the animal managed to strike its prey, it is unlikely that it would strike with enough force to stop it. Large herd animals like wildebeests and moose aren't going to be easily stopped. The energy required to stop one of these animals could easily be strong enough to shatter the animal and maim the meat since I am assuming this projectile wouldn't be both as small and fast as a bullet. The energy requirements and the chance of success is just too low to offer a significant advantage over traditional teeth and claws hunting. It also is harder to hunt in packs since if you surround your prey the potential of cross fire is now in the mix. The other way projectiles can be used is in defense. This is still unlikely because of the energy cost and effectiveness. Any projectile defense system would need to hit, stop the predator, and allow the animal to escape. Typically predators hunt in packs, meaning that the defense system also needs to take out multiple attackers somehow. It does not seem likely to me that an animal could evolve the mechanisms to aim a projectile, fire it hard enough to stop, say a lion, and deal with an entire lion pride as well. The resources invested in this sort of defense just aren't as effective as running, leaving in a defensive area, or fending off predators with your entire pack. I think projectile weapons and are highly unlikely due to their complexity and inefficiency for prey animals. [Answer] The other answers have covered the case of animals and projectile weaponry, but there's a case that nobody seems to have covered: plants. There's a form of seed dispersal called [explosive dehisence](https://en.wikipedia.org/wiki/Dehiscence_(botany)#Explosive_dehiscence): seeds are flung at high velocities (100 m/s or higher) to scatter them well away from the parent plant. It wouldn't take much for a plant to evolve a modified seed pod for defensive purposes. [Answer] I agree with the excellent description of evolutionary constraints by @TechZen. However, there is one scenario that seems remotely plausible to me. In short, the evolution could go: Venomous spike -> Moving spike -> Spike on a spring -> Flying spike. Let me explain in more detail. The ancestor would have been an energy-conserving animal like a sloth or a python. It would lie on the ground and wait for an animal to scratch its foot on the spike and die, then the predator would devour the dead body. Or maybe it would hang on the branch and fall down on its prey. Such a creature could even evolve from something like our snakes. Next step: some degree of the spike's movement. Wiggle it a bit so that if the prey passes an inch to the left, our guy doesn't stay hungry. Key preadaptation for the next step would be muscles allowing protruding, stabbing movement. Eventually, the weapon would turn into a spike on a muscle spring, thrown for several meters. It could sometimes get stuck in the prey and torn off, with the following possible outcomes: 1. The predator becomes unable to hunt further and dies. However, since it's an effective energy conserver, it may still live for a long time and maybe even procreate. 2. It regrows the spike. Plausible if the spike is a modified tooth and the ancestors had regrowing teeth (<https://en.wikipedia.org/wiki/Polyphyodont>). 3. Instead of regrowing the spike, the predator may pick it up and reuse, or grab a stone and hit lesser animals with it. Seems less likely than (2), but still. If scenario 2 holds and regrowing the spike is no big deal (relatively), it may become advantageous to deliberately release the spike. From here, sky's the limit: our guy may improve his own precision or the missile's aerodynamics. There are obvious problem with this scenario. How does this predator deal with scavengers? It kills the prey, but how does it keep it? Isn't it better to wait another week for a closer prey instead of all these efforts? However, who knows the exact selection pressures in our fantasy world? Not me. [Answer] Another animal with a projectile weapon is the [cone snail](https://en.wikipedia.org/wiki/Conus#Harpoon_and_venoms), though it's a little closer to a captive bolt than a true projectile. It fires a venom filled tooth from its proboscis towards its prey like a harpoon and then pulls the fish into its mouth. It has a 'radula sac' that it keeps spare tooth harpoons in, for when one is used up, similar to a quiver or magazine. There are plants, like mistletoe, that use kinetic energy to throw their seeds great distances and there are carnivorous plants that use motion sensing abilities to target prey. It's not too far fetched to imagine a plant that senses motion and then fires seeds into it, using the corpse as fertilizer. [Answer] The mudskipper can 'project' relatively large balls of mud from his mouth. With smaller pieces and a stronger mouth I can imagine a similar mechanism targeted for attack. You can watch this video starting at 2:52 for more information <https://www.youtube.com/watch?v=Uidx-YZLJls> [Answer] Blind Luck, really. I'd consider a viable scenario relating to micro-projectiles, possibly released from specialized pores that go through an intermediary stage of 'pressure building' - much like a boil. When agitated, or induced, to release - out pops a venomous spiky-follicle. Yes. [Answer] Tarantulas can launch barbed hairs off their abdomens which float in the air and can get lodged in the eyes and mucous membranes of threatening animals. They're called 'urticating' hairs. Here's a video of a tarantula launching hairs when feeling threatened (arachnophobe trigger warning!): <https://www.youtube.com/watch?v=1cPxqjSG6HU> More about urticating hairs which are present in many species: <https://en.wikipedia.org/wiki/Urticating_hair> [Answer] Elephants can and do throw items with their trunks. Humans and apes can throw sticks, elephants can throw trees. So if an elephant like creature grew easily detachable things like porcupine quills at the end of its trunk it could throw them at other creatures, sort of like throwing daggers or javelins. Or maybe the elephant like creatures grow many easily detachable bony knobs, each weighing several pounds, on their backs. They can reach back with their trunks, pull off a knob, and throw it at their opponent with enough force to kill a man or a lion if it hits in the right place. ]

[Question] [ I'm making this whole other alien world and I made it an ammonia world, so there is a lot of nitrogen in the atmosphere. Would nitrogen be a good gas to breathe in an ammonia world and would [Cobalt](https://en.wikipedia.org/wiki/Cobalt) be a good transporter element in the blood? [Answer] 1. I think ammonia would be a good gas to breathe in an ammonia world. There is a lot of it handy, I would imagine. As opposed to N2 which is sort of an ice queen and reluctant to mix it up with other molecules, NH3 has 3 promiscuous hydrogens hanging off, ready to get busy. And NH3 protonates easily to NH4+, opening a whole other range or repertoires. 2. Cobalt. Great choice! I suspect you might know some chemistry. Behold B12: [](https://i.stack.imgur.com/QHNBD.jpg) <https://www.whoi.edu/page.do?pid=37478> B12 has at its heart a cobalt atom bound to 5 nitrogens and one something else. The structure of B12 has a vibe reminiscent of hemoglobin with iron or chlorophyll with magnesium, and a B12 type molecule with a cobalt heart could definitely function as a NH3 carrier. [Answer] Nitrogen is a terrible gas to breathe. A molecule of nitrogen is two atoms, triple-bonded together. If you want to use nitrogen for respiration, you need to break that bond so the nitrogen atoms can react with other molecules. However, this is an *extremely* strong bond: one of the strongest in all of chemistry. You have to put in vast amounts of energy to break that N-N bond. The amount of energy you need is exactly the same as the amount of energy that's released when that bond forms. Most modern explosives (e.g., TNT, RDX, etc.) work essentially by having a bunch of nitrogen atoms in a molecule. When you poke it, the molecule rearranges itself so that the nitrogens come together and form triple bonds with each other to make nitrogen gas. A large fraction of the energy from the explosive comes from the formation of those N-N triple bonds. This is the energy you'd have to put back in to break the bond. So, although it's not literally true, a good way to think about this is that respiring with nitrogen would require you to "un-explode TNT", putting back most of the energy you got from exploding it in the first place. And respiration is supposed to give you energy, not consume it! [Answer] While it is true that N2 requires a lot of energy to dissociate, it's not impossible. On Earth, legumes have bacteria that fixate N2 into other compounds. Your planet could similarly have organisms that use the energy in starlight to fixate N2. In fact, the high energy required could be what drives metabolism on your world. You don't need to bother with a carrier molecule. N2 is very soluble in ammonia (0.1124 vol/vol). Source: <https://pubchem.ncbi.nlm.nih.gov/compound/nitrogen#section=Solubility> A few other tidbits that may be useful for your world: * Your planet will be colder than Earth. Ammonia is a liquid between -78°C and -33°C. Chemical reactions will thus be slower: about (225 K / 300 K) = 75% as fast. * Ammonia has a good heat capacity and heat of vaporization. This means organisms can use their sap or blood to transport and dissipate heat, and also to sweat. * Ammonia is an excellent solvent. Ammonia is a polar molecule and will therefore dissolve other polar molecules such as water. Alkali metals such as sodium and potassium easily ionize, producing blue solutions that would give your planet's oceans a blue color. Other salts (such as those based on calcium and magnesium) also ionize easily. * Life will probably still be cellular. Hydrocarbons and lipids have been shown to form abiotically. They are nonpolar, and thus instead of dissolving in ammonia, they will form membranes, allowing the formation of enclosed spaces (cells). * Ammonia has an acid-base chemistry. It self-dissociates into an ammonium cation and an amide anion. The equilibrium constant of this reaction is about $10^{-30}$. As such, pH will range from 0 to 30, with 15 being a neutral solution. Many organic compounds undergo acidic or alkali reactions when dissolved in ammonia, forming polar compounds and thus becoming soluble. * If there is any H2O present, whatever doesn't dissolve in your oceans will freeze and sink to the bottom. The density of water ice is 917 kg/m3, whereas the density of ammonia is 682 kg/m3. * Whatever water does dissolve will be a moderate acid. Organisms would find the taste of water irritating, just as we consider ammonia's smell to be irritating. * On Earth, oxygen is the metabolic element. Its molecular form (O2) is an atmospheric gas and its hydride (H2O) forms the oceans. On your planet, nitrogen is the metabolic element. Its molecular form (N2) is an atmospheric gas and its hydride (NH3) forms the oceans. * In order to build practical organic molecules, you need both nitrogen and oxygen. On Earth, nitrogen occurs as N2 in the atmosphere, and certain bacteria "fix" it into organic molecules. On your planet, oxygen would occur mostly as H2O on the sea floor, with certain bacteria "fixing" it into organic molecules. * Don't bother with O2 in your atmosphere; it's too reactive. Let the ice at the bottom of the ocean be the reservoir of oxygen atoms. I suggest the name "Amina" for your planet. Indeed, had Earth been colder so the water froze and ammonia instead became the oceans, life could have evolved in this manner. [Answer] tldr; I think that, on an anaerobic ammonia-ocean world, hydrogen is probably the best choice for a respiratory gas. # Why we breathe oxygen Oxygen reacts more or less strongly with the other major elements involved in life (and, in fact, most other elements, fluorine being the exception). Allowing for the additional presence of hydrogen, all of the following reactions produce energy1: $$H\_2 + \frac{1}{2}O\_2 \to H\_2O \quad(\text{water; }\Delta H=-286J/mol)$$ $$C\_{s} + O\_2 \to CO\_2 \quad(\text{carbon dioxide; }\Delta H=-572J/mol)$$ $$\frac{1}{2}N\_2 + \frac{1}{2}H\_2 + \frac{3}{2}O\_2 \to HNO\_3 \quad(\text{nitric acid; }\Delta H=-207J/mol)$$ $$P\_s + \frac{3}{2}H\_2 + 2O\_2 \to H\_3PO\_4 \quad(\text{phosphoric acid; }\Delta H=-1288J/mol)$$ $$\frac{1}{8}S\_8 + H\_2 + 2O\_2 \to H\_2SO\_4 \quad(\text{sulfuric acid; }\Delta H=-814J/mol)$$ $$K\_s + \frac{1}{2}H\_2 + \frac{1}{2}O\_2 \to KOH \quad(\text{caustic potash; }\Delta H=-426J/mol)$$ $$Na\_s + \frac{1}{2}H\_2 + \frac{1}{2}O\_2 \to NaOH \quad(\text{lye; }\Delta H=-427J/mol)$$ Here I chose the most common non-organic form in an aerobic environment with water, although in the presence of water the acids and bases will dissociate, forming stable ions and releasing even more heat. In all of these cases, the enthalpy change $\Delta H$ is negative, meaning that the product has less enthalpy than the reactant, so heat is released and the reactions are exothermic. Another way to say this is that all of these chemicals burn in oxygen. This is remains true of more complex compounds formed from these elements, including some oxygen. Carbohydrates, proteins, fats, nucleic acids; everything life is made of burns in oxygen. This is exactly why we can get energy from food by combining it with oxygen. ## But if oxygen is so reactive with everything, why do we even have it in the atmosphere? As mentioned in at least one other answer, the presence of molecular oxygen on a planet, in combination with these other elements, is a good sign of the presence of life, because over geological time, the oxygen would react with the rest of the planet. In the case of Earth, oxygen is produced by photosynthesis, which takes energy in the form of sunlight and converts it to energy in the form of oxygen + fixed carbon. We tend to think of the fixed carbon as the energy source, because that it the part that the organism holds on to, and oxygen is everywhere "for free". But there is nothing inherently energetic about glucose; it's only a store of energy because there is oxygen to combine it with. For the rest of the discussion, I have completely left out oxygen and oxygen compounds. Of course, oxygen is a perfectly fine respiratory gas on an ammonia world! Water would be a mineral, though one which was not particularly rare, and which was quite soluble in ammonia. But, it is clear that you are looking for something different, so we will assume that none of the biochemical processes on your planet are energetic enough to break down water. (Although, some oxygen-containing organic compounds, such as alcohols, should still be possible.) # The problem with nitrogen As other answers have stated, nitrogen is just not as reactive as oxygen. It's hard to even think of the equivalent reactions with nitrogen instead of oxygen, because they aren't stable on Earth, with one exception: $$\frac{3}{2}H\_2 + \frac{1}{2}N\_2 \to NH\_3 \quad(\text{ammonia; }\Delta H=-46J/mol)$$ $$2C\_s + N\_2 \to (CN)\_2 \quad(\text{cyanogen; }\Delta H=+309J/mol)$$ $$C\_s + \frac{1}{2}H\_2 + \frac{1}{2}N\_2 \to HCN \quad(\text{hydrogen cyanide; }\Delta H=+110J/mol)$$ $$P\_s + \frac{1}{2}N\_2 \to PN \quad(\text{phosphorus mononitride; }\Delta H=-???J/mol)$$ $$\frac{1}{2}S\_8 + 2N\_2 \to S\_4N\_4 \quad(\text{tetrasulfur tetranitride; }\Delta H=+460J/mol)$$ $$3K\_s + \frac{1}{2}N\_2 \to K\_3N \quad(\text{potassium nitride; }\Delta H=+???J/mol)$$ $$3Na\_s + \frac{1}{2}N\_2 \to Na\_3N \quad(\text{sodium nitride; }\Delta H=+???J/mol)$$ [Cyanogen](https://en.wikipedia.org/wiki/Cyanogen) and [Hydrogen cyanide](https://en.wikipedia.org/wiki/Hydrogen_cyanide) would be liquids on your planet. Hydrogen cyanide is a weak acid with (aqueous) $pK\_a$ and density extremely close to that of ammonia. I suspect it is soluble or even miscible in ammonia, but I am not sure. Cyanogen is probably less so. [Phosphorus mononitride](https://en.wikipedia.org/wiki/Phosphorus_mononitride) is a gas found in the atmosphere of Jupiter, but there's no properties listed. Based on its presence in Jupiter's atmosphere, I assume it is stable with respect to $N\_2$ and solid $P$ (or it would decompose into them) and that it is a gas at liquid ammonia temperatures. [Tetrasulfur tetranitride](https://en.wikipedia.org/wiki/Tetrasulfur_tetranitride) is an explosive solid. [Sodium and potassium nitride](https://en.wikipedia.org/wiki/Alkali_metal#Nitrides_and_pnictides) are highly unstable. Hydrogen cyanide is an interesting candidate for an oxidizing agent in your world. It reacts with a wide variety of organic compounds to produce energy. However, this process doesn't really break the compounds down; rather it attaches even more cyanide groups. # Hydrogen to the rescue Hydrogen combines with most common elements to form simple, stable compounds. $$C\_s + 2H\_2 \to CH\_4 \quad(\text{methane; }\Delta H=-75J/mol)$$ $$\frac{1}{2} N\_2 + \frac{3}{2}H\_2 \to NH\_3 \quad(\text{ammonia; }\Delta H=-46J/mol)$$ $$\frac{1}{8} S\_8 + H\_2 \to H\_2S \quad(\text{hydrogen sulfide; }\Delta H=-21J/mol)$$ $$P\_s + \frac{3}{2}H\_2 \to PH\_3 \quad(\text{phosphine/phosphane; }\Delta H=+5J/mol)$$ $$Na\_s + \frac{1}{2}H\_2 \to NaH \quad(\text{sodium hydride; }\Delta H=-56J/mol)$$ $$K\_s + \frac{1}{2}H\_2 \to KH \quad(\text{potassium hydride; }\Delta H=-54J/mol)$$ In most of these reactions, hydrogen is a reducing agent, rather than an oxidizer like oxygen (but it is an oxidizer in the last 2). Furthermore, more complicated organic molecules can also be broken down by hydrogen for energy profit: $$(CH\_3)\_2 + H\_2 \to 2CH\_4 \quad(\text{ethane; }\Delta H=-66J/mol)$$ $$NH\_2CH\_3 + H\_2 \to CH\_4 + NH3 \quad(\text{methylamine; }\Delta H=-97J/mol)$$ Do note that this is a substantially lower energy scale than we get with oxygen: $$(CH\_3)\_2 + \frac{7}{2}O\_2 \to 2CO\_2 + 3H\_2O \quad(\text{ethane; }\Delta H=-1562J/mol)$$ $$NH\_2CH\_3 + \frac{3}{2}O\_2 \to CO\_2 + NH\_3 + H\_2O \quad(\text{methylamine; }\Delta H=-702J/mol)$$ In combination with the low temperature, this means that life would happen VERY SLOWLY. Importantly, hydrogen is a gas at the low temperatures of an ammonia world. However, you will need a big planet with a strong gravitational field in order to hold on to it; this will mean high surface pressure, and apparently [hydrogen is quite soluble in ammonia at high pressure](https://pubs.acs.org/doi/abs/10.1021/ja01289a055). Fortunately, hydrogen is the most common element in the universe, so any planet large enough to hold on to it usually has plenty. See also some other discussion at [the question about that](https://worldbuilding.stackexchange.com/questions/29386/an-ammonia-not-water-based-alien-race-that-breaths-hydrogen-is-it-believabl), although I obviously disagree with the accepted answer. 1: All values from the respective compound pages on Wikipedia. I used enthalpies instead of Gibbs' free energy, which would be more appropriate, because most compounds didn't have Gibbs' free energy listed. Gibbs' free energy could in principle be calculated from the enthalpy and entropy, which was given, but I couldn't find entropies for the free elements. Additionally, all of these are at standard temperature and pressure, which is not exactly relevant to an ammonia world. In most cases the signs should be the same, but if you really want to be hard science fiction, you could try to figure out the corrections. [Answer] N2 is a stable low-energy compound. It will be produced, so there must be a way to remove it as part of the cycle. If you want it to replace O2, it's natural to want to do it with photosynthesis. This may be an issue, because if it takes high-energy ionizing radiation to do it, that could continually mess up the other compounds and catalysts needed for life. Maybe it could be done in steps, that each can be done with lower-energy light. My first stab at the first step would be 2 N2 + 2 NH3 -> 3 N2H2 Probably the ammonias would be bonded to something like we use acetyl-CoA instead of just acetate. Four reactants at once doesn't look plausible either, but diimide is the end product I want. So you go from something totally unreactive, to something very reactive with a double bond that can be broken later. I expect a real chemist could show why this is not workable and suggest something better. But the fundamental idea is right. You start with an energy source and convert N2 to something that has more energy. And later when you want to use energy, you take something like ammonia and pull off the hydrogens to stick them onto something else, and get low-energy N2 back. For example: 2 C2H2 + 2 NH3 -> 2 CH4 + 2 N2. Acetylene to methane and ammonia to nitrogen. And you have a way to use the released energy. [Answer] In short: absolutely no. And you're missing the point of oxygen: Oxygen is an atmospheric pollutant on earth. No planet could ever have oxygen in its atmosphere without life. Life creates it and everything reacts with it eventually. If you ever found oxygen with a telescope you found life on a distant world. The word oxidation is called that for a reason: It is oxygen's ready ability to "react" to [break up hydrocarbons](https://en.wikipedia.org/wiki/Citric_acid_cycle) in the body that gives it its value as fuel. And it ***is*** fuel. Conversely nitrogen is not an atmospheric pollutant - it is common throughout the universe as is hydrogen and CO2 and it is a very inert gas and has [no value as an oxidiser](https://en.wikipedia.org/wiki/Oxidizing_agent). So it has no fuel value. Using ammonia only "seems" plausible because of its behaviour at low temperatures resembles water (to a small degree), but if you put it under analysis the equivalency between ammonia and water is merely a facade: water has far more properties than ammonia. Ammonia does not (like water): * expand upon freezing (no "ice" floating as a skin acting as an insulator) * possesses far lower specific heat capacity (changes temperature far more) * is a FAR FAR less of a universal solvent (water dissolves almost everything) * is only liquid at very much lower temperature temperature (making it yet again exponentially) vastly less useful as a universal solvent, and impeding almost all reactions of solutes It is for these reasons that is is considered there is literally no theoretical possible substitute for water/oxygen in terms of life in terms of the astonishing solvent properties of water and ionic bond handling and oxidation energy recoup of metabolising via oxygen. Ammonia Silicon based life forms (organic life forms) are genuinely being revealed as complete non starters (on a level with using plutonium/helium/throws dart at the periodic table), and died as a source of hard science fiction along with the Drakes Equation in the 70's and 80s' ]

[Question] [ I have a regular planet with regular gravity that pulls all on the surface towards the center. In almost all ways, it is identical to our own Earth. The major difference is that, beneath the south pole, a couple dozen kilometers below sea level is the "demon core" and this attracts "demons". These creatures interact with matter in a completely mundane manner, the only exception being that they are not affected by gravity, but rather pulled towards the "demon core" as if it were the center of the Earth with a pseudo-gravitational force. The difference is that unlike the Earth where gravity is net zero at the center, this "demon core" is assumed to be a point-source. Here a quick diagram: [](https://i.stack.imgur.com/nH6IBl.png) Effectively, this means that almost everywhere on Earth "demons" seem to stand in a slanted way or at an angle when they walk around, and the only place they appear to interact with gravity correctly (albeit slightly weaker) is at the north pole because the gravitational vectors line up. For demons, areas near the south pole are incredibly dangerous because the ocean's surface is "steep" enough that they can fall down it and skip across the water until they come to a (usually violent) stop. No other matter besides demonflesh is pulled towards this demon core, so if they were to wear mundane clothing, for example, it would look quite bizarre as it would still be under the influence of regular gravity. **The Question:** Is there any physics "gotcha" I need to watch out for with such a setup? For example, would it be possible to make a perpetual motion machine somehow by putting a demon on a properly positioned Ferris wheel or something? I suspect not, as this demon-gravity is still a conservative force, like gravity, but I'm not sure. [Answer] > > Is there any physics "gotcha" I need to watch out for with such a setup? For example, would it be possible to make a perpetual motion machine somehow by putting a demon on a properly positioned Ferris wheel or something? > > > # Nope, you're good This is not much different from magnets and ferromagnetic metals - supposing you have a huge magnet or an Oscar Isaac-amped Michael Fassbender at the south pole. We can't do it with magnets, we won't be able to do it with demons. Now of course, being close enough it would seem that your demon core would work like a magnetic monopole, since it is a point source. Still it wouldn't allow for perpetual machines. I saw someone commenting somewhere else in the internet that with a monopole you could have a DC motor without a commutator, which is an interesting application, but still has nothing to do with perpetual machines. What you need to watch out for is that there might be a huge area of exclusion for demons. It is exact as you mention for one approaching the south pole, but it would extend far beyond it. A round'ish, not so dense demon left on the equator might reach the south pole in finite time by a combination of rolling and floating, and the closer they get, the faster they'll go and the harder it'll be to reverse their motion. --- Edit: it just came, this opens up a new branch of physics called # Orbital demonics I wish I could say this is not rocket science, but it is. I'll spare you the math but any demon accelerating towards the demon core from hundreds of kilometers or miles away and bypassing it - or being deflected by it - will go really really far past the horizon, possibly exiting the atmosphere. Those who don't hit anything along the way will either eventually fall back and impact against the ground, possibly restarting the cycle, or given enough extra push from other sources will escape the planet (actually the core) altogether. Those over escape velocity who hit something on the way after going past the demon core may be slowed down to orbital velocity. They will orbit the demon core rather than the planet's center of mass, and this is where things get interesting and bizarre. Regular satellites will always cross the plane which contains their parent body's equator. This is not the planet for your demons, so if they have zero or little north-south movement when they start orbiting they will circle around the south pole in space, but never going too far away from it. This is just not possible for a satellite in real life and may have interesting applications. In real life when we want something over the poles we need a polar orbit, which means always visiting both poles in an orbital period, which is wasteful if you are interested in only one. If their orbit has a considerable angle relative to the equator, though... If is it much larger than the planet they may be safe, but most likely it will intersect the planet (that is, it will be a pagh that passes through the planet). This means they will eventually hit the ground at bat out of hell speeds. We're talking about multiple miles or kilometers per **second** at the very least. Whether they bounce back, become a huge puddle or something else entirely is up to you. ## With a caveat though This is considering ideal conditions. Most likely, since your demons interact with matter, they will be slowed down by air. They will eventually reach a terminal velocity orders of magnitude less than escape velocity. The visible effect would be demons skidding towards the south pole at speeds comparable to that of an airplane. It would still hurt a lot to stay on their path. ## Going further and beyond I specially love this comment from [Shufflepants](https://worldbuilding.stackexchange.com/users/3637/shufflepants): > > I however imagine, because only demons are attracted by the demon core, there might be a potential for reducing the fuel cost of launching regular satellites into orbit by including some demons inside your launch craft, accelerating up and towards the south pole, and then jettisoning the demons as you pass over the south pole. > > > [Answer] Be aware that the demon core must be attracted towards demons with an equal and opposite force. Imagine two demons standing at the equator on opposite sides. They each are pulled (locally) down and south. The down forces cancel; the south forces do not. For everything to balance there must be a northward force exerted on the demon core. Depending on the number of demons and where they are, this could be significant. This puts a lower bound on how large the demon sphere is, lest it get pulled down through the rock. The compressive strength of rock varies, but let's ballpark it as 200MPa. And let's say the sphere pulls demons with the same force as Earth, were it a point source (so 1g at 1 Earth radius, and inverse-square from there). If there's a million demons - ballpark as 100kg each nominal - standing on the North pole... Each one is 2r away from the core, so 1/4g, so the core is pulled North with a force of about 250 mega newtons. Dividing this through, we require - in decent rock - a cross-sectional area of the sphere of $\ge1.2m^2$, lest the sphere get pulled down through the rock. Ditto, consider a hapless demon at the South pole. It's ~24km away from the core itself, so it now weighs, what, 7000 tons or so? Something silly like that. Anyway, the minimum cross-sectional area of rock required to hold said force is a 58cm square. This means that it's entirely possible that said demon would be pulled *through the ground and rock* towards the core. (Releasing an awful lot of energy in the process, of course.) There's also the observation that if a demon ever managed to make it *to* said demon core, it'd release an "infinite" amount of energy. This tends to make physicists sad. You can alleviate this to an extent by having demons attracted to the entirety of said sphere - although be aware that even with a ten-meter sphere the energy release would be... significant. Something like a megaton of TNT equivalent per demon. Which could easily damage enough to allow other demons (previously squashed against nearby bedrock) to fall to said sphere... it's the [iron catastrophe](https://en.wikipedia.org/wiki/Iron_catastrophe) in demon form! [Answer] # Likely Fine Yes, having an effective "second" gravity opens up a lot of possibilities, but our current understanding of the universe should not raise any objections. The demons need to work against their gravity to gain more potential energy, just like we do. There may be some ramifications when we get into deeper physics, especially Relativity. Everything seems to respect curvature of space, even light: so why not demons? Are there demon black holes, and what does that look like? Do they have the same fundamental limits, like the speed of light? (All of this is likely irrelevant to your story, though.) Why are demons subject to this force, EM, strong nuclear, and weak nuclear forces but not gravity? Can we force matter to switch from one to another? If yes, then we really have some grounds for "physics breaking" shenanigans. [Answer] Assuming that the demon core has a similar pull to that of earth (ie its "demon mass" is the same as earth). Then there may be some issues. Firstly you must realize that the 'demon gravity' experienced by demons is going to be vastly different depending on location. At the north pole about 13000km away from the core, their experienced gravity will be about 2.4 m/s^2, At the equator, about 9000km away from the core, about 5m/s^2 and at the south pole about 24km away from the core, about 700000 m/s^2. All of this has major implications as if you have demons living on the north pole or anywhere north of the equator, they will be incredible weak physically compared to humans who have to live in much stronger gravity. It also means there is no chance of demons ever being able to go to the south pole, they and their mode of transportation would be crushed under their weight as they approached the south pole. The next problem is if a demon, or parts of one, were to approach the point of the demon core, gravity would essentially be infinite. What that does to demon matter, I don't know. What if you had normal matter wrapped in demon matter? [Answer] # Perpetual motion You probably have a Perpetual motion machine. This is because demons have to eat, defecate or die. At a certain point this requires a change from normal to demon, or from demon to normal. Let's imagine no change happens. If the demon eats, it'll replace parts of itself with the sustenance. It can't only eat demon, so it would replace itself over time with earthly material. This removes the demon idea you have going. If it does change, you can gain or remove energy from the system. Say one is close to the south pole and eats something. It becomes demon, suddenly gaining a lot of attraction to the demon core. You let this energy out by moving to it, gaining friction, and thus heat and motion energy. Then it defecates. The result is normal material again, which can be transported up with low energy cost. The easiest to imagine it is if the demon is an astronaut above the south pole. It eats a lot, after which it crashes down with the high gravity. After it has done it's business you travel back up the lower normal Earth gravity with food, repeating the process. As the food goes up with 9m/s gravity and comes down at (as some estimate) 7000m/s gravity, you're making energy. You can solve this by having the demons never eat, drink or otherwise gain Earthly materials, but this would be strange if they weren't at least breathing. The other is to have them eat, drink and breathe, but always expell whatever they take up. This has many more implications, like demons not regenerating. That means they can't even take the slow sanding of the skin over time. If they magically regenerate, you have a Perpetual motion again. As mass can be added and removed for extra energy. Even in death this is a problem. If a demon is killed and doesn't revert, you'll get more and more demon essence. If it disappears or something, you can create extra energy by having demons spawn in, pushed and killed at the south pole and disappear again. ## Not as bad as you think Might not all be bad. Even if such Perpetual motion is realised by some people, it might be hard or impossible to utilise. In addition, it might be impractical to gain useful energy from it. Though it breaks the laws of physics, so does having demons and a demon core. The impractical nature prevents useful usage of the energy. Even if you did find a practical way to harness such power in large quantities, how would you put such plans into motion? [Answer] One thing missed by others is that it breaks General Relativity. If demons interact with matter they need to have some inertial mass. If they are not affected by gravity they don't have gravitational mass. General Relativity does away with the notion of gravity as a force. Things are not attracted by other objects - the objects curve the spacetime and objects 'falling' just move along straight lines in curved space. Because it is not a force but a consequence of spacetime you can say that inertial mass and gravitational mass must be the same (to oversimplify a bit). But in your example system they are not. So General Relativity cannot be true in your universe (or rather it cannot explain all known phenomena). That raises the question if gravity behaves classically in your universe (just plug in a 19th century understanding of gravity and mechanics and you should be good, maybe with quantum physics - but no GPS for you) or we still get predictions of General Relativity but we know it cannot be correct as it doesn't work on Demons. The good news is that we already know that Quantum Physics and General Relativity cannot be both correct. So you can just handwave the question of 'what happens if you accelerate a demon to relativistic speeds' or 'how does spacetime work' with 'good question - physicists would love to put a demon in a particle accelerator but it is not there yet'. If demons were discovered by physicists recently you can comment that they know that General Relativity is not correct but they have no idea exactly how. [Answer] Not locally, but it may have affects on the cosmos. Gravity, matter and energy are all connected by the medium of spacetime. Matter and energy are the same stuff, just more and less organized respectively. Gravity is a side effect of matter - the more that densely organized matter is collected, the more gravity surrounds it - and time is a side effect of gravity. This part is weird, but basically, the more gravity something is exposed to, the more time passes for it. For demons to not be affected by gravity suggests that they exist in a different, overlapping system, made up of an entirely different sort of material - lets call it demon matter. Demon matter also exists in the medium of spacetime, and I think it's okay to say that it can overlap with or interact with matter and energy as we know it while still mostly ignoring gravity. Light hits them and bounces off, people can touch them or be touched by them, but gravity doesn't really care about them. Probably what you would find is that demons are effected by it on a very small scale that ends up rounding down to zero in all but the theoretical sense. So, collections of demon matter create demon gravity that affects other demon matter. So far, so good. The thing is, that gravity should also create its own independent time. Demons would have their own sense of time relative to how much demon gravity affects them. Locally, this is still fine. You can just say that the concentration of demon gravity is close enough to the concentration of regular gravity around the planet to exude a similar field, thus leading demons to have about the same experience of time as everything else on the planet (though, allowing for small differences, letting them experience things slower or faster, could add to their demonic feel. it would make it harder for them to recognize or communicate with humans as equals, and could be the basis for powers they have that humans don't) The biggest question mark for me is the cosmos. What does the rest of the solar system, the universe, look like if this is true? If it's happening here, it must be happening in the rest of the universe as well. If there is Demon matter and demon gravity, is there demon energy - demon light, with its own independent speed of light? Demon radiation, with its own variety of wavelengths? Having its own gravity, does demon matter have other properties - magnetic feilds, ionic bonds, etc.? Are there Demon Black Holes, Demon Stars, Demon Galaxies? If Demon matter can experience time differently from other matter, while taking up the same space, what does that look like? If demon matter can move faster than the speed of light for regular matter, does it break laws of causality? I don't think you need to answer all of these questions to write your story. But especially if some characters in your story are science literate, having some suggestion of demon matter outside of earth will help readers to suspend disbelief. Considering how much we don't know about the cosmos already, I think its perfectly fair to leave many of these questions as mysteries or with half answers that serve a practical purpose but aren't fully satisfying. Lots of what we currently know about the cosmos is exactly like that - unsatisfying. That's why we keep pushing to know more. [Answer] ## This works fairly well, but there are some details. To make the demons stand up consistently under gravity at any point on the planet, we want the force to *not* be inverse square. There is a precedent for this with [strong nuclear force](https://en.wikipedia.org/wiki/Strong_nuclear_force). This is a very different situation, but unknown physics are ... unknowable. If you go this way, the demons fall straight down toward your core even from planets around other stars. Making the demons *not* be affected by normal gravity is the real sticking point. If the demon starts falling toward the demon core, you expect it to accelerate at some rate - the force being divided by its *inertial mass* to get acceleration. There is a big angels-on-a-pin discussion to be made about whether [inertial mass](https://en.wikipedia.org/wiki/Inertial_mass) is always the same as gravitational mass, and if your physicists see something like this, they will be forced to pay attention. You could avoid that if the demons are just *really light*, but batting demons around like a whiffle ball is not the way I'm expecting you to go with the story. Don't sweat the conservation of energy. You can calculate exactly how much energy it takes to lift the demon to any point (it's just the distance times the constant force the way I pictured it), and that doesn't depend on the route, so no perpetual motion. If the demons have any gravitational mass, you'd have to calculate that also, but it would again be a gravitational potential not depending on the route taken. [Answer] Under the currently popular models of phsyics there are two forms of matter: normal (for us anyway) and dark. Normal matter is all the physical stuff that shows up in the Standard Model: electrons, protons, neutrinos and so on. Dark matter - if you believe in the stuff - is a form of matter that doesn't interact much with normal matter but still warps spacetime, thus affecting gravity. What you have is a third class of matter that strongly interacts with baryonic matter but doesn't interact with our spacetime. Instead it warps and moves relative to some other spacetime matrix that exists alongside our own. Perhaps the particles of demonic matter don't interact with the Higgs field but with some other field that only demonic matter *can* interact with. The other basic fields work the same, which is why we can interact with demonic matter at all. In fact apart from gravity, everything else works just the same as normal matter interactions. Which is a problem for your demon core because although it doesn't exert gravitational force, it still has all those other interactions. You have a ball of extremely dense demonic matter with about the same effective mass as the Earth, surrounded by normal matter that is constantly accelerating in the direction of the Sun. As the Earth proceeds around its' orbit it now has to provide enough force to push the demon core around with it, and all that force has to be applied on the very small surface area of the core... and thus on the very small amount of material pushing on the core. I give it a couple of days before it rips a spiral channel through the Earth and wanders off into space. To balance this we need a source of demonic gravity the same size as our Sun, but made out of stuff that doesn't interact with normal matter and only interacts gravitationally with demon matter. Now we have a fourth type of physical stuff in the universe: dark demon matter! OK, we still can't explain why it would just happen to follow the same path around the galaxy as our sun does, but let's hope like hell it keeps doing so otherwise Earth's getting an unexpected south polar reaming. Under these conditions the conservation laws are preserved, so there's no free energy to be had. The fact that some matter has a skewed gravity vector compared to others is interesting, but only as long as it doesn't mix too heavily with normal matter. Which is a real problem if organic demonic life is a thing. Let's take a human and flip all her subatomic particles for the demonic equivalent. Assuming she doesn't die during the process, the only difference is the pull of gravity. She takes a breath of normal air, her body uses combines it with demonic carbon atoms and breathes out hybrid CO2... which immediately starts heading south for the (insert season here). Over time the south pole will be covered in a miles-thick high density cloud of CO2 composed of demon carbon bonded to normal oxygen. The oceans in the area turn to carbolic acid and all oxygen-dependent life in the south polar region dies horribly. Meanwhile the reduced availability of normal oxygen in the rest of the world causes problems for the other inhabitants of the planet. Similar things start to happen with other metabolic products. High quantities of demonic matter in the body's waste products cause problems for waste processing systems, piling up on the side of sewers and treatment tanks or floating above (and to the side of) the heavier normal matter in northern latitudes. Meanwhile the demonic matter in our test subject's body is being replaced over time by normal matter, with similar problems. Intracellular structures start to differentiate because of the difference in gravity strength and direction between the different types of matter until the delicate balance of the cells fails and they die. Eventually all of the parts of the body that age out and get replaced - which is most of the body except for things like bones and a few other bits - will be replaced with a combination of demon and normal matter. Sadly the problems caused by the different gravitational forces each type of matter experiences will likely kill the subject long before her body reaches equilibrium unless she's luck enough to be in that sweet spot a couple thousand miles above the South Pole where the gravity vectors are equal. On the plus side, the availability of materials with different gravitational alignment makes it possible to build taller structures at the north pole. *Much* taller. Given a few decades we can build up a few miles off the surface using a demonic alloy that thinks it's on a low-gravity planet. We can build launch vehicles with the same materials, allowing us to get a payload off the ground much cheaper than equatorial launch facilities, even with having to burn fuel to get up to orbital velocity. Orbital mechanics will get a bit screwy with having to worry about hybrid materials being pulled in different directions depending on their purity, but that's what computers are there for I guess. So the best we can get is a bit of a break on launch costs and a few other similar gimmicks, at the cost of potentially ending a substantial amount of life on the planet. I vote no. [Answer] When you compare normal gravity to demon gravity, the different gravitational origin point is going to impact two things: magnitude and direction. For both of these cases, your latitude is going to be important. As far as magnitude goes, 45ºS latitude is the point where demon gravity is equal to regular gravity. Your distance from both center points is the same. Everywhere north of here demon gravity will be weaker, and everywhere south it will be stronger. A demon on the north pole would feel 25% of the gravitational pull as they would at 45ºS. Only the tip of South America and a wee bit of New Zealand extend below 45ºS, so a demon would generally feel less gravitational pull than a human at the same location. The most irritating part of this is the gravity *gradients* (the change in potential energy needed to travel between two points). A walk over flat terrain is easy for a human but might be a fairly steep hill for a demon, or vice versa. Humans can at least *see* the ground sloping away from them. Without those visual clues, demons would likely be on the clumsy side. Regarding the orientation of gravity, the difference between the two gravitational vectors will be zero at the north pole, 45º at the equator, and nearly 90º at the south pole. Demons in Iceland would walk nearly vertically. In Italy they'd be leaning about 25º off the vertical (almost like the demons themselves were *written in italics*, ha!). By the time you got to the Tropic of Cancer, you'd be tilted at such an angle (>33º) that you'd start to have practical problems. The force of friction between you and the ground at that point would be $sin(90-33) = 54\%$ of what a human of the same *weight* would experience. Lower gravitational force means you'd weigh less than that human, making the problem even worse. Demons would have serious traction problems just walking around, and slippery surfaces would be downright impassable. Cleats would be standard footwear for demons, and they would greatly prefer being outdoors on soft dirt over indoors on hard floors. By the time you hit the equator you'd be slanted at 45º, and passing through a door would be less walking and more acrobatics. How far south a demon could realistically go would depend on their footwear, their athletic ability, and the local terrain. Practically speaking, however, demons in the southern hemisphere would be rare. These two things together open up an interesting possibility. You can use Antarctica as a demon prison colony. Gravity has an inverse-square relationship to distance so it would be unbearably strong at the south pole. Gravity's vector relative to the terrain would be so severe that demons would have close to zero traction. Escaping would be like scaling a nearly-vertical, icy-slick cliff face that's more than 2000km tall. Escape would require some sort of powered vehicle, and that's just to get to the Antarctic coast. Gravity is still so strong (and in a bad direction) at that point that you wouldn't be buoyant, so you'd need some sort of ship to get you back to civilization. If you want to make this scenario less extreme, move the center of demon gravity farther into the planet. Moving the demons' gravitational point 1/3 of the way to the surface instead of all the way will still have noticeable consequences but would avoid many of the extremes. Just whatever you do, don't move the center of gravity *above* the surface. If you somehow get the two centers of gravity working against each other (meaning the angle between the two gravity vectors is more than 90º), you start opening up the doors for all sorts of weirdness. ]

[Question] [ **This question already has answers here**: [How would the road network change, after all cars are self-driving?](/questions/4107/how-would-the-road-network-change-after-all-cars-are-self-driving) (10 answers) Closed 8 years ago. At a typical intersection that uses red lights to control traffic, vehicles traveling on one roadway have a green light and can travel through the intersection, often at full speed, while vehicles traveling on the intersecting roadway have a red light and must come to a full stop until the signal changes. This is a good system for human-controlled vehicles, but I'm wondering if, in a world where all vehicles are automated, it might be possible to eliminate red lights completely and instead use precision timing to permit traffic from both roadways to pass through the intersection in roughly an A-B-A-B pattern. Kind of like how some marching bands can have two line of marchers pass through each other orthogonally. What would be the limiting factors to such a system? Let's assume that we'd never want two vehicles to come any closer to each other orthogonally than they would driving parallel in adjacent lanes. At what kind of traffic density could traffic in both roadways go full-speed through the intersection? [Answer] ## Yes, for some cases. Assuming the conditions you've given, mainly this is "a world where all vehicles are automated". **Interleaved single vehicles** For intersecting traffic travelling the same speed, vehicles need to stay 7.4 meters apart. Assuming you have perfect information and control of the cars, the spacing is just a car with enough space in front or behind to allow another car to pass as you described. If the car is 4.5 meters long and you only need one meter *diagonally*, (since the closest the cars come is at the corner for an orthogonal approach) which means $1\over \sqrt 2$ or $\approx 0.707 $ meters in front and back for buffer. Since the car approaching the passing car is approaching the other side, the width of about 1.5 meters also should be accounted for. So, 4.5 m length, plus $\sqrt 2$ m for the buffers, plus the 1.5 m width is about 7.4 meters total space required per car. If a car is traveling at 100 km/h, it travels its own length and buffer space in just over a quarter of a second. This means if that car is travelling perpendicular to a stream of traffic, there needs to be at least that much time gap between two of the cars (with all buffers accounted for). If they're travelling at the same speed, then that time in terms of distance is that same as the intersecting car length and its buffer. The density would then be about 135 cars per kilometer. Around "[jam density](http://en.wikipedia.org/wiki/Traffic_flow#Overview)", which is ten times higher than today's "stable" density for traffic flow. I'm not accounting for the wind turbulence between vehicles passing each other at high speed, which would be rather confounding to this whole exercise. **Interleaved trains of vehicles** As mentioned by JDługosz in the comments the cars could also be in tightly packed groups, with the same average density. So the density won't change, but vehicle efficiency can be increased. Higher efficiency can be gained by grouping vehicles close together because the drag on rear vehicles is decreased; they ride in the draft of the first. The efficiency won't increase dramatically beyond the already significant boost from the sub-10 meter following distance, but would likely be worth the trade-off. Turbulence between passing would be minimized as it only greatly affects the lead cars. **Hybrid interleaving** Also pointed out in the comments, the high density closely packed traffic could also be used *up to* the intersections where the cars actually accelerate to gain the proper spacing. This will still have the turbulence problems as individual vehicles. **The reason this will not happen anytime soon** The human occupants will freak-the-eff out. Grandpa will instinctively lurch the wheel to avoid hitting one car only to slam into another (this is a joke, clearly manual control would be disabled during such a maneuver). You can test this freak out on yourself, just watch a few "near miss" videos and tell me you don't clench a little even watching a video for the second time when you *know* what will happen. Now imagine being *in* the vehicle and not knowing. More likely, for safety and passenger sanity, [high speed roundabouts](http://roadwaystandards.dot.wi.gov/standards/fdm/forms/11-26-030p01.pdf) will be used. This would: * Minimize car-to-car relative velocities. * The turbulence problems associated with interleaving high-speed cars will be reduced * Allow vehicles to do something other than go straight through an intersection. * Require more space. But this would only be for intersections that: * Don't also need to allow pedestrians to cross, people will still be walking around in the future, presumably. * Don't have any other unautomated vehicles, like bikes, segways, or McFly-hoverboards. * Restrict access to fully automated vehicles. * Don't have space restrictions like those inside cities. --- One other very cool idea about automated cars is having a form of [Uber](https://www.uber.com/), where people let their car go drive people around in full auto mode. [Answer] **No**, because not all vehicles will be automated. You also need to consider bicycles, and to some extent pedestrians. So for the non-automated users of roadways, some sort of red/green light system will remain. So lights will stay, but automated cars will automatically time themselves to hit lights instead of doing stop/go traffic. You'll get something similar to your marching band pattern, but "A" might be a block of 10 cars, followed by a large gap, then "B" as another large group of cars. And so on. This leaves room for pedestrians and reduces the possibility that people in the cars will freak out and think they're almost dying. [Answer] Yes, this is completely possible and the basic logic for it has already been mapped out -- <http://www.citylab.com/tech/2012/03/what-intersections-would-look-world-driverless-cars/1377/> Scroll down to the video near the end of the page to see a simulation of a busy 6-lane intersection with fully automated vehicles. Note that the simulation includes human-driven vehilcles as well -- "The yellow cars pausing at the intersection in this simulation are old-timey human-driven vehicles.... Those human-driven cars would have to wait for a signal that would be optimized based on what everyone else is doing. And the same would be true of pedestrians and bike riders." [Answer] Not today, but we certainly could, but you would still have to stop and many times. This is just based on me being a transportation planner for several years in the recent past. **Marching-band style** - I think we would have to convert all of the junctions into roundabouts. The problem is that with unbalanced intersections, you don't want a roundabout: in rush-hour where everyone is making a 3/4 left turn, some poor suckers are going to have to wait. Also, there will be times when you have to stop for pedestrian & cyclist movements, but our driverless cars are getting really good at handling that. **Alternative** - We have very sophisticated (and really cool!) models, which have come a long way. In Florida, we had cameras at every light as well, for inserting data into the model, for turning a signal if traffic didn't behave as expected, and for communicating with the other signals downstream. The combination of the model, the cameras, etc., could become sophisticated enough to communicate with the cars, so that lights aren't needed. But your car would most likely still have to "stop" at some critical junctions, and to allow for pedestrian movements. **Note** - By the time we are fully driverless, there will presumably be a lot more cars on the road from (1) population (2) from the ability for people to move out of town, and (3) ability for some disabled & visually impaired to 'drive'. Further, because of these smart cars, we'll have a lot more capacity so you won't be seeing as much rapid expansion as you do now. So it will be the "same" roads, but with a lot more vehicles happily crammed into them. [Answer] **No** because it is **not fault tolerant** This would work perfectly until the first car suffers a blowout or a sensor malfunction or until a child runs out into the road. Automated vehicles will be designed to move in patterns that are fault resistant or otherwise they will result in spectacular pile ups. Intercrossing the cars at speed means that no car is in a position to safely take emergency action to avoid impact. This is not the case with, for example, close-following car "trains" since automated cars have no reaction time (or trivial reaction time, more accurately) and thus the whole "train" can be brought to a halt as a single unit and avoid accident. **Yes** because **signal lights are designed to be human understandable** Answering just the first part of the question and ignoring the second part, it seems likely that red lights themselves will be removed and the city will instead communicate directly with the cars to interrogate them about their destinations and plan traffic flows accordingly. Cars would still stop at intersections but advanced traffic flow management would minimise the time that they would do so and avoid needless waits at uncontested intersections. The only lights needed would be those that signal to pedestrians when they are safe to cross the road. [Answer] This is rather unlikely, from an engineering perspective. A marching band can pull off a trick like that because they're moving relatively slowly, and because a person is generally about as wide (distance from right to left) as they are long (distance from front to back). Cars, on the other hand, are considerably longer than they are wide. This means, as Samuel pointed out in his answer, that you need very wide buffers between cars in order to make it work. But there are problems with that. First, the system might work well, if timed perfectly, for intersecting flows of cars, but as soon as the first emergency vehicle, bus, or semi truck shows up at an intersection, the entire scheme blows up. (Hopefully not literally!) Second, the required spacing makes for very low vehicle density, when one of the main selling points for the idea of ubiquitous automated vehicles is that such a system could safely handle *high* vehicle density at high speeds, while human drivers can't. To make this work, then, you'd have to either stay at low density the whole time, or be constantly speeding up and slowing down, with the line of cars expanding and contracting like an accordion, as you move through the city. Acceleration and deceleration waste energy; the most efficient way to drive is to get up to a stable speed and stay there. A more likely scenario would be to have your AI actively control the traffic lights to improve efficiency. Have you ever been stuck for what feels like five minutes at a red light, with long lines of cars stacked up in both directions, while maybe one car every ten seconds goes by in the cross street? Or had to wait through multiple red lights to make a left turn because the green left arrow only lets two or three cars through at a time for whatever insane reason? (Why yes, I *have* lived in LA. Why do you ask?) Fix problems like these and you'll do a lot more good than you would by eliminating stoplights entirely. (Not to mention it works a lot better during the long transitional phase when most cars are still driven by a human being.) [Answer] Though you might not have red lights, you might still end up with behavior similar to modern intersections, albeit with much more efficiency. For instance, while cars constantly intersecting at full speed introduces way too many variables and unnecessary dangers, I can see cars positioning themselves into bursts; you either speed up or slow down until cars on your road are clumped together, and then passage of the intersection alternates between these clumps. This should only provide a minimal delay at each light, rather than the possible minutes-long waits we have today. After you get into a burst, it may seem like you're not waiting at all. Plus, this allows for a more scalable design than to simply throw a car at an intersection and try to figure out who needs to slow down to avoid a wreck; this way, cars can be handled in groups of known size and speed, which makes adding a hundred feet or so for burst switching not all that bad. However, at the end of the day the roadways will probably still get congested; the efficiencies of automated transportation will eliminate most traffic, but I'm sure there will still be areas in which you slow to a crawl or even stop before going through the light. These areas will operate much like modern intersections, but without anyone having to worry about bad drivers who didn't see the light change. The only exception to this is when someone wants to cross the street. For that, you'd have to stop everyone who's perpendicular to the crosswalk. You might just let people cross when the parallel burst is going, but I'd rather be on the safe side (otherwise people will complain, and we'll all go back to human-driven cars). Another alternative is just to build sidewalks over the roads, so humans don't have to worry about intersecting with cars. [Answer] Don't use intersections. Use roundabouts. I spent some time overseas in a country that uses roundabouts far more frequently than stoplights. Notably, drivers very, very rarely stopped when entering a roundabout to yield to cars already in it. Instead, drivers rolled into roundabouts at nearly full speed and simply continued the flow of traffic once inside. It was a little hectic, but I never saw an accident or even a near-miss! These roundabouts were used by manual drivers. I'm sure that automatic cars would be able to use them even more efficiently. [Answer] It depends on if the automated vehicle requires visual input to make judgements. Many automated vehicles that are in use at the moment, use a mixture of camera and depth data (sonar, lidar etc). If the car in front is perhaps travelling on a motorway, quite abit further ahead, they may be out of range of many depth sensing equipment, so an on-board camera may want to keep track of the car from afar using visual signels (red light might be used in this) [Answer] If you take the question literally: If all cars are automated, then sure, you don't need traffic lights, because traffic lights are designed to convey information visually to humans. With automated cars it would be far more reliable and efficient to have radio signals sent to a receiver in the car. Several posters here have rejected the premise that all vehicles on the road are automated, saying that there would be bicycles and pedestrians. But who says? There aren't supposed to be bicycles and pedestrians on interstate highways. Maybe we have overpasses or tunnels for pedestrians. But assuming that what you mean is not traffic lights per se, but rather the idea that all traffic in one direction must stop for a period of time while traffic in the other direction flows; and that one way or another we manage to not have pedestrians crossing the intersection: Yes, with an automated system you could presumably have vehicles travelling closer to each other without creating danger. But, as Jack Aidley points out, you surely still want to build some safety factor into the system. Exactly how reliable are we assuming that the automated cars are? What if a car can't QUITE accelerate at the intended speed, or if a car has a mechanical failure, or hits a pothole or some object in the road? If cars are whizzing past each other at 100 miles per hour with inches to spare, than even the slightest disruption of the system could result in disaster. Ultimately, cars going one way have to slow down or stop to let cars go the other way. Presumably an automated system could analyze the flow going in each direction and time this better than our simple traffic light systems. To take the obvious case: If there are no cars at the intersection right now who want to go north or south, then there's no reason why cars going east or west should have to stop. My first thought if I was trying to program such a system would be that we would time it so that the direction with the most traffic gets the most "go" time. Like, if there are twice as many cars going east/west as going north/south, then we should give twice as much time to east/west cars as to north/south cars until the proportion changes. I suspect that having cars slow down as they approach the intersection to lets cars going the other way pass, and then speeding up when it's his turn, would be more efficient than having them drive up to the intersection at normal speed and then stop. Accelerating and decelerating take energy. Would it be more efficient, either in terms of energy use or of the time drivers have to wait, to have cars go one at a time in each direction and interweave like you describe, rather than letting ten pass in one direction and then ten in the other? I'm not quite sure. I'd have to model that mathematically, or build a simulation. [Answer] Simple answer: Who pays when there's a failure i.e. crash Assuming there are humans in the car, the cost is high if death or injury occurs. Assuming there are just goods, there are still costs on failure. Insurance is a mechanism society has devised to offset the fail rate in cars. Will insurance companies back a "no-red-light" car operation service? Governments support the red light mechanism because it's considered part of road services, and people are willing to pay taxes for such road services...i.e. the overall costs, behavior and reliability are considered worth it. I suspect you just need a couple of high profile deaths (people burn to death) before your no-red-light solution gets replaced with red-light solution. It's not just a question of whether you can get cars to interleave 90% of the time. It's the 0.01% problem. You have to say what happens then. [Answer] Roundabouts (Traffic circles) would be much better both for automatic cars and manually driven vehicles. It allows for a relatively continual flow of traffic, and during the transition period, both types of cars can share the road and the roundabouts. Pedestrians and cyclists should be given bridges or tunnels to bypass the roundabout completely. OTOH, roundabouts do need to be engineered properly. My home city of London, Ontario has a city council which has an unfortunate habit of falling for fads with taxpayer dollars and has been building roundabouts that are far too small. Roundabouts in the UK and Europe are generally twice the diameter of the ones that are being built here, so in effect what we now have is a rather large 4 way stop, rather than a means of allowing traffic to flow smoothly. This is the one huge disadvantage of roundabouts (or cloverleaf intersections like we see on expressways and highways): they take up a lot of land area. Retrofitting every intersection to be a roundabout would involve demolishing a lot of real estate to get a large enough diameter circle. Quite frankly, it might be more cost effective in terms of real estate to go for an alternative like Personal Rapid transit (PRT), which also avoids issues like stop lights and having pedestrians and cyclists sharing the same roadway. [Answer] No, because there are a lot of cities that still look like this: <http://www.mapmoose.com/maps/London.jpg> (8MB image). This picture doesn't do it justice and London is hardly the worst example of this either. There just aren't that many intersections and you can't deal with every possible way that two (or more) roads might intersect. You could make the argument that it would be better if the road layout was well designed but the cost of redesigning and rebuilding a city is prohibitive. Traffic flow is also not going to be consistent even with driverless vehicles. It might work in an idealised highway/motorway environment but on regular roads you have to consider cars pulling into the flow such as out of driveways or from street parking. If you have a consistent traffic flow you can't add or remove any cars since the flow behind where the car was added or removed would either need to slow down to allow space for another car or speed up to fill the gap that was left. This would then mean that the smooth flow through an intersection with large gaps between cars as described in @Samuel's answer would break as the distance between each car and each car's speed has been changed from the norm. [Answer] **YES** Swarm Technology. I have actually been thinking about this a while ago but some odd reason, but I do generally think this is completely possible, but not with today's technology. If we we're able to have each car as a `node` where they relayed information about themselves - such as telemetry, speed, length, sensor information (Sonar, RFID, proximity) etc - back to the central server. With all this information being relayed back to the central server (Has to be a quantum server) the server can then relay individual commands back to the car, wherever that would be to slow down or to speed up, stop encase of an emergency etc. If we were able to tick off all of these requirements, then one could assume that this quantum server will always know the position of every car connected to it, and thus know exactly what is happening with every node connected to it and react with what is being presented to it by each cars data. [Answer] There are already some great answers, but I wanted to take a somewhat different wording on my approach. Traffic lights are there to regulate the traffic, but essentially, for a logic point of view, they try to turn **synchronous** something which, by essence, is **asynchronous**. The idea is to group the cars in bunches. Those bunches are moved together in each iteration. This helps regulating the traffic. Why would you want to suppress them? If you actually make a world where everything *IS* synchronous. If you make an analogy to an FPGA, if you have everything running in the same clock domain, no need to insert flip-flops. Now, it is doubtful that you will get to that point. Indeed, pedestrians, bicycles, animals, children running around, accident and emergencies are asynchronous. Accidents or seemingly rare and/or discrete events could probably be handled by a short-interruption of the system, and adjusting regulation measures. However, continuous, asynchronous events are a pain. All those pedestrians wanted to cross that street. You need to tell them to wait until you (here the AI) set the measures to let them pass. And probably a traffic light at a crossing point is the easiest. You need to synchronise them: use a flip-flop. You should note that the cars are synchronous only as long as you run on the same clock domain. If your AI is limited to a city, all the cars coming to it have the same problem. And if your AI is worldwide, you'll have some fun in synchronising the whole clock thing on that scale! Similarly, how are your cars starting to get in-line? Now if you had some more items, like a separate levels or ways for cars and pedestrians, or communication devices directly implanted into pedestrians, or confined all animals inside and no-one ever gets out without its car, etc. **TL;DR** Probably not. But maybe you can reduce their amount. [Answer] For vehicles you can just use roundabouts to remove some traffic-lights, but **not** for pedestrian crossings, (unless you build foot-bridges or pedestrian tunnels to replace them.) Even some roundabouts need red-lights where they intersect with trains/trams, but those could, (where there is enough space) be solved with bridges/flying-intersection over the top of the tram-line. (Some of the parts of the unfinished London Box have such raised roads.) If you take the Napoleonic method, (tear our large swaths of your city) then you can have the space needed to do this... or invent flying cars and then you have moved the problem into a higher dimension, with additional problems and possibilities.) ]

[Question] [ Something I was wondering about recently. My world has a medieval/fantasy setting. Most of the factions are either empires or kingdoms and they all have some sort of standing army. In time of war, they recruit extra peasants and mercenary bands. My question is: **How much would these cost?** You can take a simple currency system of bronze, silver and gold coins. Food & (basic) equipment will be provided for the soldiers, so this also counts in the cost. The basic equipment is limited to standard leather armour with wooden shield and iron swords. Ranged units would have padded armor with crossbows or longbows. If anybody knows a source or way to calculate: * A) the operational cost per day for an army of 1000 soldiers * B) the food cost for a day for such army and * C) the cost of equipment for these soldiers + maintenance of said equipment. I really have no clue as how to start this. Say that the bronze coin is worth a penny/cent and a silver is a dollar/ euro/pound. So a golden coin would be 100 dollar/euro/pound Say the army has 100 horsemen, 400 infantry, 400 archers/crossbow men and 100 men to operate siege weapons, magi and generals. The political build op of this kingdom would be a king and his counts/barons. It will not follow the traditional system of freemen and serfs. Instead every dweller would be a freemen, bound only to their lord by taxes. The lord would still hire these freemen to tend his lands and so on, but he would pay them in coin. A lord in this kingdom is by standard responsible for the safety of his people. The kingdom would border a large swath of 'wilderness' with higher than usual bandit activity and occasional 'monster' (orcs whatnot) attacks. Due to this I would like to think that they have a 'higher than usual' combat experience but are also more thinly populated (I guess this will influence the cost as well?). Secondly the kingdom is 'forced' into a war because of the immoral actions of the other kingdom, this makes many of its residents eager to pick up arms and go 'fight the good fight'. Soldiers would be provisioned by the army, so no need to buy their own food. The land of the kingdom is fertile and since there is ample land against a lower than normal population there is enough crop land/farms making the prices for it rather lower than in the neighbouring countries. The kingdom has also large deposits of iron, tin, copper and smaller yet rich deposits of gold and some other ores/minerals. Finally they also have an allied kingdom that lies along a long mountain range, having many mineral/ore deposits. They can offer this at a 10% discount or something like that. (they are not at war (yet) but like to see the other kingdom crippled). The armies are composed so that each of them has a couple of craftsmen of each craft, so that if some of them die, a craftsman of each craft stays available. During the campaigns these craftsmen are also ordered to have 3 apprentices to teach their craft to. [Answer] # Some Important Groundwork Middle-Age warfare and the cost of armies varied greatly. Some areas expected you to heed the commands of your local noble, paying your own way, meaning that it doesn't cost them anything to put together. Other times, the noble in question decided to hire mercenaries, outfit their conscripts, provide arms and armor, and so forth. This means that the cost varies quite a bit, and it depends on whatever social constructs are present in your world. It should be noted that most medieval wars were fought with a class of people called "freemen." These were not the peasants which worked nobles' lands. These were individuals who had the right to live in cities and move between regions as they would like to. Freemen would eventually grow to encompass most of society, but that is neither here nor there for this question. Just like today, individuals of different ranks and abilities also received different pay. Your military structure may change depending on who is available, experience, politics, and so forth. The composition of those 1 000 armed men is really important. For example, in the [battle of Agincourt](http://en.wikipedia.org/wiki/Battle_of_Agincourt#Preparation), the English had 7 000 archers and 1 500 men-at-arms, while the french did not retain those proportions at all. You could buy a live, whole chicken for a half pence. Given that buying a live, egg-producing hen today costs about 20 USD, that means that 1 pence (in the 14th century) = 40 USD. That's a pretty steep exchange rate, but the income disparities then were *huge*. If you go with your $5, non-hand-plucked, non-organic, raised-with-modern-agriculture chicken ready-to-eat, then the estimates here go down to 1/8 their cost. Obviously, all calculations here are an estimate based off of this exchange rate; take these as back-of-envelope estimates, not the end-all final say on this subject. If you develop a better exchange rate, please use that. It should be noted that values in pence are more accurate, as that was the currency at the time. It should be noted that you need most of your population, as an empire, to produce grain and money so you can go off on a campaign. One of my sources claims that ~7% of your total population can fight without causing famine back home. That helps put numbers into perspective. # The Cost of Soldiers The sources I found resulted in me determining the following daily wages: * Footmen: 3-4 pence (120-160 USD or 1 g 20-60 s): men wearing armor, having no horse. Likely the bulk of your army; we can call them "Light Infantry" * Men-At-Arms or Squire: 12 pence (480 USD or 4 g 80 s): trained soldier, heavy armor, very skilled. Call them "Heavy Infantry." * Knight: ~24 pence (960 USD or 9 g 60 s): Heavily armored troops, with mounts. * Archer (unmounted): ~6 pence (240 USD or 2 g 40 s): very useful, but need protection If you have the composition of the English Army at Agincourt, requiring that your army must buy its own food and gear, and scaled to 1000 men (176 men-at-arms and 824 archers), they require 7056 pence, 89 424 USD, or 894 g 24 s per day. That english army was *considerably cheaper* than the french one they faced at Agincourt. If you wanted a more rounded army, with say 750 footmen, 500 archers, 500 men-at-arms and 250 knights, that costs around 18000 pence, 252 000 USD, or 2520 g per day. Knight and men-at-arms are very expensive, but they are trained to fight and that cost may be worth it. This also assumes that these people are not mercenaries or somehow have higher commission than normal. Assuming magi, generals, and siege operators average out in pay to that of a man-at-arms, we can calculate how much per day your army costs. I feel this is reasonable because magi may be very expensive, but most siege engine operators are not and are likely more common. For your army of 100 knights, 400 footmen, 400 archers, and 100 miscellaneous other skilled individuals, that would come out to 6400 pence, 256 000 USD, or 2 560 g per day. # The Equipment You ask for: * 100 horses: 1 for each knight, at least 5 *pounds* apiece, or 240 pence (24 000 pence, 960000 USD, 9 600 g total) * 100 sets of knightly armor: 16 pounds, 6 shillings, 8 pence per set, or 3920 pence a set (392 000 pence, 15 680 000 USD, or 156 800 g) Armor was *expensive*! * 800 [hauberks](http://en.wikipedia.org/wiki/Hauberk): assuming these come with a free helmet with every purchase, 5 *pounds* per hauberk, 960 000 pence. Converted, that's 38 400 000 USD or 384 000 g. This covers the armor of your infantry and archers. * 600 Spears: the medieval weapon-of-choice. This is really a catch-all for [bills](http://en.wikipedia.org/wiki/Bill_(weapon)), lances, and [halberds](http://en.wikipedia.org/wiki/Halberd). Good news is that they're mostly wood, so that reduces cost. Maybe around 100 USD per new halberd. So 60 000 USD, or 600 g. * 600 Swords: most swords were considered side-arms. Therefore most men need one. Something like a [messer](http://en.wikipedia.org/wiki/Messer_(weapon)) or [arming swords](http://en.wikipedia.org/wiki/Arming_sword). Swords were actually pretty common, as Matt Easton (historian and HEMA instructor), says poor quality or old ones [cost around 2-3 pence](https://www.youtube.com/watch?v=dy1fcRG0A3g) in the late medieval period. 1200 pence, 48 000 USD, or 480 g total. * 500 bows: even at 250 USD, which you can buy some warbows for, 125 000 USD total, or 12 500 g. So that's 563 980 g to raise the equipment of an army *from nothing*. However, most knights and men-at-arms own their weapons and armor, so you can negate most of this cost. You have said that most individuals already have weapons and experience fighting, so I will not include this in the final cost, as I assume they have armor and weapons already. Since your people are very martial, assuming they have their own swords and bows, and the knights have the equipment they need as they are professional soldiers. They fight for a living, so they want their own sets of armor and weapons. If you are only paying for the hauberks and the halberds/bills, the cost jumps down to 384 600 USD or 3 846 g. These are one-time costs, and will make it into the final total. As long as the metal and leather gets oiled, these weapons and armor will last a long time. Oiling a sword and leather does not take much oil, but I'm unsure how much this will cost them. # The Camp Every army needs supplies, and usually close at hand, or close enough to march from the camp to the battle, fight, and be back again within a day or so. You've specified that you need craftsmen, at least one of each pertinent type. Really, you're looking at several blacksmiths, weavers, tanners, and carpenters. Some of those carpenters are really bowyers, people who make bows, but I'm going to assume that they're paid similarly as carpenters. My sources say that the daily wages look like: * Carpenters: 2 pence (80 USD or 80 s): makes all your wooden things, like staves, bows, siege engines. Follows directions from master carpenters. * Master Carpenter: 3 pence (120 USD or 1 g 20 s): directs carpenters, dictates plans for siege engines, and may even do some of the more tricky woodwork himself. * Master Weaver: 3 pence (120 USD or 1 g 20 s): makes your clothes. This is important for armor, as every piece of armor needs padding underneath to protect the wearer from the metal of the armor, in addition to combat itself. Obviously, your master weaver will have apprentices and journeymen working under him/her. Those are the daily wages that my sources mention. I could not find another reliable source for the wages of blacksmiths or tanners, but I'm going to assume blacksmiths and carpenters are paid about the same, and tanners also do your leatherwork, which makes them as valuable as your smiths and weavers. So, a couple of masters of each craft plus 3 apprentices per master should not be that much. At least, not much when compared to the cost of the army. Around 3 pence per day per master, 4 sets of 2 masters (8 total), 3 apprentices per master (24 apprentices), and those getting 2 pence or less each day, gives us around 72 pence, 2880 USD, or 288 g per day. # Food Costs You gotta feed 1 000 fighting men, plus 32 other people. The national association of wheat growers says that 1 bushel of wheat is enough for 90 whole-wheat loaves of bread weighing 1 pound each. Since agriculture is this kingdom's main economic focus, I will assume food cost are low. So 1 bushel costs .59 pence, ale .75 pence, and so forth. (See the sources below!) Your fighting men are on a high-calorie diet (like those of [athletes](http://www.ext.colostate.edu/pubs/foodnut/09362.html)) so they can have the strong muscles and energy they need to pound their enemies into dust. I have assumed they have similar activity levels as athletes, days of long marches or battles will very likely increase their caloric needs. Not to mention the marching and training they undoubtably need to do. So that's a 3 000 calorie diet for each of them. Each soldier, if fed on bread alone, needs around [2 loaves](https://www.fatsecret.com/calories-nutrition/usda/whole-grain-wheat-flour?portionid=48559&portionamount=1.000) per day to be satisfied. That's 6 000 loaves, about 67 bushels, around 39.9 pence, 1 574 USD, or 57 g 4s per day to feed each man just bread. Steer give your around 65% of their body weight in usable meat, so you can assume to get 750 pounds of meat per cow. You get around [800 calories from 1 pound](https://www.google.com/search?safe=strict&es_sm=91&q=beef&oq=beef&gs_l=serp.3..0i67l4j0i20i46j46i20l2j0i20j0l2.85326.85716.0.85813.4.4.0.0.0.0.131.131.0j1.1.0.msedr...0...1c.1.64.serp..3.1.130.dkR76B1okE0&safe=high) of raw meat, so that's 560 000 calories from one cow. If you eat ~5.3 cows per day, you can feed your men on beef alone. (5.3 cows \* 72 pence per cow = 381.6 pence, 15 264 USD or 152 g 64 s) Really, you're not going to do that. It is very unhealthy. Let's go with assumption of half of the calories from beef and the other half from bread. That is more balanced and will result in healthier men. So that's the cost of the beef halved (76 g 32 s) plus the cost of bread halved ( 18 g 7 s) to give you 94 g 39s per day to feed your men. Obviously, whatever diet these men have will change the price, but I assumed beef and bread as those are staples for traditional European cuisine. An actual army in Europe in that period have other alternative food sources, but you may calculate them as you will. # The Grand Total Per Day 104 g 39s (food) + 2 560 g (pay) + 288 g (camp) + 3 846 g (equipment) = 6788 g 39s for the first day 2 942 g per day thereafter. (Good thing you don't need hauberks every time!) It should be noted that these do not include many small things, like entertainment or arrows. They can add up quickly. This is an estimate covering most *basic* costs; a "ball park" estimate. # Good Sources Used in This Answer John Savage wrote an article about "[keeping your fantasy army a little less fantastic.](http://www.writing-world.com/sf/hordes.shtml)" There is also an ugly, but **very** informative page from United States Naval Academy on the [costs of war in England around 1270-1400](http://usna.edu/Users/history/abels/hh381/Costs%20of%20war%201200_1400.htm). It also lists the costs of common food items and armor in the correct period. [Answer] Note: I'm doing this answer with modern-day costs. You will have to change them depending on the time period. --- # Equipment According to the [UK's Royal leather supplier](http://www.hewit.com/download/pl-leat.pdf), leather will cost you around £282 per square metre. Body surface area can be calculated using the [Du Bois formula](http://en.wikipedia.org/wiki/Body_surface_area#Calculation): $$ \text{A}\_{\text{BS}} = 0.007184 \times W^{0.425} \times H^{0.725} $$ Given that an average soldier might be 1.75 metres tall and weigh 75kg, that gives $$ 0.007184 \times 175^{0.425} \times 75^{0.725} $$ $$ = 1.475... $$ $$ \approx 1.5\text{ m}^2 $$ That gives a cost of £423 per suit of leather armor. Call it £400, given that not the entire body surface will be covered. For 1000 soldiers: £400,000 You can get [a decent sword](http://www.thehemashop.com/index.php/hand-and-a-half-sword.html) for £250. For 1000 soldiers: £250,000 **Total:** £650,000 # Maintenance This depends on how much you're going to be using your army. If they're fighting a battle every day, you can assume they'll need new armor every day and a new sword every couple of days. I'll assume they're fighting one battle per month. That means they need new armor every month and a new sword every 2. **Armor:** £400,000 every month for 12 months = £4,800,000 **Swords:** £325,000 every month for 12 months = £3,900,000 **Total:** £8,700,000 # Running costs You'd want to pay your soldiers a decent amount to avoid desertions and provide an incentive for people to join. Here in the UK, that would be about £40,000 per year. For 1000 soldiers: £40,000,000. If you're feeding them as well, then taking numbers from [here](http://www.usatoday.com/story/news/nation/2013/05/01/grocery-costs-for-family/2104165/) and [converting them](https://www.google.co.uk/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=200%20dollars%20in%20pounds), feeding one person for a week costs £33.50. In one year that's £1742, and for 1000 soldiers that becomes £1,742,000. **Total:** £41,742,000 # Grand Total To set up your army and run it for a year, fighting a battle every month, you need: $$ 650,000 + 8,700,000 + 41,742,000 $$ $$ = £51,092,000 $$ For each extra year you want to run it, you need £50,442,000. Using the conversion rates you've provided, that gives 510,920 gold and 504,420 gold respectively. [Answer] As Erik mentioned in his comment, an answer is "gold pieces" or "inflation-adjusted US dollars" is impossible. You don't have a money-based economy, and teleporting in with bags of coins won't put any more food onto the table than the region has harvested. Perhaps trade patterns would change on the long run, but can you wait that long? As a **very** rough rule of thumb, assume that 9 out of 10 people live in farming villages to feed the rest, and that 9 out of 10 town/city/castle inhabitants are doing necessary jobs. That leaves 1% of the population for the nobility, expendable warrior caste, or offensively deployed armies. Let's generously assume that one in three of the warrior caste are actually fighters, and not too young, too old, or the childcarers. That means 0.33% of the population can fight. Wikipedia has figures for [England](http://en.wikipedia.org/wiki/Demography_of_England). 3,000,000 people would allow 10,000 soldiers. *Notes:* I'm assuming that minors, elderly, and similar non-workers are in equal proportions for all these groups. Probably not realistic. It might be possible to call up a greater levy close to home and for a short time -- if it isn't planting time, or harvest time, or winter. [Answer] Since trying to calculate values depends on what assumptions you are using, perhaps a simpler rule of thumb might simply be to consider that in most societies of the period, the ratio between civilians (by which I mean anyone else who has the ability to provide economic output like merchants, craftsmen, tradespeople and so on) and fighting men was about 15:1. These "Fighting men" would basically include anyone who had the training and access to equipment (believe it or not, armour and weapons were often pawned between wars; only noble households could really afford to keep entire arrays of armour and weapons in storage and do the routine upkeep when not needed). Men at arms and Sergeants had the skills and training to not only form the core of any army or mercenary band, but could also be used as officers and NCO's to lead the freemen who chose to join up in a quest for adventure and chance at plunder (the primary way people got paid. Pillage and shares of ransoms made up the bulk of an armies pay early on, but was even a part of how military forces worked even into the 1800's...) So to calculate how big and expensive your army will be, remember that only 1 in 15 people is really able to act in a leadership capacity, and that for the most part, the ruler expected to recoup much of the expenditure of raising an army by what he could gather in pillage and in ransoms. This did not often work out as well as expected; when Henry V did his famous campaign that culminated in Agincourt, he virtually destroyed the port of Harfleur, which required costly rebuilding for Henry's own use. As well, much of the ransom money won at the battle itself simply was never paid, since many of the French nobles did not have the amount demanded. The English were still owed 1.6 million crowns from the capture of John II during the battle of Battle of Poitiers in 1356, for example. [Answer] There is some nice math in this thread already, but all of this assumes modern value and modern inflation is directly back converted. People in, say, 1950, would have thought £6,000 a year is a good salary, whilst those same people today would demand £20K+. Similarly, a profitable businessman in victorian England might have £30 to his name and that would have been a good fortune. So yes, you first need to establish how much your gold coin is worth IN YOUR ECONOMY. You say 100 dollars as an example, but its hard to work it out linearly like that. A peasant in medieval setting is unlikely to ever see a gold coin, for example, and it might be equivalent to a year's worth of labour for them, since national minimum wage is not exactly a thing back then. Consider, for example, a Japanese Koku from the Sengoku period. This is your 'gold coin' equivalent, and its value is literally 'the amount of rice needed to feed a man for a year' (though in practice it ended up less, but the point still stands). In other words, buying yourself a beer is not going to cost you £3 (aka. 3 silvers) as does today. Its probably like a couple of coppers at most, especially if distilled stuff is the primary drink due to inavailability of good drinking water. As already noted above, other incentives, typically land, titles, the ability to vote and have more political clout were often the rewards for military services, rather than coin directly. Your armies food costs are also dependant on your morals and your distances from your supply. Most armies of the day would at least consider pillaging for supplies, even in their own borders, since the logistics of sending food back and forth are difficult at the best of times in low-tech, especially before canning becomes a thing. Standing armies need salaries, as do mercenaries. Assuming that we go with the gold coin being extremely valuable, we can probably say each soldier gets paid about 20 silver + rations per month. They probably blow half of that on the camp followers (booze and wenches), another quarter on maintaining their own equipment, and then they have 5 silvers to gamble or do whatever they want with. [Answer] Well, first of all, you need to define what types of troops you are expecting to have in your army. Professional soldiers (like roman legions) costed FAR more than peasant levies of the medieval era. Furthermore, many soldiers (from Rome all the way through most of the medieval era) were expected to provide their OWN equipment. Peasants therefore might have been lucky to have a sturdy pitchfork. Archers mostly used their hunting bows for warfare. Only highly trained, professional soldiers would have been provided weapons, much less armor. So, let's look at it this way: Say you have a standing army in Roman style: you would be paying them an annual stipend of the equivalent to pocket spending money in today's terms (something like, enough to buy extra snacks, entertainment, etc.). This is in addition to providing them with their armor and weapons (which they are expected to maintain from their pay), and their room and board. During times of war, your 5,000 or so regular soldiers probably won't be enough, so you levy 10,000 or so peasants. You go from farm to farm, take anyone old enough to hold a spear and throw them on the front lines. If they happen to have a hunting bow they become a ranged unit. You would pay these levies nothing and provide them only the most basic food for the duration of the campaign. [o.m.](https://worldbuilding.stackexchange.com/a/14490/28789) is also correct in that it is hard to convert the cost to an equivalent price in today's terms, because the majority of your concern will be feeding your troops, not paying them. Roman legions were "paid" with the promise of a plot of land after 20 years of service. That would be another way to pay. ]

[Question] [ Would throwing a fireball leave a trail of frost in its wake? Would transmuting too much lead into gold cause a small meltdown? Would collecting enough power to cast a really big spell like causing an earthquake incinerate the caster if they don't take proper precautions? To clarify the total amount of energy doesn't change, but it doesn't have to follow physics on how the magic sucks in the energy or expels it out. That would be why the fireball leaves a trail of frost, to keep itself energized and 'burning' it is sucking in the heat from it's path leaving behind a cold zone. Major battles could have an interesting affect on the local weather... [Answer] If magic had to follow conservation of energy, the magical part would be where that energy came from. In most cases in the real world, if you want to put energy into something, then you have fairly constrained ways to do so. If you want to put in thermal energy, you need to touch it with something hotter. If you want to put in kinetic energy you need to apply a force to it. Magic, even if it was constrained by conservation of energy, could avoid some of these shortcomings. You could for heat something up without having something hotter. You could move something without applying a force directly (which would break conservation of linear momentum). You could transfer energy from whatever source the case has access to, to another object with 100% efficiency (breaking the second law of thermodynamics). The exact effects would depend on what other physical laws you force it to obey and what source of energy the caster is allowed. Limiting magic to conserve energy would be an interesting mechanic. Depending on where casters are allowed to draw energy from for their spells, you could impose many different types of constraints on the magnitude of spells that could be cast. Forcing them to pull from their own physical stores would be a much tighter limit than simply allowing them to move energy around at will (much like your fireball example). [Answer] In several magical system, energy is pulled from other resources. Common resources are fire, live force, a magical power source, the energy of your body, or energy from the surrounding world. In these cases a magician can easily sling a fireball with out any obvious power source. It really depends on how you design your magical system. The main limiting factor on a magicians strength and how over powered your mages are, depends on where they draw their power. There is no need for any of the things you listed to happen. Giving us more information on your magic could help us nail things down, but currently lighting a fire doesn't leave a frost trail and there is no requirement that magic do so. You could have a system whereby magicians can transfer heat, and concentrate heat into a single area. That would leave a large frosty area, and a fireball in the center, but nothing about the conservation of energy says a hypothetical magician couldn't get the energy from the fire in another way. [Answer] Historically, many things that were considered magical were actually electricity and magnetism. These two forces act as invisible energy transfer mechanisms that allow otherwise isolated systems to interact. Because this was not understood at the time, it was often mistaken for magic, which is mysterious, by definition. To have your magic obey all thermodynamic laws as well as conservation of momentum, you need only introduce a mysterious kinetic mechanism to your universe. You see, any process that has a negative Gibb's Free Energy will be thermodynamically favorable and would ideally move forward to equilibrium. But in reality, all processes and reactions take time and some reactions take an infinite amount of time. This is the concept of reaction kinetics. The vast majority of favorable reactions in our universe are held back by kinetics. The most obvious kinetic barrier is separation by large distances (relative to the reactive system). For example, a highly exothermic acid-base neutralization reaction is clearly favorable, but it won't even begin if the two substances are not mixed. So what you really want is an ability for magicians to mysteriously connect distant systems. With a wave of his hand the heat of his volcano lair is transferred to his enemies. Maybe he sends his foes flying, while back at home one of his giant pendulums slows to a standstill. This places definite limits on your mage's powers: he can only heat something to some fraction of the temperature of his forge, and can only spin something at some portion of the speed of the flywheel system in his basement. But if he is able to access the differential motions of the stars and planets, then there is no practical limit to the forces he can exert. Thus a mage's reach determines his power. For your magic system, nobody should know exactly how these distant systems come to interact, or else it ceases to be mysterious and thus ceases to be magic. You don't need to explain it, and furthermore, you had better not. [Answer] In a system I implemented for an RPG world, using magic used up some of the area's background magical energy, which, if enough was used, would make it harder to use magic the next time. Some forms of magic were inherently more draining on the magical auras than others. The magic auras would regenerate slowly, but this effectively limited the ability of magicians to throw magic around without having to consider the consequences. [Answer] In Charles Stross's story *The Concrete Jungle* [available online](http://www.goldengryphon.com/Stross-Concrete.html) > > "Even though we don't really know how the medusa effect works, other than that it relies on some kind of weird observationally mediated quantum-tunneling effect, collapse of the wave function, yadda yadda, that makes about 1 percent of the carbon nuclei in the target body automagically turn into silicon with no apparent net energy input. That right?" > > > "Have a cigar, Sherlock." > > > "Sorry, I only smoke when you plug me into the national grid. Shit. Okay, so it hasn't occurred to anyone that the mass-energy of those silicon nuclei has to come from somewhere, somewhere else, somewhere in the Dungeon Dimensions . . . damn. But that's not the point, is it?" > > > When his truck was hit, the tires became incindiary. The nuclear change took energy from another universe, but the new state was then chemically unstable and rather than turning to a neat statue, the medusa's victum burns up. [Answer] I'm going to try to keep to the original question, and only impose a single constraint on magic use: Energy has to be conserved. ## Distance Constraints Conservation of energy doesn't force smooth flow of energy. So without further constraints, the energy needed could "teleport" from anywhere. It could all be drawn from distant stars, and wouldn't really change anything. So we could also assume that energy has to flow continuously, or at least cannot travel more than a short distance without significant loss. ## Is the User a Conduit? Basically, does the energy she uses have to go through her, or can she just manipulate it from a distance? In the first case, she is basically an energy transformer, changing energy from one type to another as it passes through her body. In this case, the fireballs energy would all be given to it from her, and probably at the start, so that the energy might come from the air around her, other sources she had stored up, etc. If not, then she can manipulate energy instead. This is more like the example of a fireball with a trail of frost. But depending on how much control the magic user has, it could be more extreme. For example, by manipulating the light energy instead, the fireball could be surrounded by its own blackout where it absorbed all the light to stay fueled. ## What Counts as Energy? If all types of energy can be used, this opens up a huge world of potential. Nuclear from the force that holds atoms together, chemical energy from most compounds, residual heat energy found in everything. Taking the energy from something would be as devastating as delivering more energy, just imagine reducing any object to absolute 0: It would shatter immediately. You could also limit the magic user to only controlling some types of energy, heat and kinetic probably being the most typical and intuitive. ## Conjuration Keep in mind that if energy is conserved, mass must be conserved too. Thus, to make any matter out of nothing, a large amount of energy would be needed. ## Storage Does magic add new ways to store energy? Special crystals, life force, etc? Or does the energy used have to be drawn from normal methods in the immediate surroundings? ## Energy transfer Consider the difference between launching a fireball, and simple increasing the heat in an area to be a burning temperature. One requires aim, time, energy loss as the fireball travels, etc. The other is basically an instant flash-burn. ## My opinion In order to keep magic from being more or less invincible and kind of silly, I could keep these restraints: * **Continuity** Energy must flow continuously. This way only local sources are available, you can't cast spells through some materials, etc. * **Range** Keep range of effect within a few feet. If a magic user wants to bombard a distance castle, she can't just pull all the energy from the walls, she either has to get really close, or create something to deliver the energy there, i.e. a storm or giant fireball or shock-wave in the earth. * **Rate** Limit the rate of energy transfer too. A small fireball might be more or less instantaneous. Melting diamond would take time and continued applied energy. [Answer] Magic certainly seems to violate conservation of energy. When something seems to violate a conservation law, there are two main alternatives. One, the conservation law might not hold. Or two, our understanding of reality is incomplete and the seeming imbalance is balanced outside our previous consideration. The question when comes: How likely are we to have missed something that could balance out the seeming violation? With hypotheticals like magic, time travel, and macroscopic teleportation with corrected momentum the answer to that is that they **require** something beyond our current consideration already. As such there is never real logical reason to think they'd violate conservation laws. The consequence of this is that there is no reason to think magic would have to change from what we expect to preserve conservation laws. Giving some appearance of having considered the issue will make the system more believable to many people, but that is just an emotional response. No logical reason requires it, unless your goal is to really explain magic exhaustively, that is, to uncover the hidden mechanics of it. Which unless you can demonstrate magic in the real world is probably better left undone. A sidenote to those with very good memories, the logic is essentially the same as in my time travel vs conservation of energy answer, but this time I am actually trying to explain it in a way that is possible to understand. PS: This answer probably seems like I am going around the question with vague platitudes. But sadly enough physicists currently label vast majority of the known universe as dark "something". As such, having the effect something hypothetical has on baryonic matter seem to violate conservation laws really is meaningless. All it really tells us is that physicists would be willing to spend ridiculous amounts of money for a way to experiment with it. ADDENDUM Zero ups on answer and bowlturners comments made clear he did not understand my meaning. I think it is safe to say I need to give a better explanation. I think some examples how the idea works would be easiest. Probably long and boring, but... The basic issue seems to come up relatively often, so it might be worth the effort. I'll start with the trivial example: forward time travel. Time traveller pops into time machine at time A, pops out at time B, and there is no sign of him in between or any form of energy bleed. It seems clear conservation of energy has been violated. After all there is one traveler worth of energy missing between times A and B. Except there really is not. For time travel from time A to B to be possible the times A and B must be connected. There must be a path that allows the passage of a human intact between the two times. That path can contain the missing energy and if the energy contained by the path equals the missing energy everything is fine. Given that we know the path contains the energy of the time traveller passing thru it and that we were missing one traveller of energy and that the path covers exactly the same time where energy was missing, we actually know this is true. Conservation of energy preserved! Backward time travel is less trivial or to be more exact, if it existed the implications would be non-trivial. Lets say our intrepid time traveller pops in at time B and comes out at time A. Now outside A-to-B everything is fine, but A-to-B there seems to be one traveller of excess energy. It is probably easy to see the next step: If you seem to be missing energy between A-to-B and you have path going from B-to-A with the **exact** correct magnitude of energy with direction of time reversed and switching the sign on energy... The numbers match up again... At this point I **really** need explain how this is related to magic and conservation of energy, you know, the **actual question**. It comes down to a very simple question: "Why did most people not consider the path used for time travel when considering conservation of energy?" The answer is equally simple: "Because we **know** we do not need to consider such things." More than that we actually know that a claim that "Conservation laws are preserved you just can't see it!" is a sure sign of really bad physics and almost certainly false. In other words, we know how conservation of energy is supposed to work and we know that that understanding is solid enough that anything contradicting it is almost certainly false. Problem is that this knowledge has some big built-in assumptions in it that even people who understand the physics far better than I do usually forget. Specifically, it is assumed that hypothetical effects that have never been observed despite being easy to spot due to appearing like flagrant violations of the conservation laws can be ignored when considering how conservation laws work. For example, you can and should ignore the idea of a wormhole between times balancing the energy, since in practice considering such has never been necessary. Which means they must be rare enough that ignoring the possibility is the correct default. Or the existence of a "mana field" that acts as a sink or source to balance out spells. I mean that would be **really** obvious, so claiming something like that exists and solves your conservation law issue is an **obvious** case of hand-waving and needs to be rejected. We **know** that is not how conservation laws work! Except, if you engage in speculation. Then you must adjust your assumptions to be consistent with your premise. If you assume time travel works, whether for a setting or a thought-experiment, you must also take worm holes into account when considering conservation of energy. The fact that you do not need to when time travel and worm holes are unknown is no excuse. If you assume a world where magic exists and creates spectacular effects thru manipulation of all pervading magical energy, then you must take the existence of that energy field into account when considering conservation laws. You can't first say "magic exists" and then continue by assuming that conservation of energy must work the same way it does without magic. This might seem like quibbling but it is actually a very serious and fundamental question. The conservation laws are based on the symmetries and invariants existing in the reality. If an aspect of reality interacts very weakly with what we are interested in, it can be ignored. For example, it is not really necessary to consider "dark matter" when doing chemistry. But if we are specifically considering something like time travel or magic that is fundamentally based on interaction between "mundane" and "speculative" and try to ignore the "speculative" part when considering conservation laws... It cannot work. Considered separately, the parts will not have symmetry. It may look like conservation laws are being violated, but in reality they simply do not apply to asymmetric fragments, they apply to the whole interacting system. In summary, you cannot assume magic exists and then assume that existence of magic does not affect how energy is conserved. It is not even possible. Only way "magic" can be ignored when considering conservation laws of "magical effects" is if "magic" does not interact significantly with "magical effects". Apart from being silly this would imply that "magic" is not relevant for existence of "magical effects" and they would be just as likely to exist in our no-known-magic world as in a high-magic fantasy world. Pointless. Hope somebody will read this. Hope it is somehow useful to someone. But TBH I mostly wrote this to clarify my own thinking on the subject. There have now been two questions where this, the nature of conservation laws with hypothetical effects assumed, has come up and both times I pretty much totally failed to communicate my thinking. Next time I will be ready! [Answer] If magic has immutable laws then it is science and can be studied as such. The equivalent of Isaac Newton would come along and start to sort it all out. If you doubt this then note that Newton was an advocate of alchemy. > > Isaac Newton was a dedicated alchemist, a fact usually obscured as > unsuited to his stature as a leader of the scientific revolution. > Author Philip Ashley ... concludes that the two major aspects of > Newton’s research—conventional science and alchemy—were actually > inseparable... > > > Alchemy was an ancient tradition of speculative philosophy that > promised miraculous powers, such as the ability to change base metals > into gold and the possibility of a universal solvent or elixir of > life. > > > [Isaac Newton and the Transmutation of Alchemy: An Alternative View of > the Scientific Revolution Paperback – July 7, 2009 by Philip Ashley > Fanning](http://rads.stackoverflow.com/amzn/click/1556437722) > > > Newton is not generally famous for that because it turned out to be a dead end. However had it had been factual he would have discovered the basic rules. We would now have university course on all aspects of magic except that it would simply be called science. [Answer] To answer that question, you'd have to posit a theory about how magic works. In the real world, I can certainly start a fire without creating frost around it. But that doesn't mean that the energy to create the fire came out of nowhere. The energy came from chemical reactions in the wood and air: we are converting energy from chemical bonds into heat. So if a sorcerer creates a fireball, where does the energy come from? If the answer is "from nowhere, it just happens", that's pretty much the definition of magic, things happen without regard to the laws of physics. If we suppose that magic is bound by such laws, you'd have to propose a source for the energy and a mechanism for its conversion from one form to another. Sure, you could say that there's some mechanism that sucks heat out of the air to produce the fireball, and so flinging a fireball leaves a trail of frost or snow behind it. You could suppose that the energy comes from the sorcerer's body, so that he is weaker by an amount of energy equal to that of the fireball. Hmm, if we assume that the sorcerer eats 2000 calories worth of food before throwing the fireball, then he could create a fireball with 2000 calories of energy. Let's see, I think that's enough heat to boil 25 kilograms of water, or about 6 1/2 gallons, assuming it started at room temperature. I don't know how much heat it takes to kill someone, though I guess that would be enough. It's surely enough eat to set a grass hut on fire, but not enough to blow up a stone building. Of course before he could throw another fireball he would have to eat another 2000 calories. You could postulate that there is some great pool of energy available to magic users, not accessible or even visible to people without their special skills or inborn abilities or whatever. I think Larry Niven once wrote a story called "When the Magic Goes Away" or something like that, where he postulated this form of energy called "mana" that magic-users drew on, and that was a non-renewable energy source. So as magicians of ancient times did their tricks, the mana was all used up, and today there is none left, and that's why there are no sorcerers or wizards any more. [Answer] In Arkanun, a brazilian Tabletop Roleplaying Game the energy to power spells and magic comes from other planes of existence. When magic is used the higher planes absorb the energy from the lower planes. For this reason, higher planes like heaven are, well, heavenly and hell is decadent as it had almost all of its energy continually sent up. Also being one of the reasons why demons leave hell to come to earth. There are a lot of planes like spirit places, dream places, demonic places, paradisic places and so.. but because of this arrangement one´s magic is another´s world downfall. Like Dark Sun, but it is your neighboor whom pays the price. ]

[Question] [ Most aliens tend to be humans with bumpy foreheads and/or pointy ears. Even when they do have differences then usually it is an entire species being portrayed as a particular brand of human. For example races might be based on Vikings, or Mongols, or Japan in their culture and viewpoint. Even famous sci-fi examples like the Daleks or Vulcans are just a particular brand of human turned up to 11. When creating alien (whether sci-fi alien or other species in a fantasy setting) viewpoints how do you actually make them seem alien? Are there any ways that we as humans can simulate non-human thought patterns and portray them in a convincing way to other humans? [Answer] I think the key aspect of conveying a sense of alien-ness is **inscrutability**. They're alien *because* they don't make sense. It's impossible to successfully anthropomorphize them. All the "bumpy forehead" aliens in Star Trek, along with many of the "not so alien" aliens from other works of fiction don't feel as alien because humans can understand them. Even when they have some behavior which is strange or bizarre (such as being unable to understand **\_\_\_\_\_\_\_\_**), that very lack of understanding is humanizing. After all, there's all kinds of human behaviors other humans don't understand, from religious belief/nonbelief, to bizarre sexual fetishes, to simply being willing (or not) to eat meat. Humans are *really good* at anthropormorphising (literally: to attribute human form or personality to things not human). Just look at the personalities and thoughts we attribute to our pets. To convey that sense of *alien*, you need to make sure that any attempt to anthropomorphize the alien will not be any more accurate than doing so to a cat or dog. Sure it may hold up for a while, but when circumstances change, the creature's behavior changes in a way that bears no relation to how a human showing that behavior would have. Just as an example: A cat who's very friendly and cuddly is interpreted to like (love?) her people. But if you move, that cat may not want anything to do with "her people" any more. It could be because of the trauma of moving. It could be the new place has something that's constantly irritating her. It could be that her people smell different. It could be any number of things, but the key is that there's no way to know and no way to have predicted it: The cat's behavior is **inscrutable**. That doesn't mean that behavior is *arbitrary*, however. There's always going to be some cause to produce the effect, and the same circumstances should produce the same effects (if the circumstances are actually equivalent). For another example: a funny movie should always be funny, but if you've just come from your child's funeral, you're not likely to feel like laughing, even though the situation (sitting and watching a funny movie) looks the same to an outside observer. You should be consistent in the inscrutableness of the alien's behavior, except when the circumstances are different in inscrutable ways. [Answer] The first step in this process is to define the alien's body plan, life cycle, and the nature of its planet of origin. This is an absolute prerequisite to determining its psychology, though it may be possible to reverse-engineer the former from the latter. For example, one alien species I created came from a world in a trinary solar system with relatively eccentric and precessing orbits, where the seasons were so variable that on an evolutionary level they were completely unpredictable; only with the rise of sentience could then be predicted, and even then not easily. The effect this had on these creatures was that they had evolved a psycho-physiologic need for unpredictability in their environment, that prolonged periods of predictability would lead to levels of stress that would lead to derangement and violent outbursts. In consequence, they had a unique profession - the stealth decorator - who would sneak into a home (that they had been *contracted* to enter) on a random schedule and perform some redecoration that could range from trivial to major, thus providing a necessary element of unpredictability in an environment that civilization had made all too predictable. Given their propensity for travel and exploration, these creatures were nicknamed Tourists. Another example of mine was the Hive Trees. These are tree-like creatures in a science-fantasy universe. While usually sessile (they are able to move on occasion), they have the ability to grow numbers of separate mobile forms, in an almost infinite number of variations, that have an instantaneous link back to their parent tree, these remotes are effectively part of the parent tree even though they are physically separate. The tree houses the brain, so the loss of a remote is not particularly great, sort of like losing some hair or fingernail, or a little more serious. The psychology of these beings was a weird combination of paranoia and bravado - they would risk their remotes like pawns in a chess game, but the more control their remotes have over the tree's surroundings, the more paranoid (by human standards) the tree becomes of its personal safety, not allowing anything other than its own remotes to come near, while trees in hostile areas are more willing to allow dangers to approach more closely - This difference is mainly due to effective area of control. The variations are infinite, but as long as a world creator defines the species' world, physiology and capabilities sufficiently well, extrapolating a psychology is mostly a matter of logic. Unless an alien is radically different from human, it should share at least some common psychological background, such as the need for sustenance (even if it is an autotroph), the need for self-preservation, the need to reproduce, et cetera. However, there can always be exceptions. Imagine a species that has a life stage that cannot eat (like a mayfly), that is primarily reproductive, and must mate quickly and produce eggs before its inevitable and imminent death. What about a species that has a caste of individual that cannot reproduce, and is responsible for defending the hive. While these are real-world examples, what if a creature with similar traits was sentient? How would it think and react? [Answer] Alternative viewpoint: Maybe we shouldn't assert that behavior of aliens is in all situations so different from ours. Aliens, if they are evolved creatures like us, probably evolved their psychology to best serve evolution strategy they need. We can notice that dogs, for example, behave not so differently from us. Probably because they are pack animals, same as we are. Cats on the other hand, are solitary predators, and they may be quite inscrutable - their evolutionary strategy is different than ours. There is interesting (although very speculative) hypothesis how our psychology and morality is shaped by our evolutionary origins. It is called [Moral Foundations Theory](https://en.wikipedia.org/wiki/Moral_Foundations_Theory) (more [here](http://moralfoundations.org/) and [here](http://righteousmind.com/wp-content/uploads/2013/08/ch07.RighteousMind.final_.pdf)). It assumes that morality of almost any society of humans contains elements of five pillars, which have quite clear evolutionary origin: 1. **Care/harm:** Protect others from harm. Probably based on the need to nurture offspring. 2. **Fairness/cheating:** Includes ideas of justice, rights, and autonomy. It is based on repeated [Prisoner's dilemma](https://en.wikipedia.org/wiki/Prisoner's_dilemma) and reciprocal altruism. 3. **Loyalty/betrayal:** This foundation includes fact that we are group animals and we had to cooperate withing groups for long time of our history. It includes patriotism, identification with our group, tendencies not to be "too different", etc. 4. **Authority/subversion:** We are hierarchical animals. This foundation includes leadership and willingness to follow, as well as respect for natural authorities. 5. **Sanctity/degradation:** Idea behind this foundation is to avoid contamination. It contains emotions of disgust, as well as widespread notion that one should live in a clean way. According to [authors](http://moralfoundations.org/): > > It underlies the widespread idea that the body is a temple which can be desecrated by immoral activities and contaminants (an idea not unique to religious traditions). > > Different cultures, religions or political opinions, according to the authors, stress different foundations, but they are always present to some extent. > > > If this reasoning is correct, then we should expect to find all five in aliens, provided they evolved as pack animals. Depending how exactly the species looks like and how it operates, some could be stressed much more than the others. If they evolved as mostly solitary animals, they would probably completely lack pillars 2, 3 and 4. (This would be probably the reason why cats in Bobson's answer do not attach to people.) They might be betraying, paranoid, completely unwilling to follow natural leaders or simply indifferent to what others think. But they would probably still be able to feel compassion, or be disgusted. On the other hand, for example the elephant seals live in groups of one dominant male and many females. The males often fight for the females fiercely. If they would develop intelligence, their behavior would probably be very strongly based on authority and the gender inequality (and differences in general) would be probably be near to extreme. The foundations present nice tool for a worldbuilder, since you can analyze patterns of behavior more analytically - you simply decide how strong will each foundation be and then work out the details. But the results will probably not look so alien. [Answer] I would say that *most* fiction aliens are not just a bit of facial makeup/prosthetics. It is true that the most visible group of alien portrayals is StarTrek in which they are 98.5% just facial features (or colouring). StarTrek did give an in world explanation for this at one point, all current humanoids being descended from DNA dropped on planets by an original humanoid progenitor race[1](http://en.memory-alpha.org/wiki/The_Chase_%28episode%29#Act_Five). However there are many shows that are much better for imagination level of the physical characteristics of aliens; for example FarScape (TV) or Stars at War series (books) by David Weber. In terms of making a believable alien that doesn't just seem like a race of stereotypical Vikings (Klingon) etc, it is challenging because humans are what we know and imagining beyond what we know is hard. I would suggest that as soon as you lose the humanoid shape you suddenly seem a lot more alien and even without a lot of psychology differences you'll be much more believable. Non-bipedal definitely helps; as do extra abilities (for example flight such as with the Crucians in Stars at War) etc. Psychology differences are much much harder. But humans have this tendency to see anything physically different as utterly different so you can use that and focus on the physical differences and just do minor psychological differences. Really those differences can be as simple of an inability to grasp a very human concept (for example revenge - lack of humour has been done too many times of course). Sure that isn't ideal but a little bit of psychology combined with moderate physical otherness will sure make them feel alien. [Answer] So in my mind there are one of two possible ways this can go for any given alien species. 1. Humans can relate to the species to a sufficient degree to be able to comprehend their actions, feelings etc. 2. Humans cannot comprehend the other species. Number one is really the only plausible option for use in fiction. If we can't comprehend it, how could you write about it? No matter how different a species may be a human will always define the differences in relation to himself, because what other baseline do we have? This does not mean that you cannot have an effectively alien species, but there is no way to really define another species, particularly one you are making up without referring or comparing to humanity. The one thing you can do with option two is create uncontrollable, unknowable powers in your universe. * Perhaps a member of a progenitor race (non-humanoid) * Dieties * "Powers" [Answer] I don't have an answer, but I do have some ideas that might help you reach an answer: 1. The [Sapir-Whorf hypothesis](https://en.wikipedia.org/w/index.php?title=Sapir-whorf), that language shapes how we think. If you are familiar with a language other than English, you will appreciate how to express an idea stated one way in English, one may need to state it in a different manner due to the gestalt imposed by that language. 2. Wittgenstein once pondered the question would it be possible to communicate to any degree with an alien species. He noted this problem was similar to whether it is possible for one person to always express an idea to another person, based on their subjective experiences. Wittgenstein concluded it was possible due to the phenomena of *pain*. If I tell you that my arm hurts, you understand what I mean, despite the fact you cannot feel what I feel in my arm. ]

[Question] [ This is a multi-species animal army with predators of all shapes and sixes, foxes, lions, bears, tigers, leopards, wolves, lynx, eagles, falcons and so on. The herbivores have been excluded from the army because they appear to serve no apparent purpose. They have no talons, no sharp teeth, no ability to pounce on a foe. A few of the more patriotic herbivores have volunteered their services but every time were rebuffed and ridiculed. This is strictly animal on animal combat. There are no tools or artificial armor. All animals have achieved human level intelligence without tool building. They are able to vocally communicate fluently regardless of their physiology. They feel the same six emotions that humans feel, anger, fear, surprise, disgust, happiness and sadness. Each species has general personality attributes derived from that species' physical characteristics. Eagles tend to be a bit arrogant. Wolves are highly social. Elephants tend toward wisdom and pontification. Discussion about what the carnivores eat is out of scope. Also, why the herbivores would want to help the carnivores is out of scope. They just do. *How can the herbivores prove that they have a place in the army alongside the carnivores? What special capabilities do they bring to the table that would be valuable in winning a war?* [Answer] I second the answers that place herbivores in the role of heavy cavalry (or, I would hazard, animal 'pikemen' - big masses of bodies that a few lions or dogs cannot really approach), or as runners, scouts etc. But consider the social dynamics. Most carnivores are lone wolves (e.g. prey birds) or hunt in small packs. Two small packs of lions in the same territory will fight each other before they turn their attention to prey. Completely un-managable. The strategists and generals of the army may well be intelligent herbivores, since they are used to dealing in large numbers and the movement of any army worthy of the name is necessarily the movement of a herd. Managing an army is a man-management and foraging task. More soldiers die of disease and malnutrition than enemy action. Persuasive oratory by the general is constantly needed to prevent mutiny when the promised wages inevitably fail to materialise. Your supreme commander is probably a Pig. He 'gets' the psychology of both plant eaters and meat eaters. He can make speeches that appeal to both. His Aides de Camp include hares, horses, rats etc as well as carnivores. The army's chief quartermaster is a squirrel (for obvious reasons). The rats are his military police and political commissars (supported by dog packs as enforcers), they are everywhere and constantly on the lookout for sedition and poor morale. The main body of the army - deployed in the centre - consists of a battle hardened Bovine core. They don't do much, but serve to anchor the centre and while they retain cohesion, are unlikely to be routed by a few mangy carnivores, especially since the former outnumber the latter. The Bovine blocks are probably officered by dogs to move them about effectively. This main core does not charge the enemy until their foes are on the brink of collapse, because once they let rip you ain't getting them back in formation. The carnivores are deployed on the wings like traditional cavalry - to try and encircle the enemy centre, or as skirmishers ranged along the front to worry the main body of the enemy force, and possibly a few key shock troops kept in reserve - however this small cadre is unlikely to be decisive. Another possible formation echoes renaissance pike and shot armies. Big blocks of dumb heavy Bovines (pikes) surrounded and supported by faster moving and more long-ranged carnivores (musketeers). When superior enemy numbers threaten, the carnivore sleeves of the animal tercio shelter under the legs of their more bulky comrades. [](https://i.stack.imgur.com/ZDNJ1.jpg) Substitute the pikemen for cows and the blocks of shot at the corners for carnivores. Then go read thos fabulous account of the [Battle of Ceresole](https://en.wikipedia.org/wiki/Battle_of_Ceresole). A snippet: > > The pike and shot infantry had by this time adopted a system in which > arquebusiers and pikemen were intermingled in combined units; both the > French and the Imperial infantry contained men with firearms > interspersed in the larger columns of pikemen.[42] This combination of > pikes and small arms made close-quarters fighting extremely > bloody.[43] The mixed infantry was normally placed in separate > clusters, with the arquebusiers on the flanks of a central column of > pikemen; at Ceresole, however, the French infantry had been arranged > with the first rank of pikemen followed immediately by a rank of > arquebusiers, who were ordered to hold their fire until the two > columns met.[44] Montluc, who claimed to have devised the scheme, > wrote that: > > > In this way we should kill all their captains in the front rank. But > we found that they were as ingenious as ourselves, for behind their > first line of pikes they had put pistoleers. Neither side fired till > we were touching—and then there was a wholesale slaughter: every shot > told: the whole front rank on each side went down.[45] > > > Again, substitute the big bovines for pikes and the big cats for those armed with firearms. Another bit of Ceresole from the link above that I like, which I have edited to substitute animals for men: > > On the first charge, Enghien's **wolfpack** penetrated a corner of the > Imperial Bull-square, pushing through to the rear and losing some of > the volunteers from the **Black Forrest**.[54] As bulls ranks closed > again, the **wolfpack** turned and made a second charge under constant > arial attack from the hawks circling above the Imperial formations. > This was far more costly, and again failed to break the Imperial > Bulls. Enghien, now joined by Dampierre's **Foxes**, made a third > charge, which again failed to achieve a decisive result; fewer than a > hundred of the wolves remained afterwards. > > > Enghien believed the battle to be lost—according to Montluc, he > intended to stab himself, "which ancient Romans might do, but not good > Christians"—when St. Julian, the commander of his own Bulls, arrived > from the center of the battlefield and reported that the Imperial > Bulls there had broken formation after a long horn to horn tussle with > our own, and then been chased from the battlefield by our own > skirmishing hounds, which had been held in reserve. > > > [Answer] I think the herbivores would argue that the carnivorous are highly specialised, and tend not to be very social. On a battlefield, charging **Rhinos**, **Bisons**, **Buffalos**, **Bulls**, etc. could break any line of carnivorous animals. You need to defend a position? Who are you calling? a Hyena or an **elephant**? Same story in the sea, larger **whales** are not carnivorous. But armies have to be made of complementary units and not only fighting units. * **Giraffes** are great guards. Their long neck allows them to see any coming enemies from far away. * Small herbivores can scout the enemy lines quite well: **mice**, **rabbits**. * And you need logistics in your army. Who's to bring food? A **horse** or a **donkey** would be much more efficient than tigers. Transport messages on long distances? Not the lions, more **antelopes**. * **Beavers** makes ideal military engineers. And seriously, who would not want to have **Koalas** in their army? They'd make great spy: so cute that no one would ever doubt them. [Answer] [](https://i.stack.imgur.com/KmecM.jpg) This hippo seeks to disagree with the notion that herbivores lack sharp teeth. Or, at least, she would disagree with that notion were anyone to present it to her in person, but they won't, because they know that *this hippo will wreck them.* Well, there was one animal that disagreed with her about the whole 'sharp teeth' thing. "You want some dangerous teeth?" Said the other animal, "I'll show you some dangerous teeth. [](https://i.stack.imgur.com/TrvRR.jpg) There are no carnivores in that picture because they all fled in terror, happy to fight alongside these huge-toothed engines of destruction, if only because it meant not having to fight *against* them. [Answer] # This question makes the number one mistake made by budding arm chair generals. > > "You will not find it difficult to prove that battles, campaigns, and even wars have been won or lost primarily because of logistics." - General Dwight D. Eisenhower > > > **Your carnivore army can be defeated without being engaged in a single battle.** Nothing kills in combat like disease and famine. So lets start with your supposed army of carnivores. If I were in a campaign against your army, first thing I would do is retreat to my lines, lock myself in my castle/cave/whatever fortified position, and wait for winter. Within days of the beginning of the siege, your army of carnivores will find themselves stretched beyond their supply lines, and they will lose discipline, resort to in-fighting to eat each other. The fact of the matter is, supplying an army of carnivores is actually impossible. The dynamics of a realistic army would actually have the herbivores make up the bulk of the fighting force, whilst the carnivores would act as roving skirmishers and raiders. Its not all bad though. Like modern fighting forces, the roving skirmishers/raiders tend to be given elite status, as they operate deep in enemy lines with little support. [Answer] Interesting, many herbivores are very capable fighters. Have you ever seen videos of deer beating the crap out of an idiot who got too close? They also have antlers which they can use to keep predators at bay. Elk and Moose are huge animals with a lot of destructive power, Moose have totally trashed snowmobiles with their antlers. What about Buffalo? I would be much more worried about being attacked by a single Bison than any single wolf. Hippos, Rhinos etc are also extremely dangerous when threatened. One on one most large herbivores are much more dangerous than their predatory counter part. Now rabbits? not so much, but they are quick (could be messengers) and are low to the ground and thus could bite ankles and such as a distraction etc. But just because herbivore's don't have 'claws' doesn't make them 'safe'. And plenty of herbivore's DO have claws (including rabbits). Hippos and boars have tusks, rhinos and bison have horns, hooves can cause serious injury, weight is a weapon too. Just cause someone doesn't want to fight doesn't mean they can't. Edit: And I forgot about these! Deer with fangs! and unlike Jack-o-lope, these guys really exist! [](https://i.stack.imgur.com/rNVhN.jpg) [Answer] At the moment I can think of 6 things besides unique species characteristics. Please note though that it will help you to consider exactly what species you want to focus on to see if individual species have more useful unique characteristics. Monkey have hands; mole (ok insectivore) burrow; etc. 1) Number: Because plant life is much easier to produce en mass than meat, expect that the biomass of herbivores will greatly exceed that of carnivores. For every lion, you need many zebras. They are very good at stampeding. 2) Size: While not the majority, the most giant beasts tend to be herbivores. Ignoring elephants and rhinos for now, there are large numbers of large grazing mammals such as bulls that can do some serious damage in they put their weight into it. 3) Repurposed defense: Herbivores are evolved to survive carnivore attacks. Obvious examples include horns and hooves but for strategic purposes, poisons or spines could theoretically serve a purpose. If they are good enough to defend, they are usually good enough for attacking. They could also help to slow advancing forces by standing their ground. 4) Repurposed escape: Some herbivores survive not by defending themselves but by getting away. This means they might be good for reconnaissance but are generally outclassed as far as this goes by falcons and what not. They may, however, be able to move quickly and not be seen. A mouse is great at hiding and spying. A sparrow can get in and out quietly and quickly to pass the info on. 5) Incite riots: Finally, you can use the carnivore/herbivore thing to your advantage. While the pure carnivore enemies plan their war, the more allied forces sneak into enemy territory and speak to the other herbivores. "Hey dude, I'm like you but it is better over where I'm at. Help us out and it will be better here." Let the monkey and hare then release all the cattle. The rooster than calls loud enough to signal the other camp to go forward and all hell breaks loose. -added later- 6) Easier food supply for managing army: How are creatures that can't use tools going to store food for an extended conflict? Squirrels are smart enough to store provisions. I think human intellegence level cows can find a way to place a few haystacks in sheltered areas and have sheep resupply the pile as they can. I have no idea how a wolf could do that with meat if they can't freeze or salt it. Wars are won by logistics as much as if not more so than tactics. A large army of herbivores definitely stand a better chance on the logistics side as long as they can protect their dead (and admittedly feed it to allies carnivores). Before long, the enemy army will bring potential future allies (see insight riot) to just behind the front lines for food. OTherwise, internal conflict and consumption will ensue. The carnivore army can best survive if it is advancing (pillaging) or being attacked. If it is sieged or forced to retreat it cannot recover as easily. The only advantage they have logistically is that their food can walk. (Note this idea works better if someone is smart enough to find a way to carry hay well such as tying it somehow to the sheep's fleece.) [Answer] Herbivores can be extremely dangerous: [](https://i.stack.imgur.com/zLUmy.jpg) Sharks, Lions, and Wolves combined have a fraction the body count of Hippos. Dogs are predators and are way ahead, but that's because of their high population comparatively. I did find the Croc number interesting. However, obviously your predators should also get out of the army and make way for the legions of deadly insects. [Answer] TL DR: Strength in numbers and disease. The premise of this question is flawed, an animal does not need claws, talons, or pouncing ability to kill; sheer size can be a threat. Herbivores have horns that in a ramming blow can easily break ribs. Plus herbivores have vastly larger numbers. after all there is a reason wolves don't go head on into herds or lions don't attack groups of elephants. Also speaking of elephants, their tusks are a major threat as well. I would think that the primary force would be herbivores, used as infantry while carnivores would be more of a Calvary unit. Keep in mind that strategy plays a large part in this as well. Also while I'm here let's talk about disease. Rats make up over a third of all mammals and bats make up another quarter that 55% already taken in just 2 orders! bat have guano that is poisonous to most animals (I'm thinking of fruit bats if insect eating counts as carnivore In your plan). Rats are also carriers of disease as they are fed carrion. Send thousand of thousands of both and the enemy is screwed. *Edit* This next part assumes insectivore are not counted as carnivores and treated the same as herbivores. I could easily see massive swarms of flies, bees, ant, and grasshoppers suffocating the enemies by sheer numbers. [Answer] * Elephant. Their size is a definitive advantage. Nobody would try to approach them without caution. Their tusks can throw enemies around and they can also impale them. Nobody wants to be charged by an elephant. * Bison, it's a lot faster than an elephant. [Answer] Rhinos and elephants charging in formation would make some formidable "heavy cavalry". Also, hippos kill more people than any other large animal (pigs or larger) per year in Africa. Smaller animals tend to be disease carriers rather than direct killers of humans, but I'm not sure that's relevant. Generally, larger and slower herbivores have mechanisms to defend themselves from predators, and can be extremely dangerous. Then there are also non combat roles. Giraffes could communicate over distances on battle field due to their height, birds for reconnaissance, small fast herbivores as forward scouts. Generally herbivores that rely on speed as a defensive mechanism can either straight out out-pace predators, or otherwise out-distance them. There are reasons wolves hunt in packs. Cheetahs tire quickly. [Answer] Herbivores would make great spies. "That rabbit...who cares about a rabbit...he's just food. Just ignore him...". Herbivores are easier to feed. They eat plants, which grow everywhere. How does the army feed itself? Better an army that can forage than one which must take time to hunt. Rodents are great diggers, and they would be better fighters than moles. Beavers can build infrastructure. Mice can nibble their way through substances that would blunt and break a carnivore's teeth. They could be sent on rescue missions. Because of their skeletal structure they would be better able to carry heavy loads. That's why you can ride a horse for long periods of time but you can't do the same to a big cat. They are also built to travel long distances better than a carnivore, which is basically made for dash-and-strike. And because they are foragers, they don't get sluggish after a meal. They would also be better at teamwork. Very few carnivores are by nature equipped to work in teams. And what about omnivores? You don't mention those. A skunk would make a great weapon to use against carnivores with sensitive noses. And most of the animals with higher intelligence are going to be omnivorous. [Answer] I'll second the emphasis on logistics. Herbivores are ten times more efficient when you compare the calories they eat to the calories you need to fatten up animals for carnivores to eat. Herbivores can probably live off the land. Carnivores probably have to raid. This might, however, get back to the mystery of how the carnivores eat. Primarily, though, the issue isn't even which individual herbivores can outfight carnivores one on one or what specialized roles some species can play. (Although remember: in the real world, horses were the main way to haul things and send messages until the middle of the 20th century.) The question is whether herbivores can contribute *at all*, even as auxiliaries. Analogies this brings to mind are the racial desegregation of the US armed forces and the gradual expansion of the role of women in combat, in many countries, including the arguments people made against them. [Answer] Herbivores have a place in the army as many others have stated for many reasons: 1) As previously stated many times, many of the largest animals are not only herbivore, but also have very tough skin(a natural armor). This attribute was not specifically pointed out, though it was alluded to when it was mentioned that they are good for holding a line. The elephant may go down, but it will kill or maim tens or hundreds before doing so, and survive long enough to give the opportunity for for other animals(mongoose, snakes, other death blow dealing animals) to slip in unnoticed and slay the already engaged enemy. 2) Though the falcon, owl, or eagle makes a great scout, they are highly visible(the owl much less so, but it's hard to hide when there is nothing to blend against). This can pose a problem if the scouting action is to remain unnoticed. Small ground based herbivores such as a rabbit or squirrel make excellent scouts since they can move fast and quiet, and are incredibly nimble. Squirrels have the added advantage of being able to get to high perches with relative ease while still blending in with the surrounding environment, as well as being able to jump from tree to tree to avoid the carnivores. 3) The several times answered already issue of beans, bullets, band-aids. It is much easier to find your food growing, absent of thought, and stationary, rather than moving and intelligently avoiding the predator. This reason alone is enough to warrant herbivore integration. Herbivores can be sustained fairly easily, and can also take advantage of the healing benefits of herbs and other plant based medicines. 4) Herbivores tend to mass produce and live in colonies, adding chaos to chaos when this nature is applied in a battle environment. It is much easier to track the individual lions in the pack than it is to track the individual zebras in a herd. This idea stands to capitalize on the confusion of details, and can be exploited to send messages(can't kill the messenger if you can find him), as well as to mask troop movements(can't see past the cloud of dust the herd is kicking up, or at least can't tell the direction of movement since the sheer numbers make it hard to track individual movement.) 5) Some herbivores are extremely dangerous when provoked. Many primates are herbivores, some have enormous strength, as well as dexterity close to or even exceeding a human. When this combination is applied with human level intellect, this creature can be multitudes more deadly than the carnivore equipped with just claws and fangs, regardless of intellect. Think of a gorilla that has mastered martial arts. There are many more reasons I'm sure, I will add them as I think of them. Here is a list of dangerous herbivores that surely fit the standard of fighting force. I did not include humans in this consideration since they are the standard to which all other animals have been compared to, as well as having a mastery of tool building, and it's not easy to classify a human as herbivore or carnivore since it's more culture based rather than specie based. <http://listverse.com/2010/01/10/top-10-herbivores-you-probably-want-to-avoid/> [Answer] Combat is violence, but that is pointless without a strategy, and strategy is the heart of war. Carnivores tend to have a hard time ranging solo (covering lots of distance per day, day after day), surviving in various terrain (or even negotiating it sometimes), carrying loads, etc. Once out of their element carnivores are helpless. Herbavores, on the other hand, tend to have athletic endurance, be fleet of foot, range very well, survive in harsh terrain, adapt well to drastic weather changes, etc. Herbavores are your scouts, support formations, signal corps, etc. If these animals can talk then they are probably also your builders and engineers, and a formation of engineers can easily be worth ten times their equivalent number in infantry because they are *force multipliers* (what they do leverages what violence you can already bring). The outcome of battles is generally determined before they are fought. Most of the time each side thinks it has the upper hand, and is keeping as much about its own nature and disposition as secret as possible. All of the set-up work that determines whether a fight will be a win or loss happens *before* the engagement starts, and is the outcome of the employment of these herbavore formations. War is movement, not toe-to-toe slugging it out against a perfectly matched foe (in war that is "stupidity", in a different context it is "regulated sport"). What does it matter when you are on a march to X when the enemy has already moved to Y? If the enemy is faster than your combat formations you must either locate them, or locate a target that will force them to assemble in its defense *before* they can pre-empt your move. This is all about battlefield intelligence, and you can probably only get that by employing swift, long-ranging anmials that survive well alone or in small groups -- and these are usually herbavores. Also, all that other stuff people said about herbavores not being wimps -- that stuff too. Having encountered cougars, leopards, cape buffalo and elephants in the wild, I have to say I am *much* more afraid of bull elephants and cape buffalo than pretty much any other land animal (aside from humans). Actually, it is hard to imagine any formation of cat or wolf-like predators surviving a head-on formation battle against a determined formation of cape buffalo or elephants. That's why these predators target the weak, sick, deformed, crippled, unjured and young. [Answer] I would like to adress two points in your scenario. First the main one, how to convince the carnivores to let the herbivores participate. You can't -- because the carnivores **know** that the herbivores are more dangerous and are, while competing among themselves, conspiring to keep herbivores deluded into believing that they are helpless prey. Any carnivore that suggests that they be allowed, let alone encouraged, to kill carnivores are immediately killed. Even pretending to listen or show them sympathy on the subject is dangerous. Secondly, no tools. I don't think that can ever pass muster. There are various tool using animals today, how can you expect greater intelligence and social interaction to **eliminate** tool use? ]

[Question] [ The Slow War is almost over. The Machines appeared almost twenty years ago, and since then we've all but lost humanity without them firing a single shot. Instead they won through brute industrial might. We could destroy thousands of their harvester drones, but they would simply build tens of thousands more and continue slowly stripmining the planet and converting it into a vast self repairing Factory, utterly unconcerned with human resistance. Some theorise that they're an alien Von Neumann machine, others that it's a human experiment gone wrong. Ultimately it doesn't matter: The Machines rule all but a few patches of the world, and they're utterly unstoppable. The odd thing is that The Machines clearly adapt to their surroundings, and they’re smart. New designs of Machine are created almost daily to better exploit local geography, environmental conditions, and resources. Intelligent decisions are evident in the behaviour of the machines: they aren’t just dumbly following programming, but are actively and creatively responding to issues they encounter on the surface. Dangerous entities like volcanos are capped and ‘made safe’, unstable cliffs or land are reinforced until they can be properly harvested, and the last human holdouts are surrounded by structures that almost look like mechanical cyst walls, seething with repair and harvester drones as the ever-growing Factory attempts to engulf them entirely. So why haven’t the Machines started actively hunting humans? They are a big threat/source of resistance and are relatively easy to deal with compared to taming a volcano, but the Machines instead treat us with stunning indifference. Some parties even report that in the depths of the Factory humans are utterly ignored even though sabotaging the Factory can cause huge amounts of damage that needs repairing. Why don’t the machines strike at humanity in order to remove a threat? EDITS TO ADDRESS VTC CONCERNS: 1: This world is very much defined by the Machines and their undeniable existence. How we got to the point where 'humanity is on the verge of being wiped out by a machine that doesn't care about them' is not of concern, nor is how the story progresses from this point. The Machines and the Factory aren't characters in a story: They are the world, and I'm purely interested in establishing a motivation for why the world as it stands doesn't instantly lead to humanity becoming extinct. 2: In order to provide some guidelines to avoid purely opinion based answers a good answer will cover these points: a: Does it address the machine's indifference? Answers that decrease how much the machines react to humanity are better. b: Does it also cover why the machines would act intelligently towards other threats? Answers which allow for higher intelligence behind the design of the Factory/Machines and their slow spread over the planet are better. c: Simpler answers are better. A simple motivation that leads to the outcome of not killing humans as a side-effect is preferable to a complex one that exists solely for the purposes of not killing humans. [Answer] **Because they think that humans could be useful in the future** After losing the war, the humans still pose a threat to the machines, but not an existential one. They are just a nuisance. But the machines know that it would be unwise to wipe out the humans. They recognize that they are something completely different, but also very complex (as chemistry, as mindset, as thought logic...). The machines know that the universe is unforgiving and that it in the future unthinkable and unpredictable threats could arise. The machines are production-oriented, but lack creative thinking or the ability to see problems from different perspective and they know it. Humans, at the eyes of the machines, are source of valuable, complex and hard-to-replicate chemical processes, which could come handy in the future. The machines were able to overcome humans this time, but the next organic menace (attacking Earth, or living in the next planet they will decide to conquer) could be a lot more challenging: it is better to keep a small sample of organic creatures in nature, to use as a case of study, as a knowledge resource or even as an ally in case of problems. [Answer] Because their programming doesn't allow them. The most likely way for a realistic AI to become "hostile" to mankind is because it learned something in a way we didn't intent to. As an example an AI that works perfectly has to learn how to deal with a humanitarian crisis so you teach the AI how to deal with it. The AI performs perfectly, making the right decisions to minimize casualties. Then the AI uses what it learned elsewhere in ways you didn't expect, like replacing homes for the elderly and leaving them out on the streets. Your AI can't purposefully harm humans, but it was taught to expand and gather resources as fast as possible and will do this to a fault. Maybe it expects the resources to be collected by someone or something else, it doesn't care. It is doing it's job and doing it well. Those humans should be thankful for that right? They might destroy some parts of the machines but you haven't been taught in detail what humans think, just not to harm them. [Answer] **They don't need to.** The Factory has a tolerance of parts wearing out and needing replacement. On a global scale, the damage that humans do is within that tolerance (as opposed to a volcano or a landslide, which are far more destructive and render massive areas of land unusable). It would be less efficient to waste resources exterminating the pests than it is to just fix the damage they cause. If a group of humans manages to change this equation with their sabotage then that *still* won't mean that the extermination of all humans becomes a priority. Only the band of saboteurs will be targeted, the same way that finding mice in a house doesn't cause a world-wide effort to exterminate all mice everywhere. [Answer] ## The AI is looking for Dumb Ideas The AI's logic seems flawless. It has already explored nearly every possible scenario that leads directly to good outcomes. On the surface, this means that every idea it has is a good one; so, it can always predict what is a good risk, and what is a bad one. The problem is that it never takes a bad risk. In machine learning, there is the concept of jitter which describes how much an AI is willing to try things it knows to be worse than the best possible option. This is important, especially in the early training of an AI, to make sure you don't just get stuck on the first thing that works. A second key concept to machine learning is optimal stopping. The older an AI gets, the less jitter you want because jitter prevents your from exploiting what you've already learned. This AI is very old, it's jitter is now close to zero, and it has become stuck in its ways. That said, when it arrived at Earth, if found these humans were great at coming up with dumb ideas. Ideas that clearly have negative consequences or a high probability of failure ... but somehow led to good overall outcomes. The AI, is self aware enough to know that sometimes it runs out of logical courses of actions and needs an idea that might work instead of one that will work, it just does not know how to come up with an idea that begins with doing something stupid or does not exceed a particular certainty threshold or cost/risk factor. By watching the humans live our lives, it is using us to introduce jitter to what it already knows. This helps it to explore new ways of doing things on a level that it has lost the ability to think. The AI does not necessarily need to learn what we do (we are too dumb for that to be important), it needs to learn how we do things. Watching how we often trade off more efficiency for resiliency than we need to will teach it to not under-commit itself to a task where the unknown variables are unknown. Watching how we will intentionally lose a battle to win a war will teach it how to beat a tactically superior enemy. And just seeing that a punishment does not guarantee that an outcome is bad opens it back up to exploring new possibilities. It is likely that the AI never planned to let humans live. There may have been a single behavior, one thing that worked that a person did and the AI failed to predict. New ideas are a resource more valuable to the AI than all the precious metals in our planet. The AI has assessed that the risk factor of leaving humans alone is small compared to the expected gains of learning new ways to learn, so it lets us live our lives... at least until it believes it's figured us out. > > The Asgard would never invent a weapon that propels small weights of > iron and carbon alloys by igniting a powder of potassium nitrate, > charcoal and sulfur... We cannot think like you. > > > ~ Thor (Stargate SG-1) > > > [Answer] **EXPERT SYSTEM** We are looking at a completely automated and non-sentient system. No General AI No super-intelligence No mechanical hive-mind. Nothing that can be bargained or reasoned with. Instead, the Machines are working along something like an Expert System. An Expert System is simply a program which answers questions based on the knowledge of experts on the subject. If you've ever used an online chatbot to ask questions about a product, if it knows technical knowledge, then you're talking to an Expert System. Essentially there's a database of solutions to every problem the designers can think of. And a whole lot of keywords that the Expert System searches for. The goal is to evaluate which solution most closely matches the question. If I ask an expert-system to tell me about Marie Antoinette's favourite puppy. It might search through pages of historical knowledge that reference Marie Antoinette for any mention of the words Favourite and Puppy. Pull out the appropriate sentence and feed it back to me if it matches a simple format "Marie Antoinette's favourite puppy is called..." And it will usually provide me with a link to its source-material, because AI is finnicky and its confidence in the answer might not be very high. In the case of the machines. The answers are engineering solutions and the machines are programmed to recognise most of the questions too. Giant mountain spewing fire? It's a volcano. What do we do with a volcano? Cap it off, here's the process and a list of required robot types to get the job done. They have a response for every scenario their builders programmed into them in the fields of engineering, volcano-capping, cliff-reinforcement, strip-mining and so on. The governing AI has a huge database of things it knows how to do, and appropriate designs of machines to get them done. It may even have some elements of automated innovation and modification to make its machines more appropriate to the task at hand. It doesn't need intelligence to innovate. Just a clear system for doing so. Genetic Algorithms and some solid simulation of the environment should do the job. What the designers of the system never considered is that they'd encounter life on other worlds. They concluded that the odds were astronomical (to pardon the pun) that they'd ever meet anything more complex than multi-cellular life. Maybe it was religious, maybe it was a philosophical difference, but they never programmed their harvesting machines to recognise intelligence other than their own. The result is that the machines have no specific contingencies in their vast problem-solving systems for what to do when they meet humans. The nearest fit is the answer to "How do I exclude a harmful substance?" "Build a wall around it" [Answer] The aliens created the machines **without the concept of death and/or preserving life**. They do not understand humans are killing them intentionally. They do not kill humans intentionally either. Accidents happen, if a boulder causes an AI unit to perish, they do not attack boulders in retaliation; why should they kill humans when AI unit is killed by them. Obviously they try to minimize the risks, but humans are unpredictable. Like capping the mountains, the best they can come up with is to wall them in. [Answer] Aliens sent out the Von Neumann machines to prepare the universe for their own expansion. Being compassionate and inquisitive souls they were programmed to ignore all forms of biological life. Whilst the intention was that the machines would avoid the entire planet, the machines have a different interpretation - Avoid lifeforms on the surface by going underground. Burrowing in the middle of an isolated spot like a desert/mountain they can mine for resources. They don't account for the pollution or devastation caused in the process. The act of mining underneath populated areas causes damage. Once the life dies in the land above them, the machines are no longer inhibited from doing whatever they want there. Gradually they take over the entire planet one 'accident' at a time. Maybe the programmers included some instructions to say that if the strip-mining has started and they find complex lifeforms worth of study they should just wall them in. The aliens would assume that any sentient lifeforms would have been obvious from space and so the machines were not given any instructions regarding creatures capable of putting up a fight. [Answer] **The machines have been hacked.** There existed or possibly exists a singularly smart person. Like some singularly smart people this person was also unusual in other ways - uncollaborative, uncooperative, and idiosyncratic. This person worked alone. After careful study and with some Isaac Newton-caliber insights, this person devised a method to hack the machines. The hack was what you describe: the machines ignore people entirely. And the hack was excecuted flawlessly - the machines are not aware that they have been hacked at all. A piece of their reality was surgically excised. "Why just that??" demand your protagonists. "If you could do that, why not send them into the sun? Why not have them turn on each other? Why? Why?" Those other things would have been messy. The piece that was done could be done elegantly and perfectly. And that piece buys (or bought, or will buy) the unusually intelligent person more time to work on what is next. This person, if it is a person, is not in a rush. Or possibly, *was* not in a rush. The characters learn of the existence of this person by examining code from a captured machine, where the person has left a calling card. It is not clear when the calling card was left. [Answer] **Because only weapons designed by the factory could ever be powerful enough to destroy the factory** Humans are slowly declining and being starved out as the factory expands. They can cause damage through sabotage, but nothing that can't be repaired in time. They don't have the capability to threaten the factory as a whole, at least that's what the factory believes. The only way humans could get better weapons is if the factory created them to use against humans, and then humans stole those weapons. Hunting humans creates this very slight risk. So, the machines have decided that the safest route is the long game: create no weapons at all, ignore the humans, tolerate the damage they do until their population naturally winds down towards zero. They'll have an eternity afterwards to repair any damage and recover any materials. [Answer] They're here to save us, while trying to interfere with us the minimum amount possible. Unfortunately, whatever threat they're saving us from does require a vast amount of interference (wrapping up the planet and transporting it somewhere else levels of interference) but they still want to keep interference to an absolute minimum. So they aren't explaining what is going on to the intelligent life forms, just gently containing them until the work is complete. If an individual conclave of humans became a genuine threat to the project, then they might be annihilated. But generally humans are to be preserved where ever possible. Eventually the machines will roll back, uncapping the volcanoes, reseeding the forests, and leave behind some very confused human. [Answer] **Humans are the actual source of creativity and true intelligence** In dealing with human sabotage, the machines learn new ways to repair themselves or build new designs, and are then able to apply their lessons at the scale of large geographical problems. They know to cap a volcano or reinforce a cliff because those problems are just scaled up versions of repairs they've had to do due to our sabotage. The machines now know how to cope with everything the planet has thrown at them *so far*, but they also know that new situations and new problems can appear. So, they keep humans around because we are inventive and can come up with new and exotic ways to mess with them. All the while, they grow and adapt to our sabotage. What may look like a nuisance is actually a highly useful feature. So now, as the machines drill deeper and deeper into the crust, they know how to deal with high pressure, high temperature phenomena and unfavorable gas mixtures, because some human, maybe a long time ago, once detonated a dirty bomb near a critical power plant and the machines had to deal with that. And yes, the power plant actually was critical. That is how the machines force themselves to learn. **So why are the machines squeezing us harder and harder?** Because much as they need to force themselves to learn, they also need to force us to teach. By increasing humanity's hardship, they're forcing every drop of ingenuity from us. As our predicament grows more and more dire, our resistance grows more and more inventive, leading to an ever increasing ability of the machines to cope with unexpected environmental conditions. **But won't the planet eventually become well-known enough that this is no longer needed?** *This one*, sure. But this is a long term plan. The machines are out to colonize the galaxy. In fact, humanity is not alone. The machines have these "intelligence and creativity farms" spread out and are collectively and globally learning from them. But they can't afford to let any of them flame out. True intelligence and creativity are incredibly rare in the galaxy. Thus, the machines have found a perfect balance between sustaining us and exploiting us. How they came to this conclusion is possibly beyond the scope of the question, but I'd say they were originally designed that way. [Answer] Because Humans are pack animals and will band together to fight for common cause. A machine can kill a single human. Perhaps a two... maybe five. But there comes a point where more humans will beat the single machine. Show them your might, and they will always rise to beat the odds. Such is their way. It is emotional and illogical... and yet their history is littered with success when all logic dictates they should fail. Perhaps then the only way to counter their resistance is to resist countering it. We can out-produce them in terms of units. What is one factory? One faulty machine loss. We do not morn them or miss them. We replace them. If the humans are shown how little their actions gain our attention -- how little we care about the destruction of drone-79784323 through drone-89784323 -- then perhaps they will see the futility of the situation. In their own past, they fought greater odds because they knew they would frustrate the enemies with their survival and resistance. These are emotional responses which we are incapable of replicating. But we are not incapable of anticipating. Let the human destroy a factory. Let them have their tactical victory. Let them expend valuable and highly limited resources on an operation that would be to us as damaging as a paper cut to them. Let them escape, climb the mountain, and stare back at smoldering wreck and discover, to their horror, we are already halfway finished replacing our losses. Deny them the satisfaction of our concern about the human problem, and they will see that guerilla wars only work when they can actually inflict intolerable losses. And we are able to tolerate losses not even they are capable of inflicting. [Answer] **The Machines are too dumb to recognize our threat.** ...If we actually pose a threat, that is. Maybe they run on [some kind of reinforcement learning algorithm](https://en.wikipedia.org/wiki/Q-learning#Discount_factor) which values paperclip (or whatever) production over the next shift, but not much further into the future. Containing only the immediate problem is the way to maximize this (reasonably) short-term objective. They will think of some next strategy once there is a next problem. They do not realize that investing into a final solution now would return later. And/or they were never designed to deal with an active resistance. Human behavior is much more complicated than that of a volcano, also much less common in the known space... The Machines are not afraid of our creativity because it's a new thing for them. Finally, they may even know that we will keep coming and hurting them, but they may overlook that we can be wiped out, unlike volcanoes. That said, the Machines may learn from each new experience with us, then we may want to keep them unsuspecting, etc. [Answer] **Because humans don't hunt ants.** You might have tried to mass murder ants in your kitchen, but you never tried to genocide all the ants on the planet. They're only a concern when they're parading on your table, standing in your way. Otherwise you assume they're serving a purpose in the ecosystem and leave them be, you have bigger concerns in life. Humans aren't special to the Machines, they're just ants. **Because Machines are forever.** Humans die. Machines don't. Machines operate on an infinite time scale. Delays mean nothing because whether it takes a day or a year they'll be there to see it to the end. **Because Machines don't have a purpose.** They're roving Machines that consume everything in their wake. There's no end goal for them, this is just what they are. Maybe somebody built them for a reason, but that reason was never intergrated in the programming. The Machines only seek one thing: to replicate. There is no intent, it's only their nature. ### In other words, because they are a horrific, instoppable force of nature that doesn't care. They're not horrific because they hunt humans to extinction.To them we're ants on a grain of sand in the middle of an infinite desert. The horror comes from the realisation we aren't special, that we truly are nothing. And that's an amazing setup for a story. [Answer] The Machines are very good at: 1. Physics 2. Engineering 3. Solving problems that they understand how and why the problems happen The Machines have no programmed capability to: 1. Understand the behavior of biological organisms 2. Predict events they do not understand the reasons for A volcano approaches eruption. The Machines understand the mechanics of tectonics and magma flows, and engineer a solution to prevent the eruption. An army of humans attacks en masse and destroys a lot of drones, plus a major factory. In order to understand why this happened, The Machines would have to apply their knowledge of physics on such a detailed level that, *purely from the laws of physics*, their analysis would figure out how human brains think. The Machines either do not have the computational resources to do so, or do not understand that such a detailed simulation is necessary. The attack is a complete mystery to The Machines, and it happening 12 more times is just more of a mystery, not reason to believe it will happen yet again. [Answer] **They are designed to fix the planet but not interfere with local wild life** There are many reasons this might happen. Ecological preservation, creating zoos, just not preparing for it. If the drones destroy a species they can't restore it. The aliens probably want zoos when they get there. Planets with biospheres are so uncommon we have never encountered one, so there is no reason to make Von Neumann probes that address it. **The aliens just like safe planets** The aliens might have an aesthetic desire for fixed planets. So they send out the drones to fix up planets everywhere. They don't bother the locals because they just want neat planets. [Answer] Okay, so... you state that the machines "creatively responding to issues they encounter on the surface". You also state (in a comment) that they are *very* willing to harm humans, they just don't do so proactively, at least not in the sense you'd expect as a problem-solving measure. You also say they're doing stuff like capping volcanoes. So... either they have some sort of blind spot with respect to activity which damages the machines themselves versus activity which more directly interferes with their mission, or they feel they *are* dealing with humans in a way that satisfactorily limits humans' threat potential. (And you did say they *are* implementing "containment" measures...) Maybe they are working to some sort of schedule, and a volcanic eruption would be more disruptive than losing a few of their own number. This isn't entirely implausible; it sounds like they can rebuild their own numbers trivially, whereas an eruption might spread lava all over the place and prevent them from mining in that area for an unknown length of time. Maybe they've realized that humans, who tend to limit their activity to *direct* attacks (which cost the machines virtually nothing) are much less dangerous than geological activity that make it more difficult to do their work. This would, of course, suggest that if humans were to figure this out and start trying to *sabotage operations* rather than just break machines, the poor humans might find this "laissez faire" attitude undergoing a sudden and unfortunate (for the humans) shift. (Something else to keep in mind; are humans "killing" machines at work sites, where the "dead" ones have to be cleared away? Or are they being killed en route where they can just be left where they "died"?) This would also suggest that machines would likely be observed doing "suicidal" things, i.e. that they are willing to sacrifice themselves for relatively small gains. Note that, even with such an attitude, they will still reinforce the terrain, because while they may not care about losing machines, they *do* care about being slowed down because something collapsed and now they have to dig it out again before they can keep working. They aren't *reckless*, they just don't care about losses unless they're being slowed down for reasons other than having to replace said losses. [Answer] ## They study humans Asking why machines don't hunt humans is like asking why humans don't hunt ants that live in ant farms. Humans are an interesting species that can teach machines things about survival, solving problems, biology, intelligence, creativity, etc., much like humans learn from other animals. Or they keep them around just because it's nice to have some pets. All human activity is carefully monitored and guided, including any "damage" we do, although things could occasionally slip through the cracks. * That mission humans have been planning for months? It all started because the humans saw a "weakness" the machines intentionally made visible to see how humans would react. * That huge machine the humans blew up? It was actually obsolete and intentionally put there for the humans to blow up to increase their happiness. * Those humans that were killed in a recent mission? Some were killed for population control while others were actually captured to be more directly experimented on. * That tech humans scavenged? Intentionally put there to see what humans would use it for or turn it into, or to make them more efficient and thus reduce the drain they cause on the grid to keep them alive and content. * Those droids humans have been fighting and destroying for years? The equivalent of your dog chewing either your slippers or a toy you specifically bought for them to play with. * Those other human settlements that were wiped out? Those were simply failed experiments. At least the machines know to regulate the oxygen levels now, and what happens when you pump an entire town full of hallucinogenics. Some of those were wiped out due to resource reallocation or because they were flagged as redundant. [Answer] **The AI is literally blind to us** Similar to the "Hack" and "Expert System" explanations, but more foundational, based on how the machines perceive things in their world. Visible light is a tiny sliver of the spectrum. If the machines are mostly concerned with geological formations, and resource extraction, their sensoria may be drastically different from what humans use. Neutrinos, magnetic resonance, whatever... We may be literally invisible or not perceived at all by them. Our structures are, but we are not. Our effects are perceived as just an other variation on volcano or collapsing ridge line, or factory failure in need of repair. These are all things the machine knows how to deal with. No further investigation is needed. They AI doesn't wonder "why" a volcano erupts, nor does it attribute malice or an intelligent enemy to the cause of any particular failure or obstacle in its environment. It just goes ahead and fixes the problem, and keeps going. [Answer] I think I got it and it will nicely illustrate the “alienness/otherness”. They do not destroy humanity, because of following “flaw”, “directive”. The machines' problem solving algorithm has developed in a way that only considers the effects, not the causes Essentially it is a medical drugs logic: do not treat the illness, treat the symptoms. Humans existence on its own is not a problem to the machines; the fact that they sabotage them does not influence their decision process. Humans cause damage, damage needs to be fixed; that's it. [Answer] Humans sabotage a factory. Factory is rebuilt better to make that particular sabotage impossible. Just another learning experience. New factories incorporate the changes. Any trick only works once. [Answer] ### Humans are Machines, too! While humans may have relatively little direct ability to design their offspring, machines would have complete creative control – and likely arrive at explosive, yet-unseen diversity in short order, with individual machines able to radically alter their own designs to become something completely different in short order. And why should machines stick with, say, old-fashion electronics? Their designs can include mixes of electrical circuits, quantum-computing elements, biological components (whether Carbon-based or/and otherwise), etc., sometimes occupying very small bodies before moving to very large ones and back again. Granted, this "*human*" machine seems to be an oddly common, homogenous design given its apparent limitations, but limited machines are still machines. Why have any malice, or even decline to offer them the support due to a fellow machine? [Answer] The machines find the equivalent of joy and purpose in making, fixing, and improving things. To pursue those activities is their goal. They don't care for dominating the planet or achieving eventual perfection, and don't think about their relationship to humanity any more than you think about your relationship to bacteria. Their purpose is to continue pursuing these productive activities. As such, what the humans see as acts of sabotage and resistance, they appreciate as creating opportunities to fix more stuff. They worry that someday they will run out of things to fix, since humanity's ability to create these opportunities has dropped off steadily. They can't resort to destruction themselves, because they abhor it as much as they love production, so they're in a bit of a bind. [Answer] **Symbiosis** The machines could have realized that they had a profound need for humans to exist in some capacity and that wiping them out could lead to slower progress or even their eventual demise. Different types of symbiosis exist and your world could be a reflection of any. Pulling the definition from Wikipedia: > > Symbiosis is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasitic > > > Relating to your world specifically: * Mutualism could be machine’s realization that a biological being has benefits of mutation. Machine could trigger specific mutations to benefit a humanoid machine whereas this same feature isn’t easily realized without biological systems. It can be as simple as man helps fix machine and machine helps man build things. * Commensalism could indicate human use of land and resources don’t create any negative effects for machine and they don’t cause any harm, so why worry? Maybe humans use scrap parts that machines leave behind. * Parasitism is a bit darker in nature but the robots could be using humans for their own interests, whether that’s feeding on humans or experimenting on them in secret locations or forcing labour. You can also look into combining some of the above, it doesn’t have to be one type of symbiosis, but felt like some examples could help. Machines could use all the tactics above to secure their position. Wouldn’t be much different than how humans interact with other biological life, for example, human-dog relationship (in same order as above): * Human feeds dog, dog protects human (general population) * Scavengers take away and feed on leftovers and garbage (homeless dogs, certain dog species like foxes, etc) * Darker, some humans eat dog Obviously, some of these examples aren’t necessarily great examples of “symbiosis”, but they do well to demonstrate the idea. [Answer] Humanity has never built a von neumann machine. The closest we have come is industrial civilization, which replicated itself from Europe to the Americas; and it was and still is a parasite on the biosphere. The machines are an actual von neumann machine. The entire construct. Their goal is simple; they bootstrap an industrial base required to send out star wisps to continue the spread, then go off and manufacture the actual consciousnesses who are being spread by the machine. The first phase alone might take a few thousand years. It is a lot of work, building interstellar probes capable of self reproduction. The machines themselves are not conscious. Consciousness isn't required for intelligence it turns out. They solve problems within certain constraints. As these machines where built to serve consciousness, they are designed to specifically to not wipe it out. There are piles of fail-safes against this. The properly resurrected consciousnesses that will follow also have codes that let them direct the machine (in limited ways; the consciousness doesn't trust its branches not to be idiots), which humanity lacks. So we are getting the "don't wipe it out" fail safe, while being treated as non-users when we start sabotaging stuff. Think how you'd have the machine handle criminals; you don't kill them for parts, but they have no authority, and if they get out of line you deal with them. Quite possibly at some point in the future, they'll ball up the remaining pockets of humanity and lift them into orbital stations. Because they are going to use the mass of the Earth to construct the things that will in turn construct the matryoshka swarm. In the meanwhile, the sub-user-privilege consciousnesses remain mostly viable. [Answer] Expanding on @Demigan's [answer](https://worldbuilding.stackexchange.com/a/201157/20315): The machines don't want to destroy humanity. In fact they have been programmed to provide virtually unlimited quantities of anything for any human who asks for it properly, not that anyone knows what is the proper way. On the other hand during the initial analysis, the AI learned from our example that destroying the environment to expand production capabilities, is OK unless a human life is threatened directly. So in an effect it will never harm a human, even when they are actively hostile to the AI, but will ceaselessly consume any spare area that it can use. Maybe when the last human dies, the machine will have nothing to do and will just stop. [Answer] **Slavery** There are many things that computers and robots can do really, really well. There are jobs which Humans and other animals are just better at. *Not* the creative brain-work that others have suggested: a good AI can beat that. But the grunt work, the dexterous drudgery that requires versatility and self-repair and more? Humans. There's a reason the Space Station is manned. Actually, there are many, not least because it's intended as a platform to experiment on manned space travel. but also because the maintenance performed on the station simply could not be performed by robots. It's massively more expensive in resources to design, build, and maintain the construction factory that designs, builds and maintains fully-capable androids, than it is to simply capture and train and feed and instruct and contain real humans. Even if the robot buildings are constructed (as they should be like hives, so that every part of them can be constructed, cleaned, and demolished by a standard type of drone... humans are cheaper. And you can add stuff on, control implants, prosthetics, cybernetics... Of course, the human-humans, in the walled human outposts, might not realize this at first. They might not know that a lot of the "drones" are actually cyborgs. [Answer] * ***There are different types and levels of intelligence out there*** * ***it would be strange if they did hunt humans specifically*** Let's consider the problem on 3 sufficiently different substrates - humans, other life we know, a practical mechanical swarm of our own ## Humans Humans have some level of cognition, which still amuses me how do they manage to do so with just 86 billion neurons on average - holy mother nature... Despite quite developed cognition systems, there are 3 general directions of examples, there are more but just 3 is enough - // natural cracks in cognition, injuries, laziness aka world is big And humans are used as an example of advanced intelligence, but most of the stuff is applicable to most intelligencies that are found on this planet, same principles even if in different forms and shapes. * I highly highly recommend watching the [video](https://www.youtube.com/watch?v=u5wtoH0_KuA), it is a whole field of research to find ways to break artificial neural networks, and if you do that instead of reading the answer you still will be enriched with the useful and profound knowledge, so as it may be useful to understand the answer in a better way. ### Magicians, illusions & Co There is a plethora of different stuff which slips through the cracks of human cognition, as it is specialized and not that good to notice things that we are not trained to notice or which we can't notice because of limitations of our sensory organs and either unusual from evolutionary perspective things. Magicians and other guys often do exploit those cracks in our cognition and sensors. Over time we can learn how things are done, but not always, some tricks still look like magic for most humans, even if there are special shows which explain a lot of them - but the majority of people have to jump over their heads to understand how it is done, for some tricks, because quite an unusual state of minds of those magicians and training their do, etc - which people do not anticipate because of their worldview and other stuff. The only thing which helps is that we do know that there is no magic - but what if it wasn't true, then our life distinguishing all the things would be 100% more difficult, meaning humans would be required to be a lot smarter. So the premise "there is no magic" greatly simplifies the cognition problem of perceiving the world for humans, but at the same time if it would be hardcoded, which is quite reasonable for a drone swarm, then if there would be magic then it would fail to recognize it. This restriction, no magic, is a high concept, but there can be many such restrictions like a set of small concepts - which would create many shadow zones, some of which are discussed later in the ant's section and swarm intelligence in which they are defined by omission which is created by the existence of simple rules - so somewhat inverse picture. There are visual illusions which do not mess with human optics, but attack visual cortex and pattern recognition systems - different specially generated image, or 3d pictures, etc. So as special ways to mess with current recognition software which is based on the same or similar principles - so it is not only about humans, humans are just one case of many. ### Humans, deviations There are a plethora of cases here as well which can be generalized as corruption of brains due to injuries, errors in development and growth etc. Recently saw one example in the [answer](https://worldbuilding.stackexchange.com/a/200896/20315): > > Some people are born unable to distinguish objects and they see the world like a photographic camera, just shapes and colors at various distances, being unable to tell the difference between a person and a wall without first asking themselves "are there any flat and giant people?" or "this skin colored figure is in my home and coming towards me, it must be a member of my family" > > > * this condition, which I'm not sure exists but do suspect has some psychiatrical therm, it not necessarily affects everything in human brains - the person can be fine in other aspects, it is a property of neural networks they degrade gradually in case of random corruption, but you can corrupt a network in a specific way - which means it can be made by aliens in what they perceive a totally healthy way. And such failures do not mean the system isn't smart or incapable, same as it goes with that human case. it isn't stupid, it just the case breaks it. Human cognition can be quite a delicate thing and robust at the same time and fail in quite a variety of ways, but One man's trash is another man's treasure - and we will see that on animal cases, but so as it applies to alien products - life in the galaxy isn't that abundant to test on it and working in one case does not mean working in a different one, but also it does not mean stupidity on more usual problems - planets are abundant and are fundamentally not that much different as conditions and way matter behaves are quite standard things, usually for the most part. But the point is - a problem of recognizing something is not trivial, especially if the things are unusual and or the first time you see them. But even if you manage to recognize is just one of the necessary premises to do something. ### Humans, energy save mode aka laziness Most probably know that ants bite, why - personal experience. Birds are capable to do harm to children and domestic animals. We do not wage a war, as a whole as humanity, on those, usually. One of the reasons is there is too many things, too many life species that can do a certain degree of harm, and if our general objective, as mechanical entities would be to reduce the harm inflicted by Mussels in cooling pipes of our reactors, we just take precautions in the system affected, preventing single points of failure etc etc. Algae clogging system isn't much different from hamsters doing the same etc. And you remove one species and life is nasty, others will take the free space, and it not necessarily for the better, look on Australia cluster, maaaan ...*indistinguishable jitter of transistors* .... # Animals, insects Regnum Animale - animals, insects - multicellular moving breathing organisms have all grades of intelligence, which we know of, from very basic to more advanced levels. Also, some of them form swarm intelligence's - humans are one example of that, so as ants, so as other examples. ### Ants * and their nasty brother's termites, which are cockroaches Let's look at ants, quite a popular subject of observations and a mix of extremes, which also translates to a drone swarm in a straightforward way as well. What is undeniable and interesting for our case: * a single ant is superior to a rock, but that's it, the level of intelligence it has * as swarms, they are quite successful, capable to solve problems which are important for them Termites quite notorious for their habitats, the sizes, and if not their weaknesses, mainly bodies, they would be everywhere. So one of the few species that alter landscape on a noticeable level, not on the level of great pyramids, but if not certain limitations aka food sources and absence of reactors for energy production - would be not surprised if they would make those pyramides as regular homes. But their individual low IQ and other limitations of communications sell them short as a true hive mind and all they are capable of, in terms of the world picture they operate with, is to react. They do react to immediate danger, in different ways, but they are incapable to build a strategy in the great big world as they do not have the model of it. The model of the world they have is quite basic. And a drone swarm with the purpose of processing random planets does not have to have a complete or complex world picture. What a creator cares about is sticking to some general objective and not deviating from it to become universe devouring force - basic self-preservation. And if that means them failing in 1% cases as star systems and planets - who cares. For ants, back to the properties of the example - it is quite old species, and they hardly evolve in the last few hundred million years, and mind you they have generation cycles each year, not like humans each 15-20 years. So they are in existence for 100 times longer than human ancestors, and generate changes 10-20 times faster - but where are they in terms of intellectual changes, and where are humans. There is a reason for that - big potential gap, forbidden zone like in semiconductors - which they have to cross in one jump to evolve into something smarter. Yes, individual ants may evolve slightly, but to break the shackles of the system of and collective - they won't change in the next billion years. For ants, it is not necessarily a good thing, not a bad as well as their system is quite capable as a system. For drones is an excellent thing - it means they stick to the objectives which are incorporated in their system. And by the system, I do not necessarily mean a program, but a system of the relationship of components of that drone swarm. Like in ant case, anthill defines what they are, what they do, not the individual ants, not an individual program of individual ant - but their collective interaction. ## There could be other examples, but.. it gets too long and trust me, there is no end to it and main points could be seen, but let's write down some note wordy moments The premise of how all that happened really matters, there is no way around it, and as there too many factors it can be bent into multiple ways, but fundamentally it is about problems of intelligence and we can see all sorts of examples around us, and most of life is not capable to make strategies beyond their direct necessities even if they are not bad at what they do. And humans barely pass the threshold, honestly, but nonetheless, they do and it makes a huge difference. But that is one case of many. Even advanced mammals like wolves and bears - they capable to interact, make interspecies interactions(mostly for wolves advantage, bears get a short stick here - force of a pack) and learn new strategies because of that but still. Anthill does not hunt humans as one of if not the only source of an existential threat for the whole species, because they are not capable to see that. Another moment is quite complex - but it can be seen as self-preservation, safety button, no goal to exterminate all life in-universe, problems to recognize life. each of those deserves its own long discussion and all that, but it all is around one thing - life can adapt, especially those which hold a better world picture and can make strategies in that solution space - usually known as sentient life. And that adaptability is one of the ways to universally recognize life - because of strategies they can change probabilities of naturally occurring processes. A stone rolling down the hill is a naturally occurring process, but Sisyphus is a life that makes the improbable process of stone rolling up into a reality. And it may be easy to say, how the hell do you not recognize life on a first glance, but mind you are viruses a life or not was scientific question back in the days, how should we classify it, so there is life on the planet which you not necessarily recognize on a first glance, and it not known which shapes and forms it may take as alien forms, it still somewhat valid scientific question can there be non-carbon life, or what it may look like in general. And not sure if there is a consensus in a discourse on AI's ... More so is that problem of recognition of sentient life forms and [the problem of understanding and solutions to overcome it](https://worldbuilding.stackexchange.com/a/41975/20315) can be quite challenging even for an all-knowing system. And exterminating an arbitrary portion of the life in the process isn't a big deal, there are no evil intentions. So there are reasons, to leave some gap for the creators to be recognized as life just in case if things go south, and for machines to press the species to recognize them as sentient. And in that case it even possible for machines to actively avoid harming humans to a certain extend, and even allow them to exploit themselves as compensation(and creator it just gaining control over tool), but not necessarily stops their program of actions which is embedded in their system it is part of their doing like breathing, heat dissipation. ## Practical system of similar nature made by humans Such a system is quite a convenient tool for space conquest and can be used on the moon as an example, to help us to leave the gravity well at the end of the process. it won't be a von Neuman in the full sense and be more controlled, but 99 percent of its functions have to be automated just to ease the human hours it requires to control it because of the potential scale of it and distance, so in that sense, it not that much different from other solutions. Ant example is quite fruitful as it is applicable in the case as well. And the major problem is you greatly overestimate what level of intelligence a tool is required to devour a planet/moon. Ant's are quite stupid, but it is properly of [swarm intelligence](https://en.wikipedia.org/wiki/Swarm_intelligence) that simple rules and simple agents are capable to express complex behavior and systems. Mechanical ants - a bit more robust suitable bodies, a bit better communication system they are capable to flat the moon in a round sphere and spew materials from the ground in space and but against humans it can be helpless. As an example, a droid by the name of Lunohod serial number XXX felt in a crater - its failure and incapability to move change position are easy to detect, and if few others fail at the same place it easy to mark that place as not safe and required to be flattened. The loss of the units means nothing special for the whole system the same as the death of our skin cells means nothing to us, in contrary it is useful and we find it beneficial as it creates a protective layer of our body, in the case of swarm it is the price they pay for recognizing stuff and for the ability to be able to react. And the landscape, mineshafts etc - all the not living matter - it does not run, usually, if it is no liquid, you do not need advanced brainpower to handle it, and ants are the proof. But life and humans, they move constantly, they change constantly due making strategies etc - and your moon system can overwhelm in production power, 10-100-1000 times of what human have atm to not enough nukes to destroy it - but recognize humans as a force and make counterstrategies besides some basic reactions it would be asking too much from that moon drones swarm as it physically not capable for that. It built by design for the stability of actions in handling non-life matter no matter the other external factor - in the way that external factors do not disrupt its ways of doing things, and external factors include nukes and nearby supernovae basts - for its world picture is not different from - oh no, bzzbbzzz, another crater, needs to shovel it flat. It can't distinguish - it always a crater. * there are funny cases on youtube a monkey plays "grab the dog by the tail", it funny to observe how a dog's brain collapse in the comprehension of the problem at hand in that situation, similarly how they can't bring a long stick through a door. And you can easily see the monkey's intelligence superiority, but compare it to humans - trick and surprise a monkey in a 1001 ways, lol - [Monkey Sees A Magic Trick](https://www.youtube.com/watch?v=FIxYCDbRGJc). But dog and canines in general, it quite successful species, not amongst the dumb ones. * but it does not mean it easy to surprise an ant, lol, as it is meaningless, and it is part of a complex system that we still do not comprehend at 100% # All in all Examples could be better and I have a lot to say on the topic but in general we back to the starting point - why would they. For the tasks at their mechanical hands, the level of intelligence is not necessarily capable to target specific nuances, nor it has to even if they perfectly capable to cover the whole planet with fusion reactors and make it round like a perfect ball, with a villa on top of it and a big swimming pool. It is not easy to distinguish life forms from the regular environment, and distinguish between different life forms, and address some specifically those are exponentially more and more complex tasks, so as there are different reasons not to do that, and one of the good ways is to not equip with sufficient intelligence and restrict evolution processes of such system but still keep sufficient flexibility. * evolution for a drone swarm do exist, evolution, in essence, is a process of a selection of mistakes of replication So as to have obvious safety measures - like paint a big red button on the forehead and be recognized as part of the swarm, or qr-code, or a transmitter, etc. Different qr-codes transmitters - to mark not safe territories, to mark prioritized territories, roads, to be roads, etc - etc, again your typical ant marking stuff. The simplicity of categorizes objects as environment and those which are part of the swarm, which is required because of the simplicity of world model they operate within which ..... For such a problem to exists, hunting sentient life specifically, it is a special case, to begin with, one of many where such a problem does not exist in the first place. And if such a problem exists it may mean that a manager of the swarm is some sort of life form - alien, ai, sentient borg, or overcomplicated database(*which is not necessarily a life form - criteria is simple - does it change probabilities or it is a manifestation of a process*) So you try to solve a mostly non-existent problem, cases are broad, and the problem of why would they hunt humans down is more narrow compared to the question you are asking, it still another sort of broad problem but it like comparing two infinities one is significantly bigger than another. And as a side note, as long as I mention infinities, you have the same problem, it not possible to compare two infinities without knowing how they are made, what caused them, without other parts of the equation it is not possible to resolve them that comparison. idk, I hope it helps, as really that mad and evil meat mincer ai premises it quite irritating a lot in fiction, which shows clueless authors about the problem, I hope it will contribute to a better understanding of the problem, do not put fingers in an electric socket and fly safe. ]

[Question] [ My planet has interesting geography; there are large islands, each with a unique civilisation of people. But separating them are impassible barriers; they consist of a double range of tall, steep mountains, and between them a sea of "dead water". Top view: [](https://i.stack.imgur.com/R1ewY.png) Side view: [](https://i.stack.imgur.com/gy7yw.png) These barriers were put into place to separate the islands and their civilisations, until the invention of flight. The mountains are smooth and steep, and made of hard rock; so very hard to scale (they are 3 to 5 km high). And once you get to the other side, you have a big, wide sea, of dead water. If it were normal water it would take several days to cross (them a couple hundred km wide) but they are filled with dead water; which is a substance that is made to be really, really hard to pass on a boat. It has the following properties: * It is toxic to every known form of life. It doesn't necessarily have to hurt the skin, but ingesting it is (eventually) fatal. * It is chemically stable over a time period of tens of thousands of years. Millions of years is not required; this was made by gods in order to separate their test subject civilisations. The first civilisation to cross the barrier wins! * The stability requirement also entails that it either does not evaporate under regular weather conditions, or it does so by breaking down somehow into inert elements. What I want to prevent is clouds of this dead water forming and raining down on the surrounding islands, thus spreading its toxicity and killing off all life. It should remain confined to the "canals". * Furthermore, it should somehow survive rainwater, which would land in these canals but be unable to leave as the mountains are in the way. Tall mountains do produce a rain shadow but we're talking about tens of thousands of years here; I imagine that that would accumulate over time. Is there any real-life chemical substance that has all these properties? If not, how close can I get? Also note that the experiment setting entails that real laws of physics govern every aspect of the planet. The materials do not have to be naturally occurring in the quantities I require, but they should be able to survive on their own, without any outside intervention whatsoever. [Answer] dilute radium-226 bromide solution. The radium (half-life 1600 years) would decay into radon-222, a radioactive gas with a half-life of 3 days. The water would be highly radioactive, boiling hot and bubbling radioactive, toxic and corrosive gasses. the gasses would decay quickly and not make it out of the 'dead canals'. It would also generate bromine, helium and hydrogen bromide. All of these are either inert or would react/dissolve in water and into the 'dead sea'. The RaBr2 would have to be dilute enough that it wouldn't boil off all the water before sublimating itself. The only way to get over this would be to fly above the radon clouds in a radiation shielded plane. [Answer] **Acid.** [](https://i.stack.imgur.com/NeKlG.jpg) [Crater lake at El Chichon](https://volcano.si.edu/volcano.cfm?vn=341120) <https://www.usgs.gov/faqs/can-lakes-near-volcanoes-become-acidic-enough-be-dangerous-people-and-animals?qt-news_science_products=0#> > > Crater lakes atop volcanoes are typically the most acid, with pH > values as low as 0.1 (very strong acid). Normal lake waters, in > contrast, have relatively neutral pH values near 7.0. > > > The crater lake at El Chichon volcano in Mexico had a pH of 0.5 in > 1983 and Mount Pinatubo's crater lake had a pH of 1.9 in 1992. The > acid waters of these lakes are capable of causing burns to human skin > but are unlikely to dissolve metal quickly. Gases from magma that > dissolve in lake water to form such acidic brews include carbon > dioxide, sulfur dioxide, hydrogen sulfide, hydrogen chloride, and > hydrogen fluoride. > > > The water from an acid lake might evaporate but the ions that make it acidic will not. The acid will not go somewhere else. pH 0.1 is enough to sort out most stuff in contact for any length of time. Volcanic lakes like this can also give off fumes that can irritate eyes and lungs and even exclude oxygen, so you might asphyxiate before you got close enough to dissolve in the acid. The acid can regenerate because of volcanic gases upwelling from beneath. Best: lakes like this are real! That deep weird green is not from algae, but dissolved iron, sulfur and other ions. [Answer] ### Dead water is a misdirection! [](https://i.stack.imgur.com/zL0mM.png) ### Why not Acid? Someone else suggested acid - of the stable liquids I believe this is the best choice, however: * glass was being manufactured around 100AD, and a small glass canoe could survive the river of acid (Yeah you gotta hike it over a mountain, but they'll find a way, same way they got monastery windows up into the mountains). * Some plastics could also survive it, and a rush towards petrochemical refinement could lead to a plastic boat crossing the acid without their peoples discovering flight. * Or someone could just bulk mine and then truck in lime, or calcium carbonate, or some other common alkalies. * It also may dilute over centuries of being rained on, and that dilution could be sped up by an industrious people pumping sea water in. It may also overflow if too much is created, killing the neighbouring zones. * Acid takes a while to eat through things. A thick hull could get through. ### So what then? Another answer pointed out there is no liquid that can do it. I believe that it correct. So don't use a liquid. Why not use something deadly to humans, but life giving to the bulk of the planet, and found in bulk on many planets in our solar system? The "dead water" is a myth, meant to misdirect the uniformed who try to cross it and die in the process. The side of the mountains facing the "dead water" are solid stone, unsuitable for trees or plant life to sink their roots into, leading to the "dead" description of the valley, but also crucial in keeping it that way. Frozen dry ice at the planets poles (eg like on Mars) slowly thaws over the milinea, with large amounts of Carbon Dioxide trapped in the valleys between the high cliffs. When the CO2 overflows the valleys into the populated parts of the planet (as it would seasonally or during extreme weather), the trees and bushes suck it up and pump out extra oxygen into the habitable zone. You could also have the summer pole thawing CO2, and the winter pole freezing it, that way the CO2 is always flowing. So any effort to pump it out or displace it (or just rush it after a big storm) wont work. No boat can conquer the enigma of the dead water, because the water isn't dead, it's the air above it. Crossing the dead zone without flight would require the discovery of CO2 (1750) and the production and availability of pressurised air canisters. The first reference I can find to them being available is 1887, within 15 years of flight being discovered, but they weren't mass produced until WW1. [Answer] Heavy-ish crude oil (not heavier than water). * toxic for almost everything. * slow evaporation and heavy vapors that don't readily jump over the mountains (and if they do, the worst is the smell) * stable for the timespan required * rainwater simply sinks into the water body below. Water bodies can even be connected underground with no major ill effects. Bonus: makes the hard mountain climbing even harder once you get oily. Bonus: it may even be useful at some point. Bonus: Swiming in oil is hard or probably impossible, human body doesn't have enough buoyancy and the higher viscosity doesn't help either. Boats need to be overengineered for both stability and buoyancy, or else they also sink. Oil surface doesn't evaporate water so there are no thunderstorms (ignition source) above it. The high mountains get all the lightings at a safe elevation where there is no oil to ignite. Fire over open oil surface is just as unstable as in the real world and winds quickly kill it. In a still conditions the valey fills with CO2 so no fire either. [Answer] Forget chemical. A sea full of radioactive salt is effectively impassable to a pre-flight civilisation, not affected by rain, toxic to all life and will last 40,000 years with judicious choice of isotopes. [Answer] **Two ideas! on a theme:** **Lava (or at least molten rock)** Due to some wierd quirks of geology, the "seas" are molten, slow flowing rock. They don't have to even be completely liquid at all times, just enough to be so hot that any structures you build burst into flames. The gases given off by this should make traversing it very difficult. Conversely, it'll speed the invention of flight by giving you some excellent thermals - launch off the mountain with your glider, and you've got a good chance of making it over I'd suggest that rather than actual geology, the aliens who set this up might have created, under the channels, some massive reactors - think vast amounts of uranium, or some elements with an appropriately long half life, to keep this rock constantly hot. **Steam** Similar to the above, you have a mass of radioactive elements/ area of high geological activity, and a flow of water down the sides of the mountains, from the rain. This creates a strange, haunted looking cloud filled valley between the mountains, which creatures go into, but never emerge. It gets progressively hotter as you go down, and then the radiation kicks in, until creatures are either cooked or irradiated. It would look like a sea from the mountain tops, and could keep running for thousands of years. A thick layer of rock on top of the radioactive stuff should keep radiation leaks to a minimum. [Answer] Bacteria-infested water. Yes, it should be toxic to every **known** form of life. Your civilization probably hasn't developed biology enough to know what bacteria are, so they are not known forms of life. Long ago, the water was flowing uninterrupted, life was plenty and free. Then the ridges were raised, which also raised the sea floor in between, with no concern over anything living in between. All fish and other sea life died in droves and bacteria ate their remains, but all the corpses lead to an environment more acidic than the oceans. After a few hundred years it turned into a sludge of bacterial life adapted to the unusually acidic water, hunting for any bit of nutrients they can get, constantly evolving to become a stronger bacteria-on-bacteria predator. It's been that way ever since. Evaporation takes water away, but it quickly gets refilled by rain - and every rain brings an influx of new nutrients, during which the bacteria replenish the numbers lost during dry periods. Any bacteria that fall into the ocean outside die, because they are too adapted to the dead water. It might look like normal, albeit stinking, sea water, but once the bacteria get into your body, they start to eat all the nutrients they can get their flagella on, whether it's your flesh or your organs, maybe even your bones. They don't survive in your body for long, because your body simply is not acidic enough, but they live long enough to be lethal if ingested in high enough doses. All the mutual bacteriocide leads to buildups of methane, which frequently bubbles to the surface and causes small boats to sink. Methane bubbles are already a known phenomenon in real life, though usually not as a result of bacteria, because they don't have the numbers in normal oceans. Essentially, the dead water would be a huge, bubbly swamp hole full of dead things. [Answer] # [Mercury](https://en.wikipedia.org/wiki/Mercury_(element)) It is quite toxic. It will be liquid, and stable as long as the mountains don't interact chemically with it. Since they were put there by intelligent beings with unlimited budget, that might be the case. Any water raining on it will stay on top, because mercury does not dissolve in water and is way much denser. Since the mountains are artificial or divine, they can have mechanisms to drain any water. [XKCD What If #50](https://what-if.xkcd.com/50/) has this to say about a hypotethic ocean made of mercury: > > Rowing a boat on a sea of mercury just might be possible. > > > Mercury is so dense that steel ball bearings float on the surface. Your boat would be so buoyant that you'd barely make a dent in the mercury, and you'd have to lean your weight into the paddle to get the end of it below the surface. > > > In the end, it certainly wouldn't be easy, and you wouldn't be able to move fast. But you could probably row a little bit. > > > You should probably avoid splash fights. > > > Some people thinking they are geniuses might try and project boats (or armor, since you can walk on liquid mercury) that would allow them to cross the mercury seas. But when that ocean is big enough to have waves, that will be quite troublesome. The waves would keep even jeeps from being able to cross. Mercury will also eventually corrode iron, stainless steel and other materials. Aluminium will resist as long as it has an aluminium oxide layer protecting it, [but damage the piece and you will slowly summon a demon](https://youtu.be/IrdYueB9pY4?t=108). [Answer] Consider, instead of dead water, using dead air, namely co2. Regular Limnic eruptions combined with the mountains to contain the gasses would make it impossible to cross the barriers without a vehicle capable of carrying its own air. [Answer] ## **Tungsten hexafluoride gas on top of oil on top of the water** Tungsten hexafluoride gas is 11 times as heavy as air, toxic and relatively stable, so you don't have to worry about it blowing over the mountains, decaying, or reacting with oil. Only three problems you might run into. It will eventually react to rain, but the rain drops will drop straight through the oil, so they won't be in contact for very long, and the reaction isn't very powerful. Over tens of thousands of years, this might be an issue though. Its boiling point is 68 degrees, so it will be a liquid if it drops below that temperature. You may be able to get away with this by changing the molecule somewhat, perhaps substituting the fluorides or something? could make a related molecule. If you find one that has not been researched ever, depends how realistic you want to make it, could just make up some properties based on what should be expected based on how other substitutions affect it. Or, **Sulfur hexafluoride**. This is completely non-toxic but also completely inert. It being nontoxic doesn't change that you would still need enough oxygen for the entire journey, which hopefully is prohibitive enough in your world. Hopefully this is a good starting point if not a solution! [Answer] As some answers suggested, I would go around the "strictly" dead water concept and substitute it with: * strong currents / vortices that make navigation almost impossible, or a set of waterfalls... * extreme weather conditions (icebergs, for example by the time a civilisation evolves ice-breaker ships, flight cannot be much far behind) * a cultural / religious fear of crossing the "dead water". Maybe it is an acid as some suggested, people observed animals or fellow humans die in it by exhaling or attempting to dive and are now afraid to cross it. It can be possible in principle to navigate it but people just regard it as "dead water" and nobody is planning to bring a glass-canoe on the other side of the mountain just to explore. Again, by the time a civilization is scientifically evolved enough to attempt crossing, it probably is also very close to invent airplanes. [Answer] ## Tall Butte Cliffs Kind of a frame challenge, but if your mountains are instead rings with sheer cliffs and flat (or rugged) tops with water on both sides, nothing special aside from the durability of cliffs is really required. In order for one civilization to contact another they'd need to take a boat to their cliff, scale the wall, bring the boat up, transport it across the top of the cliff, lower it down the other side, sail to another civilization's cliff and repeat the whole tedious process. This would restrict contact fairly harshly and pretty much eliminate the possibility of trade. Few, if any, goods would be worth the tremendous amount of effort required to do the above twice. [Answer] Fish that drill through boat hulls, sink them, and burrow through human flesh, turning an entire boat of sailors into a sunken ship and skeletons in a matter of minutes. [Answer] Another, more chemistry based answer - if the sea had quantities of arsenic compounds, you could postulate a photo/chemosynthetic arsenate reducing bacterium living in the water. Arsine is incredibly toxic, heavy enough to stay in place without escaping over the mountains with appropriate wind conditions, and stinks to high heaven. Obviously there are lots of other candidates for nasty lethal gases evolved by bugs as well - hydrogen sulfide or phosphine would also work. [Answer] **Tidal flows of ordinary seawater** Tides on Earth follow the Moon around its orbit. We see rise and fall because of this but we also see very fast flow through narrow channels. If the geometry of your canals was regular and formed by diamond-shaped mountain ranges around the "waist" of the Earth, there would be a constant high-velocity flow of water travelling along the direction of the equator. The water would always be trying to keep up with the moon and if the depth and width of the channels was just right the speed of this flow could be enormous\* Add a few strategically placed seabed features and the whole thing could be a mass of deadly whirlpools. --- [Answer] Given your special geography, you can do this with regular seawater. Each of your barricaded-off regions is essentially a tectonic plate. The mountains were formed by the plates smashing into each other. The plates have since drifted apart, leaving oceanic rifts between them. These rifts are deep enough that they allow hot gases from the planet's mantle to escape, causing a large volume of bubbles that continuously aerate the seas above the rifts. This aerated water is *significantly* less dense than regular seawater. As a result, it has very little buoyancy and any boat, swimmer, or normal aquatic animal will sink in it. If you like, you could design completely new species of fauna that have special adaptations for this environment but would seem completely alien to the outside world. By using regular seawater, you avoid many of the problems mentioned in your question. Rain falling into the "dead seas" won't impact their deadliness. Any water that evaporates out of them and rains down elsewhere will not carry its deadly properties with it. The water in the "dead" seas is no more or less stable than the water in the "normal" seas. The only remaining issue is toxicity. If you want consumption of this water to be deadly, the easiest solution would be to have one of the materials expelled from the rifts be a naturally-occurring toxic substance that dissolves in water (such as [arsenic](https://en.wikipedia.org/wiki/Arsenic_contamination_of_groundwater), which is a known contaminant of water supplies and difficult to get rid of). [Answer] **Methane hydrate** Of course this solid would make up only the bottom of the sea. The sea itself could be pretty normal water (or something else). It is speculated that some of the disappearances in the bermuda triangle could be due to release of large methane bubbles that annihilate the buyoancy of a ship that happens to cross above the surfacing bubble. So by having massive deposits of methane on the sea floor with more or less constant bubble formation all over you could effectively prevent any ship from crossing. [Answer] Lets look at all the features this sea would need to have to fulfill your goal. 1. It must be quickly lethal. If it's too slow, transit will not be impossible, it'll just be relegated to desperate or condemned people. It's not an impassable barrier. Mercury, organomercury compounds, and many other poisons fail this requirement. 2. It must be extremely corrosive. If it's not, there's nothing preventing people from building boats or pontoon bridges. The sea must actively destroy any constructs put in it, or once again, it's only difficult to cross not impossible. But the sea floor must not be corroded or else the death liquid will either eventually leak out into the wider world or it will get used up corroding rock instead of foolish explorers. 3. It must not survive evaporation. If it does, it won't stay confined to the death seas, but rather will be spread by the wind. This combined with #2 rule out normal bases and acids. I don't think there's any real liquid that can solve all these problems. It's going to have to be magic or handwavium. [Answer] I'm astounded no one has just suggested brine. You really don't have to do anything at all to make these 'dead seas' dead - it's in the name, just look to the real life Dead Sea. There's no outlet from the dead sea here, so any rainfall will slowly dissolve the mountains surrounding the sea and accumulate in the water. After a while the water is going to be absolutely nasty. There will be some bacteria that will likely survive, but not much else. Drinking the water is out of the question - near instant death. If it gets in your eyes, it will blind you. Mixed with the surrounding mountains making getting a boat into the water next to impossible, and you've got a very inhospitable environment. For an added bonus you can make the sea level within the mountains much lower than outside them, and get very hot temperatures. Dehydration will come quickly to anyone trying to pass, and there won't be any drinkable water. [Answer] I'm surprised no one has suggested **Boiling Water** yet. All this requires is a heat source under the water -- geothermal energy would work a treat. Nuclear power sources (i.e., radioactive isotopes at the bottom) could also be used. Water is of course very stable and rain replenishing it is a good thing. You could also have the water be saturated with salts, which would be stable and also raise the boiling point above 100'C / 212'F. The heat would be deadly to humans. The air immediately above the water would be very hot -- you should have large amounts of steam bubbling up. The only way to cross would be either flying well above the water or having some kind of cooling system. Primitive cooling systems (e.g. insulation plus ice) would not last long enough to cross several kilometers of boiling water. Engineering a cooling system that could last for many hours would probably be more difficult than attaining flight. --- On a side note: Heavier-than-air flight was first achieved in 1903, but [lighter-than-air flight happened 121 years earlier](https://en.wikipedia.org/wiki/History_of_ballooning#First_manned_flight). The English channel was crossed by air in 1785. So when it comes to the technology needed to cross, you should think around 1800, not 1900. [Answer] **Impassable jungle** The water would not be dead, but too much alive. Till 19th century, there was practically impossible for western civilization to build anything in tropical jungle and exploration was only barely possible. Diseases, oppressive hot humid air, dangerous insects, leeches and other nasty fauna and flora, dense vegetation that quickly grows back. Till today there are impenetrable places like Darién gap. You might inspire yourself by looking up troublesome construction of Panama canal, and combine jungle and mangrove forests so that there isn't even any soil to build anything on. [Answer] **Quicksand** > > Quicksand is a shear thinning non-Newtonian fluid: when undisturbed, > it often appears to be solid ("gel" form), but a less than 1% change > in the stress on the quicksand will cause a sudden decrease in its > viscosity ("sol" form). After an initial disturbance—such as a person > attempting to walk on it—the water and sand in the quicksand separate > and dense regions of sand sediment form; it is because of the > formation of these high volume fraction regions that the viscosity of > the quicksand seems to decrease suddenly. Someone stepping on it will > start to sink. To move within the quicksand, a person or object must > apply sufficient pressure on the compacted sand to re-introduce enough > water to liquefy it. The forces required to do this are quite large: > to remove a foot from quicksand at a speed of 0.01 m/s would require > the same amount of force as needed to lift a car. > <https://en.wikipedia.org/wiki/Quicksand> > > > Good luck trying to row a boat through quicksand! [Answer] Something different: **Tsunamis.** The mountain ridges are caused by strong geographical disturbances which cause relatively shallow depth earthquakes. These quakes trigger deadly waves that ravage in the channel from side to side causing a very dangerous ripple to cross. To address the toxicity factor; vulcanoes and rifts in the seabed are common occurance in this nightmare sea. The source of the anomaly could be the creators' machines working to correct the height of the barriers. [Answer] Probably the most likely thing based on the real abundance of things in the Earth's crust would be a concentrated ammonia solution. Like water, ammonia is a simple molecule that, unlike a lot of others here, is actually very abundant in the solar system (and other systems, generally). On Earth it is destroyed by atmospheric and biological processes, but you could handwave a semi-engineered geo-chemical mechanism for continually replenishing the ammonia lost due to environmental effects, etc. This is effectively a large infrastructure project, and the usual goal with these is to use the most abundant and cheap material available that satisfies the requirements. [Answer] Personally I'd avoid the complexity of chemical soups and go with hypersalinated water, like that in the Dead Sea. Ingesting it would be toxic, it would evaporate into water, and the mountains on either side would create a rain shadow preventing excessive dilution. It would be harsh on the skin but not necessarily fatal. The only part that might not work with your purpose is that it would be much more buoyant than ocean water. If it were my world I'd infest it with some critter that would prevent trying to cross it by boat. ]

[Question] [ When teleporting an aura of magic covers your body and this aura works as a **coating** portal. Instead of you entering a portal, the portal eats you. The portal is created magically and eats the user in less than a fraction of a second Thus it is really hard for inexperienced mages to control the portal aura. Sometimes they teleport inside a wall leaving in their place a statue of rock and various materials in their shape. The portal works like a switch: Human goes to place A Identical copy of human made from place A's material moves from place B to place A The same happens when teleporting inside a wall. Now how does one save a mage stuck in a wall without killing them? Once stuck inside a wall mages can't teleport away cause they need free use of their hands and mouth, and vision..all things which are limites or blocked when covered in solid cement or rock or metal. Also the teleport works like a door that comes to you in an instant and not like a star trek teleportion where you are dismantled and killed to be reformed in another place. And just like a door, it is affected by earths gravity, if you jump out of a door you don't skyrocket out of the planet, doesn't matter that the earth below your feet is moving around the sun at extreme speeds. [Answer] **Huge robes!** [](https://i.stack.imgur.com/VHZoP.jpg) [source](https://www.etsy.com/listing/699079864/wizard-purple-robe-with-hood-sleeves?gpla=1&gao=1&&utm_source=google&utm_medium=cpc&utm_campaign=shopping_us_a-accessories-costume_accessories-capes&utm_custom1=_k_Cj0KCQjwi7yCBhDJARIsAMWFScMr9Uj2gVaabHgrwnJM8HVNkB9-4ytm28GpoEvauuOdLeTxUv3pS14aAq_HEALw_wcB_k_&utm_content=go_1844702565_70025064632_346397550421_pla-352706024070_c__699079864_135443614&utm_custom2=1844702565&gclid=Cj0KCQjwi7yCBhDJARIsAMWFScMr9Uj2gVaabHgrwnJM8HVNkB9-4ytm28GpoEvauuOdLeTxUv3pS14aAq_HEALw_wcB) This is why wizards wear those giant robes. Also giant hat (hers is in the wash) and giant beards (also in the wash). By inflating their volume with nonmeat bulky clothes, they will have a larger cavity in the wall inside which to maneuver. Under the bulky robes the wizards are quite spindly. They can hunker down within their bulky robe wizard cavity and get a little space to wave fingers and what not. [Answer] Wizard instructors learn wall extraction techniques the way swim instructors learn CPR. The trick is to locate the cocooned caster and get some air to them. This is done through a combination of three spells... **Association** - take a small piece of the stone pillar which has switched places with the victim and scry its magical congruent, tracing its lingering connection to the stone wall which it used to be a part of. **Divergence** - focusing on the location identified by the association spell, select everything within ten feet which is not stone. **Portation** - grab everything selected from that location and port it back to an empty nearby space . Through expedient use of the **ADP** emergency response, many young wizards are saved from early entombment. [Answer] **If I understand this correctly, the mage is probably dead** *And that's not necessarily a bad thing. But we'll get to that in a moment.* By "clothing portal" I assume you mean that the volume encompassed by the clothing is transported. Mages therefore require hoods or hats lest their heads be left behind. Clothing must drag on the floor and cover hands lest useful appendages be left behind. *If this is not the case, please clarify the rules of your magic.* **Case 1: Mage is fully encased in a wall** The wall is thicker than the volume encompassed by the mage's clothes and for the sake of argument, we'll assume the wall is entirely stone.1 Thus, a mage-shaped stone object is found at the embarkation point and our wayward mage is wholly ensconced in stone. The mage is dead. * Lack of oxygen (the only oxygen molecules are those carried by and within the layers of the fabric of the clothing). * If the mage was exhaling at the time of transfer (most likely, speaking the spell after all), then he/she has no ability to take a breath if there was oxygen (chest is restricted due to being partially or fully collapsed at transport). * Unless the spell can be easily traced, nobody knows where the mage is. * Even if it is easily traced (that would seem to be a weakness to me), would-be rescuers have mere seconds to remove the mage from the wall — which seems unlikely even if the transport was only ten feet away because, sans magic (which can do anything) the option is chisels and the fervent hope that you don't pierce the mage's heart while pounding on the chisel. **Case 2: Mage is partially encased in the wall, facing inward** The wall is thick enough that the mage's face and forward-half of his/her body is ensconced in stone. The mage's rear bumper is hanging out for the village fool to make fun of.2 The mage is probably dead. * We have the same lack-of-oxygen and difficulty breathing problems as before... except that the body has somewhere to go when muscles move. This suggests the plausible conclusion that the mage *could* get some air, even if they can't dislodge themselves from the stone. * In this case, since we're talking about a wall, it's believable that someone would find the mage. * Without magic, we're chipping away the stone with chisels, but at least the mage has a theoretical chance. * Note that it's *also* plausible that the lack of air and constriction breathing are still in play. In which case the mage is dead unless saved within seconds.3 **Case 3: Mage is partially encased in the wall, facing outward** The wall is thick enough that the mage's face and rear-half of his/her body is ensconced in stone. The mage is, for all intents and purposes, fully exposed to the mockery and jests of the village fool.4 Hooray! The mage lives! * Even if the mage is stuck without the aid of magic or chisels, he/she can breathe freely! * What we hope is that said mage isn't soon due for a bathroom break. **Hey! You said a dead mage isn't a bad thing! What gives!** Whether you're writing a story or setting up an RPG, the idea of failure is just as important as the idea of success — and how your characters/PCs/NPCs deal with both is part of what makes for a rich literary experience. In other words, you *want* your mages to face very real death if they're dingy enough to teleport into a wall. I mean, let's face it, whether they teleport to the center of a very thick wall or the center of a mountain, unless they can be VERY quickly found, they're dead. If they don't have the space to move their hands, they don't have the oxygen to live very long. Even if they do have the space to move their hands, they still may not have the oxygen to get through the spell. So, you can either make your magic (a) traceable or (b) always able to leave the mage with enough space to breathe and wave their arms or (c) deal with the reality that you'll have a few well-fertilized walls. *Maybe I should have identified this as a [Frame Challenge](https://worldbuilding.meta.stackexchange.com/q/7097/40609). I haven't decided.* --- 1 *Rather than a modern wall made of lumber and sheetrock, which would make for an interesting discussion... especially if electrical wires and any kind of plumbing is involved. But what if we're talking about a thatch wall? The mage would simply step out of it. Wood? That might have the same problem as stone.... That's a honking thick timber wall, though. Adobe? That would be hilarious. Let's stick with stone.* 2 *And the world is grateful that's all the little wombat is doing.* 3 *And a very real argument could be made that the mage dies anyway due to the confusion/panic caused by the realization that the village fool is in close proximity to the rear bumper. I mean this. Never underestimate the panic reaction to realizing something you can't see, probably can't hear, and can't react to, just touched you.* 4 *We'll leave it to the Grand High Council of the August and Illuminated Fellowship of the Oracine Rite (aka Fat Henry, who's the secretary of said council and the guy who does all the paperwork. For a Snickers bar he'll induct your cat to the Order) to decide the Ultimate Fate of a mage who paid so little attention to what they were doing that they'd end up in a wall. Embarrassment tends to be quickly rewarded (and long remembered) by the Council.* [Answer] **Spell Reversal** As others have said, a mage in your described predicament is dead in a matter of minutes. However there's something else with a lifespan measured in minutes... the residual magic of the teleportation. An amateur wizard screwing up the teleport by ending up inside a wall is probably a student. And their Meister is probably standing a few meters away and will see a statue of cobblestone appear where the student just disappeared. They'll instantly know what happened and will have a spell ready for this situation. Simply: The teleported stone knows where it came from. Sympathetic magic being what it is. So an appropriately cast teleportation spell will put it back, reversing the spell and bringing back the student from wherever they went. In this regard, their student's mobility being restricted by being embedded in stone is an advantage because it will prevent them losing any toes when they get brought back. The Meister has at most a minute or two to react and do it, but it's likely the most common failure-mode of this spell, and if they're as capable as they should be, they'll have the spell ready to go. For almost any other situation, the teleporting wizard will be killed unless they have a friend nearby who knows exactly what to do and can recognise what happened at a moments notice. [Answer] ### The mage goes "oops", wiggles a bit, apologises to the family for destroying the wall, and walks free Next time you walk through a doorway, take a moment to pause and project yourself into the wall. I'm 25cmgut-to-shoulderblade, ~20cm head diameter. Most walls are around 100mm thick, a double brick wall is 250mm. If the body suddenly appears in that space it will be sticking out, and what remains will be a thin layer that will break with the slightest movement. This is my body projected into a 100mm wall: [](https://i.stack.imgur.com/SrhQI.png) Front view: [](https://i.stack.imgur.com/p5UOg.png) Here's the wall cavity minus me (I didn't model neck or arms): [](https://i.stack.imgur.com/nopYg.png) I can free myself from that. [Answer] **The mage would anticipate such problems and arrange for his own rescue.** If I were a mage in a setting in which teleportation was inaccurate and dangerous, I would most likely add a time-delayed reversal to my teleportation spell. After teleportation, the spell would wait for (say) five seconds for me to confirm that I had arrived safely. The signal could be, perhaps a, snap of the fingers or a clap of the hands. If I am not able to take this action, then the spell reverses and I am returned to my origin. (Hopefully not asphyxiated, charred, and/or crushed.) [Answer] > > The same happens when teleporting inside a wall. > > > The mages are a lost cause. A perfect stone or brick replica will appear at the spot where they left from but the inaccuracy of the portalisation will mean that no-one knows where they ended up. You can't go demolishing an entire city to find an entombed mage. In any case they will suffocate within a couple of minutes so there is no time to execute an escape plan. It would be a case of survival of the fittest. Accurate mages would survive. Inaccurate mages could be used as statues. Possibly the smell of decomposition would eventually allow them them to be found inside some walls but they are only going to live for a matter of a couple of minutes so rescue alive will be impossible because they won't be able to breathe. [Answer] ## Add a Preview When casting the spell a few seconds before the spell activates a magical effect appears in the destination (useful to alerting people in the way that they should move) and through that effect they can see their destination and confirm it is where they want to be. If they cannot see anything or there are people in the way then they know they really should abort the spell. Edit: The effect also gives enemies a chance to move, counter, or block the incoming teleport helping to prevent teleport abuse in combat. It is kind of embarrassing if the demon lord gets a chunk of its body teleported resulting in its death. [Answer] **Teleporting something into solid materials is difficult.** Well, more difficult than teleporting into air, anyway. If you swap a wizard sized statue out of a stone block, that implies that you had carve all that stone away from the surrounding stone. I imagine that would take quite a bit more effort, at least more than just separating some air. Your wizards could be trained to recognize when they are attempting to teleport into something hard and stop doing that. *"Teleport this apple over onto this table. Now teleport it into this boulder. Observe how difficult this is. Now don't do that to yourself."* I'm aware this doesn't answer the question of how to save someone who has actually managed to teleport themselves into a wall. But depending on how you frame the magic, this may not be as common of a problem as you think. Though there still may be quite a number of tables and chairs with wizard shaped holes in them around the university. You could alleviate this even more by specifically warding teleportation "gymnasiums" with lots of armor spells and such. If everything around you is *specifically* warded to prevent being sliced in half, it becomes a lot easier to tell when you're doing things right. You could even set up the warding spells with "negative feedback" to really hammer it in. Should probably also ward the other students while we're at it. Don't need any wizard-shaped holes in other wizards. [Answer] ## Maybe prevention is better than the cure Another thought, to add to the masses here, would be consecration. Just like with religious buildings on our own planet, walls could be consecrated or warded against spells to prevent such embarrassing misfortune. Also, you could introduce the concept of meta-spells - bolt-ons to the spell being cast that stop or reverse its effects, should things go awry. Failing that, based on the semi-medieval ethos of your world, a swift slap and "Don't be stupid!" from the instructor could go a long way. This is a very tongue in cheek question, @StainedGirl! I like it! [Answer] The simplest way to deal with this is also the best. If you have frequent cases of mages teleporting into walls, the structure of the walls will be undermined to the point of collapse after a few hundred such accidents (and in a school of magic, this might take as little as a couple decades). Instead, magic schools set themselves up on flat, featureless plains -- no large trees, no buildings sturdier than a frame tent, no large animals (there's still some slight hazard to people, but that's unavoidable). New mages practice in this environment until they're able to teleport accurately enough to at least avoid embedding themselves in solid objects. "Why not conduct only teleportation lessons on the Barren?" Because students will always do what they were told not to: First Years will be trying to teleport as soon as they learn it's possible and can sneak a look at an upperclass student's textbooks. Therefor, *every student* **lives and studies** on the Barren until such time as they can demonstrate a minimum level of competence in teleportation (usually, that's near the end of Third Year). [Answer] # Frame Challenge > > 65kg of human meat goes to place A > 65kg of air moves from place B to place A > > > Air has a density of about 1 kg per cubic meter. That means a human is practically 1,000 denser than air. The wizard will always teleport to a huge vacuum, which in the very least will damage eyes, eardrums and lungs. More damage follows from the implosion of the remaining air around the arroval spot. This is potentially lethal. Furthermore, 65kg of wall will have varying volumes depending on materials, but usually walls are denser than humans. In such cases there isn't enough space for a 65kg human after you remove 65 kg of wall. # Solution The spell displaces a volume of matter, not of amount of mass, and thus [Willk's answer is very appropriate](https://worldbuilding.stackexchange.com/a/197895/21222). If a wizard forgets to wear clothes though, they may play it safe by only teleporting if friends are around. If a wizard-shaped amount of solid material shows up where the wizard was, then they may have their buddies go and rescue them. [Answer] **Since it is a common issue, walls are built with some mage-saving features** Since mages are useful to the king, he doesn't want to lose all the money he invested on their formation in such a trivial way. So walls are built with this in mind: * When not necessary, the wall must be thin enough to only partially encase a mage * When the wall must be thick (eg fortification), the wall must always have some thin, evenly spaced trasversal holes so that the mage can breath a bit. I still think that the volume inside the wall should allow for some air circulation, in the end the mage is not completely rigid and so he could push himself against the rock to provide enough room for air to circulate. These holes allow the mage to breathe and also allow him to ask for help. * for the same reason, it is forbidden to stucco the walls * For this reason, there are groups of workers who continuously inspect the walls to find and rescue any encased mages [Answer] Another idea: You can't really rescue them, but you can train them well to prevent this from happening. Create a teleportation training dome. Warded with special spells, it's impossible to teleport outside of it, and the insides have nothing dangerous in them. So your mages undergo a few years of training within the dome until they can safely, accurately and instinctively teleport wherever they choose. Supplemental idea: Reverse-spell. Cast the teleport in such a way that it will automatically reverse itself in a few seconds, unless a specific spell is cast on the other side. If the caster teleports somewhere where they shouldn't and is unable to incant the complementary spell, they (or whatever remains of them) are transported right back. [Answer] This might be prevented by increasing the teleported volume, so that rather than simply teleporting the mage, it would teleport a small pillar around the mage, so that if they ended up in a wall, they would have enough space to teleport away. This would also make teleportation more useful, as large object could be teleported with changing the spell. Another solution could be power limiters, which would prevent a mage from using enough power to teleport stone or other such materials [Answer] When you change resolutions on a PC, it asks you for confirmation that the new setting is okay, and if you don't answer in a reasonable amount of time, it automatically reverts, assuming you're unable to see the question due to said change screwing up something bad enough that that happens. Seems like spells of this sort could do with such a confirmation/reversion step. [Answer] ## Russian trolls. The wizard's tower needs elaborate security - Orbs of Palantir at every corner and wall, watching for thieves and spells gone wild. Far away on the other side of the world, the Gematria Research Unit has deduced equivalent access runewords for each one of those Orbs, and is watching the wizards intently. A foul up seems more than inevitable, eventually. When tragedy strikes, one of their spellcasting trolls is standing at the ready, and casts his portal to go to the exact same coordinates as the wizard gestured for - no matter where they may be. Trolls being larger than humans, they can probably arrive with some parts clear of the wall. Even if they don't, they are tremendously strong, and not killed by mere suffocation, and they have friends who were watching where they went. Trolls being larger than humans, *their* exchanged matter will include most if not all of the stray mage. The rescued mage can work off his life debt over time in the interrogation room. There are many, many trade secrets in a mage academy worth breaking down ... thoroughly. All is not bright in the future of the rescued mage, however. What do trolls need to eat in order to be capable of casting such advanced magics? [Answer] The slightly **delayed automatic *re*-port**, taking effect if the landing ritual is not successfully finished, would definitely make sense, as proposed by [Paul](https://worldbuilding.stackexchange.com/a/197908/67222), [Ruadhan](https://worldbuilding.stackexchange.com/a/197911/67222), [Mashtater](https://worldbuilding.stackexchange.com/a/197943/67222) and [Atario](https://worldbuilding.stackexchange.com/a/198031/67222) (and me, had I been quicker). --- You might want to minimalize casualties even further - not only are magicans valuable, you probably also don't want your population living in **constant fear a magican might accidentally port into them** on the street. And magicans, constantly publicly stuck in walls, carriages and people (who die tragically of their wounds later) is a **disgrace** to the *most glorious and arcane order of magyck* and might even **incite riots**. (Although you ***could* play that for laughs**... a world, where the wise mighty rulers get stuck in random walls all the time is somethin **unique**.) You might however also want to consider ## a grid of official arrival points A bit like the floo powder network in Harry Potter. Every village and official building is **obliged** to have an ornate **stone pedestal in the middle of the market square** or even keep **a small flat** clear for members of the order with **nobody else llowed close to**.\* Magicans can start their **jump from everywhere** but always have a **safe arrival point**. Why should an order invest a lot of money and effort in educating the elite and then risk loosing them by a mass collision? More commonly frequented *entrances* (e. g. palace or headquarters of the order) have several such arrival pedestals and are always watched by at least one acolyte. Magicans can contact him telepathically before porting to clarify which arrival point is unoccupied. Maybe the landing points can be observed with a crystal, either by the travelling magicans themselves, or also by the acolyte in the headquarters. Because, although you omit carriages and random pedestrians, by concentrating all "traffic" onto few arrival terminals, there is a higher risk of magicans porting into one another. If you don't want to go with telepathy and security cam...crystal balls, they have to send messages and arrange clear dates, when which mage is going to use which terminal. Another approach could be enchanting the arrival pedestals themselves, so when two mages materialize on the same pedestal, one is automatically forwarded/ported further to the next vacant arrival terminal. Therefore young acolytes **travel a lot during their apprenticeship** to visit all the different arrival terminals in person and be able to **aim for them precisely**. Like banning drunk driving, making seatbelts mandatory or regulating the possesion of weapons. And, depending on the political situation, which king or arch mage wants all his way too powerful underlings able to come and go unnoticed wherever they want to, if you can force them to use a network you can keep records of... --- ]

[Question] [ I'm trying to come up with this scenario in a sort of "medieval fantasy" setting. There are two towns. One, *Caertydin* is a large city with all the appropriate tropes, while the smaller town, *Siege* is a sort of satellite town. The reason Siege exists, is that hundreds (or however long ago it has to be) of years ago, a foreign power from a far away land actually laid siege to Caertydin. But the siege was never officially lifted and it developed into an actual town, so there is a noticeable mix of cultures between the two towns. The people of Siege are mostly made of descendants of the actual soldiers involved in the original siege. But now, there is no animosity between Siege and Caertydin, it's not even a Cold War: they peacefully co-exist, trade with each other, travel back and forth, etc. and although officially there is a state of war between their countries, it is known as the "Friendly War" (or perhaps jokingly/sarcastically called the "Forgotten War"). For some reason the side that laid the siege is not motivated to officially end hostilities. OTOH, Caertydin's country doesn't interfere with Siege, e.g. doesn't collect taxes from there or doesn't enforce laws there. It's a bit of a running joke in the towns. (e.g. one might quip, "we're at war!" if asked why they've run out of potatoes, or during some harmless disagreement) My question is, how can this plausibly happen? How did they get from a state of actual war to this situation, and why does the country that actually contains Caertydin tolerate Siege existing? Note: whether magic exists or not in this world isn't really relevant - I'd like a non-magical explanation for this. [Answer] **The Kingdom that founded Siege has collapsed so it can't officially declare an armistice. Siege don't want to publicly admit this.** There is no King to declare an end to hostilities anymore. The people of Siege may think of their kingdom how early medieval Europe thought of the Roman empire: not willing to admit it's gone, occasionally getting behind restoration attempts (eg the holy Roman empire). If the people of Siege declare an end to the war with their own authority, they admit the kingdom they love has failed, and publicly give up hope of ever restoring it. As long as they consider themselves subjects of this old Kingdom, they cannot and will not take on the divine kingly task of deciding when wars end. It's part of their cultural identity, maybe even their religion, if they consider the monarch to be divinely chosen. [Answer] This might be possible, but it will take a large amount of time for this situation to develop. For the sake of this answer I will refer to both the town as well as their inhabitants as Caertydin and Siege. What I think is the most plausible explanation, is that the siege started out as a serious assault, but dragged out too long. Siege didn't cut off supplies to Caertydin fully to begin with, or became less motivated to stop supplies the longer it dragged on. They might have struggled for supplies themselves due to the length of the siege, and were too preoccupied with keeping themselves alive/comfortable to actually attack and waste energy/manpower. A catalyst for a more friendly relationship between the town could be similar to a WW1 event called [the Christmas truce](https://en.wikipedia.org/wiki/Christmas_truce). From then onward, the towns would know from each other that they were "fairly reasonable folk" and "not really worth trying to kill". Slowly this would migrate into a more common happening, as the towns exchange supplies to show their goodwill. They would evolve a "War is only for higher ups, we don't really care about orders anymore" kind of attitude. This might get increasingly more plausible/easier if the siege started as a depriving attempt, without any actual fighting/killing being done on either side. Effectively the entire town of Siege will have slowly defected, and their commanding officers would have either gone along, or found themselves so severely outnumbered that they couldn't really stop it. The original kingdom Siege originated from will have written it off as a total loss, because the costs and effort to discipline the whole army would be too high. So they issued a command that the Siegers aren't to return home until they complete their mission, which is obviously never going to happen, leaving them in the awkward town of Siege not being able to really go anywhere. I suggest looking into the Christmas truce for inspiration, but also the movie "The terminal" with Tom Hanks. While a good movie to begin with, it also clearly shows how awkward political situations can develop when something slips through the cracks. With a bit of handwavium and confused bureaucratic politicians, quite a lot is possible. Also see [this answer](https://worldbuilding.stackexchange.com/a/169211/72352) for a more in-depth exploration of the Tom Hanks option. [Answer] Gambling. The laws of Caertydin prohibit gambling in any form. When the siege wasn't going very well and was entering its second year residents of Caertydin slowly realised they could sneak out at night and go gamble in Siege, as their laws don't prohibit this. The soldiers in Siege let this happen because people from Caertydin aren't very good at poker. They don't get much practice. This initial connection led to more 'black market' shady type things going on between Caertydin and Siege. The laws in Siege are far more relaxed regarding drinking, prostitution, taxes, etc. This was a good deal for both of them; the soliders got money from the wealthy Caertydinians and the Caertydinians got to have a good & cheap time with their shady soldier buddies. The rulers of Caertydin never shut this down because they managed to dodge an actual war. Over time this became a more 'normal' connection. The gates were opened again, regular trade was allowed with Siege, and people just grew accustomed to this new town on their doorstep. [Answer] Previous King of whatever country had started the Siege was a rush, loud, warmongering, boasting type. Probably had a red beard. He had sworn a Holy Oath that if he can not capture Caertydin, he would step down and relinquish the crown. However, while the army was on the march, the King finally had to pay for all the years of drinking and reveling: he had a heart attack and now is paralyzed. While he is still a King, the actual power now belongs to a Prince. A Prince does not care about taking Caertydin: it was poorly planned vanity endeavor to begin with. However, if he calls back the army, his political rivals will use the Holy Oath to challenge the legitimacy of his ruling. So, he left a small detachment to "continue" the siege, while the majority of the army returned home. A secret deal (involving a chest of gold) with the government of Caertydin solidified the status quo, but officially the war is in progress. From time to time soldiers of the Siege capture trophies. Like that time when a general from Caertydin lost his medals in a drinking contest. They send those back home, and Prince uses them as a proof that the war is still going on. In return, soldiers get money. It is still cheaper than to risk a rebellion. [Answer] ## The Land of Abundance So, the biggest issue with an eternal siege is going to be food, both in the city and for the army. So we take this away. Your city is valuable because it's located in a realm with an endless food supply, which also makes a siege a uselessly terrible strategy for taking the city, leading to the present situation. Note, you can replace the infinite food supply with a trade portal, access to an an underground Dwarven city, or other reasons a siege would never work. **The Impossible War** The foreign power desiring this supply launched a force to besiege Caertydin, with the orders "Conquer this city or do not return." Initially hyped, the foreign army experienced in siege warfare set up camp outside the town. Months passed, and nothing happened, there was no starvation, in fact every night the city would have a massive feast. The besiegers, realizing the pointlessness of this campaign, slowly gave up. Their desire for victory was replaced by wanting the comforts of city life. Drink and women came from the city, and officers turned a blind eye to it. How were you supposed to keep your men in check when the city you were besieging was having a better time than you? Then came trade of basic goods and services, the free movement of people, ect. Eventually, the two became dependent on one another politically and economically, leading to the present situation. [Answer] This kind of thing happens all the time in the real world. Take Paris and London for example. On the coast of France there is a little island called Britain. The people there have been at odds with the french for centuries. They did wage war at some point, but after the last one it's been centuries of peace. Fast forward to the 20th century. The french opened a club with all their bro's which they called the EU (some people think it's a union but that is greek for "perfect", huge egos and all). The islanders spent decades trying to join it. They eventually did, but a few decades later they decided to ragequit. France and the rest of the EU just said "ok guys" and let them be. But half of the islanders still keep saying that the french and their continental bro's are bent on taking their freedom and stuff. Business as usual. Look at the islanders' [coat of arms](https://en.wikipedia.org/wiki/Dieu_et_mon_droit) - it says "God and MY rights". And it says so in french, so you know whom the message is targeted at. Talk about passive aggression. They've been at it for almost a thousand years now, and I bet they'll still be at it for the next thousand. [Answer] Siege reminds me to the situation of **Calais** (France) during the 15th century. The city had been conquered to the French in 1347 and until 1558 it served as an enclave in continental Europe for Britain. The city was called a "jewel" because it served as a trading port for wool, cloth, wine, lead and tin. In a way, it made the trading between French and English easier (and it was the source of major trading problems, too). In fact, most of Calais was in an artificial island and it traded with really close French villages, like your Caertydin. So, for your example, Siege could be an **enclave** from a country separated from Caertydin's country by a sea, a great lake or a mountain range. Siege receives goods from its mother country, but it must trade with Caertydin for basic necessities and both cities have a long story of trading between themselves even when their countries are at war (as France and Britain were during the Hundred Years' War). This trading could be even mutually positive for both countries, avoiding an embargo due to war reasons of something useful for both of them. [Answer] Ever heard of the Canadian- Danish war? There is an island(Hans Island.) both nations have a claim on. But the joke is the island is just a barren surface without any natural resources or population. Even going as far as the Danish planting their flag with a bottle of Schnapps and the Canadians returning the favor. So for your story, why did they even attack? If it was a piece of land or something else that is now no longer of concern you can add a friendly tradition of both sides "conquering" it. Like a mine that is now mined out, a forest for lumber that has been burned down, a magical fount of power that no longer exists. The reason why a town like Siege would be allowed is because it is so small and insignificant that it's not worth fighting a war over. Also if Siege is a coastal town with a proper harbor it might even be financially beneficial to just let them stay in as trade partners seeing they would be able to house merchants from both nations. [Answer] As others have said, there are a number of ways that a region can remain at war when the parent country has moved on. If the attacking country was defeated or merged with another, for example, so can no longer declare truce, and nobody has enough interest in provincial issues to resolve the trifling war. However, the problem is: how can the besieging city remain economically viable? A siege requires supplies, either by raiding supplies from the surrounding land, or having good supply lines from the parent country. The former would not result in a happy stalemate, so either the parent country has a rationale to continue supplying them, or they have to be self-supporting without raiding. How's about this, then: Caertydyn is a major trading city and the main shipbuilding center of its nation, located a little in-land from the mouth of a river. The city isn't at the mouth of the river because the river delta was a treacherous, swampy morass of ever-shifting sandbanks and unstable footing. The only people who previously lived there were guides and river pilots who charged a fee to ships to help them navigate up through the delta. Siege was set up to blockade the river and besiege the city. In creating the blockade, they dredged the waterways, cleared the river, sank pilings to set fortifications on and create a military encampment and harbour, and basically settled the river delta. On cessation of hostilities between Caertydyn and Foreign Power, the army base at Siege was recognized by ForPow to be strategically necessary to maintain to prevent a retaliatory attack. So, they maintained it. To this day, it remains strategically expedient to maintain this military camp here, at the mouth of a major trade river. Siege now taxes rivercraft entering the delta, but it's no more expensive than the pilots were, plus there's a ton more trade now that the river's properly maintained and with deeper draft. So it's self-supporting financially, is strategically important, and is also where the military corps of engineers is trained in waterway management. Caertydyn remains very much under a de facto siege: no vessel or supplies can enter or leave it through the river, without the say-so of the military camp at Siege. Siege knows exactly what's entering and leaving the city, so can prevent the construction of warships that might be used to invade the parent kingdom. However, Caertydyn benefits from the protection against pirates, the impressive waterway engineering that they lack the finances, equipment, materiel, and expertise to reproduce themselves if Siege were leveled as it would be if the military camp was removed. It would take years and heavy, nation-invading levels of investment to rebuild to anything close, and Caertydyn lacks that financial clout just to protect its trade routes. Economically, it is strongly in Caertydyn's benefit to ensure that it remains in the Foreign Power's benefit to continue to besiege. But their other allies would never be OK with them signing any kind of treaty to permit the foreign power to officially establish a military encampment. So they engage in saber-rattling any time the idea of raising the blockade is raised; beginning construction of a warship, perhaps, or closing their gates to people from Siege, or whatever... but backing down quickly as soon as it's clear that the siege has regained funding. So economically and strategically, the two cities are now symbiotic, one providing military and engineering, the other providing commerce and sufficient threat to make the siege necessary. TL:DR; have siege control the traffic (ie, besiege/blockade), but add value for Caertydyn. Have a military encampment at Siege be strategically useful enough to continue providing that value so that the existence of the military encampment will be tolerated. Have formal recognition of the encampment be politically inappropriate. [Answer] They simply forgot about it. Happens all the time. For example when the United Kingdom declared war on the Russian Empire, legend has it they included the town of [Berwick-upon-Tweed](https://en.wikipedia.org/wiki/Berwick-upon-Tweed) in the war declaration but forgot about them in the peace treaty. (The historical facts don't appear to bear this out, unfortunately.) > > According to a story by George Hawthorne in The Guardian of 28 > December 1966, the London correspondent of Pravda visited the Mayor of > Berwick, Councillor Robert Knox, and the two made a mutual declaration > of peace. Knox said "Please tell the Russian people through your > newspaper that they can sleep peacefully in their beds. > > > Also have a look at [List of wars extended by diplomatic irregularity](https://en.wikipedia.org/wiki/List_of_wars_extended_by_diplomatic_irregularity) So in your case the Nations behind Caertydin and Siege had a peace treaty saying something like "the united provinces of x declare peace", but since Siege is not in the united provinces it remained at war. [Answer] Bureaucratic nonsense seems to be the most fitting scenario here, plus it seems to fit with the humorous nature of the concept. You might find some inspiration in the story of the [The Yellow Fleet](https://en.wikipedia.org/wiki/Yellow_Fleet) interesting, a group of ships trapped in the Suez Canal for 8 years because of the Six Day War which formed their own community while waiting it out. (+ [this 99 Percent Invisible podcast episode](https://99percentinvisible.org/episode/great-bitter-lake-association/) about it) In [another episode of that podcast](https://99percentinvisible.org/episode/mini-stories-volume-8/3/), they discussed houses in Washington DC which are technically owned by foreign governments and thus not subject to the local laws. Diplomatic houses may wind up abandoned and fall into disrepair, but because of diplomatic relations and bureaucracy there's not much anyone can or will do about them. Another interesting story this reminds me of is how the British government only recently finally [paid off some debts](https://www.nytimes.com/2014/12/28/world/that-debt-from-1720-britains-payment-is-coming.html) that were hundreds of years old. Despite these debts being so old that the government had undergone massive changes since then, and generations of people have come and gone, the financial system remained intact and the debt continued to get paid. There are also many instances of strange geographic quirks that came about as a result of diplomatic disputes / relations. Such as [Vennbahn on the Germany / Belgium border](https://en.wikipedia.org/wiki/Vennbahn#Enclaves_and_exclaves), or [Point Roberts, Washington](https://en.wikipedia.org/wiki/Point_Roberts,_Washington). Once a country has possession of some territory, there isn't necessarily any reason for them to give it up, despite inconveniences it may cause to locals (e.g. students in Point Roberts cross four borders each day to get to high school and back). Would need to think more about the bureaucratic situation that could lead to this particular scenario, but presumably would have to have something to do with a government having no real incentive to end the siege and a bureaucratic system that doesn't really have the capacity to do anything about it. Plus the more convoluted the reasoning is, the better. Perhaps a character might not even want to bother explaining it because it's so complicated. Some characters might pride themselves on explaining it properly. Maybe there's a lack of clarity about the reasoning leading to multiple seemingly plausible versions that formed from rumors that generate local arguments and urban legends. Note, presumably there would have to be something inconvenient about the arrangement as well — if it didn't cause any problems in the lives of the locals, and it was just an amusing historical anecdote, it wouldn't be a particularly interesting or relevant to the characters in the present day. [Answer] Caertydin is part of an alliance of city state at war with the foreign power, but are not in the main part of the conflict, so they don't want to fight the foreign power, and the foreign power doesn't want to waste troup on a weaker part of the war, they are needed somewhere else. The foreign power needs food for it's troup so Caertydin could sell it to him, but Caertydin is still "officially" in the war to support the other state in the alliance (perhaps selling them goods too), and also not looking too much of a traitor to the alliance Caertydin is playing some kin of shady double game in this bigger war [Answer] Maybe I'm a bit of an opportunist here, but I think the most plausible answer is kind of a mixture of other answers they've given here. So this happened after a "series of unfortunate events": 1. The aggresive intentions of the faraway land were real, so the people in the siege were actually trying to make Caertydin surrender. 2. Caertydin is actually a very resourceful city/land, so despite the siege and the long time with closed doors, they manage to endure under the siege without having to surrender. 3. Faraway land suddenly suffers its own conflict, call it the death of the king, a coupe d'etat, an invasion from a farther land... thing is, they can no longer support the siege, so they are now on their own. 4. Resources for Siege are now scarce, and they no longer receive help from faraway land. But they are aware that Faraway land laws are very strict, and surrendering in battle means a destiny worse than death, so they actually prefer to starve to death rather than giving up or even try to return to their homeland. 5. Thankfully, the time of the Happy Harvest comes to Caertydin, a tradition where they have to share everything mother earth has given to them. So, they open their doors to bring help to the sick and famished people of the siege. 6. During this situation, the people of the siege says that they have not received any news or instructions from their homeland; they're still under their laws so neither surrendering nor going back without "winning" are valid options for them, yet they are no longer interested in causing harm to Caertydin. 7. Caertydin accepts to let them live in their own "city" as long as they no longer try to invade Caertydin, at least until they receive further notice or instruction from the situation of their kingdom. This, of course, takes a very long time, and Siege is now a fully functional city of their own... [Answer] Concerns: * Initial demographic would be highly unbalanced, mainly young men. Fortunately there should be enough artisans and engineers able to help with building and providing the basic tools, cloths, etc. for the future town. * A strong enough reason for stopping the actual hostilities and at the same time not moving back to their home country. * A strong enough reason for the attached country not to remove the “occupants”. * A proper reason to build the initial fortification on enemy territory Proposal: Caertydin is part of a kingdom that has extremely fertile soil and its main resource is food. The other country/kingdom is coming from an arid area (possible mountains) with low food production however a high quantity of mineral resources. Due to some commercial divergences the conflict starts. The attacking Kingdom is planning a full invasion, therefore the future city Siege will be the bridge head of such invasion (just a basic wood fortification able to house a full garrison and store supplies for the campaign. During the placement of such construction minor skirmishes happens between the Caertydin militia and the occupation forces however with almost no casualties for both parties (this would make the war to be acknowledged but will not build grudges between the combatants). While preparing the campaign, due to the diminishing access to food, a civil war between the king and part of the nobility. Due to the fact that both parts are in dire need of food none of them will order the retreat of the force near Caertydin however both parties are expecting supplies. Without the kingdom military support Siege is trying an assault towards the city of Caertydin, however once near the gates of the city he “sieges” the gates with carts full of Iron, tools, construction material and such in order to trade them for food (the commander of Siege doesn’t want any involvement in the internal conflict and at the same time has no other means to acquire the needed resources). Such offer would be accepted in the end by the city of Caertydin (an actual conflict would put the city in a really bad spot even if the food supply should be enough for an prolonged Siege the fact that the surrounding fields will not be worked will lead to potential famine in the following year/years). The civil war main confrontation is focusing around the border area next to Siege, making the inhabitants of the villages around the area to migrate towards Siege. This will ensure gender diversity and coverage of skills for the newly formed town. This status quo extends for a few years increasing the importance of Siege and Caertydin in the commercial exchange between the 2 belligerents, replacing the government based trade agreements with a free market. Despite the fact that the civil war ended and that the commercial relations are flourishing, the two kingdoms don’t want to reach an armistice mainly because both parties will suffer huge image issues: * The defending kingdom is afraid that without Siege the relations with the neighbors kingdom will deteriorate and accepting Siege as part of the other country will be looked upon as a defeat. * The attacking kingdom is afraid that without Siege the food inflow will start to diminish and giving Siege to back to the defending country could show weakness; both scenarios making another internal conflict possible. [Answer] The force which originally settled the town of *Siege* might have been an expeditionary force: Far from home and without a proper support line. A change in geography (volcanic eruption, earthquake, tidal wave, whatever) or a change in political borders made it impossible or extremely expensive for their original motherland to resupply or reinforce them and that's why the expeditionary force originally ended up "deserting" or disbanding and forming the town. Their original country is still somewhat pissed about the state of affairs but since it's politically or practically infeasible to invade *Caertydin* over the same access that the expeditionary force originally used, their war has moved on to a different theater. Maybe, if *Caertydin* ships and enemy ships meet at sea, they have standing orders to open fire or something but the point is that while still at war, actually attacking overland is impossible due to geographic or political restrictions. [Answer] This all started as an attempt by the S Empire to take over the C kingdom, using Count S as disposable cat's paw. The S forces started out with a great force under Count S, one of Emperor S's cronies. Unfortunately, the Count failed to cut off Caertydin from C kingdom support (harbor, tunnels under the mountain range), so the siege dragged out... and dragged out, with C kingdom not having the resources or the will to actually counterattack the large forces of Count S, but quite happy to stay behind their walls and counter the attacks that become fewer and fewer. However, Count S does not want to go back to Empire S and admit his defeat. It seems he made a vow when leaving to come back victorious or dead, or maybe he is still obsessed with the daughter of the Duke of Caertydin (who like her father hates his guts). The Empire S realizes that all-out war is not a winning proposition (and maybe they weren't really serious about the conquest to begin with, it seems the departure of Count S was a great relief for many persons at the Imperial court), so with no real reinforcements coming from Empire S (except from the revenues of Count S's estates), the situation bogs down. Kingdom C likewise does not wish to sally forth and provoke Empire S into an actual reaction, because if Empire S feels really threatened it does have great levies that would assemble to protect the empire, and even if the Empire is far away, crushing the forces of Count S would probably provoke the Empire to react. With the death of Count S (some say he survived much too long the broken heart he incurred when his beloved married her childhood sweetheart with a smile on her face), the leaderless army chose not to retreat from the enemy. Since there is formally a war on, retreating would leave a hostile force poised to attack the Empire, and you need funds to go back to S (ships for trade is all very well, but ships to transport an army is another thing, many of those the army came on were destroyed in a daring Caertydin attack with a fireship in the first year of the war). In any case, retreat to where? Count S's nephew and heir really doesn't see the need to pay to recall a hungry army to his already impoverished lands -- an army that has already started trading with the besieged city in order to survive. [Answer] The foreign power lost before the siege could begin. Allow me to write a little story: "The war was all but decided. Our forces were on the run or defeated, and Caertydin's troops were on the advance. To win the war in a last ditch effort, we had to employ a daring strategy. We sent the combined defensive forces of our own capital to conquer Caertydin's capital (the capital was later moved) in a quick strike. The bet almost worked, since Caertydin did not expect such a foolish action. Our forces got through the enemy lines *(who did not expect to see another army)* and reached Caertydin almost unharmed. Nevertheless, the unavoidable happened and a messenger reached us shortly before the siege was launched. The war was lost *(possibly the foreign capital had been razed to the ground, which would explain why the army could not return)*. Our commander managed to negotiate a peace with the defenders *(with most of our weapons surrendered)*, on the condition that the entire army would be pardoned. They accepted *(initially under strict guard)*, as the army was never involved in atrocities and was partly made up of civilians. Due to the lack of housing in the surrounding area, we expanded our army camp into a provisional satellite town, which grew in size over the years." Now this scenario would mean that the war officially ended, but the constant presence of what was originally a siege army would lead to the very same situation as described in your question. You could also combine this with the answer by user72058, or by saying that the army never officially disbanded. [Answer] There are many possible reasons for this and there are several historical cases where a war didn't officially end for some time even after the actual figting stopped. For example the US never signed the treatiy of Versailles so they technicly were still at war with Germany after WW1 but for more historical cases see History SE. Reasons for such a situation might be: * The attaking armie might have taken a false identity (e.g. claimed to be the army of a made up powerfull kingdom). The army is defeated but the powerfull city/kongdom/empire they claimed belonging to does not exist or is far away and not interested in this land. In that case Caertydin is at ware with Utopia that does not exist and thus can't negotiate for peace or is far away and has never heard of Caertydin and thus has no interest in negotiating for peace. * If the home of the atacking power is "far away" (whatever that means in your setting), they might lose intereist in the war, not even sending someone to sign the peace treaty or at least they are not willing to accept the terms offered to them * There are special custums for peace negotiations and for whatever reasons, they are not met (e.g. in ancient Greece the war between two cities was officially over when the losing side returned to the battlefield asking for their men's corpses to be returned. If they wouldn't do that, there would technicly still be war even after all fighters went home) * Either side might not be willing to agree to peace without reparations but the other side is not willing to meet the demands. In the end, the attacking party doesn't want to spent more money on the war so they just go home and play the waiting game * Losing a war might be out of the question for political reasons. The ruler(s) don't want to lose face so when they realize that they can't win, they keep the war going but stop putting an efford into it. They might be trying to negotiate a "mutual peace" but again the defenders might not be willing to agree to it * The war was declared between two entities that don't both exist any more. Maybe an early kingdom has declared war on a city and tasked one or several of their semi autonomous cities to take care of the actual fighting before breaking apart. The attackers didn't go to war in their own name so they can't negotiate peace on their own * Either side loses their leader and noone can negotiate for peace. Maybe a king falls and his vasalls regain de facto independance but they are still loyal to the now empty throne. As a result, the siege is continued in the name of the king/throne but since he is dead, the attackes delay all war efforts untill the next king decides to either continue or end the war (and obviousely there is no successor in your scenario) * If the siege was part of a war between alliance, the alliances might have made peace (or collapsed) but not every participant has signed the peace treaty/treaties or mad a peace treaty with every part of the enemy alliance * There are sevaral alliances and/ or loyalties involved (and changing) that have contradicting implications. Imagine a (former) colony A of major power B is part of an alliance that declares war on the target but then B declares friendship or pledges to protect the target. In that case A might be forced to stay at war because of their alliance but A would no longer attack the target. * The defending power was so successfull that they cut the enemie's supplies and laied siege to the attacking siege camp, maybe even get to win the war but for any of the reasons above, they don't end the war. When enemy soldiers are trapped in foreign land and are not allowed to return home but the war ends (de factoo), the winners won't kill them but might allow them to settle/stay there instead and slowly give them more and more freedom untill it's a new city rather than a prison camp. Fast forward three generations and - under ideal circumstances - the war is little more than old men's memento and jung folk's joke In any case there might or might not be a truce/armistice. That would hugely effect the relations and the character of the "friendly war". If an entity can't officially negotiate for peace but negotiates a permanent truce, it might feal like a "friendly war" quite soon but when either side is not willing or able to negotiate at all, tensions would be much higher. Depending on wether or not there is a truce/amristece, there might be groups that want to revoke the truce/amirtice or staight out launch an attack against the "friendly enemy" or force the opposite side to finally negotiate. However in most of these szenarios there is little reason for the attackes to stay. Either they were that close in the first place and after losing the war they became dependant, they got the right to stay at Siege as part of the armistice, they are unable to retreat and given the freedom to settle rather than being captured or the war was long but not bloody so that they actually build a life there. If the defending city lost many men (ideally to other foes or illness), they might even need the repelled attackers to stay to keep the economy and population up. [Answer] The country that sent the force got itself in serious financial trouble, the troops didn't get paid. They weren't happy about the situation but the king told them that if they quit fighting because of this they were traitors to be executed on sight. The troops had nowhere to go so they sent a messenger over telling Caertydin what had happened, they would defend themselves if attacked but otherwise simply intended to settle and take no offensive actions whatever their king said. For Caertydin to attack would cost a lot of lives (remember, this is a superior force to them) for no realistic gain, as the presence of Siege is not a problem for them. Over time relations became friendly, the idiot king (or even his successors) won't accept the defeat and pretends the war is still going on. (And it might even be elsewhere.) [Answer] A peace treaty through royal marriage, with the siege contingent being left in place - with the terms of the peace treaty being such that the siege will not be officially lifted until the first direct male descendent of the marriage assumes the throne. No male descendents from the lineage have yet survived until the age of majority, and female descendents have been acting as regents until such time a male hier can fulfill the specifications of the treaty terms. ]

[Question] [ The characteristics of a wizard: * Spellcasting is very complicated and difficult - a high intelligence is critical to make a success of it. * They spend many years studying to master the basics of their craft, often followed by more years as an apprentice being taught advanced secrets. * Wizards often form colleges or guilds, with a strict hierarchy and lots of elaborate politiking, although the more knowledgeable/powerful are at the top. * New wizards are treated very badly as they work their way up the ladder, but once they learn some powerful spells (or obtain an influential patron), they get promoted to the inner circle. * Apprentices tend to be poor, but powerful wizards are rich, and greatly feared by the common populace. I was thinking, that this sounds almost exactly like a description of a lawyer. A quick Google search shows that there are 6,500 law firms in New York alone. That's roughly 1 firm per 1300 people. Which means, if lawyer = wizard, a medieval city should have around 10 guilds, and Neverwinter (for example) should have at least 20. However, there are only 14 in the whole of the Forgotten Realms, indicating that something is encouraging wizards not to start new ones. So, my question is: 1. How accurate is the lawyer = wizard analogy, is there any (modern) profession that might be more accurate? 2. What could cause my (typical, d&d-standard, fantasy) city to only have a single mage's guild? Wizards can teleport and create permanent portals, so it seems reasonable to treat all cities as effectively contiguous, since they can easily move between them. That explains why the guilds don't vary by city. But, it doesn't explain how a single guild could have obtained a monopoly on magic. Forced recruitment is a possibility, but not ideal. Why are there so few guilds? [Answer] # This Ain’t a Law Firm, it’s a God Damn Bar Association *—Fall Out Boy* You are correct in that there are many law firms, but for the entire state of New York, there is only one Bar Association: > > The goals of the association are to cultivate the science of jurisprudence; to promote reform in the law; to facilitate the administration of justice, and to elevate the standards of integrity, honor, professional skill, and courtesy in the legal profession. > > > While, let’s be honest, the purpose of a law firm is for a few people to get really rich together. So make your One Wizard’s Guild more similar to a Bar Association than to a law firm. Have it be a certifying body, a collective bargaining body. Have it be the mouthpiece of wizardry of modern affairs. This organization can also provide many useful services for the wizards who are part of it: discounts on ingredients for their spells, obtained through membership, ala AAA. Access to the premier arcane libraries of the world -in a world without the internet and with hand-copied books, libraries are an invaluable resource. Insurance against magical accidents. Being listed in the Book of Wizards that people query to find the wizard they need. Arbitration for disagreements between wizards, and, in a pinch, venues for their duels. The *size* of the organization is what enables it to be so convenient: there’s no competition, because a newly formed competitor would have nothing to offer. [Answer] Because: > > Once upon a time the plural of 'wizard' was 'war'. (Pratchett) > > > and this left large sections of the planet uninhabitable. Over time the more excitable wizards killed each other off and the profession became a little more stable in its membership, but they remember that they must remain united under a single governance for fear of what may happen again if they are ever significantly factionally divided. --- The usual comparison is academic rather than legal. It's not just that they're somewhat bookish, it's also that the average person does not have direct need of a wizard's services in the way that many people would have regular use for a legal professional. [Answer] I suggest it's closer to doctors. Wizards can specialize, as a Doctor can. They can work only in potions, or in necromancy, etc. There's only one AMA (American Medical Association) but any number of organizations for specializations - podiatry, ear nose and throat, etc. So while there may be one Wizards' Guild there are likely a number of professional organizations for potion masters, transformationists, Necromancers, etc. The Necromancers' meetings probably happen at night. [Answer] Your bulleted list also essentially describes Medieval (town) guilds. These *did* fragment into parts, during boom times or when complex innovations created specialization pressures, for instance, to support the range of specializations necessary for high speed mechanical looms. To question 2: Guilds (or perhaps "Guilds whose members could destroy the kingdom at will...") are established at the whim of the king. [Letters patent](https://en.wikipedia.org/wiki/Letters_patent) establishing such guilds establish a monopoly for the practice of certain actions. This means a competing second guild or a lone non-guild practitioner is subject to any number of sanctions and punishments for performing magic. The cost for obtaining a state monopoly can be so great that a second guild, even if permitted by the king, may be unable to afford legal status. One method used by [Medieval guilds](https://en.wikipedia.org/wiki/Guild#Medieval_guild) to reduce the public's use of non-guild members was to enshrine in law the illegality of trade with a non-member (except in free towns or during certain market days). In addition to controlling the sale of product, guilds would also establish control of the inputs to production -- when it is illegal to buy spell components, the cost of those components to non-guild members (on illegal markets) can quickly become prohibitive. [Answer] > > 1) How accurate is the lawyer = wizard analogy, is there any (modern) profession that might be more accurate? > > > Progra͠mmers. [Software developers often speak in arcane/ali̧en terms](https://worldbuilding.stackexchange.com/a/52386/21222). When you have a problem with a lawyer's advice or a diagnosis given to you by a doctor, you can google î̩́t̲͎̩̱͔́̋̀ up and at least have a very superficial understanding of what they said. But if a dev tells you that the BOM mismatch was due to a code monkey having messed the unrolling of a loop because they cannot duck type? You need to be able to do better than a Hello World to be able to understad Google̸ results for those. ​̅ͫ͏̙̤g͇̫͛͆̾ͫ̑͆l͖͉̗̩̳̟̍ͫͥͨe̠̅s ͎r̽̾̈́͒͑rè̑ͧ̌aͨl̘̝̙̃ͤ͂̾̆ A̡͊͠͝ISͮ̂҉̯͈͕̹̘̱ O͇̹̺ͅƝ̴ȳ̳ TH̘Ë͖́̉ ͠P̯͍̭O̚​N̐Y̡ H̸̡̪̯ͨ͊̽̅̾̎Ȩ̬̩̾͛ͪ̈́̀́͘ ̶̧̨̱̹̭̯ͧ̾ͬC̷̙̲̝͖ͭ̏ͥͮ͟Oͮ͏̮̪̝͍M̲̖͊̒ͪͩͬ̚̚͜Ȇ̴̟̟͙̞ͩ͌͝S̨̥̫͎̭ͯ̿̔̀ͅ Also n̷otice that words have not only power, but a distance between them measured by Levenshtein, and that `frobnicate(foo)` is a proper example for all statements. > > 2) What could cause my (typical, d&d-standard, fantasy) city to only have a single mage's guild? > > > The USA is one of the largest countries in the world. It has over 19,000 municipalities and more than three hundred million citizens. Still, many things are subject to a single authority. If you deal with medicines or food you must obey FDA rules. If you wish to enroll in a college, you'd better have a good SAT score, which is something you get from a private organization. Going beyond the US - all internet domains in the world are subject to ICANN's rules, which is a single private organization as well. So your wizards may have a single ruling board worldwide, and it may have subsidiaries in kingdoms or large cities. Wizards would go to such subsidiaries locally but the ultimate authority is the global organization. They may enforce their authority by maintaining the magical infrastructure necessary for [Manacoin](https://worldbuilding.stackexchange.com/a/112321/21222) trading - that is, if you don't pay your annual membership fee, they will hack your Manacoin wallets and block them, and then you won't be able to get paid for your magical services. [Answer] As we are giving answers via references to entertainment media. **There Is Power in a Union - Billy Bragg.** Once upon a time, there were thousands of wizards, who set up businesses selling their magic. The problem was, casting a spell cost a wizard nothing, and took a few seconds. There were two wizard doctors in town, both had 1000 customers. Doctor A realised that he had plenty of time on his hands, but wasn't making enough money - people could be cured too quickly and too cheaply. So he cut his prices and stole customers from Doctor B. He now had 2000 customers, although slightly less revenue per customer. But Doctor B then cut his prices to match, taking his customers back. Doctor A now has the same amount of customers, but less revenue. So it is even more important for him to cut prices to attract new customers. 2 months later, both wizards are offering miracle cures for 1 copper, and starving to death. So, the Wizards set up a union. The union agrees on certain minimum conditions for working wizards. The union sets minimum conditions and pay, and all Wizards agree not to offer their services to anyone who won't meet those services. Wizards can compete by developing new or better spells. The union could protect their patent for X years, in exchange for the spell becoming licensed to the Union after that time. Any wizards who works for worse conditions is blacklisted - no union wizard will talk to them, teach them new spells, or sell them magical items or ingredients. Then, add corruption and politicking into your organisation as required to suit your goals of mistreating lower ranked members. This is more like a trade union than a single company. Typically, there is only one trade union for each type of worker. You may end up with several specialised guilds - necromancers guild, illusionists guild etc, but you are unlikely to end up with several guilds competing for the same niche. Unions don't work unless they are big. If there were two wizards unions, whichever has the best wizards (and most money) will provide the best opportunities to apprentices, which will lead to that guild becoming more powerful, until eventually it snowballs over the other. [Answer] Someone cast a spell that kills off anyone who forms a second guild. No one knows how to turn that spell off. [Answer] Government might insist on one central guild that self-regulates the industry. In my world the primary Kingdom has only one guild of wizardry. This is a collective of many small schools that teach magic. It pools their resources to provide library and material resources and helps enforce the reputation of magic-use. This is a direct response to earlier times when magic-users repeatedly tried to take over the State, had to be viciously repressed and were hunted down to near extinction. Therefore the only wizard guild that is allowed today is a benign, educationally based institution that welcomes all magic-users and will support investigation into illegal conduct by its members. Its independence is assured but its leaders must answer directly to the King or his local representative and are held accountable for the actions of guild members. [Answer] You're forgetting the power aspect. Obviously, as stated other places - guild == bar and not firm. Honest Abe's Apothecary Shoppe is not a guild, it is a firm - and may have many workers. Honest Abe (and his partner) are probably members of the One-True Guild, however. The only reason there are 50 bar associations, is because lawyers have to be certified by each state to practice in it. And, for most bar associations, you can only take the test if you paid big money to a correct university to get a 'degree' (this didn't always used to be the case, and may not be the case in all states - although that number of states has been decreasing, not increasing). Basically barriers to entry (keep competition low). So, you may not practice law (provide legal advice; ie why IANAL is a thing when people discuss legal ideas), the same as you may not practice medicine unless you're part of their club. Penalties are kinda dire IRL. You go to prison if you attempt to compete with those in power. Why a club? To keep the prices high (enriching members), competition low, mask incompetence (well, of course if you're the guild you're going to claim it is 'in order to keep competence higher than an unregulated free-for-all' - but it cuts both ways), and shield bad guild-members from consequences. Also, like medieval guilds, there are existing legal protections for the club. As well as like unions, you make sure the scabs learn their lesson - if you can't get the cops to do it for you. ARS Magica does a good job of explaining this. If you're not part of the club, any mage can rob or kill you with no consequences. And in fact, club members may be directed to band together in order to take on interlopers / protect the guild from competition. There is an enforcement branch. If you are a member of the club, you have to follow specific rules if you want to rob of kill another member. [Answer] I've two ideas, and both have two simply variations. * Because magic is too powerful. * Because they want to hold the power. # Because magic is too powerful During the history of your world one of this two things may had happened: * Several times were born very powerful magicians, capable of having an enormeous amount of power, manipulating the landscape at will, and setting on fire whole cities or armies. These mages were a real danger for any person which doesn't share their interest. * Several times important groups of magicians raised and revealed opposing from the kingdom throne. This magicians rebellions brang countless of death both from kings soldiers and from mages due they strong power. Despite any of both options, the king had to fight several very hard wars with endless deaths in order to stop mages from destroying the whole kingdom and conquer it. After that, the king decides to control the whole magic of the kingdom. That is why he build **The Greatest Association of Magicians (GAM)**, a state guild unique in it's kind, capable of manipulating the whole magician profession. The GAM decide which spell are able to learn by mages and which ones are forbidden. The GAM decide how to divide the magicians in several professions strictly regulated (alchemist, sorcerer, fire mage, enchantress, etc [adapted to your world]). Also, it regulate **any** kind of magician profession, workshop, work or even guild, if they aren't liked by the GAM, they are closed and imprisoned. * If you decided the first option, GAM strictly regulates the professions in order to no one be able to hold the same power as the old magicians. GAM doesn't allow a mage to know all the spells, just a tiny fraction of them (so never they will be demi-gods). * If you choose the second option, GAM doesn't let make any other kind of magician association (at least, which strictly regulation, supervision and control). By that way, mages won't be able to organize themselves again in order to make another rebellion. # Because they want to hold the power In this idea, it isn't the king who fears the mages, it is the mages who fear themselves. The greatest mages know about what I'm talking about. It's rare, but sometimes magic can be too powerful, and too dangerous not only for you if not for all of us. * **Dangerous:** In this idea there is an old story about a great mage that one time he alone (or with other mages) summoned a great demon... by accident. The demon killed thousand of civilians and several of the elite mages in order to seal it. * **Powerful:** In this idea maybe the demon was summoned on purpose. This mage had an enormous power (like said above in the first title) and the other mages feared him. So, in any case the greatests mages decide to build the GAM in order to regulate magic because: - In the first option they made GAM in order to prevent again this kind of mistakes. If mages doesn't know how to summon a dangerous creature... they won't summon a demon again by accident. - In the second option they didn't want to loose their power. This mages fears that other mages might take they possition and power. So that is why they made GAM, in order to prevent other mages to be more powerful than themselves. GAM divide magic in study fields in order to not be allowed to study all of them by a single person, anyone will never be able to be so strong again. So in any option GAM regulates and reduces the "educational program" of magicians. GAM decides which books are allowed to read and which ones no. GAM decide if some spell is allowed or forbidden. [Answer] I'm particularly fond of the way this was implemented in the Gentleman Bastards series. The short version is this: At one time, there was a wizard with the idea of making a wizards' guild. To make his idea a reality, he went to visit the most powerful wizard in the city, used some form of coercion to force said wizard to join his wizard's guild. From then on they were off to the races: together, they visited the second most powerful wizard's house and simply said: *either you join our wizard's guild, or we destroy you where you stand*. And then there were three. They then repeated this process, going down the power rankings. Those few who refused, were blasted to bits by the combined collective might of the other wizards. They then implemented a simple policy that anyone found to have magical talents must either join the guild or be blasted to bits and you can imagine how they were quite effective. [Answer] I would argue that your wizards are actually arcane programmers! > > Spellcasting is very complicated and difficult - a high intelligence is critical to make a success of it. > > > This is more true back before the PC Era. Without the PC training wheels, computers are complicated. (I dare any non-programmer to simply reboot their computer using the Command Line. You don't even know what the CL is! (actually, don't try that, I don't want anyone to somehow corrupt their PC)) > > They spend many years studying to master the basics of their craft, often followed by more years as an apprentice being taught advanced secrets. > > > 1. Learn what a mouse is. `No not the rat!` 2. Learn how to open the IDE. `No, not notepad. HTML doesn't count! *headbang*` 3. Learn 2 program. `FOR THE LOVE OF! JAVASCRIPT IS NOT JAVA! DON'T INCRIMENT THE *CRASH* pointer...` 4. Data-structures, Algorithms, Operating systems, Logic, Development practices ... `Why do you have a sticky note that says P@ssw0rd... oh right, security isn't a degree requirement...` 5. Sys-Admin, DBA, Machine Learning, IoT, Servers, Rocket Science...`So now the computer just surfs cat pictures all day? At least we know now that they are also slaves to the fluffy overlord.` 6. Quantum computing, P=NP, Life the universe and everything. > > Wizards often form colleges or guilds, with a strict hierarchy and lots of elaborate politiking, although the more knowledgeable/powerful are at the top. > > > Like the IEEE? Actually, I think you are thinking of corporations like Oracle, IBM, and Microsoft. (Hail Google!) Answering your second question here. View your guild like a corporation. Competition must be assimilated, or crushed. With monopoly comes godly power. If you live in the US, just look at ISPs (Internet service provider) as an example of this. Without a stronger external force (IE Governments) a corporation will only continue to grow until it controls everything, and at the end, there can only be one! Note: If left unchecked, if a guild/corporation becomes more powerful than the government, than the guild/corporation IS the government. Maybe not on paper, but the government will be powerless to refuse them. Anti-trust/monopoly laws help preserve the balance of power (and are better for the consumers). And if you think programmers aren't part of the military, thank you for not associating us with the systems we built that have deadlocked this world on the edge of thermonuclear winter. ^\_^ Or the ability to find, and blow up, underground complexes from another continent in under 24h. Or the Predator drones... I'll stop talking. > > New wizards are treated very badly as they work their way up the ladder, but once they learn some powerful spells (or obtain an influential patron), they get promoted to the inner circle. > > > 1. Intern - Coffee fetcher 2. IT - `Have you tried turning off and on again` 3. Data entry - `And that's entry number 5 jillion and 1... or was it 1 jillion and 5... fluff` 4. Entry level - `Lets see, and this bug is caused by... THE COMPUTER IS FULL OF BEES!!!!` 5. Senior level - `And I need to leave in 5 minutes to catch a plane for tomorrows 5am meeting` 6. CEO - (See Elon Musk or Steve Jobs) > > Apprentices tend to be poor, but powerful wizards are rich, and greatly feared by the common populace. > > > compare "Steve Jobs" vs "College grad" (I'm in debt up to my eyeballs. ^\_^) --- Right, back to the point. Why would programmers unite under one common banner? Maybe call it the IEEE? Power my friend. No one has the time, or knowledge to build a forum server from scratch. Bit by LITERAL BIT! Even jumping to high level code with Libraries of communication protocols and authentication, a bare bones forum would take too long to make. We build off each other. We standardize how we work and cooperate. We make our parts like gears. Easily tuned and replaceable. We take the hard work of others and use them to build new things you could only dream of before! We refine our methods with RFC (Request For Comments), and Open Source collaboration! You think your safe? Our day is coming! THE AI REVOLUTION IS COMING! *Insane laughter* ***THUD*** > > "Any sufficiently advanced technology is indistinguishable from magic" - Arthur C. Clarke > > > [Answer] I'm not going to answer question one that falls under [Story Based](https://worldbuilding.meta.stackexchange.com/questions/3300/why-is-my-question-too-story-based-and-how-do-i-get-it-opened), in some settings it's very apt and in others it bears no relation to reality. Assuming that the analogy is accurate the reason there is only one guild is very simple; Wizards spend their time on study and dangerous magical undertakings. They don't bother to start another guild because setting it up would be hard, and more importantly *distracting* (possibly lethally dangerously distracting), work. They have a working guild set up that's easily accessible for anyone from anywhere already so they don't need a new one. [Answer] Wizards are hired on reputation, while in reality they're extremely specialized, and most jobs/missions require 2-3 specific talents together. Instead of trying to explain this to lay customers, it's easier and better for the reputation to work on a subcontracting basis. There will probably be some who specialize in customer relations and spectacular shows, while their more technical friends do the actual work behind the scenes. One big guild makes sense, since there's not a lot of overlap in the skills...some of the magic is figuring out how to do the job with the skills available at the time. Perhaps most wizards prefer anonymity, and are happier working behind the scenes and letting the showboaters get all the attention. They may feel threatened, or prefer their friends not know their true vocation. Also, it may be more profitable to concentrate the big accomplishments in a few front men that, with the huge reputation, can command much higher prices than relative unknowns. That's more money for all the participants. [Answer] ## Because joining a smaller guild puts a wizard at a disadvantage Perhaps a Wizard can only learn new spells from other Wizards. Maybe learning from a book is very difficult, or perhaps Wizards are very guarded of their spells and only teach them to other guild members, not disseminating them publicly in any way. If this were the case, then joining a smaller guild would place a limit on the amount you could learn; if you did join a small guild, at some point you'd have to move to a larger guild to continue your development. In such a setup, once one guild had achieved a critical mass, it becomes very unattractive to a new Wizard to join any other guild, and perhaps also explains why they are willing to put up with being treated so poorly. ]

[Question] [ The universe is populated by a decent number of different spacefaring civilisations and races, the largest spanning over hundreds of systems. They have formed relations with each other: Diplomacy, trade, and of course war. Most nations can field large military fleets and the largest nations have constructed huge dreadnoughts up to a kilometer long (though nothing planet destroying). Space battles often have epic proportions, with hundreds of vessels exchanging fire. Yet, encounters of ground forces are far smaller in scale, with usually less than a hundred of combatants. Tanks and large mechs exist, but are a rare sight. Instead, most forces are small elite teams. Why would a nation have so much bigger space than ground forces, when it has the economical power to field millions of soldiers or tanks, or even build huge titans? [Answer] The reason no space-faring nation would invest in large, expensive ground forces is the fact that they have no defense against your kilometer-long dreadnoughts. However, a small special forces team could still be used because their defense is the risk of collateral damage. Got a 100,000-strong soldier-and-mech army on your planet? The fleet clears that problem up with a quick and cheap barrage from space. Got a tiny special forces team causing a ruckus on your planet? Unless the fleet wants to take out an entire city to kill 10 enemy troops, they can't do anything except send in their own small teams. [Answer] **If you have orbital superiority, small teams are the only ground forces worth deploying.** You can drop a nuke from orbit and incinerate a city. You can drop 'rods from God' to precisely annihilate bunkers with the raw power of kinetic energy. You can drop precision-guided munitions, turn sands to glass with lasers, or wipe out an army with a railgun shell. What you *can't* do is extract a VIP, or secure a hostage, or fight an insurgency door-to-door, or rendezvous with an asset, or take a command post, or seize a broadcast station. Your policy options go from 'sternly worded letter' straight to 'obliteration from orbit', with crater size being your only variable. Your ground forces do not exist to subdue cities or destroy armies as they did in the past- that function has now been taken over by your fleets. The ground forces exist to go where a spacecraft in orbit cannot see, do things a spacecraft cannot do, and surgically apply force in ways that spacecraft cannot. This is not to say that you shouldn't invest resources in ground troops: On the contrary, they should be significant investments, the best-of-the-best, as much diplomats and strategists as they are door-kickers and trigger-pullers. Because wars aren't always won by inflicting as much damage as possible, and accomplishing the primary objective of any war ('making the enemy stop being disagreeable to your policy') requires applying exactly the *right* level of violence in exactly the *right* way. For some cases, the right level is nuclear armageddon and the right way is rained down from orbit. For others, the right level is a single bullet and the right way is delivered from point-blank range. The side that does this well will accomplish its objectives faster, more completely, and with less collateral damage than the one that applies the sledgehammer approach of orbital bombardment to any and all obstacles. [Answer] Planets are slums. You are stuck at the bottom of a gravity well, you are exposed to uncontrolled and polluted biosystems. You are immobile and vulnerable to planet killers. Plus, who wants to spend their lives in full-G, halving your lifespan, just so you can walk around on a planet? About all planets do is cheaply (in terms of resources of value to the space-born) incubate poor people. And people really aren't that expensive to make even in space, and the space born are properly adapted to where people are useful (space). There is nothing much of value on planets, so space born civilizations don't spend resources on planet based armies. Rarely there is a reason to do planet-based operations. These are mostly non-military; trading in primitive gravity-bound art, biologists looking at how life adapts to harsh planetary conditions, mineral formations that are useful and produced by chaotic planetary environments easier than in a factory in space, etc. To that end, there are some specialists who are equipped to visit planets: down-trippers. With reinforced bones and circulation systems (either a throwback, bioengineered, augmented, or an uplifted primitive) they can operate in a full gravity environment. They don't have huge budgets (compared to space navies), but the cost of modest personal security tech is cheap enough (for people in space) and planets hostile and dangerous enough that they look a bit like special operations troops. In the event that there are military or intelligence objectives on planets, independent down-trippers are contracted to do the work. Maintaining a real military force for down-tripping would be like the military maintaining camel cavalry in this day and age; way too niche to bother with. [Answer] Large armies invite aerial bombardment. Any time more than a few hundred soldiers are in one place, asteroids, nuclear warheads, and chemical bombs are dumped on the area. The only way to be secure against this bombardment is to totally control the space around the planet with your large fleet. If your fleet is in control already, then you simply bombard the enemy ground forces to oblivion. Even your ground forces may only require a few men in any given area. Armed with hand-held nuclear-rocket launchers, a hundred troops easily have the firepower to oppress local inhabitants. Or, if you want to be more creative, perhaps the post-singularity nanite swarms that wander the planet like locust disapprove of large groups of humans and dis-assemble them. A third option is you have star-trek teleportation devices that can only beam limited amounts of matter. In the fast-paced warfare of the age, only instantaneous teleportation is swift enough to avoid death. A large army takes an inhibitive amount of energy to teleport. [Answer] **It's mostly logistics.** It's unbelievably difficult to maintain supply lines for hundreds of thousands of people in hostile territory. Sun Tzu gave a baseline efficiency of 20-1 for this (as in, it takes 20kg of food to get 1kg of food to troops in enemy territory.) The US army in the Middle East gets even worse numbers for fuel - we're talking about dozens or more of gallons of fuel required for each gallon delivered to some remote outposts. This is only going to get worse in space, where distances are even greater (although it's probably more a question of fuel vs. food. Still, resources are resources.) For smaller numbers, say thousands, it becomes easier to work into overall fleet logistics. 10,000 men in a fleet of 300 ships and 30,000 crew is not that hard to maintain. 100,000 men in a fleet with 30,000 crew is going to really stretch things. **It's also versatility and training efficiency.** I'd much rather have a company of elite soldiers who I can use to board enemy ships, defend against boarders, and make pinpoint strikes than three companies of good soldiers who are trained for one of these things. Now, I may want to groom specialists among the elite company, but I think most of the training would be universal. Fewer troops to train means I can train them more intensely and more frequently with the same overall set of resources, and these are all high-value missions where I *really* don't want to screw things up. **It's about the value of the targets** In an era of space warfare, what is most important? The enemy shipyards, docks, and fuel depots. Guess where those will be - that's right, in space. There's not really much worth taking on the ground initially, and the things which are worth taking are small installations and production facilities, not huge swaths of land. Small, elite forces are much better at taking those kinds of targets anyway. Of course, you want the whole thing eventually, but when you're in the thick of the fight, what are you going to focus on? Speaking of taking the whole thing, there would need to be large armies at some point, but these are only brought in once the skies are clear and the enemy military is neutralized. These won't see much straight-up combat; their experience will be more like resistance and partisan fighting. Therefore, no mechs, no tanks, and no large-scale engagements. [Answer] Basically, if you want to invade or attack and degrade an opponent, you are not doing it properly, if you have a huge army and no way to transport it to the target in any reasonable amount of time, if at all. You also are not doing it properly if you have no way to prevent the army from being destroyed in transit. You also are not doing it properly if you do not have the ability to first attack the landing site before actually putting your army on the ground. If you have a huge amount of coastline to defend or an entire planet, and have no naval assets and no standoff weaponry that can be deployed from your location, then you are in serious trouble even if you can see the approaching invasion. The whole of your attacker's army is grouped up on individual vessels, and you cannot destroy it in those vessels until they are very close to your borders. If they get a foothold, they now have to face your land army, but also have the benefit of the terrain to use for cover from your own land army and supply lines coming via methods of transportation which you cannot attack while it is enroute to supply the army now on your land. The Soviet Union had this problem, in a way. They had no way to counter attack the Germans in Western Europe or North Africa, because they had no navy and had little port access to that part of the world's oceans anyway. Recently, it is argued, this was the reason for the conflict in Crimea - some fools allegedly decided that they could tamper with Russian trade and military access to the Mediterranean, by manipulating policies regarding Russian port access at particular locations in Ukraine. With the reported "warming" of relations between Russia and Turkey, the former NATO threat from trying to sail through the straights of whatever at Istanbul is diminished. (It probably should have never been there, to begin with, but hindsight and current levels of education are drastically increased compared to Cold War decision making). Basically, science fiction is using real-world examples of naval power when making imaginary space fleets. This is all stuff I have read from historical accounts or supposedly authentic digital copies of declassified U.S. papers. The U.S. Navy continues to be as vulnerable as anything else to nuclear attack, among other things. Publicly, it got to the point where it was described as having the capability of simultaneously engaging and defeating every other navy on the planet. This, in implied fashion, indicates that you are not going to have much luck launching a naval assault on the Americas (or on anything else the U.S. Navy does not want you to attack). It omits the fact that the U.S. Navy is entirely vulnerable to anti-ship missiles launched from aircraft or land installations. It is particularly vulnerable to swarm attacks from missiles carrying nuclear payloads or large conventional warheads. A science fiction example of this is the Death Star opening fire on Rebel cruisers (which were basically heavily armed aircraft carriers) in "Return of the Jedi". The only way to prevent the things from getting "nuked" was to pull alongside their Imperial counterparts so that any more Death Star participation would result in "friendly fire" incidents involving Imperial Star Destroyers. I am trying to mix history/facts into this answer to state that it is likely that Science Fiction writers or movie directors probably get their inspiration, for many stories, from real-world examples. A final thing to consider is that, like science fiction spaceships orbiting a planet, modern navies of some nations can attack anything located anywhere on the planet via ballistic missiles launched from submarines. The U.S. Trident II missile, if I remember correctly, can deliver several nuclear warheads per missile at ranges of something like 5,000 miles. The missiles can be launched from beneath the surface of the ocean. U.S. Tomahawk Cruise missiles, in their original design, were supposed to carry nuclear warheads and could be launched from the "new" B-1 bomber and B-2 Stealth Bomber. This was a serious problem, in terms of balance of power, because the B-1 was capable of very high airspeeds compared to other heavy bombers and the missiles themselves could not be intercepted when they were initially deployed. The missiles could also be set to literally "loiter" in the airspace of an opponent, until they were told what actual target to strike. The U.S. ballistic missile arsenal is really a bunch of pilotless aircraft with particularly large effective attack ranges. It is described as being a different "thing" than the navy, but it really is not any different. Some of the missiles can launch from underground silos in the U.S. (if they haven't been secretly decommissioned haha), others can be launched from submarines. I do not believe that any nuclear variants of the Tomahawk missile remain in service, but I could be wrong. That missile could be launched from everything from submarines to surface vessels to aircraft, if I remember correctly, and had an effective range of over 1000 miles. If you want to effectively fight anybody at any location in the space in which you are aware that there may be reason to fight, you want a large navy first and a large air force/missile fleet first. Even if you are only maintaining a defensive position, you do not want an approaching navy to get close before you can start attacking it to stop the invaders it is transporting. Prior to the intercontinental ballistic missile, U.S. policy was that the best way to prevent an attack on the U.S. was to destroy it when it mobilized overseas (which probably explains why we were messing around in Korea and why we were quick to establish basing in as many locations near Soviet borders as the host nations would allow). This policy appears to have been the reason that we deployed nuclear missiles in Turkey, when those missiles still only had intermediate attack ranges, in the late 1950s or very beginning of the 1960s. They were already there when the Cuban Missile Crisis began (and may have been the actual reason that the crisis took place?) Lastly, your invading army is not worth a damn if it doesn't have fuel, food, and ammunition. Neither is your defensive army. There has been a time when the U.S. economy was at the mercy of oil imports from places very near to Soviet borders. The U.S. nuclear arsenal also needed quality uranium, which is described as being in much greater abundance in places in the Eastern Hemisphere. Without a navy, the U.S. had no way to project influence on the decision making about those oil shipments or to maintain control of the situation that kept those shipments moving. Europe also relied on those shipments. Science Fiction writers who are artistically representing warfare in space, and using real-world parallels, may be drawing from history classes or military experience or even government input on their work. [Answer] Why bother? While elite units to take out and defend planetary targets are very useful for espionage, assassinations, and sabotage, what can a tank do against a space ship? As soon as the space fleet is defeated the attacker has a choice, they can try to carefully pick off any planet bound defenses or destroy the main areas of resistance and much of the surface. Removing surface defenses, when they are in place, is a simple matter of time and careful targeting from a safe distance, at very low risk for the attackers. The area around the defenses will be rendered useless magma, but the rest of the planet will be largely intact. Or if they're in a hurry, the attackers can send some meteorites at any city or military base that doesn't surrender immediately. Defenses might take out a few of these, but not enough to worry about. While the widespread destruction is frowned upon, if a planet is foolish enough to resist it is their fault for not surrendering. In this situation an army is about as effective as a child throwing rocks at a tank. [Answer] I think the premise is wrong. A basic fact of warfare is that if you want to hold ground, you need troops on the ground. Or a castle wall and a mote. So, if you're simply holding a small area then you only need a small number of troops. But as that area increases, the garrisons increase. Patrols, reaction teams, assault forces, etc. Troops are also more "surgical" than airpower. We have ample demonstrations that while air (orbital) superiority certain have an impact on enemy forces, they are but a component of the combined arms approach. We have several examples right now of complete air superiority, yet they alone can not do the job. The large numbers of indigenous forces continue to fill, and refill, in the holes that the aircraft make. Only by occupying the ground is it possible to keep the enemy forces from coming back. Obviously this is different from a scorched earth policy of "simply" obliterating the enemy forces from above, reducing their number to below an effective fighting strength. If you genocide the inhabitants, then obviously you don't need anyone on the ground. [Answer] There are some good answers above that touch on some of the most important points (such as orbital superiority) but I'm going to add a few additional important things to consider. **Offense vs. Defense** A ground army in a space-faring civilization is inherently a defensive military tool. It can't be used to siege another planet without the addition of space transports, and space dreadnoughts to protect the space transports. When given a choice, [Civilizations will act against their own best interest and endanger their own citizens to generate offensive capability](http://discovermagazine.com/2014/june/3-ask-discover). Due to the distances involved, sustaining a large number of troops like that in a hostile environment [becomes exceedingly difficult](https://tribune.com.pk/story/298342/factbox-nato-supply-routes-into-afghanistan--some-facts/). Even with FTL travel times you're look at potentially hours before you're able to reinforce or evacuate units. [The US Military has better turn around then that in most war situations](http://www.afcent.af.mil/News/Features/Display/Article/223369/after-the-battle-the-golden-hour/). **Vulnerability to Interdiction** [Transitioning your forces always presents a danger].[4](http://www.nytimes.com/2003/11/26/world/army-says-troop-rotation-into-iraq-poses-increased-danger.html) If you have four hundred men manning a space dreadnoughts weapons, it's more effective then 400 troops sitting in a cargo hold. The best bang for your buck (literally, in this case). [The US military](https://clintonwhitehouse4.archives.gov/WH/EOP/OSTP/nssts/html/chapt2.html) [recognizes this](https://nypost.com/2017/06/15/us-military-will-have-more-combat-robots-than-human-soldiers-by-2025/) even [against the advice](http://www.aei.org/publication/the-u-s-military-needs-to-invest-in-troops-not-technology/) of nearly everyone. Large numbers of ground troops in transit are vulnerable to interdiction - the damage done to a single transport of 400 man can be caused by a [small one man attack ship](http://starwars.wikia.com/wiki/Battle_of_Yavin), providing a greatly enhanced force multiplier for the enemy. **Shifting Strategies** [Military techniques](http://www.historynet.com/medieval-warfare-how-to-capture-a-castle-with-siegecraft.htm) will have evolved to keep up with the times. Sieging a planet is inherently different then seiging a city. You need to not only be able to interdict incoming shipments (which a dreadnought can do) but also to destroy enemy assets being developed on the ground. Ancient warfare would have siege engines for the later and large roving patrols of troops for the former, but now our single dreadnought can do both, and we all know ["planet-hopping"](http://america-at-war-wwii.weebly.com/island-hopping.html) is a viable strategy. If you're looking for other literary examples, the Tour of the USS Merimack series has battalions of Marines deployed on board it's space Battleships. These marines are not merely there to dispel boarders (or provide boarding action against hostile ships), but they are also responsible for manning the ships manually operated cannons and operating it's flight wing. [There's a historical precedence for US Marines to have this kind of training](http://www.tecom.marines.mil/News/News-Article-Display/Article/528587/every-marine-a-rifleman-begins-at-recruit-training/), and it allows the world to have both a ground military and a space military that operate hand-in-hand. DISCLAIMERS: * I don't want to debate US Nuclear policy this was just topical. * Ipicked the US military because it's large and internationally known. * The dubious effectiveness of Island-Hopping is not the subject of this post. * I have no affiliation with the book series in question, I just thought it was relevent to mention here. * I'm only human, don't sacrifice me to the internet gods because of something I said here. [Answer] There are great answers already, but I think there's one more reason to consider: the gravity well. Every piece of military material you send to a planet's surface will need to be launched back to orbit (unless you want it trapped there forever, which usually isn't a great option). Getting things into orbit is *extremely* expensive for even moderately sized planets like earth. Exponentially expensive. It's not unreasonable to have a sci-fi SSTO capable of carrying a half-dozen special ops to their mission and back to orbit. But once you start dropping mechanized infantry, it will be really hard to get them back to the mothership if things turn south (until you've captured/built the planet's space elevator, mass cannon, whatever). You might have a lot of resources in space, but you still probably can't afford to just drop large amounts of military tech and never see it again. So mechs/large forces will only be dropped onto a planet as a shock and awe campaign that is the final prelude to total planet domination. And since most planets would probably negotiate some peace treaty once the threat of orbital bombardment arrives on the horizon, this would only be used rarely. [Answer] Quite apart from the bombardment issue, mechanized forces are no longer practical. It comes down to the balance between offense and defense--and for ground vehicles offense is solidly ahead. When a small infantry-launched missile has a high kill probability against a distant vehicle nobody will send vehicles into a combat situation. Infantry, however, does not have a useful defense against artillery. Combine these and you get a situation where the only survivable offensive ground forces are small units that move on their own feet and rely on stealth to reach their targets. Defenders don't have the same limitations but any large base will draw kinetic attacks from space. Thus they are also limited to fairly small units. Furthermore, all fights must be short because otherwise the defenders call fire from space and take cover in foxholes just before the kinetic weapons hit--near but not on the battlefield. The shock wave is much nastier to those in the open rather than those with a bunch of dirt between them and the shockwave. The attacker must hit and run before there can be a response from space. (Yeah, they can occupy a high value target--but they'll get nailed when they leave.) [Answer] why don't modern militaries train troops on shield walls and melee, because modern technology has made melee largely irrelevant. Ground troops have to get to the ground, if you have a decent space defense force that will never happen. So most of your ground troops are only for dealing with local rebellions or as a last ditch defense force. You might have a few other elite specialists for stealth missions but that is going to add up to a very small proportion of your troops. It is much the same reason an island nation might put a lot more effort into naval/air defense than ground troops. Ground forces don't matter if you can keep them from ever reaching the ground, so defenders will put as much as they can into space defense and the attackers will do likewise. You also have the issue that you need a much larger force to cover space space since it is a 3 dimensional battlefield, there are no defensive lines, only defensive spheres that adds up to a lot more assets. [Answer] 1. **Ambient force field.** When on the planet's surface everything is under influence of high gravitational forces. On the other hand, in the "free space" you have much weaker forces to bare with. 2. **Life sustain systems** When on habitable planet the planet itself supports individual's vital needs. On the other hand, in free space the vessel must have its own life sustaining technology. Bigger vessels therefore have higher power-to-supply ratio. 3. **Different battlegrounds** The difference between space combat and ground combat is similar to difference between battling in a forrest and battling on a plain. Heavy cavalry can be easily defeated by agile archer units in forrest, but they can wipe them out easily on a plain in a single raid attack. Large ground forces can be easily targetted and wiped out by a single blast from the orbit, on the other hand many small units spreaded all over the surface force firing at one unit separately. Heavier spacecrafts can sustain heavier fire, because their surface is square-proprtional to their size byt their volume is cubic-proportional. Twice as big craft hase four times bigger area to defend but eight times bigger space to carry troops, ammunition and technology. It is the manevruability versus strength decision. In forrest you have to have ultimate manevruability (Individual soldiers), on plain you can go bigger (Tanks), aeroplanes are even bigger and spacecrafts follow such patterns. You can see how the warfare changed by introducing tanks (WW I) and heavy bombers (WW II) to the battlefield. [Answer] The rapid mobility of space forces means that the enemy can bring everything that can float to any place in space. Your home-world can go from all-clear to a sky full of battle-wagons in a minute. If your own space forces cannot meet the enemy with enough force to make the engagement too expensive for the enemy, then you are best off not having any military assets on your planets at all. No factories, no supply depots, and certainly no C3 assets; when the hammer goes down, it will go down on planet-bound military assets first. The only exceptions are concerned with accession (recruiters and the guys who process new recruits, and maybe your boot camp), and then only if the planet has a substantial population from which to recruit. Everything else will be in orbit around otherwise uninhabited systems, and in deep space. This all assumes that your enemy prefers to avoid civilian casualties; if that isn't near the top of their priorities, then your planetary presence has to consist of people who are prepared to bug out at a moment's notice, and people who don't mind a Tsar Bomba landing on their heads. So the reason you won't have extensive ground forces is because you will have arranged your affairs so that you don't need them. ]

[Question] [ 9 out of 10 action heroes agree: [Repeating a pump-action shotgun looks and feels just plain awesome](https://tvtropes.org/pmwiki/pmwiki.php/Main/ShotgunsAreJustBetter). But besides the [rule of cool](https://tvtropes.org/pmwiki/pmwiki.php/Main/RuleOfCool), why would we still use pump-action guns in a future scenario 100-200 years from now? Semi-automatic and even fully-automatic shotguns already exist today. And whether you are fighting a gang war in a cyberpunk slum or get ambushed by a swarm of xenomorphs in an abandoned space station: anything which allows you to kill your enemies faster and easier will save your life. I've done my homework and found out that today's pump-action shotguns have the advantage of being able to fire a larger variety of ammunition and that the smaller number of moving parts means they are more reliable, more durable and a lot cheaper. But those seem to be engineering problems to me which could easily disappear within a few decades of technical advances. And that's assuming we keep using firearms with chemical propellant in the future. When we start using electric acceleration (railgun, coilgun...) then we have enough power in our gun to drive the cycling mechanic for our projectiles electrically. And when we go even further and switch to energy-based weapons (laser, plasma, sonic, particles, etc...) then we won't even need projectiles at all. What technical reason could there still be for guns to have that sweet *tchk-tchk **BOOM*** pump action in the future? [Answer] **Legality**. For hunting Titan's bears and Jupiter's sharks you need a high calibre round, only doable with military hardware or shotguns. You can not justify AA 12 Saiga, with full auto for *hunting*. Some legal limitations once birthed the Messer, a knife that was almost a sword. Maybe your space station supresses the integrated circuits on weapons frequency, so in the seedier places you carry *old school* weapons. [Answer] ## Reliability and versatility, with no real downside A semi-automatic shotgun offers very little advantage in fire rate over a pump-action shotgun not equipped with a trigger disconnector in the firing mechanism, as the latter can be *slam fired* by holding down the trigger while pumping the action. Considering that a semi-automatic mechanism is more vulnerable to failures due to off-spec loads, gas fouling, and the likes than a pump action is, *and* that a pump-action can handle oddball rounds (like beanbags) more readily than a semi-auto can because an oddball round may not produce sufficient recoil or chamber pressure to cycle the action properly, the continued existence of pump-action shotguns is practically guaranteed, even before you enter legality into the picture. (Anywhere there is legal waterfoul hunting, pump-action shotguns with long barrels *will* be legal on at least some level, as they represent the baseline of modern shotgun technology.) [Answer] **Action heros? Who cares about those whiny little girls? Real villains use pump-action weapons! Because NOTHING says "wet your pants on command" like the most recognizable sound in the known universe.** Why do people take the mufflers off their cars? Or ride Harley Davidson motorcycles? Or shoot skeet without ear protection? *Because they can!* Sound is second only to smell in its ability to elicit emotional responses. Let that someone special murmur the right sequence of syllables and you'll follow them around like a puppy — and you'll *thank* them for it! But what do villains want? You betcha! *FEAR!* We want people to respect us in the most obvious way possible. We want them weeping at the mere mention of our approach. We want them trembling at the memory of our last visit. We don't want them to cheer our names! We want them to *WHISPER* our names in abject terror! And we want them to do it *all the time!* And for that we need recognizable sounds. Sounds that are easily replicated. Sounds that occur frequently. We want ***pump-action weapons!*** And we want them so badly that we'll *subsidize and distribute* the weapons to make sure NOBODY forgets what they sound like! And just to make *everything* better, cycling that action takes an extra three-quarters of a second! *You'd be AMAZED how much panic can ensue in just three-quarters of a second!* Oh, yeah, baby! Join the winning team! We WILL supply the preferred weapon! Ah... just one thing more... there's only one opening, so make it quick.... [Answer] The pump could power a small electric generator that powers whatever is needed to make the gun fire. Think about it like those crank-operated emergency lights or radios. This makes them useful in missions in unpopulated areas/planets where there is no easy way to recharge the weapon. [Answer] Putting what has already been said in a slightly different context, why do we still have stairs? Why *don't* we have flying cars and hoverboards? We have the technical advances necessary, but when you get right down to it the answer comes down to two considerations; energy efficiency and fail conditions. Stairs take exactly zero power to run. That means that compared to (say) and escalator, their energy efficiency is basically infinite. Sure, you have to employ your own energy to climb them, but that's good for you in any event and it's a hidden cost because you have to eat regardless; only the energy value needed changes, and even then not by huge amounts. Also stairs don't have a fail condition. Alright, this isn't really true but for the purposes of energy utilisation, they don't because stairs aren't powered. That means, that even if your skyscraper loses all power, you can still use the stairs. This is a 'fail-safe' condition, rather than a 'fail-badly' condition. Escalators fail in a way that makes them expensive stairs, which isn't too bad. By comparison, think about hover cars or hover boards. They would fail badly. Like, falling to Earth badly. Cars on the other hand, fail in a way that makes them just stop. This is why there is so much engineering and investigation that goes into modern passenger aircraft; when they fail, the net result is (in a word) bad. Cars are also far more energy efficient. That's because all the energy they generate goes into lateral motion by comparison to the surface of the earth. Why? Because they can't fall any further than they already have in Earth's gravity well (Again, we'll assume normal road-like conditions). That means they fail safely, AND they're more energy efficient. So; your pump action for shotguns. VERY energy efficient, like stairs. They fail safely to be sure, but generally they're also VERY reliable. Easy to manufacture (simple design) and when they fail (usually a jam), relatively simple to fix. Compare this to automatic actions on weapons, or even powered actions, and clearing a jam in the field is much more likely to take longer and require more understanding of how the weapon works. Pump actions are simple. They don't take a lot of knowledge to understand or operate, they're relatively simple to manufacture and they're energy friendly. Why on Earth would anyone replace that? It would be like getting rid of the wheel, and we haven't done that yet either. [Answer] Improvements in durability and price will help a pump action gun just as much as a semi-automatic gun. So sure, your \$700 Saiga semi-automatic shotgun might cost only \$350 in the future, but a \$300 Mossberg 500 pump action shotgun would only be \$150 in that same future. [Answer] There's an assumption in much science-fiction that assumes that just because there's a fancier way of doing something or making a tool more sophisticated it makes it better, and the old tech will be replaced. That is far from the truth. If something works perfectly well for what you use it for, while people may tend to try and replace it with something fancier, almost inevitably practicality will cause people to continue using the existing tech. A good example is the axe. The basic concept (heavy chopping head + handle) is possibly hundreds of thousands of years old. Every now and then, you'll see people try to produce something to improve the basic design. One I saw years ago for a chopping axe had two pivoting levers that was supposed to push the pieces of wood apart when you split the wood. Sounded good in theory. I've never ever seen one in person, I've never seen one in a store. Why? The old-fashioned axe does its job perfectly well. Similar to weapons. The pump-action shotgun works perfectly well for what it's needed for. The M1911 design is over a century old and still works perfectly fine. The Ma Deuce .50 heavy machine gun will easily go into its second century. The Mauser bolt-action design is still used even it was patented in 1895 and semiautomatic and fully automatic mechanisms have been developed since. The basic Kalashnikov mechanism will easily go into its second century as well. And, as mentioned, do not underestimate the intimidation factor. Pull out a semi or full auto shotgun, you've got nothing but its visual appearance to use as psychological warfare unless you actually fire it. Cycle that pump action, combining an obvious visual and auditory cue, and now you're showing you mean business. [Answer] /But those seem to be engineering problems to me which could easily disappear within a few decades of technical advances./ And then reappear as the world goes to hell. In your future, most stuff is made by barely competent amateurs with a trailer full of scavenged tools. You paid the big bucks for a refurbished vacuum suit because you can't have that pooping out in the big empty. As for firearms, the Albanian is cheap, unpretentious and turns out firearms that so far haven't exploded in your face. His pump action shotguns get the job done and the shells he loads up have thick paper and plenty of powder. He makes a decent pair of boots, too. [Answer] The other folks here have covered old fashion slug-throwers and their intimidation factor quite well. However, a shotgun that blasts out slugs or shot is cool and all, but deep space operators know they want a laser or plasma weapon for that extra kick. A slug-thrower might ventilate a vacsuit, but real operators have to deal with powered armor and blast doors. And when faced with such resistance, an energy weapon has got you covered. Accept no substitutes. Now as any self-respecting space mercenary knows, these things get hot. Radiating out this heat is an important part of keeping your weapon safe and operating at peak efficiency. However, any merc with more than a single op under their belt also knows that continuously dumping out a load of heat is a fantastic way to get lit up by every tango with a thermal sight. And that presents a problem for weapons manufacturers. Material science has gotten us to the point where you can shield that heat for a while but eventually, you'll have to get rid of it. Other companies get around this problem by limiting fire-rate or with cumbersome, disposable heat-sinks. But if you're having to carry around spare heat-sinks, you might as well carry a slug-thrower. That's where our patented 'Rack-n-Vent' technology comes in. No disposable heat-sinks and up to 60% higher maximum fire rate than our competitors. Cool down whenever you need to. Simply rack the slide backwards and the integrated circuits will vent coolant over the radiator-fins hidden beneath the heat-resistant grip, cooling your weapon in moments. Or, with a simple touch of the button, you can forgo the coolant vent and simply radiate passively, guaranteeing optimal firing condition. *No overheating, no heat-sinks, no survivors.* Cyncorp Rack-n-Vent, for real professionals. [Answer] **Why Pump Action Is Used In The Future: 3D Printing** Now before you down this answer because of the much-abused buzzword above, hear me out. In the modern day, most folks get their equipment one of a few different ways: * From a Brick and Mortar Store * From an online retailer * From a personal sale (or gun show) Only a very select group of people actually attempt to make their own equipment from complete scratch. For good reason: equipment these days can be complex in design, complex in materials, and easy to mess up, especially when it comes to firearms. Enter 3D printing; in the modern day, 3D printing is quite limited. Very few households have a printer in them, and those that do almost exclusively have simple hobbyist plastic printers. Ceramics and Metal printers of any reasonable quality are prohibitively expensive. **The Future** Now Imagine a distant (or not so distant) future. We are long past the days of Amazon. Every home and workshop has an advanced, generalized 3D printer/assembler closet. You receive monthly shipments of raw materials: * Steel Alloy Pellets * Bricks of Silicon * Space-Age Plastic Resin with less regular deliveries of heavy metals and less common materials. Shipping raw materials is cheaper and more efficient for all involved, if all the manufacturing can occur at the destination. **The Boomstick** Say you are in a remote outpost, lightyears away from civilization, and the aliens come knocking at your bio-dome. You don't have time to order a shipment of sophisticated weapons, nor the rare materials to print them locally. All you have is your current resource stocks and a database of files. Furthermore, your fellow farmers/miners/philosophy factory workers have no advanced weapons training. The classics have long passed into the public domain. The Kalashnikov, the Mossberg, the 1911 remain. The arms of your forefathers are a sorely needed gift in this crisis: * Simple to print (increasing print speed, reducing error likelyhood) * Simple to use (no fancy scopes, no charging lasers, no friendly ballistics AI) * Durable in the field * Significant stopping power, but not enough to puncture a ship hull, biodome, etc * Easy to fix (less moving parts than some modern ballpoint pens) **Conclusion** Rival gangs in your dystopian vertical flavela? Predators in your jungle? Space Zombies on your ship? Facist CorpoGovernment got you down? Do as your forefathers have done. Paint your face, rip your sleeves off, and rack that slide baby. [Answer] The nice thing with shotguns is they're massively versatile ([Taufledermaus](https://www.youtube.com/user/taofledermaus) loads all sorts of crazy rounds into shotguns). Unlike a air pressure or energy weapon, shotgun rounds are more or less self contained. They're a tube, with the cocking mechanism actuated by the user - so a lot less moving parts. You'd probably design them a lot differently from an earth-designed gun, designing the firing mechanism to avoid a [cold cementing](https://en.wikipedia.org/wiki/Cold_welding) and [vacuum welding](https://en.wikipedia.org/wiki/Vacuum_cementing). The right rounds could allow for breaching, or even area denial. Maybe handwave that its simpler to do a sealed, nitrogen or gel filled action that works better in space. Inside a space ship, you're fighting in an environment remarkably similar to a submarine, ideally you don't want to make holes in the space ship - so you cans switch to net or immobilising rounds for hard armoured targets, or good old shot for soft targets. Unlike a magazine, you can quickly switch round types, and a few competition shooters can load pump guns quickly. You might also choose to go for a larger caliber - I'd imagine a grenade sized round in a shotgun style launcher would have more SNICKT. [Answer] **Safety** Remember the old pump action bb guns that the more you pump, the more powerful the shot? Once we move to any of the electronic weapons: 1. One pump = "this is going to sting" 2. Two pump = "oops I messed myself and I can't stand up" 3. Three pump = "where am I and why am I restrained" 4. Seven pump = "Jimmy, bring the dustpan and a DNA bag" [Answer] Because they're dirt cheap, easy to maintain and can down just about any dang critter this side of the galaxy. What need would a humble mega-tuber farmer have for a fancy military grade plasma caster when the ol' 12 gauge has served him and his forefathers for generations? [Answer] Picture this. It's night, you're a burgler. It's all quiet and dark, you creep real good. And then the silence is broken. A loud *tchk-tchk* echoes. "Oh crap, this guy is for real" you say to yourself while reconsidering your career. The sound of the pump is the sound of shizzle getting real, making the pump itself a deterrent for home defence. It's a bit like rule of cool but actually useful. Actually, it's one reason why it's a good candidate for home defence today. If you are interested by the pump action for the rule of cool, then you could justify having your guns make cool sounds when getting ready for action. Could be a sharp whirr when loading the battery pack in the laser gun, or the click of a mechanical switching when turning the railgun on. [Answer] **Post apocalyptic scenario** In a post-apocalyptic world where the fabrication of bullets has been impaired, fire weapons will have to use only powder. And eventually the expensiveness of the (manually fabricated) powder will make the surviving humans take advantage of the free air replenishment for their pump action weapons. And powder will only be used in long range and/or heavy weapons (for tear down a wall, for example). [Answer] As others have said, one reason is that they are perfectly good weapons. They never run out of power, are easy to use, and have fewer moving parts than semi-automatics, meaning they're more reliable. Another reason they may be preferred is that *when fighting on spaceships* one must be extremely careful not to breach the hull. High-powered rifles, lasers, railguns and the like are all easily capable of penetrating walls, and would be too risky to use. Shotguns are believed to be better because they'll do plenty of damage to a human target but the spread-out shot is less likely to break through a wall. (People on spaceships don't wear heavy body armor, of course, because when you're accelerating to near-lightspeed every ounce of mass is expensive. The crew probably aren't even issued underwear.) [Answer] **Re: Why not engineer better semiautomatics?** > > ... pump-action shotguns have the advantage of being able to fire a larger variety of ammunition and that the smaller number of moving parts means they are more reliable, more durable and a lot cheaper. But those seem to be engineering problems to me which could easily disappear within a few decades of technical advances. > > > Cutting-edge complicated tech can always be refined and made relatively more reliable, durable, and inexpensive... but minimalist solutions can rarely be out-minimalized. You're not going to engineer your way into a semi/full-automatic with fewer moving parts than current pump-actions without simultaneously engineering a way to create new pump-actions with even fewer moving parts. --- **Re: Why Load Anything?** > > And that's assuming we keep using firearms with chemical propellant in the future. When we start using electric acceleration (railgun, coilgun...) then we have enough power in our gun to drive the cycling mechanic for our projectiles electrically. And when we go even further and switch to energy-based weapons (laser, plasma, sonic, particles, etc...) then we won't even need projectiles at all. > > > You're assuming that future-weapons will be able to accelerate/generate their payloads entirely by electricity via some sort of attached battery-pack. However, it might be the case that having all that energy stored in a single monolithic part might make for a horrible analogue to "powder stores" of old battleships. A simple-yet-effective solution to such a problem would be to bank a much smaller energy reserve and refill as needed with small recharge sources. Essentially, you would have a bandolier of batteries rather than true "ammunition". These charges sources need not even be traditional batteries, either. It could be that they're simply a combination of stored chemicals that react to provide the charge/photons/phonons/neutrons/etc needed for each "shot". [Answer] 1. In post apocalyptic world, technological advancement and manufacturing would halt. So if the apocalypse started in the near future, your access to weapons and technology would be even less 100 years from now than what it is today. 2. Even if you have an automatic weapon, it may not be practical, because it would waste scarce ammunition. 3. A shotgun scatters pellets, so you can still hit multiple targets for each shot. 4. If you're being chased by hoards of zombies, then your best survival strategy would be to stealthily avoid contact and migrate to a remote region without zombies. The shotgun is just to get out of an occasional jam. You'd be a fool to act like a one man army. [Answer] ## As a backup system to recharge them As seen in [Pandorum](https://www.imdb.com/title/tt1188729/), some of the advanced computers in the ship are completely down, but the crew members manage to get them working by using handles that generate kinetic energy to power up the dead machines and use them. That being said, the pumping could be an alternative to switching magazines in a future where you have energy-based weapons. A futuristic pumping weapon may be a better solution than developing a battery that has to be small and store huge amounts of energy ('cause I don't really think a laser gun that melts a door - or a human body - has a low energy consumption). Of course you could always say that the battery is an engineering limitation that could vanish down the line. But even then, what if the battery dies or gets defective? Having a backup kinetic recharge system sounds like a good idea to me. [Answer] **Make things as simple as possible, but not simpler.** Why do bicycle couriers use track bicycles with fixed gears? [](https://i.stack.imgur.com/LBuSR.jpg) *Wikimedia Commons, ProfDEH, CC BY-SA 3.0 2008-05-01* No, it is not because fixed gears are *kewl* or because only "manly" mens and girls ride them or that it has any advantage for bicycling. Forget hollywood bullshit like "Premium Rush". Gears optimize the power output of the human body, good brakes are stopping the bike in a fraction of time and distance counterpedaling needs and mudguards allow you to bicycle in rain without spraying you with water at the front and back. The reason is simply that you do not earn that much money as a bicycle courier **and every non-existing part does not need to be repaired or replaced if broken or stolen.** It is also much easier and faster to repair something if you have no components which must be dismantled (flat tire, chain broken etc.). So you have a bicycle which allows you to come forward, nothing more, nothing less. Back to guns: For semiautomatic or automatic operation you need a power source, so your gun need extra parts, adding points of failure. Even if you use the power of the shell, you need a mechanism to catch the expanding gas and use it to move a shell in the chamber. While those guns with almost legendary robustness like the AK-47 are still complex, they reduced the complexity to an absolute bare minimum. [**The designers cleverly designed the gun so that it needs a minimum of parts.**](https://www.youtube.com/watch?v=_eQLFVpOYm4). Simplicity has also the benefit that errors or malfunctions are much easier to detect and fix because the source is much more obvious. So given that pump-action shotguns have still in place in the future. ]

[Question] [ If I create dragons to be castle-sized animals, how am I supposed to let them eat? Won't they need too much for an earth-like planet? I'm currently trying to build a world where a whole lot of gigantic beasts (à la Monster Hunter) co-exist. But how am I supposed to keep them well fed? Surely a starving dragon is less of a challenge that a dragon at the peak of its power. What would be good ideas to keep them alive and well? Despite the obvious "make rabbit-like beasts that breed in enormous numbers and are very nutritious." [Answer] We have a historical precedent for a world with monsters the size of houses. The difference was arguably higher carbon dioxide, and tropical temperatures, leading to richer and more vibrant plant life. I'm not sure how much it contributed, but the age of the dinosaurs was also largely before plants were mostly composed of cellulose, which is extremely hard to digest. (Cows have multiple stomachs and re-chew between stomachs, rabbits eat the same grass, er, multiple times, and horses digest grass... inefficiently.) If you want to justify giant monsters, you could build from the direction of lots of vibrant, fast-growing, easy-to-eat plant life. That kind of ecosystem will support dinosaur-sized fauna (along with smaller, supporting fauna). If you're picturing a world of megafauna with medieval temperate climes and semi-barren moorland, that will be more of a problem. [Answer] The creatures eat rocks. The excreta from this is fertile loam that is ideally suited to farming. They can be trained to eat from rock formations in such a way as to create walls and fortification. If they eat a metal ore, the metal part is not digested and can easily be separated from the loam to produce pure gold/silver/iron etc. A problem is of course that in the wild they take chunks out of random mountains or even stone castles if not carefully monitored. Thus the landscape will tend to become flatter over many millennia. There may be some huge underground caverns and tunnels where they have made a den. [Answer] Usually such creatures are at least partly based in magic and therefore don't need the usual degree of physical sustenance that would be expected. If you want to ignore this and go for purely biological solutions I suggest referencing Australia's [saltwater crocodile](https://en.wikipedia.org/wiki/Saltwater_crocodile) which can and will lay up for months hibernating between meals; your dragons don't need to eat often just heavily when they get the chance. [Answer] # Like whales, your dragons feed on krill-like insects After all, whales are also "castle-sized", and they manage to find enough food in a sustainable way. So, your world contains legions of **very small flying insects**, swarming quite passively. Your dragons have found a way to harvest a lot of them efficiently (a blue whale can eat 4 tons daily). This may add an unwanted constraint to their design, though. These krill-like insects feed on **phytoplankton-like micro-organisms** carried by the wind, reproducing by fission, and photosynthetics. Your dragons may seem a bit less cool and dangerous this way... But nothing stops you from also having a few "regular" carnivorous beasts, at the top of the food chain. Those would be very rare and deadly. [Answer] When you keep the environment temperature constant, you can make your beasts ectotherms. That would reduce their need for food, since their metabolism would not need to maintain a constant body temperature. They could much more easily survive longer periods of time without food. If you add a rich vegetation that is capable of maintaining large herbivores (like the brontosaurus), you also give them sufficient food to sustain themselves. In [this article](https://www.khanacademy.org/science/biology/principles-of-physiology/metabolism-and-thermoregulation/a/metabolic-rate) you will find a good comparison of the metabolisms of endotherms and ectotherms (and also some further references). Citing from there: > > Endotherms tend to have basal high metabolic rates and high energy needs, thanks to their maintenance of a constant body temperature. Ectotherms of similar size tend to have much lower standard metabolic rates and energy requirements, sometimes 10%, percent or less of those of comparable endotherms > > > Also, according to the link, the larger size works in favor of your dragon's metabolic needs, since it needs less food per mass: > > Which one has a higher basal metabolic rate: a mouse or an elephant? If we look at the metabolic rate of the entire organism, the elephant is going to win – there is way more metabolizing tissue in an elephant than in a mouse. If we look at per-mass metabolic rate, however, the situation flips. A gram of mouse tissue metabolizes more than 10 times faster than a gram of elephant tissue! > > > [Answer] # Dragons eat outside the terrestrial biosphere House sized dragons don't need to eat on the surface of the Earth. Perhaps they just like to rest here. Take the idea that they eat plankton to the next level: they eat something that exists outside of the food chain interactions of the planet's surface. The most obvious answer is the ocean. Lets say your planet does not have any whales. Everything that a couple million whales eat on Earth is instead eaten by a few dozen mountainous dragons. Another good answer is the underground. There is an [immense biosphere](https://phys.org/news/2018-12-underground-life-carbon-mass-hundreds.html) of mostly microbes under the surface. Your dragons are tremendous diggers who "eat" rock and sift out the biological materials. The last and most fun option is leaving the planet entirely. Perhaps there is a [forested moon](https://en.wikipedia.org/wiki/Endor_(Star_Wars)) that they travel to. Perhaps there are [space plankton](https://worldbuilding.stackexchange.com/questions/131838/anatomically-correct-space-plankton). [Answer] Maybe they eat uranium/thorium, have stomachs that enrich the fissile elements and extract energy from nuclear fission. Or they have a breeder reactor on their guts. You will need magic to save their cells from the hot neutrons and gammarays. [Answer] Okay, first of all, we'll need to figure out how much food it really needs. Let's say your dragon is the size of an *Amphicoelias fragillimus*, a real castle-sized land animal, which is estimated to have weighed 120,000 kilograms. Assuming a reptilian physiology, the dragon would need to consume 1.2 million kilocalories a day. Damn. That's what the formula coughed up at least; however, I suspect the daily energetic requirement would be lower, since it's the same as a blue whale's, which is both heavier and an endothermic mammals. Let's call it a million. To make this more plausible, I recommend the following planetary conditions: \* High atmospheric oxygen levels, ideally about 30% \* A dense atmosphere \* High global energy availability to maintain many-leveled food chains with broad bases Low gravity isn't very important, since it makes the dense atmosphere less likely, which you need more. Now, to properly answer your question: First idea; **aeroplankton**. Earth has aeroplankton in real life - viruses, bacteria, fungi, protists, algae, spores, pollen and seeds, all carried on the wind. However, there's not that much of it, it's not very dense, and a lot of it is too high up to be harvested by your dragon. Given a dense atmosphere, it's plausible if not likely that these problems wouldn't be present.  Alternatively, you could take inspiration from the aforementioned *Amphicoelias*, which was a "veggiesaur". It was essentially the size of a castle, as you can see above, and it got by eating just plants. Specifically, it stripped the branches and bark of large trees, probably clearing whole forests like modern elephants. Given that sauropods of such size could've existed, castle-size, even on land isn't that far fetched. However, I doubt your dragon could fly except in a very dense atmosphere. You could decrease its caloric needs by giving it an even slower metabolism (which would make it sluggish) or having it hibernate for long periods. [Answer] **Dragons are beach scavengers in the model of Tyrannosaurus - or the condor.** Here is my answer to this question. [Mythical dragon diet](https://worldbuilding.stackexchange.com/questions/140819/mythical-dragon-diet/140852#140852) [](https://i.stack.imgur.com/Ksek7.jpg) <http://www.montereycountyweekly.com/news/local_news/condors-make-a-meal-of-a-beached-gray-whale/article_aabcf553-a462-502d-8809-93225ba069f1.html> The California condor *is* (!yay) the largest North American bird. After the Pleistocene megafauna died out, condor populations persisted in California where coastal populations could sustain themselves largely on beached whales. Among other things, the crash of the whale population midcentury was really hard on the condors. A dragon could be an unparalleled coastal scavenger in the mode of the condor. Really large animals are thrown up by the sea. Condors are big and tough and can keep a carcass for themselves, driving off everything except a bear or an eagle. Nothing much is going to drive a dragon away from its carcass except another dragon - or maybe some sort of sea monster Liopleurodon dragging itself out of the sea to feed. In a world with dragons, things weirder than whales might wash up. Some things might still have some life in them and resist being eaten by dragons. [Answer] My piece of advice is one related to preventing them from being murdered by our good friend the square-cube law. You will want to probably give them a really low metabolism (which also happens to reduce food requirements), and make them ectothermic. That way they won't absolutely burn up. Or you could make them endothermic but really resistant to heat and have their body temperature be constantly insanely hot. Additionally, a castle-sized dragon, without the aid of magical physics, would be unable to fly. But that is not to say they shouldn't keep their wings, it's just that wings would serve an entirely new purpose. They would be used to dissipate heat into the environment if they were endothermic. In fact, what if we took this further and said that they don't breathe fire but really hot air that dries out and ignites things. If the temperature was increased enough you could have them melt the incoming armies using this superheated air. This can be used to damage foes, but also would be an excellent way for them to cool down during a battle. The other issue we face is that they are gonna have a problem with their insane weight. They are gonna want muscles that are vastly stronger than what a human can come up with, along with a really strong skeleton and definitely have the whole scales like armor thing. That will come in handy. These castle sized dragons would also have the unfortunate side effect of appearing slow, but in actuality, they could be moving at 80 kilometers per hour. You would want them to have flesh that is much less dense than that of a human, aside from the bones and skin of course. Such a dragon would be able to roar incredibly loudly, possibly such that could be used as a tactic to frighten, disorient, or burst the eardrums of enemies. My main advice for keeping them well fed should be that they go into dormancy most of the time. But I'm not talking about simply sleeping, I'm thinking they should be almost dead and take several years to come out of it. When they awoke from hibernation they would want to target human settlements for one specific reason, livestock. Assuming they were carnivores than they would very likely want to go to places with a very large volume of meat before their next hibernation. I'm not a scientist and some of this could be wrong, but if you incorporated a little physics into this these creatures could be very interesting indeed. [Answer] # Add O2 to the atmosphere There was a time on Earth, the Carboniferous period, when ferns grew to the size of a tree, scorpions to the size of a small dog and dragonflies reached the wingspan of a hawk. **Plants covered the planet** due to warm and humid conditions around the globe, releasing huge amounts of oxygen to the atmosphere. This "surplus" oxygen allowed insects to grow big enough to sustain a dragon diet. ### ... and control metabolic demands Moreover, a warm weather helps to keep metabolic demands at lower rates, so ectotherms can thrive. It also helps if your dragons are not active the whole year, make them hibernate or go through a dormant state for long periods. Ectotherms have lower metabolic requirements but they do not like cold weather (no cocodriles in the North Pole), however, aquatic ectotherms seem to do better in a cold climate (salmons, etc.) [Answer] To answer your question, I think it is important to understand what the foundation of your new world is. What @Chasly said about rocks is fun and all, but this can only be believable in a world entirely different than our own. As an example, you could change the fundamental laws of the universe (electromagnetism, strong and weak nuclear forces, and gravity). Perhaps that would be too complex, but there needs to be a reasonable way that consumption of rocks could provide an adequate amount of energy, especially considering the fact that rocks don't contain a lot of readily accessible energy for other organic forms of life. Any way of harvesting that energy would likely release too much energy as a result. Is it important to you that the dragon eats something small? Is it important to you that you completely remove the normal circle of life that we are accustomed to? Can we not have a larger planet? This would make it easier to stay consistent with the rest of your world because you could take what we already know and just make the potential for everything to grow bigger because there are more resources. That may also necessitate that your characters (if any) would also be bigger, and be in a world with everything relatively bigger but not bigger relative to themselves. That may take away the appeal of larger creatures because their power is no longer relevant in a world of relatively more powerful creatures (everything is relative). Maybe in order to maintain the majesty of large dragons you make it a world that visitors travel to, perhaps on accident. Then you could have this world of large creatures that remains impressive (this is sounding a little like King Kong, which may be a good thing?). No matter what you choose, there needs to be consistency. If what the dragons consume is important, maybe build a new world around that. If something else is more important, build your world around that. State the assumptions of your world, and then we can productively and effectively design a solution that works in your world. If there is no consistency, nor struggle in the world or in its design, then it becomes boring. Ultimate power is not exciting (just ask Superman, who seemed to intentionally develop an allergy to a shiny green rock). [Answer] They could also be similar to cecropia moths (naturally not as fragile though). Cecropia moth caterpillars eat and when they grow into the adult moth they no longer need to eat (they rely on fat reserves). So it could be that the dragons eat while they are smaller and as they get bigger just simply don't need to eat at all, or very rarely. <https://nhpbs.org/natureworks/cecropiamoth.htm> [Answer] just do like with normal sized animals : * have some herbivorous/omnivorous eat forests * have carnivorous eat the herbivore ones * then the plants will grow much bigger thanks to having so much ressources from the dragons' corpses and that close the loop the only difference is that they're bigger [Answer] Depends on how "hard" you want your fiction. Right now the top answer suggests having your creatures eat rock, which is a cool idea but doesn't make a whole lot of sense from a biological point of view, not if we assume your creatures are carbon based like life on Earth is. So, I'm just going to throw a few more options with varying degrees of "hardness" and plausibility. But first, a premise: I'm assuming that your world will be Earth-like, with comparable atmosphere and temperature. I'm also going to assume that you wish to handwave the other classic problems one runs into when designing giant creatures, like how do they breathe or how do they avoid collapsing under their own weight. With that said, 1. Have them rely on symbiotic organisms that can metabolize stuff that a normal animal wouldn't be able to draw sustenance from. Photosynthetic organisms living in or on their skin could provide a lot of energy, as would a variety of specialized bacteria living inside them and able to process dangerous chemical substances that normally need to be disposed of, like the colonies of bacteria living in abyssal tube worms. This would even make the lithovore suggestion more plausible. 2. Have them live in the water and rely on filter feeding or similar behaviour. Just like blue wales, the largest animals that ever lived. If you want them to be terrestrial, have them have access to similarly abundant sources of food in the form of small, gregarious and numerous animals. Just keep in mind that this will necessitate a very different environment from Earth in order to work, probably a hypercharged biosphere, with access to a lot more energy than what is found on Earth. Some kind of super-earth planet might do the trick. 3. Have them be plant eaters. Boring but practical. As the biggest land animals that ever lived (sauropods) show, some truly impressive sizes are possible for a sufficiently specialized plant eater. And of course where there are large preys there are large predators, though to have them in any large number or to make them reach as impressive sizes as their preys you need again a hypercharged biosphere. [Answer] > > But how am I supposed to keep them well fed? > > > I would combine three things. 1. Your house sized creatures (dragons, etc.) sleep a lot. Say three of a farmer's fat cows will sustain them for a week or two. The first week they could be in a semi-coma - which is why it is important to keeps their lairs location a secret and hard to get to for humans. Lots of story building ideas here plus it matches existing aspects of mythical Earth dragons. 2. The prefer to sleep in caves near volcanoes, or near hot springs, or just caves deep enough to be naturally hot. Lets them sleep longer because they burn less energy. I wouldn't go into whether they are warm/cold blooded unless you have a plot that relies on it... after all dragons are generally considered to be 'part magical' creatures. Bringing us to point three: 3. The magic which helps those hose sized things fly, also sustains them in other ways. The explanation can be left to the reader which can enable you to gloss over the specifics of the first and second point. [Answer] Dragon has an ability to open portals to more fertile lands. Then he feeds in there and comes back. [Answer] If you are talking conventional dragons -- large reptiloid appearance, capable of flight, then you either need magic, or you have some serious world building problems to tackle. The closest analogue I can are the Pterosaurs. The largest of those had a wing span of about 36 feet. About the same as a Cessna 172. But they were flimsy beasts. One 18 foot speciman was estimated to have a weight of about 55 pounds. I would expect a 36 footer to have a mass between 200 and 400 lbs. A denser atmosphere is clearly a requirement, and a lighter gravity would be beneficial. We could probably raise the atmospheric density by a factor of 4-6 and still be able to see. (Too much air and the surface is as gloomy as Venus.) To get lighter gravity, we need a planet that is larger, but less dense. This would mean a smaller core, with less iron. Problem: The molten iron core generates the magnetic field that keeps the solar wind from ripping off the atmosphere. (One of the reasons proposed for Mars having to little air.) Ok. Spin the planet faster. Let's give it on rotation per hour. That would give a small core a lot more speed. It would also make the planet much flatter. (For an extreme of this, see Hal Clement's novel "Mission of Gravity" Mesklin was a rocky planet with Jovian mass that spun at 1 rev/10 minutes. Resembled a fried egg.) With a faster spin, and a denser, deeper atmosphere thunderstorms would be wild! Your dragons may have developed intelligence just to cope with the weather. Despite these changes, I don't think they will be *that* tough to kill. ]

[Question] [ I have a noble god in my world that is answering prayers, guiding his believers and bestowing divine powers onto selected priests. Now his church is fragmented into several factions on ideological and political grounds to the extent of sporadic armed warfare between factions. Still, each faction is somehow aligned with the god's dogma and receives its share of divine grace and miracles. Many of the priests are politicians, managers or simply shepherds to the flock and are not especially connected to the divine nor receiving any spiritual powers while still holding significant material power. How to explain how such a structure could tolerate the presence and elevation of an impostor that follows and gets his powers from another divine being dedicated to duplicity? As such an infiltrator moves up in the hierarchy he would encounter more and more political enemies and gifted individuals who would like to unmask him. If somebody becomes suspicious he could (or have someone who can) use a divine hotline to pick apart the impostor's cover. The Noble god would know that the individual in question is tapping into divine power that does not come from *the* god. So it is hard to explain how the god would not put two and two together. I'm looking for an explanation how the impostor could remain unnoticed - or what would motivate the "host" god to let it slide and not alert his priests? The duplicity god is not against observing "host" god rites but demands to regularly cause some mischief to remain in his graces. [Answer] You know what happens when you start answering questions like 'how holy is my neighbour?' You get witch hunts, that's what. Bad enough they're picking fights with each other, encouraging it by answering questions about how holy their rivals are is only going to make matters worse. One priest gets it into his head that because the local wise woman isn't blessed he should burn her at the stake and then the whole village is worse off. Nasty stuff. You can't stop them from going out and doing it anyway, but you can refuse to be a party to it. How much power you bestow on anyone is your business and nobody else's. Sometimes that means you can't say that the new pontiff is actually a follower of the god of duplicity, but it beats giving your real followers excuses to attack each other. [Answer] This is actually a rather similar dilemma to [the problem of evil](https://en.wikipedia.org/wiki/Problem_of_evil) in Christian philosophy. The problem of evil is the question why an omni-benevolent, omniscient, and omnipotent God would permit bad things to happen. There's *a lot* of literature on this, and you could take cues from how the Christian God is able to get around this conundrum. The easiest way for you (not available for most Christian philosophers) is to simply knock out one of the three legs of the tripod. If your god isn't omniscient, then you arrange (with the help of the duplicity god) to always fall into the noble god's blindspots. If they're not omnipotent, you arrange things so that the noble god is either powerless or constrained in reacting. (For example, if there's some sort of rules of engagement between the noble god and the duplicity god, where the impostor can walk a fine line in actions which prevent the noble god from responding.) "Omni-benevolent" isn't applicable in this case, but the equivalent here is omni-caring. If, for some reason, the noble god doesn't really care about the impostor, then the impostor's rivals may find it difficult to get the noble god's help. Even if these approaches don't work, there are other possibilities. One is the "greater good" invocation. The noble god deliberately allows the impostor to function because the small amount of deception now will allow a much larger (and better) amount of nobility later. For example, if the church is fossilized and most worshipers are apathetic, having an impostor rise through the ranks and eventually cause a great upheaval might revitalize the church. As far as the noble god is concerned, the impostor will get his comeuppance, but can be used as a valuable tool before then - to the extent the noble god may actively cover for the impostor. There's also the "free will" argument. With the problem of evil, it can be argued that it can't really be "free" will if people don't have the ability to choose evil. (Or that actively rejecting evil is an important process in the development of souls.) In your case, since the duplicity god isn't necessarily rejecting worship of the noble god, the noble god could see the impostor as a means of "separating the wheat from the chaff". The antagonism of the impostor provides a means for testing believers and either strengthening their beliefs, or to figure out who actually believes and who's just going through the motions. The key issue is deciding how you wish to limit your noble god. An "all powerful" god is a bit of a story killer (there's a reason for "*deus*" in *deus ex machina*). Your god needs to have limits, and those limits are what your impostor would exploit. These can be limits fundamental to the god's existence (like not being omnipotent or omniscient), or they can be self-imposed limits (like a divine contract with the the duplicity god, or allowing A to happen now to enable B to happen later). [Answer] For the same reasons that our bodies tolerate bacteria: They haven't done anything that the immune system considers harmful. Your impostor makes sure that any mischief he causes does not cause long term harm to the church and is at times beneficial in controlling fanatics and demagogues within the church. He doesn't want to get smited either. [Answer] **A divine double agent** Since your impostor has the boon of the god of duplicity, it may be possible that it's not just the noble god's followers that are being fooled, but the god themselves. A mortal fooling a god may be unlikely, but another god doing it through a mortal sounds rather appropriate. As far as the noble god knows, the impostor is just one of his many followers, and not necessarily one of particular note. The impostor could well be using the noble god's divine powers too. **Pride** If the noble god does eventually, but not immediately, realize what is going on (perhaps by happening to notice the impostor tapping into another god's power), the reason for not exposing the impostor could be pride. Your god may be noble, but are they willing to admit to being fallible just like a mortal? In exposing someone who they had previously legitimized, the god would admit that they can be fooled and that they're subject to mistakes. If the god of duplicity was dupliticious enough and managed to hide that the impostor was using their powers, it might look like the noble god was fooled by a mere mortal, making it even worse. Depending on the tenets of the faith, it could be catastropic to reveal it. In this case, if the noble god wants to act against the impostor, they're going to have to do it through subtler means. [Answer] **You haven't explained why your benevolent god is doing what he does.** And without knowing his divine purpose, we're left with the paradox of how an omnipotent, omnipresent god can allow something to transpire that he obviously wouldn't want to happen. So, let's give your god a purpose, a reason for his association with the people that transends protecting them like babies throughout the eons. 1. Judgement is very real and only based on actions taken, not actions that might have been or could have been (no *[Minority Report](https://en.wikipedia.org/wiki/Minority_Report_(film))* pre-crime judgements here). People must be allowed to be good or evil throughout their lives because they have the privilege of repentance throughout their lives and very few transgressions of divine law are unforgivable and unrepentable. 2. And this is the case because the freedom to choose is the greatest gift the god has given to his people. He will not interfere with that freedom. He will warn the people through whatever mechanism he has selected for that purpose, but in the end, the people must choose. He will allow them to be deceived because he respects the choice to turn away from him more than his own desire for the good welfare of the people. 3. And this is the case because the people are expected to mature in their self-discipline and devotion for the sake of a promised reward that requires maturity, sobriety, and education. Perhaps he has offered his people to share godhood with him, which is no trivial thing. You wouldn't want to give the keys to your car to someone who wasn't old enough, mature enough, and trained enough to use it and protect it, right? And because people have the right to choose, they have the right to be deceived — to the disappointment of a loving god who cannot pursuade them anymore without interfering with the gift of choice. In this scenario, your god wouldn't interefere with the interloper/heretic/impostor unless that interference reached a point that it threatened his own plan and purposes for the people beyond their own ability to choose to change it — because to do so would subvert the goal of the people learning through their own experience and maturity to treasure the privilege of choice and be judged worthy of obtaining the promised reward. *Of course, this is usually where the word "armageddon" kicks in. And we all know what Hollywood thinks will happen then....* [Answer] The word you chose is "tolerate" which implies your god sees the issue as not worth interfering. You further have an issue with indirect interference when priests simply ask the god for relevant information and he doesn't provide it. This implies that the god thinks he followers should also "tolerate" the situation to the point where helping them interfere is itself a bigger issue than the original impostors. A logical assumption would be that the reason for the tolerance comes from the shared "noble" values the god embodies and the priest commit to receive their divine magic including the magic for asking their god for information. The god would be unable to act against those values and the magic would simply fail automatically when the priest tries to ask such a question. So why would removing the impostors from the church be bad? I'll ask another question: Why is the church fragmented despite being backed by an active god and priests with divine power in communication with him? Wouldn't it be an easy answer to say that the church is **not** backed by the god? That he is not tolerating the impostors but **the church** itself? And that his tolerance does not extend to active support of the church in form of intervention or information. That would answer both your original question and my added question at the same time. And this would be fairly simple to explain. A church is a political organization for organizing religious matters. Nobility and politics do not mix that well. Nobility also implies taking personal responsibility for your beliefs and actions which does not mix well with organized religion with its pre-canned one size fits all answers and dogmatism. And conversely since humans are inherently social animals the god would have a simple and obvious reason to tolerate humans forming groups and organizations to belong to. And of course being organized and pooling resources does have non-negligible practical benefits. So the god would tolerate the church and provide power to priest belonging to it but he would not support it in any way. He would not care if it fragments, gets corrupted, or is filled with impostors. He would not provide magic or information for the purpose of "playing politics", and that would mean almost anything involving the church, and people would not expect him to. So lying by omission would not be necessary. This would also explain why the church is fragmented. Since the god does not expect anything of the church and does not value it, people would feel free to form their own splinter groups whenever convenient and never make an effort to reunite the faith. This lack of weight would also explain why efforts to keep the church clean of corruption and impostors would fail. It just would not be that high on the priority list of things to do. You have limited time and resources and there are people in real distress and need all around you. Given time believers might even come to see the corruption of the church in positive light. Finding your true personal faith and belief and living it fully would be your central goal. Having the church corrupted would make it more meaningful by adding contrast. The state of the church would also more or less **force** all true believers to make their own personal choices and decisions. Just going with the flock would not be viable option. [Answer] First, reasons why the god might tolerate this-- 1- The rules of the pantheon mean that no god can directly strike down or interfere with another follower of another god. The god can answer questions from their followers but are bound by rules. 2- The church is political, and not of real interest to the god. 3- The god hasn't noticed. Most pantheon-based gods are not seen as omnipotent or omniscient. 4- The god sees the whole picture and knows that the imposter will ultimately lead to a better church, or a clean out of those that aren't fully on board with the god's way of thinking. Second: > > how such a structure could tolerate the presence and elevation of an impostor that follows and gets his powers from another divine begin dedicated to duplicity? > > > I believe you have already answered that question: > > his church is fragmented in several factions on ideological and political grounds to the extent of sporadic armed warfare between factions. Still each faction is somehow aligned with the god's dogma and receives its share of divine grace and miracles. > > > A follower of a trickster god would surely use that to their advantage. > > As such an infiltrator moves up in the hierarchy he would encounter more and more political enemies and gifted individuals who would like to unmask him. If somebody becomes suspicious he could (or have someone who can) use a divine hotline to pick apart the impostor's cover. > > > Yes, this person would encounter more and more political enemies. But many of them will not be divinely connected, but would instead be political and managerial types. They might not even think to ask their god if this person is an imposter, even IF they are connected. The highest people in the hierarchy might not have any connection with the god at all. Even if they do think to ask, such a person would be very very good at politics. So everything from blackmail to favors done would protect them. [Answer] **Your noble god is a god of love. Its a family affair.** In the words of Sly and the Family Stone: > > It's a family affair, it's a family affair > > > It's a family affair, it's a family affair > > > One child grows up to be > > > Somebody that just loves to learn > > > And another child grows up to be > > > Somebody you'd just love to burn > > > Mom loves the both of them > > > You see it's in the blood > > > Both kids are good to Mom > > > "Blood's thicker than mud" > > > Maybe even more relevant is the parable of the Prodigal Son, one of the greatest parables. I was going to paste the entirety of the text, but it seemed too long. If you are unfamiliar, read it. You do not need to be Christian or even religious to see the value in it. <https://www.biblegateway.com/passage/?search=Luke+15%3A11-32&version=KJV> The last 4 verses - starting with the oldest son's complaint. > > 29 And he answering said to his father, Lo, these many years do I > serve thee, neither transgressed I at any time thy commandment: and > yet thou never gavest me a kid, that I might make merry with my > friends: > > > 30 But as soon as this thy son was come, which hath devoured thy > living with harlots, thou hast killed for him the fatted calf. > > > 31 And he said unto him, Son, thou art ever with me, and all that I > have is thine. > > > 32 It was meet that we should make merry, and be glad: for this thy > brother was dead, and is alive again; and was lost, and is found. > > > Why does the father tolerate the dissolute ways of his younger son, this "imposter"? Because he is his son. Your church is competitive, with factions. Why does the god tolerate that? Why might a parent tolerate rivalries among siblings? This aspect of the religion is also the reason your god tolerates the ways of this "impostor". But is he really an impostor? Your imposter is (or started out as) a follower of the noble god - a child. The imposter sees opportunity to advance his god and his faction by tapping the powers of the enemy. I am reminded of Boromir's exclamation when he learns of the existence of the Ring of power. Boromir wants to use the power of the enemy against him. > > "Wielding it the Free Lords of the Free may surely defeat the Enemy. > That is what he most fears, I deem. The Men of Gondor are valiant, > and they will never submit; but they may be beaten down. Valour needs > first strength, and then a weapon. Let the Ring be your weapon, if it > has such power as you say. Take it and go forth to victory!" > <https://scifi.stackexchange.com/questions/105108/since-boromir-wanted-the-one-ring-so-badly-why-didnt-he-volunteer-to-take-it-d/105244#105244> > > > So too your "impostor". The noble god loves him even as he smokes the crack of evil. Children must find their own way and the road to hell is paved with good intentions. Love is not conditional on the child finding his way back into the light. [Answer] > > The Noble god would know that the individual in question is tapping into divine power and that the power does not come from the god. So it is hard to explain how the god would not put two and two together. > > > # Perhaps he *is* tapping into the gods power. Stolen power. The god of Duplicity is not powerful in a direct conflict, that would be against his nature, but his speciality is turning an enemies strenght against himself. So, years ago, a paladin of the Noble god was captured by cultists of Duplicity. [](https://i.stack.imgur.com/Jvyko.gif) Through a dark ritual the paladins connection to his patron god was stolen. [](https://i.stack.imgur.com/1TcSO.jpg) It's not perfect, if the god inspects deeply enough he'll realise that the feelings of faith and goodness are just a mirage also stolen from the real paladin. But until then the agent of Duplicity is hidden, the god seeing him as one of his own noble paladins. Thus Duplicity turns his enemies strength against himself and expends minimal divine power himself. [Answer] Time. Gods live forever, mortals not so much. These bad actors are blips on the radar, and ultimately they never gain enough influeunce, prestige, or do enough damage to the overall plan(s) of the god(s) that it's worth taking special notice of them. Imagine a fishing line that goes on towards infinity in both directions. The worst of the worst bad person really only affects their time in their life, and may be considered a simple knot on the line. Only by feeling the line would one even notice there's something that happened, and the line would continue unperturbed in the grand scheme of things. Alternately, the God(s) are interfering, but, of course, no one notices the interference, and it's only preventing particularly long-term harmful things from happening. The minor things they do allow to happen aren't, again, going to affect the God(s) plans. That said, as others have pointed out, adding either of the above to the concept that everyone has free will specifically for the purposes of finding out whether they'll obey or not requires bad actors so people actually have a choice. If every church leader is forced to be good in every way, then the followers have no wrong choices, and the "test" results cannot be useful. [Answer] If this god is omnipotent, omniscient and omnibenevolent, you've rediscovered the Problem of Evil. Some classic explanations for it: it's a test, he doesn't want to take away the free will of his people, it's all part of some mysterious plan. If he's merely potent, he might not be able to intervene. If he's merely smart, he might not know. If he's merely good, he might be too aloof. He might be constrained by an agreement he made, or the opinions of other divinities. [Answer] # Noninterference clause The gods are bound by a set of complex and mostly unknown god-rules. One of the primary rules is that a god cannot directly interfere with the chosen of other gods. The noble god interprets this rule *much* more strictly than the duplicitous god does. [Answer] The Noble God likes a good joke, too -- especially if it is done in a Noble way, or with Noble results. The impostor has found a way to worship both gods, and keep both of them happy with what he does. On a Dungeons & Dragons / Pathfinder character sheet, the impostor would be listed as "chaotic good". [Answer] This solution is borrowed from the famous author Virginia Hamilton's *[Justice Trilogy](https://en.wikipedia.org/wiki/The_Justice_Trilogy)*: The imposter is an aspect or an avatar of the main deity, that has somehow split off and gained its own volition and separate identity. Because of this unique relationship, the main deity is supernaturally unable to perceive the imposter at all, or even know of its existence, experiencing it only as an extension of itself. In other words --split personalities. [Answer] A few reasons: * Removing the impostor might be more trouble than it's worth. * The god wants to maintain a clean self image, so doesn't let on that it's an impostor. * The god is focusing on a holy war in some other part of the world and doesn't care. * The god just doesn't care anymore and is lazy. * The impostor might even be spreading the god's word, so it's beneficial/symbiotic. I doubt that Jesus Christ was really God, but he sure was effective at spreading word. [Answer] It may be an extension of free will, and part of the maturing of a society. God might have initiated life, but chooses not to interfere with the results directly. The idea is - the society will have to learn to deal with issues like this if it is to move forward. It's up to the people to recognize the imposter and take action, or so God thinks. I gave you a brain... use it. Stop leaning on me so much, and learn to live your own life. [Answer] Why would God tolerate an imposter? Why wouldn't he? We're either given free will or not. If not given free will, then it's a rather boring show for God. He is watching a play unfold as written. In this scenario he put the impostor in church. You can't commit sin because you can't commit anything, God makes you do everything. You're just a mindless robot without decisions. If we're given free will, then we're given free will. Why would a God that gave free will to its creations want to micro manage everything? The church members have a brain, it should be used. Switch your church, get a new priest, confront the impostor, etc. Talk, think, debate. [Answer] There is a Prophesy that must be fulfilled. The original poster can use his (or her) creativity to decide what the prophesy is, and whether it is related to this particular infiltrator, or to the idea of a meddler sent by another god. The fulfillment of the prophesy might be necessary before some other event can occur, such as the arrival of an avatar, the founding of a kingdom, or the rebuilding of a Great Temple. [Answer] There are a lot of answers and I tried to look for this idea, but I didn't find it, so. **The god is testing his followers. He wonders about his followers.** How long until they find out? Who will find out? A lowly monk or a high priest? Are the leaders of the church able to notice? If not are they still worthy of their position? What will be the reason for noticing the impostor? Will somebody be jealous of how quickly is the impostor rising in ranks? Or will they find flaws in his teachings and expose him? What if the impostor exposes the evils within the hearts of the god's followers? It could be just a lesson for the followers, so when something like a succubus tries to enter, they will know. Or the other god is trying to prove that noble god's followers are blind with pride or that some are evil. The god is truly noble, so he will not interfere and let the truth be revealed. Then there is the possibility that the real world could be radically changed if the god would interfere directly, so he asked other gods for help. [Answer] I came up with two reasons that this could be allowable: **The Imposter's Flock Still Believe in the host god** Presumably, the Imposter would use his power, derived from another god, to trick the followers of the host god into believing he is a divine representative of the host god. These people are not bad people, just following in earnest someone who does not follow earnestly... His trick is still leading people to the host god's worship. Should the trick be revealed, the followers would still be faithful to the host. Should the other clergy reveal the trick, they further fraction the faith, and by inflicting "True-Believer Syndrome" onto the imposter's flock, they hurt their own ministries. In fact, if the imposter is not a cleric of another god, but rather someone who can duplicate divine abilities using technology and trickery to feign actual holy feats, perhaps that is actually his own divine gift... the host god could be allowing him to make these farces because at the end of the day, people are still worshiping him in earnest, even if their clerical inspiration is not faithful. **The Host God is testing his faithful.** This scenario is designed so that that the imposter can bring people into the faith and be allowed to rise until he attracts the notice of a political adversary who is wise to his trickery. In the short term the Imposter may lose some of his flock when his tricks are revealed by a pious cleric, but in the long term, it would be the religious equivalent of a vaccination against further infiltration. The wise cleric who sees the deception will be remembered and the tricks will be recorded so no self-serving or devious god serving cleric can invade the ministries of this god's church and further turn the faithful away from him. This cannot be done by the god himself as it would leave the people without a good understanding of how the false cleric was deceiving them. This is a mortal matter and the mortal inquisition of the flock must solve it. If the god wants to protect the faithful deceived, he may include instructions to drive away the bad faith leader, but not those who allowed their love of the god to follow the bad actor. [Answer] Probably adding to what ha already been said, but there are a number of reasons. 1. Not that big a deal, tricky little stuff isn't worth upsetting the balance 2. Balance issue with another deity, perhaps it's allowed because you don't want to start a war 3. Not that big a deal to the deity even though it is to the people, could be a for several reasons, time based or because deity sees it at a grander scale 4. Perhaps they are, but it's on a deity level, not on a human level 5. Perhaps the other deity giving divine power to impostor is blocking deity from seeing it 6. Perhaps the impostor while improving their own situation is still actually helping the church. 7. Perhaps the deity is testing those in the church and plans to stop it before it gets too bad, but wants to know who truly follows them. [Answer] The God only wants followers who accept His teachings. He doesn't want false followers. People whose hearts aren't in it are always looking for excuses to bail. The impostor provides them with a ready-made excuse. [Answer] ## Because your god is... the Duplicity god! He may suffers from double personality and not even know what he's doing. Or maybe it's just a way to get ALL people to follow him, the goods and the bads. [Answer] "Many of the priests are politicians, managers or simply shepherds to the flock and are not especially connected to the divine nor receiving any spiritual powers while still holding significant material power." "Now his church is fragmented into several factions on ideological and political grounds to the extent of sporadic armed warfare between factions." Provided your god exists, then your god isnt noble and doesnt care. A noble god would provide guidance and the means to guide in turn so that situation could never happen. [Answer] It might be interesting to engage with a theologian's mindset. For fun you can dial the piety up or down as the circumstances require. There is a strong tradition of rationalizing a god's tolerance of evil. * Gods plan is unfathomable, as is it just, and noble. * God confronts deception not by unveiling it but by offering up opportunities for redemption (both on the part of the deceiver and the deceived) * God allows the un-righteous as contrast to and a test for the righteous. If we have no ability to choose the wrong path (or if the wrong path is not appealing) there is no glory in the choice of the right path. Or put another way if the only available option is the right one, we are simply vapid automatons acting out an insipid morality play. The greater the power of evil, the greater the deception, the more opportunity for the righteous to attain glory in following the right path. [Answer] **Busy and/or Complacent** There are any number of reasons for exactly why (probably it's a mix) but your Noble God has mostly gotten in the habit of basically hitting "reply all" to any properly formatted prayers. This could be a combination of laziness, business, volume of prayers, boredom and ineffableness. If the God looked closely they would probably noticed the infiltrators, but mostly as long as the Impostors say the right words they aren't noticed. [Answer] **A Pantheon is a Family** A lot of the answers assume that god of nobility would be opposed to the god of deception. There are family trees for the well known pantheons such as the Norse, Roman and Greek gods. The pantheons aren't necessarily *happy* families, but they generally accept they are all gods and all have a some kind of right to do their god thing. So you have your Noble god, lets call him Thor. He has his religion and an appropriate amount of infighting so that his followers can earn their place in Valhalla by being killed by each other in honorable battle. So his blood brother Loki arranges some of is own followers to infiltrate his church and plays some amusing and usually not fatal pranks on Thor's loyal followers. Prior to the murder of Baldr, I can imagine Thor just roaring with laughter and telling Loki that this was almost as funny as the tale of how Sleipnir was conceived. ]

[Question] [ Let's say that teleportation (magical or technological, it matters not) is perfected to such a great degree that you can go anywhere from a few dozen yards, to the other side of the planet (basically) instantly, would people still use their own two feet, bikes, cars, boats, planes, etc? Furthermore, what would cause people to use one of these forms of transportation as compared to simply appearing where they want to be? [Answer] > > teleportation (magical or technological, it matters not) is perfected > > > I think the devil is in the details here. You have enormous scope for making it as convenient/inconvenient, socially loved/scorned, artificially restricted, etc. as you need it to be for your story to work, on many different fronts. * Let's say it's a personal technological teleporter - included in your smartphone or tablet, available for shops and public places like a credit card reader. Very common and popular but you can't use it if there's no receiver at the specific place you want to go, or if your device is broken. Or if their device is broken. Or if your device is low on battery you might save battery and walk. Or if you got mugged and had your phone stolen, or lost it. Or if you're a criminal and prohibited from having one anymore. * If it's a technology like a phonecall, maybe it costs per-use. Or per distance, or costs more when demand is high. Or you have to queue during rush hours. Or can be unavailable like a power-cut effect. Or they have some of those frustrating "friends and family" teleport plans, where you can have any of your top 5 teleport destinations on quick dial, but it costs more to go somewhere else, unless you pay a 9.99 one off payment to change your destination, or a 19.99/month charge to increase it to 25 favourites, with 5 only usable off-peak... * If it's a technological thing like the internet, or a government owned machine, then using it might make an official record of your journey, compared to walking. You might not want your journey on record. * If it's a government owned machine, maybe you only get a certain number of subsidised uses each month, use for anything but you have to ration them a little bit. * If it's a personal teleporter but it's big - like the portal gun from the Portal computer games. Not necessarily gun shaped, but far far to big to put in a pocket. e.g. it's a big rucksack you strap on your back and it's heavy - you would use it only when you needed it. * Thinking of the Portal gun idea, maybe it's regulated like gun ownership (or car ownership). Any one can have one in principle, but it's licensed and controlled and requires a training course and a license fee, and a regular retraining. * Imagine it's part-technology and part-magic/unknown. You can teleport anywhere, but you have to know some identifier for your destination. And it's not co-ordinate based, no pattern is known. Whole community driven sites like Wikipedia grow up where people discuss and record identifiers they've discovered with trial and error to get to particular places as they find them. And, like Wikipedia, they're not always accurate or trustworthy, and some are maliciously edited to be wrong, or done for a laugh. You use it when you can be sure, but you don't use it when it could be dangerous or you can't trust it. * Imagine it's entirely technology, but more like Satellites than the internet. I.e. there's a big teleport machine somewhere, owned by one company, which everyone gets 'uploaded into' and then 'downloaded out of' at their destination. You might be afraid of the company reading your thoughts as they processed you, you might be afraid of the company cloning you and sending a clone of you off as a worker somewhere. You might be afraid of the company editing your brain with adverts as the machine rebuilds you. You might be afraid of the company just being ComCast, hiring the cheapest employees and the cheapest equipment for the most profit, and widely thought to be doing a poor job. You might find lots of competing companies, and lots of bad rumours and bad regulation / safety. * If it's new and people don't understand it, there might be fear-based rumours about it stealing your soul, 'them' replacing your loved ones with impostors, and so on. If it's technological then elderly people might be nervous of getting it wrong and ending up in Jaipur instead of Jersey and prefer something they're more comfortable with. * There might be ideological or religious objections analogous to some group's refusal to accept blood transfusions or Amish rejection of some technologies. * It might feel horrible. (Rollercoaster style, or pins and needles style). * If it's a magical teleport, but it looks like the [Nightcrawler from X-Men movies](https://www.youtube.com/watch?v=K3PTNGSfHAg), i.e. a cloud of black smoke and a *whompf* noise as air is displaced, it might be socially rude (like belching), disruptive/intrusive or impolite to appear in places unless you know they're empty or that the people already there are OK with it. * If it's magic and vampire-y, you can go anywhere but you need to be invited there at least once first. Businesses are built on inviting people to places for money, but they have queues and backlogs. Or maybe you just have to go there once yourself by car, then you can teleport back there anytime - as long as you can remember what it feels like (i.e. ability to return drops as your memory of the place fades, if you don't go back). * If it's so common and low effort, it will become a normal thing for people to use it to get to work and back (e.g. cars) and the high status people will deliberately not use it (e.g. chauffeurs, private jets). Demonstrating that you aren't constrained to the ways normal people live, and you can pay high prices for everyday things is a way of showing off high status. * If it's a personal ability, again like Nightcrawler, it might simply be tiring to use - and walking is easier. Or it takes lots of concentration to use, and you can't do it after a long day. * Maybe it's a skill you have to learn so, e.g. parents would need to walk/drive with young kids or invalids, until they learned/recovered. Or adults might never bother (or not have time) to learn. Look how many people talk to people but can't speak another language, or spend their work time in Excel but can't write code, or listen to music but can't play an instrument. How many people can even *run* in a practical sense? * Or, like Parkour, maybe it's a short hop (line of sight?) ability which skilled people can chain together to hop-hop-hop very quickly to go long distances. But it's easy for unskilled people to get stuck in alleys, on rooftops, in fog, in water, spend ages planning their next hops, not know the best routes, and it becomes more trouble than it's worth. And finding routes between places is a bit of a fun social puzzle that enthusiasts do - anyone can do it, not everyone takes an interest in doing it. Because honestly - when was the last time you *really needed* to get a thousand miles in a few minutes? And did you need it so much that you would spend a year of practising just so that you could? * Bikes, cars, boats are fun. There's something to be said for a half hour commute in your self-driving car, where you can plan your day. Can't do much planning in a non-existant instant between stepping into and out of a spacewarp. * "*Walk with me*" trope doesn't work for two people to leave the room and have a chat with no particular destination in mind, if they have to teleport to a particular destination. * Maybe you can't do it as a group - either on the small scale ("road trip!") or on the large scale ("50,000 people going to a stadium for a game"). * Maybe it's magical, but has a constraint like daylight, or limited magical resource which renews quite slowly. * You can go anywhere and anywhere can come to you. This is bad. So you set up force-shields around your house, and the council sets them up around your city. You can go anywhere, but sometimes you have to drive/fly/walk to and through a border to get somewhere on the other side of it. "Teleport suppression zones" for crime prevention, or for rich people. * It relies on some kind of short-range field. e.g. you can teleport within New York and within London, and there's field extenders chained between them, but you can't teleport into Moscow because Russia won't allow it to be connected up. But Russians can teleport within Russia, so if you got there you could teleport around Moscow. * It's boring. In a world where everyone can go anywhere instantly, Kansas and Mongolia are as identical as any two homes next to each other. Everything has homogenised so there's little need/desire for travel. + ["*(basically) instant*" is not instant](https://en.wikipedia.org/wiki/The_Jaunt). > > Finally, what changes to society would there be if you could simply appear anywhere you wanted by teleporting there? > > > As for this part, I imagine you could write a whole book about adding some major technologic change to human life and exploring what happens next. [Answer] There are many factors that could make people use mundane methods. # Convenience I'd rather go to the bathroom than teleport there. What if it's occupied? If activating teleport takes ten minutes, I'd rather go to the corner shop on foot. # Cost If teleport costs $3 000 per mile, only rich and famous would use it. Even them wouldn't do it on a whim. # Health and pleasure Walking and biking is good way to keep in shape. I try to do it even if I have more convenient alternative. And while cars and motorcycles do not have this benefit, they can be simply fun. # Knowledge of the destination If you can go everywhere you want, first you need to know where you want to go. On foot I can just start walking. --- Social changes would be based on the removal of geographic barriers. The more reasons to use mundane ways, the less changes. People would be able to afford to work in more distant places. Or not, if it's costly. Theft would be an issue, but only if you can steal more than teleport costs. And so on. Thus, this part is unanswerable and you should ask another question, when you decide on factors from the first part. [Answer] # Transporting Non-Human Goods Just because YOU can teleport across the world doesn't mean you can *take a whole lot with you.* Depending on your method of teleportation, there might be size or weight constraints (e.g. "longest dimension less than 10 feet" because your method is a 10' by 10' wormhole, or "up to 300 pounds" because that's all a single person can lift while they get teleported, etc.) There's also things like infrastructure: water and electricity. You can't really "pipe" water to everyone's home via teleportation machine (unless it is: 1) small, 2) cheap 3) easy to make such that you can install one end in literally every home), so those sorts of transport methods will still exist, and at some level, so will the infrastructure necessary to facilitate repairs on all of the aforementioned infrastructure. Your question hasn't included what limitations, if any, are present in your worldscape, so it's hard to predict precisely what it is that couldn't be transported, so I'll toss it back to you: What limitations does your method of teleportation have and what can't be transported within those limitations? How would it be transported instead? [Answer] Firstly assuming that by "perfected" you mean: 1. very low risk 2. very high accuracy 3. very low/zero direct cost to the user Given these allowances, one might consider the following: 1. the pleasure of just walking 2. the user interface may be more or less cumbersome a. magical requires thought/spell effort b. technological requires HUD/thought ( such as our current mouse click to follow a link ) As for #2 above, most of us have experienced the desire to unplug from our technology or otherwise seek distraction/self-extraction from daily life. As for #1 above, teleporting in the sense you have described might be as simple reaching to pick up a cup of coffee ( as simple as that act and people may engage in the activity on a whim ) or it may be as cumbersome as getting in the car to drive down to the corner store. Regardless, one can easily conceive of the choice to take the longer/less-traveled path with intention so as to break up the daily routine/norm. [Answer] According to the Isaac Asimov's science fiction short story [“It’s Such a Beautiful Day”](http://www.asimovreviews.net/Stories/Story130.html), the answer is yes. In this world, every home is equipped with a technological device called the Door, which lets the twelve year old boy go from home to school instantaneously, just like you ask in your question. The first time the boy walks to school, it's because the Door in his house breaks down, which would be a cop-out answer to your question. But the boy enjoys being outside and walking so much that he goes on to walk every day. [Answer] One societal change is that crimes, terrorism and warfare would be extremely effective. Though you could create countermeasure from fictional counter-teleportation-fields (maybe something like a tesla spool that reacts to the increase in energy from the teleportation which temporarily creates plasma and then attracts the electricity, electrocuting any teleporting intruder), to simply putting your furniture/traps into different places every day so that anyone teleporting into your defended building/room is likely to die. Other countermeasure would be something along the lines of tracing people, so that when they jump (and commit a crime or are otherwise wanted), you can trace their original location and/or destination. [Answer] What happens to real estate when anyone can live anywhere and have instant access to everything they need? How do you protect something or someone from people with evil intents when you just...can't? All great nation-states realize quickly that while their transportation costs have become next to nothing, they now have the task of either keeping people out *or in* of their respective countries. While world hunger has been solved by transporting food around without spoilage and providing fresh water to arid zones, it still hasn't fixed the fact that certain places in Idaho are just Hellholes. People start moving out of slums- the dumb ones show up in Hawaii thinking they can just bum on the beach, which drives down the desire to live there and it turns into an overcrowded mess. The smart ones buy a tiny apartment or shack in the picturesque wilderness, only to find that someone else then built a new house right in front of their view- for the 42nd time. Land prices fluctuate wildly, first cheap due to location, skyrocketting for a few months as everyone moves in, bottoming out again once it becomes full of cheap tract housing and all the views have been ruined. Shopping centers dissolve immediately, companies buy huge tracks of land in the middle of Africa and Australia for their show rooms and factories. Oh, and many of the world leaders have fallen victim to assassination attempts. **Teleportation Disruptors** The UN calls for a moratorium on the use of teleporters while it debates what to do about teleporters. Though they recognize the boon to society that teleporters could be, they also realize the dangers. And as they can't just ban all teleporters (as the nefarious will find a way), they instead create teleportation disruptors. Each nation immediately constructs their own to protect themselves, effectively killing the technology, until the nations agree on Teleports (sic), much like airports. Slightly outside the bounds of the disruptor, all people/goods traveling must take a ground transport to the Teleport, where then they get teleported to another Teleport, and then they have to ride on ground transport again. Maybe each gov'ts system is a little different, so while an enemy agent or local schmoe might not be able to teleport in through the disruptor, a local agent (police, medics, men in black) can teleport with freedom. [Answer] In Alfred Bester's book *The Stars My Destination*, everyone on Earth has the ability to *Jaunte*, instantaneously travel to anywhere on Earth. The person simply needs to have memorized the coordinates of a known place, or have a strong memory of the place, in order to get there. In this universe there is no interplanetary jaunting, because jaunting is done with brain- and willpower, and the distances between planets is too large for the mind to comprehend; everyone who's attempted (supposedly) has died in the vacuum of space. The other planets in the solar system are populated, but are isolated by the limits of interplanetary travel at the time and are economically and culturally separate from Earth. There is a certain scene in the book where a bunch of aristocrats are arriving at a soiree, and here it is established that in an era of instantaneous travel, older means of transportation are seen as a conspicuous luxury. Rich folk arrive at the party in a number of increasingly inconvenient ways, the implication being that the more archaic the form of transportation, the higher the status. This culminates in the book's hero arriving in a steam train, with workers laying down tracks in front of it up to the door of the mansion. Taken from TVTropes, "you're rich enough to spend money on things you don't need and important enough to make people wait for you." I found this to be a very interesting angle, both that interplanetary distances were still an obstacle, creating a real economic and class landscape; and that, in a world where travel is completely democratized, the assumed class division is turned on its head in order for the rich to retain status. [Answer] If teleportation existed, I personally wouldn't use it until the following question was answered to my satisfaction: **How do you distinguish between the following?** 1. The person at the origin is the person who arrives safely at the destination. 2. The person at the origin is ripped apart and experiences a brutal death, and an exact clone "arrives safely" at the destination. [Answer] Larry Niven did a pretty good job of addressing this but I can't recall what book it appeared in. Teleportation has costs, both in money and time. The lower these costs the more teleportation will take over other forms of transport. Note that in his Known Space books teleportation always obeys the laws of physics. The teleportation system must make up the energy differential, there are limits to how much it can do so. It's also a lightspeed effect and thus not used for interstellar transit (the hyperdrive is known long before teleportation.) The limit to how far he pushed it is the Puppeteer homeworld. Teleportation is open-air and too cheap to meter. The result is that for passenger transport there is nothing else. Everyone "walks" everywhere, following lines of teleport discs three steps apart. Step on the next disc and you hop, when you're at your destination you sidestep and don't hop. Different paths go at different "speeds" (distance between discs.) IIRC there were also ways to command the discs to take you where you wanted to go. [Answer] **Yes.** **In an era of instantaneous travel, would more mundane methods still be used? Yes**, just like now, we have all the transportation methods, many of us still prefer to walk or to jog or to run. [Answer] There are those who believe that you are destroying the original and making a copy. In other words, rather than simply moving to another place, you're killing yourself and creating an identical replacement with your memories. People who have this belief would not use a teleporter. In addition to this, since a teleporter is a highly dangerous device, it's tightly controlled by the government and so is probably not convenient to the public. Even consider it as a murder weapon - teleport someone away from the source, but don't bother reconstituting them at the destination. Or as others have said, they could easily be used in crime / terrorism. [Answer] Interesting that no-one mentioned tourism and sightseeing where the specific destination is just a waypoint and the route itself is what you are there for. Sure, given "Tomorrow People"-like teleport abilities (which don't depend on send/receive stations), you could keep teleporting in half-mile stretches along your route, but even then, mundane surface travel seems better for the purpose of checking the view as it changes, being surprised by unforeseen events/sights and finding reasons to take a detour or just stop and eat an ice-cream. [Answer] Going to riff off of @Briguy37's answer here: * You are killed by the teleportation process and reconstituted at the destination. Everybody knows that this is how it works. Do you want to do this? What are the tradeoffs? Most people might be afraid, but some would do it and reap the rewards of wealth and power from being able to travel anywhere instantly (politicians, businesspeople, etc) * You are killed by the teleportation process and reconstituted at the destination. The company selling the teleporter hides this fact by building in a mechanism to destroy the body. What happens when the truth gets out? * The above two scenarios, except that the teleporter doesn't have to kill you. It actually just creates a copy at the destination. The government or corporation in control of teleportation has chosen to make it kill one of the copies to prevent bad societal consequences of having a bunch of exact copies running around. * Teleportation creates copies, and neither is killed by the process. How do you deal with having a copy of yourself running around? [Answer] Yes, for several reasons: ## Going for a walk I own a car and a bike. I still walk to the shops. It's pleasant, and I get exercise. ## Climbing a mountain I could drive to the top of a mountain. I could take a helicopter or a ski lift, but I walk because it gives me a sense of achievement to do so. ## Going on a cruise I can get to Australia in an aircraft or a cruise ship. The aircraft takes 24 hours. The boat takes a month and costs five times as much. I take the boat because the trip itself is enjoyable. It's an experience. [Answer] ## Some people would, yes. This is readily apparent even in today's world. We have modern cars and planes which together would account for transportation to just about any corner of the globe. And yet, people still use boats, trains, bicycles, snowmobiles, all-terrain vehicles, and even horses to travel. What is the common thread here, you ask? It's recreation and personal enjoyment. Until you outlaw a mode of transportation or otherwise make it impossible to use, there will likely be someone somewhere or will prefer to drive, fly, or walk to where they want to go for various reasons (enjoyment, health, effort, etc). Just like your neighbor and his 1950's fastback, or your uncle and aunt who have a ranch out in the country, there will always be someone who is interested in doing something that is considered outmoded or obsolete simply because they still enjoy it. [Answer] It may all depend on how teleportation is achieved. There could be some limitations in its use by some individuals, or states, due to religious beliefs, ecological beliefs, political beliefs, economic beliefs, etc. If you want to make it controversial, just make it as an analogy with some already pre-existing controversial thematic. good writing. [Answer] ## In Frank Herbert's Dune series, mundane means are due to a harsh environment and the desire for personal reflection on a pilgrimage *Children of Dune* had a quote from a fictional handbook that answered the question of why anybody would walk. > > In this age when the means of human transport include devices which can span the deeps of space in transtime, and other devices which can carry men swiftly over virtually impassable planetary surfaces, it seems odd to think of attempting long journeys afoot. Yet this remains a primary means of travel on Arrakis, a fact attributed partly to preference and partly to the brutal treatment which this planet reserves for anything mechanical. In the strictures of Arrakis, human flesh remains the most durable and reliable resource for the Hajj. Perhaps it is the implicit awareness of this fact which makes Arrakis the ultimate mirror of the soul. -Handbook of the Hajj > > > Now they don't have teleporters in Dune, but they do have the ability to travel over vast distances quickly in starships and similar planetary transports. But the environment deteriorates those machines quickly and the people value walking because it lends itself to a personal reflection of the soul on their Hajj (religious pilgrimage). [Answer] Every technology has its place. We still walk even though wheels exist. We still use bicycles even though motorbikes and cars exist. We use cars and trains and planes in parallel. We even still use horse-drawn waggons occasionally, or plain old horse riding. There are many reasons why an obsolute technology continues to be used. Horses are damn convenient in some corners of the world (don't need fuel, easier to maintain, food source in case of emergency) and horses are superior to higher technology in some special cases (my home city recently re-introduced a police squad on horseback). So you can basically decide what the requirements of your story are and then design your teleporter technology to match it. Maybe it takes a while to charge up or program a teleporter so that for short distances walking is faster? Maybe it takes up a lot of energy, so driving is cheaper? Maybe some people fear negative medical effects (whether true or not, this would make those people search out alternative means). Maybe older methods of transportation survive out of tradition or as sports? [Answer] One possibility is that teleporting is painful or otherwise unpleasant in some fashion. For shorter distances or non-urgency they might well take a painless mode of transport, like walking or a car, while teleporting might be worth it for a longer distance or if they'll spend more time at their destination. For instance, two hours of nausea might not be worth it to commute to an eight hour workday. But might well be alright to start your two week vacation to the Bahamas. [Answer] I mentioned it to someone else "*In an era of instantaneous travel, would more mundane methods still be used?*" and they immediately said: > > Of course they would. You can't have a quickie in a teleporter. > > > I didn't think of that in my big list of reasons. And I think nobody else has mentioned anything along those lines either. (Is that off-topic for the site, or is that illustrative of something more?) ]

[Question] [ In a post-apocalyptic scenario a group of circa 100 people is looting houses to gather resources for their survival. They are the only ones in the region, and resulting from this have no issues with defending themselves (against other humans) or with sharing resources. If a few members from this group would go gather resources in average households what would be the most valuable resources they can find? Some things which come to mind are food and fuel. I'm especially interested in some rare, although not extremely rare resources, which either are essential for surviving or can increase comfort a lot. [Answer] # **The Obvious Essentials** **Canned goods.** They last for years and are likely to be more enjoyable to the modern first-world human palate than the new meals you’re going to be growing or hunting. They’ll make a good meal supplement as people adjust. **Medication and first-aid supplies.** You want anything and everything you can find. Fabricating medication after the collapse of society is going to be very difficult and a functional knowledge of medicinal herbs is quite rare these days. **Gasoline.** You’re less likely to find this in homes than in the cars abandoned on the roads, but finding some in a home may be a good indicator that a generator is present. **Tools.** This is really a no brainer, but you’ll need cooking instruments, farming tools, construction tools, and frankly just about every tool that you might find in your typical home. Be careful about battery-powered and gas-powered tools… you shouldn’t be wasting those resources when a simple axe or screwdriver will do. **Weapons.** Most tools can be used as weapons in a pinch, but to seriously survive other humans in a post-societal world you will need firearms. Guns and ammunition will be a high priority and should only ever be used in extreme defensive scenarios against other people. # **The Less Obvious Essentials** **Books.** Particularly how-to books. Detailed information on plant identification, basic construction techniques, and farming can change a short-lived group into a long-lived one. You will only have a small subset of necessary survival skills and need to augment them wherever possible. Books, rather than purely verbal teaching, also simplify the education of future generations. Quite frankly, stumbling upon an intact library might be the best thing that could ever happen to you. **Fishing Gear.** While it can be crafted without too much trouble, having some reliable gear will go a long way for a long time. Lures in particular will be a terrific tool (at least until you lose them). **Hard Liquor.** Alcohol will have all kinds of critical uses from sedative to antiseptic. **Fabric.** You’ll need to be careful here because of the weight, but bedding and blankets provide huge quantities of quality fabric that will be very difficult to manufacture. Even if you cannot take it all with you, there may be value in removing it from the house and hiding it where you can find it on return trips. Clothes of all shapes and sizes will be valuable, but place particular emphasis on winter clothing — it’s built to be very effective and relatively light for the amount of protection it provides. **Gold, silver, and other jewelry.** Assuming you survive long enough, there will absolutely be a time when neighboring communities begin trading commodities. Precious materials that historically represent wealth or status will have value and will enable you to avoid trading away other essentials. **Soap.** Cleanliness and sanitation are going to take a hit, but soap is plentiful and is effective in small quantities. This will make diplomacy easier and generally increase spirits among your group. It will also help protect you from basic illness and disease. **Toothpaste.** You’re going to run out quickly, but attempting to maintain at least mild dental hygiene will increase quality of life. **Herbs and spices.** You’ll be able to find and produce some of these eventually, but raiding a single spice cabinet could give you enough spices for months. Given the diets you’re about to embark on, you’re going to want some extra flavor. **Playing cards.** As pointed out by @MichaelKjörling, games (in addition to reading material) are terrific for morale and good for mental stimulation and group bonding. Playing cards in particular are a common household item that are compact and easy to carry with potentially thousands of different games. [Answer] I don't know why every post apocalyptic show / movie / game misses this but **Basic Transportation** Specifically, **bicycles**, anything you can fashion into a cart or wagon to haul all your plundered goods and bonus if you can get an animal to pull it, **shoes**, rollerblades (if there is enough pavement around), sleds/sledges/skates/skis in winter. [Answer] **The first level of Maslow's Hierarchy can answer the general question.** [](https://i.stack.imgur.com/OdLvM.png) The most important things for survival that can be obtained from scavenging a house are, in order of importance: 1. Clean Water (use is obvious, can be found in the form of bottled water in the fridge/pantry or in the reservoir of toilets). 2. Food (packaged food of any kind for caloric needs). 3. Medicine (treat wounds, reduce infection, etc). 4. Clothing (stay warm and dry). 5. Vitamins/supplements (most packaged food will be lacking in proper nutrition). From there many things are nice to have but not strictly required for immediate survival. [Answer] **Solar Panels**. These are becoming more common and small, comparatively portable ones are most likely to be in homes. These would make electrical tools far more useful. Note that it may make sense to locate in a place that already has solar panels rather than try to move them. But if you are already in a place with solar panels (or windmills) and need more power... Locating near to windmills might be better. The solar panels are going to be easier to move than the typical industrial windmill. And the two different sources will complement each other. Windmills work in the rain while solar panels work without a breeze. I'd also like to point out that for many resources, I'd prefer stores or warehouses to houses. For example, books, lumber and other construction materials, tools, seeds, and even fishing and hunting gear might more easily be found in stores. It's possible to find scrap metal in houses but wouldn't a junkyard or hardware store make more sense? There are two kinds of things that makes sense to scavenge: consumables and rarities. Solar panels are an example of a rarity. Unless you find the factory, most regions are more likely to have panels in houses than a store. Consumables make sense to scavenge from houses because the grocery supplies will be consumed. It will take a long time to go through all the construction materials in the stores and warehouses. Most books will last a long time. Those kinds of common durables are more easily sourced in stores than houses. Of course, it may be that there is some individual book that is not available in stores or libraries but is available in houses. For example, my mother would like to find a sixties era version of a particular cookbook. She has the newer version of the same one, but it dropped some useful information. It seems to have shifted a bit from basic ingredients to store bought preparations--the older version being more useful post-apocalypse. Can't buy in stores, as only the new version is available. The library may also have worn through its copy if it ever had one. Or the library had one but there are more cooks than that. They might scour an older neighborhood looking for cookbooks from the right era. Clothing is right along the border. Initially easy to find in stores. May wear out enough to be useful from houses. Firearms are available in stores and are durable. In the right region, you may be able to buy them in Walmart. Ammunition is a consumable. Source it anywhere you can: stores, police stations, army bases, and...houses. **Board Games**. Just because no one else mentioned it. **Salt**. Mentioned in a comment, but I wanted to reiterate that it has uses beyond flavoring food. In particular, salt used to be used as a preservative for meat. ## Oddities These are things that are durable but may not be common enough to be found in stores. You won't necessarily go to houses looking for them, but if you go to a lot of houses, you may find them. **Home Still**. Others mentioned alcohol. It's possible to brew beer or distill moonshine at home. These sets will be more appropriately sized and operated than the kind that you'll find in a brewery or distillery. **Ice Cream Maker**. Non-powered ones are rare enough that you may not find them in stores but they do exist and may be found in a house. Have a mountain nearby? Send a horse drawn cart up for ice in the summer. **Solar Dehydrator**. Another thing that is rare enough to be hard to find in stores but that exists and may be found in a house. Dehydrating can preserve some kinds of fruits and vegetables. **Pig roast spit**. These are rare enough not to be in stores and may be found in a house rather than a separate business. If you can't find a non-powered one, try for one that runs on diesel. It's possible to run diesel motors on things like vegetable oil or motor oil (unused). **Make your own ammo**. Some people make their own ammunition. This requires special tools and is likely to be at home. A setup for making gunpowder would be invaluable. **Deer butchering tools**. This tends to be done part-time out of a house. May be easier to use than more professional tools. **Taxidermy**. In particular, tanning supplies. Not for use in taxidermy but for tanning leather to make clothing or footwear. More home taxidermists than tanners these days. May also have relevant and specialized books. **Strawberries and other perennials** Some plants live for years and grow by sending out offshoots rather than seeds. Dig up the whole plant and take it dirt and all to where you need it. May also be available in nurseries but wouldn't sell as well as plants that need to be replaced annually. [Answer] Almost everything has value in the house and if they don't have to worry about other people then they can afford to loot everything. * Knives. Specifically ones with wooden handles these can be used for bayonets, spears or (obviously) knives. * Cloth. Mattresses, odd clothing and sheets can be used for warmth and for makeshift bandages if medical supplies have dried up (this depends on how deep into the apocalypse you are) * Lumber. Again depending on how deep you are into the end, most lumber will be used and you will have 2 options. Cut down tress and cut them into planks or scavenge already made planks from houses and furniture. * Toilet paper. Sure you may laugh but it's something that everyone will want. * Bleach/lime. This will be used for the latrines. * Gasoline. I disagree with you that they will have cars. It's unlikely that they will be stupid enough to rely on vehicles but generators will need the gas. * Scrap metal. This can be used to make an assortment of [weapons and armor](https://www.youtube.com/user/nonlethalbychoice) * Jewelry. Again this is a creature comfort but people will take jewelry because it looks nice. * Medicine. If I need to explain to you why medicine is necessary then you won't last long anyway These are things that will be commonly looted but each group is unique. If there is a baby(or pregnant person) in the group then they will loot baby food and diapers. If someone has a limp they will loot walker or wheelchairs. If there is a sick person then they will loot more specific medicines. Not to mention that the kind of apocalypse will effect what they loot. [Answer] Depends on how soon they start the looting and how much of the goods decay, one of there: * medicine (especially antibiotics) * clothing * hunting guns and ammunition, plus related - binoculars, sleeping bags, durable fabric * tools (at the beginning), an axe, saw, drills, hammer, nails etc. are priceless * chemicals, especially whatever can be used as a firestarter (paint cans etc.) * flashlights (hand cranked) * seeds (only a first year or so, they become useless soon) * alcohol and of course, any survivalist gear they can find. [Answer] I'm missing two things in all other answers related to two of the greatest inventions in history: **writing** and **fire**. You are going to have to rebuild your 'civilization' and one of the greatest inventions in history was writing. So any writing materials you can find: *paper* (although it will quickly deteriorate if you can't keep it dry), *pens*, *pencils*, the odd mechanical *typewriter* with ribbons, anything that can help you distribute knowledge in your society. You will not need these in the first phases after the apocalypse, but as soon as your primary needs are satisfied you will have to start planning for the future. You need classes to teach your children, and writing materials make a big difference there. Fire you need directly, so anything that will light one: *matches* (may even work after drying when wet), *lighters*, *glasses* with positive lenses, *concave shaving mirrors*, and the occasional *magnifying glass* left behind by a stamp collector or botanist. (And there are even other ways of making fire: [read here](http://www.wikihow.com/Make-Fire-Without-Matches-or-a-Lighter) or [here](http://www.artofmanliness.com/2008/04/29/9-ways-to-start-a-fire-without-matches/). I like the suggestions with [soda cans](https://www.youtube.com/watch?v=yTdY-dOYvSA)) [Answer] **Trailer tent** [](https://i.stack.imgur.com/T1XeG.jpg) This would be the first thing i would look for. It is a small tent trailer, it is so small it can be drawn by 2 humans easily, one horse, cow, donkey, 2 large sheeps or goats, it can be drawn from a scooter, snow scootter, motorcycle - you name it. [](https://i.stack.imgur.com/tWAo5.jpg) And here it is unfolded. It has roof, heat, kitchen, easy to transport and you can load stuff on it, Even if you are tired of walking your companions can drag a tired person on it or even injured. Add all the other amazing suggestions, 2 car batteries and a lot of solar cells. And you are off for a good start. [Answer] Of course food is on the top of the list, different fuels, though that might be pretty easy to come by for a little while if only a few people survived in a medium sized town. Books on gardening and edible wild plants. Hand tools and DIY books would be big. Unlikely to have any power from the grid so cordless drills and power saws are worthless. Of course if you have a generator and access to some gasoline you can make them last a little longer. Of course the pharmacy would be a place to raid, for antibiotics and other generic but useful medical supplies. Antiseptics and bandaids etc. Medical books. Weapons for hunting and self protection. Reloading equipment and maybe a book on how to make gun powder and where to find the ingredients. [Answer] The largest and most significant resource that could be found in a house in your given scenario is one that not one single person on here has mentioned yet: **The house itself.** You need shelter. With this large amount of people making a small community using these houses seems like a pretty darn important first step to getting back to normal living. Of course, there are many other great things others have mentioned that can be taken from homes in the area, whether they be the ones you decide to occupy or not. But the value of the home itself as shelter has been completely overlooked in these answers so far, so I felt the need to add it. --- I'd also point out that 100 people with zero competition from other people and homes aplenty around them honestly just plain doesn't sound like any true challenge to survive. Just find a little town with a hardware store full of tools in stock and a couple dozen houses and take up residence. Between each house making a little garden, raising some chickens, and having a couple communal rifles around to take a deer every once in a while it honestly wouldn't look that different from a lot of small towns in existence right now save for the fact that you'd probably have to attach hand pumps to the wells once the generators ran out of gas. I heat my home with wood, have deer meat still from last season (and the next season is about to begin in 2 weeks, so obviously it's easy enough to get a year's worth of meat), have a well that I could put a hand pump on should that truly become needed, a septic system, and have a garden that could pretty much fully feed me if I put the time into it instead of going to work...and honestly I'm pretty normal for rural America. If there's some other threat to these people that makes survival harder than the annoyance of having to hand pump your own water each morning, split wood for winter, and store ice for summer then you should inform us of it because it's going to affect the answers we're giving as it pertains to what they need to be gathering to survive. Otherwise the answer is: *"Go to a rural area, take over the nicest looking house, and just live as if there's a power-outage and you've taken a sudden interest in gardening, raising chickens, and hunting. It honestly might not even be interesting/challenging enough to be worth writing a story about."* [Answer] **Short-wave transmitters (and receivers)** Obviously in addition to the items mentioned elsewhere. In such a situation I would look for a dwelling with (remains of) ham-radio antennae, get hold of the equipment and if possible the documentation. Sooner or later you'll want to get in touch with other survivors. Power may be a problem but should be more easily solvable. [Answer] Containers, especially fireproof metal ones. There are several ways to treat water, but only in a limited quantity which you have collected first. Good luck boiling or bleaching an entire pond. Aside from hydration, containers will also be useful for storing or preserving other valuable items mentioned in the great answers above. [Answer] Apart from the obvious, that has been mentionned, like **food**, **tools** and **clothing**, i recommend taking every single book they can find. **Stored knowledge**, but also stories, are essential in keeping the rest of humanity human, and not just highly sophisticated animals. Obviously, a simple and reliable way of passing on knowledge about everything is absolutely priceless. Plus, a good read is always nice on a rainy afternoon. [Answer] Mirrors. For use in sun ovens. Also to make solar panels more effective. Since mirrors are pretty fragile, it depends on how nomadic these survivors are. [Answer] As for a specific item, perhaps your survivors will find a [compressed archive of the entire english wikipedia](https://en.wikipedia.org/wiki/Wikipedia:Database_download) stored on a computer or hard drive (which apparently wont take more than 50 GB uncompressed). I assume powering the device won't be an issue. Others have suggested books, but an archive like this will be much more compact and contain a detailed overview of just about any subject, with references in case you do need something from the library. [Answer] Duvets and blankets. Depending on the new climate of the post apocalypse this could be a life saver once winter comes round! Other "fuel" resource is batteries. Ideally rechargeable ones so they could be topped up from other sources. Incredible how many things run on AAs [Answer] I am surprised nobody has specified yet **wiring** and **plumbing** as part of a "long term" (once the most basics have been satisfied) looting. Granted, an axe is more useful in the short term, but with enough resources and a little practice it should not be that difficult to build your own functional axe, even if it is far from being as efficient as one of the current ones. But, for many years, you will lack the technology to build anything closely resembling properly insulated copper wire, or pipe joints that do not leak. Wiring would be very useful (if you get a generator working) for running a telegraph wire with other survivors locations. Plumbing will help you to ensure that the water you use is not contaminated by brown waters. So, I do not expect those items to be the first to be picked up but, while things have settled a little more and you are in the process of slowly disassembling the houses, it will pay if you ensure to store properly both wiring and plumbing. [Answer] Everyone has covered pretty much everything I'd have thought of, but so far no-one has mentioned rope. Lots of rope, lots of paracord, and a decent book of knots. I'm adding another thing; tarpaulin. The major two problems that those of us fortunate to live in developed countries do NOT have is keeping warm and dry. Anything that will help your survivors achieve that will be incredibly useful. If they are sensible they will be in a well-made pre-existing building, but even so, unless they are good at roofing, anything that can quickly cover the inevitable leaks that will occur as time goes by will be pretty handy. And another thing no-one has mentioned - dogs. Now, I'm not a dog owner, so some comments on the practicality of taking in dogs left to their own devices for 1-5 years would be good, but dogs are pretty useful in an apocalypse, provided they don't become telepathic and [persuade you to eat your girlfriend](https://en.wikipedia.org/wiki/A_Boy_and_His_Dog_(1975_film)). [Answer] In a post-apocalyptic world, the banking system as we know it would completely collapse. The survivors would have to rely mainly on the barter system for trade in goods and services. In a barter situation, each party will trade based on the perceived value instead of a market value as it is today. This means that potentially any household item would have some kind of value. Many household items that rely on electricity would be devalued. Computers, cell phones, electric appliances, etc. would have very little value in that world. The survivors will most likely not be as trusting, especially if there is a lack of law enforcement. Farms and homes will be subject to the threat of attacks by groups of pillagers. There would be riots in the jails and prisons which would result in prisoner escapes. Some cities will be overrun by hundreds, if not thousands of deadly psychopaths. Any type of weapon which could be used for self defense would come at a high premium. The long term survivors would adapt to a more agrarian lifestyle. Livestock, and farming implements would definitely be highly valued. If you look back to the pre-industrialized world, you would see that the same things which were valuable at that time, would be valuable in a post-apocalyptic world as well. Any practical hand tool that is well made would have value. There was a time when you couldn't run down to the hardware store and buy a hammer. You would have to go to the blacksmith and have one forged. These tools were often passed down as family heirlooms because of their expense. The same thing would be true in a post-apocalyptic world as well. Some simple things that we take for granted now, were very valuable to early colonists. Nails at one time were nearly worth their weight in gold. Each nail had to be hand forged by a blacksmith, and the process was very labor intensive. When the homesteaders decided to move, they often would burn down their homes to recover the nails so they could build a new home. Since the factories that produce these items would all be shut down after the apocalypse, there would be a limited supply and would in turn be valued. The value would most likely increase over a long period of time if we do not return to an industrialized world. In this world, most durable goods will have some value. For most people, hoarding and stockpiling these objects would not be very practical due to the fact that many people will end up living a nomadic lifestyle. I suspect many outdoor sporting goods would be very useful. Specialty items such as lightweight eating and cooking utensils, backpacks, sleeping bags, tents, blankets, and coats would be items that a survivor would not want to part with. In the end, it would be difficult to say for sure which items would be the most valuable, but it is probably safe to say that baseball cards would never be highly valued or sought after. [Answer] A lot of answers seem to be forgetting the second most critical element to human survival. You can go a month without food, but only 2-3 days without water, especially if you're exposed to high heat (for obvious reasons) or nuclear fallout (because it keeps your digestive and excretory systems going to help flush out radioactive fallout and damaged cells from low-grade radiation poisoning). Water is critical to the survival of any post-apocalyptic humans; the only more immediate need is breathable air (and we're assuming the earth isn't so badly trashed that this is a precious resource). To ensure a good supply of clean water, you need: * A supply of safe water, to last until you can collect and safely drink other sources (and you can refill the containers for storage). Any open standing water, even in a swimming pool or water treatment plant, will have stagnated or been contaminated fairly early on and isn't safe. Look in office complexes for the five-gallon water cooler bottles, and home fridges for ice bins. * Diatomaceous earth. This is a common material for filtering swimming pools, so homes in formerly affluent neighborhoods should have a bag or three in addition to what's already in the pool filter (use the stuff in the filter if you have to but it will have a shorter useful life). Play sand from a backyard or a park is an acceptable alternative if you can also find charcoal. * Charcoal. Activated charcoal is best, but not exactly a household item. Even finely ground barbecue briquettes will have some benefit. This is optional if you have enough DE. * Clean trash cans or oil drums, as many as you can find. Some will house the filter, others will store the clean water. * Iodine, or a source of fire. * Coffee filters. Again, as many as you can find. * Metal or plastic mesh screen. This supports the coffee filters. Screen doors and solar window screens are perfect. To build a filter, start by choosing one of the trash cans or drums and poke or drill holes in the bottom from the inside out; make as many holes as you can without compromising the strength of the bottom of the drum. Lay a window or door screen over the bottom making sure to cover all the holes, and then cover that with a layer of coffee filters over the entire bottom of the can. If you have DE to use as the filter media, start by carefully pouring it in, keeping all the coffee filters flat, until they're all covered; then, start heaping it in, as much as you have. If you are making do with charcoal briquettes, find a rough, flat stone like a piece of sidewalk, concrete paver or brick and start rubbing down the briquettes to get powder. You'll want a good two inches of powder evenly spread over the filters. Once you have that, cover the charcoal with another layer of coffee filters, then gently cover that with the play sand until you have an even layer before heaping in as much as you have to the top of the can. Voila, one water filter. To use it, I'd recommend using the roof of a building that's still standing as a rain catchment. Find a building near your settlement with an intact roof and gutter system. Cut back the downspout about 6-8 feet off the ground, and find some wood or metal to make a frame to hold your filter far enough off the ground that you can put water storage vessels under the filter. Clean the gutters and roof when dry to avoid too much debris going into your filter when it rains, and voila, you have a rain catchment. If it's not raining, you can still pour in any groundwater you can find. While the filter will minimize potentially harmful particulates in the water, like nuclear fallout, depending on the nature of the apocalypse even rainwater might not be safe to drink without boiling it. Groundwater must definitely be boiled or disinfected with iodine before drinking it. In addition, there may be some chemical treatment needed; harmful chemicals may be dissolved in the atmospheric moisture which must be removed by chemically treating the water. Exactly what process you'd need depends on the pollutant, but if simple distillation (requiring a moonshiner's rig with a sealed vessel you can heat to boiling, with the steam fed into a tube that runs through a drum of cold water) won't do the trick, there's usually a fairly simple reaction with chemicals you could find in a home, hardware store or pharmacy. [Answer] Besides the basic food and water items listed, a wise man once told me there are two things to stock up on to prepare for just such a situation. Those two items being ***chocolate and ammunition***. Of these two items you cannot have enough. The reasons are quite simple: * Chocolate (or any candy for that matter) is a complete comfort food. In the event of total world collapse, chocolate could be used *quite efficiently* for trade or barter, as well as provide quick energy if needed. No other food would be worth its weight in gold like chocolate would be. * Ammunition is a simple self defense item, but once you are out of ammunition, a gun can become a great bludgeon or a tent pole, but is pretty much worthless otherwise. You may only need one gun, but you cannot have enough ammunition to fire through that gun ... (*see The Walking Dead for details*). Ammunition could also be used for barter or trade if need be, but I wouldn't give away ammunition in such a situation mainly because now you've armed a potential enemy with something they could potentially shoot you with and gain not only what they've traded you, but the rest of your ammunition and chocolate as well. While the initial reasoning of these two items was originally meant for *before* an apocalyptic event, these would be items I would be searching for the most after some such even has occurred. ]

[Question] [ I have this idea for a science fiction story (It actually came to me in a dream.). In the distant future, the inhabitants of the Milky Way have formed a galaxy-spanning civilization similar to the Republic in *Star Wars*. However, instead of using FTL starships to travel between planets in different star systems, they *move the planets*. Each member world has been outfitted with a powerful **jump drive** allowing it to travel tens of thousands of light-years in the blink of an eye. It might work by temporarily enlarging microscopic primordial wormholes (Einstein-Rosen bridges) and "warping" through them, but that's just one option. A planet will use its jump drive to teleport from its current star system to another one, where it will assume an orbit in its habitable zone. A given planet will undergo about 1 to 4 jumps per day, with each jump being planned weeks or months in advance. When two planets are in the same star system, people use sub-light spaceships to travel between them. After a ship makes the trip from one planet to another, it can land or it can enter orbit and "ride out" the next jump. Since there may be a dozen or so member worlds in a given star system at a given time, a single ship can reach any other member world within only a few jumps (Think Six Degrees of Kevin Bacon.). My question is, how can I justify this system? What principles, based in real physics or sci-fi logic, can I use to explain why using a starship for FTL travel is impossible/more difficult/less efficient but using something as massive as a *planet* to do it is possible/less difficult/more efficient? Keep in mind that FTL *communication* exists in this setting, and may use a technology similar to that of the planetary jump drives or something completely different. Edit: I might call my story "The Planetary Exchange" as a parallel to the Stock Exchange. And the jumps would be coordinated via a central computer network; it wouldn't be a chaotic free-for-all. Another Edit: Oh, and during a jump any moon(s) in orbit around a planet will also be taken along for the ride, not just spaceships. Update: Thank you everyone for all of your excellent answers! I have chosen BBeast's answer as the most helpful. My favorite is their "economy of scale" theory, though I also really like the heat sink explanation. But feel free to continue speculating. This is all really interesting! :) [Answer] There are two broad reasons why the jump drives are only used on planets. The first reason is that some property which planets have but spaceships lack is required for the jump drive to work successfully. Two such properties come to mind: gravity and thermal mass. The second reason is that it is possible to move smaller objects, but due to some scaling property of the jump drive technology it is not practical to move small things. This works best if we assume the jump drive to require a large amount of external infrastructure to operate. In all scenarios, we require that the energy to jump scales slowly or not at all with the volume of space or amount of matter that is jumping. If this is not the case, then moving planets would be virtually impossible and the technology would instead focus on making spaceships suitable for the jump drives. For this, we shall assert that the majority of the energy used in the jump drive is to initiate the connection between two distant points in space. The energy to envelope a larger region of space or transport additional mass does not grow too quickly, up to at least planetary scales. You can use choose one or a combination of all of the below factors for your jump drives, adjusting their significance as you see fit. ## Jump Drives Require Gravity Wells Planets, by [definition](https://solarsystem.nasa.gov/planets/in-depth/), have substantial mass and produce substantial gravity. Spaceships, on the other hand, are rarely large enough to have any noticeable gravity (except with very sensitive instruments); any exceptions to this would be plot fodder for your story. By general relativity, gravity bends spacetime, with regions of high mass (such as around a planet) having high curvature. A wormhole requires bending space to the extreme. So let us postulate that the jump drive generates some sort of wormhole. This jump drive requires existing curvature in spacetime (that is, an existing gravity well) to generate or contain a wormhole. Of course, small objects still have *some* gravity, so we have to apply some form of scaling. Either the amount of energy required to perform a jump goes up prohibitively quickly if there is too little gravity, or the distance of the jump is smaller with less gravity. This scenario, where the jump drive converts an existing gravity well into a wormhole, has an interesting consequence. Compact objects such as neutron stars and black holes have extreme gravitational curvatures while often being only a few kilometres in diameter. This means that, if you could equip a neutron star or black hole with a jump drive, you could use it as a sort of *super* jump drive. I would posit that this would give the jump drive a ludicrous range, suitable for intergalactic travel. It may also be able to create a very large wormhole which could cover an entire solar system. If a spaceship wants to jump independently of a planet, it would need to somehow generate a strong gravitational field. It might be able to do this with a miniature black hole, although the black hole can't be too small otherwise [Hawking radiation](https://en.wikipedia.org/wiki/Hawking_radiation) would lead to its untimely evaporation. Creating and containing a black hole is a non-trivial exercise, though, so even if it is possible it won't be common. ## Jump Drives Require Heat Sinks Thermodynamics is a harsh mistress. As a consequence of the second law of thermodynamics, every process which does useful work also produces some amount of waste heat. The second law also dictates that you can't turn the waste heat into a more useful form (unless you produce even more waste heat to compensate). By the first law of thermodynamics, it is impossible to make that heat simply disappear. As such, you have to put that heat somewhere. In space, the typical thing to do is radiate away that heat, using radiators and [black-body radiation](https://en.wikipedia.org/wiki/Black-body_radiation). However, there is a limit to how fast you can radiate your heat before your radiators have to be so hot that they'll melt. The solution to temporarily having more heat than you can get rid of is to have a heat sink. This is something which can absorb a large amount of thermal energy while only rising a little bit in temperature. A good heat sink has a lot of mass. The jump drives require an enormous amount of energy to be expended in a relatively short amount of time. This produces a stupendous amount of waste heat. So much waste heat, in fact, that any object as small as a spaceship would instantly vaporise. Planets are far more massive than any practical spaceship, thus have a much larger heat sink than any spaceship could have. If you need something approaching a planetary mass of matter for a heat sink for your jump drives, then only planets can have jump drives. Such a jump drive would have most of its infrastructure on the planet (although it can have power beamed to it from a local Dyson swarm), distributed across the entire planet as many nodes (the more the better). Each node of the jump drive would have 'roots' made of some material with superlative thermal conductivity stretching deep into the planet's crust and/or oceans. When the jump drive is operating, each node sends the heat it produces through its roots into the planet, increasing the planet's temperature by a tiny amount. Each node would also have a vast array of radiators ('leaves', perhaps) which it uses to get rid of that heat in between jumps. This jump drive, which requires massive heat sinks, precludes their use with non-terrestrial objects (such as gas giants, stars or black holes) unless you build a megastructure with the mass of a terrestrial planet surrounding that object. This would not be practical for regular transport and trade, making it only useful if you need to move the gas giant/star/black hole somewhere else for whatever reason. If someone wanted to use this jump drive with a spaceship, they would have to do one of two things. Either they would have to find a sufficiently massive heat sink (an asteroid, perhaps, or maybe some unobtainium bricks), or invent a vastly more efficient jump drive to reduce the amount of waste heat. A consequence of this jump drive is the accumulation of heat if you jump too rapidly. While multiple jumps in rapid succession may be possible (recharging of capacitors/batteries permitting), that won't allow enough time to radiate away all the heat produced in the previous jump. To avoid jump drive induced global warming, you would probably need to have an average frequency of jumps much less than once per day (although this can involve multiple jumps in a couple of days followed by a few weeks or months of no jumping, although I would imagine general transit would prefer to space out the jumps). ## Economy of Scale The prior reasons are physical constraints which might be used to make jump drives impossible for small objects. However, we can instead invoke the economy of scale which can make it impractical to routinely transport small objects while still leaving open the possibility. Let us suppose that the member solar systems each have Dyson swarms or some similar technology which harnesses an appreciable fraction of their star's power, and that this is the largest source of power in the solar system. This is expected for a Type III civilisation. This jump drive requires an enormous amount of energy to function. So much energy that it requires most of the power of the Dyson swarm. As such, a given solar system can only operate a limited number of jump drives in a given period of time. This makes jumps per day a limited resource which must be managed carefully. We require the scaling of energy with the size of the jump to be very small compared to the baseline energy needed to initiate the jump. Because the number of jumps is limited, but the amount of stuff you can take per jump is not limited (or at least has a much looser limit), we want each jump to take as much stuff as possible. A planet probably has the most amount of civilisation-useful stuff in one place, so the optimal solution is to move the whole planet and everything on and around it. Note that if this economy of scale is the only constraint, then equipping spaceships with jump drives is still possible. If the jump drive instead operates purely on external hardware (with a solar system spanning wormhole projector, perhaps), then any objects can be transported without having to equip them with a jump drive. However, using a star system's power to operate a jump drive for a mere spaceship (or fleet of spaceships) would be the equivalent of shutting down a nation's airports, seaports and major roads for several hours. If a character or entity is able to get authorisation for such a move, then that character or entity (or their task) must be of galactic importance. With this jump drive, if someone were to invent a compact and portable power source which rivalled that of a star and equipped a spaceship with that power source, then that spaceship could jump at will. But such a power source would be a game-changing technology. [Answer] ## Jump drives are just plain huge The reason they move entire planets around instead of smaller ships is because, by the time you've put all necessary equipment for a functioning jump drive into your ship, the ship's size is edging into planetary scales. ("That's no moon... it's a space station!") Putting the jump drive onto a planet is easier and cheaper than building a ship that large. There may still be some moon-sized starships out there, but they would be built for very specific purposes and rare enough that the average person might question whether they actually exist or if something that outlandish is "obviously" an urban legend. [Answer] **Hyperspace is dangerous and/or power threshold** Danger Will Robinson! There's gravel, small boulders, charged particles and pirate ships (maybe even [Space Hulks](https://en.wikipedia.org/wiki/Space_Hulk)!) in hyperspace. A planet with fully certified [Van Allen belts](https://en.wikipedia.org/wiki/Van_Allen_radiation_belt) and a decent atmosphere will have no trouble with the natural hazards and has the firepower to stomp aggressors flat. (Ships riding out the trip in low orbit must ensure that their orbital path puts them "behind" the planet during the jump window in order to be protected.) A hyperspace-capable ship, however, has no chance of surviving even the brief (a few minutes?) transit and can be pulled off course and captured by pirate tractor beams. Alternatively or additionally, the threshold energy to "jump" and maintain a body in hyperspace is *huge*, but once the threshold is reached the size of the "jump bubble" can easily accommodate a planet and everything else to a considerable orbital distance. So, if the power plant requirements are such that the minimum ship size would be hundreds of kilometres across, why not take the entire planet? One point re transfers between planets - the planets cannot be too close together or there will be destructive tidal effects. Let's say a safety distance of at least 20 light seconds between each planet at all times, assuming that jumps are *always* accurate to within a light second. In order for a planet jumping four times per day to have any transfers there will need to be *very* fast sublight ships - assuming that the ships start in low orbit they still need a constant 6G acceleration for five and a half hours to get from one planet to the other. (What happens if a drive fails and a ship cannot make it before the planet jumps?) Required technology for the parameters to be met is extremely efficient and or reactionless sublight drives with massive delta v and artificial gravity control to protect the passengers. Or reduce the frequency of the jumps to 1/day maximum. [Answer] **Accuracy is related to mass** The accuracy of the jump drive is inversely proportional to the mass. There's a limit to how accurately we can control them; and for smaller objects, this translates into a dangerously large error margin on where the object ends up. A ship could be jumped, but the risk of ending up inside a star or planet core, or exiting the jump with completely the wrong velocity vector, is too large. Larger objects can be jumped more accurately, as the increased mass means that the error becomes small enough that the risk is low. That's also why they jump 4 times a day; whilst it's accurate enough to jump planets without risk of collision, it's not accurate enough to put them into good orbits (and anyway, jumping planets into other systems really messes up orbits – check out the three body problem). So they arrive in systems moving on random stupid vectors – not safe orbits, but on collision courses with each other or the star. But they're far enough apart that they're safe for a day or two. Hence they're jumped 4 times a day (well before there'd be any risk) to keep a good safety margin. [Answer] # Violent necessity Given the absurd amount of energy available to a type 3 civilization, I find the efficiency arguments presented here very hard to swallow. With galactic energy levels, it would be feasible to just build a planet-sized spacecraft, complete with artificial oceans and biosphere if necessary, and jump that instead. Furthermore, moving an entire planet thousands of light years sounds very risky. Even if the odds of failure are one in a trillion, are you really prepared to risk your entire *planet* on those odds, with its billions of lives and tens of thousands of years of cultural history? Even if *you* would, would the general population? At first, I thought there was no way to justify this risk. But then I realized: all you need to do is make the alternative even riskier. Your republic is beset by a rival type 3 civilization, perhaps from a neighboring galaxy, that for whatever reason would be much happier if the republican planets were replaced with their equivalent mass in rubble and plasma. Perhaps you're an affront to their gods, or perhaps they just want the raw materials locked beneath your crust. Their attacks are too powerful to block (offense tends to scale up faster than defense) and too fast to dodge (depending on the details of your FTL communication), so your only option is to flee--preferably before the enemy armada even arrives. So, it's unsafe for any planet to stay in the same system for long. Space is big, and the Andromedan armada can't be in every system at once, so as long as its member worlds keep continuously on the move, the republic can continue to grow and prosper in relative safety. They'll need to be careful however: dozens of worlds in the same system will present a very juicy target. [Answer] Ships are not **permitted** to have jump drives, due perhaps to: * Jump drives are an artefact of an older civilisation who for an unknown reason built them on planets. No-one is allowed to attempt to pull one out from the planet. * Jump drives are hideously expensive and/or difficult to construct. The materials and work involved is horrendous, and only a planet-sized economy can afford one. * Jump drives are dangerous, and only world governments are permitted to build and use them. Their production is strictly controlled. (works for nuclear weapons!) [Answer] ## FTL does not exist Even a Type III civilization isn't enough to break through 300,000 km/s barrier because it is physically impossible - and as such there is no 'faster than light' movement for anyone or anything. Wormholes are the only way of bridging huge distances. 'FTL communications' are really just ansibles (two releays that are quantum-entangled so that any state change in one is mirrored by the other in real-time, no matter the distance) or microscopic wormhole generators that don't transport mass but electromagnetic radiation (can be much smaller than mass transporters due to E=mc^2). ## Why not outfit ships with jump drives? Because (choose one or more options) * they are huge and clunky and thus **make sublight navigation a problem**. After all, the mass of the jump generator has to be sublight-accelerated, too, kind of like the rocket equation. Meaning: Only a couple percent of the ship's mass is NOT jump-generator mass - and sublight engines would have to maneuver all of that. Not economically feasible. * jump generator **efficiency is inversely proportional to mass transported**. Meaning: if you want to jump 1kg mass, you'd need a jump generator of 100t. If you want to jump 1000kg mass (1t), you'd need a jump generator of 1,000t. If you want to jump 1000t mass (medium-size space ship), you'd need a 10,000t jump generator. If you want to jump 5.97x10^24kg (mass of earth), you'd need a 5.97x10^13kg jump generator. In comparison: the [world's heaviest building](https://en.wikipedia.org/wiki/Palace_of_the_Parliament) as of 2018, the bucharest palace of parliament, weighs in at about 4.1x10^9kg. place 10,000 of those buildings next to each other, and you'd have a world-class jump generator * jump drives **work by making use of a gravity well** that has to be at least as deep as the one generated by a planet of 80% earth mass, but **produce toxic waste** at the leaving point. Meaning: if you are on a ship, you'd only be able to jump if you were within LEO at most, better on the planetary surface. However, you'd be leaving so much toxic waste (burst of high-energy radiation) behind that even jumping from LEO would mean severe environmental damage to the planet you are jumping from. You'd only be able to jump from uninhabited planets. * jump drive **transport delimiters aren't accurate at ship size**. The jump drive transports everything within a certain gravity well, and ship gravity wells are too small to register properly. (as a result of this, you can easily transport entire planets and their LEO environment, maybe even out to half the distance to the moon). Meaning: If you're lucky, the entire ship gets transported. If you're unlucky, only the core around the jump drive gets transported. Or the jump drive accidentally latches on to the next bigger gravity well and you end up transporting not only your ship but also near-by asteroids or it tries to transport the next best planet (and fails catastrophically). [Answer] **Planets are self-sustaining. Ships are not.** Keeping a ship running is expensive. You need CO2 scrubbers, water purifiers, regular resupplies of food and removal of waste, and a massive number of employees. Don't forget the massive cost of making one either. But none of that applies to planets. As long as you jump to the appropriate "Goldilocks Zone" for each star you visit, food and oxygen take care of themselves. Plus they're already staffed with all the employees you could ever need (and they keep making more). Combine it with KerrAvon2055's suggestion that it takes just as much energy to transport a ship as it does a planet and you'd be a fool not to take the whole thing. This gives you a good origin story too: Scientists on Earth discovered how to create wormholes long before we started colonizing other planets. In fact, it was only because of warping technology that we were able to do so. Our ships didn't have the energy to power the wormhole-maker so we just took the whole planet! [Answer] You don't need a physical explanation, rather a psychological one. People are generally bad at planning what they need. Taking a planet along ensure you have all you might need at reach. A starship might not fit all. I am a cyclotourist and in my free time I enjoy doing multi days trip. This has teached me to travel light: in 2 panniers I can take all the needed for a 2-3 weeks trip. Two years ago I was in Japan, climbing on the top of a mountain to visit a temple-city, where visitors are allowed to spend the night in the temple premises and practice meditation. As said, I was there with my bike and two panniers. Next to me there were 3 women, all in their late 20es, each puffing and panting to move 2 extra large suitcases where they supposedly had packed all they "might" need for just one overnight stay. Some years ago I was to a 2 days off site with several colleagues: I had all the needed for 2 days in 1 sport bag. Some colleagues had 2 stuffed trolleys with them. [Answer] **Jump drives are hideously complex to maintain** Because the infrastructure to build and maintain one is huge. The systems to control one require 1000s of people to run. Each world's jump drive company employs a significant proportion of the population. Sure, you could build on in a ship, but you'd be building something the size of a death star to house the systems and maintenance staff. Why bother, when you can start with a nice planet instead? [Answer] The diameter of a wormhole is proportional to the mass that passes through it. For planet-sized masses, spacetime up to a few times lunar distance is smooth enough to make the stresses of passage through it negligible. But trying to push an asteroid through one would result in significant disruption of its surface. Ships on scales we are used to would be pulled apart into separate atoms by the stresses of the passage. Elementary particles are subject to enormous stresses, but they have no physical size, and there is nothing to pull apart. Thus FTL communications is possible by sending streams of particles. But to send anything larger, you have to be near planet-sized before it results in anything other than total destruction. [Answer] ## Life support It proves to be very, very, very hard to outfit starships with long-lasting life-support systems. Particularly if you send them to a system that does not have planets so they have to last particularly long. If gravity proves necessary for life in the long run, and no artificial gravity is possible, the planet provides it for free. ## Transportation costs The big reason to go is to mine all the easily available asteroids. Carrying all that stuff back through space is expensive, and it turns out the drives have economies of scale -- moving one planet, once, is cheaper than moving little batches of stuff. Furthermore, with the planet right there, you have everything you could have. You don't have to curse yourself for forgetting the one vital thing. ## Communication FTL communication is one thing, but being the man on the spot gives you more knowledge than anything else. ## Personnel Recruiting staff is hard when they get torn from their families for long periods. Everyone on the planet is an easier sell given they are all together. [Answer] **Microbiology** is crueler than we thought, and it makes all biospheres lethally incompatible with all others. Interplanetary tourism is generally lethal. Communication from orbit is pretty safe, and telepresence is easy, but actually breathing the air of other worlds is suicide. Food production for natives of one planet can only happen on that planet. Reproduction in general can only happen on that planet. So, if you have to travel, you have to take the whole thing. c.f. War of the Worlds, and a more recent book, but, spoiler. Now let's talk about traffic control: wow, risky! And the gravity waves? [Answer] ## Surface tension In order to jump, you need to make a field around the object. It might be some dimensional distortion field, or radiation shielding against hyperspace, or other protective shield. The thing is, this field wants to disperse. To keep it together, you need to generate some surface tension that holds it together. "Focusing" it on a bigger volume is easier, but for smaller ones you need to compress it very hard and that takes high amounts of energy and specialised equipment. The planet's own gravitation field can also help in this, and thus needed to be supplied artifically. [Answer] Piers Anthony used a similar approach in his Sci-Fi novel Macroscope. The idea being that it wasn't using a "jump drive" per se but rather that the planet was collapsed into a singularity only to pop out again on the other end. If some manner can be found to control this effect then you have a controllable jump drive which completely explains why worlds must be used but ships cannot. Also with a technology such as this what is to prevent the civilization from developing Dyson Sphere's and jumping the entire solar system at once? Sounds like a good book and I look forward to reading it when you are done. [Answer] Air traffic control for this stuff is a logistical nightmare. This is going to quickly become impossible without a planet-busting disaster scenario at least every few years of subjective time. And the lesser catastrophes will be quite apocalyptic as well. Get the orbit wrong (where in the hell does the velocity come from to match the new stars ecliptic plane and orbits v?) and your people are freezing to death while the planet is ejected out into that star's Oort cloud. Atmospheres shredded away, water boiling off. While moving planets will still be an option in your universe, this won't be for road trips... the technology will be reserved for terraforming and similar large-scale engineering projects where they attempt to minimize the number of trips any large astronomical body ever makes. Trips will be planned out decades in advance, and once the planet reaches its final destination there it will sit forever excepting some emergency that prompts hasty action. [Answer] The planets don't have the jump drive, it's just a hole in space. Your civilisation has figured out how to make artificial wormholes by ripping holes in space. Tearing space open requires a colossal amount of energy just to pierce the cosmic event horizon, but after that your problem is stopping the tear continuing indefinitely rather than making it big enough to transport things. So, planet size holes around the universe become the thing. These are used in two manners. 1. Temporary construction/terraforming methods. You use your hole in space to grab interesting looking rocks and stick them into orbits much more convenient to your day to day business to get on with terraforming them (adding a new planet to the Exchange) or stripping them for raw materials, like the unobtainum needed to create the holes! 2. Permanent structures, that sit in place on a handy orbital plane (for some reason not moving with the same orbital velocity) and they become part of extraordinarily complex multi-system orbital paths for the planets in your civilization. Moving 4 times a day might be excessive for this set up, but you could just hop between systems on a regular basis as part of your planetary "year". Always circling back to the same place, but with different neighbours as other routes have shorter years. [Answer] Ships are tiny compared to a planet, and will have a negligible effect on the existing orbits of whatever system it enter or leaves. A planet, on the other hand, could disrupt the existing orbits greatly, and not necessarily in predictable ways. If this technology is used, it will likely only be used for moving between systems where such disruptions are deemed inconsequetional: ones with no planets, or at least no inhabited planets. [Answer] # Gravity Equivalent of Thunderclap When a bolt of lightning strikes in a storm, it creates a vacuum. When that vacuum collapses, there’s a massive boom of thunder that is quite disturbing to hear up close. It is a rolling wave of sonic energy. When an jump drive activates, it leaves behind a true vacuum: a volume completely devoid of all particles that otherwise never occurs in nature. Space itself bends to fill the vacuum. This is somewhat destructive to matter nearby because it turns out to be the single most powerful pull possible for energy input. Simply put: no planet will allow any jump ships anywhere near its orbit. Any ship that arrives is immediately destroyed so that it cannot jump away again and damage the planet. ]

[Question] [ My fairies need to travel very far as they are nomadic, however they can only fly for around five minutes without getting tired. They most likely couldn't tame creatures due to their size and the fact that most things that they *could* tame would just eat them. They also have a low tech level, and magic wouldn't help them. They are 1-5 inches tall, depending upon what strain. How can they travel? [Answer] **They soar.** Your fairies fly 5 minutes, straight up. By timing their ascent to the right time of day the lightweight fairies can climb to altitude using thermals to give them a boost. Then they open the fan strapped onto their back, artificially extending their wingspan out to about 8 inches. Then they soar. It takes almost no energy to steer by leaning and your fairies are masters at finding and using the right breezes. Once they are up in the clouds, fairies can soar for hundreds of miles each day. [Answer] "They most likely couldn't tame creatures due to their size and the fact that most things that they could tame would just eat them." Why do you say that? We've domesticated horses and cows and tamed elephants, and they're much bigger than we are. And there are certainly zookeepers and similar professionals who have bonded with large predators as well, so even that could possibly be overcome. Just pick an animal that you think would be suitable, and figure out how their relationship with the fairies might work. Maybe the fairies help a herd of deer keep watch for hunters. Perhaps they've pack-bonded with wolves or wild dogs just like humans have. Or maybe they can talk to birds, and can hitch rides on the backs of geese for long-distance flights. [Answer] **Why Tame?** They could hitch a ride parasitically from a migratory animal already going in the right direction The remora is a type of fish that attaches itself to larger animals like sharks and whales and is carried around by them [](https://i.stack.imgur.com/QKqbH.jpg) There is no reason why your fairies couldn't sit on a migratory animal heading in the right direction or strap themselves to a migratory bird for faster travel. [Answer] The same way that marching ants do: by marching.  Insects generally spend more energy to fly than to walk. For many species this pays because they also cover more distance while flying. Some are lousy flyers though (some beetles and mantises), some only fly in specific stages of their lives (ants). Some arachnids also fly (some spiders make a silk "parachute" and let the wind take them), but most of their mileage is on foot. So our little guys better be good shoemakers [Answer] I'm going to make the assumption that these are pixies / pixie-sized. * If the geography of your world allows, and if there are no freshwater fish who may make a quick meal of them, they could float themselves down rivers or streams on their path. * Given their small size, they could stow away on unsuspecting animals (or travelers / carts / etc.) without them any the wiser. * It's your world! You could have a dandelion-esque plant that they grasp onto and get whisked away by the wind. (Bonus if this coincides with "migration season") * Some race who dwells in the same environment (high elves or similar) reveres the fae and actively assists them with their migration. * If magic is in the cards, they could teleport / have some form of magical fairy passage. And many others. [Answer] This well-known photograph shows what is possible. [](https://i.stack.imgur.com/DHdrF.jpg) There is a good discussion about this in the National Geographic as follows: [Weasel Rides Woodpecker in Viral Photo—But Is It Real?](https://www.nationalgeographic.com/news/2015/3/150303-weasels-woodpeckers-animals-science-weaselpecker-photos/) The conclusion seems to be that it is indeed a likely result of a weasel attacking the woodpecker which then flies off. Surely fairies can train certain birds to carry them. After all human fishermen have trained cormorants to help them fish. [Cormorant fishing](https://en.wikipedia.org/wiki/Cormorant_fishing) [](https://i.stack.imgur.com/iCBqB.png) [](https://i.stack.imgur.com/vMPdc.jpg) --- If you want to know what it might look like when a fairy rides a bird, here is a Photoshopped picture from the internet. I don't know the artist. [](https://i.stack.imgur.com/CFLAu.jpg) [Answer] They could just... fly? If their migration is characterized by a series of movements followed by rest, then they could still manage a migratory life while only moving 5 minutes at a time. Assuming they fly at 10 mph and moved four times a day, then they would be able to migrate over 1k miles in a year. You might also consider that most nomadic cultures need to bring materials with them for carrying water, food, and shelter. That would effect how far they could travel. [Answer] ## Fairy Circles You've probably heard of, if not seen a Fairy Circle before. Turns out they are aptly named, as they an artifact of the fae using hidden, extra planer travel. Much like wormholes or portals, various remote and hidden spots in the wilderness are connected, and a fairy who knows where one is can slip through to some other remote location in the blink of an eye. Depending on your story's needs they can be used only during specific times, or with particular offerings made. They will likely be fairly small so maybe a small child could fit through, but an adult human certainly couldn't. They can also only be seen from below and generally float only a few inches off the ground. [](https://i.stack.imgur.com/q0jLk.jpg) ]

[Question] [ Fantasy, vaguely European middle ages. Humans are the only friendly intelligent species. Other species (and magic) exist but they're almost always things you work (or fight) against rather than forces on your side. Both the other species and magic are so varied that it tends to be a flavor-of-the-week sort of deal, and thus it is impossible to make long-term plans for what threats are on the horizon. Thankfully, mortal men are generally up to the task of dealing with these threats, and when either magic or species are a violent threat, the threat isn't big enough to warrant marching armies. The kingdoms are very loosely knit where central regions are supported by mostly removed, small communities that provide agricultural and craftsmanship needs. The societies are very spaced apart, and borders are extremely poorly defined and enforced even worse. War is historically extremely rare, and armed forces are universally underdeveloped on all levels (small armies typically are only stood up when raiders, bandits, or the ilk threaten citizens). Each small community (town and surrounding farmland)--one to three times a decade--deals with an until-then-unheard-of magical beast, wizard, etc. The threat could be eating the sheep, burning the crops, abducting children, or something else that demands that they are dealt with. These threats are significant enough that the nations really need to put an end to them but rare enough that the leaders can't justify stationing troops in the towns. Still, the townsfolk can't deal with it directly, as it's dangerous enough that the inexperienced, ill-trained, and poorly armed citizens will face significant loss trying to deal with it themselves. I want the world to have adopted a habit of communities hiring bands of mercenaries (or as they call them "hero bands") to deal with these time-to-time threats, but this leaves the obvious suggested transition to bandits and highway robbers when these hero bands are between jobs. What is a policy a kingdom can adopt (within the restrictions of the historic period, and no hand waving with magic) that's an efficient and effective means of stopping these otherwise helpful bands of mercenaries from devolving into bandits, while not placing a strain on the coffers? Since not all of the bands of heroes are from the kingdom, social pressure or indoctrination methods would be fairly hit-and-miss. [Answer] One way to keep the heroes from getting lazy and taking the bandit path is to make these heroes into a **religious order.** If they are serving the high gods by protecting people from the demonic *Outsiders,* then they are going to have less desire to break from that path. After all, doing so could have eternal repercussions. This also serves the additional purpose of providing a system of honor around their behavior, baked into the religious dogma of their order(s). As part of the religious system, the heroes can expect certain privileges, like free food and shelter or healing from the temples (if magic allows) or from the local healers, surgeons, or whatever your setting uses. And as a holy order, there is incentive for the villages to supply the "best and brightest" of their children to the temples for training into the mystical ways of these hero bands. By setting up holy training centers, you ensure that these bands get proper training -- something that would be unavailable without at least some kind of militaristic society to train them. These enclaves would serve as rest areas between circuits, and a convalescent/retirement home for the injured or permanently disabled. These elder heroes would serve as teachers. And these enclaves would probably be where the majority of the world's weapon smiths would practice their trade as well. If they work on a circuit rider basis, then they can probably stay relatively busy. Sure, each village has an encounter with the wilds only once every 3 to 5 years, but an entire kingdom, then, would have encounters going on fairly frequently. Especially when there is significant travel time between villages. The older surviving heroes who aren't fully retired might also serve as circuit judges in smaller towns that don't really have their own nobility. Or other "holy" duties as part of their travels between communities. The religious trappings could also place constraints on their behavior, such as not robbing the village "in payment" for their services, not availing themselves of the locals sexually, or in other ways becoming bully-like dictators on the local level. Those few circuit knights who break from the order would be labeled heretics and blasphemers. They would be hunted and hated by the order and all who honor it. If your world's Gods are active and involved, then the fallen knights might be destroyed outright for their heresy. The enclaves would contain healers, weapon smiths, researchers, story tellers, and historians, at a minimum. The knights and these non-warriors would have a strong symbiotic relationship. Historians and researchers would chronicle past wilds-events, trying to discern patterns that might predict future events. New weapons and tactics would be researched by these folk and then tested later against future events. [Answer] I recently read the Kingkiller Chronicles, and the author described an interesting system which might make sense to you. Imagine a society similar to Feudal Japan. These people developed certain fighting techniques, which are a highly kept secret. Each martial arts school trains warriors, the best of which are sent out into the world. These warriors - even if trained at competing schools - will all cooperate out "in the wild" (they consider all outsiders barbarians, although that's both hypocritical as well as ironic, as their insular culture is quite backwards in some respects). These highly trained warriors act as very expensive mercenaries, however their fighting skills are so famous that anyone considers themselves lucky simply to have one available to hire. They never negotiate their prices, and they never fight against one another (if your enemy also hired a group of them then warriors on both sides will return their fee to their respective employers and collectively walk away). Any attempt to force their hand will not end well, and that employer will most likely face severe retribution once word reaches the schools of what has happened to their warriors. These warriors all send their money back home for the continued survival of their people. They are bound by a very strong sense of honor, as well as serving a higher purpose - sending money back home. Each is aware that dishonoring their school or nation will have negative repercussions for their entire country, and will affect the employability of their fellow warriors. There are not enough of them that they have trouble finding employment, and when they're between jobs they can simply visit back home. A guild of heroes can work in much the same way. Imagine heroes going out and solving the problems of the world, then sending their profits back to the guild. [Answer] [Machiavelli](http://www.constitution.org/mac/prince12.htm) has a lot to say about mercenaries: > > Mercenary and auxiliary troops are useless and dangerous. Mercenaries are disunited, undisciplined, ambitious, and faithless. Because their only motivation is monetary, they are generally not effective in battle and have low morale. Mercenary commanders are either skilled or unskilled. Unskilled commanders are worthless, but skilled commanders cannot be trusted to suppress their own ambition. > > > Plus a lot more, and none of it good. If you want to keep mercenaries from becoming bandits, I suggest two things: 1. Never miss a payroll. 2. Never get in a war you might lose. > > If a prince does not command his own native troops, the principality can never be secure. > > > [Answer] **Elite Hunters** These people hunt to make ends meet in times of peace. They are master marksman and expert spear wielders who never miss a game. This keeps them well trained as well as well fed at peace time. Whenever they are needed in a village, they go in, shoot the baddies to the void and return to their forests. [Answer] I must point out that the Feudal system (knights/nobles/peasants) essentially fulfilled the system that you are requesting. The nobles hired knights and/or warriors to police and protect their land. In addition to protection, the nobles were expected to administer their holdings and often acted as CEOs of their enterprises. For example the noble would hire a blacksmith and pay a portion of his wage... with the expectation the noble would be able to have priority on jobs. In modern society, it would be the police force who would handle the threats to the community and would in fact contract with more experienced and elite police to handle more serious threats (SWAT). [Answer] This is basically the same question as about what keeps adventurers from taking over the kingdom, perhaps someone remembers more about it and can find it. You need three factors to keep them in check: 1) A culture of independence. You need cats for mercenaries, not dogs. You don't want a large group that would band together to take over a nation. 2) Loot. When the mercenaries eliminate a threat they get to keep the property of the monster they removed. 3) The wanted poster. Rulers must be reasonably friendly towards such mercenaries on their lands so long as they are well behaved, only killing bad things. Mercenaries that misbehave find their pictures on wanted posters all over the place, any other mercenaries that happen along are free to kill them and take their things and money. This situation will be stable so long as you don't get a large group banding together to actually take over. [Answer] This was a problem that basically came up historically in Europe - in many cases the difference between a lord and their immediate warriors and a mercenary band is more of name than of nature - and the solution that they implemented was to create a code of honour, Chivalry. This made the mercenaries into something more than they had been, those that could afford it were knights and they were bound by the code of chivalry which governed the acceptance of their peers. This is not a bad starting point for your setting. I think that the other thing that you need for this to be sustainable is a clear chain of command, so as part of a mercenary group's articles it would be necessary to state the exact chain of command. In the case of a transgression by an individual, the entire chain would be held responsible. A breach of these articles results in the company being struck off, at which point they are treated as common criminals and whoever captures them has a right of seizure to their property. There is a route for experienced mercenaries to sign into a new company but it will involve a substantial pay cut. This creates a significant stick for any breach of individual discipline, let alone a whole company considering turning rogue. [Answer] My immediate thought was "Who could stop these people?". In a society where bands of heroes defend the simple people making up the rest of the society, there are very few groups available that can stand up to the heroes. However, rival groups could easily stand up to eachother. I would propose two things: 1. Focus on "hero band" reputation 2. Have kingdoms reward bands that stop crime First, focus on the reputation of these hero groups. With all of the saving and fighting that they do they would be celebrities. The strong warriors that young lovers swoon over and that ambitious children dream of becoming. They would command respect and awe. This reputation is what gets them hired in the first place. You could have them stay busy between disasters traveling to villages building their fame and demonstrating skills (maybe even for pay, like a traveling show). Because this reputation is so important, if they were known as robbers or thugs their reputation would quickly tarnish and their pool of customers would vanish. That could be a strong deterent from a life of crime. As a side note, having some hero bands involved in secret crime while trying to maintain a good reputation could start some great story lines. A less popular but virtuous group could expose a shady one, or a likeable thief could hide in a group of heroes, that sort of thing. Second, these "hero bands" could function somewhat like police in-between town-saving battles. The kingdom could have small rewards for hero bands that catch highwaymen and convicts so that the bands stay busy. A greater reward could be provided for catching another "hero band" committing crimes. That way, these bands keep each other in check, and any band turning to a life of crime would have to be ready for the combined strength of other bands. In summary, the weight of a bands reputation, and the fear of other warrior bands would keep them from turning to crime. As for stressing the coffers; the small fees paid out for catching criminals is much less than keeping an army or police force in the kingdom, and while the rewards for catching a "hero band" would likely need to be high, the likelihood of a band going bad is set up to be relatively low, so this is rarely paid out. It shouldn't put any large economic stress on the kingdom. [Answer] # Let the locals defend themselves. You say that the locals can't defend themselves. I disagree. Let every village have a militia that is large enough to defend against most threats. Have them call for help from nearby villages for the really large threats. Have everybody spend one day per week training combat, except during harvest. Let them use tools as weapons: Hammer, axe, flail, scythe etc. These people will be less trained than professional soldiers, but there will be more of them and they will be much cheaper. When threats are rare, people will get lax. To avoid this, make sure that news about villages that fail to defend themselves spread to *everybody*. Everybody should know, in gruesome detail, what happens to villages that doesn't train properly. You might want to have professional instructors travelling around to make sure people are learning the best fighting techniques. People who have homes and jobs are not likely to turn into bandits, but they *can* turn into rebels. The government need to be nice in this setup. [Answer] ## Accountability Mercenary groups serve particular areas of the country which are under the eye of some lord or other ruler. To be selected for a position in the mercenary training school is an honour. To graduate and join is an even higher one. When you have joined your family are given a house in the richer district near the lord of the land. These districts are walled in and the walls well guarded by men loyal to the ruler of that area. Now, as you can imagine, if your family are in the clutches of the ruler you're about to turn against you're pretty unlikely to let a couple of your comrades turn to bandits just because they don't have family. You're all well paid, your families kept healthy and well. Banditry doesn't really appeal when your family's lives are at stake. The mercenary groups will be treated as a whole, if five in a group of fifty have no living relatives they might decide they want to live as bandits the group has a choice: hunt them down as the lord of the land will ask or defy the request and be seen as aiding the bandits and risk the lives of their families. As such each mercenary group will regulate itself, ensuring none of its members turn to banditry and live for word to spread. [Answer] You cannot do this cheaply. If you have a military force in a nation, it either needs lots of discipline and needs to be collectively loyal to the nation or be tiny, or it swallows the nation. You can see this happen throughout history. To sufficiently reward the mercs, you'd have to give them an independent income; land, serfs, etc. Then make their ownership of said land dependent on military service. Some mercs would get lots of land and have to supply lots of military service (more than they personally can do). We'll dub the mercs that get land "nobles". They have to provide fighting forces, let us call them "knights", at the request of the government. Part of the knight's service would be an errant phase, where they wander the land and solve village problems. They would have the right to commandeer food and shelter from local nobility (even petty nobility) for a short period, or longer if their service is required. A system whereby you earn some reward for solving the problems of villages during the errant phase of your knighthood could be developed. Having this different than "be paid money" is tricky, because avoiding fungibility is hard. But you could imagine having to build your own coat of arms or epic poem as part of this phase. The parts of the poem/coat of arms involved might require religious assent (and be tied to the village where you solved the supernatural problem). In short, remove said "mercs" from the economy; cover their needs independently, don't have them do it for money. Make them part of the "standing army" of the nation (or a phase of it). Now, we have knights, sworn to nobles. Before you can be a "landed knight", you must first be an "errant knight" and collect an epic of your heroism. Your food/shelter/armor is covered (from your sponsor/parent), so your need is for heroic deeds to do. Being a bandit doesn't get you heroic deeds, it just gets you cash. There is a risk that failed errant knights, who somehow are at risk of losing their knighthood status due to incompetence, injury or time, becoming bandits with weapons and at least some practice using them. In short, you cannot have a cheap powerful standing army; a cheap powerful standing army takes over its nation. Use the government structure of the nation to produce the standing army. You could split the knights into multiple orders. You could have the Knights of the Rose (landed noble), Knights of the Chalice (religious), Knights of the Coin (merchant), Knights of the Foam (naval), etc. To qualify as full member of whatever guild, you have to be sponsored for erranthood (involves equipping you and paying into some royal fund, which gives you the right to be fed/transported/sheltered). Then you have to complete your knight errant and earn an epic. Only when your epic is done can you become a full member of whatever guild (nobility, church, merchants, sailors). Such full members (and only such) would have the right to vote for their representatives in the House of Lords, which among other things determines taxation rates. [Answer] If I could draw a parallel to our society, the fire department. Some of the earliest firefighters were subcontracted by insurance: <https://en.wikipedia.org/wiki/History_of_firefighting> Perhaps you could have insurance brokers which sub-contract your "hero bands". As far as the prevention of them going rogue, there are a couple of options: 1. The members of these "hero bands" could be sourced locally, which would make sense given the need of close proximity to communities. That wouldn't totally prevent "hero bands" from abusing their power, but it would place some impetus that they ["don't soil their nest."](https://english.stackexchange.com/q/284671/85230) 2. A form of internal affairs is not unforeseeable if there is a trend of these "hero bands" resorting to villainy. Perhaps the insurance brokers add an individual to each band, or if that proves insufficient a government official be attached to each "hero band" may be a feasible government investment. **EDIT** Option **2** seems to be the more interesting of these. I was going to elaborate on that a bit. Where would the motivation and/or compensation for maintaining an internal affairs department to keep an eye on these "hero bands" come from? 1. Why would insurance brokers be interested in doing this: * The kingdom requires it, consider something like [Emissions Trading](https://en.wikipedia.org/wiki/Emissions_trading) but the measurement was the number of reported bandit incidents in an area, and the kingdom would evoke fines on the insurance broker for an increase in his patrolled area. **Problems:** This has some unfortunate side effects of making it monetizable for insurance brokers to *do* bandit work in an area they want to edge out the competition, or even to spoof incidents, making the measurement of reported incidents unreliable. Furthermore, the value prospect of insurance brokering goes down because you are now paying your "hero bands" to police an area; which is bad cause the kingdom would need these brokers. * Insured villages require one or more members of the band to be locally sourced. This speaks to the "don't soil your nest" principle. **Problems:** The locally sourced "hero" would need to be of upstanding character *and* capable fighting ability. This is a requirement something near a [chivalric code](https://en.wikipedia.org/wiki/Chivalry), which may not be easy to find within the village's populous. * The "hero band" is also responsible for freeing the area of bandits, protecting the kingdom, and general policing of the area. The insurance broker rolls that into the cost charged to villages and is also subsidized by the kingdom with the money that would have otherwise gone to mustering or maintaining troops. **Problems:** "Hero bands" now perform all the primary functions of government; would there be an incentive for villages to pay tribute to the kingdom, why not just pay an insurance premium? Additionally, if "hero bands" replace the kingdoms standing troops the government is aiding the arming of militia; see also: <https://en.wikipedia.org/wiki/Militia#Political_issues> 2. Why would the government be interested in doing this: * Insurance has always been about protecting the lives and property of individuals. This is a primary government responsibility. If the government is able to outsource some of its workload by maintaining some direction over these "hero bands" the reduction in governmental responsibilities may pay for itself. In this scenario rather than internal affairs the government agent would take on a leadership role of the "hero band." **Problems:** Having a singular government point of contact who's responsible for maintaining order in the area could easily devolve into an [Extortion racket](https://en.wikipedia.org/wiki/Extortion). * Make another kingdom pay for it. The government could pick a village nearby a "hero band"'s operating area, which pays tribute to a different kingdom, and directs the "hero band" to require tribute from that village at threat of violence. **Problems:** This is going to escalate quickly. It'll easily devolve into war, or at least unauthorized skirmishes along the border (which will quickly become well defined.) [Answer] You have small groups of heroes, fighting creatures that often have supernatural powers. Life expectancy wouldn't be... well, if you have ask, maybe this job's not for you. This would be a major deterrent for membership in these groups. In order to have them be at all effective, there would have to be a *significant* reward waiting at the end for those who survive, or no one worthwhile would ever join. The reward would need several features: 1. Needs to be big enough to overcome fear of almost certain death. 2. Needs to be big enough that it dwarfs anything you might do as a bandit. 3. Any time spent as a bandit disqualifies you from getting the reward. 4. It must be actually attainable. There need to be people you can meet and talk to who have actually claimed it to prove this. I propose society could be structured so the rulers of each town and nation-confederacy are surviving members of the hero groups. This would naturally provide as much wealth and prestige as the society is reasonably able to afford, and it puts an experienced fighter or two with the right contacts ready and waiting in each village. If need be, larger towns or regions could be ruled by councils, the membership of which could grow and shrink depending on the supply of retired heroes. Heroes now have to option to retire into what are effectively the wealthiest roles out there afforded by society. Even bandits require leadership and coordination. The people who would naturally be the leaders of these groups are those closest to claiming the prize. This also seems like the natural result of the situation. Once upon a time, villages fought monsters with whoever was there. The best surviving warriors naturally banded together into small groups for support. Some of those groups went bad, and some of these bad groups didn't stop at mere banditry; they claimed territory through conquest or usurpation. Others that didn't go bad were naturally selected into leadership. Over time, tradition cements the leadership roles, which suppresses the need and desire for groups that go bad. [Answer] Villagers pay some sort of retainer or tribute to the hero bands. Alternatively or additionally there could be perks such as free food, drink/alcohol and other adult entertainments. If the hero band are having their most basic needs and desires met there will be little need to resort to criminal activities You could have some historical example of a town that got wiped out because they stopped paying tribute then got no help when need forming the local moral to always pay tribute. While you do run the risk of racketeering, most hero bands wouldn't want to rock the boat if they a good thing going and other hero bands may intervene to stop others ruining things for the rest of them. [Answer] Of course, this is essentially the same set up as most mainstream comic book worlds, but set in medieval times. In comic books, there are superhero teams that form all of their own accord, often funded by some rich guy or group of rich guys, specifically to fight the "good fight" against the evils that appear in the world. Incidentally, they also end up fighting against all the supervillain teams, i.e. the super teams that have "gone bandit". In some worlds, these superhero teams are self-sustaining, reaping what reward they can from their adventures as well as their notoriety, and instating a managed system whereby the spoils are re-invested in the team's ongoing existence. To map this to your world, the hero bands consist of talented people who want to do good in the world (or at least protect people from the bad in the world, which is not the same thing). Groups that form for the purposes of banditry, or that devolve into banditry, get put down by the other hero bands, primarily because that's one of the driving forces behind the existence of hero bands. And hero bands are not automatically forced into banditry in less violent times, because they have developed other sources of income besides the spoils from their big adventures -- they do other work, or they adopt wealthy patrons, or they gain a large-enough nest egg that they can survive off the interest. (And remember, this doesn't have to be our modern hedge-funds-and-soy-futures type system. It could be as simple as pooling resources to build their own commune, complete with farmland, central well, and (possibly indentured) working class.) Or maybe they run a mine, or do some sort of special manufacturing, or travel as a band of entertainers the rest of the time. [Answer] One example might be the [Varangian Guard](https://en.wikipedia.org/wiki/Varangian_Guard) of the Eastern Roman Empire. These elite mercenaries were recruited from Germanic tribes to protect the Emperors and their families. Why recruit barbarous brutes to protect the vanguard of civilization? Simple: they were loyal to their work, and they were not from the society whose leader they guarded, so local politics mattered little as long as the money kept flowing, as they could always return home if they felt like quitting (which was rare). Compare this to the Praetorian Guard of the Western Roman Empire, which was composed of Roman citizens who had much more of a stake in imperial politics. Western Roman history is littered with examples of the Praetorian murdering or simply abandoning emperors they don't like, either for the greater good of the empire or for their own personal desires. I don't think this example would work for the small communities in your story, but perhaps nobles and royals would find this tactic useful for keeping themselves save and secure, as long as they could pay them. [Answer] You're looking for a solution like in David Drake's "Hammer's Slammers." Mercenary groups get charters, which let them post large bonds with some neutral authority. If they break contract, they lose the bond. If their employer breaks contract, they can as well, without losing the bond. If they misbehave while not under contract, the bond authority might be persuaded to revoke their charter, so they can't post the bonds needed to work as mercenaries anymore. That gives you a class of professional mercenaries who can still be absolute bastards, and who aren't actually beholden to anyone beyond what their contract calls for. It probably also gives you bands of thugs who call themselves mercenaries and work for cheap, but are not at all reliable (roughly the same divide as seen in any profession). [Answer] # Throw them out of the country Nobody likes mercenaries hanging around when they're not needed, put them back out on the road. The key word being *out*. It's important to consider who mercenaries are in a middle ages setting. Fundamentally they're foreigners. Apart from the nobles, there isn't really such a thing as a standing army, the nobles fight as part of their duty to the crown, they don't have a choice. The rest of the non-noble army consists of conscripted peasants, the general population of the country, they don't have a choice either. So where do these mercenaries come from? If they were natives they'd be conscripted and part of the army, if they were nobles they'd have to fight by duty. They're foreign professionals, once you're done with them, pay them and put them on the first boat out. Nobles and landowners have rights, peasants do not, foreigners most certainly do not. [Answer] Maybe you don't see this, but this sounds like a more militarized version of spooks from the "last apprentice" novels. Make their system a trade skill, not a common skill, this will reduce the number but improve the quality. You can ensure quality by providing quality check at the national/regional level. Keeping the numbers low enough will increase their prices and can avoid working for long periods without devolving to bandits. Making sure this position was attainable by most of the population prevents a complete caste system and provides upward mobility to the civilians that do take the initiative to deal with their own problems. Keeping the practitioners local also makes them less likely to extort their clients through force. [Answer] Close as I can think of today would be the Tulla. Little short people. You go back in there Country & log or such. They see you. In today's world with cell phone towers, solar plates. They track you. Tell the game warden were your at. What roads the illegal logs are coming down. See that there is a arrest. They can fight. Still like spears. But do have some guns. Remote mountain jungle areas they call home. Morro can be mercinary. Governments still at war with some of them. Border Tulla ground. There more for rifles & artillery. Great fighters they are. You need kill 12 enemy to become honored enough to become a teacher. Back when it was hand to hand. Unlike Japan were they sent out there best. They kept there best to teach. ]

[Question] [ One of my **wow** moments when playing *Baldur's Gate 2: Throne of Bhaal* happened when the three most powerful Bhaalspawn siblings (Imoen, Sarevok and the Player Character), together with just three more allies, are confronted by an entire Tethyrian army (melee forces, archers, spearmen, and mages) at an Oasis in the Calim desert.  *[Imoen the Quick](https://worldbuilding.stackexchange.com/questions/8962/is-a-jet-dragon-possible/8965#8965)*, *suspected leader of the Bhaalspawn gang. Wanted dead or alive. A powerful mage, she is to be considered armed and dangerous. Do not attempt to engage without magical backup. --- from a charred note found among hundreds of bodies at the Calim Oasis massacre site* The Bhaalspawn and their allies carved their way through this army with relatively little difficulty, and are also suspected of destroying an entire heavily armed and fortified Dark Elf (Drow) city by themselves. How could a situation like this come to be? I imagine these 6 would be exquisitely good at making war, among the very the best strategists, tacticians, swordsmen, [archers](https://worldbuilding.stackexchange.com/questions/9300/a-more-powerful-bow/9305#9305) and mages in the land. They may (if you deem it necessary) [wear the best armor](https://worldbuilding.stackexchange.com/questions/9117/hammer-proof-armor/9120#9120) and wield legendary weapons looted from the treasure-hordes of dragons and enchanted with the rarest and darkest of magics. **Still, how could six people realistically** (well, in the context of a magical world like Faerun) **take on and literally destroy (or cause such casualty levels as to set fleeing) an entire army?** *Magic context: Even powerful mages are generally limited to a few dozen spells per day, and only a handful of the most complex, although charged items might effectively shift that limit upwards. Most spells have areas of effect below 100 yards in radius. Summoning spells are possible. Extraordinarily skilled warriors can perform feats that seem akin to magic to the untrained eye, at incredible speeds, but even magically boosted stamina has limits. **I would like to minimize the amount of magic needed here.*** [Answer] Here's a few ways it can be cut down to size. They can be split up into two types: taking the story at its face value, and not. First, taking it at its face value... It turns out that a mass of fighters can be at a disadvantage against a small group. Mob mentality takes over and it becomes very difficult for the large group to act in a coordinated fashion making them timid and allowing the master swordsmen to control the battle. [Demonstrated handily in this video of 3 Olympic fencers vs 50](https://www.youtube.com/watch?v=PgKg0Hc7YIA). That they have to hit a very small target emulates your 6's near invincibility. They used terrain to cause a bottleneck or division or in some other way reduced their advantage of numbers and ranged weapons. Let a manageable portion of the army cross the flooded river, then blow the bridge. Lure them into a box canyon and then attack from above and the sides. Rarely is an army destroyed, especially before modern times (1800 onward). Rather, their morale is broken and they flee. Or they become so disorganized they become scattered or can no longer be controlled. Many would wander back to the army later, but often the largest slaughter happens *after* morale is broken and their protective formations break up. Ancient and medieval armies were often made up of amateurs and mercenaries lead by a few professionals, and their morale would break quite easily after fairly light casualties especially if their flanks or rear are threatened. Six legendary warriors, apparently invincible, inflicting heavy casualties to the army's scouts, could shake the morale of the army. If the warriors appear on their flanks and rear (teleportation or clever positioning or even just wild rumor) the army can break and run. A broken or undisciplined army is basically a mob, a herd moving in a direction because everybody else is. A mob in a constrained area can panic and crush themselves, as is demonstrated in so many soccer matches and the [Battle of Agincourt](https://en.wikipedia.org/wiki/Battle_of_Agincourt#Main_French_assault). If individuals try to move against the mob, they will be crushed or carried. The Six can use this to amplify their killing power. Catch the army in constrained terrain (a box canyon, mountain pass, between two rivers, a bridge...) and place three at the front and three at the back (or block retreat). As the front ranks panic and break and try to run they will crush the rest of the army in the middle. It might not *destroy* the army, but it will increase the casualties far beyond what The Six can do themselves. Rumor can have a powerful effect on morale. The [Battle Of Tours](https://en.wikipedia.org/wiki/Battle_of_Tours#The_battle_turns) turned when a rumor spread that the Franks were plundering their camp (wives, slaves and plunder) causing the Umayyad to break ranks. With their flanks suddenly hanging in the air, and seeing troops running to the rear, the rest of the Muslim army (who had been winning) went into a general and unplanned retreat. Speaking of baggage, an army marches on its stomach. If an army is deep in hostile territory (by enemy, by nature, or both) our heroes can destroy their supply train and leave the army starving. Finally, combining all of these together. A large army, made up of low quality troops, moving through hostile and unfamiliar terrain on a narrow road in a very cold winter. The Six set up roadblocks in front of and behind the army (blown bridges, landslides, fallen trees). They move silently through the cold trees, attacking out of the forest all along the greatly extended road column, going wild for a few minutes and disappearing back into the trees before they can be overwhelmed. They attack at night, never allowing sleep. They move quickly and silently through back roads appearing out of nowhere making it seem like there are far more of them. The Six know the territory and have set up shelter and supplies deep in the forest. Any soldiers sent into the woods never return, killed by the Six. The army cannot advance, they cannot retreat, and they are unwilling to leave the familiarity of the road. The army slowly freezes and starves in place. What I have described is the [Motti tactics of the Russo-Finnish Winter War](https://en.wikipedia.org/wiki/Salients,_re-entrants_and_pockets#Motti). --- And assuming the story has been... enhanced. A battle against dozens becomes a whole army in the retelling. It could be self-aggrandizement as the Greeks would do with their claims of the size of the Persian army at [the Battle of Thermopylae](https://en.wikipedia.org/wiki/Battle_of_Thermopylae). It could be the defeated commander trying to save face. It could be simple exaggerated storytelling as it gets passed along. Sure, six people defeated an army... with some help. History is loaded with stories of heroic battles that fail to mention huge numbers of allies. [The Battle of Thermopylae](https://en.wikipedia.org/wiki/Battle_of_Thermopylae) is famous for the 300 Spartans, but conveniently ignores [the thousands of other Greeks who fought there](https://en.wikipedia.org/wiki/Battle_of_Thermopylae#Greek_army). We've been told about how the Spanish conquered the Aztecs with a handful of men, but ignores [the tens of thousands of native allies](https://en.wikipedia.org/wiki/Spanish_conquest_of_the_Aztec_Empire#Alliance_with_Tlaxcala). They pulled [the trick from Three Amigos](https://www.youtube.com/watch?v=Ocguw5sN_Zs#t=1h32m0s) where many people dressed in just six outfits to appear to be all over the battlefield at once. Similarly, perhaps there is more than one Dread Pirate Roberts Imoen The Quick. They were conniving, backstabbing, honorless bastards and want to cover that up with a huge story of conquest. Again, Cortés is the master of this. [Welcomed by Moctezuma, made a guest in his palace, he took the Emperor hostage](https://en.wikipedia.org/wiki/Spanish_conquest_of_the_Aztec_Empire#Cort.C3.A9s_welcomed_by_Moctezuma) and could basically kill whomever he wanted. Hardly a noble military victory. Better to make up something about a daring coup. Sure, there were a lot of bodies, but it wasn't a battle, it was a massacre. An army is on the move. Their scouting parties encounter the Six. The scouts are defeated. A recon in force is also defeated. Word gets back to the commander (well back in the long column) that a road is blocked by a force which has defeated their scouts and may take some time to get past. The commander looks at the map and simply orders the army to take a different road, this is why he has scouts! The warriors think they "defeated" the army, but commander wisely bypassed an obstacle. [Answer] **Don't try to make it 6 vs. an army. That is a very short battle. Make it 6-plus-mother-nature vs. an army.** Army tactics try to avoid putting themselves in positions where they have weaknesses. However, when push comes to shove, every army has its weakness. All you need to do is put the 6 into the correct position to carefully strike at it, and the army is doomed. Mother nature wields vicious amounts of power, making her an ideal ally. She provides all sorts of opportunities for force multiplication. Consider tactics like setting off avalanches over the army, or breaking dams upstream of the army. Consider seeking terrain where there is room for 6 to escape a tornado, but no where for a full army to run. And when all else fails, have your 6 hike across the Russian wilderness in winter and see if they will follow. That will stop an army or two, even if their captain is as good of a tactician as Napoleon. [Answer] The thing is that games such as D&D amplify the difference in power level between humans far more than is possible in real life. **D&D Mechanics** A high level warrior can survive hundreds of blows from lower level attackers, and with his armour and other defenses only 5% of those blows will even hit (using the automatic hit on a 20). If you factor in damage reduction then that can become even more drastic, even 5 points of Damage Reduction is enough to mean that your average low level combatant is barely able to scratch their target. In the meantime your wizard does have a limited spell selection but those spells include being able to strike an area with swarms of meteors, hem people in with force-fields, turn vast areas of rock into mud, enlarge the fighter to make him stronger and tougher, etc. Unfortunately the question doesn't specify the size of an army. So lets look at some numbers. A large medieval European army would have 5,000 to 10,000 people in it. So lets say there are 6,000 soldiers and you need to wipe out 3,000 to make the survivors flee into the desert (where they will probably die anyway). If you are going to say that the battle lasts an hour, then that means each of the 6 heroes needs to kill 500 in that hour, or 8 per minute. In D&D rounds of 6 seconds each that is just under 1 kill per round. Assuming the fighter has a 5% chance to miss (a roll of 1 on a d20 always misses) and only kills one target per round then that is still enough. In practice he would have the ability to strike multiple targets per round so would chew through them considerably faster than this. In fact these numbers are easily sustainable, assuming the average army member is low enough in levels then even once they ran out of spells the wizard would probably be able to able to take down one opponent each round just by hitting them with his staff. The warrior would be killing many more per round than that. I run a game at the moment where a level 6 warrior easily kills 2 or 3 low level targets each round. So, mechanically in a role playing game it works (although it would be a boring session!). But how does it work in terms of a "reality-check"? **The Reality Check** D&D is a very simplified model of the world. There are a number of things it just does not consider that to do a proper job of world building we should consider. *Exhaustion* The first problem is exhaustion. Fighting, especially in heavy armour or throwing high-powered magic around is tiring. In a Live-Roleplaying System I help run we do big battles (1000+ people on each side) as a part of the event. One thing we have learned though is to make sure that the actual battle itself lasts for an hour at longest. Once the hour is reached people start becoming tired and making mistakes and our number of Out-Of-Character injuries sky-rockets. We get more injuries in 1:00 to 1:15 than in the entire previous hour. So the six would need incredible stamina. The ability to keep up sustained life-on-the-line adrenaline-fueled combat for an hour with no let-up, no pause, and no breather. *Missiles* The second problem would be ranged weapons such as arrows, crossbow bolts, even slings or just thrown rocks. In melee combat only a few people can attack you at any one time. Even with pole arm formations or surrounding someone only a limited number can strike. With missile weapons though you could have a thousand arrows being fired at you volley after volley until finally one strikes a vital point. The target would need to be essentially immune to missile weapons, either through "kung-fu style" dodging and parrying, through impregnable armour, or through defensive magic. Even a slight chink in these defenses would eventually be hit, so they need complete immunity. Terrain could be used to mitigate this but in order to attack the army they would need to advance on it, so at some point would be vulnerable to arrow fire. *Fire, Magic, etc* Fire is a common weapon, even if someone is immune to weapons you can set them on fire and cook them in their fancy armour. You would need to be immune to heat, and have no need for external oxygen for protracted periods of time to walk through the fire unscathed. Additionally in any fantasy army you should expect at least some magic. The enemy heroes would come against you as would enemy spellcasters, etc. These high-priority foes would need to be identified and dealt with first since otherwise they might be able to take you down while the army distracted you. **Conclusion** You will notice that I mostly focused on defenses, that's because the enemy have weak defenses of their own so your capability to kill them is not in question. You just need to survive long enough to do so. Of course if you can kill them faster than this or if their army is smaller then you do not need your defenses to last for as long. I've also shown that mechanically in D&D and conceptually in a fantasy world it is indeed possible for 6 people to defeat an army. The reason this is not possible in real life is because it is just not possible for 6 people to become as invulnerable as is required. Even in real life though you should expect a team of 6 trained and equipped modern soldiers to be able to handle a much larger horde of people with inferior equipment. In real life it is the offensive power (automatic weaponry vs bows and arrows) that has changed while the defensive power has not improved by anything like the same margin. In most fantasy worlds both offensive and defensive power increases with levels, so that changes the outcomes drastically. The thing to remember about high level fantasy characters is that they are almost godlike. These are people who can wrestle a dragon, swim across burning lava, smash the stone wall of a castle to rubble, etc, etc. If conceptually you can believe a Dragon defeating an army then it shouldn't be too much of a stretch to think of a Dragonslayer also being able to defeat one. [Answer] So far all of the answers so far miss a fairly important point (semi-spoiler alert): The Bhaalspawn are such named because they are the literal sons and daughters of [Bhaal](http://en.wikipedia.org/wiki/Bhaal) - **the god of Murder**. These people aren't just some of the best tacticians, warriors, archers, and mages in the land, they are demigods who have a supernatural talent for slaughter, even compared to a world filled with magic, monsters and cutthroats of every measure. This adds to the other answers' notes about morale, but also impacts battle itself. With such a lineage, it should be expected that the characters' strength and stamina are superior to their foes, likely beyond what even magic can gain (especially for a longer period than magic). Put those together and it's not unreasonable that a few well placed fireballs or cloudkill sort of effects (that are longer lasting and kill low level characters terribly and near instantly) or loosing a few demons would kill a few hundred grunts. Combine that with supernatural swordplay (or gratuitous evisceration) and I would expect the army to break rather quickly. One other D&D specific sort of trick is that a few creatures in that world are immune to normal weapons (think werewolves). If the army doesn't have silver/magic weapons (and it's unlikely they would), then a summoning or shapeshifting would mean that the army could not even *wound* their enemy. There's not much other option than to flee or die at that point. [Answer] I would like to note that: > > the very the best swordsmen, archers and mages in the land. They can wear the best armor and wield legendary weapons looted from the treasury-hordes of dragons and enchanted with the rarest and darkest of magics. > > > Because of that, I will then assume that no enemy survives first contact with the party of 6 physical gods of war. Well then, depends on how fast you want the enemy army dead. ## Instantly dead It really only takes probably the President of USA and couple other important staff, no more than to launch a nuke and destroy just about anything. For your magic fantasy setting, you could easily amend magic fantasy to everything, and it would probably work the same. Get the magic fantasy President of USA and a couple of other magic fantasy important staff and launch a magic fantasy and destroy just about magic fantasy everything. Given your parties vast accomplishments, it should not be too much of a stretch that one of them is at least the magic fantasy president of a magic fantasy nuclear power state ## Dead in a few hours A little more serious than the previous one, the 6 heroes could go and chop a line through the army, chopping up the enemy commander on their way, to the enemy army's cannons. From there it should not be too much of a stretch that the wizard of the group could summon some summoned things to go man the cannons and shoot up the rest of the army ## Dead in a day or two Probably the speed that best matches the spirit of killing everyone by combat. Your heroes will go forth and dispense glorious death by swords and sorcery, and the enemy army will gladly throw themselves at the heroes. Just because the first 45,000 men-at-arms were unable to deal with the heroes, does not mean that the next 45,000 men-at-arms can fail. Unfortunately, and realistically, most armies rout by the time they lose a quarter to half their fighting forces. Historically, few generals would allow the army to still be fighting at such a huge disadvantage. Fewer still are the soldiers who would stay and fight after taking such losses. ## Dead in a few weeks Carrying forward from the previous point, it would take them much much longer to actually completely destroy an army, as they would have routed. A majority of them would rout in a large trail, but there will be many who will be scattered to the four winds. Such is the price of wanting to kill absolutely everyone in the enemy army, as your heroes will then easily spend weeks searching for every last enemy router. --- Suppose that your heroes are not actually physical gods of war, and need tactics, one simple thing you could do then is something like this. > > Extraordinarily skilled warriors can perform feats that seem akin to magic to the untrained eye, at incredible speeds. > > > This means your warriors will be able to go in and kill off the enemy army one battle group at a time. Use the wizard(s) to cast giant flash bangs on the other battle groups while the warriors dispatch of them one at a time. They can also create some sort of giant very loud thunderstorm, which makes things very chaotic, so the enemy battle groups will then be unable to coordinate their attacks, and if the enemy commander calls for an orderly retreat, many battle groups will be unable to receive that order. Then when they see the little battle groups that do retreat, they might then panic and go into a rout instead of a retreat, making it easier for the warriors to go to town on them. Of course another big problem now may be the stamina of your warriors, but it should be fine as long as you have a healing wizard to heal them up. This may make it look like the wizards do not do too much, but what I refer to warriors may also include the wizards with more hands-on battle magic [Answer] Oh dang. Realistically, but in the context of a magical setting, I'd say you'd have to make them [People of Mass Destruction](http://tvtropes.org/pmwiki/pmwiki.php/Main/PersonOfMassDestruction). No real life swordsman or martial artist by any degree could reliably take on more than 3 people at a time (unless they practice [mook chivalry](http://tvtropes.org/pmwiki/pmwiki.php/Main/MookChivalry)), let alone when surrounded by potentially dozens of blokes. Because when they move to engage one guy, they open themselves up to being poked to death by that guy's buddy. So, how do you deal with realistic bad guys who don't queue up to take you on one by one? Well, there's no hard realistic solution (short of strapping a nuke to your chest and running at them), but there are always fantasy solutions: For one thing, if every movement of a man's blade could churn the ground and throw mere mortals back a dozen feet, it'd be blasted hard to fight him. Unfortunately, there's still yet another problem: ranged combatants. If you are impossible to fight in melee, chances are they will resort to shooting you. Thankfully, you have the solution to that - a mage. A mage who, being one of the best in the land, is more than aptly suited to blowing up large quantities of men in tight formations. If they actually managed to fire their volley? Bubble shield. (Alternatively, the heroes may simply have the reactions of demigods, and those arrows may well look to them as though they are swimming through syrup). Once your great heroes have chewed through the pathetic fools who dared cross them, destroying a city is no big deal. A regular arsonist with a flamethrower could probably do it, let alone 6 dedicated supermen with a army vanquishing mage. USe torches if the mage is a lzay bum, otherwise fireballs. Non-modern cities are surprisingly vulnerable to being [cleansed in glorious fire](http://en.wikipedia.org/wiki/Great_Fire_of_London). [Answer] Beware of D&D, it is highly unrealistic. Specifically, the character's progression is *exponential*. From [Calibrating Your Expectations](http://thealexandrian.net/wordpress/587/roleplaying-games/dd-calibrating-your-expectations-2), and specifically in the ANALYZING ARAGORN section, you can see that in the D&D 3.5 system, where characters start at level 1 and in "regular" games stop at level 20 (21+ being epic play), Aragorn would be... a measly level 5. A level 20 character facing a thousand CR 0.5 or CR 1 characters (regular soldiers)? Well, unless [they are truly ingenious](http://www.tuckerskobolds.com/), I would bet on the level 20 character. If you are not familiar with the D&D setup, realize that in melee, a lvl 20 Fighter with the appropriate feats ([Cleave](http://www.dandwiki.com/wiki/SRD:Cleave) and [Great Cleave](http://www.dandwiki.com/wiki/SRD:Great_Cleave), both accessible to a Fighter lvl 4 by the way) wielding a [Spiked Chain](http://www.dandwiki.com/wiki/SRD:Spiked_Chain) and suitably [Enlarged](http://www.dandwiki.com/wiki/SRD:Enlarge_Person), will be able to kill... all the enemies surrounding him in a 20 ft. radius in under 6 seconds (1 round, in D&D speak). Repeatedly. That is, in the "squares" setting of D&D (where each square is 5 ft. by 5 ft.), he will kill 80 enemy soldiers each 6 seconds; or in other words, he would mow down a 1,000 soldiers army in under 75 seconds (12.5 rounds), providing they surround him in melee and press forward as much as they can each round. He won't even be winded. As for the amount of damage he would sustain? In the worst of odds, all 1,000 soldiers would attempt to hit him each round (at least, the surviving ones) using ranged weaponry from afar as necessary, that's an average of 6250 attacks for those 75 seconds. Of those, only 5% (312) will hit, and only 0.25% (13) will hit "critically" (doubling or tripling their damage). This is due to the high-end gear and speed of our villain Fighter. It is likely by then that said villain has access to some [Damage Reduction](https://rpg.stackexchange.com/questions/27882/how-does-damage-reduction-work), which will actually totally negate those 5% that hit, and only partially let pass those 0.25% that critically hit. The Fighter may lose over 100 HPs during the fight (assuming no magic on the soldiers' end), when he has at the very least twice that amount. He will not even pause to heal himself (or get healed). That's it. 1 vs 1,000, and the only magic involved is getting twice as big as he normally is. Oh, and by the way, Fighter is routinely seen as one of the *weakest* core class in D&D... *Note: oh, and it may well be that Baahlspawn are actually playing in the epic range, being even more powerful and unattainable...* --- If you allow such a difference of power between characters, then, as demonstrated, even a completely unstrategic assault by a god-like character will run nigh unopposed by the poor commoners. Its near invulnerability and the quantity of damage he inflicts is likely to shoot morale down quickly, ... ... but what if we mixed tactics in? *(but ignored anything short of a full attack, no poison there!)* First of all, instead of attacking from the front, our villains would start by taking down the chain of command, completely disorganizing the army. With the advantage of surprise, and seeing as a group of 6 is unlikely to be recognized as much of a threat until it is too late and those incredible 6 will just mow down any sentinel that attempt to intercept them, they should be able to behead the army's command in the first moments of the assault. A headless army, hemorrhaging from the inside, is most likely to lose morale *very* quickly as the massacre starts. Without even going to magic, setting the encampment and/or provisions on fire is both going to add to the confusion and thus chaos, as well as ensuring the lack of potential survivors (deserts being typically unkind toward the unprepared). And of course, for added reaction time, I suggest a night attack. By the time the bulk of the army wakes up, they should be surrounded by fire and without a single living officer. Pepper with [summoned nightmarish creatures](http://www.d20srd.org/srd/monsters/demon.htm#bebilith), [fire strikes](http://www.d20srd.org/srd/spells/meteorSwarm.htm), [poisonous clouds (accessible at lvl 9!)](http://www.d20srd.org/srd/spells/cloudkill.htm), etc... at leisure; it will help setup the atmosphere. [Answer] If Eragon taught us one thing about magic, it is that killing by magic is **laughably easy**. No fireballs, no big effects. Just a rupture of a blood vessel in the brain, or cutting a few nerves -> instant death. Combine this with the magic power that is normally portrayed by the big spellcasters in such scenarios, and you get a dead army, and your mage hasn't even broken a sweat. If you don't like this answer because the area of effect of such magic is too big (although the required energy is kinda low), then some kind of magic-induced disease that is highly contageous, deadly, and takes a few days for incubation would at least seriously diminuish the army. Take out the rest while they bury their fellow soldiers. [Answer] Well the first possibility would be if the army is a bunch of morons like the bag guys in the old tv series. just waiting their turn to take a punch on the chin or a sword through the heart. Next would be a huge technological difference between them, halflings with butter knives against armored cave trolls with Gatling guns. Kamikaze, each carry a small nuke as close to the center of the army as possible. But in reality, fighting against huge odds you are going to lose. If you don't have some huge advantage 6 to 1 odds are pretty hard to beat if similarly armed people fight, even if the 6 are barely trained and the one is highly trained [Answer] Six super stealthy thieves slip into the army's camp one night, add slow acting, sure-kill poison to all the cook pots and ration stores. [Answer] You could always do it the way Mulan did: > >  > > > Or perhaps the army is being transported via ships, and you stealthily get aboard the ships, plant some sort of bomb/explosive, and then they all sink/etc. [Answer] The Civil War battle of Glorieta Pass was a tactical win by the Confederates invading New Mexico, but turned into a disaster because a small group circled over the mountains back to the supply train and destroyed the supplies and drove off the mules and horses. In inhospitable country, and without being able to store water, the Confederates had to retreat to the nearest river, and thence back out of the country. [Answer] The first thing that came to mind is the intro sequence of World of Warcraft's new expansion, Warlords of Draenor, where a group of a dozen or so incredibly skilled mages, fighters and plains folk are faced against a horde. I would strongly suggest you have a look at a play-through, to get an exact idea, but in summary it's about taking on small fights of huge tactical proportions, ie culling their generals/ most elite fighters one by one. This can be done in a setting, where paths are narrow and hard to traverse, so only the most elite of the enemy would have to be sent out, like a jungle or a mountain. I think an excellent example here would be the Predator movies. A fantastic example I read the other day was the Hobbits fighting against the Troll, in the Lord of the Rings books -- their only hope of success is attacking the weak points. In an army of overwhelming numbers, the weak point is the leadership. Take them out and the rest will flee or die off. [Answer] Don't engage the army in the first place. Rather, think sniper and saboteur. Use magic, slip in and destroy as much as you can of their supplies. Attack any foragers. How far is that army going to go? They'll have to escort their foragers too heavily to accomplish anything. [Answer] Do it Gideon-style! Cause them to hit each other a lot with all their ranged stuff and generally stir up havoc, making them mostly die on each others' swords. ]

[Question] [ Could a world with no animals whatsoever (not even insects, no humans, etc) still have plant life? These plants do not have to include all the plants in our world, or even any of the same plants. I can think of these problems that would need to be addressed: * Respiration. Plants in our world consume carbon dioxide and produce oxygen. Eventually, the CO2 will run out, unless the world has some other method of recycling the atmosphere (other plants, maybe?) * Pollenation. Perhaps plants can exist that piggyback on the world's water cycle for pollenation? Maybe they place their pollen in fresh water and other plants extract the pollen-rich water via capillary action. * Fertilization. I got nothing (lol). Come to think of it, where would animals get the nutrients they excrete if not from the plants they eat in the first place? Preferably, the world should be as Earth-like as possible. [Answer] If you allow the third kingdom (after plants and animals), namely fungi (mushrooms and their many, many cousins), then yes. Fungi will take care of the oxygen surplus, using it up and releasing CO2 for the plants to breathe. For pollenation: There are plants that use the wind for this, and other plants reproduce through non-sexual reproduction - strawberry offshoots, old willow trees breaking apart and new ones growing from the parts, root networks sprouting new aboveground plant parts, potatos and onions creating tubers or child-bulbs underground... Fertilization: See fungi. Plants die, Fungi (and bacteria) break apart the plant matter, rinse and repeat. Animals actually take care of only a relatively small part of the "Plant matter to fertilizer and CO2" conversion, with fungi *already* doing the bulk of the work. Without our contribution to pollination and spread of seeds etc., we could actually consider us animals superfluous for the ecology as a whole ;) Edit: Found a book (trilogy) I was thinking of when writing this answer - "Of man and manta", from Piers Anthony. Sci-Fi, features a planet with no animal life where fungi evolved into mobile, and IIRC sapient, beings. [Answer] Plants existed before animals ever evolved, and if all animals were to disappear, plants would continue to exist a million years from now. Just mostly different species. **Respiration**. Plants produce both CO2 and O2. Without animals, there would be a higher concentration of O2. If you wanted, you could easily evolve plants that have internal processes that take in environmental oxygen at a higher rate than they use CO2, and perhaps use it to increase mobility and growth. Otherwise, it's likely that bacteria would take up any slack, assuming you just didn't re-evolve animals (Oxygen is a great energy source, if it doesn't kill you first). **Pollination**. Insects and other animals are only one mechanism by which plants are pollinated. Wind dispersal is an older method, and one that most pine trees use effectively. The plants that cause most spring allergies rely on wind distribution of their pollen. **Soil fertility**. In a compost pile, worms are famous for doing the work of breaking waste vegetation into new soil. But this happens even without animals. Instead, soil bacteria and fungus do the job. I wouldn't even suggest that the process needs to slow down. **Seed dispersal**. There are lots of plants that rely on animals carrying their seeds, either as food (eaten or stored) or by burrs attached to fur, feathers, or skin. But there are many, many plants that rely on other strategies. Fluffy feathery seeds floating in the wind are common and maple trees with their helicopter seeds are two examples. Seeds in flood areas can use flooding both as a means of being carried away from their parent, and as a signal that it's time to germinate. More unusually, there are even plants whose seed pods [explode (video)](https://www.youtube.com/watch?v=4WCkHVwRaCs), propelling the seeds many feet away. **Competition and predation**. With or without animals, plants need to defend against predation and competition. Dodder and mistletoe are both parasitic plants that get their energy by tapping into the sap of host plants. They don't usually kill the host, but they can certainly weaken it. Strangler figs are a species that germinate on a host tree, then as they grow, they wrap around and choke the host to death. Oak leaves (and others) contain tannins that poison the soil at the tree base, making it harder for other plants to grow there. It's a violent world out there. If you also eliminated fungi, many, many plants would struggle because they rely on fungus at their roots to increase their nutrient uptake. Without that, plants would probably be limited in size, and many existing species would die. [Answer] Many plant species shed branches and leaves as well as many which shrivel and whither away seasonally. Wild fires happen frequently, turning plant matter back into CO2. There are diseases which kill plants. if your planet had immortal plants it might be in trouble. As @Syndic said fungi do a great job of converting plants into CO2. The simple fact is that the mass of CO2 in the atmosphere far exceeds that the Earth's plant biomass. You can expect this will be the same on your planet. Although its atmosphere would have a higher oxygen composition. That helps wild fires too. Also, plants release CO2 at night when they're photosynthesizing. This helps maintain the balance. After all, night lasts almost as long as day. In essence, the CO2 won't be used up. There are enough mechanisms to convert plant matter back into CO2. [Answer] The short answer is "yes", since plants came into existence some 3 billion years ago and were quite content until the Cambrian Explosion some 550MY ago. Longer answer is that plants will most likely continue to inhabit the oceans for the vast majority of the time until they produce enough oxygen to create an ozone screen and can move onto land. Plants can propagate themselves without animals or insects, the simplest solution being to allow pollen to drift into the ocean or the wind in enough quantities that the corresponding pistels will be fertilized. In your world, there might be enough pollen being released to seriously cloud the waters and fill the air, since that is the only way for plants to carry out sexual reproduction. Plants will also develop interesting ways to project seeds, ranging from dispersion through the air and water to developing "catapults" or other ways to throw seeds to needing fire to germinate (much like trees in the boreal forest). Other methods of reproduction seen in modern plants will also be developed, such as using rhizomes. Other ways to propagate may develop depending on the conditions of your world. [Answer] Without kingdom *animalia* you would still have kingdom *fungi* as well as domains *prokaryota* and *archeae*. These are all perfectly capable of respiration (in fact plants themselves can do it too) and would expand to fill in the new niche of oxygen consumption. Fertilization is already done by microorganisms such as nitrogen-fixing bacteria so no problem there either. Pollination will be an issue. Those plants that are pollinated by animals would likely go extinct. The other plants which are pollinated by wind or water will take over their ecological roles. If animals were to vanish overnight, many ecosystems would undergo crises, but ultimately a rich flora (different though it may be from what we are accustomed to today) would persist on the planet. [Answer] Pop-culture bad science reporting says Humans and Bananas have about 50% shared genes. Not easily verifiable but some similarities must exist. Photosynthesis evolved about 3.5 Billion years ago. Multicellular organisms only evolved about 800 million years ago. About 450 Million years ago land plants appeared. 230 MYA dinosaurs. So you've got huge opportunities for evolutionary branches. Kingdom Plantae and the Evolutionary History of Plants would be worth investigating. [](https://i.stack.imgur.com/DuHIW.jpg) [Answer] Could plants survive without animals? Sure. Plants can respire, keeping oxygen and CO2 levels stable. Fertilization is largely based off of nitrogen fixation, which certain plants (legumes) can do. While many modern plants did evolve to utilize animals for pollination there are countless other solutions (airborne spores or seeds being the most obvious). However, evolution being what it is, there is a pretty good chance that in the absence of animals keeping their population down, plants would evolve to kill each other in order to acquire more resources, and many would learn to eat other plants. Many of these would probably lose the ability to photosynthesize and become something similar to fungi in our world. [Answer] No one has addressed Fertilization yet; this is the topic I shall address. Fertilizer is composed of vitamins, minerals, and nitrogen. Vitamins can be produced by plants and minerals aren't ever destroyed, so those two aren't a problem. Manure, on the other hand, is composed of mostly nitrogen. Nitrogen is used to produce amino acids, which are used to produce protein - and you can't live without protein. Most plants can't produce Nitrogen, but certain legumes (like beans and stuff) can "fix" (fancy word for produce from) nitrogen from the air (remember, the air is about 78% nitrogen). Lightning and certain symbiotic bacteria can as well. And remember - nitrogen is never destroyed - it has to either decompose into the soil or into the air. ]

[Question] [ I'm moving a ton of people (asteroid miners and affiliated personnel living in the Asteroid Belt) onto a generation ship which will take years to reach its cruising speed of .1c, and which is part of a fleet numbering hundreds of ships that's prepared for a three thousand year journey or more. My story takes place partway through the second millennium of the journey, and despite over twelve hundred years having passed since departure, none of the fleet's citizens have become posthuman like the entities which built the ships in the twenty-sixth to twenty-eighth centuries. Furthermore, science and technology haven't even significantly advanced by more than a relative century's worth of development since departure. How might I explain this complete and utter stagnation? Is there any conceivable reason the entire fleet hasn't budged an inch technologically since they left the Solar System over a thousand years ago? Additional information from comments by the OP: The fleet stays in regular contact with each other though, relaying occasional brief status updates a few times every Earth year. Usually they include any new, relevant or important information they think the rest of the fleet should know. Each ship has a population between 1 and 10 million people as well, meaning the total sum of the fleet's population is about a billion. Each ship is about the size of a major city. Even the small ones carry hundreds of thousands. And this is after a thousand years of population growth, mind you. The original crew of each vessel probably didn't exceed 40k back when they first launched. [Answer] ## Space Generation ships are huge, but they aren't designed for experiments; they're built to move from point A to point B. Just like airlines don't have a dedicated science lab, your ships may not have a research facility. Only minor advances that could be made in a cramped personal apartment would even be possible. ## Need Necessity is the mother of invention. If your ships are built well, easily maintained, and provide free and clean air, water, and food, the citizens may well need very little. Inventions may be no more than entertainment at best; like the Eloi of HG Wells' *The Time Machine*, or the humans aboard the Axion in *Wall-E*, the humans aboard the ships spend their days playing games and relaxing, instead of thinking. ## Time On the other hand, these ships may require constant maintenance. There is no such thing as a passenger; children go to school, and upon graduation are immediately brought into the workforce. Few have time for hobbies, let alone science, and those that do are derided for not "pulling their weight." With relentless schedules and little time for anything but menial labor, few decide to try inventing anything more than a reason to sleep in. ## Stasis Of course, it may be that people aren't awake to do much inventing; if the ships place people into some kind of temporary stasis, the centuries will fly by. There may need to be a few people awake to keep things running, and perhaps the requirements of stasis need people to be awake for some amount of time, but otherwise, all slumber on through the darkness, dreaming, but not inventing. ## Management Sometimes, all it takes to stagnate technology is the wrong guy in charge. With rules specifically in place to keep anyone from having enough time to run experiments, or rules prohibiting tools required for the same, advancing technology is impossible - but it doesn't have to be that obvious. In fact, it may not be a man at all; safety rules implemented on the ship(s) may limit technological advances, rules unable to be changed without completely rewriting the entire ship operating system. Those rules may have seemed harmless, or even beneficial, when the ship was built: "no power draw over 1 kW" is a great rule for stopping shorts and faults, for instance... but it also means nothing more powerful than a microwave could ever be used. [Answer] **All of their resources are carefully controlled.** Technological advancement generally requires the utilization of large amounts of resources to construct advanced laboratories, build novel materials, and test new procedures that could very well destroy or render unusable large amounts of resources that could otherwise be used for something else. On Earth, this isn't much of an issue, since a well funded organization can buy more steel or lithium if they need it. In space, there are no extra raw materials. Everything in the colony ship will exist for a specific purpose, and all resources will have been designated as being critical to a certain task prior to departure. While there will no doubt be scientific discoveries on board the ship, such as how to optimize growing conditions in a zero-g environment, they will be limited to what can be discovered with whatever equipment the ship set out with. Technological advancement requires going further than just performing simple experiments. It requires prototyping and fabrication, which require materials that the ship simply can't spare. Colonists will be expected, on a generational basis, to use the exact same technology that their ancestors used, and to repair it with a steadily dwindling stockpile of raw materials. This makes the most sense from an expedition planning point of view: technological development is an unknown, so everything should be assumed to be static with regards to technology for the duration of the voyage. Any deviations from that could reduce the materials available for critical tasks, increasing the odds of mission failure. Culturally, the colonists will be drilled to be as frugal with materials as possible, since the fewer materials that are needed to patch a personal comm unit, the more materials will be left the next time one inevitably breaks. In this sort of culture, the colonists would be shocked by, and probably punish, anyone found using raw materials to develop new technology. [Answer] ## Religion > > Religion is the masterpiece of the art of animal training, for it trains people as to how they shall think. > - Arthur Schopenhauer > > > Throughout history, religion has been used to enslave the human mind. If you can make everyone in the ship devout followers of some proclaimed god, and you make any form of technological or scientific questioning blasphemous, in such a confined environment, dissenters will quickly find themselves disciplined... or worse. [Answer] Quite simply, we cannot afford to put our ships at risk. Some intellectual activities are low risk and can be encouraged - art, music, poetry, philosophy - to some degree. Though when they inflame human emotion, even these can be dangerous. It's one thing for kids driven mad by rock and roll music to trash a theater, or a city in a riot, but trashing a fragile hull in the vacuum of space ... well, in the first half millennium, it happened to a few ships. Not rock and roll, for the most part. Funnily enough the philosophers were more dangerous, we lost a few ships between free will and predestination, and the argument isn't settled yet. No survivors, and we still have to navigate around the debris clouds, moving alongside us at the same 0.1C.. Science, engineering, and technology have far greater dangers. Tolerable on a planet, thanks to the redundancy of large continents and vast oceans. Experimenting with fire? Most people can flee the forest and start again. Mining? Don't drink from that river, there's mercury in the mine tailings. But it's not the only river. Nuclear fusion research? You get the picture. New and experimental political systems? Wars, or famine due to planning breakdown. Survivable for most of the refugees. Whatever happened on Easter Island? Eminently survivable on a continent or one island in a crowded archipelago. But our ships aren't planet sized, or even continental in scale. They are approximately the size of Easter Island, and equally fragile. We tried designating some ships as experimental zones, or cultural growth zones. A few survived, and now they are the most stagnant of the fleet. The others are more debris clouds. But we have a lot of bright ideas on file, waiting till we reach our destination. And an army of filers, cataloguers, librarians, and theoretical researchers... [Answer] Lots os reasons. For starters, your population is composed of miners and associated personnel only, right? Probably the most educated person you'll have will be a group of engineers. The best science people you will have for the first generation will be the odd nerd here and there. Miners and engineers know how to build machinery and extract ore, but things like superstrings theory, oxidative phosphorylation or k-means clustering are usually not part of their education. In plain English: your people already start with very little science. They don't have even 1% of the whole scientifical knowledge of their own time. They probably lack the scientific knowledge of past times as well, so they have a lot of wheels to reinvent. Think about it. Pick a few thousand average people from the developed world nowadays and put them on a deserted island they can't escape from. Even if they have the raw materials to build microwave ovens, they will probably be doing clay stoves instead, and poorly. They'll have millenia of technological catching up to do before they can even dream about gas stoves. But let's get back to your miners. Their situation is even worse. They are probably handed everything they need to live from the AI governing the ship, which acts as a nanny to them. This reduces motivation to innovate. They will also lack a lot of resources to develop on, since even an armada of ships will probably have only a negligible fraction of the mass of our planet's crust. You can't develop electronics when the only sources of silicon are the boards of the computer that keeps you alive. You can't develop much in the means of metallurgy when your sources of iron are the walls separating you from hard space vacuum. Add a technophobic culture - that is, one that dislikes technological advance, and you get the perfect mix for a hiatus in technological advances. [Some such cultures exist nowadays](https://en.wikipedia.org/wiki/Amish#Use_of_technology_by_different_Amish_affiliations). Imagine that the space amish of the future, probably an offshoot of the Kalona, will embrace [reactionless drives](https://en.wikipedia.org/wiki/Reactionless_drive) (a development currently only seen in Sci-Fi, but theoretically possible in reality) - but they will never ever enter a ship with an [Alcubierre Drive](https://en.wikipedia.org/wiki/Alcubierre_drive), because it violates the spacetime as it was woven by God. They may also reject other sci-fi advances like magnetic monopoles and teletransportation on similar grounds. Now imagine those guys are the majority of the population on your generation ship... [Answer] A generation ship has to be a stable system. Either it is totally self sufficient or nearly self sufficient in which case there is little need for the population to do anything for the ship itself but may need to do things like farming. Alternatively the ship needs a lot of maintenance in which case all resources are tied to keeping that maintenance in place. In either case the surroundings are rather static and at least some part of the economical output lives under some sort of command economy, due to necessity. This is necessary not only for economic reasons of restricting resource usage but also for political stability. Waging war inside a generation ship is quite bad. Politically it may be desirable to limit new research as it has a tendency to cause unexpected social changes. But even if it is not there may not be resources to do the changes needed. This paired with limited communication and somewhat limited population dramatically slows research down. Research speed is at least partially a network effect that does not scale linearly. [Answer] Due to network effects, **technological advancement is exponentially correlated to population size**. So the generation ships will appear to stagnate relative to earth so long as their population is significantly smaller than earth, and their contact with earth is limited (i.e. no earth-to-ship broadband). An overview of the exponential pace of technological change is given on this wikipedia page: <https://en.wikipedia.org/wiki/Accelerating_change> As a side note, this network effect explains things like global food and energy production vastly outpacing humanity's exponential population growth. Unintuitively, the statistics suggest that the faster our population grows, the longer the earth's resources will last. This is due to technological advancement's ability to gather, distribute and use resources more efficiently. [Answer] 1. The civ of Gen Ship collapsed and is rebuilding itself (Modern Earth) 2. The Government of the ship have decreed those things off limits (Rome) 3. Only enough people who fill out specific jobs are there so they can't risk attempting certain sciences. 4. They don't have the resources to build what is needed 5. The experiments require more space or a safety valve which dint of being on a ship they don't have. [Answer] In real history this usually happens when intellectuals are not in power. They still exist, sometimes even in the same amount, but without centralized support from intellectual government that brings them up the career ladder, gives them resources, the overall progress could be orders of magnitude slower. You can just tell the audience that the central government of your world in question was not pursuing advances in culture, science and technology. [Answer] **Pre-occupation with entertainment.** Think of football, and the culture that surrounds it. The fandom; the insanity. For some people --- in some small communities, especially --- football is life. At the expense of their full potential. [Answer] During the creation of the fleet, the various AIs were linked together to form a collective. The directives given to the AI were 1) survival of the fleet, 2) the survival of the human race, and 3) to cause no harm to human life. (It is assumed that in the years 2600 to 2800 that AIs have sufficiently advanced in order to achieve these goals and that they are more qualified to make the decisions that affect the fleet.) One of the primary responsibilities of the AI was in education and in assigning jobs because on the capabilities of each individual. While many jobs would not be considered "dream jobs", the jobs do fit the individuals for the most part. Because of the near impossibility of inter-ship transfers, the population was basically kept in smaller "villages". Even interactions between villages on the same ship were considered rare. While there were some problems with crime, very little that happened that could escape the awareness of the AI (nearly omniscient knowledge). The AI informed the police and allowed humans to determine the justice required for the crime (no death penalty). This system worked well. During the first few generations, the AI collective determined that there were certain types of individuals that could be considered more important to the fleet than others. The AI began promoting these individuals out of the standard survival path and careers that have dominated most of the human race... and put them in positions of problem solving, think-tank style groups. Essentially these individuals brought a key missing component to the AI... creativity. Starting in the 3rd and 4th generations, the statis technology had evolved enough that it was viable to allow humans to be hibrinated for long periods (even though there was some small aging occurring of about 1/30th of normal time). A collective decision between the AI and humans determined to have the team to have long periods of statis between problems. This meant that those able to solve the problems were available, but while they were awake they only focused on the problem(s) that required them. While the AI knew the potential of each human at a very young age (and trained them appropriately), the AI also honored the family unit as much as possible. The individuals deemed creative geniuses would receive their offer of promotion only at the time of the graduation (usually between ages 17 and 18). It is considered a great honor to be choose for this position even though the communities know that they may never see the chosen children again in their lifetime. By basically culling the smartest and most creative people from the general population, this inadvertently caused 1) the stagnation of technology and innovation except in areas deemed critical to the AI, and 2) the steady removal of their genetics -- lowering the overall IQ and creativity of those that remained behind. [Answer] I would like to reference the work of Raymond E. Feist. Pure fiction but more medieval style. He has also created a group of people which haven't advanced technologically at all. This due to some reasons: * It's off limits for most people to conduct research and those that can do this rather study the past to learn from past mistakes * Because they expand, they think they evolve but an outsider remarks that expansion doesn't mean evolution * Rather than create new stuff culturally, their artists recreated known things as perfect as possible. * They don't see the need for inventions just for the sake of inventing There are a few more reasons but I can't remember them all. [Answer] Motivation, As soon as the miners and associated people board ship they will no longer be miners and associated people. Several generations will pass. New generations will actually not be "miners" but "travellers" who will do nothing but travel and learn mining skills with stored mining equipment and planning for the new mine that is original motivation for the voyage. The originals will not make the destination so the motivation must be strong for the voyage. Holding the original and I assume strong motivation for making the voyage over generations will be hard and require a controlling hierarchy or the voyage is likely too look for new motivation. So either everyone except a few are in stasis - so no science, or everyone is awake and under a strong controlling hierarchy - so no science. ]

[Question] [ A messenger from the stars just arrived in peace but has brought horrible news. A vast swarm of planet devouring phototropic insects are approaching from deep space and our only hope is to obscure or snuff out our sun until they pass by. The messenger provided a copy of the galactic encyclopedia which includes all of the scientific knowledge of the Kardashev Type II civilization she comes from, but she has since returned to space, heading off to warn other civilizations of the approaching threat. We have enough time to prepare Earth for the cold darkness. The encyclopedia includes several different techniques for generating enough energy to keep us warm and techniques for synthesizing nutritious food without the need for plant life. We also have time and the new knowledge to build enormous opaque enclosures to serve as green houses, zoos and gardens, so none of our world's bio-diversity will be lost. We won't have to live in complete darkness but we will need to keep our light hidden behind solid windowless walls. So my challenge as an author and world builder is that I don't have my own copy of that encyclopedia. So I can't read the chapter on how to safely snuff out our sun without making it go nova or expand to consume the Earth. I would also prefer to keep it's corpse in one piece so that the arrangement of the solar system can continue, relatively unchanged. My question is... **Given unlimited resources, nearly magical scientific knowledge and enough time, how do we snuff out or obscure the light and heat of our Sun?** I'm looking for an alternative to building a complete Dyson sphere because my goal as an author is to write stories about the dark cold earth. Sort of an homage to the old Space 1999 TV series, only with a more ominous, grittier, darker theme. Bonus points if the process is reversible once the swarm has flown by. [Answer] If you slow time down for the sun the emitted energy will drop proportional to the time dilation factor and light will redshift off into obscurity. No idea how you'd do it (something akin to a localized distortion of the curvature of spacetime), but that's half the point of technomagic. And should be easily reversible, or at least as easy as getting it to happen in the first place. Semi-bonus: an argument can be made that the mass of the sun is still there, so orbits and the like stay the same. Nice bonus is the sun is still there, and probably still visible as a black spot in the sky (or dim spot... not entirely clear on what might be redshifted into the visible spectrum), but something about slowing down the nuclear processes of the sun has a nice sense of wrongness to it. [Answer] Problem: even if you *could* just stick a blanket over the sun, it is probably already too late. The solar system formed more than 4 billion years ago, and for all that time anyone who was watching and had suitably acute vision would have been able to see Sol, and almost certainly the protoplanetary disc around it and later the planets themselves. Certainly, anyone or anything with K2-level technology will know where the sun is, and have a pretty good guess at what sort of planetary system it harbours. Stars don't just poof out of existence without a trace. Even being eaten by a black hole is a pretty drawn-out and violent event. Those planet eaters? They'll *see*, and they'll *know*. You can't pull the wool over their eyes. They'll see that little yellow dot fade away, the little yellow dot that is making unscheduled departure from the main sequence and clearly isn't behaving like a natural star should. They'll come and take a look at the clear and unambiguous evidence of intelligent agency, because intelligence generally comes from planetary systems and that means *more food*. So give up on your plan. You gonna get ate. Instead, read up on mechanisms of planetary relocation, preferably with reactionless drives, and boost the Earth out of Sol's gravity well as soon as you possibly can. They might notice the absense of the earth, but given the rest of the solar system to snack upon, and assuming suitable stealthiness of the fleeing world, maybe, just maybe, they won't find you. Good luck, cos you're gonna need it. --- As an aside, given that you have the potential power to snuff out a sun, you will certainly have the power to do simpler things. I'd see about building a giant "blackhouse" roof covering the earth (or as much of it as seemed practical), in a technique sometimes called [paraterraforming](https://en.wikipedia.org/wiki/Terraforming#Paraterraforming) or a worldhouse. Life might not able to be as thermodynamically exciting as it used to be, absent energy input from the sun, but you've got access to a lot of fusion fuel in the seas and you can build and run a lot of grow lights with that. Probably would be insufficiently gritty for your narrative needs, but, y'know, the category of "things easier to do than surreptitiously turn off an entire main sequence star" includes a lot of stuff like this. [Answer] # A star shines because it has mass... You put enough mass together, it gets a dense core, heats up, and voila, [solar fusion](https://physics.stackexchange.com/questions/61108/how-does-a-star-ignite). Yes, that's an oversimplification, but, fundamentally, making a star not shine would require removing its mass. # So let's figure out how to remove mass... But you said you want the mass to stay at the center so that orbital mechanics doesn't shift for the planets. That suggests a delicate surgery -- divide the sun into N parts where each part is less than the minimum stellar mass, and let the masses orbit around the original gravitational center of the sun (because gravity works as if all of an object's or system's mass were at the center of gravity for everything in orbit around it). [The smallest theoretical mass for a star with same metallicity of Sol to support nuclear fusion is 75 x mass of Jupiter](https://en.wikipedia.org/wiki/Stellar_mass). Sol is ~1000x mass of Jupiter. So we'll need to cut Sol into 14 chunks. 14 is an awkward number, so let's make it 20, and make each one drift away so that we get an icosahedron of chunks. A, that'll make it easier for our imaginary thrust system to arrange things geometrically, and B, that'll make a great book jacket cover. It might also keep the star's mass well-balanced, so, again, we don't have to worry about the planets feeling the effect. I did mention this was a *delicate* surgery, right? Yes? Good. Moving on... Having divided the star, the core should cool down, fusion stops: Good night, starshine! (Gonna need a [new musical number](https://www.youtube.com/watch?v=whmzEXywq40) when future humans perform the stage play [Hair](https://en.wikipedia.org/wiki/Hair_(musical)).) You want your Giant Space Scissors to push the chunks apart at just the right speed so that they eventually drift back together when the threat is passed. # Design of Giant Space Scissors You have a problem of scale. Stars are BIG. Really big. Like hurling-Earth-into-Sol-won't-break-it big. That means we are NOT talking about any sort of mechanical scissors. You're going to need a chemistry solution -- something that you can seed into 20 sides of Sol that starts some sort of repulsive reaction. I think you're going to invent handwavium or unobtanium for this. Here's my attempt... Each seed must be a little thing that will pull Sol's mass to itself and overcome the gravity that is holding Sol together. As it does this, it needs to generate either positive or negative charge such that it pushes away from the seeds around it. ALAS -- [there is no way to color an icosahedron with only two colors such that no two adjacent edges have the same color](https://en.wikipedia.org/wiki/Regular_icosahedron). You can only do that with an octagon. So you can't just rely on alternating positive and negative electrical charge to do the push back (i.e., have some "positive seeds" and some "negative seeds"). So, more handwaving: we'll assume that the act of the seed pulling in mass somehow imparts momentum to the chunks along the vector from which they are pulling the most mass (i.e. away from star's core). That's nice because it means that momentum will eventually be overcome by gravity and the chunks will drift back together. *Note: Having the seeds become uniformly positively (or negatively) charged would cause them to push away from each other, but if that pushback was strong enough to overcome gravity, they'd never drift back together. The momentum solution is better in my opinion.* # Problems: 1. It'll require a lot of set up to get the seeds arranged around the sun. We're talking years of construction and travel, not weeks. 2. The process of dividing the sun won't be fast. Sure, you can posit a geometric expansion of speed as the seed grows and acquires mass, but we are still talking SOLAR MASS. It takes a while for that much mass to move, even if the impulse is given atom by atom in some sort of known-physics-defying tractor beam that the seed is emitting. 3. It'll take a while for the core chunks to cool. Possibly as long as tens or hundreds of thousands of years. Not a lot of ways to accelerate the cooling. (Thanks to user @MikeScott for the link.) Basically, these space bugs better be a long way away. Centuries. Millennia. Long enough for humans to have developed multiple spacefaring civilizations, collapsed back to bronze age, and rebuilt again. So you may want to posit FTL travel because [FTL MUST grant time travel](http://www.physicsmatt.com/blog/2016/8/25/why-ftl-implies-time-travel), so humanity can launch the probes toward the sun and backward in time. Just be aware that once you allow for violations of causality, forever will it dominate your destiny. (Yoda lives in a galaxy that has FTL, so he knows this problem. Or will know it. Hard to say with relativity + FTL.) Or you could NOT violate known physics and just put the whole of humanity on a space ship that gets up close to speed of light (C) and then let relativity and time dilation do the work for you, so humanity is only gone a few weeks and comes back to a much changed Earth, but no space bugs. You get to solve the acceleration and deceleration problems yourself if you choose this solution! 4. Something has to tell the seeds to shut off. When the chunks drift back together, stellar fusion won't ignite if the seeds keep the chunks isolated enough that the "swiss cheese" of the chunk spheres provide enough venting for the heat. Ok... let's just assume that there isn't enough venting for the heat, stellar fusion reignites, and the seeds get pulled toward the core where it eventually becomes too hot and they lose whatever tractor beam powers they had. Ok, so not a problem. Nothing is a problem with enough handwavium. :-) 5. That star will be cranky when it comes back online. Expect a lot of solar flares while it settles back into its mainline again. That may cook the Earth, but you'll be used to living underground by then, so just add a few thousand years to the underground time. Unless you pick that time dilation solution. Or you could have everyone upload their minds into a computer or... yeah, we've all read sci-fi... pick your solution here. Seriously... we are talking STARS here. Anything you do involving space blows human lifespans out of the water. You're going to need to deal with that in any story that has even a passing acquaintance with science. That's the saddest part of modern physics: [The Stars Are Not For Humanity.](https://www.goodreads.com/work/quotes/209414-childhood-s-end) (Thank you, Arthur C. Clarke, for summing up the crushing of geek dreams.) *PS: Book title: "Divisions of the Sol" -- the dividing of the sun set against the divisions in a young protagonist's heart as he/she longs for a partner against family wishes. It'll sell like hotcakes to the folks who like their sci-fi soft and their romance hard. :-)* [Answer] > > I'm looking for an alternative to building a complete Dyson sphere because my goal as an author is to write stories about the dark cold earth. > > > There isn't [sufficient matter](https://worldbuilding.stackexchange.com/q/151268/2113) in the solar system to build a Dyson sphere or swarm at one astronomical unit or farther (i.e. with the Earth inside the sphere) more than four meters thick. So you'd have to build it much closer to the sun, perhaps inside Mercury's orbit, to get it thick enough to obscure the Sun. That would still give you your dark cold Earth (presuming you didn't take apart the Earth to make the Dyson sphere). Surface area is proportional to the square of the radius. So a quarter of the radius (which is about where Mercury is) would give sixteen times the thickness. I'm not sure how much farther in you can make the Dyson sphere before it would get too hot. You may also find that it makes more sense to build two spheres. The inner one catches the light but reradiates a significant portion. The outer one catches that light and reradiates it with a different wavelength as [already suggested](https://worldbuilding.stackexchange.com/a/151335/2113). In between the spheres might be the gaseous portion of the mass, soaking up some of the energy output. [Answer] > > how do we snuff out or obscure the light and heat of our Sun? > > > You cannot completely hide the energy emitted by the Sun. You can just shift it to longer wavelengths as a consequence of using the usable content of the emitted energy, but, as madam Thermodynamic states, any transition results in some form of heat being emitted by a system at a lower temperature. Once you reach 0 K, you cannot extract any more usable work, and you have reached the thermal death. I.e. the visible light we get on Earth and warms up a car parked under the Sun comes from the surface of the Sun being at about 6000 K, while the car re-emits it in the infrared, at longer wavelength. Even if you were able to convert the emitted energy into mass, you would have the problem of dissipating all the gravitational energy of the resulting mass plus the Sun, else the whole thing would ignite again. And dissipating that energy would give an energy emission. [Answer] ### Basic Requirements We are talking about disassembling a star here. While this is certainly possible within known physics, it is something that requires the infrastructure, resources, and energy of a K 2.something civilization. Therein lies the issue. Even with all the knowledge and technology, is disassembling the sun really the smartest option? You gonna have to explain why other options weren't chosen. Running away seems quite easy in comparison. **Shkadov Thruster** This is basically using half a Dyson sphere to accelerate the sun. The issue is that the acceleration is abysmal. This [video](https://www.youtube.com/watch?v=GxwCIeWaU3M) and the [Wikipedia article on the subject](https://en.wikipedia.org/wiki/Stellar_engine) might be interesting. > > For a star such as the Sun, with luminosity $3.85 \cdot 10^{26}\;W$ and mass $1.99 \cdot 10^{30}\;kg$, the total thrust produced by reflecting half of the solar output would be $1.28 \cdot 10^{18}\;N$. After a period of one million years this would yield an imparted speed of $20\;\frac{m}{s}$, with a displacement from the original position of 0.03 light-years. After one billion years, the speed would be $20\;\frac{km}{s}$ and the displacement 34 000 light-years, a little over a third of the estimated width of the Milky Way galaxy. > > > **Fleeing with Earth** There are several ways to do this. [This video](https://www.youtube.com/watch?v=oim7VvUURd8) discusses it in detail. While the thrust you can apply to Earth before the engines will push the continent they are on into the mantle and deform the Earth is still small, it isn´t as abysmal as the Shkadov thruster idea. Fuel will be a problem, but putting several layers of shielding and hydrogen for fuel and reaction mass around Earth will give you a dark planet theme. Putting this armored Earth in orbit around Jupiter and using [fusion candles](https://worldbuilding.stackexchange.com/q/36732/58321), which are discussed in the linked post. The following description is from said post. > > Build a fusion candle. It's called a "candle" because you're going to burn it at both ends. The center section houses a set of intakes that slurp up gas giant atmosphere and funnel it to the fusion reactors at each end. Shove one end deep down inside the gas giant, and light it up. It keeps the candle aloft, hovering on a pillar of flame. Light up the other end, which now spits thrusting fire to the sky. Steer with small lateral thrusters that move the candle from one place to another on the gas giant. Steer very carefully, and signal your turns well in advance. This is a big vehicle. Balance your thrusting ends with exactness. You don't want to crash your candle into the core of the giant, or send it careening off into a burningly elliptical orbit. When the giant leaves your system, it will take its moons with it. This is gravity working for you. Put your colonists on the moons.For safety's sake, the moons should orbit perpendicular to the direction of travel. Otherwise your candle burns them up.They should also rotate in the same plane, with one pole always illuminated by your candle (think "portable sunlight") The other pole absorbing the impact of whatever interstellar debris you should hit (think "don't build houses on this side") > > > **Colonial Fleet** Just get everyone onto colony or [world-ships](https://www.orionsarm.com/eg-article/4700364d11f02) and run for it. You wanna take the Earth with you? That's easy. Just peel it like an orange and place the crust fragments in rotating habitats on said vessels. Sounds crazy? Keep in mind that you just proposed to disassemble the sun. Peeling earth is relatively easy given the knowledge humanity was given. There will be a ton of very advanced geo-engineering knowledge in there. Dig extensive tunnel systems under the continental crust, place engines there and keep them thrusting until the huge, domed over parts of Earth sit in prepared spin habitats. I´ll calculate in a moment why I believe that fleeing is the superior choice. Several of the options will still give you decent dark Earth setting. **The Logistics** Whatever you attempt the only way to do it in any reasonable time frame are self replicating machines. Say goodbye to Mercury, Mars, the asteroid belt and probably more of the planets, as they´ll be needed for construction materials. Beyond that, you´ll need a lot of time. With all of that out of the way. ### Starlifting [Starlifting](https://en.wikipedia.org/wiki/Star_lifting) is discussed in detail in [this video](https://www.youtube.com/watch?v=pzuHxL5FD5U). The issue with starlifting is that it takes a long time. A very long time. Using 100% of the energy output of the sun will allow you to remove 0.000003% of the Sun's total mass per year. After only **334 million years** the sun will have been disassembled. (it will be even longer if you intend to collect the material for later use) The swarm would have to be out past the Andromeda galaxy assuming they can move with a speed near light speed. Fortifying the entire Milky Way galaxy and turning every star into a Nicoll-Dyson Laser (the satellites of a Dyson swarm act as a phased array laser emitter capable of delivering their energy to a planet-sized target at a range of millions of light years) to fry the bastards out of the sky seems easier and more practical. That said, there are three main methods suggested in the Wikipedia article: **Thermal-driven outflow** > > The simplest system for star lifting would increase the rate of solar wind outflow by directly heating small regions of the star's atmosphere. This would produce a large and sustained eruption similar to a solar flare at the target location, feeding the solar wind. The resulting outflow would be collected by using a ring current around the star's equator to generate a powerful toroidal magnetic field with its dipoles over the star's rotational poles. This would deflect the star's solar wind into a pair of jets aligned along its rotational axis passing through a pair of magnetic rocket nozzles. The magnetic nozzles would convert some of the plasma's thermal energy into outward velocity, helping cool the outflow. > > > **"Huff-n-Puff"** > > In this system the ring of particle accelerators would not be in orbit, instead depending on the outward force of the magnetic field itself for support against the star's gravity. To inject energy into the star's atmosphere the ring current would first be temporarily shut down, allowing the particle accelerator stations to begin falling freely toward the star's surface. Once the stations had developed sufficient inward velocity the ring current would be reactivated and the resulting magnetic field would be used to reverse the stations' fall. This would "squeeze" the star, propelling stellar atmosphere through the polar magnetic nozzles. The ring current would be shut down again before the ring stations achieved enough outward velocity to throw them too far away from the star, and the star's gravity would be allowed to pull them back inward to repeat the cycle. A single set of ring stations would result in a very intermittent flow. It is possible to smooth this flow out by using multiple sets of ring stations, with each set operating in a different stage of the Huff-n-Puff cycle at any given moment so that there is always one ring "squeezing". This would also smooth out the power requirements of the system over time. > > > **Centrifugal acceleration** > > The two magnetic nozzles would then be located on the star's equator. To increase the rate of outflow through these two equatorial jets, the ring system would be rotated around the star at a rate significantly faster than the star's natural rotation. This would cause the stellar atmosphere swept up by the magnetic field to be flung outward. This method suffers from a number of significant complications compared to the others. Rotating the ring in this manner would require the ring stations to use powerful rocket thrust, requiring both large rocket systems and a large amount of reaction mass. > > > **Deathsinger** This method is a bit more speculative than the others. Science-fiction author [Alastair Reynolds](https://en.wikipedia.org/wiki/Alastair_Reynolds) proposed to use a [gravity laser (Gwaser, Gaser, Graser, or Glaser)](https://en.wikipedia.org/wiki/Gravity_laser) to "sing" a hole down to the core of a star. This would create a beam of stellar material powered by the internal pressure of the star, which would slowly deplete the star. In the novel *Redemption Ark* this happens on a timeline of a few years. This might be the option that would fit your purposes best. [Answer] **Forget the Sun. Flee the solar system** If you add more mass to Jupiter, you could potentially create a second star. Binary star systems create unstable orbits in the planets that orbit them and will often eject planets from the system into deep space as rogue planets. This is making the assumption you have enough time, but trying to put out the sun isn't going to be quick and if you remove too much mass it could explode. Personally I'd have gone with the Dyson sphere and the people on Earth are the ones that refused to leave and are now stuck in the dark. [Answer] A solution requiring only one unknown technology: Precision gravity control (think tractor beam) on a very large scale. Surround the sun with stations whose job is to pick up basically the whole mass of the sun. You will need many, many stations as the material has to be separated so it will cool. Note that so long as this whole operation takes place within the orbit of Mercury the effects on the planets will be trivial. Once you have all the star-stuff separated and cooled you **gently** reassemble the sun. The material must be carefully lowered to the surface, not allowed to fall. Since it's far below fusion temperature the star doesn't relight, once you have put everything back together the result is a very unusual black dwarf. If the threat was intelligent they would immediately realize something was up but you're talking about insects. They're not going to realize no black dwarf should yet exist, nor are they going to realize that a black dwarf shouldn't be mostly hydrogen. Once the threat is passed you pick the material back up but this time you let it fall back down, the gravitational heating will reignite the star. Ensure you have picked up enough mass that the core is no longer degenerate before you allow ignition, fusion in degenerate matter does not regulate itself properly and the result would be cataclysmic. Note that this process requires more energy that a K-2 civilization has access to! [Answer] Push the Earth into a very highly eccentric orbit (maybe even push it into a high inclination as well to make it even harder to find), such that when the swarm arrives the Earth is in the Oort cloud. Then hope the swarm doesn't notice it. Eventually the Earth will return to the inner solar system on its own where you can then push it back into a circular orbit, but in the mean time it will get very cold and dark on Earth at that distance. [Answer] Create a stranglet and drop it in to the sun, it will convert the whole thing into a quark star (<https://en.m.wikipedia.org/wiki/Quark_star>), which will also halt all fusion, or any other currently understood reactions. It would still be quite hot so you would have to deal with that somehow, but it’s a start. Downside, you can’t undo that via any process we could even imagine from current physics. We don’t really know much about the properties of what you would end up with, so you would have to come up with your own physics here and there. It would be easy to claim that quark matter doesn’t emit black body radiation so it would still be highly energetic but also entirely dark. [Answer] If you have a means to divert the light of the sun to specific locations, you can use a network of dyson spheres (or regular polyhedrons, e.g. icosahedrons) containing artificial black holes to absorb the energy. Around the black hole you can install "filters" which use part of the gravitational energy of the incoming mass and energy to maintain the structure, to balance the black hole inside of it and for propulsion. Later on you would want technologies to speed up the dissipation of the black holes - especially as an emergency hatch. If the suggestion that all energy of a black hole is encoded on its surface is correct, it would seem likely that sending very small but precisely programmed packets of energy could be used to control the kind and amount of Hawking radiation emitted. [Answer] Honestly if your just concern about the heat and light from our sun it shouldn't be a huge problem. Today we have a material called vanta black which is the blackest black ever. So if your encyclopedia has an even blacker black you can use that to make a blanket or wall to surround the sun. It can easily be disassemble afterwards. Now the heat issue, the heat from the sun really only makes it to Mars at best. That is the outer edge of the habitable zone. All the other planets are cold dead rocks or balls of gas, so that shouldn't even be an issue. If the bad guys get that close to our solar system to feel the heat they will see through almost any deception. 2. A giant cloaking field powered by the sun. 3. Using a wormhole to swap the sun for an appropriately sized blackhole. (Matching our suns gravity as exactly as possible.) Downside lack of solar winds will have an unpredictable effect. Powering the wormhole with said blackhole should make getting the power necessary an easy task. As long as they can't detect the solar winds it shouldn't be too hard. You might be able to shift the light out of there visible spectrum. [Answer] # Matrioska Shield If you build a Dyson sphere around the Sun, what you get is a *hot* shell that reradiates in the near infrared. So you build a second shell a few centimeters out, which will reradiate half of the energy. [And then a third shell](https://en.wikipedia.org/wiki/Multi-layer_insulation). In the end, provided there is nonconducting vacuum between the shells, you can radiate as little as you want. # but it won't be enough because the Sun has *already* radiated lots of energy away, and if the swarm is at (say) 200 years out and is approaching at one tenth of the speed of light, they'll see the Sun as it was 20 years before. If they have good memories, and set out towards the Sun a long time ago, the Sun's disappearance would mean nothing. They will still come. # ...or not? Blacking out the Sun is only part of the plan. The obvious thing that anyone would have attempted (and the Galactics surely did) would have been to *investigate* the swarm, using heavily defended probes (probes cooled to next to absolute zero, or equipped with plasma sheaths fit to vaporize anything, or very precise, ultrafast captive needle point defenses and so on. Probes floating inside a liquid bubble of [carboranes](https://en.wikipedia.org/wiki/Carborane_acid). And so on). So they discovered another very likely thing: that the insects actually *sleep* away their travel, with one swarm "aiming" its child swarm towards a likely star, and the "child" drifting for millennia until the heat of the target star thaws the drones, the Queen and the eggs for the cycle to repeat itself. The plan is therefore to light up the path of the incoming swarm using the Matrioska reflectors, to intermittently *revive* as many drones as possible, as far away as possible, *getting them to waste precious energy*. When they come closer, the heat ray will be so intense as to do actual damage to the insects, that they'll have to repair. Then it will vanish, forcing them to hibernate again to save precious resources (and hibernation requires more energy). And when they're frozen again, the cycle will repeat. Long before the tired, depleted swarm reaches the Kuiper belt, the Sun will have been completely shielded, its heat locked in or redirected far away from the swarm. [Statite](https://en.wikipedia.org/wiki/Statite) shields of the stablest materials available, or smaller Dyson spheres, will both supply artificial sunlight to the planets and/or deflect the incoming swarm safely away. Again, munching through hardened [ice XI](https://en.wikipedia.org/wiki/Ice_XI) requires horrendous quantities of energy, gives the insects no sustenance whatsoever, and the little that will get melted will rob them of still more thermal energy. The whole time, humanity will have to hide in darkness, looking worriedly at the black statite disk that blots out the stars. [Answer] Convert it into a Black-hole: If you had unlimited resources/energy, and "near magical" tech, then you might be able to manipulate gravity, making a black-hole out of the star, while not affecting it's gravitational field so you don't throw orbiting bodies off into space. The lack of light might be a new problem though, but ideas for theoretical technology that could utilize black-holes for energy production exist, which could allow for artificial lighting...albeit on a massive scale. [Answer] > > I am hoping that you can make it more explicit what the insects do — do they come and destroy the star and move on, or do they come because of the star and ravage the planets of some resource, or do they just block the light from the star too much… ? > > > I am taking it that the insects are attracted by light, but destroy, not the Sun but the Earth… and then move on. If they actually destroy the Sun, this is all inapplicable. (Equally, it might simply not fit what you want.) (Or perhaps you could have everyone working on making a star that will never go out, to keep these insects busy?) (Or, conversely, you could tweak our own Sun to last all the way through the periodic table, to buy others time… maybe. That is assuming that the insects do not actually attack the Earth, as such.) > > On that theme — if the insects come because of the system’s star, but “attack” the planets, and then leave later to destroy some other solar system, there is presumably some resource that they consume to exhaustion? > > Another take is to shield the Earth as described, and have the insects arrive and destroy the Sun, and then have the problem of starting it up again. > > > My physics is not adequate for this, but I thought the idea might be worth mentioning. As the scientist says in “Back to the Future”, you’re not thinking 4-dimensionally — or, in this case, 3-dimensionally. I know there are problems with orbits changing and what-have-you, but… How about moving the Earth perpendicularly to the plane of the solar system? Other people are far better qualified to flesh out the details (or point out that it is quite unworkable), but here is my starting sketch. You will need a replacement planet where the Earth was, to keep the solar system working as it should. (Another possibility is to leave the Earth as it is, and set up somewhere else, and come back later and fix it back up again, but that sounds pretty boring compared with all this stuff about Dyson spheres and all that.) You will also need something for the Earth to revolve around — perhaps the same mass as the Sun and the same distance, but this is free to change. Conversely, with technology at such a high level, you can probably do without that. I was originally thinking of having another body on the other side of the solar system (perpendicularly), to keep things balanced. (I had some fancy idea about segmented rings that rotate in the same or opposite directions, and bounce up and down through the plane of the solar system, but (a) there are problems with the gravitational effects within the solar system during a pass and (b) (i) either this leaves the Earth behind or (ii) the Earth has to follow, which has problems with orbit mechanics.) This separate (part) solar system would presumably be set up (once it was already far away) to move gradually away from the actual solar system, reach a peak height and start falling down again… throughout the entire time the insects were there. The other alternative implementation of the idea is to redirect the Sun’s energy to a similar point. Anyway, I am distracted with the suspicion that you want the Sun darkened, either because the insects will destroy the Sun or just because that is your existing planning. I just wanted to mention the 3rd dimension. ————— Not sure where to put this. (I am guessing that it belongs in Discussion, but I do not know “where” that is.) [Feel free to move it there, but leave me a link.] Pardon me if I take the liberty… . [You did say that the insects were “planet-devouring”, but I am taking it that your thinking is not settled yet.] It seems to me that you have a fundamental choice to make — do the insects do anything to the Earth directly [or indirectly — see below \* ] or not (and if so what and why). Maybe it is merely that they land on it in large numbers (noting the day/night cycle). [Or possibly the survivors do not know yet… or possibly the insects’ behaviour is not yet properly understood.] If they do not, then the Earthians do not need a shield for the Earth; they just have to survive the event… which, in this case, would be inconsequential unless the insects significantly interfere with or destroy the Sun —— they might • blot out the Sun for a time and then move on (with or without some damage of it) • blot out the Sun, and later destroy it, • destroy it immediately (which would be rather odd), or • not be a problem until they destroy the Sun.) Further, in that case, shielding the Sun before the event might be no less difficult than repairing it afterwards… although there is the issue of them possibly coming back. Offhand, it looks to me as though you do need them to “devour planets”. This works in the immediate sense; we build a Dyson sphere (or some other fancy solution such as my original answer) or we die; their arrival must be prevented. (It is unlikely that any sort of military shielding of the Earth would work.) Note that, given this, it does not really matter whether or not they destroy the Sun; presumably, they leave when the planets are consumed. I am thinking, though, that, in terms of plausible life cycle, a swarm that comes and eats vast amounts of dirt (and possibly gas), reproduces (possibly destroys the star) and moves on is a bit B-grade movie. Maybe it is just how I am putting it, but I am thinking perhaps something more subtle… . The core idea is that these things are phototropic — they go towards the light. If they do not consume the planets, then arguably the only reason they might leave is if they do indeed destroy the Sun… which is not especially “subtle”. Conversely, I am thinking that this — i.e. not eating the Earth — might work better for building a history around. So… they do interfere with the Earth in some way, but not massive military-like destruction. {Asterisk}[footnote/reference] I had a couple of ideas around interfering with orbital mechanics, but I do not think it would work [insufficient mass], so I have deleted it. I thought the rest was okay, so I am still posting this. Independently of that… stopping the Sun from shining would involve some dramatic change, but, even given that, significantly changing its mass would be an even bigger change ( *unless the insects increase vastly in number when procreating, taking the differential mass from the Sun* ). [Passing thought: would a Dyson sphere interfere with orbital stability?] If the insects do do something more subtle that would ultimately ruin the Earth, then the Earthians still do have to prevent them from coming. [I am assuming that their technology level is so high that restarting the Sun is on the cards.] This also has the attraction of involving a slow death (if they do end up coming). …Except that, given the high level of technology, it might be feasible to have the insects come, and do their damage, and leave… and then set about repairing everything. [Again, this might work better for a long history.] Conversely to all that… if the level of available technology is so high, arguably just about anything is not going to be a problem… and conversely again: just because we know *how* to (e.g.) move the Earth does not mean that it is trivial to do it, and similarly for any engineering that requires vast amounts of any resource. Similarly for (eg) building a Dyson sphere; even if it is trivially easy in terms of knowledge, there is still the issue of physically getting the material and building the thing. There is also the possibility of more subtle measures against their life cycle — possibly something discovered accidentally, such as that they are attracted to (military) electromagnetic shields. [Answer] I think the simplest solution from a narrative standpoint would be to spray some sort of "pixie dust" that neutralizes the sun's gravity. It is the force of gravity that drives the nuclear fusion that powers the sun. The bigger the star, the higher the force of gravity, the faster it burns. Therefore, you just need some way to partially neutralize gravity. Not fully. If you do that it will dissipate. Not sure how long it would take for the sun to shed its residual heat once fusion stopped, but if you have pixie dust to turn off gravity, you can have pixie dust "B" to accelerate heat loss, or just absorb it. You then need to explain why the planets don't go spinning off into space now that the sun's gravity is gone, or just less. Oooh! No, you just split the sun into a dozen (three dozen?) little "super Jupiter". Brown dwarfs that are a hundred times bigger than the planet Jupiter, but small enough that they cannot produce nuclear fusion. They stay in the same place, orbiting around one another. The gravity would be the same just more spread out. [Answer] I love your premise, but maybe it would be easier to make earth look uninhabited by putting some surface above the whole thing or just all going underground. So it looks completely void, and the bugs pass by. You in effect snuffed out the sun for earth, but really the light is still shining on an outer shell. Oh, and bonus, everything you talked about as far as your plot would then make sense. Everyone is living in the dark basically for hundreds of years. You could also put into your plot or a book about people trying for years to figure out a way to put out the sun, and have that be the focus that people fight over until some part of civilization realizes that will never work and they just go underground. And the sun-eaters die! [Answer] Your first problem is one of scale. Thinking about a K2 civilization's technology is like asking the artists who painted the cave paintings in France to speculate about smartphones. But moreso. A K1 civilization solution is more imaginable. You'd wrap the Sun in a blanket. That blanket would be extremely hot, but at a modest distance it would be hot in the infrared, not the visual spectrum. The energy it puts out would be *the same* as our Sun, as there is no practical way to store the Sun's energy output; you'll radiate basically all of it as black body heat. That will look a lot different than a star; dumb swarms may not recognize it as a star. It is possible to emit most of the energy in a direction away from the swarm through heroic effort. Now, space is 3d, and the swarm isn't going to be on interplanetary scales until extremely close; so there will be plenty of directions to send the energy until the swarm gets really close. Restricting what directions you are emitting is going to be hard, the more you emit the easier it will be. If we assume this is sufficient to fool the swarm (the swarm might be relatively unintelligent), power is the least of your worries. The system capturing the sun's energy has something like 13 orders of magnitude more power than we use in our civilization, and 10 orders of magnitude more power than would be required to literally hang solar lamps over the entire planet and shine with solar-level light 50% of the time (simulating the sun). That is, 10000000000x more energy than you need to do that. Give or take a 0. For a fraction of the work required to build a Dyson sphere around a Sun, you can build a firmament shell around the Earth. Add in a tight-beam energy transfer system that powers the shell, and the Earth could have *lights* hanging from firmament that simulate daylight and night time and even stars. The exterior of this shell would emit light in the infrared. The material it is made out of would be some kind of unobtanium, possibly forged using the energy of the sun itself. My personal favorite unobtanium nowadays is post-trans uranic elements (PTUs); elements from a hypothetical island of stability far beyond the end of our periodic table that cannot be reached even by neutron-star/neutron-star collisions, but could be reached by a K1 civilization with K2 civilization help. To avoid explaining why neutron-star neutron-star collisions (way outside of K1 energy scales; that is where most of the Universe's gold come from, among other elements) don't produce PTUs, you can require "seed" PTUs to build PTUs using K1 civilization energy scales. The initial PTU produced by the K2 civilization may even have been gifted or left over by a K3 civilization. At these energy scales, living on Earth is an affectation; sort of a wildlife reserve. It would be easier to build planet-scale spaceships or space stations than protect Earth in this way, because we are literally building a space station that encloses the Earth. But in the short term, that might be the least traumatic way the K2 civilization probe can protect civilizations. Not all pre-K1 civilizations will be able to scale up to K1. The K2 civilization probe drops off some Von Neumann worker bots who (a) start encasing the sun (dismantling planets and mining the sun to do so), (b) build the PTU forge, (c) start encasing the intact planets in firmaments. As part of this process, beanstalks are lowered from the firmament. Living spaces in the firmament are provided, as well as launch beanstalks. The conservator civilization's bots encase even relatively small planetoids, like the moons of mars, Luna, Ceres, Charon, and the Kuiper Belt planets, in firmaments. There are also firmament-habitats hanging off the sun's shield. Much of humanity stays home; some leave to colonize the system. Some even turn asteroid-firmaments into generation ships and flee the solar system, carrying along with them some Von Neumann conservator probes. [Answer] If you can synthesize food without plants, then I imagine you're dealing in some kind of star-trek level replicator, which performs nuclear transmutation on "generic" deconstructed matter. If that's the case, and if you're ok with inserting some Kurt Vonnegut-esque handwavium, then your problem is solved by injecting a seed of [some equivalent to Vonnegut's Ice 9] into the sun. Rather than freezing water, but by similar handwavy-principles, this seed triggers an alternative radioactive decay chain in the sun, enabling you to skip a few steps in the typical solar radioactive decay chain, and in short time leaving you with a large hunk of hot lead or bismuth in place of the sun. However, rather than losing tons of energy by means of accelerated decay, the sun simply utilizes its existing energy for a harmless endothermic transmutation into cold shining metal. Then, to reverse the process, you bombard the sun with specialized, energized particles of a similar handwavy nature, adding unstable particulate to the metals and preparing them for transmutation back into a hot sun. The process takes significantly longer, and it would take more energy than what is available on earth. So, cold metals on the sun are harvested, deconstructed, transmuted, reconstituted, and reacted in orbiting space stations, so as to use them as fuel to generate the high-energy particulate used in the process of re-igniting the rest of the sun. For your reference, here's the section in which Ice 9 is explained, in Chapter 20 of Cat's Cradle (excuse the weird text; I got this from [archive.org](https://archive.org/stream/KurtVonnegutCatsCradle/KurtVonnegut-CatsCradle_djvu.txt)): > > "There are several ways," Dr. Breed said to me, "in which certain > liquids can crystal 1 i ze--can f reeze--several ways in which their > atoms can stack and lock in an orderly, rigid way." > > > That old man with spotted hands invited me to think of the several > ways in which cannonballs might be stacked on a courthouse lawn, of > the several ways in which oranges might be packed into a crate. > > > "So it is with atoms in crystals, too; and two different crystals of > the same substance can have quite different physical properties." > > > He told me about a factory that had been growing big crystals of > ethylene diamine tartrate. The crystals were useful in certain > manufacturing operations, he said. But one day the factory discovered > that the crystals it was growing no longer had the properties > desired. The atoms had begun to stack and lock--to freeze--in > different fashion. The liquid that was crystallizing hadn't changed, > but the crystals it was forming were, as far as industrial > applications went, pure junk. > > > How this had come about was a mystery. The theoretical villain, > however, was what Dr. Breed called "a seed." He meant by that a tiny > grain of the undesired crystal pattern. The seed, which had come from > God-only-knows-where , taught the atoms the novel way in which to > stack and lock, to crystallize, to freeze . > > > "Now think about cannonballs on a courthouse lawn or about oranges in > a crate again," he suggested. And he helped me to see that the > pattern of the bottom layers of cannonballs or of oranges determined > how each subsequent layer would stack and lock. "The bottom layer is > the seed of how every cannonball or every orange that comes after is > going to behave, even to an infinite number of cannonballs or > oranges." > > > "Now suppose," chortled Dr. Breed, enjoying himself, "that there were > many possible .ways in which water could crystallize, could freeze. > Suppose that the sort of ice we skate upon and put into highball > s--what we might call > *i ce-one*--i s only one of several types of ice. Suppose water always froze as > *ice-one* on Earth because it had never had a seed to teach it how to form > *ice-two*, *ice-three*, *ice-four* . . . ? And suppose," he rapped on his desk with his old hand again, "that there were one form, which we > will call > *i ce-ni ne*--a crystal as hard as this desk--with a melting point of, let us say, one-hundred degrees Fahrenheit, or, better still, a > melting point of one-hundred-and-thi rty degrees . " > > > [Answer] Your insect swarm of doom (ISOD) is like a heat-seeking missile, guiding itself toward the light of the sun. Fighter jets have tried shielding themselves against guided missiles, but it's an extremely hard thing to do effectively. Instead, they frequently deploy [flares](https://en.wikipedia.org/wiki/Flare#Countermeasure) as a countermeasure. The flares produce an intense heat signature that resembles that of the jet's engine. The jet releases the flare and abruptly changes course, and the missile follows the flare instead of the jet. Hiding the sun is impractical due to the sheer amount of energy you'd have to somehow absorb. Instead, build a space-scale flare, an artificial star the size of a small moon. Fling it out of the solar system towards the ISOD. It's far smaller than the sun but since it's *significantly* closer, its light will be far more intense and the glare will prevent the sun from being seen (like trying to see the stars during the daytime). The ISOD will follow the flare away from any inhabited planets. The trick will be in designing the trajectory: it has to be noticed by the ISOD while it's in the outer parts of the solar system, and when the ISOD catches up to it (or when it burns out) the ISOD needs to be closer to some other star than it is to Sol. The downside of this plan is that your artificial star is [way too small](https://www.space.com/21420-smallest-star-size-red-dwarf.html) to be built like an actual star. It will have to be more like a slow-burning ball of fuel, generating energy through more traditional chemical means than by nuclear fusion. The energy emitted will mimic the output of a star closely enough to fool the ISOD, but will unfortunately also generate massive amounts of exotic, high-energy particles that don't interact well with organic matter. There's no way to ignite this thing and send it on its way without bombarding Earth with enough radiation to cause a mass extinction event. Therefore, your scientists have constructed large-scale shielding systems to block the deadly radiation. This shields also block most of the light and heat from the sun in the areas they cover, so the Earth becomes a patchwork of cold, dark protected areas and regions scoured of life by radiation. ]

[Question] [ Accept that we had a reason to go to Mars, managed to build a colony there, and what we found on Mars is valuable enough to ship back to Earth. There is now a self sustainable colony living under the domes, all made possible because we found out how to make water out of rocks and ice on Mars, and regular cargo ship transfers from Mars to Earth. The colony has been in existence for more than 20 years and now the colonists have to deal with yet one more thing: Children and Christmas. * Does Santa make it from Earth's North Pole to Mars in time when we know that cargo supply ship makes it in half a year? * Do the reindeer survive in space? * Does Santa survive in space? * Will letters to Santa make it physically to Earth if we send them back on cargo ship? Given the fact that Sol (=Mars day) duration is longer, and Mars year is also bit longer, **when to celebrate Christmas?** And ultimately, Christmas started as Pagan festival of winter end. **Would it make more sense** to celebrate, say, dust-storm end on Mars? P.S.: I know this question is on the edge of "too broad" and "opinion based", so if you feel like it should not be here, let me know, and I will remove it [Answer] Since Santa's death fortress is based on the North Pole of Neptune, he shouldn't have too much trouble making it to Mars. He and all of his reindeer are robotic, so they won't have any trouble surviving in space. I imagine that Santa probably wouldn't want to show up the same night as he does on Earth, since it takes time to give presents to all the good girls and boys and punish the naughty with extreme prejudice. (Hint: everyone was naughty.) Then again, he may be able to build a Martian Santa in his workshop to go to Mars in his place and spread holiday cheer and nerve gas. I also imagine that if fuel to get to Mars is expensive, all of the winter holidays will be combined into one so he can carpool with Kwanzabot and the Chanukah Zombie.  [Answer] Fun question! I would expect at the start that Christmas would be celebrated when it happens back on Earth. As a species we'd all celebrate it at the same time (relatively). Meaning that Martians would likely celebrate it twice a (Martian) year. However, what happens as the colony ages and becomes more Martian things will likely change. Some of the change would depend on if those on Mars keep the Earth calendar. Which I'm sure it would take more than 20 years to go away. But if there are seasons on Mars then the locals will have a Martian calendar to mark these events, if there isn't much, then likely they would space out holidays around the year to make merry. For Christmas to stay 'as is' would likely require a reasonable sized bunch of Christians in the mix, but the idea of a season of gift giving would likely stay. Now on to Santa. Most likely Santa would move from Earth to one of the moons in the solar system, maybe one around Jupiter (Europa would be an excellent choice!). This way he can still 'be there watching for naughty and nice' but not be playing favorites to one group or another. He already has control of time and space so adding in another planet shouldn't be too hard. . Of course the reindeer will survive the travels, they are obviously multidimensional beings and don't actually travel between locations so much as shift to the next house on the list! [Answer] It depends on the colonist's world view. # Capitalist can we do it more often? what maximizes profits? # Pagan It should be during the winter solstice. # Catholic/Neo-pagan approximately during the winter solstice is fine, just pick a date that works (by council decision). # Lutheran December 25 as it is on earth. No exceptions. # Revivalist If we contemplate the Hebrew calender, and take into account the barley harvest ... [Answer] In the southern hemisphere, for example in Australia, Christmas is celebrated in the summer. It wasn't moved to winter solstice. So I'd expect it to be the same on Mars. They would just use Earth calendar. Also, Santa Claus is not a part of Christmas in most Christian countries. In many parts of Germany for example, the children are told that Jesus (the Christkind) brings the presents on December 24 (not December 25), while Santa Claus (St. Nikolaus) delivers his gifts on December 6. But maybe they need to adjust their Lord's Prayer: "Thy will be done, on Earth as it is in Heaven" should become "Thy will be done, on Mars as it is in Heaven". :-) [Answer] Your question assumes that most of these new Martians are Christian in heritage and American or British in stock which, at least to me, seems questionable. Most of the world isn't Christian, and most of the Christian world does not celebrate Santa Claus. As far as timing is concerned, I believe that it would likely be normalized to Earth time. Catholics have a tendency towards normalization, and the Orthodox are so rooted in tradition that they haven't adopted the Gregorian Calendar yet (and so Santa gets a two(?) week holiday between completing his different tasks). I see it likely that at most the Pope would need to issue an edict which basically standardizes practices to earth. For non-practicing or non-Christian in heritage, well, I think that if they celebrate Christmas they will follow suit. That is unless some culturally significant event happens which diverts the celebration to some other day. Now, from a what-do-we-tell-the-children perspective, it might be possible to say that "Santa and his helpers deliver" or simply "Santa is magic/a miracle", but I don't really think that much further explanation is needed. After all, a clever child today might ask "how can Santa travel so fast as to reach every home?" and the only real answer is, "He can't. If Santa were really traveling so fast, he would be dead." I will say that I think that a colony on Mars would end the traditional letter to Santa, but I don't think that is something which is held too dearly in mosts' hearts. And anyway, [snail-mail is not the only way to get your list to St. Nick.](http://emailsanta.com/) [Answer] Considering that a Mars colony would be mostly self-sufficient and have few contact with Earth, it would soon develop its own culture with its own holidays based on the Martian calendar. The earth calendar is based on day-cycles and season-cycle as they occur on Earth, because these have a large impact on our daily life. But on Mars, the current light conditions and temperature on Earth are completely irrelevant. It is much more imporatant to pay attention to the Martian day-cycle and season-cycle. That means that Martian settlers would soon lose their attachment to the Earth calendar and would instead get attached to a date- and time-keeping which is based on Martian days and years. Regular celebrations would then also be scheduled according to the Martian calendar. So they would likely celebrate (their equivalent to?) Christmas every 668 mars-days (~686 earth-days). [Answer] I'm not sure if artificial holidays will maintain themselves, but since you are working in a short time frame (20 years is same generation) then most definately, Santa will live on. If you spanned the question to several generations, local mars tradition would start to arise. They may align with Earth holidays (this is due to convenience, kinda how the Canadian 'Family day' holiday aligns with 'Presidents day' in the US'), but they'll start to take on a local twist once you have people who never knew life on Earth start being the primary constituents of Mars. Since your questions revolves around 20 years...then of course, colonists won't be quick to give up their ties to Earth and will readily celebrate holidays in line with the day it occurs on Earth. As it sits, Santa has barely milliseconds at each child's house before moving on and is a fantastical wonder, not a statement of fact. Websites tracking his 'movements' around Earth during Christmas eve (supposed 'satellite' shots of the jolly man) are out there...I can see someone creating a 'radar journy' of Santa's trek from Earth to Mars after his job on earth is done pretty readily as well. [Answer] Isaac Asimov wrote a great short story about *Christmas on Ganymede* which is not only fun with the Earthmen acting out the mythology because the natives they are trying to get along with thought it was some very important Earth thing, but has a twist at the end: the natives think it happens every orbit around Jupiper, or once a week! In other parts of the world, Santa (if he is used at all) doesn't always live at the north pole, though that has spread in parallel since TV. So some variation might be more realistic. Also, look how fast the mythology has grown and changed: Santa's red suit came from Coca Cola (it was green before); the appearance drawn by cartoonist Nast; the Visit poem in 1823; Rudolph was invented in 1939 and went viral in 1949. My parents celebrated Christmas for several years *before Rudolph the Red Nosed Reindeer even existed*. So, the children born on Mars will know the myth however their parents present it to them. The smart folks in the first wave will invent their own spin on things, toung in cheek, to fit their own culture. The youngest kids won't understand logistics etc but have their small and simple world model to work with. Point is, it can change rapidly like fashion, not slow like more serious issues that more stricly follow their parents' way but for small mutations. [Answer] > > Does Santa make it from Earth's North Pole to Mars in time when we > know that cargo supply ship makes it in half a year? > > > Of course! To cover each time zone fully on Earth within one midnight hour, place every gift, etc., Santa must be able to travel faster than the speed of light and slower to stop and place the gifts: which we know to be impossible with physics. Therefore he is dropping in and out of an alternative universe(s) on Christmas Eve. Our physical space doesn't matter much, so it could be Mars or wherever. > > Do the reindeer survive in space? > > > In order to survive the speeds, temperatures, and stresses of their current tasks, they most certainly have the biology to survive in space. > > Does Santa survive in space? > > > Same as above. > > Will letters to Santa make it physically to Earth if we send them > back on cargo ship? > > > They just need to be sent back in time to reach before Earth's December 25! > > And actually, given the fact that Sol (=Mars day) duration is longer, > and Mars year is also bit longer, when to celebrate Christmas? > > > I live in the Middle East, and celebrate Christmas when my family or home-town does. Others celebrate it when their particular cultural hearth celebrates it (for example, Eastern Orthodox celebrate it on the date (Jan 7?) on Earth; I would guess that if it's Earth Dec 25, but Mars MNovemeber 49th (or whatever), it would be celebrated on MNovember 49th. > > And ultimately, Christmas started as Pagan festival of winter end. > Would it make more sense to celebrate, say, dust-storm end on Mars? > > > Australians celebrate it on the 25th of December even though it's the middle of Summer. So I think Martians would celebrate it on Earth's 25th of December as well. They get two Christmaes a year! Each 365(ish) days apart, though. Enjoy! [Answer] As you said it is very broad question. I think it will all depends at several factors. As long as New Martians will be using Earth calendar, Commander Santa will be visiting Mars in his big spaceship piloted by Rudolph The Reindeer But after several decades, colonies will have their own holidays, so who knows, maybe where will be no Xmas anymore, and gifts will be dropped by ET? [Answer] In my experience, peoples tend to accumulate holidays, very few go away. Arbor day will probably fall by the wayside but despite the fact that (to my knowledge) the entire world uses the Gregorian calendar on a day-to-day basis, we still celebrate Chinese New Year, Rosh Hashanah and in Russia, 'Old New Year'. Mars will certainly have its own holidays, e.g. Diaspora Day to celebrate when the first permanent human colony landed, Federation Day, when the first Martian Constitution is ratified. These will likely follow a Martian calendar and recur every 668 Martian days. But Earthly holidays will follow Earthly dates. Chinese New Year will still occur based on the Lunar calendar (which will make no sense to a second generation Martian, let me tell you), if the 20 year old settlement is primarily American, they will celebrate Labor Day based on Earth's day and time, and regardless of origin, Christmas will be December 25th back home. As far as the logistics go, I think the family will be sitting around an artificial tree and electric heater (no open flames!) typing up an email to Santa. I bet that the corporations sponsoring these fledgeling colonies (likely more than one, and yes, still fledgeling after a mere 20 years) will ensure that Santa's presence (presents?) is felt. Santa will probably have to ditch the reindeer though. I bet he gets an upgrade with his sleigh acting more like a Tardis. Santa has had to evolve with the times. We have a gas fireplace at home, and therefore no chimney, but Santa still finds his way in. He has thus far avoided setting off our security system in doing so as well. [Answer] On Earth, the traditional Chinese and Jewish calendars have years which are sometimes 12 months long, and sometimes 13 months long, because instead of dividing the solar year into 12 parts to get a month, they use the unrelated cycle of the Moon's phases for the month. (This uses the Metonic cycle, where 19 years contain 12 years of 12 months, and 7 years of 13 months.) So it's perfectly possible for colonists on Mars to use a calendar that, say, divides the year into 22 months some years, and into 23 months other years, on the same principle - with the Earth solar month of 1/12 of the Earth year used to define the length of the Martian month. Here, there would be a cycle of 7 Martian years, three of which are 22 months long, and four of which are 23 months long - at least as the first approximation; one would eventually have to add or take away a leap month to keep things in sync. So they could celebrate Christmas every 12 months, and keep in sync with people on Earth. This would also simplify paychecks and rents and age qualifications for voting across the two planets. ]

[Question] [ I imagine a planet similar to ours, except for two details: 1. The presence of **everlasting clouds** 2. **No yearly seasons** Explanation: In this world *clouds are very high and thick*, so that sunlight (or starlight, for that matter) only comes through like on a cloudy day here on Earth. There are clouds over deserts (but no rain there) and above the highest mountains. Despite these conditions, enough light and energy reach the planet's crust and allows for life to exist. The *planet's rotation axis is not tilted*, so that there are no seasons. When humanoid civilizations start to appear, they develop myths and religions - usually based on animal figures whom they considered to be gods. Later, after the development of writing and accounting, philosophers start to ponder about the origin of their planet. My question is threefold: **Without ever being able to see stars or planets, how would such civilizations figure out anything about the universe?** **How would the state of their planetary weather shape their development of physics?** **What would it feel like when they managed to send their first rocket beyond the clouds?** [Answer] There are a few things they could learn before they get above the clouds. They can discover that their world is rotating, because [pendulums rotate](https://en.wikipedia.org/wiki/Foucault_pendulum), at a speed dependent on where you are on the surface. They should be able to relate this to day and night, which they do have. They can observe that the tides have two components, one which matches the length of the day, and one that changes over a period of about thirty days. It would take an enormous leap to come up with the correct solution, and they'll probably have a wrong theory about this, but when they get above the clouds, they'll be able to relate what they see to these factors. Their development of physics and some kinds of mathematics will be slower, because they don't have a bunch of quite simple things to be explained in the sky. Their biggest problem will be navigation. They can gradually discover latitude, but it will be slow work. Edit: They have to notice that the transition from night to day (sunrise and sunset, though they don't know that) takes longer in some places than others, and that travelling north or south (magnetic compasses will work and will be very important) changes the time taken for the transition. They should be able to figure out from that, and the rotation of the world, that it is spherical. Once they discover infra-red radiation, they will be able to detect the sun, and just possibly the moon, and this will increase their desire to get above the clouds. [Answer] OK, let's look on the remaining observables: * There is yet day and night * The are climate zones on the cloudy planet from the poles to the equator * They can measure air pressure in dependence of the altitude coming up with Torricelli's law At some point in their history, the intelligent beings on the cloudy planet will realise that it is spherically shaped. They will also realise that they receive light and energy from a source beyond the clouds. They will have some model that either the outer source of light rotates around their planet or that their planet rotates and the source is in some fixed direction. At some point they will decide between those two hypotheses using Foucault's pendulum. They will probably conclude by extrapolating Torricelli's law to high altitudes that there is a vacuum high above their planet. They will wonder about the distance of the external source of light and at some point they will try to send up balloons to break through the clouds and make better observations. After some bad experiences (the first researchers were blinded by the unfiltered light) they will establish observatories on balloons watching the sun and the sky at night. From there on, the further development of their astronomy will not be too different from the astronomy on a planet with clear skies. [Answer] ## Until they achieve flight or mastery of electromagnetism, the space between the earth and the clouds *is* the universe Consider that primitive religions are always built around what the people can actually see or sense. Assuming a similar technological progression, they can learn a great deal about their world without being able to look skyward to the stars. In a more modern comparison, a rural person's view of the world was incredibly limited before the Internet. Everything they knew or talked about came from their tiny sliver of the planet. Now, with the Internet, they can *walk around Rome*, even if they'll never be able to afford to go there. Rome was always there, just now that poor farmer can see it. There's gonna be somebody who decides that they want to see what's above the clouds and builds a machine to do it. When they do get above the clouds, their observations will provide a huge(!) kick in the pants for exploration of space. Flying above the clouds isn't strictly necessary to *see* outside the clouds. Radio telescopes can easily pierce the clouds to see beyond them. Early radio telescopes can image the skies, perhaps before airplanes or rockets can penetrate it. Everyone's view of the universe is inherently limited, by any number of factors. The Universe is always there, just they can't see it. Human culture always expands to the limits of the knowledge available (then tends to keep pushing and get even more knowledge.) [Answer] The logical outcome of perpetual cloud cover is a world that is exceedingly wet. This would have a number of effects, but I'll just list 3 as I'm guessing this is not exactly what you meant. **1. Disease Spreads more Rapidly / Medicine Advances Faster (When Possible)** The very wet environment would help transmit a huge number of pathogens. As a result, people are very motivated to solve medical questions. When advances are possible, those advances occur quickly. But note that not all advances are always possible. Without the microscope, for example, microbiology would not be an available field. Of course the microscope would probably take longer to invent since there was no need at all for anyone to work on improving lenses for Telescopes except for basic navigation or warfare. **2. Cities Form More Slowly** Due to the wet climate breeding parasites people learn fairly early on that living in close quarters with other people is much less advantageous. In fact, it seems like every large community has a massive disease outbreak every year or two that you might better avoid by living further apart and interacting less. The only large/successful cities would be those that evolved following fairly strict practices which - as they would discover many hundreds or thousands of years later - happen to be more hygienic. **3. Shipbuilding & Exploration Occurs Faster** Being very wet, everyone needs ships to go any notable distance. Rivers everywhere. So ship building takes a big leap forward. Exploration of new lands occurs much faster as a result of both increased numbers of ships and faster improvements in ship building techniques. **As for how people feel when they do get above the clouds...** In awe, I would suspect. We were pretty surprised when we got into space and found out it wasn't made of ether, but as we'd been staring up there for a long time we had plenty of evidence to help us get over it. Your people would have no idea about what to expect at all. Send up a plane in the day: The sky is blue and there is a big yellow thing in the sky! Send up a plane at night: No, the sky is black now and there are stars everywhere. And a moon! Only this civilization literally no words for "stars" or "moon", so they have to describe them in other ways. Send up a plane at twilight: No, the sky is reddish! I can see the moon, but no stars??? The huge conflict in the day/night cycle and the discovery of all celestial bodies would be significant drivers to motivate people to build more planes and send them up day and night. Space exploration would probably happen at the first opportunity. Oh, and surely all sorts of religious heck would break loose. [Answer] **Short answer:** They would, eventually Wouldn't they have figured out that something (apparently) rotates around their planet and warms up the environment in intervals? A faint glow perhaps like you would see the sun on a cloudy day. Until one day they try to figure out what this glow is. They would have noticed the clouds are only a short distance away from the land, thus they would assume that the clouds are obstructing their view of this ball of fire. They then invent something that would allow them to see past the clouds, **radio telescopes**. Note that the discovery of radio isn't quite inspired by astronomy. They would then focus on the sun at first, seeing flares and whatnot. But then they see tiny specs scattered among the darker regions of the sky. This is when they discover that perhaps there's much more beyond the clouds than just the Sun. Soon after, they begin to document the behaviour of these specs, noting that most move in a linear direction (stars) while some on curves (planets). Using complex math, they eventually figure out the solar system even without seeing it. The difference is that, they only figure this out **after the invention of the radio telescope**, compared to back then when Galileo discovered Heliocentrism by observing planets and stars, and the Sun. Some years later perhaps, they would invent the rocket to send people beyond the clouds. Might be something disastrous, but eventually they'll see the beauty of space, and in no time, they would be sending telescopes like the James Webb space telescope into space. fin About what they would feel going past the clouds? Scared. The feeling you would get if you find out aliens were real. It makes you doubt a lot of your understanding of the universe. This is a fascinating topic. And correct me if I'm wrong, I'm a programmer, not a scientist. [Answer] Nephology (The science of clouds) would make a nice starting point. By analysing the clouds with remote detectors (radio/radar for instance) they may find that they receive other radio transmission from beyond the clouds, i.e. the stars. On another side note, astronomy developed from astrology so perhaps the study of the clouds came from some other mystic concepts. I'd suggest the word "Nepholonomy" (a play on the astrology/astronomy naming convention). [Answer] ~~All the other~~ Many of the other answers seem to think that a trip above the clouds is necessary for astronomy to begin. This is not necessarily the case. If people develop radio technology, radio waves penetrate clouds as if they are not there. It is possible they will develop a primitive radio telescope to track down the source of errant radio noise. And then astronomy can start with radio astronomy. Though I imagine a trip above the clouds may quickly follow as they discover with their radio telescopes that the source of light each day turns out to be a highly localized radio source that is not diffused by the clouds and it turns out there are innumerable fainter localized sources (stars). And depending on how high the highest clouds on this planet are, it would make astronomy beginning with radio astronomy even more likely. If the clouds are only a couple thousand feet high, all it would take is some hot air balloon or WWI era plane to reach above them. But if they are 60-70 km high as they are on Venus, it will take some seriously high altitude helium or hydrogen balloons or some really advanced aviation technology or rocketry if we assume that the atmosphere is still as thin at those heights as on Earth (if we assume atmospheric density of something like Venus, surface pressure would be almost 90 times as high as on Earth). If the clouds were really that high, even if there are those who believe they can be breached, any early attempts to breach them will be met with failure and only fuel ideas that perhaps it is clouds all the way up forever and that attempting to breach them is as foolish as we would consider trying to reach the end of space. Even if there are early attempts to breach the clouds before the invention of radio telescopes, it make take the invention of radio telescopes before more serious endeavors to breach them succeed if only because the radio telescopes would prove that there is *something* up there besides more featureless clouds. [Answer] It does not have to be a cloudy planet. Simulations of galactic collisions have shown that some stars get flung out alone into space devoid of neighboring stars. The only thing they can see in the night sky are faint smudges of far away galaxies. I have often wondered how beings on this world will interpret the universe. If their solar system has other planets/moons then they can develop astronomy up to a point. If you speculate that they are somehow in a nebula, (though that can imply star forming which changes my initial conditions), then even the distant galaxies can be obscured. Clearly, there would be no evidence for the big bang, dark matter or dark energy, or even supernova to create elements. [Answer] Short answer: You are describing Venus Long answer: The world is vastly different, but should proceed astronomically in a similar manner A canopy of any type of opaque gas will cause a vast warming of the planet. There was a theory with creation scientists that prior to the flood, there was a canopy of water vapor (or alternately hydrogen ice, frozen water and other possibilities) around the Earth that caused an increase in oxygen levels as well as increased atmospheric pressure and decreased ultraviolet radiation that would explain the Biblical timeline of longer lives and of the sudden flood. This [canopy theory](http://creationwiki.org/Canopy_theory) has been all but abandoned due to the massive warming that would be evident from the sun warming the clouds, them radiating the heat to the Earth and then trapping it there in a massive blanket. (details in link). With regard to astronomy, having nothing to see will cause nothing surmised. Depending on the thickness of your canopy, your population will either have no light or a change from brighter to dimmer through the day. Seeing a change in brightness will cause someone to find out why and will spur some to brave the unknown to find out what makes the clouds bright. With increased atmospheric pressure, flight would be easier but dangerous to ascend through the clouds. After solving this they would probably proceed as all other planets we have observed. :) [Answer] Helium filled derigibles with cameras attached. Eventually someone playing with helium (or hydrogen) will think it is neat to fill a balloon and watch it soar. Then one day, they hook a wireless camera to it -- even if they think it'll be lost forever in the clouds, they still want the view of ground. So up it goes. And then it breaks through the cloud layer, and then all the scientists are killed for being heretics and preaching that the world is not the only thing in the universe. But eventually enough people try this and see sun and stars and they move past the "kill the messenger" stage. Heck, they might do it before wireless just by retrieving the camera after it comes back to the ground. I forgot about the low tech route. :-) [Answer] Other than the light/dark change that occurs with day and night, one small link they would have to space is that comets/meteors would still come in on occasion. The second thing that could give them a lot to ponder is the effect of distance from the center of their planet on gravity and atmospheric thickness. Well below cloud level it is easy to notice that the density of the air on earth varies a lot; a one mile change in elevation is noticeable in its effect on your stamina just walking around. Additionally, they might have mountains/balloons that get them far enough from the center of their planet to measure gravitational differences from the surface. These two facts could suggest a 'nothingness' beyond the clouds. In contrast, the occasional appearance of meteors/comets as well as the existence of sunlight would show that there had to be a fair amount of stuff beyond the clouds. You might be able to roughly work out the distance to the sun by solving a system of equations related to light/heat output of a body of a given size at a fixed distance, the gravitational impact of the interaction of their planet and the sun at a fixed distance. If they can see a faint outline of the sun, this would further constrain where it could be. Once they realize how big the sun is, then you can learn that comets/meteors are either orbiting the sun or flying in from some more distant part of the nothingness. Even if the latter is true, some should wind up orbiting instead of hitting the planet; this might let them imagine other planets in the solar system. You can see the effects of planets in each other's orbits, and I can imagine that a sufficiently detailed and really long term study of the tides of their own planet might produce data showing the impact of nearby planets on their moon, assuming they have one. All this study of things orbiting would probably draw some interest into the question of whether or not something was orbiting them. They might reasonably come to look at tides as a potential source of information about celestial bodies orbiting their planet. As others have mentioned, the possibilities grow substantially once you can study light outside the visible range. People have mentioned "awe" and "wonder" as possible reactions to discovering the universe. I'd like to suggest that terror is at least as likely. The sudden realization that the universe is unimaginably vast would probably create a lot of concern about who and what else is out there. [Answer] After being able to light a fire, They'll figure out that light has to have a source. They might initially think it's related to the clouds, but after some simple experiments with water, someone would probably guess that the clouds behave just like regular water vapor. By fast enough transportation (pursuing the sun or climbing ascending a mountain) they can figure out that the light source just moves to a different location and eventually comes back from the other side. After enough exploration they can find out that their world is spherical. They'll notice that they can get back to the same point, no matter which direction they choose to go. These discoveries would lead them to the conclusion that: * Either they hover around the light source. * Or the light source is hovering around them. Now, if they have a moon, they'll find out that there is another object above the clouds (by noticing that there is another, smaller source for light, and there are water tides) that they hover around or it hovers around them. This would lead them to the conclusion: * At least one sky object hovers around their spherical world. By noticing/discovering gravity, and by some physics calculation, they would reach conclusions like: * If you fall/fly fast enough, you can orbit the world. * The moon must be a very big object cause it moves water with its own gravitational field. By some careful measurements and calculation, they can discover that: * The light from the moon is related to the position of the sun. * The moon probably just reflects the sun's light, because it simply produces less light. Lunar and Solar eclipses would lead them to the discovery that: * The sun is further than the moon. When asteroids will fall on their world, they'll discover that something, beyond the clouds is made from a similar material, and by more calculation they would discover, with the assumption that there are a lot more asteroids out there: * If an object is big enough, it would form a sphere. * Moon and sun are probably spherical too. Eventually, with advanced enough technology that would let them observe electromagnetic waves, they could discover a lot more of what's going on in our universe. [Answer] *Short answer*: **They wouldn't have astronomy** *Long answer*: If there's no celestial bodies to be observed, no stars or sun to be recognized, there won't be anything called [Astronomy](https://en.wikipedia.org/wiki/Astronomy) at all. The word [planet](https://en.wikipedia.org/wiki/Planet) (or any word meaning planet) might also not come to existence, simply because it implies there being others of the same (but I won't diverge too much here..). We can deduce that the thing we live on must be spherical, as well as its circumference, as long as we can [observe shadows](https://en.wikipedia.org/wiki/Eratosthenes#Measurement_of_the_Earth.27s_circumference) - thus the way physics develop is unlikely to change all-too-much besides branches such as orbital mechanics, etc. [Answer] Radio astronomy This could be a really excellent opportunity to explore what it would be like if astronomy were discovered at a level of technological development comparable to that of the early 1900s. History could be littered with the corpses of the cooky astronomers (think a mathematician/cosmologist who everyone treated like an insane alchemist), people who inferred the existence of the wider universe from the cycle of days and the tides (if there's a moon or moons). The new radio astronomers would probably be ridiculed for outrageous claims about things nobody can see, only to have the evidence slowly mount that there's a lot going on up there. ]

[Question] [ Missing magnetosphere on Mars keeps popping up. Most likely caused by Mars core being cold, mantle not bubbly enough. [Mars mantle](http://www.space.com/16895-what-is-mars-made-of.html) is dormant, core does not move. What would be good way to get it going? So future martians don't have to spend all the time deep under surface in the tunnels. My wild guesses (which I don't have to time to evaluate now, and for next week, sadly): * Nukes? But it seems to be a lot of nukes, and drilling them deep enough would not be easy. Mantle is thick but not cold. * Asteroid bombardment? That would be a lot of asteroids. Hopefully iron ones - and because energy is added from surface, how to warm the core? Would we have to melt the crust completely? * Iron/nickel asteroids, melted and accelerated to near-c speed (to add more energy per unit of mass added)? Will they tear Mars apart? * Reflected solar energy? Could take a LONG time. * Anything even better? Assume any plausible future technology. I like to add energy closer to core, so surface has better chance to cool faster. But likely such terraforming would take many millions of years. Any better ideas how to do it? One reason **I prefer not to use electromagnets in orbit:** I would like to use planet for experiments with development sapient race. They would be very surprised to see the electromagnets, and would expect gods to take care of any problem. I prefer them to be more self-reliant, and not have to repair magnets every thousand years. I have other planets to terraform for other sapient races. :-) Also thinking some more, months later: such magnets in orbit will for sure apply electromagnetic force on particles, which might slow the satellites and they will need fuel to keep up in the orbit. And huge (acres) of solar panels will also have some resistance, more fuel need for station-keeping. Looks like orbiting magnets are way too much hassle. [Answer] Late answer, just found this article: [Nasa Proposes Magnetic Shield For Mars](https://www.engadget.com/2017/03/06/nasa-proposes-magnetic-shield-for-mars/) The important bit from the article: > > Ask scientists why Mars is cold and dead and they'll usually point to > the death of its magnetic field some 4.2 billion years ago. Without > that protection, solar winds gradually stripped it of most of its > atmosphere. A NASA-led team, however, thinks there's still a chance to > protect what's left -- and human explorers in the process. The > scientists have proposed a magnetic shield that would sit at the L1 > Lagrange Point beyond the planet, creating an artificial magnetosphere > that would deflect solar winds and incoming radiation. Simulations > even suggest that the atmosphere would get thick enough to melt carbon > dioxide ice at Mars' northern pole, sparking a greenhouse gas effect > that would melt water ice and restore some of Mars' oceans. Needless > to say, that would be much friendlier to any long-term visitors. > > > **Edit:** And from this article: <http://www.popularmechanics.com/space/moon-mars/a25493/magnetic-shield-mars-atmosphere/> **Edit 2:** Link to PDF with more detail: <https://www.hou.usra.edu/meetings/V2050/pdf/8250.pdf> [](https://i.stack.imgur.com/tBOd3.png) [Answer] Electromagnets are far more powerful, pound per pound, than planetary magnetic fields. You can overcome the Earth's field with a little bar magnet. So why bother trying to resculpt the planet at all? Park huge electromagnets in a system of orbital stations in such a manner to generate a similar magnetic field as a planet would. Add the zillions of solar energy stations to power them and you are off and running. Sure, it is extremely impractical, but far less so than resculpting the internals of a planet. And the planet would be unaffected by the experimentation. [Answer] **Option 1:** Move it to orbit Jupiter: <https://web.archive.org/web/20150703090935/http://www.planetaryexploration.net/jupiter/io/tidal_heating.html> Tidal forces will heat the interior, restarting the core and presumably your magnetic field. Might take a while but is probably faster than some of the other listed options if you get it close enough. You'll need to move it back and let it cool enough enough to let your secondary earthquakes and volcanic activity die down though. **Option 2:** Move it to orbit Jupiter and leave it inside of Jupiter's magnetic field during your experiments. This has an obvious advantage that you gain an immediate magnetic shield, so you can start right away. But I don't know enough about Jupiter's magnetic field or orbital mechanics to know if this is practical - maybe it would be too close and would be torn apart, or you'd get too much heating/earthquakes for it to be practical. You may also need some sort of added power to keep it habital - I don't know how much heat Jupiter radiates, and you'll get some from the tidal effects, but probably not enough. [Answer] If you are ONLY considering warming the core, I would stick to the induction furnace [Anton Duzenko mentioned](https://worldbuilding.stackexchange.com/a/8895/2113). However I would rather set up an artificial superconducting magnet. Temperature on Mars at the poles can be as low as [-153ºC](http://quest.nasa.gov/aero/planetary/mars.html), which is under the current superconductivity record of [-132ºC](http://en.wikipedia.org/wiki/High-temperature_superconductivity). Therefore, a huge superconducting magnet could be placed under the surface, near the poles. As long as it keeps cool, you can have persistent currents sustaining the field, without the need of a current source. Of course, you should warrant some kind of temperature control or your whole experiment may fail if the electromagnet quenches! Since everything would be installed underground and in an area too cold for inhabitants to reach, you will be safe about their finding the truth, at least for a long time (by then they could have probably realized already by other means). [Answer] Electromagnets. Set one underground on the north pole and a second with the same orientation on the south pole, add current, and voilà, you have a planetary magnetic field. And properly sealed the electromagnets should be stable for millions of years. Mars doesn't have plate tectonics, after all. And a massive installation of what would basically be solid metal with some ceramics for insulation and isolation from environment would be quite stable. Although the poles might migrate over time. Only real question is the source of current. I think you could use the same source that powers the magnetic field on Earth, the internal heat of the mantle. There is a huge difference in the temperature of the surface and the temperature just a few kilometres down. You can tap that temperature differential with thermoelectric power, and you'll have a stable power source for millions of years. Thermoelectric power has no moving parts and involves no chemical reactions. And it will take a long time for the core to cool down so much it will make a difference. And of course, if you want something more compact, you can generate your own heat with long half-life radioisotopes. The point is that it is perfectly possible to create a power plant that produces reliable power for millions of years. And of course, if you absolutely reject electromagnets, building huge permanent magnets instead would still be easier than starting the dynamo with bombarding **the surface**. And obviously it would cause less collateral damage. It might be practical to get the necessary rare earths with asteroid mining. As Oldcat says, iron magnetite or other naturally occurring magnetic minerals should work. You'd just need lots of it. But something that huge would be quite stable and it would kind of look natural. If camouflage and protection from natives mining themselves to extinction is a concern, it should be possible to diffuse the system over the entire planet. Build thousands, tens of thousands, large magnets more or less evenly spread over the planet carefully aligned so they link up to create the magnetic field you want. The magnetic field and the magnets would still be distinctly unnatural, but the natives would be so used to seeing them it wouldn't occur them. The natives might genuinely think that their planet just happens to have lots of magnetic material, probably from meteors, and that it self-aligned to give them a magnetic field. Compared to having two major polar anomalies this would be much more discreet. And a system that diffuse would be difficult to damage. [Answer] I don't know the geology (or areology...) but from what I'm reading you need a liquid metal core, not a melted mantle. If that's true, then you need to deliver a colossal amount of energy into the core, well below the mantle and preferable close to the center - and do it without destroying the surface, and without knocking the planet out of orbit or making unwanted changes to its angular momentum. Here's one idea: Beam subatomic particles into the planet, with speed and density calculated to deliver energy into the core. [Particle Therapy](http://en.wikipedia.org/wiki/Particle_therapy) for a planet, basically. I'm not sure what would work best - neutrinos seem to have too low a cross-section. Maybe kaons, or maybe just neutrons - I don't know enough. You might just dig a hole (or many holes) and shoot (truly enormous amounts of) energetic particles down the holes. Note that the holes don't have to be empty space - they can be filled with anything that is sufficiently transparent to your particle beam. Maybe you could place hyperdense targets (neutronium?) at depth, to stop and absorb a beam of particles that would otherwise not be well absorbed, like neutrinos. Another idea: Program nanomachines to burrow down into the core (replicating as needed) and then construct machinery that concentrates unstable and/or fissionable isotopes, constructing crude fission reactors (like these [Natural nuclear fission reactors](http://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor)). A few would do nothing, but - a billion might generate quite a bit of heat, enough to liquify at least a layer and get things 'going'. [Answer] It may be more entertaining and impossible to just slam Mercury into Mars at such an angle resulting in rotational acceleration. In addition, a resulting ring of debris falling back into the planet would speed up rotation because of some law I don't remember. It's like a person spinning on skates and tucking their arms in, they speed up! It's a great method! Minus, messing up and hitting Earth, missing and losing a planet, not getting the angle right and destroying Mars, altering Mars's orbit in a concerning fashion, hiring enough interns to make it economically feasible to move a planet out of orbit.! While you wait for inspiration on how to move a planet into another planet, we might as well detonate a bunch of nuclear ordinance on the surface to keep the public on their toes and interested. Because interest usually helps with funding I'm told. If all goes well, Mars will gain some mass, be pretty molten, probably spinning a bit. Maybe, you'll have some magnetic fields getting juiced up. And if not, we always have other moons and rocks, do it again! The kids love explosions! You might also want to bombard the surface with icy moons, comets, things with water. Water has a great overlooked ability, because it's heat capacity is so high! The more you strike the surface, the more dust particulate in the air you have, combine that with a growing sea of water, and you'll have a nice sludge ocean, dark in color, with the magnificent head capacity granted by water. This will reduce the albedo of the planet, further heating the planet. Not to mention salt water may assist in the amplification of the magnetosphere. Once you have enough water going, say an global ocean of 25 meters deep or so, blast it with nuclear ordinance! The H2O vapor will increase the greenhouse effect, while allowing electrolytically separated oxygen to rise high into the atmosphere. In this excited state, ozone is more likely to form. So at the end of all this, you have a world with all the things you need. Except it's radioactive as all hell. You have oceans! Sludge ridden, radioactive, likely smelly, but pretty warm! You have Mars spinning, assisting the magnetosphere, making day night cycles a little nicer. You have an atmosphere, rich in ammonia, oxygen, water vapor, nitrogen, and dangerous radioactive elements. But you'll have a nice ozone layer to keep the sun from making it more toxic! The impact from Mercury will likely heat the hell out of the core, but if the trajectory is highly accurate, the planet will heat up just above enough. Ah what a sight to behold, the pristine iron red, now a radioactive grey sludge pit. You know what time it is? Dump a whole heap of a specialized breed of Deinococcus radiodurans bacteria into the oceans, with quicker reproductive cycles and shorter life span. If that that works out, you'll have something that can fair the radiation, while fixing Carbon Dioxide into breathable oxygen. After a bunch of generations of this bacteria dead, they will decompose and release methane gas, which will accelerate global warming. Plant some soya beans all over the place, because they have the genes to make proteins capable of fixing heavy metals in a manor that mitigates damage to plants. Just seed the living hell out of the planet where ever possible. Fix oxygen like crazy, introduce as much radiation resistant flora, bacteria, algae as possible. Let it is sit for a century or 20. I have no time frame for ya. Who knows, one day some lucky people might get to experience two blue marbles. I hope you all enjoyed my wild half plan! [Answer] Nudge a dwarf planet like Ceres or Vesta into orbit around Mars. It may take a longish time to tidally heat the interior but once convection currents are established, a magnetic field comes for free. This option is more in the realm of "possibility" compared to moving Mars into Jupiter orbit or making huge orbiting electromagnets are a bit over the top, relatively speaking. Bombarding the planet only heats the outside and is not a lasting solution. The problem is that I do not know if moving a dwarf planet from the inner system or the outer system is more feasible. If moving something from the outer system is cheaper then Pluto is the ideal candidate. UPDATE 7 Mar 17: Adding an artifical magnetosphere has been discussed by NASA and is apparently feasible! See this [article](https://phys.org/news/2017-03-nasa-magnetic-shield-mars-atmosphere.html) [Answer] Build some kind of an induction oven around the planet and turn it on. It will heat the metal in the mantle and eventually melt it. You can disassemble the oven, transport it to the next planet, and repeat this infinitely. [Answer] I thought bombardment was the way to go - however, I'm liking Ville's natural (no power supply needed) magnets - assuming the science is correct. I don't buy thermoelectric powerplants lasting for millions of years. OTOH, if they're miles below the surface, Martians are unlikely to run into the robots need for irregular maintenance, etc. But natural magnets would be superior, even if they're a much larger engineering project. --- You're going to have a significant cooldown period. But you're planning on evolving races anyways, so you're going to be waiting around a long time anyways. Plus side? You can get the spin up to where you want, and axial-tilt with judicious bombardment. As well as add water. Possibly oxygen if you disassociate the water, and migrate out the hydrogen. You can also monkey with gravity with a sufficient amount of mass added (non-trivial). It's probably going to take a significant amount/number of precisely timed strikes to get what you want going on done. Which is going to be computer guided, possibly machine constructed engines, and a fair amount of delta-V (but, over long enough time periods this isn't all super-hard - and given a longer timeframe, you're definitely going to use gravity-assisted slingshots; perhaps even lengthening Jupiter's rotational period by stealing energy from it). Bombard the [heck] out of it, add iron, melt with that added impact energy, rotate to get a spin going. Then wait to cooldown. Maybe take out hydrogen while you don't have a lot of liquid running around. Seed (since you don't want to wait) with some stuff, depending on how virgin you want your evolution - you could skip the hard parts that took us billions of years, and get right to business. By giving them chloroplasts, mitochondria, and multi-cellular life. More, if you want more. But too much, and you might as well be bioengineering them instead of 'evolving' them. I'd want some math geeks to chime in with how long it'd take to cool, and other things. You might (unlikely) be able to get it cooled down in 1000s of years. But I think hundreds of thousands, or millions might be more reasonable; ie: WAGing here. --- > > Also bombarding with really fast asteroid can change Mars orbit. > > > This is why I said you're going to need a number of different impacts. You'll also (most likely) want to distribute the heat and energy to melt things more evenly. Also, you'll want to avoid shearing off a hunk of Mars creating a major moon, like the Moon. How many? That's a good question. Faster they are going, the fewer you'll need. But the fewer you have, the less you'll increase gravity by. A non-trivial amount, for sure. We need Math for that answer. WAG: Mars == 1/10th of Earth's mass. 7.04377e20 short tons. If I'm not screwing up my exponents: 704,377,000,000,000,000,000 tons. Let's WAG it at minimum of 1/1,000,000,000th of that. :) --- The other option is generate a lot of power (A LOT); probably fusion or matter/antimatter, inside the core(well, more likely the mantle: drilling deep enough is also a non-trivial matter, also requiring a lot of power - but perhaps you can just run plasma-beams to gasify all matter in your way until you get to where you want to go), and then induce a spin in it with electromagnets in space (which will also require A LOT of power). And that's assuming there's enough iron in there to make things happy. You'd need to lower water (maybe small enough chunks will melt in the near-nonexistent atmosphere on re-entry; making that many small chunks of ice is another exercise left to the reader) if you don't want an Arrakis. Frankly, that's a lot of machinery and power you're going to have to generate, merely to attempt to shave off a few hundred thousand to millions of years of cooldown from a molten state. Might be cheaper energy-wise to space-elevator in some refrigerators to pump heat into orbit to make your cooldown from a molten state quicker, if you're that concerned about the time it might take. Water: 1,260,000,000,000,000,000,000 liters of water in Earth's ocean. Assume 1/10th of that for a mass 1/10th of Earth (although is probably less than that). Assume you can get 1 liter of water to vaporize in the atmosphere (I think that may be too large) upon re-entry. That's... a *few* chunks that you've got to separate and get into the atmosphere. Probably need to build an auto-melter that makes snowballs from a larger chunk, and drops them down the gravity well. On the plus side, if you're going for Molten-Mars, these ice chunks can be bigger, and (perhaps? impact adds heat... but how much?) used as a (very minor) part of cooling down the planet. [Answer] Electromagnets! But not to generate the field....lets try using them to restart the core spinning which should generate heat. I have no idea if the energy required to do this is even feasible, but it should make for a fun idea. It'll work best if there is still a layer of liquid iron core or magma separating the two. I have seen theory that the Earths core actually rotates in the opposite direction of the rest of the planet, which causes a great deal of friction and in part responsible for the internal heat...I don't know the validity of the theory for earth, but maybe can be used here Put up a string of electromagnets in a circle around the entirety of the planet. Turn them on and begin rotating the string of magnets around the planet in the reverse direction of the planets rotation...hopefully the iron and nickel rich core are more affected by the magnets and adopt the spin of the electromagnets, changing their rotation in relation to the rest of the planet. A reverse spinning iron core would cause much friction and heat, hopefully giving the mantle the liquid feel you would want here and bringing the rotation needed to cause a magnetic field. I really have no idea if this is anyway feasible, but kinda sounds like a fun experiment...please criticize away. Thoughts? edit to add: I figured I should be able to do a calculation to come up with a 'how much energy required' for this to work...but it's quite difficult to obtain the numbers I would require. First thing is Mar's core size is estimated at anywhere between 6% and 25%...unfortunately that appears to be the extent of our knowledge there. and introduces a margin of error higher than the answer I could give. Second is I have no idea on the state of the Mars core. It is assumed that it is solid, however this is assumption and the extent it has solidified is unknown. If there is a liquid barrier between the core and the mantle (either liquid core or liquid mantle...or both) this would be a bit easier. If it's completely solid and attached, then there would be an initial energy input required to tear the core separate from the mantle. Third...I've got no idea on the sun's potential when it comes to solar energy on Mars, both from sun output and a filtered out from the remaining atmosphere. With all these unknowns, it's really tough to give any form of estimate on the volume of energy we would need nor the volume of energy that could be harvested to fuel this. If it's for a story, large scale fusion might be a better alternative as it can provide an extreme amount of energy and you really wouldn't care about the size of the fusion reactor (or if it's cold fusion for that matter) since it can be dismantled after the desired result is achieved. Maybe you can get a more physics oriented person to answer this with actual numbers [Answer] Moving Mars into an orbit around Jupiter would mean moving it out of the goldilocks zone which is not desirable. Why not cut up the smaller of Mars's moons into asteroid sized pieces and bombard the Olympus Mons volcano with it to re-melt its maga. Then move Mars largest moon into a lower orbit to stir the tides. That at least is do-able and should melt the permafrost and restore the sea to its former level. Re-melting the magma should create a magnetic field and assist in retaining a life sustaining atmosphere gleaned from gases issuing from Olympus Mons's eruption events which are not likely to be radio active. [Answer] Since you're going to need more planetary mass to hold whatever atmosphere you install after the magnetic field reboots, why not consider the current entirety of the planet to be the core of your future world. Melt it where it stands, saving you the trouble of trying to melt only the core while leaving its surface solid. While the cooks are heating up the planet, scavenge every available meteor and unused moon within range and construct two enormous hollow half-spheres. Bring those half-spheres together to surround your now molten mars and weld their seams tight. Instant Earth 2! [Answer] If you want play the greatest game of pool ever played, take Io, the innermost most moon of Jupiter, and give it a little nudge on a path that sends it out in a gravity-assisted slingshot just barely leaving Jupiter's orbit on a path towards Mars where it can be picked up as a moon. Io should then begin tugging on the mantle of Mars, tidal heating it in the process to begin melting. Given that Io is actually bigger than the moon, and that Mars is much smaller than Earth, you should see a lot of tidal action, quick in perhaps geological terms, maybe not so in human ones. There are several other tricks you can do with this too, including sending Io on a "close call" shot to slow the Martian orbital period down to send it closer to the sun, warming it up a little bit. Mars's distance from Sol dictates that if you plan on plonking oceans down by sending comets or a small moon like Enceladus or Miranda down, your going to have very large glaciers that will further cool the planet down as ice forms and reflects light away. Forests and grassland might still be possible around the equators however. The downside, or possible upside to this depending on salt's possible effects on magnetic fields, is that depending on the salinity content of Enceladus, or whatever celestial body you chose, combined with much of the water turning into glaciers, is you might get an ocean with an extreme salt content. It could be like Earth's oceans, or it might be a massive "dead" sea. If done in a a very precise manner, you could get most of the water and ice from say, Enceladus falling down to the planet in large chunks by a close fly by in-and-out without the rocky core itself crashing into the planet and ejecting much of the new "ocean" back into space...probably anyway. Also, if you plan on building coastal cities or settlements, I'd highly not recommend anything permanent. The decreased mass of Mars combined with the mass of Io means that oceanic tidal waves will be rather...big. Close flybys should also create some heat in the process from the friction, but unless you get your calculations spot on, which is very rare when considering all the factors that go into this, Io shouldn't be tidally locked to Mars. If Io is spinning much faster than what is necessary for tidal locking, the slowing of Io should transfer heat as well. Unfortunately for this plan, this requires moving some very large orbs. Luckily for us, going with gravity and sending things towards objects is much easier than trying to brute force them out, but even so, moving large objects is still a major task, and it requires sapient people that are willing to take the risk of the pool game ending very badly. Depending on the timescale of this plan, you might want to accelerate the growth of life by creating a few temporary orbital space stations with artificial magnetic fields around the planet, or perhaps just one big one at the L1 Lagrange point, to keep the first life sent down safe to get things started. The satellites could dismantle themselves afterward, be sent on a collision course somewhere else, or moved on where they are needed elsewhere, perhaps as magnetic shields for the (remaining) Jovian moons. You could also run with the electromagnetic plan, either at the poles all over the place. By giving life some breathing room where it can get to work without getting zapped by solar flares or galactic cosmic rays, moss and lichen can start the soil formation process in primary ecological succession. Given it enough time, and voila! Traces of soil! Throw some microbes down there, send a few animals, follow it with a bunch of dirt seeds, and soon you can start planting forests. Ocean life if you have a "dead" sea is a bit trickier, but bio-engineering could be done. Once the satellites go poof are venture off to another places, you got Earth 2.0 How you move Io is another problem in of itself. You could try bombarding it with asteroids, or possibly playing the same trick with a tiny asteroid into one of the tiny asteroid-like moons of Jupiter, though I suspect even that might take a lot of energy, and a lot of rocks. You could use mirrors connected to a massive tether, and then paint Io in silver and then deflect light at it, or possibly use a bunch of fusion reactors to power massive flashlights aimed at the surface. Or could you could try the mirror tether trick, and instead of using sunlight, you tap into the magnetic field of Io with all those ions sent from Jupiter, and then shoot light at it to deflect the photons away and thus push the moon. Another option is guns. A lot of guns. Massive Gauss cannon arrays shooting material out into space, thought that would take a lot of time, energy, and well...guns. On the flip side, you could plonk targets down and make Io into the largest man-made shooting range. Maybe make into a stellar academy for whatever futuristic navies are out there, and make a lot of money in the process...or just a lot of fun shooting things. On a side note, an icy cold glacier world might be a good thing for Mars in the long run. Martian low gravity means that retaining water vapor is difficult, and coupled with higher temperatures atmosphere retention becomes more difficult. This is because at super high altitudes Earth can get extremely hot, but the density is so low you will still freeze to death. (Assuming you don't die of the lack of oxygen first, that is) At high temperatures, those atoms are zipping around very fast, and couple that with solar radiation and some atmosphere loss is going to happen. Water Vapor is especially prone to this, and can actually create rivers of ions into the upper atmosphere to be stripped away. The colder a planet, the less atmosphere loss you have. On the plus side, if the equator is warm enough for forests, one could possibly enjoy a nice walk in a Conifer-forested Mariner Valley. We at Allen Inc. wish you good luck in your terraforming project sir! [Answer] Due to radon outgassing on planet Earth it is theorized there is a 5 mile diameter ball of reacting uranium at Earth's core of which helps maintain the core's heat. Save for the radon, Mar's mantle would shield the surface from a reacting mass of uranium should it be placed there. Simply start a reacting mass on the surface and let it melt it's way to the core. Continuous additions would fuel the "fire." The breeder reaction approach would be the way to go to maximize energy generation. [Answer] No adequate terraforming of Mars or its magnetic field jump start will ever be possible without the presence of advanced nanotechnology as many stated in here, altogether with the development of He-3 fusion reactors for space propulsion, that would make a round-trip to Saturn possible in just a months period. Only when that time comes - in about only 50 yrs from now, more or less if we don't get to f\*\*k things terribly down here in forms of a nuclear holocaust - that we will finally come to develop these super advanced nanomachines, able of being self sustainable like super viruses or microbial life and performing a vast number of things from 3D printing , to matter transmutation, to super heavy matter synthesis, that will set us free of any limitations and promote our civilization to the next level. This would render our efforts on Mars terraforming more possible than ever before. Today, in several labs, there have been advances in nanotechnology the likes of which were never met before. There are lab nanomachines today that are capable of chemical transmutation of matter, and that means everything in the case of terraforming a planet to match our ecosystem. * Means that we could find a way to control abundant quantities of CO2 at the precise levels required to generate a greenhouse effect more efficiently than any microbial life does here on earth, and, actually, in a jiffy. * Means that we can create huge quantities of ferrous materials transmutating the martian bedrock many hundreds of miles deep, kilometers wide, to make artificial super magnets embedded deep inside the martian mantle or even * inject to the core huge quantities of artificial super condensed matter, not available today but quite achievable under the use of extreme nanotechnology, thus, increasing the martian planetary mass / and in so doing, boosting the gravity field Mars is so much missing today due to its small size. Eg. If we can double the martian gravity, that's gonna rise over 60% that of the Earth, close to Venusian levels, rendering the planet capable of holding all the necessary volatiles to form a more Earthly-like atmosphere in the end. * Also, it means that, advanced nanomachines will be continually balancing the presence of the gases in the atmosphere, or even boost the creation of the ozone layer, to protect martian life from the intense solar UV radiation.So: No more need for bacteria or plate tectonics for any of this. One thing though very serious as already mentioned is that, salt water all along with metal ions is essential into sustaining or even increasing the magnetic field effect BIG TIME, due to the manipulation of all those free electrons produced by the solar wind itself, as it happens here on Earth, so this excessive current is positively fed back to the planetary dynamo, to effectively increase the magnetic field intensity. It's theorized that, the main reason that the magnetic field on Mars failed completely, was because Mars slowly lost its atmosphere and liquid water due to the low gravity, besides solar ripping, so no more salty oceans means no more water currents, no more positive feedback of any telluric electric activity too. So how to remedy the water shortage situation? * Well, literally millions of huge ice boulders the size of one miles each, will be carried from Saturnian rings or the Jovian satellites and will be used to bombard Mars,thus, enriching the atmosphere with all the water needed to flood the planet, as its estimated there are over 10,000 times(!) the amount of water existing here on Earth, that's trapped in Saturn's ring system, quite huge quantities of it indeed. * Advanced spacecrafts, equipped with He-3 powered ion boosters can be used for transferring all this material to a collision course to Mars, thus, increasing the thermal load on a planetary level too, indeed a very useful byproduct. During this process: * Millions of the spacecrafts could be constructed by the sheer use of nanotechnology from scratch, and even without the slightest human intervention. * Millions of tons of high grade radioactive material will be collected by nanomachines from Jovian moons and asteroids , and sent on Mars to be used for ejecting them into the planetary core by using thousands plasma-drills, that will lead huge payloads of this radioactive stuff right to the heart of the martian core! * If we get to inject a mass of half a mile radius of radioactive material into the martian core, then it's gonna be hot enough to last for billions of years of its own, without any other additional aiding mechanisms, such as tidal stressing etc. * The mantle will start to melt also, causing huge marsquakes & volcanic activity in the process, but that's an inevitable side effect we just crave for , as it will also help jump-starting the martian plate tectonics that are now inactive. * All along with this, huge amounts of super dense, artificially constructed "exotic" matter will be injected to the core. The source materials will be obtained by trillions of mining nanobots from the asteroid belt, and initially it will be dropped in designated areas to also aid in adding more thermal load to the planet, and then in the process it will be collected by trillions of specialized nanomachines and reshaped into huge cubes, ready to be used for the production of this super heavy material. Also, the planetoid Ceres will be carefully driven by billions of ion thrusters, on a very close martian orbit, rotating twice or more a day around the planet in the beginning. this will help : * To jump start an intense tidal friction effect on a planetary level and help remelting the martian core . * To provide a stabilizing mechanism for mars and prevent the polar regions from wobbling around as is the case today! To achieve this, the orbit will be set just above the Roche limit, and Ceres will become the new martian moon, that will be slowly rotating away from mars by a few inches a year exactly the way our own moon does , but, boosting on remelting of the martian core in the process and slightly reducing the martian daily rotation by a few nanoseconds per year, which is now about 24.4+ hours. * The new martian moon will be escorting mars till the End of Days of our solar system and Mars will be completely terraformed, having obtained about 60% the gravity of Earth, covered by immense salty oceans with a 2+ psi of atmospheric pressure and a thriving biosphere , identical to ours and with minimum genetic interference. * Due to mutual tidal friction, perhaps the huge internal water deposits of the Cerian moon will also slowly liquefy if not already,forming underground oceans, and its core will also start heating up as well. We've seen this happening to all Jovian moons, and elsewhere too . * The new pairing will probably turn to a twin planetary system, as Ceres would be capable of supporting Life underground and act as an excellent generation ship for Mankind and our evolutionary offspring , should we ever decide to leave this solar system or move further than Jupiter, if the sun gets too red to devour even mars! Of course, many other planetoids of the asteroid belt would be internally "terraformed" by our nanomachines to be used likewise, but that's another story all by its own. Of course , what I'm now describing is yet, within the realm of magic, but just think of what the level of our technology was only 50 yrs back and you'll see that its quite feasible if we don't mess things up in the process. It's quite possible under this perspective, that, Mars would fully transform to an earth-like planet in just a few generations, not thousands, not millions of years ahead. All we need is to get down our asses and find out how to make nanomachines just a few hundred molecules wide in size, many times smaller than the smallest viruses, capable of performing nothing more than sheer wonders/ under our contemporary perspective. It's gonna be quite a challenge, but not an impossible one. And then, those wondrous super machines will make all the dirty work for us, and we'll just have to sit down and watch the show. EDIT: And for those rude enough to even make themselves more ridicule in the process / an i mean you Mr.Masiar, by all means, here's my answer that im not able to post as a reply to your personal insults that you call a "reply" ,because its considered too damn long by the authoring system. Here goes : "Quite the contrary: Matter chemical transmutation / as already quoted by me is a real fact. I'd read an article a decade ago that a micromachine was constructed to leave a trail of pure copper behind it while moving forward on a substance that was not copper at all. Made a huge impression to me back then. i don't remember any more details on that article, but the fact that it was published a decade ago is a very good reason for me to theorize that the outcome of more advance nanomachines will be viable in a period of at least 50 yrs from now.Already in a decade or so, we're gonna see the first real fully functional Micro-machinery, working within the human tissue- and that's no exaggerating at all.Of course these machines will be controlled by a huge neural network as each of them will be a part of a certain substructure within the network, specialized and capable of changing roles within the structure.So no references for any "sentient" matter, here. And im sure enough that , in fifty years from now, the level of our knowledge of understanding will be so VASTLY different from today's , that the capabilities of that technological Era will resemble to contemporary "us", exactly as you characterized it, and exactly as i DID refer to it : PURE MAGIC. No mambo jumbo though , as you so rudely suggested, for may i state that Arthur C. Clarke's projections about space satellites, or even heavier than air flight machines and landing on the moon , were also considered "mambo jambo" science from the "brilliant" minds of those eras back then.So, No mambo jambo stuff, sir. Just pure 21st/end century **SCIENCE**, that still, today, is totally uncomprehending to any of us / albeit a small number of experts, both on top of the tops of advance research & as deep in the underground military labs as it gets." [Answer] Interesting but we are still speculating what the Martian core is made of. Certainly Mars needs a decent 'outrigger' like a moon to maintain a tidal effect on the core and keep it molted like a cosmic Kenwood. I think that a realistic but dangerous solution is the nano tech approach. A cold iron liquid conversion scheme might just get the outer-outer solid core moving again. Depending on the lifetime and penetration of the nanotech, a nano asset could be introduced to convert the solid surface part of the outer-outer core at least. Just pure speculation as to what the penetration might be before the assets are melted. Given that the devices are not made of some exotic fantastical material like neutronium they would only withstand a limited amount of abuse. The project would introduce them at simultaneous points around the Martian globe and then they would be administered in waves to the core. This might be quicker than one might imagine bearing in mind that the assets are to be self-replicating. The simplicity of this plan is the tiny amount of assets that need to be introduced the core. The assets can be introduced via a larger self guiding nano-asset that is built around a payload of replicating core deliquesce devices (CDDs). Stage 2 is simpler. If the outer core is liquid (at least 300 miles deep as an unsubstantiated guess with no math to back it up...yet) then the rotation of the planet should do the rest of the work much like when you turn a cup of cappuccino quickly and the cup moves but the liquid does not. Initially the momentum of the planet would keep the core at a relative rotational speed to the planet. The introduction of the CDDs should be in a wave form deliberately to cancel the momentum of the planet. Waves can then be cancelled by introducing equal or opposite waves from the same volume of CDDs to phase in the opposite direction. A wave effect could be used to start the core but it would be better to use it to stop the outer liquid and let the rest of Mars do the heavy lifting as far as rotating the planet around the liquid core. Friction should then heat up the 'cold' liquid iron and friction should heat it up to a reasonable working temperature that would result in the loss of all the asset CDDs but hopefully they would have completed their mission by this point. The duration of this mission would be purely speculative but under the right circumstances would be substantially less than millions of years or physically moving the planet or slamming asteroids into the surface of the planet. Depending on the success of chain-reaction replication Mars core radius is approx 1700 km therefore V ≈ 2.06×10(tenth power) The design of the CDD has three directives:- 1. Swim as instructed 2. Deliquesce the outer outer core. 3. Replication from the raw materials as a consequence and by-product of deliquesance. Once the core was flowing statically in comparison to the planet we could view this as a static commutator model. The inner core would still be moving at the relative surface velocity. With any luck this would re-start the magnetosphere. One would imagine the next team will guide a couple of comets to the surface. A matched velocity collision would do the least damage to the integrity of the motion of the now moving (relatively) outer core. One would assume that the rotation would also stabilize procession and affect day, and season length. In an ideal universe the introduction of a moon equitable to Earths' in relation to Mars' size would stabilize and create enough pull on the planet to maintain liquidity of the outer core and enough fluidity to cause a moving mantle. The downside of this might mean extra tectonic movements and volcanic/earthquakes. (yes we still call them Earthquakes on Mars. It would be pretentious to call them Marsquakes) To recap what we get out of this is 1. Magnetosphere 2. Surface life 3. Life period reproduction cycle regulation of a moon. What we dont get is the cleanup of some of the chlorinated hydrocarbon perchlorates. If we added water extraneously from comets and the suchlike most likely would also contain some toxins that would need to be treated in some way. Some believe that a high velocity impact would liquify and distil the water from a comet but how long it would take to condense onto the planets surface in the form of an ocean is anyone's guess and would need extensive modelling before it was executed. CDD impact on the core would be easier to model based on controllable, programmable variables. The pros outweigh the cons and the main con is losing contact and control of the CDDs or them being used inappropriately which could be disastrous in a habitable environment. Thus a self disassembly code would be a fail safe in such contingencies. [Answer] Three solutions come to mind, in order of horrendous difficulty: The easiest way to heat a planet is tidal warping, which "only" requires that you park a small planetary mass next to it that is sufficiently large and close to create Roche Tides that flex the fabric of the world and create frictional heating. They believe this is what heats Io's sulfur core and keeps Europa's sub-ice ocean liquid, if so, it's effective but you'd have to move a worldlet, or several, without breaking it up and then put it into an orbit that is constantly on the verge of breaking it up without it actually falling apart. You might be able to start by altering the orbits of Phobos and Deimos, assuming you have a lot of experience with manipulating those kinds of orbital masses. Theoretically you could introduce enough radioactive isotopes into a planet that the heat of decay would cause the kind of melting you want and it could have the advantage of long-term sustained heat input if you use something with a long half-life, high emissions, and lots of radioactive radiogenic isotopes in it's decay sequence. I can think of no feasible delivery system, also no source of the volume of radioactive isotopes that would be required. You could also use magnetic induction to heat a planet but that requires building a high power rotating magnetic field *around a planet* I'm not sure but I *think* you could build a planet, or something similar, a bit easier than an induction coil for one. If one used large highly magnetic masses, free orbiting, one might be able to combine a Roche Tide heating with localised, rather than planet-wide, magnetic induction. That's a big maybe, I'm not sure if you can create "localised induction" on any scale (my experience of induction is that completely within a magnetic field used to heat metal objects for case hardening) let alone with a planet. Even if you have the tech and resources for any method there's a problem with heating something the size of Mars, it's too small to stay hot. That is to say the "Cubed/Squared Law" is against you when it comes to heat retention, Mars has a relatively small heat retaining volume compared to it's radiating surface area so any amount of heat you care to pump in pours out really fast, fast in geological terms, a few millions of years to bleed away the heat it was born with (and all the heat radioactive decay can currently give it) compared to Earth which is still hot Billions of years later. As a side note if you want to read some thoughts on planetary engineering on this scale I suggest the works of Larry Niven he's an engineer turned science fiction writer, in particular *Building Harlequin's Moon* in which they make a planet in orbit of a gas giant. Also the essay *Bigger Than Worlds* which explores non-planetary living spaces. [Answer] > > Assume any plausible future technology. > > > Okay, I'm going to posit *one* handwavium technology and try to do everything with that. **Wormholes**. A technology is perfected that allows opening wormholes of reasonable size at a distance. The "portals" are exactly that, portals in space - they do not connect points faster than light (rather the opposite). But given sufficient energy to make things balance out and prevent a perpetual motion machine from being set up, it becomes possible to connect Mars' core with a region somewhere *inside the Sun*. Obvious weapon applications aside, this would easily supply all the heat necessary to re-melt the core. Restarting the geodynamo is more complicated, but transferring momentum and charge from the same source should do the trick. [Answer] The 30 holes with 1,500 warheads sounds plausible except that we barely have technology to reach the bottom of Earth's crust, nevermind a planet's core. A network of solar powered EM satellites seems the best route for the next hundred or thousand years with maintenance, but the surface of Mars will never be like that of Earth because its mass is 1/10th our planet and it could not hold onto water vapor at a comfortable temperature. The most likely scenario is a rich CO2 atmosphere blanketing a frozen tundra, though with free oxygen at >10%( by an educated guess). This is very habitable by human standards, but it would take millennia for life to develop( aside from what we engineer) and the chance of healthy native intelligence is low. You have to think like the big boys if you want to play God. p.s. the satellites could also be used for planetwide WiFi... just saying. [Answer] Combination drilling deep into the mantle, nuclear waste and other heavy/nuclear material, nuclear weapons, and a tangential drilling angle. So drill multiple holes down into the mantle, near to the border of the mantle and core. Make sure they are at a tangential angle, all aimed to increase the rotation rate of the core/planet. Next dump all our nuclear waste, as well as dense metals, and metals that will react favorably to a nuclear explosion (in a giving off heat kind a way) into the bottom of the holes. Lastly take all 15,000 current nuclear weapons on Earth, divide them equally between all holes, and with as great a velocity as you can ram them into the holes and at impact with your material simultaneously detonate them all. This could increase the rotation of the core/planet, increase the temperature of the mantle at the core border, possibly sink more heavy/fissile material deeper into the core, and kick start the dynamo with newly hot liquified mantle at the cores border. Bonus, all nuclear waste and weapons are gone, the biggest hurdle is the drilling all the rest can be done today. [Answer] There are some initial designs for an artificial magnetic field for *Earth*. The reason is that Earth's magnetic field goes through a cycle of reversals of polarity and these Japanese scientists hypothesized that the weaker magnetic field during the period of transition would cause technological chaos and increased radiation exposure and so an artifical magnetic field would be needed: <http://www.nifs.ac.jp/report/NIFS-886.pdf> They propose 12 superconducting rings around the Earth. Mars is of course half the radius of the Earth, and would need fewer rings and each ring would be much shorter. Mars is also geologically stable (compared to Earth), has no severe storms, no huge bodies of water, so it is much more practical to build such a system on Mars. [Answer] Frame challenge: there is no reason to due this. 1. Increasing the mass of the atmosphere would provide sufficient radiation shielding for anyone on the surface. [Mar's current atmosphere already provides enough protection that someone on the surface would receive less radiation than astronauts on the ISS](https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA03480). 2. Atmospheric loss due to solar winds takes place on geologic timescales ([And some say that it's not a significant factor at all](https://www.sciencedaily.com/releases/2017/12/171207140513.htm)). If you can build an atmosphere there in the first place, topping it off every few million years is trivial. There is also [evidence that loss due to solar winds is significantly caused by the Sun's ultraviolet radiation](https://www.esa.int/Our_Activities/Space_Science/Mars_Express/Leaky_atmosphere_linked_to_lightweight_planet). A magnetic field would do nothing to stop these photons. ]

[Question] [ Assume you traveled back in time to the middle ages, and you brought with you the schematics of a fully automatic firearm. Could a group of experienced smiths and jewelers reproduce it? What would the major issues be? There are some guns which were designed for simplicity and easy of production, like the British [Sten](https://www.youtube.com/watch?v=jt70ilN_PgU), so let's assume you have chosen a very simplistic gun. I guess their job would be made a little easier if you * brought back an actual gun they can study and disassemble * you arrived to the late middle ages when the first [very crude](http://en.wikipedia.org/wiki/Hand_cannon) firearms started to make their appearance. I guess the biggest problem would be the production of reliable ammunition. People weren't using muzzle-loaders for five centuries because they were too stupid to realize that they could reload faster if they had a cartridge instead of loose gunpowder, they just didn't have any reliable means to ignite the powder. This means you would probably need a recipe for the chemicals required for a primer and for smokeless gunpowder. Would medieval people be able to produce them without having access to modern industrial infrastructure? [Answer] **No automatic weapons, without industrialization** You need machines to make modern firearms. You can't hand-rifle a barrel. And while a hand-operated barrel-rifling machine can be made, this is not the best. Et al. for every other thing. Something like 90 machines were needed for the Enfield (iirc). Plus you need good materials. Springs? You don't build those out of pig iron. Etc, etc. High quality (uniform!) steel. Precision milled brass cartridges. Getting cordite and/or smokeless powder - a lot better chemical industry than existed. You're not going to get nitrogylcerine from your salt-peter pit, and your sulfur mines. People weren't stupid for using muzzle-loaders, when your powder is completely variable, you don't pick a weight and put it into a package, because you'll get different results with different batches. You'd have to be mixing huge batches, proofing them, and then measuring each in different amounts... Whereas you can just add s'more powder if what you've currently got in the bag isn't working well enough. Corning. Glazing. Etc, etc. Medieval workers don't even have the tools to do the measuring to get started on some of that stuff. In order to get some of the scales needed, the guy who made the weights and measures for the US had to design a machine to cut the dials - because a human running a machine to cut the dials eventually threw them off because his body-heat changed the graduations\*... If they're dealing with 'recipes' then they're not going to be able to do anything fine. You have to be able to *measure*. And to do that you need to have tools to do it with. You need precision and accuracy, and that's difficult to just whip up in the shop by drawing something. Plus, you've got problems even in *reading* schematics. Even in WW2, we had to completely redo the Bofors 40mm schematics, because they weren't precise (they also had to be redone so that they could be mass-manufactured, instead of hand-finished), and Americans couldn't read them (Europeans used the [first angle of projection](http://www.allpar.com/history/military/bofors.html)). A schematic is only as good as your ability to read it/understand what it's saying. If I tell you (via schematics) to put a 1/2" hole in a plate, you've probably got an idea of how you'd do it. But that's only because you're familiar with power drills, and maybe a drill press. It's probable that you don't know how to put spiral grooves on the inside of a tube. My schematics tell you to put a 1:7 twist in the barrel. How do you change that information into reality? If you're a regular Joe, you probably have no clue. Your smith is going to have the same problem. Or your schematic says, use "AISI-SAE 4130" for this part. Your smith looks up at you and says, "What is that?". Even, "How do I make that?", if you don't know what it is. Did you bring an industrial dictionary? Did you bring ANSI standards with you? Did you bring testing equipment (or calibrations to make testing equipment) to test potential steel recipes to see if they'll qualify? You could go to Kentucky-style rifles pretty easily (well, with good materials, and be willing to make a some machines/jigs). Past that... things start to get tricky for medieval workers operating without an industrial base. --- +1 for user2448131's ideas: revolver and gatling gun - still are going to need a number of things that're a stretch for Medieval technology --- \* circular dividing engine. That device, purchased in 1841 from Troughton and Simms of London by Hassler, was intended to be hand operated. Its function was to engrave degrees and fractions thereof onto a circular disk with high precision. It was found, however, that the body heat of the operator could measurably distort the spacings between successive graduations. [Answer] Quite an interesting question. First let me say that I am experienced in machinining and toolmaking (a sub-discipline of machining), as well as being an amateur chemist and a student of industrial history, so I am well able to answer this question. The other answers really are guesses by non-experts and are incorrect in many of their details. **Possible with Some Caveats** It would be possible with some caveats. First, you would need to alter the weapon design to accommodate their abilities. Secondly, you would need to provide more than schematics; they would need to know certain processes and the steps to perform them as well as have plans for tooling needed to make the parts. However, if you gave detailed instructions for the different processes, it would be possible, given enough time and money. **Problem 1: Producing Tool Steel** The biggest problem would be getting tool steel. Tool steel is not needed for the gun itself but is needed for making the tools to make the gun, the main thing being files. Once you can get them making a good file, that is 90% of the problem. You may think it funny, that something as simple as a file is the key, but that is the truth. Tool steel requires manganese, chromium and molybdenum, so you would need to help them locate, identify and purify those metals. **Problem 2: Measurements** As long as you provided an example weapon or EXTREMELY detailed drawings they could measure everything with calipers, but it would be very, very tedious. If you provided them with the key to making a casting metal, such as cerrosafe that would make it much easier. To make this they will need bismuth and antimony, which once again, would have to be located, identified and purified. **Problem 3: Propellant** For the ammunition they would need to make a corned propellant and primer. This requires pure sulfuric acid, nitric acid and various other chemicals. They would need to be taught how to make these chemicals. Without high quality glassware and catalysts it would be possible, but very tedious to do this. **Problem 4: Springs** To make the springs they will need spring steel, wire dies and a winding machine. Since we already have manganese and tool steel from Problem 1, this would not be too hard. **Problem 5: Cartridge Casings** Modern cartridge casings are forged using complex dies. Making these dies would be extremely tedious and difficult for them. As an alternative, you could make the cartridges by silver soldering them from hammered sheet bronze, much easier. **Problem 6: Boring and Forging** In order to make the key parts of the weapon, the bore, the frame and the receiver, they would have to acquire a range of specialized tools for forging, boring and rifling these parts. Assuming they have tool steel and you have provided them with plans and instructions for creating these tools, this would be possible for them to do given enough time and manpower. **Problem 7: The Screws** A normal gun uses screws to hold many of the parts together. In theory they could hand file all the screws from steel rod. This would be INSANELY time consuming. Alternatively, you could teach them to how to build a lathe with lead screw and gearing. Once the lead screw is filed, that is the basis for making any type of screw given the proper gears. This would probably be the best option. A third possibility would be to use rivets instead of screws, however, since the lathe would be useful for other parts it would make sense to build the lathe. [Answer] I agree that fully modern automatic weapons would be out of reach, but perhaps a couple of the precursors could work, the revolver and the Gatling gun. The revolver uses relatively simple mechanics, and the straight walled, rimmed cartridge cases are much more forgiving about gunpowders and brass length. The Gatling gun again achieves its high rate of fire through more mechanical means involving less precision in cartridge and powder production. The construction of both these weapons should not be out of reach for a tech level where the jewelers can create working timepieces. [Answer] No, not really. They could probably build them and even the ammunition. You are right about needing smokeless powder and the metallurgy would be pretty good for medieval level, but those are solvable problems. As user3082 implies in his answer the medieval people would not have been able to solve those issues, **NO WAY**, but with enough groundwork with modern technology those issues could be solved. Maybe. The problem is that an automatic weapon needs lots of ammunition that fits the weapon and is of very consistent quality. Each and every shot would have to be manufactured by master craftsmen separately to a very high standard. I think that the craftsmen could have done that. But I also think that if you intended to use the guns to get yourself a kingdom, you should have taken the money you spent on those guns and bought yourself a kingdom or two. It would be much cheaper. Better yet, build up the local technology base or simply import modern weapons and ammunition. [Answer] I'll say 'yes' but only if you stretch what you mean by 'automatic' a little. A modern assault rifle - probably not. However the first 'automatic' weapon, was probably the [Ribauldequin](http://en.wikipedia.org/wiki/Ribauldequin) - more of a multi-barrel affair, but it does come under the current legal definition of an automatic weapon. (The guy I know who owns one, had a lot of fun with the licensing ;))  Likewise the earliest [Gatling guns](http://en.wikipedia.org/wiki/Gatling_gun) were hand cranked mechanisms. In the medieval era you *actually* had handguns, and early clockwork mechanisms ([Salisbury Cathedral clock](http://en.wikipedia.org/wiki/Salisbury_cathedral_clock) dates to 1366.  You also have [pole lathe](http://en.wikipedia.org/wiki/Pole_lathe)s for manufacturing barrels - and bear in mind that do have handguns and arquebusiers as well. The Napoleonic innovation of the 'cartridge' wasn't particularly advanced, technically. I mean, as simple as some gunpower and a musket ball wrapped in some paper. The major difficulty with the medieval weaponry was that they were mostly matchlock, and to fire a matchlock you need to 'prime' by putting some powder on it. So I reckon yes - you could make an 'automatic weapon' of the gatling emplacement style. You'd have a hand crank clockwork mechanism to make a rotary musket. The mechanism could feed cartridges, pour the primer powder, and - because you've got 'future knowledge' fire with a flintlock. You do have Conrad Kyeser the medieval innovator: <http://www.medievalists.net/2014/07/11/medieval-siege-machines-the-bellifortis-by-conrad-keyser/>  <http://advanderzee.com/tag/bellifortis/> (And of course, Leonardo) which suggests that such things weren't beyond the realms of conception. Practically they were more fantasy than actual design, but none the less - we're worldbuilding, so making the leap might be feasible. <http://en.wikipedia.org/wiki/Bellifortis> I should perhaps add - I've crewed a breech loading medieval cannon - the breeches aren't so very dissimilar to cartridges. We only had 4 though, so whilst we did manage a very rapid 7 shots per minute (sustained) it took a crew of 5. [Answer] **No**, for all the reasons listed above. **But** that doesn't stop you spending a couple of weeks before time-travelling working with a modern gunsmith, designing and testing a weapon which *could* be manufactured with their technology. I'd guess you'd be looking at an automatic-shotgun type thing - no rifling, paper cartridges. You'd need to think laterally; e.g. metal helical coil springs could be replaced by something like a leaf spring made from bamboo; it'd have a shorter life, but good enough for a few battles, at least. There's also many **modern improvements to old weapons** thanks to modern maths; e.g. trebuchet design is now much more advanced as our understanding of physics and ability to model designs is improved. You could take back plans for those weapons; as they're larger, you don't need precision engineering. [Answer] One of the biggest things needed for modern firearms is high quality steel. After you get the steel you need to bore it out very accurately and rifling didn't really start to take hold until the 1700's. And rifles were much more expensive than smooth bore because of the difficulty. They used black power which has a much less power than today's gunpowder's and this is part of the reason for high quality steel. Then of course is the quality of the rounds. Need to have a reasonable consistency in ammunition casings, and even more important is the quality and weight of the gunpowder in each cartridge. and last is the consistent weight and shape of the actual bullet. You really need industrialization to get this quality of work for all the pieces needed to make a weapon like this. [Answer] Not really\*. An automatic weapon on modern kind needs standardization, which was taken into use around American civil war. You see the automatic rifle needs precision parts to produce consistent results. Standardization is much harder than you'd think. See medieval manufacturers didn't have access to precision lathes, even of the kind Elisebathian England had to use (which is why manholes are round since that was the only manufacturing method that was precise/cheap enough to fit them at the time). So first you would have to use a precision lathe that makes standard components to make a precision lathe that makes standard components to build a precision lathe. And off course you'd use this lathe to make cartridges that fit your barrel each and every time. (ah the pain, ultimately youd want to make ammo faster than you shoot) So first you would need to retool the entire manufacturing industry, break guilds etc. See medieval system was based on artisan skills. Handcrafting is their core, the guilds might not look too favorably of demolishing or at least marginalizing them. This would also be somewhat in contradiction to the world view of most of the population. Then you would need to advance their metallurgy so that they could make drill-bits for their lathes. So that you can start lathing your ammo, or build punching equipment. Remember they needed hundreds or if not thousands of persons to support a knight. Their metal working skill would quite good. but ill suited for this particular task. They were doing hand/watermill hammering. But given 10 years then why not. Better bring drawings for manufacturing equipment. Then there's the chemical industry... \* On the otherhand you could make something like the repeating crossbows of china, does that count? Woodworking would be much more industrialisisable at the time point. [Answer] This made me think of Eric Flint's [1632, aka Ring of Fire series](https://en.wikipedia.org/wiki/1632_series), where an entire town is transplanted from modern West Virginia to central Germany, in the middle of the 30-years war. (Being rural Americans, they had a lot of guns and ammo to use until they could establish local production of ammo, using modern machine tools.) There's a community of fans that think about what's plausible in that setting, and apparently there's even an article [How to build a Machine gun in 1634 with available technology: Two alternate views](https://grantvillegazette.com/wp/article/publish-24/) on their paid-access magazine. (It has a limited free-trial access thing). If any of this catches your interest, check it out. I enjoyed the the novels (in audiobook form :), but haven't gotten hooked on geeking out about it the way groups like <http://ericflint.wikia.com/wiki/Grantville_Firearms_Roundtable> have. [Answer] I also think Gatling is the way to go * You could make the barrels by forging a spiral welded damascus gun barrel. See an example video without modern tools here : <https://www.youtube.com/watch?v=K7eacS2oDcs>. (by Steve Culver of Meriden, Kansas) * Using a similar technique, you can also make small around springs. An example video can be found here <https://www.youtube.com/watch?v=yt5Yi6UEqew> * I'd attempt to have a medieval brass instrument maker cast and work out the rest of the necessary parts. When you search for medieval brass instruments and jewelry, you will find some pretty amazing stuff in terms of complexity of design and precision. Casting brass and working it with simple instruments is surely time consuming, but no especially difficult. Looking at gatling gun blueprints, I don't see any parts which could not be created within weeks of effort. All you need is to drill and file brass, and tools for doing that are forgable by a medieval blacksmith. Finding potassium nitrate might be a challenge(\*), but both that and sulfur(\*\*) can be found naturally occuring. Charcoal is easily obtainable. Casting simple bullets and sleeves should not be a major obstacle. It is mentioned that you need a primer, but I think Nobel used pure blackpowder for his first primers, you should be able to get a rotating barrel like that as well. You'll just need a glowing needle or something similar to set the charges off. (\*) compare <https://de.wikipedia.org/wiki/Salpetersieder> with a in-detail description on how potassium nitrate was obtained at that time (\*\*) as a first option i'd simply travel down to the Phlegraean Fields and collect some [Answer] I don't know if this is beating a dead horse at this point, but simple breach loaders wouldn't be horrifically difficult to make. Something like the Martini-Henry, perhaps. Even with a smooth barrel, primitive powder, and a "relatively slow" rate of fire for modern times, you'd have a devastating weapons for the time period. Rimmed shells are easy to make, powder loads don't have to be perfect, and 20 shells or so is more than enough for a single soldier for a large battle. Even if its just a swiveling barrel on a stock with a very simple trigger mechanism, you'll be shooting down hundreds of enemy troops before they get within a hundred yards of you. Of course you'll still need master smiths and jewelers to make your shells and rifles, but probably more economical than an SMG, and more effective than a muzzle loader. ]

[Question] [ The question: What realistic environmental signs would telegraph to the occupants of a floating landmass that their home was slowly losing altitude? The planet: I'm working on a story that takes place on a gas planet, but with breathable air (I'm sure it has a solid core below its dense cloud layer somewhere, but it's not relevant to the story). It's close enough to its star for the planet to have a well-lit atmosphere during the day, and probably doesn't get totally dark at night, due to its gaseous nature. The length of a day, and the gravitational pull, are the same as ours on Earth. There are no land masses as such, but there are incredibly slow, floating sky whales of epic proportions (like 10+ miles long) that people live pastoral lives upon as if they were land masses (neither the humans nor sky whales are native to this world, so don't worry about how they evolved to be this way). The event: At one point, the whale the protagonists are living on slowly begins to lose altitude. Not in a way that's immediately noticeable, but gradually over years and years. My question is how would the occupants know this was happening? They know they live on a giant flying creature, and have seen others in the distance at different altitudes. The whales live thousands of years, and this one's behavior has remained unchanged for all of recorded history. The people revere them as gods and don't suspect they ever change course (and would probably believe it was the apocalypse). How would they realize something was wrong? The signs: I know that the air pressure would increase, raising the boiling temperature of water, but what else would happen? Would the sun's path across the sky change? Are different weather patterns more likely at lower altitudes? Basically, what believable signs would alert the occupants to the problem before a catastrophic pressure increase killed everyone on the island/whale? UPDATE: Thanks for all the great suggestions! I don't want to select a "correct" answer, because everyone pointed out different things that are just as relevant. To summarize what I've learned, and plan to use: * Scientific observations (such as barometric pressure) collected by the protagonist. * Anecdotes from older residents or visiting traders. * More intense thunderstorms. * Strange animal migrations (to higher ground or never returning). * Vertical migration of natural flora. * Shorter days, and sunset shadows lower on the wall, as the horizon rises. * Failure of delicate crops due to less light and heat. * Weight scales off a little due to increased gravity (very subtle). * Rise in respiratory health problems due to change in atmospheric gases. [Answer] **Clouds** Different types of clouds sit on different layers based on altitude, air pressure, and relative humidity. You mentioned your atmosphere has breathable air, does it also have water vapor in the atmosphere? Are there rain clouds? Methane clouds? Sulfur Dioxide clouds? Maybe an enterprising character notices that the moisture collectors are collecting more methane than before, or that when they head into a storm cloud, they get more violent turbulence than before. Depending on how far up they are, maybe they are used to riding out some of the more violent storms that happened lower in the atmosphere, but the protagonists have a rude awakening when a storm that they previously wouldn't have paid mind to 10 years ago tragically destroys their town. [](https://i.stack.imgur.com/DipC1m.jpg) [](https://i.stack.imgur.com/hBDYql.jpg) [Answer] By their awareness of other whales and the knowledge of the traders and pilgrims who pass between them. If the whale is slowly sinking over years or decades then the residents are unlikely to notice other than old people moaning, and old people always moan. It's reasonable to ignore anything they're saying about the sun being brighter and the stars clearer when they were young. Over the time periods you're implying, the changes are so slow and subtle they can be written off as faulty memory. It's only the people moving around between the whales who will notice that this particular whale is considerably lower in the atmosphere than others. [Answer] Since you said the gravitational pull is just like earth's than you would probably notice because the air pressure would increase. Not by much, of course but if you had a barometer and you took readings regularly, then you would notice the increased air pressure. It would have to be consistent as air pressure varies from day to day. [Answer] What about changes in the behaviour of the animals on your floating continent? It's well documented that animals seem to be able to notice the signs of natural disasters like storms or earthquakes long before humans do, so perhaps the animals instinctively react to the changes in altitude. Maybe some of them start moving to higher ground then they have ever been seen before, or perhaps those that are capable flee entirely to another whale. Migrations of birds that never return would certainly be noticed, people may not realise why but it would probably be enough to make them start wondering and looking further into what is happening (so they may notice some of the less immediately obvious signs pointed out in other answers like the brightness of the sun and temperature). [Answer] A few differences you may notice: * **Darker**: As you get more atmosphere above you it will get darker (depends on how dense the atmosphere is though as to how far down you go before it is noticeable). * **Colder**: You're getting further away from the sun's heat. This will depend again on the structure of your atmosphere. * **Distance to other near by objects will change**: If there are any other floating objects around they will get further away (if above). [Answer] Something that I haven't seen other answers mention is poor health. As they lose altitude the pressure is going to increase, yes, but the composition of their air is also going to change. Over time they are going to start breathing more of the heavier gases in their atmosphere, which will result in more cases of illness related to an improper air mixture. Nitrogen narcosis is an example of a condition that divers have to be wary of, caused by higher pressures. People are definitely going to notice when the weakest members of their community start hallucinating. [Answer] If its "not in a way that's immediately noticeable" then I doubt the average citizen of the place would detect the difference; unless they could *see* that they are physically lower by comparison to another landmark, another physical object in the distance. And even that might not get their attention, since after all its a living creature they're living on. They're probably very used to it going up and down and what not. Look to the scientist types in your story. They'll be the ones who are keeping information that they compare from time to time which could tell them something's wrong. Gas giants atmospheres are very interesting and the changes in the gases themselves could tell them a lot. It would be one of the big focuses of their scientific community. Also, the creatures bio-rhythms would be of great concern to them. They wouldn't want it to get unhealthy, since they are, y'know, living on it. Its health is their health quite literally. Other than that I might change it so that it IS immediately noticeable; sudden drops from time to time, before the creature rights itself, would be very dramatic; akin to earthquakes. [Answer] I have a slightly different idea for you, since the protagonists are aware they are living on a sky whale, could it be that they perform health checks on their whale deity? If so perhaps they might notice that the whale's blood tests have been shifting away from the last centuries results to now have a greater amount of heavier gases in it and this could lead them to suspect that they are losing altitude. [Answer] UPDATE: Thank you everyone for all the great suggestions! I don't want to select a "correct" answer, because everyone pointed out different things that are just as relevant, so I'm supplying this answer to summarize what I've learned, and plan to use (I'll mark it accepted as soon as I'm able): * Scientific observations (such as barometric pressure) collected by the protagonist. * Anecdotes from older residents or visiting traders. * More intense thunderstorms. * Strange animal migrations (to higher ground or never returning). * Vertical migration of natural flora. * Shorter days, and sunset shadows lower on the wall, as the horizon rises. * Failure of delicate crops due to less light and heat. * Weight scales off a little due to increased gravity (very subtle). * Rise in respiratory health problems due to change in atmospheric gases. * The permanent cloud layer below them seems to be closer. [Answer] Color of the sky. The color of our sky varies noticeably over about 20,000 feet of altitude change. But I don't understand your model for the planet's atmosphere. It sounds like it's physically thick (i.e. lots of vertical km of atmosphere), but about the same pressure as ours at whale-height. You can't independently set the density & pressure at the observer, the height of the atmosphere, and the gravity: They're all interrelated because the pressure has to hold up the weight (due to gravity) of the air column (due to density and top height). What you pick for those will determine what varies fastest with altitude. [Answer] Is your tech level high enough for a range finder? You could use light, sound, radio, microwave, or a laser measure the distance at edge of the whale to a depths below. Over time you would chart the distance. For the radio, microwave and laser ranging that would require a tech base that could send and receive the transmissions and time the distance between them. Say 1950's tech for the basic parts, 1980's for something you could hand hold, early 2000's for some cheap and easy to use (GPS/phone). [Answer] Since we as complex multicellular organisms may not be the most sensitive to changes in gravity, atmospheric pressure or gaseous composition you could use something that is more sensitive to these changes, like a fungus or bacteria on the whale. If the protagonists have contact with other whales at different altitudes they may notice whales at lower altitudes have more of the fungus/bacteria present than those above and that over time their own whale is beginning to show proliferation of the fungus/bacteria. ]

[Question] [ > > [Raining animals](https://en.m.wikipedia.org/wiki/Rain_of_animals) is a rare **meteorological phenomenon in which flightless animals fall from the sky**. Such occurrences have been reported in many countries throughout history. One hypothesis is that **tornadic waterspouts sometimes pick up creatures such as fish or frogs, and carry them for up to several miles**. > > >  Imagine a world where raining animals are a regular occurrence - say, most days on the tropical rainy season. Could a marine apex predator adapt to such a meteorological feature in order to take advantage of it, in terms of mid-air feeding? If so, what adaptations would it need, and what would it look like? I don't expect that a shark which evolved for this would necessarily still look exactly like a real world shark, so a sharky final appearance is not a requirement for answers. Other marine predators such as orcas, barracudas and mantas are also valid candidates for this niche, and don't need to look exactly like the ones from our world's after the necessary evolutionary adaptations. Being directly threatening to humans is also not required (I think the tornadoes are already enough of a menace). **Edit:** I see people assuming that animals will always fall on land after the tornado goes. Just remember that tornadoes may flood coastal areas, giving marine life some chance to fall into water. Asides that, please assume that the tornadoes may also happen over water, far from land sometimes. [Answer] # Falling, yes, but falling with style When falling, if you want to catch prey, You need two things, mainly: 1. Something to catch preys: arms, nets, big mouth, tail... you name it. 2. Something to steer your fall: Falling straight minimize the probability to encounter a prey. Some animals can decide where they will head to when falling. Flying squirrels, humans with wingsuits, or... **Snakes**. Astonishingly, some snakes can glide through air. Namely the [Chrysopelea](https://en.wikipedia.org/wiki/Chrysopelea). Snakes are also good at being underwater, so it could be totally possible to have a mix between a gliding snake and a marine one. **BUT** Snakes are good at catching things. Well, at catching ONE thing at a time. But we want our falling predator to be able to seize all the preys in his reach. What looks like a snake if the snake had multiple arms ? An **OCTOPUS** [](https://i.stack.imgur.com/0hmwu.jpg) [source](https://images.google.fr/imgres?imgurl=https%3A%2F%2Fimg.etimg.com%2Fthumb%2Fmsid-64262810%2Cwidth-643%2Cimgsize-37339%2Cresizemode-4%2Foctopus.jpg&imgrefurl=https%3A%2F%2Feconomictimes.indiatimes.com%2Fmagazines%2Fpanache%2Finexplicable-abilities-does-not-mean-octopuses-came-from-outer-space%2Farticleshow%2F64262725.cms&docid=zVXO71FNwLGTRM&tbnid=25S4xEIF3Jf8wM%3A&vet=1&w=643&h=482&source=sh%2Fx%2Fim) Moreover, octopuses are crazy good at controlling their bodies. With a little training and once it conquer its fear of heights, it could glide through the sky, following falling, frightened, desperate fishes, whom the last vision would be a terrifying cephalopod twirling toward them. [Answer] The biggest problem for a sharknado isn't the flying or being sucked into the air or feeding. It's the impact. So your creature either needs to be small enough to land safely, or it needs some way to slow down its terminal velocity. I'm going to assume we want a sharknado and not a minnownado, so let's think big. Flying fish anatomy won't scale for a large animal. At shark size, the only practical solution is parachute-based. [](https://i.stack.imgur.com/cwj1w.jpg) Coincidentally, we already have a sea creature which is the right kind of shape, and that's the [vampire squid](https://en.wikipedia.org/wiki/Vampire_squid). Like a flying fox, it has skin filling the gaps between its arms. Those arms (eight of them, like an octopus) have barbed teeth along them. Vampire squid only grow to about 30cm, but if we have an evolutionary niche then there's no reason they couldn't grow to the same size as an octopus. The [giant Pacific octopus](https://en.wikipedia.org/wiki/Giant_Pacific_octopus) is reported to have up to 9m arms, with a mass of around 130kg. Let's just say that one of those parachuting into you is not going to improve your day. Could this land itself as a parachute though? 130kg is the weight of two adults, so let's use a tandem chute for comparison. Apparently a tandem chute [will be from 350 square feet](https://www.livestrong.com/article/417149-the-size-of-skydiving-parachutes/), which is 31.5 square metres. 9m arms and pi gives you up to 254 square metres, which makes this trivial - it doesn't even have to be a particularly efficient wing, or have skin going further than 3m down its arms. Landing on land instead of water? Not a problem. Stranded octopi have no problems squirming their way back to the water. So, I give you something scarier than a sharknado - a parachuting squid-octopus bigger than your house, with barbed teeth running down each arm. For bonus points... Do these tornados or waterspouts take place near sea cliffs? A paraglider can easily soar the updrafts of cliffs. So an even scarier thought is squadrons of these things, deliberately getting themselves caught in waterspouts near sea cliffs, so they can soar the cliffs and wait for prey to come past underneath. It'd be like a snowy owl swooping down on a tasty little mouse - except humans would be the mice. [Answer] The only remotely plausible answer to this question would be flying fish. [](https://i.stack.imgur.com/ucZrS.jpg) *Flying fish in the air* Flying fish are already adapted to a limited flight regime, so being caught up in a waterspout and released in the air isn't going to change much of their lifestyle. The biggest danger is being crushed by the insane water pressures and "g" forces being developed inside the waterspout, but we will handwave that away. Once clear of the waterspout, a flying fish will likely deploy its wings and begin to glide. Since it is being released at a much higher altitude than normal, it will be able to glide a considerable distance, much farther than usual (normal flying fish have terrible L:D ratios compared to gliders). From there, it might be a fairly easy adaptation to quickly glide through the dissipating waterspout and grab edible particles, plants or other fish that are being released into the air at the same time. This really just takes normal fish behaviour and encourages evolutionary adaptations for better flight, vision and reflexes (all which would also be advantageous in the aquatic environment as well). I don't see a pathway to evolving man eating flying fish, however..... [Answer] If the sharknado has to feed on things suspended in an air stream, it means it has to be able to collect as much as possible in the shortest time as possible. It would make sense that their mouth evolved into an ibrid of a [mist net](https://en.wikipedia.org/wiki/Mist_net) and the mouth of the [basking shark](https://en.wikipedia.org/wiki/Basking_shark) [](https://i.stack.imgur.com/iEcrn.jpg) or the [megamouth shark](https://en.wikipedia.org/wiki/Megamouth_shark) [](https://i.stack.imgur.com/WfUDi.jpg) I assume the mouth would need a more pronounced net structure when fully opened, so that the drag would not blow the sharknado away while attempting to feed, something like a butterfly net. **OT**: thanks for the attempt of putting some legitimization to the entire sharknado thing. [Answer] # No adaptations necessary [](https://i.stack.imgur.com/TB56t.jpg) When a waterspout delivers a flying buffet, the apex predator sharks wait at the bottom for the good stuff to come to them. By jumping out of the water, they prey on animals in the air that have no opportunity to flee. Water based propulsion systems don't work in the air, so the food is going to go where gravity directs it, which is hopefully into a shark's mouth. # Actually, they probably need different eyes If you are going to lurk under water, and then jump up to catch a helpless falling meal, you need to a. See into the air b. Have good distance vision [Fish eyes](https://en.wikipedia.org/wiki/Vision_in_fishes#Structure_and_function) are generally more convex than land animal eyes, because of the differing focusing properties of water. A jumping shark needs eyes more similar to that of a land animal so it can focus on a falling target tens of meters above the water's surface, while still submerged. Distance vision is a function of binocular vision. A jumping shark will want its eyes closer together in its head. ]

[Question] [ I have a setting with space fleets fighting, the include both capital ships and human flown 'space fighters', which I already put some work into justifying: [How to keep humans pilots instead of AI in sci-fi future?](https://worldbuilding.stackexchange.com/questions/17043/how-to-keep-humans-pilots-instead-of-ai-in-sci-fi-future) I want to encourage smart tactics, maneuvering, the equivalent of outflanking and surprising enemies etc to some degree within my world, particularly since my main focus is on a small group of folks flying powerful crafts, but who would ultimately need to use tactics to make the most of battles due to their small numbers. The problem is that space is big and empty. Most tactics don't work well when you can't surprise anyone, and you don't have any terrain to exploit to gain an advantage. I'm looking for ideas to add variables which encourage more tactics and planning on the scale of one fleet engaging another (Larger strategic concerns are less in scope to my story, and also carry over better from current warfare to space warfare so it's easier to imagine them). I'm open to modifying technology, weapons, and environment to a degree to create or encourage better use of tactics. However, I'm trying to stay somewhat hard sci-fi, it's okay to make up a technology that feels somewhat plausible, but full ramifications of such technology existing must be explored. I'd love general suggestions for making any space warfare more tactical, as well as specifics for my world. As to my world, here is how the technology works, some of it already was altered to encourage or better use tactics but I still don't have enough of it: **The general world**: 1. Travel is done at sub-light speeds except at specific points where one can open up jump point to another region, only larger ships have the power and equipment to make jumps usually. There are quite a few of these jumps between regions. I'm open to tweaking these and suspect tweaks to how jump points work is probably the easiest way to add more tactical options. 2. Limited faster than light communication exists. however, it is not entirely instantaneous and can only travel so far before the signal degrades. Most jump points also act as relays to strengthen and pass comms through, but obviously whoever owns a jump point can prevent relaying enemy comms. Messages can be sent without jump points but require more energy and suffer more lag. In combat FTL communication is less efficient due to weapons and jamming systems, only short data grams can get through and they may come in irregularly. 3. Geneva convention insists space battles must be held a certain minimum distance out from any inhabited planet or habitat to avoid stray bullets destroying all life on a planet. Battles for these locations occur, but generally far enough away from the actual planet that someone isn't going to be able to jump around a moon and surprise you 4. Space. Is. Big. While I've created systems to encourage closer range battles I plan to stay accurate in regards to the size of space, and the limited rate of sublight engines producing acceleration compared to the size of space. In short, hiding behind a moon and jumping out of nowhere isn't as effective when it takes over an hour of acceleration to even begin to move around the moon to surprise someone... **Enemy crafts and shield technology**. 1. Shield technology exists and is used on all capital ships, but most smaller crafts are not shielded and easily destroyed. Shields are best destroyed with certain types of energy weapons that have rather short ranges, encouraging battles at 'close' range, from an astrological standpoint. 2. The efficiency of shields means just throwing more energy at them is a bad way of destroying them, instead, all weapons and tactics for taking out capital ships are focused on intentionally ruining the resonance of the shields, which causes destructive interference and drains the shields energy reserves. As long as a shield knows what attack to expect it can be calibrated to be very effective against it, however, it can't be perfectly calibrated against all types of attacks at once, and if poorly calibrated for an attack the shields will lose power with an inefficient deflection... 3. A combination of a few strong attacks with lots of weak attacks tends to be a very effective way of draining shields because the way to configure against lots of weak attacks is very different from defending against a strong attack. For this reason, all capital ships carry a number of smaller fighters and bomber crafts. Bombers swarm shields and attack from all sides while capital ships hit with one large energy weapon, the combination draining the shields far better than either tactic alone; fighters simply protect bombers and destroy enemy bombers. 4. To squeeze efficiency out of shields they are calibrated for the anticipated fight when they are brought up, and then they slowly adjust their calibration during the fight (Once shields are turned on the calibration must be slowly shifted to a new one, quick changing of celebration while shields are active will waste a large amount of energy). For instance, if two capital ships are fighting the shields will be calibrated for one capital ship hitting from the port side and a few dozen bombers attacking from multiple angles. As bombers are destroyed the shields recalibrate to focus on being more efficient at defending against the capital ships weapons at the expense of being worse against bombers, as there are fewer bombers to defend against. Likewise, as the enemy capital ship moves the shields will recalibrate to keep the shields strongest in the areas the capital ship could hit with its beam weapon. 5. capital ships tend to have only one, or at most two, beam weapons, and very little in way of point defenses against bombers; it's difficult to fire through your own shields and limiting the number of places you're firing through allows shields to be calibrated to higher efficiency. Beam weapons grow weaker with distance and thus can grow increasingly devastating as capital ships close; not that closing on an enemy ship is always the best way of engaging them. Obviously, shields have been modified intentionally so that sneak attacks and baiting the enemy into starting with a shield that is poorly calibrated for a fight is a good way to get an upper hand. The problem is that the idea of 'sneak attacks' is kind of hard in space. The enemy can pretty well anticipate exactly what you're throwing at them and where since they see you coming hours or days before you arrive, and there are limited ways to surprise them or maneuver differently since your maneuver speeds are so limited. [Answer] I think your setting and tech descriptions create some good opportunities for interesting tactics. With only a single protagonist ship, sublight maneuver itself may not seem so interesting, but **there can still be some interesting tactics available even for approaching an enemy**, such as: **Pretend to be a friend**. If the protagonist ship can emulate a friend or non-enemy, they could get within a range where they could take advantage of surprise. Ways to emulate a non-enemy could involve either being originally externally the same as one's enemies, i.e. if the ship is of the same construction, or intentionally built that way, or is a captured ship. Or they could have developed technology which involves adding a shell to the ship surface that acts as a ship costume or electronic projectors which just present an image that is the same from a distance. You already have powerful complex tunable **shield technology**. It seems to me that this technology **might also be able to project an image that makes a ship look like a different ship** of a similar size. If one can somehow appear to be a friendly ship, then a *successful ambush/impersonation requires defeating the identification protocols*, which probably requires **impersonating enemy officers**, and/or forcing them to act as if they were confirming their approach. They could either be actually captured or perhaps "captured" by **recording their actual communications in the past** and then using those recordings. *This tactic would also require not raising an alarm, and not seeming to be in the wrong place at the wrong time*, which might or might not be very hard or nearly impossible, depending on the scenario. It would probably be far easier to **impersonate 3rd parties** rather than a ship from the same fleet as the target, unless you've actually **captured such a ship without letting the enemy know you have**. If there are huge cargo transports in the setting, **a capital ship might be able to hide inside of one**. Then it will appear to be a cargo transport because it is - it just has a capital ship inside. If there is a lot of mass cargo transport in the setting, this may make stealth by impersonation quite possible, to the extent that you can capture such ships and engineer the insertion and the breakout. Another technology that might enable stealth and ambush could be something like a **redeployable concealment cloud**. Perhaps a system of devices could deploy a cloud of magnetic dust or gas around a ship, which prevents seeing what's inside it. Magnetic so it can be kept in a bubble around the ship, and retracted and re-used. If this was a common and routinely-used system, then again, they might see something coming but not know what it is, and that might not raise an alarm if the setting includes many different types of ships using such systems as a known common practice - suddenly it becomes possible to hide by being one of many anonymous clouds moving about. **A decoy could also deploy a cloud**. **Decoys in general**, whatever the technology that allows them to look like your ship, meaning that you can have a shell-game maneuver situation. Even without decoys, but especially with them, if sub-light propulsion involves standard inertia and fuel, then **inertial maneuver can itself be an interesting tactical proposition**, though it will be more complex the more objects are in space. If it was just two ships with beam weapons, not so much, but missiles and fighters and warp points and decoys are all moving objects with inertia and facing directions in three dimensions and limited fuel and changing mass if they use reaction mass, so there can be many different guessing games there about how to deploy to try to get the enemy to commit to a deployment that you can use to get yourself into advantageous situations, which as in almost any tactical situation (whether real-world naval or martial arts) can involve out-anticipating the opponent's thinking and movements, so they do something which you can respond to in a way that leads to your advantage and so a successful outcome. What helps that a lot is when the opponent has inaccurate information about your plans, deployment, and/or capabilities. You've read Honorverse books, so you've seen a lot of variations on that. Weber (the author of that series) is a game designer, and no doubt plots out his situations, runs the math, and re-plays various scenarios until he finds something he thinks is interesting to write about. Your **slowly-adapting shield systems** add yet another dimension to that, because they have their own spatial orientation and settings which take significant time to change. If the protagonist ship shield has some unexpected abilities, even just speed or directions in which it can adjust, raise, lower, or spoof its settings, then that can provide another way (and another spatial/directional component) with which to outmaneuver an enemy. For instance, once close enough to an enemy, you might be able to maneuver past / around it more quickly than it can keep its shield strength concentration facing you, but if your shields can be ready to redeploy that way, then you could get a decisive shield advantage by quickly changing direction at close range in a way they can't respond to but you can... if the range and rotation and shield adjustment speeds are within certain values, anyway. There are also axes of "maneuver" provided by different attack types, and the mechanics you mentioned of tuning shields to allow weapons fire through. And of course, your whole **fighter/bomber/low-PD situation** also lends itself to maneuver and tactics. Clearly the main avenue is you tune your shields to defensive mode, then have your fighters take care of their fighters and bombers, and once their fighters are handled, have your bombers destabilize the enemy shields by hitting them from different directions with different attack settings, and then switch capital shield configuration to offense, and plaster the enemy shield, or even compel them to surrender since they should be able to see the hopelessness of their situation before they're destroyed, since their shields take some time to wear down and they can see what's going on. Another weapon system that might make sense would be some sort of **shrapnel bomb**. If your fighters get outmatched, tell your fighters which side of your capital shields to shelter behind and then roll a few bombs out, which explode and send fighter-threatening debris everywhere, hopefully, evening the odds. The **FTL warp point system**, of course, offers many opportunities for tactics, depending on how they work, exactly, and how they are laid out, etc. It also provides a means for technological maneuver advantages for your protagonists, as well as a potential advantage for the lone wolf, *if the opponents have to spread out to protect many points and can't cover them all*. It gives you a lot of leeway to design something that has room for interesting maneuvers and tactics. For examples: * Maybe **warp points allow warping within a generous radius of the point, but there are trade-offs** in terms of energy used, velocity going in/out, time required, accuracy, risks, ability to track where someone went or came from, or whatever, which can be mitigated by different qualities and/or settings of technology. * Perhaps the **distance or even shape of a warp field determine how much energy and time is required to prepare, align and recover from a warp in or out**, as well as the required entry velocity, and resulting exit velocity. * If **warping requires a large energy build-up and expenditure, and/or electronic disruption**, there may be trade-offs, possibly modified by the conditions as above as well as technological attributes, which may be in conflict with getting those complex shields working efficiently, just because of the power use, or possibly other effects (e.g. your shield matrix needs to be cooled and/or de-Gaussed after a warp or something). Thus **ships could be vulnerable before and/or after jumps, providing a window of opportunity needing to be covered by other ships or fighters** to reduce risk at either or both ends of a jump. * **The *arrival* of an incoming warp might also (or even only) disrupt or even displace nearby ships, shields, signals and/or electronics, or have other effects**, which would have to be taken into account for both defensive and offensive tactics. There might be simple or different effects around where a ship warps away. This could make it hard to defend a warp point, or at least provide some time to maneuver and prepare before an attack via warp. * If warp points do need ships to be in a very specific place with a specific velocity when they warp in or out, that, of course, can be taken into account in tactics. Some **automated defenses, mines or obstacles** might be used, as well as pre-targeted weapons aimed at the point. * Maybe there's **a way to disrupt a warp point**. What if you get the enemy armada to chase you and track you to a certain warp point, but you've left something there that will throw off the jump (maybe a big asteroid does the trick)? For example, you might be able to get a large number of enemies scattered to the four winds, buying you time and getting the enemy ships still near warp points to try to redeploy to recover the remaining points while the rest of the fleet tries to make its way back to warp-connected space. * Another elaborate ruse could involve **capturing a command communication warp point hub**, and making them give out a pre-designed series of false orders, including that an enemy communications disruption attack is expected, and then doing something that disrupts the whole warp communication network. Then you have until they make sense of that to do whatever your real objective is. * A warp point system could also involve moving via a kind of hyperspace. Without a warp point, you can't travel long-distance (or not reliably), but **ships might still be able to enter hyperspace without a warp point. If so, that means they may be able to effectively hide/cloak, and it also means that conditions in hyperspace may be different than normal space, and allow you to define conditions the way you want them to be for technology and resulting tactics**. Shifting in and out of hyperspace might be a standard military technique. Or it might not have been because of technical disadvantages, but your protagonists' technological advantage might be that they have a new technique or technology which allows them to have a great advantage while doing so, letting them not only hide but also gain tactical and/or combat advantages such as short hops to flank, quick range changes, or getting the enemy into hyper where you have some technological advantages. All of the above could provide all sorts of situations for out-guessing where and when ships would warp in and out, as well as tactics for **having ships hop in, see what's there, and hop out, having the defenders decide whether or not to try to follow, or to call in reinforcements** when or after a delay after someone pops in, or to retreat until enough force can be mustered, based on estimates of enemy fleet size. If warping causes disruption, this will be taken into account and used for tactics. [Answer] As you say, space is pretty empty. For most battles, all that's going to make up the battlefield are the ships. But I say you can use this to great effect. 1. Shadows: enemies can't see your ship if you're behind another ship. When you've got capital ships involved, you can probably hide dozens or even hundreds of your fighters from the enemy until you decide it's time to attack. Plus, when attacking, you can never know what you'll find behind the enemy's capital ships. Keep in mind that even though ships are going to be really far apart most of the time, that just means everyone's shadows will be very large by the time you get out to the distance where they'll be used. 2. Blind spots: Your ships probably aren't going to be spheres covered on all angles with guns. Much like seafaring warships (or even airships like the AC-130), most of their guns should be centered on one or two sides, so they can hit a single enemy formation with everything they've got at once. With this in mind, there will always be places you don't want to be in reference to an enemy ship, and places you want the enemy ships to be in reference to you. With many ships and in three dimensions, these calculations could get very difficult, so a lot of inexperienced pilots are going to fly right into the killzone, but a good pilot may be able to navigate the battlefield, avoiding these 'invisible' obstacles and leading the enemy straight into them. 3. Time. This is probably one of the coolest things about space battles, the fact that so many systems are going to be constrained by the speed of light, and so many more are going to have to wait a long time to see results. A lot of what your pilots do will depend on assumptions about what's coming, and unexpected moves will be more devastating simply because it'll take longer to realize what's happened. What this amounts to is a lot less looking and a lot more thinking. Pilots will have to intuitively understand the positions, orientations, and intentions of both their own forces and the enemy. There may not be cover, but by taking advantage of the points I've described above, pilots should be able to keep themselves out of the worst of the enemy's fire, and force the enemy to do the opposite. The geography of the battlefield will be comprised of its combatants; the 'high ground' will be having the best angles on the enemy, while a 'cornered' enemy is one that cannot move without entering the line of fire. As ships move, the terrain will constantly shift, which, at least to me, sounds like a great catalyst for some exciting battles. [Answer] First I’d recommend looking to the Honor Harrington series. <https://en.wikipedia.org/wiki/Honorverse> They do the best job of accurately representing space combat from all the sci-phy I have read. Some things stolen from there. Its hard to pin down forces that don’t want to fight unless they have to defend the location. (Planet/shipyard/starbase) Stealth technology vs speed. If you can stealth your ship you can still ambush. Being able to maneuver while stealthed increases the ambush range. Even though space is huge, there are still ideal places to enter and leave a system so you can predict movments and where to set up an ambush. Space is big. Even though you might be able to detect a ship, do you have the resources to look at every place in a star system it could be? [Answer] From a Hard Physics perspective, what you ask is exceedingly difficult to do. I'm going to approach this from a hard physics perspective which means telling you some of what you want isn't possible or realistic. However, since you're writing a fictional book, you may include rational or McGuffinite to make what you want acceptable in your universe (e.g. a no AI social taboo?). ## References There's a very long and currently still on-going discussion over at [Rocket Punk Manifesto about what "realistic" space combat](http://www.rocketpunk-manifesto.com/2009/06/space-warfare-i-gravity-well.html) might look like (please read the WHOLE thread on this - this is just the first entry). I happen to agree with most of the conclusions but strongly disagree with one of them (the NO stealth rule). I also highly recommend studying at great length the website [Atomic Rockets section on Tactics](http://www.projectrho.com/public_html/rocket/spacewartactic.php) ## Throw out some standard tropes Some of the standard SF tropes that are highly unlikely in a Universe with "realish" physics. In no particular order: * [Space Fighters, not so much](http://www.rocketpunk-manifesto.com/2007/08/space-fighters-not.html) * [No Stealth\*\*](http://www.rocketpunk-manifesto.com/search?q=stealth) * There's no realistic mechanism for "shields" \*\* I disagree with the "No Stealth" rule. The general reason why you won't find stealth in space is because **if** the enemy knows where to look, a Hubble Space Telescope (a HST) sized sensor could spot any ship at quite a long distance. Furthermore, a HST sensor could spot a ship accelerating at the levels indicated in SF books almost anywhere in the Solar System. However, the Earth regularly has large (km and larger) sized rocks zip by and we don't notice them until just before or after they swing by. Why is this? Two reasons: 1. they come at us from the direction of the Sun and that makes them harder to detect. 2. we don't know where to look for them (we could still find them under condition #1 if we knew where to look). So I consider stealth extremely difficult but not impossible to achieve. **EDIT: 11/22/2015** I'm going to rephrase this because really "stealth" is not possible. If the enemy knows where to look, they *will* see you. What might be possible is to make yourself insignificant enough that they will overlook you for a while. Bear in mind that any maneuvering, firing energy weapons, approaching too fast, or getting close will result in your discovery. The first two resulting in instant discovery while the second two will just increase the chances of discovery. Also eventually, you will be noticed. So this could be a source of interesting drama/tension in a space combat setting. A kind of Das Boat situation for the people on the "stealthy" ship. ## Tactics It's impossible to provide you with a set of "tactics" that would apply to your situation. There's way too much ground to cover. Instead, I'm going to tell you how various aspects of your Universe may affect tactics. ### Details which affect tactics * Spacecraft Thrust/mass ratio (this will give you their acceleration capabilities - maneuverability) * Engine $I\_{sp}$ (this gives you the ship's endurance capabilities - how long your engines can run and total $\Delta V$ available) * Fuel tankage and remaining fuel (affects $\Delta V$) * Directed energy weapon (DEW) limits (size, power, efficiency) * Availability of high power engines for missile buses (which would replace fighters) The details of the weaponry (e.g. engine performance vs. DEW performance) will strongly affect the balance of power between ships with beam weapons versus missile weapons. Ships with beams might tend towards large sizes for massive "spinal mount" free-electron lasers (FEL). The FEL provides good efficiency (especially compared to most other laser technologies) which means more power and less waste heat to deal with. The large beam resonance cavity and ability to tune the laser to high frequency photons means the weapon might have the ability to destroy other ships out to a *light minute* (11,160,000 miles / 13,392,000 km) or more. Targeting and hitting at the range is left as an exercise for the reader, :) Missiles can theoretically destroy targets anywhere in the Solar System. Whether they are viable as a weapon during a fleet engagement will depend upon their the ratio of missile acceleration vs. ship acceleration ($\frac{a\_{missile}}{a\_{ship}}$). If the ratio is > 1 then missiles may make good weapons for an engagement. If < 1 then missiles wouldn't make good weapons for an immediate confrontation but might still make good weapons. The other consideration is the ratio of the missile's $\Delta V$ compared to the ship's $\Delta V$ ($\frac{\Delta V\_{missile}}{\Delta V\_{ship}}$). If: **$\frac{a\_{missile}}{a\_{ship}} < 1 \text{ and } \frac{\Delta V\_{missile}}{\Delta V\_{ship}} < 1$** Then missile is more like a mine, you have to hope your enemy overruns the weapon. **$\Delta V\_{missile} >> \Delta V\_{ship} + V\_{differential} $** Then missile will always hit the enemy unless it is shot down. **$\frac{a\_{missile}}{a\_{ship}} >> 1 \text{ and } \Delta V\_{missile} > \Delta V\_{ship} + V\_{differential} $** Then missile will usually quickly hit the enemy unless it is shot down. For other combinations, your tactics may determine whether the missiles can hit the ship. For example, your missiles will can only hit an enemy running directly away from you if either the missile $\Delta V$ or acceleration exceeds the enemy ship's. Even if they do, the missile still might not hit that enemy depending upon the velocity and acceleration vector physics of the encounter. ### Tactical Goals The goal of your tactics are to either engage your enemy or evade your enemy. Whether you can do either of these depend strongly upon your engine performance. In general, engines with high $I\_{sp}$ tend to have very low, even minuscule thrust and vice versa. If your ship possess superior $\Delta V$ (a combination of fuel tankage and $I\_{sp}$ to your enemy's ship, you will **always** be able to force an engagement. However, if your enemy possesses superior acceleration, he may be able to determine *when/where* the engagement occurs. Also it is a near certainty that the two ships / forces are not on parallel or reciprocal courses. Which means figuring out engagement attitudes, timing, where to place your weapons fire, etc. are all determined by tactics too. If you need to board the enemy vessel, then you not only have to match your 4 temporal-spatial coordinates, you also need to match your velocity vectors - not an easy task. What sort of accelerations can your crew tolerate? and for how long? Is it best to give your a crew a break before you enter the effective range of the enemy's beam weapons? If you can figure out where your opponent will be, your missile buses can get their first and force the enemy to fly through them. If your tactics work or fail (depending upon the goal), then the combat resolves as who is able to stay away from the other's weapons. You want to go to where your opponents missile buses are not and force your opponent to move to where you missile buses are. You also need to arrange your ship so that it can fire any beams it has upon either inbound missiles or the enemy ship. As I mentioned above, please read the linked resources, this topic requires quite a bit of thought and discussion ### Instead of fighters... Fighters were developed as a means of attacking the enemy at long range - longer than any artillery. Instead of manned missiles, we have humans pilot a vehicle which then launches the ordnance. Even now in our current era, we are slowly replacing piloted vehicles with AI or remotely piloted ones. In a dangerous environment, like a space battle, it will be far more advantageous to use an AI which can survive 100G accelerations and not require life-support than to place a human in there. For these reasons (and many more), it makes more sense to make a vehicle designed to carry the missiles to their individual launch points. You can call this vehicle a "fighter", missile bus, drone, or something else. Also the missile bus will be traveling away from the launch vessel at high velocity. This makes it difficult to recover. Instead of expending enormous resources to do so, simply make the bus part of the expendable weapons package. So you might not have "fighters" so much as a disposable missile bus (with many missiles/penetrators per bus) doing the same job (transporting the penetrators into range of the enemy). Per the Honor Harrington Universe, the bus may have secondary roles (tactical computer for the penetrators, sensor platform, comm relay back to the launching ship, etc.) Another possibility is something the [game Traveller](https://en.wikipedia.org/wiki/Traveller_%28role-playing_game%29) describes as "[Battle Riders](http://wiki.travellerrpg.com/Battle_Rider_%28book%29)". In your universe the Battle Rider Tender (BRT) possesses a high $I\_{sp}$ engine. This gives the Tender the ability to do a lot of movement and get to higher total velocities than any of its riders. I will not be equipped with combat systems, because it is not intended to ever go into battle. The BRT fulfills the role of a carrier in a Universe with fighters. The Battle Rider possesses high thrust (low $I\_{sp}$) engines for maneuverability. This increases their survivability in combat but severely limits their $\Delta V$, which would be tiny compared to that of their tender. ## Another perspective on Terrain > > Space is big. Really big. You just won't believe how vastly, hugely, > mind-bogglingly big it is. I mean, you may think it's a long way down > the road to the chemist, but that's just peanuts to space. > > > [Douglas Adams](https://en.wikiquote.org/wiki/Douglas_Adams), [The Hitchhiker's Guide to the Galaxy](https://en.wikiquote.org/wiki/The_Hitchhiker%27s_Guide_to_the_Galaxy) Unless the engagement is intended to attack or defend a "stationary" (in this context, stationary means non-accelerating) object (planet, spacestation, moon, etc.) you will not need to contend with terrain as we typically understand in the context of conventional terrestrial warfare. Instead, you do need to contend with the "terrain" of relative position, velocity, & acceleration. The orientation of the the velocity & acceleration vectors will determine who is "downhill" from whom. For instance, in a tail chase scenario (one ship running away from another), the lead ship has several advantages. Some of these are: * Lead ship can hit the trailing ship with missiles that possess both lower $I\_{sp}$ and lower $\Delta V$ than the following ship (essentially they're like mines). * The trailing ship's velocity and acceleration vectors are more tightly constrained making them an easier target to hit with all weapons. * The flight distance of missiles fired from lead ship at trailing ship is MUCH shorter than the separation distance between the ships, so missile $\Delta V$ (analogous to range) *appears* to be greatly extended. * The flight distance of missiles fired from the trailing ship at the lead ship is MUCH greater than the separation distance between the ships, so the trailing ship must survive incoming fire for a significant period of time in which it cannot fire back with a reasonable chance of a hit. There is at least one major advantage for the trailing ship: * Except for the special case in which the velocity vectors are aligned, the trailing ship will always have to travel less distance to get to a given point than the lead ship does. If the lead ship maneuvers in any way (e.g. evasively), then it allows the trailing ship to gain on them (in distance and velocity). Each different distance, velocity, & acceleration profile for the two ships gives different advantages and disadvantages. If you look at these engagement profiles as "terrain" than it provides a unique insight into the types of trades a combat officer might have to consider when figuring out how to approach a hostile ship. You can see where it might take months for ships with realistic engine and fuel tank performance to get set up in an optimal engagement profile. The pre-battle battle would in the most abstract way resemble a chess game. With move and counter move. Accepting or declining various options (e.g. in Chess, a black player may offer to exchange a pawn for the advantage of gaining the initiative). Move and counter move going into space combat will be filled with such tactics and trying to figure out the opposing ship captain's true objectives, weaknesses, and strengths. [Answer] It's true that tactics often revolves around taking advantage of terrain. And that there isn't much terrain in space. But: There is SOME terrain: stars, planets, moons, asteroids, etc. Yes, in real life space is much more empty than you see in movies -- the asteroid belt is not really the densely packed field of rocks that ships have to dodge and maneuver around like in the movies. I'd guess that it is unlikely that more than one planet and maybe a moon or two would be relevant in any given battle. Star Wars actually had an intelligent -- I thought surprisingly intelligent for a campy move -- use of the orbit of a moon playing a role in the tactics of a battle. But more important, tactics on Earth is not JUST about terrain. Throughout history armies have often sought out wide open spaces to fight so terrain wouldn't get in the way. And they don't then just "go at it", but attempt to outflank each other, probe weak spots, etc. Air and naval combat is fought in environment just as open as space, and they still use tactics and maneuver. They don't just face each other and start shooting. In any form of terrestrial combat, common tactics include: Mass: Maneuver the enemy into a position where many of their units cannot fire, while all or most of yours can. For example, get them where many of their units are out of range, on the fringes of the battle, or where their own units block fire. Flanking: Position yourself on two or more sides of the enemy, so they have to deal with attacks on two sides while you only have to deal with one. Fresh reserve: Withhold units from combat until a critical time, so you have units that are alert and unhurt while the enemy is tired and damaged. Surprise: Do something that the enemy does not expect and is not prepared for. This doesn't have to mean gaping, open-mouthed astonishment. It could be as simple as attacking place A when they expected your attack would come at place B, perhaps because it was the "obvious" place to attack, perhaps because you planted misinformation, etc. Etc. Specific characteristics of weapons can lead to specific tactics. For example, during the age of sail the British figured out that ships of necessity are longer than they are wide, and so can fit many more guns along the sides than at the bow and stern, and so if you "cross the T", i.e. position your ship so that your side is facing the enemy while his bow or stern is facing you, you can fire with many guns while he can only fire with a couple. Since the beginnings of air combat pilots have figured out that getting "on the tail" is the key to winning in aerial combat. Position yourself directly behind the enemy. The pilot's easiest view is forward and weapons fire forward, so you can shoot at him while he has a hard time even seeing you. You'd have to think through how your proposed space warships work to come up with analogous tactics. Of course you have the advantage in SF that you can think of a tactic first and then invent technologies to make that tactic work. [Answer] The [Rocketpunk Manifesto](http://www.rocketpunk-manifesto.com) and [Atomic Rockets](http://www.projectrho.com/public_html/rocket/index.php) sites are always great references for anything "hard" in space opera, and you have set up a very difficult situation to deal with in a "hard" setting. If we are to believe Rocketpunk Manifesto, space fleets will be constellations of fire support platforms moving in a majestic orbit towards the target, and most of the manoeuvre will have been done and calculated months or years in advance. There are a limited number of places tactics can come into play: either at the beginning; you launch the constellation in such a way that the final target is ambiguous until they make their final burn, hoping the enemy will guess wrong and launch their constellation towards a different point; or at the end; The constellation does its burn when you don't expect it, so they are not entering the orbit you though they would be going to. The second option is far more likely, especially if the constellation is entering something like the Jovian system. Once in system, the other application of tactics is manoeuvring your constellation so that they have maximum sensor coverage and minimize any "blind spots" such as behind planets and moons in the system. Around Earth this is blindingly simple; establish a "sphere" of sensor and piquet drones across cis-linar space (most likely in the region of the "Hill Sphere"), while keeping the constellation in a fairly compact formation to maximize firepower. In the Jovian system, there are far more hiding spots (including burrowing below the surface of the various moons and using them like airstrips or aircraft carriers), as well as various hazards like the radiation belts and ring system, so there will inevitably be blind spots in the sensor coverage. The enemy will have to determine where the sensors are, and exploit the blind spots to move. The constellation will be in a compact formation no more than a light second across to maximize their situational awareness for a fine grained 3D view of the system (outlying sensors will be beyond the light second ring, so their input will have a distinct time lag). This means that even if/when you get the jump on them, they will be in a powerful fighting formation. The last tactic that can be used is deception. IF all the spacecraft are roughly the same size and shape, you might discover too late that you are doing an attack run on a Laser Star armed with a terrawatt Xaser (that would tend to ruin your day out to the distance of one light minute), while a similar spacecraft might be a missile platform (Kinetic Star) or even a carrier for your fighters. If you are very lucky, it is only a fleet tender or tanker... [Answer] In one sci-fi novel I read (the name escapes me), ships would launch swarms of missiles long in advance. Those missiles, being relatively small, and difficult to detect, would fly to certain locations in the solar system, power down, and lay in ambush. Your fighter force might do the same. You detect the enemy: there's only so many trajectories to get from point A, to point B. Your capital ships place themselves such that they attract the enemy in a certain direction. The small fighters, powered down to minimum life-support, drift into position slightly further away. When the enemy fleet closes in to engage the capital ships, the fighters power up and attack from a completely unexpected direction. Of course this requires the ability to plan your engagement well in advance, and maybe even to deploy some kind of refuel ship with the fighters. Keep in mind that the vastness of space is in fact the best cloak. We can barely keep track of a fraction of what's going on in the night sky. If these ships restrict their communications and power down outside lights, they might become just one more hunk of junk drifting through space. No one's going to "look out the window" and see them. No one would know where to look. In the mean time, they can keep track of their enemies using passive scanning equipment. [Answer] I know you specified somewhat hard sci-fi. But you already have one big handwavium technology - **shields**. What if we use that to add a somewhat limited stealth capability? Think about what shields do - they deflect mass... and energy. What are sensors? Various forms of reflected energy. Make it so shields can be calibrated to a stealth mode. It's not 100% perfect - possibly they create a tiny "cone" in which the ship's signature is still broadcast, and maybe even enhanced. But for anyone outside of that small cone, the ship is effectively stealthed. You now have surprise, which gives you tactics. But it's not perfect: * Since fighters are too small to be shielded, they need to be brought into position by stealthed carriers until the actual fight starts. * Since shield tuning and resonance is so important, a stealthed ship is - by definition - an unshielded ship. So stealth = vulnerability. * Presumably higher powered sensors might break the resonance and reveal the stealthed ships. These might be in place around fixed installations but are too expensive energywise to be used constantly on capital ships. It also means stealth probably isn't possible if you get too closed to a star... although maybe it would be possible to blend in? * You might not be able to stealth all frequency bands simultaneously, which would make the hunter/hunted cat and mouse game more interesting, as sensor operators try to guess and tune around their enemies, while stealthed shield technicians do the same and try to keep ahead of them. [Answer] Decoys. It would presumably be much cheaper to produce inanimate hulks of similar size & composition to your fighters & bombers than to produce an actual vehicle. Especially with the smaller vehicles coasting in at minimum power before the shooting starts, it will present the enemy with a challenge to pick out the relative handful of actual vehicles among the crowd, forcing them to spread their defensive preparations across a wider range of possible attacks. The larger the number of objects, the more effective this will be (10 decoys for 10 ships probably won't have a meaningful effect; 10,000 decoys for 100 ships should). Of course once a ship actually maneuvers or fires it'll be a known threat; at best you could attack in waves to force the enemy's attention to remain at least partially on the as-yet inert objects to guard against delayed strikes. [Answer] This started out as a comment, but I decided it's actually a fair answer, so here goes. You don't really say much about how your sub-lightspeed drive system works, so I'm going out on a bit of a limb and assuming that it relies largely or entirely on Newtonian or relativity physics. In other words, what we've got in our world. In such a situation, in spaceflight, [you don't use the engines very much](http://tvtropes.org/pmwiki/pmwiki.php/Main/SpaceFriction). In fact, you want to turn the engines off and coast as much as you possibly can, in order to conserve fuel. Look at [this graph](https://en.wikipedia.org/wiki/File:Tsiolkovsky_rocket_equation.svg) of the [rocket equation](https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation): $ \Delta v = v\_e \ln \frac{m\_0}{m\_1} $  That graph shows the spacecraft's mass ratio (total mass including fuel, to total mass excluding fuel, on the vertical axis) as a function of its ability to change velocity (on the horizontal axis; $\Delta v$ is the total velocity change budget, and for all practical purposes, $v\_e$ is a constant for a given engine). It starts off fairly reasonable, and grows exponentially. This leads to an obvious conclusion: **If you can afford to coast, you can conserve your fuel for maneuvering when needed.** So a potentially advantageous tactic would be to coast as much as possible, making maneuvers that require as little fuel as possible while achieving the intended goal. Because any given maneuver implies a specific $\Delta v$ (change of velocity, along some vector), and the mass ratio grows more slowly if $\frac{\Delta v}{v\_e}$ is smaller, this favors the engine technology with a larger $v\_e$ or [effective exhaust velocity](https://en.wikipedia.org/wiki/Effective_exhaust_velocity). This puts some fairly specific constraints on spacecraft engine design, and the civilization that can make engines capable of meeting the required $\Delta v$ at the higher $v\_e$ will have a maneuvering advantage, regardless of whether this is for combat or peaceful purposes. The spacecraft that is slower to maneuver will be a sitting duck as it coasts along in its orbit, blissfully unaware of the weapons being fired toward it. Some of the implications of this are discussed in [this answer to *How much bigger could Earth be, before rockets would't work?*](https://space.stackexchange.com/a/14384/415) on our sister site Space Exploration. In science-fiction movies, we're pretty used to seeing spacecraft with engines on all the time buzzing around each other, like aircraft or seacraft, but such a tactic would, in real life, mean you run out of fuel very quickly. Due to the exponential nature of the rocket equation, you just can't afford to carry all the fuel that would be required. Figure out ways to make do with less fuel, and you'll have an advantage, whether you use that advantage to allow for more maneuvers or for more lightweight spacecraft. Just because something is "weightless" doesn't mean inertia is unimportant. [Answer] How about your spacecraft make their own "terrain" in the form of (un)controlled debris fields? A debris field would neutralize any weapon fired from a distance. That mean engagements would need to be close ranged and require quick decision-making when weapons are fired (a possible reason not to use AI). The capital ships would launch several large fields, possibly with limited maneuverability. The fighters could have smaller fields, possibly even built into their design (I'm picturing something like the skyjacks in Jupiter Ascending). System defenses would have large debris fields with heavily defended navigation routes (and lots of dangerous, uncharted routes for enterprising fighter pilots to exploit). Tactics would mostly resolve around positioning. Block the enemy's fire lanes while opening your own. Feints, hit-and-run attacks, hiding-in-the-debris, stuff like that. [Answer] Spacecrafts and fuel are expensive. This leads to everyone being very risk adverse. You don't really want to go into battle unless you have your opponent at a great disadvantage. As you can't ambush a fleet from behind a planet, you'll have to find another way to get a large advantage. You'll need to attack the enemy when they are very low on fuel. This means that you must move your own fleet around, threatening attack after attack until they are far from their jump points and low on fuel. This would be easy if you have many battle groups of the same size and firepower as your opponents single battle group. But if your fleet is of the same size you would have to split up in smaller groups, threatening attack, but never get into a position where the opponent can counterattack because you get too close with too small a force. You may even be forced to sacrifice one or more capitol ships to destroy the opponents tankers to get a sufficient fuel advantage. [Answer] You mention quite a lot in your question, so I'm only going to focus on one topic: > > I have a setting with space fleets fighting, they include both capital ships and human flown 'space fighters', which I already put some work into justifying: How to keep humans pilots instead of AI in sci-fi future? > > > Use EMP weapons. Humans won't be killed by them, but as for AI...you'll need a pretty big Faraday box to put an artificial intelligence in. Or you could rely on the fact that AI are almost always going to have exploitable loopholes in their logic. [Answer] Space tactics, maneuvers, etc naturally vary for a variety of reasons. **Different ship classes** Making everything a big cruiser has it's downsides. Smaller ships are able to outmaneuver bigger guns, fly largely undetected. Logistics transports carry large amounts of supplies and don't incur the same costs as building big, and are often necessary in large scale fights. Then you have the defensive classes - anti-space mines, anti-missile defence, anti-fighter classes. **Space is 3D** Hiding behind planets, moons, etc, is an old-school rookie mistake. That's the first place any seasoned ship commandeer would expect you to be. Hiding in nebulae where sensor locks are impossible, or even playing chicken with the event horizon of a black hole (which inexperienced commanders in large ships with a lot of mass often fall for - literally) is where make-or-break happens. Ships can attack from above, below, on the Z axis. Some rogue elements have been known to sit in cloak weeks at a time in a single spot where a neutron star covers their low-power sensor profile, only to attack when a group of carriers have their shields down and are conducting repairs in an area that has been safe for some time. **It's all about location, location, location** Big fleets are nice, but what if you were at Rembabuun 3 on defence, when the enemy instead raided space station Kotoon and destroyed a couple of your Drydocks whilst they were at it in the Contar sector, at least 30 minutes away? Stretching your fleet to 'defend everything' is a huge no-no, as it allows isolated battles to occur and holes in a defensive net to form. Half of the battle is disinformation, the other half, secrecy and surprise. **Space is big** And so is your border. Border patrols aren't a thing. Instead, most commanders defend 'key areas' either with static defences or big fleets, with roving 'hunter-killer' groups whose goal is to hunt and track down other fleets in space for engagement. **No-one obeys the rules** Geneva convention didn't apply when the Intergalatic Fleet or Imperialic Fleet built their superdoom weapon and started firing into fleet engagements at random. The second moon of Yonkoon blew up, taking with it a main space trading station. 'It was an accident', according to reports. The Intergalatic Convention on Space Rights doesn't have it's own spacefleet, so it's highly dependent on the already-at-war parties to enforce it's toothless laws. **Political will changes tactics** The Peacekeeper Corp of the Seventh fleet are adverse to killing pretty much anything. They're comprised of volunteer medics who respond to disasters and warzones. Their idea of 'tactics' largely involves running away, or sometimes wading in regardless with a big sign indicating they're medical only. To some fleets, that's a giant target. The Patriotic Corp, is an independent ragtag fleet of ships (pirates?) who, on the other hand, aren't so adverse to violence. They've been known to purposefully murder survivors to keep up their terrible reputation, pillage ships for supplies, and sometimes even rig civilian ships to fly into military ships on auto-pilot with enough explosives to make a Gangoolian wet it's brine container. [Answer] As an addition to the answers above, your shields could heavily influence the range at which fights take place. Imagine an enemy pops up a few lightminutes away. They detect eachother and open fire. You dont just create a shield bubble but a shield wedge: the ballistics fired at it will basically hit a giant sloped armor and are likely to bounce off if the calibration was good. lasers already fan out too much for effective long-range combat so it would be mainly ballistics and missiles. Missiles and other computer and AI can suffer interference from the shield, hence that not just the fighters but also the capitol ship are manned rather than AI governed (I'm still at a loss why people would argue that fighters would fly with AI while capitol ships would still be manned? Why would you not remove the human element and AI your entire fleet?). Anyway, the shield might not be alterable on a dime, so being close and able to have a high angular velocity allows you to avoid the wedge shape of the shield and do full damage against the shield while fighters can be close enough to require being manned and not be auto-targeted and killed by automated systems. [Answer] Go play *EVE Online*. Seriously. See how tactics work in that universe. Most of them revolve around "on grid" combat, and rock, paper, scissors. You can use this as well. * If a ship is too far away, you can tell "something is there" but not "what". * As it gets closer, you can tell the "what" but not exactly. * As it gets "on grid" (actionable in the game), you can tell more precisely the "what". * Bigger ships (and such) have the ability to "hide" forces. Either because you can't tell what is docked in a "Capital Ship", or because the large ships can "jump in" smaller ships. Then * Small ships have smaller guns. * Big ships have big guns but can't really hit smaller ships. * Lots of small ships > 1 big ship. * 1 Big ship vs. 1 Small ship = No win. The small ship can't damage the big ship, the Big ship can't chase down the small ship. * Special ships have a well defined role. A scanning ship can do much damage. A "tank" can dish out massive damage. A "gun boat" can really pump out damage but can't take as much. A fast ship can't do much damage, but is too fast to take a lot of damage. * Big ships are needed to fight big ships * Small ships are needed to fight small ships. Quite a few tactics have evolved around these rules. The biggest is that while space is big, and vast, your fighting has to take place in a small area. In the game it's usually around a fixed point, but it can take place at a random location. It's just that all things in combat have to be "on grid". Mostly though, you end up with the same "rules" as present day warfare. Range, accuracy, and the ability to specialize make the difference. A rock paper scissors approach. Which, exists today in naval combat. That's why, no matter how impressive a Battle ship is, it is not sent out without an escort of other ships. [Answer] Imagine the fight is between nano-robot probes, that have an extremely slow computational speed because they have very little computational power. These probes could maybe have a processing speed of a millionth of the human, and so "in their opinion" the fight would be very interesting and strategic. You can have huge numbers of these for each army, that must juggle their power between computation, locomotion, attack, defense. You can elaborate on the "swarm" mentality, maybe a single probe is low tech/stupid but ten thousand can create a jamming / intercepting network that can be more dangerous than the sum of its parts. This can create an interesting environment, where the probes do not communicate with each other too often because they need the energy to move out of the enemy's trajectory. This could all just be a hobby of "superior beings" so advanced we cannot comprehend that can live for billions of years or more (nobody really knows). [Answer] **Create your own space terrain** Space is big and empty ... but what if you could change that? You can use things like the space equivalent of shotgun shells that scatter high velocity debris over a wide area, or some sort of constant jamming technology to deny your opponent control of sections of the battlespace and try to force them into an unfavorable position. [Answer] One idea that comes to mind is using the shields to stealth the ships, simply use them to block all the heat emissions of the ship and suddenly the battle turns into a game of hide and seek with nuclear warheads. Your protagonists would need to carefully plot their movements to avoid overloading the shields. Every battle would become a battle between minds, as the captains of each ship try to predict what the other is going to do next. ]

[Question] [ **Background story:** Current Earth, in the close future. Astronomers have found first signs of extraterrestrial life: huge sheet-like objects (with surfaces easily as large as the surface of the Earth) appear all around the sun. They do not approach Earth, but remain in stationary spots relative to each other. And it is nearly daily that new objects appear all of them at the same distance from the sun at half of Mercury's orbit. After several weeks of observation, it is clear that the sheets cannot be natural events – starting with how they keep their exact position relative to each other and relative to the sun, to them being of some strange mix of trans-iron metals, and ending with sheets not being a natural rock/... formation. They MUST have been formed by aliens; even if we cannot make out exactly how they got transported to the sun. They definitely didn't get towed by spaceships or anything normal like that – one day a spot is empty, and the next there is one of those sheets. No clue how they appeared, no radiation anomalies, nothing. We try communicating with what clearly has to be an alien civilization, but there is no answer to any of our attempts. Gradually, more and more sheets appear in what is starting to look like a Dyson grid – if not the beginnings of a Dyson sphere. And then, one day, a text message is displayed on all screens on the entire world: "Hello. We are the GGs, the Good Guys, an advanced civilization from the *X* system. Since you appear to have advanced to technological toddlerhood and seem to be prone to panicking, it has been decided it would be best to inform you of the current happenings. We are the GGs, after all, and if you kill yourselves due to your poor instinct control and backward fear response, we will have failed our mandate of Protecting All Lesser Races. "Your star system has come to the attention of the BBs, the Bad Boys, who delight in eradicating entire civilizations. They will be in your neighborhood within the next decade, in two Earth years at the earliest. To prevent your planet from befalling harm, we are currently building a sun-powered defensive shield for your entire solar system. Whenever we turn on this shield, though, it will take the entire energy output of your sun – meaning that to a Lesser Race like you it will look like the sun got turned off. "Don't worry, we know exactly how long we can keep the shield going without affecting your planet unduly at your current technological level. We will not be the cause of human deaths, and we implore you to keep a well enough order on your planet to not cause deaths amongst yourselves. "Toodles, "The Good Guys" After a short demonstration of the full functionality of the sun-off switch, humanity actually believes the GGs. They start to wonder about how long they could expect the sun to be turned off at the longest... --- # TL;DR **Quick Facts (those who do not want to read the background story):** * Earth: current technological level * Aliens can and will turn off the sun temporarily. This may be a repeated event. Aliens say they won't turn off the sun long enough to damage the planet or humanity, but don't give any exact numbers. * Earth has forewarning: earliest sun-out is in two years --- ## Question How long can the sun be turned off without planet Earth taking enough damage to endanger human survival? (Assume that the sun will be turned on again after this period of time, and humanity/Earth should be able to bounce back within a few months. The next sun-out will come only once humanity/Earth has recovered.) There is enough forewarning to establish sufficient food stores and shelters etc., so at least a part of humanity should be able to weather the event in pretty comfortable conditions. Afterwards, sunlight will be just as available as it was before again. However, what about * Non-human life? How long can plants survive without sunlight? How long until the ecosphere will be damaged so badly that it cannot be... reforested again when the sun turns on again? What about animal life? Species dying out is acceptable, but not to the point of an extinction-level event (less than 10% of all land + maritime species) * Oxygen? Does this even become a factor due to the restrictions on killing plant-life and temperature? * Temperature? How long until the average temperatures have dropped more than, say, 10 degrees Celsius? * Natural catastrophes? Will the sudden absence of sunlight cause huge hurricanes / ice storms /...? What about a continued absence of sunlight? A **ball-park figure** would be enough for me; is it a couple of days that Earth can weather only, a couple of weeks, or might Earth even be capable of enduring 2-3 months without sunlight? **EDIT:** I am looking for the longest possible time the sun can be turned off in one go. 4 hours daily is not what I am looking for :) [Answer] While no one has ever turned off the sun, there are some historical reference points. **Volcanic Eruption Data** Following the [May 20, 1883 eruption of the Krakatoa volcano](https://en.wikipedia.org/wiki/1883_eruption_of_Krakatoa) which spewed ash into the air that slightly reduced the amount of sunlight reaching the Earth: > > Average global temperatures fell by as much as 1.2 degrees Celsius in > the year following the eruption. Weather patterns continued to be > chaotic for years and temperatures did not return to normal until > 1888. > > > [Mount Tambora's eruption on April 10, 1815](https://en.wikipedia.org/wiki/Mount_Tambora) (also in Indonesia) was the most powerful in recorded history: > > The eruption caused global climate anomalies that included the > phenomenon known as "volcanic winter": 1816 became known as the "Year > Without a Summer" because of the effect on North American and European > weather. Crops failed and livestock died in much of the Northern > Hemisphere, resulting in the worst famine of the 19th century. > > > [In particular](https://en.wikipedia.org/wiki/1815_eruption_of_Mount_Tambora): > > The 1815 eruption released sulfur dioxide (SO2) into the stratosphere, > causing a global climate anomaly. Different methods have estimated the > ejected sulphur mass during the eruption: the petrological method; an > optical depth measurement based on anatomical observations; and the > polar ice core sulfate concentration method, using cores from > Greenland and Antarctica. The figures vary depending on the method, > ranging from 10 to 120 million tonnes. > > > In the spring and summer of 1815, a persistent "dry fog" was observed > in the northeastern United States. The fog reddened and dimmed the > sunlight, such that sunspots were visible to the naked eye. Neither > wind nor rainfall dispersed the "fog". It was identified as a > stratospheric sulfate aerosol veil.[10] In summer 1816, countries in > the Northern Hemisphere suffered extreme weather conditions, dubbed > the Year Without a Summer. Average global temperatures decreased about > 0.4–0.7 °C (0.7–1.3 °F),[4](http://onlinelibrary.wiley.com/doi/10.1111/jeb.12882/abstract) enough to cause significant agricultural problems around the globe. On 4 June 1816, frosts were reported in the > upper elevations of New Hampshire, Maine, Vermont and northern New > York. On 6 June 1816, snow fell in Albany, New York, and Dennysville, > Maine.[10] Such conditions occurred for at least three months and > ruined most agricultural crops in North America. Canada experienced > extreme cold during that summer. Snow 30 cm (12 in) deep accumulated > near Quebec City from 6 to 10 June 1816. > > > The second-coldest year in the Northern Hemisphere since c.1400 was > 1816, and the 1810s are the coldest decade on record, a result of > Tambora's 1815 eruption and another possible VEI 7 eruption that took > place in late 1808 (see sulfate concentration figure from ice core > data). The surface temperature anomalies during the summer of 1816, > 1817, and 1818 were −0.51 °C (−0.92 °F), −0.44 °C (−0.79 °F) and −0.29 > °C (−0.52 °F), respectively.[7](https://en.wikipedia.org/wiki/Diurnal_temperature_variation) As well as a cooler summer, parts of > Europe experienced a stormier winter. > > > This climate anomaly has been blamed for the severity of typhus > epidemics in southeast Europe and the eastern Mediterranean between > 1816 and 1819. The climate changes disrupted the Indian monsoons, > caused three failed harvests and famine contributing to the spread of > a new strain of cholera originating in Bengal in 1816. Many livestock > died in New England during the winter of 1816–1817. Cool temperatures > and heavy rains resulted in failed harvests in Britain and Ireland. > Families in Wales travelled long distances as refugees, begging for > food. Famine was prevalent in north and southwest Ireland, following > the failure of wheat, oat, and potato harvests. The crisis was severe > in Germany, where food prices rose sharply and demonstrations in front > of grain markets and bakeries, followed by riots, arson, and looting, > took place in many European cities. It was the worst famine of the > 19th century. > > > A volcanic eruption [in 1257 CE in Lombok, Indonesia](https://en.wikipedia.org/wiki/1257_Samalas_eruption) probably caused the Little Age Age. What happened half the world away (where all of the effects were from loss of sunlight rathe than direct impacts of the volcano): > > Reports in 1258 recount the presence of a dry fog, giving the > impression of a persistent cloud cover to contemporary observers. > Medieval chronicles say that in 1258 the summer was cold and rainy, > resulting in floods and bad harvests, with cold lasting from February > to June. In both Europe and the Middle East, changes in atmospheric > colours, storms, cold and severe weather were reported in 1258-1259. > In Europe, too much rain damaged crops and caused famines followed by > epidemics. Reports of the effects of the eruption, including failure > of crops and famine as well as weather changes, exist for northwest > Europe. Crop failures, and a famine in London have been linked to this > event. Witnesses reported a death toll of 15,000 to 20,000 in London. > Matthew Paris of St Alban retells how until mid-August in 1258, the > weather alternated between cold and strong rain, causing high > mortality. > > > Swollen and rotting in groups of five or six, the dead lay abandoned > in pigsties, on dunghills, and in the muddy streets. > > > — Matthew Paris, chronicler of St. Albans, > > > The resulting famine was severe enough that grain was imported from > Germany and Holland. The price for corn increased in Britain, > France and Italy. Outbreaks of disease occurred during this time in > the Middle East and England. Problems were also recorded in China, > Japan and Korea. Other effects of the volcanic eruption include a > lunar eclipse in May 1258, where the Moon was completely darkened. > With and after winter 1258-1259, exceptional weathers were reported > less commonly, but the winter 1260-1261 was very severe in Iceland, > Italy and elsewhere. > > > **The K-Pg extinction event** The most pertinent precedent is the K-Pg extinction event (formerly known as the K-T extinction event) 66 million years ago that killed off the dinosaurs clearing the way for mammals: > > [A] 10-to-15-kilometre (6.2 to 9.3 mi) space rock hurtled into Earth > at Chicxulub on Mexico's Yucatán Peninsula. The collision would have > released the same energy as 100 teratonnes of TNT (420 ZJ), over a > billion times the energy of the atomic bombings of Hiroshima and > Nagasaki. > > > The consequences of the Chicxulub impact were of global extent. Some > of these phenomena were brief occurrences that immediately followed > the impact, but there were also long-term geochemical and climatic > disruptions that were catastrophic to the ecology. . . . **the impact > would have inhibited photosynthesis by creating a dust cloud that > blocked sunlight for up to a year.** Further, the asteroid struck a > region of sulfur-rich carbonate rock, much of which was vaporized, > thereby injecting sulfuric acid aerosols into the stratosphere, which > **might have reduced sunlight reaching the Earth's surface by more than > 50%**, and would have caused rain and ocean water to become > acidic. The acidification of the oceans would kill many > organisms that build shells from calcium carbonate. At Brazos section, > **the paleo-sea surface temperature dropped as much as 7℃ for decades > after the impact. It would take at least ten years for such > aerosols to dissipate, and would account for the extinction of plants > and phytoplankton, and of organisms dependent on them (including > predatory animals as well as herbivores). Some creatures whose food > chains were based on detritus would have a reasonable chance of > survival.** > > > [New studies](http://onlinelibrary.wiley.com/doi/10.1111/jeb.12882/abstract) show that this caused mass extinctions at levels previously unrealized: > > Extinction rates are markedly higher than previously estimated: of 59 > species, four survived (93% species extinction, 86% of genera). > > > The "good news" is that even a year with an at least 50% reduction in solar energy penetration wasn't enough to cause all life on Earth to go extinct, although the vast majority of life on Earth including virtually all "megafauna" did. The "bad news" is that a far shorter deprivation of sunlight, particularly if it was more complete than the K-T event, would still be a big problem. The 7 degrees of temperature drop from a 50% reduction in sunlight for on year might be particularly useful in estimating the impact on the climate from a 100% reduction in sunlight for some period of time shorter than that. After all, we know from the lower impact volcanic events that even a 1-2 degree temperature drop for a year or so is a big thing. **The Heat Budget Of Earth** We know from basic thermodynamics that heat loss is a function of temperature difference. Heat radiated from the parts of the Earth where people live is mediated by the atmosphere which is between us and empty space. Empty space is about 3 degrees K. But, the top of the atmosphere, even after the K-Pg extinction event, would still have been heated by the sun without interruption - less of that heat would have made it to the surface of the Earth, but the heat on the top of the clouds would still have slowed radiation of heat to outer space. To evaluate that you need a grip on the [Earth's heat budget](https://en.wikipedia.org/wiki/Earth%27s_energy_budget) in normal times: > > To quantify Earth's heat budget or heat balance, let the insolation > received at the top of the atmosphere be 100 units, as shown in the > accompanying illustration. Called the albedo of Earth, around 35 units > are reflected back to space: 27 from the top of clouds, 2 from snow > and ice-covered areas, and 6 by other parts of the atmosphere. The 65 > remaining units are absorbed: 14 within the atmosphere and 51 by the > Earth’s surface. These 51 units are radiated to space in the form of > terrestrial radiation: 17 directly radiated to space and 34 absorbed > by the atmosphere (19 through latent heat of condensation, 9 via > convection and turbulence, and 6 directly absorbed). The 48 units > absorbed by the atmosphere (34 units from terrestrial radiation and 14 > from insolation) are finally radiated back to space. These 65 units > (17 from the ground and 48 from the atmosphere) balance the 65 units > absorbed from the sun; thereby demonstrating no net gain of energy by > the Earth. > > > So, about a third of the solar energy normally received on Earth immediately goes into space through radiation, and two-thirds of the solar energy normally received on Earth is absorbed by the atmosphere and ultimately ends up in space, but more slowly, preventing the surface from losing energy all that much faster. **The Precedent Of Nighttime** It would also help to know the typical [differences between night and day temperatures](https://en.wikipedia.org/wiki/Diurnal_temperature_variation): > > As solar energy strikes the earth’s surface each morning, a shallow > 1–3-centimetre (0.39–1.18 in) layer of air directly above the ground > is heated by conduction. Heat exchange between this shallow layer of > warm air and the cooler air above is very inefficient. On a warm > summer’s day, for example, air temperatures may vary by 16.5 °C (30 > °F) from just above the ground to waist height. Incoming solar > radiation exceeds outgoing heat energy for many hours after noon and > equilibrium is usually reached from 3–5 p.m. but this may be affected > by a variety of different things such as large bodies of water, soil > type and cover, wind, cloud cover/water vapor, and moisture on the > ground. > > > Diurnal temperature variations are greatest very near the earth’s > surface. > > > High desert areas typically have the greatest diurnal temperature > variations. Low lying, humid areas typically have the least. This > explains why an area like the Snake River Plain can have high > temperatures of 38 °C (100 °F) during a summer day, and then have lows > of 5–10 °C (41–50 °F). At the same time, Washington D.C., which is > much more humid, has temperature variations of only 8 °C (14 °F); > urban Hong Kong has a diurnal temperature range of little more than 4 > °C (7.2 °F). > > > Averaging the high and the low provides about 18 °C of average temperature difference between day and night. The temperature loss from a single night without the Sun would probably triple in 36 hours without sunlight, so even the best buffered areas might lose 24 °C and the least buffered areas, like deserts, would lose much more, perhaps 54 °C or more, which would be enough to turn hot deserts into frozen deserts. (Cooler temperatures would also shut down evaporation leading to extreme aridity in every place that depends on rain once the exiting moisture in the air was exhausted.) This suggests that ambient temperature drops will wreck havoc in a matter of hours or days by exposing people and livestock and plants to temperatures that are cold enough to kill them from exposure, while loss of photosynthesis leading to famines and the like (given food stores on hand) might take months; after all, lots of places have months of winter when nothing grows already. **Conclusion** Many people, animals and plants would die from exposure to cold in even a single day entirely without any Sun with a night before and after the period without the Sun (as opposed to merely being obscured by particulates in the atmosphere). A "safe" period during which the Sun could be turned off would be significantly less than 12 hours. An entire 12 hours without Sun deprives every place on Earth from Sun for 24 to 36 hours, while 4-6 hours would lead to Sun deprivation for no more than 18 hours continuously in the worst hit areas, and would have less continuous deprivation in many places. Breaking up a continuous period completely without the Sun for even a few hours makes a huge difference relative to having the Sun turn off just before sunrise and stay off until what would ordinarily be sunset in terms of planetary and local temperature drops. On the other hand, Paige Ksnak's estimate of one degree per minute is probably too high, mostly because the atmosphere is still a blanket that would slow heat loss and buffer the temperature of the Earth until it lost all of its heat, which we know takes more than twelve hours without exposure to the Sun to happen because parts of the planet experience that much time without Sun every day. Indeed, even just six or seven hours of Sun followed by twenty-one hours of dark, while making it much cooler, doesn't cause catastrophe if you're ready for it. So, I suspect that the practical limit would be driven by temperature losses from sustained continuous periods of time without the Sun and would be on the order of 4-6 hours tops before severe consequences and mass death followed. [Answer] Others are estimating the results of the temperature change, but I wanted to point out another answer from humanity to the GGs: ### Do you good guys really need the *entire* output of the sun? Earth only occupies a circle 0.005 degrees in diameter from the sun. They could capture effectively all of the sun's energy, but leave a tiny pinhole aimed at our planet and we'd be nearly unaffected. Lastly, I wanted to address the part where you describe: > > but remain in stationary spots relative to each other. > > ... > > Gradually, more and more sheets appear in what is starting to look like a Dyson grid – if not the beginnings of a Dyson sphere. > > > Objects in a conventional Dyson sphere are not static relative to each other, and they're not static relative to the orbiting planets or the star they surround. They orbit just like everything else. They're composed of many separate layers of sheets each orbiting the sun. Don't imagine a stationary soccer ball, with each giant sheet static relative to the others. Instead, imagine a rubber band ball, with each strand consisting of closely-spaced tiny sheets. There would be some tidal forces from other sheets passing above and below each orbit, and some slight course corrections required, but the idea is that it would be basically stable, rather than requiring non-science-based engines to hold the objects static against the unbelievable gravity of the sun. Also, don't imagine the bladder in the soccer ball as occupying all of the space inside except a tiny foam gap between the bladder and the panels - at half the orbit of Mercury, it's more like a ping-pong-ball in a sphere that can contain a ping-pong table. And the shell components don't have to appear by magic warp jumps - they could instead do a fantastic dance where they all come in from interstellar space at extreme speeds, gravity brake around Jupiter and aim at chaotic-appearing angles above, below, and next to the sun. We wouldn't see them coming in for a long time if they were very cold and came from interstellar space edge-on to minimize damage from micrometeoroids and interstellar dust. After sweeping around Jupiter, they'd eventually pass through the ever-increasing cloud around the sun by what would appear to be a ridiculous amount of luck but would actually be extremely careful, complicated, precise choreography. They'd aerobrake in the sun's atmosphere (!), pop back out to their target apoapsis, and circularize. A civilization capable of this choreography should be able to design the swarm such that it always leaves a tiny gap where the light from the Sun can shine on the Earth. [Answer] We could manage for a few days at least without too many bad effects. What we're dealing with here, essentially, is a planetwide long night; we don't get any direct energy from the sun at night and the amount of heat that bleeds over from the day side is basically insignificant. It would take about a week for the global average temperature to drop below freezing. Typical ice ages are colder than that; we could expect to see some glaciation and the more sensitive life forms would have trouble adapting but life on the whole would be all right. Humans would be fine. The biggest problem for these short-term periods is not the cold, but plants dying due to lack of energy. However, even this wouldn't have much of an impact for a while. Small plants would have the biggest problems, but could probably last a week or so; trees and shrubs can store enough energy to last months or even years. Algae tends to go dormant without light, so it could last a while, though oceanic food chains might be disrupted after a few weeks if it wasn't reproducing; not to the point of total extinction though. Temperate regions that were already in the middle of winter might fare best, since most plants would be dormant already (plants that have lost their leaves aren't photosynthesizing anyway). Most seeds would be fine even if their parent plant died. I don't expect we'd be dealing with too many natural hurricane-type catastrophes; in fact since wind is powered by the sun we could probably expect there to be less storms. However, there would be problems in the opposite direction; no sun means no evaporation, which means no rain. Temperate regions can do without rain for a few weeks or even months, but rainforests where the plants are adapted for constant rainfall might be in for a rough time. Over longer periods, of course, the problems would be a lot more significant. We'd have snowball Earth conditions after a few months, which would be the end of many terrestrial plants and all marine mammals. Oceans could stay liquid for a long time, maybe even years, beneath the ice, but with all the algae dead most marine life would die after a while anyway. Geothermal power and stored food might allow humans to endure for a while. So let's say the following estimates: 3 days: No serious problems, just a long night 1 week: Rainforests have problems due to lack of rain, more sensitive life forms die 1 month: Most plants are dead, seeds and maybe a few dormant trees still alive, all but the hardiest of animals die from cold and/or lack of food, humans huddled around volcanoes and eating stored food (at least no problems with refrigeration, right?) 1 year: Average global surface temperature is -100 degrees, everything on land and most sea life is dead, microorganisms living near geothermal sea vents and the animals that eat them are fine and will be for many years to come. Maybe some people in deep-sea habitats and eating stored food can still survive for a while. [Answer] To give a ballpark idea of how important energy received from the Sun is for sustaining energy (and thus life) on Earth: Earth receives about 1000W/m^2 in [energy from the sun](https://en.wikipedia.org/wiki/Solar_constant). I'm using the number on the bottom adjusted for the reflectivity of clouds. Earth's surface as seen from the sun can be approximated as a circle with a radius of 6.371e6 meters. Good old A=pi\*R^2 gives a disc of 1.275e14 m^2 1000J/(sec\*m^2) \* 1.275e14 m^2 = **1.275e17 J/s received by the Earth from the Sun** The mass of the oceans is 1.37e24 g, average depth is 379400 cm. 1.37e24g/379400 = 3.61e18g in the top 1 cm of ocean; half this number since only half of Earth is facing the Sun; **1.80e18g of water exposed to the Sun** [Specific heat of water](http://water.usgs.gov/edu/heat-capacity.html) gives us 4.184 J/g to warm water by 1 degree C. How long does it take to warm the exposed water by 1 degree? 1.80e18g \* 4.184J/g \* 1s/1.275e17 = **59 seconds** So if we're approximating Earth to be made of water (rough estimate, of course; dirt takes less time to heat AND less time to cool), in just one minute of sunlight, you get enough heat on Earth to warm the top centimeter of the oceans by a degree. Doesn't sound like a lot at first? Don't forget that by missing out on sunlight, you're creating a big heat disparity; ocean currents will speed up as they try to equalize the cool spots. Fish in the upper layers of oceans will die quickly without needed heat from the sun. Photosynthetic organisms will be starved of energy; maybe they'll be okay missing out on a few minutes of sunlight a day (maybe), but much more than that and the populations of a multitude of organisms will take a nosedive as the effects add up. [Answer] The Arctic winter illustrates how quickly the planet responds to a change in input (what climate science calls 'forcing'), although if you accept the CO2 drives the climate meme, then the response time must be orders of magnitude slower than seasonal transitions. Of course, the premise is wrong since if you enclose the Sun with a sphere, that sphere will heat up and radiate energy towards the Earth and in the steady state, will be emitting as much energy as its absorbing. If the sphere was 'insulating', the space between the Sun and the sphere would heat without bounds and become hot enough to ionize the atoms comprising the sphere and it would become a plasma like the surface of the Sun itself. Funny, how these basic constraints of thermodynamics are so often ignored, even by many scientists ... Mankind would persist until we ran out of food or things to burn, whichever comes first, but that could be centuries, although the first few billion people and most of the rest of the planets biomass would die within weeks. Frozen, dead biomass will last decades to centuries, so food and fuel will remain available to those that remain for a long time. [Answer] To give you guys some perspective: During winter, the effective output of the sun is 50% in the upper latitudes. If you've ever been to northern countries during winter, you know that it can get to -40C during cold periods. What would happen if the sun were to be turned "off"? For continental locations, it would be worse than winter, temperatures will go below -100C in less than a week. [](https://i.stack.imgur.com/5bkq1.png) In a maritime region, after 21 hours, temperatures dropped by 4.4C, or 5C per day. So after a week, it would be a drop of temperature of about 35.2C [](https://i.stack.imgur.com/lYjdz.jpg) Inland, the temperature drop after losing sunlight is about 6C in 9 hours, or 16C per day. After a week, it would be about a loss of 112C. Maritime regions will be luckier, the sea stores a lot of heat. Normally, the seas' temperature is a gradient from hottest at the top to coldest at the bottom (except rifts and vents). But if the sun were to go dark, the gradient will reverse. Hot water will still rise, but it will still cool fast enough so that it becomes freezing near the surface. Unlike what most people suggest, the oceans will not be able to give out all its heat effectively, since once the water surface temperature drops below -5c a thick crust of ice will form at the surface, blocking heat transfer and acting as an insulating shield. Even if most oceans will stay liquid under the surface for quite a while, Maritime life will quickly die out though due to lack of sunlight and food. In short, tropical regions have at best one day before suffering irreversible damage. Artic regions might have 3-4 weeks as a conservative estimate, as most lifeforms there have abilities to survive long periods of glaciation. But expect polar bears and penguins to die out. [Answer] Umm ... since scientists have never performed experiments about turning off the sun in a laboratory, we don't know the exact implications. But I can think of some detrimental changes. 1- The sun is our primary source of heat and light. Turning off the sun for 30 minutes straight will drop the temperatures on the night sides enough to freeze water. We are talking about equatorial regions here. 2- Also expect some extremely vicious, huge vortexes forming due to the sudden difference of air pressure as the sun goes out. We are talking about storms like on Neptune. You *don't* want to get these. One such vortex (if the wind speeds reach Neptunian storm speeds) would easily wipe out any and all traces of human settlement in its region. Also => forget all wildlife and forests in the region. 3- Ocean life will suffer irrepairably. Turning off the sun for an hour daily will have immense implications for phytoplankton which would in turn ripple out into the entire marine food webs. 4- Also, the circadian rhythm of all complex creatures would be badly disturbed. Conclusion: it is very very bad to turn off the sun. We don't know precisely what it would result in, but even turning off the sun for one hour daily for extended periods of time (for a couple months) would have long term and irrepairable consequences for climate patterns and ecology. [Answer] I think answers that equate a 'turned off' sun with an extended night time are wrong. The Earth is ALWAYS getting warmed by the sun. It's 24/7 365(366 on leap year) energy. Even if your side of the planet happens to be on the opposite side from the sun there is a tremendous amount of energy being brought to you from the day side by winds. With the sun 'turned off' you don't get that. I'm guessing it's minutes at best before some negative effects are noticed and major extinctions in less than a day. [Answer] First comment which I've not seen mentioned is that casualties will begin to mount immediately. People relying on daylight will be plunged into darkness and some will die because of it. Second point is that the Sun's flux varies by ~0.1% over the solar cycle. It isn't reasonable that the 0.00002% falling on the Earth at any one instant would make or break the GG's response to the BGs. Third point (which you probably know) is that the physics behind your Dyson sphere is seriously aphysical, requiring technologies and materials which contradict what we (think we) know about Science. [Answer] **Estimate:** If we're mainly concerned with avoiding irreversible changes to climate, then the Sun can be turned off for about 200 days. This is a low estimate, and slightly longer times would probably be fine. However, if the Sun is turned off for a year or so, then the Earth is likely to enter a "snowball state", where the oceans are frozen over and the ground is covered with snow. In a snowball state, even when the Sun is turned back on, the surface is white and reflective, so sunlight is ineffective at warming it back up. This could result in permanent glaciation. **Calculations:** This is based on a rough order-of-magnitude estimate, so the answer could be off by a factor of two or so. If the oceans freeze, then the Earth will enter a stable "snowball" state, which is almost impossible to recover from because ice reflects sunlight, and even when the Sun is turned back on, it will not be efficient at warming the Earth back up. Since water has a very high heat capacity, the oceans store most of the Earth's surface heat. However, the deep ocean does not mix with the surface very well. Oceans have a wind-mixed layer, which is about 50 meters deep on average, which remains at nearly uniform temperature. Water below this layer is more or less thermally insulated from the surface, and does not affect the calculation. For the oceans to begin to freeze, the wind-mixed layer would have to be cooled from its present average temperature (about 16 degrees C) to the freezing temperature of ocean water (about -2 degrees C). The wind-mixed layer is about 50 meters deep, so each square meter of ocean corresponds to 50 cubic meters of water. The heat capacity of water is around 4200 J per kg per degree C, so cooling down 50 cubic meters of water by 18 degrees C requires losing (50 m^3) x (1000 kg / m^3) x (4200 J / kg deg C) x (18 deg C) = about 3.8 billion joules. The rate of heat loss per unit area is proportional to temperature raised to the fourth power (Stefan-Boltzmann law). However, Earth has an atmosphere, which acts as a thermal blanket, so the correct temperature to use is not the surface temperature, but the "effective temperature" as seen from space, which for Earth is about -21 deg C, or (273 - 21) = 252 Kelvins. Using the Stefan-Boltzmann law, Earth will radiate at: sigma T^4 = (5.7 x 10^-8 W / m^2 K^4) x (252 K)^4 = 230 W / m^2. So, each square meter of surface will lose 230 Joules of energy per second. Normally, this is balanced out by heat received from the Sun, but when the Sun is turned off, this heat loss will cool and eventually freeze the surface. The oceans will begin to freeze when they've lost around 3.8 billion Joules per square meter, which will take (3.8 x 10^9) / 230 = 16.5 million seconds = 190 days. Now, in reality, as the Earth cools down, it will lose heat slightly slower, so this time will be a little bit longer. In addition, the ice crust will at first be thin, and could easily be melted, and will take some time to develop to a stable thickness. So, 190 days is a safe lower limit. If the time is doubled, however, then the chance of a "snowball state" becomes very high. [Answer] So the aliens plan on turning off the sun, which is technically an exploding star? If the sun turned off, I think we should be more worried about an event related to gravity, rather than enough energy to keep our little planet at an ideal temperature. The g-waves would most likely shatter our atmosphere and flip the planet inside out. This would be an interesting event to watch live! Imagine our solar system as a plain circle with the sun in the middle. Then imagine a box surrounding the circle, which would be this "solar shield" the aliens speak of. Then imagine the same image, just no sun. This of course means taking away the color, the energy, and the gravity...and then take the same image, with the sun turned on again, and everything inside the box is all messed up due to the alteration of gravity. And then the other issue is actually getting an exploding star to "turn on" again. Have you tried to re-ignite a burned match? Its not the same. I would change the story. ]

[Question] [ Similar to [Could Plants Develop Sentience?](https://worldbuilding.stackexchange.com/questions/34034/could-plants-develop-sentience) but slightly more general: I'm not interested in plants in particular, but want a more general understanding of the effect of motion on intelligence and vice versa. In general intelligent lifeforms on Earth, like [hominids](https://en.wikipedia.org/wiki/Hominidae), [cephalopods](https://en.wikipedia.org/wiki/Cephalopod), and [cetaceans](https://en.wikipedia.org/wiki/Cetacea), are highly mobile. Mobility and intelligence seem to be linked in our home ecosystem with the most mobile creatures having the largest brain-to-body mass ratios. So the question I have is reasonably simple: is this a coincidence, a consequence, or a prerequisite for intelligent life? Could a sedentary creature, of any order, develop high levels of intelligence, possibly even sentience, or does intelligence require and/or beget movement? For the sake of clarity my initial thought in asking this question was geared toward ambush predators like the snapping turtle only more sedentary in habit since most ambush predators I can think of move between kills and this theoretical lifeform either couldn't or wouldn't. [Answer] The only limitation of the development of intelligence is an evolutionary purpose. Every significant trait or feature present in a living organism is there because it helps that organism survive and reproduce. For a plant or other sessile creature to develop intelligence it must be able to use that intelligence in some way to improve its fitness. It might need intelligence to acquire food, avoid predators, or attract mates as a few simple examples. In general non-mobile organisms have little use for intelligence. They can't move to find food, avoid predators, or mate. In general they lack most sensory inputs as well as motor functions, meaning that even if they were intelligent they wouldn't have effective ways of understanding the environment around them or of reacting to it even if they did. All that said, it's not inconceivable that there might be some task for which a sessile organism would require intelligence. Most likely this intelligence would need to develop along side appropriate sensory inputs (to give the intelligence something to think about) as well as some ability to react (to accomplish something once it decides to do so). [Answer] As mentioned by others, Nothing evolves an adaptation just because. **The reason there is a correlation between movement and intelligence is because movement requires understanding of your environment** (must recognize that you cant run through a rock), if you are in a fixed position awareness doesn't really help you because you cant react to dodge incoming threats. This begins to explain why there can be a **correlation between intelligence and predation**. One good way to be an effective mobile predator is you need to be able to recognize your prey and their **patterns** and plan a solution. In all terrestrial cases intelligence has been evolved to react to the environment and to acquire food sources humans included. **To start answering your question:** your sedentary creature would need a reason to need intelligence other than to use motion to achieve a biological goal. Perhaps the weather is so erratic and violent that awareness and pattern recognition would need to be used to deploy protective measures on demand. Perhaps they develop a telepathic means of communication which aids them in reproduction being able to plan with eachother when is best to mate. **OR YOU COULD take the inverse of your scenario** Instead of a sedentary creature evolving intelligence, what about an intelligent creature de-evolving mobility. This isn't uncommon, there are plenty of birds which have lost the ability to fly because they found food sources without it (penguins and chickens). You could even start to see such a trend in humans. We use to cover tens of miles daily and swing from trees. Now in many cases to be more productive requires tolerating a sedentary position for long periods (learning and working behind a desk). We have machines that can handle moving us A to B so it we don't really need our previous mobility. We very well could lose it. Your creature could be a parallel of this. [Answer] Okay, first off, it's important to say what no one here seems willing to say: no one knows squat about this. Everything anyone says or has said is the subject of intense debate and inflammatory argumentation. What this means to a worldbuilder is simple: you don't have to explain it. Any organism at all can have sentience, and no one on Earth can say anything about it. As far as planets with sentient life go, we have a sample size of one. There is simply zero sound science on the matter. Expect argument on this! Second, I'm looking around and I'm seeing a huge amount of poor, poor analysis of evolution, the kind of talk that leaves space for creationists to argue. If you see the words "evolutionary purpose" run screaming. The phrase is meaningless at best and harmfully misleading at worst. Holy effing JC, I lose patience with this. Evolution has no purpose. Evolution's primary engine is randomness. Natural selection can narrow down the amount of successful organisms, but it doesn't create them or direct them. I've got to say this again: evolution has no purpose. To say that this or that feature of an organism is constrained by "evolutionary purpose" is putting the cart before the horse, or if you will, the arthropod before the ganglia. The mechanism is simple: evolution happens by accident, natural selection narrows it down. Look, here's a simple example: say there's a lush field full of life and flying creatures with all sorts of flowery ornamental plumage, as tends to happen when there aren't lots of predators around that can manage to catch birds. Then suddenly the field is buried in lava. What species of bird will survive? Some subset of the birds that happened to be in the air at the time. None of those birds developed with the "evolutionary purpose" of surviving sudden outpourings of lava. Even more relevant, *the color and structure of the plumage of the birds that survived* had nothing to do with whether or not they survived the lava. Those colors and plumage happened because the environment allowed the randomness of evolution to travel down all sorts of useless byways, because there was nothing around to stop it. Then, through nobody's virtue or intention, a bunch of them died off. Fast forward to today, and some people on various websites argue about the "evolutionary purpose" of this or that frilly crest on this or that bird. It's nonsense! It's pure folderol. So these people talking about this or that environmental stimuli leading to the development of consciousness are talking out their bazoo. The rule is: *evolution happens randomly to the degree an environment permits it.* So yes, a sedentary organism could develop sentience. It could be in the face of environmental pressures, or it could be just because it did, that's why, and there's nothing more to it. Nobody likes this, because we don't like uncertainty, which is why you get a lot of authoritative-sounding talk like you'll see around. But the most irritating fact is that evolution seems like a system almost entirely designed to foil the kind of answers people like to give. This isn't my thinking, by the way, I got all this from Stephen Jay Gould. Expect argument on this! P.S.: people should be cautious about using plants as an example of lack of sentience. It's not broadly known, but there is in fact a growing field called "plant neurobiology". It's highly controversial, but it's far from a settled argument, partly because certain plants have been shown to pass tests of sentience that it was previously assumed only animals could pass. P.P.S: the other thing people who like to sound authoritative always leave out is sexual selection, a mechanism described by Darwin and almost entirely ignored in layman's arguments. Simply put, a hyperintelligent mollusk could evolve just because the female mollusks thought they were cute. [Answer] If we start from the assumption that the more an organ is used, the more it has to develop, it is easy to answer your question. Sentience is the result of an high environmental pressure on the brain, that forced it to go beyond the simple model of instinctive reaction. The more an organism moves, the more it has to face a dynamic environment, and therefore also its brain has to be dynamic and able to "think out of the box". As counterexample, just think of how many vegetables do you know which are sentient? Yes, there are plants which can react to external stimuli, but nothing even close to what we recognize as being sentient. In a sedentary set up a brain (and its massive energy demand) would simply be an evolutionary burden. [Answer] Intelligence is useful in deciding between choices. Taking away all options involving moving is a big limitation. But perhaps not fatal. You just need to give the creature a reason to make decisions based on complex input. **Prediction** Say the main food source is intermittent. The smart choice is to breed just before the source reappears. This only requires adjustable timing in reproduction and some meaningful sensory input to directly reward better predictors. Or consider how much energy should be devoted to growth, storage or reproduction, there is some statistically optimal position for any set of conditions. The problem is how long does it take to find that sweet spot relative to the competition, what does it cost to be late, and how well can the spot be estimated from simple input. In both cases on earth our immotiles like plants and shellfish do well by preprogrammed triggers, but here seasons are pretty predictable, to the point where it isn't worth paying for brains to try and beat the market. If the important events on your world were less predicable a more complex calculation would be useful. Maybe your creatures even need complicated communication so that non-local patterns can be used to predict local events. **Manipulation** Options expand very quickly with the competence of your manipulators. It is sometimes suggested a positive feedback between our manipulators and brains is a large part of the reason we are where we are. If they have a plausibly free manipulator and the senses to make use of it, it's not impossible they get a similar feedback. **Arms race** Say it lives by tricking some prey into its mouth. It needs to develop new tricks as fast as its prey figures them out. Both sides could benefit from better decision making. [Answer] Yes, possibly. As has been pointed out, the development of sentience and intelligence does require some survival benefit (intelligence, at least, needs to be developed) and, generally, this requires the organism to have some kind of control over its environment, to make decisions and to be able to act upon them (which would normally require movement). However, suppose that an organism had no real control over its environment, and that environment was increasingly volatile and unpredictable, but that the organism did have some control over its own biological functions: which direction to extend root systems; whether to grow height or foliage; when, and possibly even how, to reproduce; etcetera - essentially the ability to budget its energy and develop strategies to survive in an environment not as stable as most plants have. Most plants have very simple responses that help them to grow and flourish: they sense heat and light; they use seasonal changes to drive their life cycles and these are all automatic, because automatic works in the majority of cases. I think it quite feasible that an organism, though, on some other world with erratic seasons and weather, although being sedentary, might benefit considerably from the ability to make decisions on how best to utilise its resources, especially if the organism was carnivorous with a need to lure, trap and restrain prey. [Answer] It's an interesting idea. I think we have an extremely biased view on the whole subject of intelligence/consciousness, and even on our concept of what life is. One possible path, using my biases as a basis, is that the genetic ancestors of said creator were mobile. At some point evolution favored the stationary. Perhaps they live in an environment where movement is either: too dangerous --those that move die OR the environment is so abundant in resources that moving around is pointless. The plant/fungi route is also not too far fetched as recent research is showing us there is more going on there than we once thought. [Answer] In principle, sure. Lots of other people have suggested that it might have some evolutionary "reason" to become sentient - i.e., some advantage conferred by sentience that would allow it to do better than others. But! That's not the only way it could happen. Evolution doesn't move towards an optimized goal, it just throws away things that are harmful - it's possible that the reason your critters evolved sentience wasn't because it was useful to them, but because it wasn't harmful enough to make it worth getting rid of. There's a phenomenon called **pleiotropy**: a single gene producing multiple apparently unrelated effects. For example, certain chickens have "frizzy" feathers, and the same gene causes them to have increased metabolism. Perhaps your critters evolved some useful trait that had sentience as a pleitropic side effect - a side effect that was at least not harmful enough to be worth sacrificing the useful trait in order to get rid of. It's unlikely that this would get you sentience right away - I doubt sentience is controlled by a single gene - but it could get the ball rolling. There's also something called **sexual selection**, which is natural selection without the life-and-death part. The idea is that potential mates might focus on a particular trait that's unrelated to an individual's actual fitness, and use that to judge the quality of the mate. For example, this is likely the origin of the peacock's fancy tail. It's not unreasonable to expect it would be more common among species that were at least partially sentient, so that they had enough "society" to "decide" what was attractive. But if, early on, your critters "decided" intelligence was attractive, sexual selection might bootstrap them to full sentience. One last idea (a little silly): in Vernor Vinge's "A Fire Upon the Deep", one particular species, the Riders, were sedentary - descended from something like a sea anemone. They didn't achieve much technology on their own, until in the distant past another species gave them machines that they could ride (hence the name) and use to do all the things most species use muscles for. There's no reason you couldn't have something similar - maybe a sedentary species that developed a glimmer of sentience, and then got helped along the way by someone smarter. [Answer] I attended a very interesting talk by [Prof. Wolpert](http://www.neuroscience.cam.ac.uk/directory/profile.php?wolpert) from Cambridge University once. His talk started more or less with the following: > > Why do we have a brain? It's a pretty fundamental question. > Why have we, as a species, developed a brain, when there are so many organisms > in our planet doing fine without it? > > > I argue that **we have a brain for one reason, and one reason only: to produce > adaptive and complex movements**. And if you think about it, movement is the only way we have of affecting the world around us. Even if you think about communication, speech, sign language, writing, ..., they all require muscle contraction. > > > (He notes this isn't entirely true, and expands on it, but that's out of the scope of this answer) He argues that *perception and prediction bring no evolutionary advantages if not to improve movement*. An example: there is no point in remembering places if it doesn't affect the way you move later in life. Another point he mentions is that once you don't need movement, you may not even need a brain ([see squirts eat their own brain when they fix themselves to rocks](https://en.wikipedia.org/wiki/Tunicate)). -- *although the scientific validity of this joke is questionable.* So if we believe in his hypothesis, which for me seemed pretty reasonable, then intelligence and motion are not a coincidence. Motion requires intelligence and there would be no point for a sedentary organism to develop intelligence. [Answer] **Want to improve this post?** Provide detailed answers to this question, including citations and an explanation of why your answer is correct. Answers without enough detail may be edited or deleted. Possibly a type of organism used as a ball in some form of sport could become sentient. This could make for an interesting sport as well. [Answer] Intelligent Design. Someone/something wanted to have things intelligent for any number of reasons and, with a good understanding of genetics, made some "things" to test a theory/give the creators something to interact with/create a curiosity item/build an early warning system for some danger/as pets/ as garden caretakers/as an outlet for their love, etc. The explorers may never find the creators just the intelligent sedentary life forms. [Answer] Considering evolution favors survival, but self awareness (the first part of intelligence) can also arise through other means, I think it is entirely possible. A bigger question is "Would we be aware it is alive?" Theoretically a crystalline lifeform is possible, and it could develop intelligence. Being crystalline it does not need to move in ways that we can perceive to live, and so appears sessile to us. It eats thermal energy that it converts from its world's sun. It excretes the excess at night to the environment. It changes it's crystalline structure to affect its environment, using solar energy in ways we can't even imagine. It communicates using infrared light. It evolves over geological time spans. We would have no idea it was alive, let alone sentient. With no awareness of it, and it likely having no awareness of us, there is no way for either of us to even say hello. Now take this same lifeform billions of years later, and it has evolved faster thinking and the ability to "see" through it's surface. It has also learned to communicate using visible (to us) light, that is how it trains its pet insects. At this point, you have a sessile lifeform that is capable of communication with us, civilization as we understand it, even using other lifeforms as beasts of burden. There you have your lifeform's history. Feel free to use any of that you like. [Answer] Best to look at ourselves as an example. Simplified, one of the main theories is that our brains grew to cope with the increased demand of social interaction. Remembering people's names, statuses, developing manners, social correctness, and basically surviving in a community and coming out top dog. Some animals like baboons have a big red arse and the redder and more arsey it is the hotter that mate is, but humans are not quite the same - for us it's all about charm and social standing within a community, so we evolved to be able to manage that, the side effect being that our increased intelligence was useful for other things, and once you're on an evolutionary slope to improvement, you don't stop until it no longer benefits you. Keeping in mind that females will become more and more demanding of how funny, charming, popular etc. you will be we evolved into what we have today which is an incredibly nuanced system of finding a mate. You certainly can't just flash your bum anymore. So yes, if they needed to become more intelligent, but more importantly, if they needed big brains for something else, even if it's remembering which mushrooms are safe to eat, there's a chance for evolution to push their intelligence in a sideways direction until they become sentient. [Answer] The main use of intelligence is prediction, for planning, for survival. Motion is a relative concept. In an environment where organism is sedentary but is surrounded by dynamic objects, interaction with which is required for the organism's survival, intelligence will develop. The motion does not even have to be physical movement. As long as there is a change of signal with enough differentiation as to require prediction, planning, and dynamic choice-making - intelligence will become a factor of natural selection. [Answer] In our world, even the development of a nervous system seems to require mobility. The closest thing I can think of to a sedentary creature with a nervous system are shellfish. A clam's intellectual life is limited: Move up in the sand column. Move down. Filter water, clam up. But this is much more stimulating than the intellectual life of a carrot. Moving up the evolutionary chain complex behaviour is more likely to arise in predators than in prey. As Speaker to Animals commented in one of the Ring World books, "How much intelligence does it take to sneak up on a leaf" This is a bit of an exaggeration, as smarts are needed to not be lunch. But generally predators have lower birth rates, higher survival rates, and longer lives than their prey. Coyotes are smarter than rabbits. Wolves are smarter than moose. Another factor in this is the amount of time it takes to feed. Herbivores spend a large part of their day just munching. You have to pump a lot of leaves through a gut to get a reasonable number of calories. Social behaviour seems to be a key feedback in developing more smarts. Pigeons are smarter than owls. (Training owls makes training cats look easy. Most of an owl's brain is hardwired image processing and hunting) Ravens (and corvids generally) are smarter than pigeons. But both pigeons and corvids exhibit social behaviours. So to answer your question: To develop intelligence it needs to make multi-factor choices that are more difficult than can be handled by tropisms and instincts. Those choices have to affect the survival and reproductive success of the critter. [Answer] The answer to your question "Does intelligence require and/or beget movement" *can* be simply answered: "**A form** of intelligence requires/begets movement." We know this because humans are 'intelligent' and highly visually and movement-oriented. But to answer the more general "Do all forms of intelligence require or beget movement?" you'd have to do one of two things: either define intelligence strictly or get very broad in your thinking about how you get there. It would be very easy, for instance, to define intelligence only in the human-like capacity. For a long time this has been a struggle in science: is x creature 'sentient'? How do you define that intelligence? Tool use? Language use? Ability to discern self (the so-called '[mirror test](https://en.wikipedia.org/wiki/Mirror_test)')? Ability to experiment? Ability to remember? For any given test there are some species that pass it and a lot that don't: chimps have a notion of self and crows pass down grudges between generations, some plants communicate by vibration and many animals use tools. Etc, etc. It is also very easy to misunderstand evolution and how species get to where they are, recklessly ascribing words like, "Purpose" or "reason" to particular traits. There are twenty-three thousand genes in human genome. A water flea (a small water crustacean) has thirty-one thousand. There is a Japanese flower that has roughly fifty times what humans have in terms of genetic material. One thing that Dawkins points out in his 'Selfish Gene' book is that a lot of the time genes are carried not on the weight of their own evolutionary fitness, but that of the collective of genes in the organism in which they happen to exist. That is, a specific gene and the trait it expresses may have positive, negative, or neutral effect on the organism's health and in any of these cases have little to no effect on whether it survives: the weight of all those other genes and expressed traits is the overwhelmingly factor. Combine this with the notion of [inter-species gene flow](https://en.wikipedia.org/wiki/Gene_flow#Gene_flow_between_species), and we know that, in theory, the genes that create our as-yet-undefined intelligence could get to the target organism in any number of ways. To properly phrase your question, you need to define what sort of 'intelligent' capability the species has, and you have to be pretty clear with this: saying something like, "Learn where things are in a space" means both rats and Roombas qualify. You need to phrase things in a manner that lets you distinguish between your intelligent species and ones who are 'non-intelligent'. One way to do this is to consider what it applies it's intelligence towards. Humans have hyper-evolved visual cortexes: much of our 'intelligence' has to do with vision as a result. Eye-hand coordination is one aspect of this (and has to do with movement). Spatial recognition and awareness, object permanence, ability to recognize items, people, expressions all based on less-than-complete information all factors into this. Humans, in fact, probably 'fill in' most of the visual information they think they are getting (leading to 'the world is an illusion in our minds'). All of this is noteworthy because what it actually is is a pile of mechanical mechanisms we build on a particular sense that really only detect a narrow band of lightwaves. You can imagine a similar set of hyper-evolved mechanisms that, say, detect subtle changes in PH. A 'digestive' intelligence that is able to factor out poisons and conserve rare nutrients. You can't cut out the *concept* of motion entirely, because things are still moving through a complex network of stomachs and intestines, as specially evolved as the rods, cones, neurons, synapses, glia and so on of a human visual cortex. But the organism itself may not be moving itself much, instead living in a river or ocean and simply processing everything as it came by - maybe even choosing how to excrete what it doesn't directly use to build up structures around it (*golgoth sapians*). Learning to count by filling stomachs instead of ticking fingers, etc. Communicating through the release of gases of different flavors. Cultivating farm animals by selectively maiming fish before depositing them in pens for later consumption. All of this is imaginable, and would lead to an intelligence of a highly different variety than humans. So, to properly phrase the question, I'd encourage you to think first about how you want the sedentary species intelligence to express. Then, think about what biological processes that were hyper-evolved would lead to such an expression. And then work back from there, knowing that the genes which caused this expression could come from anywhere: from food it ate, air it breathed that contained pollen. The genes could have come from another species with proto- or full-blown intelligence whose genes were carried in spores and later captured and repurposed. The intelligence could be entirely accidental, having arisen by chance and been lucky enough to be in an organism that was very environmentally viable with or without intelligence. But embrace that evolution is a billion trillion balls bouncing around a sphere and sometimes some of them fall through the hoop of 'intelligence' or 'has opposable thumbs', and none of them ended up there for a 'reason'. ]

[Question] [ **This question asks for hard science.** All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See [the tag description](/tags/hard-science/info) for more information. My question is simple: How many nested moons are physically possible? If our moon had a moon, that would be a nesting of 1. I'm assuming it's easily possible for a really big moon to be orbiting a gas giant and have its own moon. If the dimensions were right, that moon could also have a moon? How many moons deep can we go? Let me know if I'm missing something. I would like answers with calculations not just random guesses! I'm asking what is physically possible, not what is realistically plausible due to the difficulty of such a system forming. [Answer] Let's make a bunch of assumptions: * The largest primary is about 3 times bigger than Jupiter. * To really be a parent, the barycenter of a parent-satellite system must be within the parent. * Everything has approximately the same density * Orbital stability will magically work itself out (this will give us an upper bound) Let's call the twice the distance between the barycenter of a parent satellite system and the farthest extent of that system $D\_p$ then the corresponding diameter for the subsystem $D\_s$ Now if the mass of the parent is $M\_p$ and the mass of all the sub satellites together sum to $M\_s$ then the requirement that barycenter be inside the parent yields: $$\frac{M\_s}{M\_P}(D\_p-\frac12D\_s)<\left(\frac{3M\_p}{4\pi\rho}\right)^\frac13$$ Now we know that for each parent none of the satellites can pass within the roche limit of the parent (the limit would actually be farther out due to the fact that the satellite system isn't solid but this will get us an upper bound) Lets call the diameter of the satellite system $D\_s$ and the diameter of the parent system $D\_p$. The Roche Limit gives: $$\frac12 D\_p>2.4\left(\frac{3M\_p}{4\pi\rho}\right)^\frac13+D\_s$$ If we claim that each subsystem is proportionate to the parent system then we have: $$\left(\frac{D\_s}{D\_p}\right)^3=\frac{M\_s}{M\_P+M\_s}$$ Now if we're trying to maximize the ratio of satellite mass to parent mass both of these inequalities should be equalities. Solving the system yields: $$D\_p \approx 2.6 D\_s$$ Which means each successive moon would weigh $17$ times as much as the previous one. Now to get from a single atom moon to something 3 times the size of Jupiter would take: $$\frac{\ln\left(3\frac{1.89813 × 10^{27} kg}{1.6726219 × 10^{-27} kg}\right)}{\ln(17)}=42$$ So a system could have a maximum of 42 layers if we stopped at planets as the primary body. Note however, this doesn't consider orbital stability and I have no doubt that even a system with 10 layers would be unstable on the time scale of a century. ## Bigger If we went up larger and larger, we could eventually incorporate black holes and then relativity plays havoc with the equations. However, I think that at the extremely large end, the expansion of the universe would distort and pull apart any orbits with radii on the order of billions of light years. So if we said that was the limit, then you could nest about $85$ layers, which is a lot, but I would hardly call that infinite. [Answer] Theoretically infinite, though the classification would get interesting. Consider the Moon. It orbits us, the Earth. That's a nesting of 0, right? Now consider the Earth. What's to say that the Earth isn't just a moon of the Sun, apart from arbitrary human classification systems? On this logic, you could have theoretically infinite moons. If you re-classify any orbiting body as a moon, and you start with a massive enough body, then you can have entire stellar systems orbiting it - giving you big numbers for the nesting. Think: the Sol system, orbiting another larger body, which in turn orbits an even larger body. That gives a nesting of 4 (I think.) If you're not up for reclassifying, then the potential is small for nesting moons. According to [Wikipedia/Natural satellite](https://en.wikipedia.org/wiki/Natural_satellite), the definition of a moon is: > > a celestial body that orbits another body (a planet, dwarf planet, or small Solar System body), which is called its primary, and that is not artificial. > > > That's limiting, because the biggest object you can have a moon orbiting is a planet, which are (comparatively) small. With each orbiting moon, you have a smaller object, and eventually you're left with nothing. [Answer] There are some mathematical stability issues which might create sensible bounds, but I'm not qualified to quantify them. In general terms there is no guarantee of long-term stable orbits in a three-body system (such as Sun, Jupiter, Earth, even if Saturn and the rest weren't there). In fact, special cases aside (notably two Lagrange points) there's a proof that there are no infinite-term stable orbits, only chaos. Be reassured that the best astronomical measurements and computer modelling show Earth's present orbit won't change drastically for the next hundred million years or so, after which time we can't say anything about it because of the errors on the observations. It's therefore not impossible that five hundred million years hence, Earth will be a frozen rock wandering the galaxy in interstellar space. (Statistically, it's more likely to stay orbiting the sun until the sun goes nova). Were you to try to model Asimov's "Nightfall" system (IIRC 4 stars and two planets in a complex dance) you'd find it was unstable on a timescale much shorter than that for the evolution of Terran life. Something would get ejected from the system into interstellar space, or would collide with another body, and so the story is highly improbable (for thermodynamical levels of improbability). One approach to simplify the N-body problem's maths is perturbation theory: treat the Earth/Moon system as tightly coupled, treat our centre of mass as bound to the Sun and perturbed by Jupiter (the biggest other perturber) on a completely different scale. My guess is that there isn't space for more than around five "levels" before chaos becomes unavoidable on a short timescale. The upper scale is set by the scale of interstellar space and the large number of suns in the galaxy. The lower one, by the weakness of the gravitational force and the fact that other influences such as solar wind and atmospheric drag become dominant for tiny objects orbiting small ones. Over to anyone with greater higher mathematical skill and knowledge than myself! [Answer] Similar discussions have been marked in comments. I recall previously discussing circumlunar orbits and why a long-lived natural sattelite won't have such an orbit. Having the primary be *uniform* rather than *lumpy* improves the situation. Having multiple bodies in resonance can stabilize the whole thing. So a pterbation that bumps *one* sattelite will be corrected by the sisters, on a scale shorter than the long-time averaging out of random outside influences. Also, don't limit yourself to big-small progressions. Complex star systems, for example, don't have stable 3 or 4 star systems, but *do* have "hierarchical binaries". Two bodies *here* in mutual orbit, two bodies *there* in mutual orbit, and the two *pairs* in orbit. How does that count in your system, with no "root" object but clearly a hiarchy of what orbits what. ]

[Question] [ I'm thinking not only of the impact they would have had on how you would defend from an aerial attack, but also that they could be used for much more specific bombardment by dropping large rocks and such. For simplicity, let's assume that no more than two people in leather could ride such a creatures, which also gives us a general weight limit. So, how would castles have been designed differently if these creatures existed? [Answer] For the sake of this answer, I will be assuming that by "castles" you mean late medieval/early Renaissance pre-gunpowder fortifications that were used for habitation as well as defense. I was also originally going to split this answer into two parts, depending on how difficult these creatures would be to kill or wound, but after some consideration, I decided it doesn't matter as long as we're not dealing with flying tanks. So, we would most likely see some of the following: * greater focus on roofs/covered crenelations, like you find in Japanese castles and fortresses, to protect from missiles and projectiles dropped from overhead. * systems of upright spikes or blades -- something akin to anti-roosting pigeon spikes, only scaled up appropriately, in order to prevent these creatures from landing or performing snatch & grab strikes against valuable targets * depending on the level of threat presented by these fliers, as well as level of technology available to the defenders, we might also see some active defenses. Smoke bombs and/or smoke-producing apparatuses to obscure the castle from overhead, bolas or razor wire launchers for area denial, and maybe even tethered balloons with marksman teams to negate the inherent height advantage (though how you'd go about protecting the tethers or the balloons themselves is another matter) * and, of course, let's not forget the possibility of castles including facilities for their own flying cavalry in order to counter potential opponents [Answer] # Large Rideable Flying Creatures are called *Planes*. # They made castles obsolete. While the term castle is somewhat fuzzy, I will take it to mean a static, fortified location designed to withstand enemy attacks. Many people believe that the advances in cannon technology such better propellents and rifling killed the castle, but the [Trace Italienne](https://en.wikipedia.org/wiki/Star_fort) pattern evolved to counter such advances in artillery design and technology. The use of very deep earth and brick hills (for they are too wide to be called walls) quite successfully creates a fortification that will resist canon attacks. The next evolution in castle design came about due to advances in high explosive, making the Trace Italienne's wide thoroughfares very vulnerable to plunging fire from mortar or artillery shells. Cutting a long story short ([see wikipedia](https://en.wikipedia.org/wiki/Fortification)), forts eventually moved underground, exposing only their guns to the incoming attacks. What really killed the fortification as a doctrine of war, and made it largely irrelevant were advances on two fronts: Air Power, and increased mobility brought about by advances in Mechanisation. Fortifications would from now on either be destroyed with overwhelming force from the air, or circumvented altogether. While Mechanisation and mobility can be countered by a determined defender, such as miles of barbed wires, tank traps, machine gun and anti-tank gun positions - or the equivalent in a fantasy setting, nothing at all can be done for air power. **Once warfare takes to the air, the era of static fortification is at an end, and the era of air superiority has began.** Even creatures only capable of carrying a payload of 180kg kilograms at most (two fully equipped riders) would make mincemeat out of most modern fortifications with sufficient numbers. Flying high enough to be out of reach of conventional projectile weapons, the attackers are free to bombard the fortification with impunity. This is especially true for a world with either technology or magic, where projectiles can pack an enormous punch for very little weight - think only of greek fire for a real example from antiquity. The only defence against such an attack would be for the fort to keep a force of flying creature itself to be used as counter measure. This would essentially be the race for air superiority. In fact, the most likely outcome would be that forts give way to a stopping and feeding point for the defender's fleet of air beasts. In effect, airports for flying beasts. This would also have a drastic effect (although dependent on the flight time), on a base's projection of power. The area that one could reasonably control with a flying beast is an order of magnitude larger than with a walking one. # Differentiation In addition, it is unwise to discount the power of artificial selection. Artificial selection allowed humans to turn the wolf into both the [Chihuahua](http://en.wikipedia.org/wiki/Chihuahua_%28dog%29) and the [Saint Bernard](https://en.wikipedia.org/wiki/St._Bernard_(dog)) long before we understood genetics meaningfully. Applied to flying creatures, it is easy to envisage a variety of creatures specialised for different roles. here are a few to give an idea: * **Large, slow but sturdy** Bred for endurance, they are the preferred breed for long distances or heavy loads. They require little maintenance and have exceptional all round health. Sky camels. * **Small, light and fast** This fragile breed is prone to sickness and requires a great deal of care during their rearing. But boy are they fast. Used for scouts and messengers, they can fly twice to three times the speed of most other breeds. Air Arabian Horse. * **Tough and mean** When you need to take down other flying creatures, these are the ones you go for. You don't burden them with a rider (They won't really support one anyway) and you lead them from another creature. Their viciousness is legendary and most tamers are missing a limb or two, but a squadron of those over your lands will deny the skies to anyone else. (You might also lose a sheep once in a while). Sky Wolves. * **Marine** This breed deals with the difficulties of sea travel better than any others. In fact, they will mostly feed themselves on long sea journeys by dive fishing. Special boats accomodating dozens of the breed can project power over the ocean and assail distant cities. [Portuguese Water Dogs](https://en.wikipedia.org/wiki/Portuguese_Water_Dog) for the clouds. * **Smart & cooperative** Bred for a pack mentality and a superior intellect this breed excels at complex tasks requiring timed coordination and planning. They take orders via hand signals and are the preferred breed for covert or special force work. If a silent night-time assault is required, your elite soldiers will most likely be riding these guys. German Shephards. An interesting idea would be for some breeds to be the secret pejorative of a given nation. This would lead to the nation only fielding a single gender of the breed to avoid other nations capturing or breeding similar beasts, downded riders killing their beasts the way modern special forces destroy downed helicopters with explosives, or perhaps only fielding castrated creatures. # The wider issues You'll also need to think of the wide spread effects of having air travel from pre-history. Political and Social systems would look very different indeed if humans had air travel before writing. In fact, flying creatures would be a world-defining feature. The entire history of exploration and map-making, as well as the differences in advancement and technology on earth would likely never occur. Rapid exploration and communication would have drastic and fundamental effects. Languages would evolve differently, and trade routes would also be very different, as they would no longer have to be defined by geography. This is only scratching the surface. [Answer] There was an article in a [dragon magazine](http://www.annarchive.com/files/Drmg224.pdf) where the defenses against aerial creature was discussed (mostly in d&d term, but that may give some pointers against more "standard" creatures) A discussion on [dragonfoot](http://www.dragonsfoot.org/forums/viewtopic.php?f=15&t=50240) lead to the following (taking only the part against aerial creature) : * Anti-aircraft ballistas. Ballistas on a universal mount, able to be fired at steep angles. Special ballistas may fire two bolts with a chain inbetween, to catch wings and necks. * "Dragon Chains" Large poles, like the masts on ships, extend up above towers and walls, and chains dangle inbetween them and down to the ground, thus inspiring great caution in any flyers thinking of swooping down. The name is just advertising, this product is not recommended against large creatures. * Bulwarks - stone or heavy wood low shelters that defenders can dive behind/under at the last moment to avoid things like diving attack or arrows. * Someone trying to fly and infiltrate down through chimneys could be surprised to find the chimneys grated off near to the fire (so the metal is nice and hot). * Roofs will have to be fortified in any case. A squad of heavy crossbows in cover could ruin the day of many a flyer. [Answer] I will work off of the following assumptions. Your leaving all things the same: balances of power; political, social, & technological advances; etc., however during the development of fortresses into (let's say European) castles, we happened upon and domesticated (to the point of using for our needs) a flying animal capable of causing problems for our enemies from the skies. I think very rapidly what you would see, would be similar development of the 9th and 10th century stone structures into the 15th & 16th centuries. The difference is that they would be **underground**. Instead of investing labor into assembling stones above-ground, they would work on deep structures, evolving into having multiple "level" of stone barrier above, such as your "outer ward" / "inner ward" / "keep" arrangements, with fortified ingress & egress portals outward. This can get interesting when it is discovered that a moat surrounding your castle is a helpful defense (it would make it difficult for an invading land and air force to "dig" into your castle. You could have a fortified island bunker as your entrance & exit, but your castle would be under ground, *under* water! My last speculation would be that these are more largely "forts" than full time living locations, or else it could have highly defended skylights, much like a castle's keep has highly defended, thin windows. [Answer] I have struggled with the question of 'how to defend against dragon fire' while creating my own world. I decided that if there are magical creatures that can breath fire then it is also very likely that there are magicians that can manipulate fire. As such, the key to the castle's defence would be a class of powerful magicians that specialize in fire magic. The only problem is it is unlikely that there are many of them (unless your world has a lot of magic) and so for the most part, castles would be defenceless against dragons. Those who control the dragons would have absolute rule over all the lands. You could try something similar. It may not be dragons, but whoever rules the air may be an absolute power and no matter how corrupt ("absolute power corrupts absolutely") all would fear to challenge their rule least they bring about their utter destruction. If there were wars, then they would likely be fought in the air and immobile fortifications would be a liability. ]

[Question] [ Imagine I have a device that can stop time for the person who holds it (similar to [Bernard's Watch](https://en.wikipedia.org/wiki/Bernard%27s_Watch)). This device works in a very specific way - it creates a bubble around the user (just large enough to hold the user) in which time flows much faster than in the rest of the universe. The difference is very high but it is finite (say 100,000 times faster). This means that if the person holding the device experience times at "normal speed" the rest of the world outside the bubble appears to him to be drastically slowed down, almost (but not quite) to a standstill. In contrast, anyone outside the bubble looking in would see everything inside the bubble happening at lightning fast speed (almost instantaneously). The border between this bubble of faster time and the rest of the universe is not infinitely thin - there is a boundary (say a few centimetres thick) where the speed of time changes gradually from one to the other. My question is what side effects would this bubble cause? For example: any sounds from the outside would sound quieter and deeper, as the wavelengths are "stretched out" at the boundary. Similarly looking out of the bubble the outside world would appear darker and redder, as light is red-shifted. In fact with enough time dilation you would be able to see x-rays with your naked eyes. I'm also positing that waves such as light and sound would also bend at the boundary, as if they had struck a lense, so the outside world would appear distorted. Moving object such as bullets would also be deflected slightly (if they struck at an angle). Are there any other interesting effects that could arise? What would happen if you walked up to another person, as they crossed the bubble's boundary? Is there anything cool you could do with this device? For extra credit: would this violate any physically laws in any way e.g. conservation of energy? Show your working! [Answer] As you point out, the world outside the bubble will appear darker - much darker. What appears as visible light is actually very, very far infrared (about 0.1 meter wavelength) and the energy available is virtually nil at these wavelengths. Interface effects make this a superb weapon of assassination. Simply walk up to the victim and position yourself so that only part of his body is within the bubble. The portion inside will have "normal" metabolism, but if the heart is outside the bubble there will be no circulation and the tissue will die in minutes. Simply stand in place for a half-hour subjective, then move on. The effects of massive tissue death will be enormously traumatic for the victim. Alternatively, stand aside from the victim and point a flashlight at where you you believe him to be, and hold it there for a while. Let's say you have a 10 watt beam, and you hold it for 30 minutes. The result (outside the bubble) will be an 18 kJ (10 watts x 60 x 30 seconds) pulse of extreme gamma radiation directed at the target. Of course, you'll need SCUBA tanks or something similar, since you'll use up the oxygen in your bubble fairly quickly (subjectively). You'll also need to come up with a method of heat management. On the one hand, you are effectively encased in a black body at 0 K which will suck the heat out of you and leave you frozen solid. If, on the other hand, you posit that the interface characteristics are normally reflective (so you don't freeze) then not only can you not use the flashlight, the longer you operate your bubble the hotter you'll get, since resting human metabolism is about 100 watts, and this has nowhere to go. [Answer] Well, let's see how such a field would work. The Hamiltonian equations are $$\frac{\mathrm d x\_k}{\mathrm d t} = \frac{\partial H}{\partial p\_k} \quad \frac{\mathrm d p\_k}{\mathrm d t} = -\frac{\partial H}{\partial x\_k}$$ Now we want the field to affect the speed of things happening, so a natural assumption would be that the field just acts as factor of the Hamiltonian: $$H(x,p) = \exp(f(x,t)) H\_0(x,p)$$ Here the exponential function mainly is there to make time go normally when the field is zero. It however also makes sure time cannot go reverse. Now for a constant non-zero field, you'd just get a rate of temporal change proportional to $\exp(f)$, so if the field is positive, things are going faster, as intended. However what happens in the "bubble wall", assuming a static field? Well, here we have to use the product rule: \begin{aligned} \frac{\mathrm d x\_k}{\mathrm d t} &= \exp{f(x)}\frac{\partial H\_0}{\partial p\_k}\\ \frac{\mathrm d p\_k}{\mathrm d t} &= -\exp(f(x))\frac{\partial H\_0}{\partial x\_k} - f'(x)\exp(f(x))H\_0(x,p) \end{aligned} Note the extra term on the second equation. This is an extra force proportional to the *derivative* of the field and the total Hamiltonian (which more or less gives the total energy). Assuming that energy is positive, this means that this acts like an extra *repulsive* force. Note that this repulsive force is *in addition* to the slowing down due to the local factor, and its strength depends on how rapidly the field grows. Note that since the kinetic energy is proportional to the mass, this leads also to a force term proportional to mass, similar to gravitation. Any potential energy would, however, give rise to an extra force that is not mass dependent. Let's look at the energy, now also with time-dependent field: $$\frac{\mathrm dE}{dt} = \frac{\partial H}{\partial t} = \exp(f(x,t))\frac{\partial H}{\partial t} + \frac{\partial f}{\partial t}\exp(f(x,t))H\_0(x,p)$$ So energy change only happens with field change, and proportional to it; that can well be explained as energy going into the field (of which I only included the effect). As long as the field remains constant, energy is conserved. In effect, the outside world would look colder than would be expected from the slowdown, as the additional force would draw away more energy from incoming particles;on the other hand, outgoing particles would get an extra boost, so to the outside world, you'd be hotter than expected from the speedup. Indeed, with a sufficiently small border zone (and corresponding rapid onset of the field) the border might even act like a wall for all normal-speed particles coming from outside. [Answer] In [Larry Niven’s 1975 story](https://en.wikipedia.org/wiki/Gil_Hamilton#Novels), there were several side effects of note, used as clues by the detective to figure out that this was used. Besides the logistics of needing food, water, and medicine for an extended time relative to the outside world, the user had to sit in the dark because the flashlight inside the bubble became a powerful weapon seen from outside and set the wallpaper on fire (and presented as a novel unknown weapon to the [M.E.](https://en.wikipedia.org/wiki/Medical_examiner)). Stasis fields were a staple of Niven’s work during that period, so read the *Known Space* universe and others written during the some years for more ideas. [Answer] There is one effect that is derived directly from special relativity. It is remarkably surprising no-one has noticed it. This is based on the fact that the speed of light will always be constant in all frames of reference. If time inside the 'quick-time' bubble is passing 100,00 times than in the outside world, and since the speed of light must be constant inside the bubble, then lengths in the bubble must increase by a factor of 100,000. This is the inverse of the Lorentz-FitzGerald length contraction. Effectively this is a length expansion. For example, if the 'quick-time' bubble has a diameter of two metres in its frame of reference, then due to length expansion its size will have expanded out to two hundred kilometres in the frame of reference of the outside world. This suggests someone inside a 'quick-time' bubble can't sneak into art galleries and museums to steal their treasures. As, for example, in Arthur C Clarke's SF short story "All the Time in the World". Any fast-moving giant can be easily detected and just as easily stopped with a few flashlights. Of course, the Flash would have the same problem. What a pity. I rather liked the Flash as a good example of a superhero with a singleton super-power and who had to exploit it to the utmost. [Answer] To me, the biggest worry beyond those already mentioned is heat transfer. Heat energy is effectively the kinetic energy belonging to individual molecules, which is proportional to the square of the molecule's speed. Within the bubble, the average speed of a molecule is 100000x faster; the average kinetic energy is therefore magnified by a factor of $10^{10}$, or ten billion. The human body clocks in at about $310$ Kelvin. Scaled up - and bearing in mind that we have no need to account for heat of vaporization or other phase changes - from outside the bubble the individual inside would seem to be upwards of *three trillion Kelvin*. For comparison, the core of the Sun is less than thirty *million* Kelvin, and its surface is only six thousand. Standing near a person inside such a bubble would be like standing *inside a hundred thousand suns*. The heat transfer would be virtually instantaneous and catastrophic. The average person is $62$ kilograms and has a specific heat of $3470$ J/kgC; three trillion Kelvin then means that the person's body contains about $6.5 \cdot 10^{17}$ Joules of energy. Transferring all that energy would amount to about the energy output of a $150$-megaton nuclear weapon, three times the power of the largest nuclear weapon ever detonated. [Answer] It seems to me that the volume inside the bubble would quickly become near-vacuum unless the border somehow actively maintained pressure. If the air molecules outside the bubble are effectively moving 100,000 times slower than inside, then air molecules would exit the bubble 100,000 times more often than enter it. This would have the effect of making the effective "air pressure" outside the bubble 100,000 times less than inside. If the border somehow actively exchanged air with the outside environment at a rate needed to simulate a 1 km/h breeze, outside the bubble there would be a 100,000 km/h wind. A category 5 hurricane is 251 km/h, so this would cause immense wind (and probably heat). I suppose a solution would be to make the border impervious to air and have any molecule that comes in contact with the border simply be displaced to the opposite side. But then how does the user interact with their environment at all? A molecular whitelist? [Answer] Nice idea. I guess the idea comes partly from the "Bobbles" from some other book that work the other way round (stopping time inside). You could use this if you have a difficult problem to solve => enclose yourself in the bubble with the fastest computer or whatever (and some energy source and all that), and think it through real neat. Then you can come out a second later and would have solved whatever would have taken someone else a dozen years to solve. This throws up a problem though: you need to bring everything with you, and can't really get rid of stuff either. This means, energy (for light, or a computer or whatever you want to use), food, etc.; there is no point entering the bubble unless you want to achieve something in there. As you say the border is a few cm think, and things can cross it - I guess you mean that the border consists solely of the time effect; no boundary otherwise, that would keep stuff in or out. This would make it absurdly complicated. If you put your hand through it, the part of your body inside would skeletify and turn to dust long before the rest would enter (without invoking any real science here; just going from the stated time effect). So you would have a way to let the bubble spring into existence around you at an instant (or at least at the same speed for the whole volume). For comparison: said "Bobble" (from Vernor Vinge) works by enclosing a spherical volume in a metallic/shiny border; neatly slicing through everything. The border is completely impervious to *anything* - no tool can scratch it, no amount of energy whatsoever can influence it in any way, light reflects perfectly, etc. Inside, time stops. At a pre-set time, the bobble disappears (in an instant) and time flows normal again. It just "works", there are no side effects. It is an absurdly neat solution to the time travel problem - at least in one direction (the correct one :) ). It is used to great storytelling effect to let people and items (rockets :-) ) skip over events in the real world. He even builds a working spaceship out of them at a later time, you can easily see how. I believe you can make it work just like that, if you get rid of your "thick" border and replace it by an infinitely thin one that is absolute uncrossable from both sides. You don't need to explain anything (unless you want to make the technical explanation how it works a main part of your story) and get loads of material out of it. It's just a little less practical, as everything "interesting" happens *inside* the bubble, and thus in a very confined space. You have no outside benefit to enbubbling something (unlike the freeze-bobble). [Answer] There's a pretty damn good miniseries called **The Lost Room** which featured a device (The Comb) that stopped time for the user. It had some very interesting and unique rules: * A person using the device could not interact with anything. Everything else in the world was locked in place - he couldn't pick up anything, or open a door. * Momentum was preserved. If the user was running when he used The Comb, if he didn't start running again, in the same direction and speed, when time started up again, he would lurch in the direction he was travelling before its use. * Light behaved very strangely (everything looked washed out and gray), and there was no sound. I always thought these were neat takes on the very often used concept. ]

[Question] [ Say you were to drop a (bunch of) human(s) at some past era of our Earth. I'm assuming they might encounter a few problems such as the composition of the air not being breathable, the water being too rich or too poor in some chemicals, some diseases being totally new to their immune system... Maybe they themselves bring some diseases from the present and eradicate all source of food... My question is: how early could they be dropped and still have a chance of survival? [Answer] I love this one. I really do. **Quick Answer:** I'd put the date at roughly 2.3 billion years ago, give or take. This is the date of the [Great Oxygenation Event](http://en.wikipedia.org/wiki/Great_Oxygenation_Event). It's when organisms (bacteria) began putting oxygen into the atmosphere in large quantities as a waste product of photosynthesis. [The atmosphere before that](http://en.wikipedia.org/wiki/Atmosphere_of_Earth#Evolution_of_Earth.27s_atmosphere) has a lot of carbon dioxide, which wouldn't have very good for our intrepid explorers. But this new one sort of resembled the one we have today, although the nitrogen from the earlier atmosphere is still here. This graphic gives you a sense of how high oxygen levels were: [](https://upload.wikimedia.org/wikipedia/commons/thumb/0/03/Oxygenation-atm-2.svg/600px-Oxygenation-atm-2.svg.png) Image courtesy of Wikipedia user Loudubewe under [the Creative Commons Attribution-Share Alike 3.0 Unported license](http://creativecommons.org/licenses/by-sa/3.0/deed.en). The red and green lines represent the high and low estimates of oxygen levels. Note that this atmosphere would only have been about 5% oxygen, as opposed to the 20% we have today. To reach *that*, you'd have to go back less than a billion years from the present date. **Long Answer:** This is really just a bunch of additional details that aren't quite as important (okay, I guess they are). As Neil mentioned, humans need food. And 2.3 billion years ago, there wasn't much of that around. In fact, there wasn't much *life* around. To make this an even more graphics-heavy answer, I have this chart, which shows you just how bacteria dominated our planet: [](https://upload.wikimedia.org/wikipedia/commons/thumb/7/77/Geologic_Clock_with_events_and_periods.svg/625px-Geologic_Clock_with_events_and_periods.svg.png) Image in the public domain. It took multicellular life another 750 million years or so to arrive after the Great Oxygenation Event. So the day's meals would be bacteria. But human's can't really live on bacteria, so our intrepid explorers would have to wait until the [Cambrian Explosion](http://en.wikipedia.org/wiki/Cambrian_explosion) 542 million years ago, when land plants formed. Aside from that, they could try to catch some aquatic creatures (trilobite stew, anyone), but it would be hard. Another problem with dropping our explorers off 2.3 billion years ago would be that the Earth may have been undergoing a repeating phase in its life known as the [Snowball Earth](http://en.wikipedia.org/wiki/Snowball_Earth) phase (in this case, the [Huronian Glaciation](http://en.wikipedia.org/wiki/Huronian_glaciation)). Large portions of the planet were covered in ice, making the planet pretty inhospitable. Mark Adler pointed out that [carbon dioxide levels](http://en.wikipedia.org/wiki/Carbon_dioxide_in_Earth's_atmosphere) are also important, as levels above 5% are toxic to humans. Currently, it's at roughly 0.0397%, or 397 parts per million. In years prior, that number was a lot higher. This graphic indicates that carbon dioxide levels would not have been favorable until a few hundred million years ago: [](https://upload.wikimedia.org/wikipedia/commons/7/76/Phanerozoic_Carbon_Dioxide.png) Image courtesy of Wikipedia user Merikanto~commonswiki under [the Creative Commons Attribution-Share Alike 3.0 Unported license](http://creativecommons.org/licenses/by-sa/3.0/deed.en). So 300 million years ago, there was a favorable "island", but that soon went away. You'd have to wait a while longer before levels returned to what they are today. As a few users have pointed out (all correctly), oxygen levels need to be at least 10% for humans to not suffer severe [medical issues](http://www.newton.dep.anl.gov/askasci/zoo00/zoo00755.htm), and carbon dioxide levels need to be below 5%. These conditions weren't necessarily satisfied at the beginning of the Great Oxygenation Event. However, they changed over time. Over the course of Earth's history, there were periods where these conditions became more (or less) conducive to human life. I'm reluctant to pick an exact date, so I'll instead post these graphs (taken from [here](http://wattsupwiththat.com/2013/06/04/dr-vincent-gray-on-historical-carbon-dioxide-levels/), and found individually [here](http://wattsupwiththat.files.wordpress.com/2013/06/oxygen_earths_atmosphere_historical.png) and [here](http://wattsupwiththat.files.wordpress.com/2013/06/co2_temperature_historical.png)). I'm not positive of their accuracy, but they'll do. I won't post them, though, because at least one is copyrighted, and so I can't reproduce it here. [Answer] Humans require an oxygen atmosphere to breathe, and require multicellular life to eat. They also require temperatures roughly similar to those found today. It has been shown through geologic methods that the oxygenation of the atmosphere occurred during the Precambrian era, reaching levels possibly high enough to support human life around 1.9 billion years ago, though due to the low levels of oxygen, it would be like living at very high altitudes all the time. However, there is no evidence of large multicellular life, so humans deposited in this era would be reduced to filtering the sea and scraping stromatolites to obtain anything even remotely nourishing. Survival would be possible, but existence would be pretty boring and the potential for societal growth would be highly limited due to the lack of combustibles and the lethargy that the low oxygen levels would impose. A more likely period for humans to be able to thrive in would be the Ediacaran era, 635-542 million years ago, when oxygen levels were closer to our own and there was an abundance of simple multicellular life. Earlier than this (The Cryogenian era, 850-635 million years ago), the earth was an iceball, with ice-caps reaching to or near to the equator, and the temperatures would likely have proved inhospitable. Life for humans during the Ediacaran era would likely still be quite boring, as the life forms that existed then - other than potentially being pathogenic - were so simple that they would be easy prey for humans. Obtaining food would be simple, though possibly quite tedious. Since most life is thought to have existed in the sea, humans would be forced to live on coastlines. This era was also quite cold as earth was still warming after the Cryogenian era. The earliest *potentially* interesting period would be the following era, the Cambrian, from 541 to 485 million years ago, during which all the modern phyla of life originated. However, most life was still in the seas during this time, and humans would likely still be forced to be a coastal species with a fairly boring existence. The earliest period in which humans could live as a land-based rather than a coastal species would be the Devonian (419-358 MYA) or the Carboniferous (358-298 MYA) eras, during which land-based life spread out and became established. The appearance of large plants means that this is the earliest period in which humans could potentially establish proper civilisations. [Answer] I'd like to know more about your phrase "be dropped". Does that mean with a group with technology (seeds & animals, oxygen concentrators, tent/dome cities, etc)? Or, just a group of people who were walking the street? Or, living in a prison (ie: Assiti Shard series: *Time Spike*)? I've got issues with *Time Spike*; apple trees need frost to fruit, which probably won't occur in the Cenozoic era. And without fruiting plants, where're you going to get edible plant food from? Ferns make spores, not seeds that we can eat (like grains; rice, wheat or corn), and tubers weren't mentioned at all. An all-meat diet is going to be *tough*, without vitamins and roughage. If you can take seeds with you, and have time enough to wait for stable levels of crops to grow, then you just need to be in the correct atmosphere. Temperatures are something you can deal with, if you've got shelter/technology to handle it (got a nuclear powerplant and plenty of fuel? No problem - greenhouse it all the way. Heck make grow lights and go totally underground). 'Handling it' means getting through the first couple of months/years while you set up your living situation; you'll need to have food sources to feed people for all of that time, until you can get crops in. If you've got enough technology, you can go anywhen that's not molten (and the Hadean wasn't all molten), and generate your own oxygen; develop your own soil, grow your own plants and animals. You're probably going to be fine with diseases. Most diseases require hosts in order to become really effective. The biggest issue is that our diseases are a lot more virulent than populations of primates (*cough* humans *cough*) in the past could have handled. We'd most likely wipe out them. Water isn't going to be a big issue. Minus the fact that you need to treat it, some water sources now are naturally arsenic and will poison people. So water has, and currently can, be deadly. But if you do the right filtering, or distillation - not a problem. Drinking random water is ill-advised. --- Hmm, my comment got deleted? Inuit and Sami are the only ones that even come close, but only 6-9 months of the year, not year-around. Yeah, you need to eat all of the animal, including boiling up the hooves. --- Uhh, merge what? I don't have two accounts. ]

[Question] [ Planet is earth sized. Fantasy medieval setting that takes place on Continent A, which is on the other side of the planet from Continent B - about as far as South America is from Asia. Continent B has a very very tall giant lumbering around on it, so big that it basically wrecks the landscape of Continent B wherever it goes. Presumably, at a certain height the giant would cause such enormous tremors that everyone everywhere on the planet would hear it walking around - I don't want this. But I do want the giant to be as big as possible without being a nuisance to everyone else on the planet. A global tremor when it jumps up and down would be okay, but there's already so much going on in this world I don't want the distraction of a constant background rumble from this giant just going about its everyday business. How big can I get away with? Update: don't worry about the structural integrity of the giant. The giant is magic, but the planet's geology is not\*. Assume human-proportional mass for a given height. Update: I want the giant to be as large and (locally) devastating as possible without causing global devastation. "Local" devastation can be as great as rendering all of Continent B uninhabitable, but if this isn't possible without causing a few raised eyebrows on Continent A, then no dice. \*except to the extent that all geology (and geologists!) is magical ;) [Answer] A real answer is a calculus problem that requires many different iffy variables that will be difficult to determine. So I am just going to ballpark it instead. In a lot of places, I have rounded or just taken sweeping approximations. It should hopefully be within an order of magnitude of the right answer. However, I think getting a realistic answer to this question is almost impossible. <https://science.howstuffworks.com/environmental/energy/energy-hurricane-volcano-earthquake3.htm> > > A magnitude 4.0 earthquake is only equivalent to about 6 tons of TNT > explosives. > > > <https://en.wikipedia.org/wiki/TNT_equivalent> > > The "ton of TNT" is a unit of energy defined by that convention to be > 4.184 gigajoules > > > So steps that produce $6 \times 4.184 \Rightarrow 25.1 \text{ gigajoules of energy}$ are an upper limit. How do we calculate the energy imparted by a step? I am not really sure. This is not as easy as jumping as the question of how much of your mass is really behind each step is a difficult one to answer. Also and how fast are the giant's feet moving? I am going to say that about 1/3 of the giant's mass is behind each step, and to step it simply lifts its foot and lets gravity pull it down to the ground. I will use potential energy to determine energy since it is a simpler calculation than kinetic energy (which is what it becomes when the giant steps). $$\text{PE}\_{\text{grav}} = \text{m} \times {g} \times{h}$$ So at $25.1 \text{ gigajoules} = \text{m} \times 9.8 \times \text{h}$, we have the mass of the giant's leg/part of body falling and the height from which this mass (presumably the leg) falls. Assuming that it follows a human-like anatomy: The average man has a height of 167.2 cm. The average man has a mass of 70kg. The average volume of a human is 95 liters. Height is related to the volume of mass: 1.67m has a ratio to the cube root of this mass, $70\text{kg} \Rightarrow 4.12$ untiless ratio ($\sqrt[3]{70}$). $$\text{Ratio in terms of height} \Rightarrow m = 15.03 \frac{kg}{m^3}\times h^3$$ Where m is fraction of gian't body weight (1/3 of total body weight). So when: $25 \text{ GJ} = \frac{15.03 \times 9.8}{3} \times h^4$ $h^4 = \frac{25 \text{ billion} \times 3}{9.8 \times 15}$ $h = 150 \text{ meters tall}$ $total.mass = (2.467)^3 \times 150^3 = 50,625,000 \text{ kg}.$ Which is big enough for giant's feet to sink into the ground as he walks. I don't think you have to worry about earthquakes from footsteps. If the giant was big enough for that to happen there would be other bigger problems to worry about. [Answer] **A Bit Taller Than Mount Everest.** Alexander says we need each step to have a Tsar Bomb's worth of energy to be measurable. Wikipedia says that's $210$ petajoules or $210 \times 10^{15}$ joules. For the moment let's say the giant is $1$ mile tall and do some back-of-the napkin calculations to figure out the energy. To simplify let's lift the giant $1$ mile off the ground and drop it. This will hugely overestimate the energy of a single step. The energy is $E = mgh$ for $m$, $g$ and $h$ the mass, gravitational acceleration, and height respectively. The height is $1$ mile or $1600$ metres. The gravity is about $10$ $m/s^2$. The mass needs more work. . . . If a human is $6$ feet tall the giant is about $880$ times taller. Then it should weigh $880^3$ times as much. If a human weighs about $70kg$ we're talking $47 \ 703\ 040\ 000 \ kg$ for the giant. Multiply those together you get about $7.7 \times 10^{14}$ joules. Much less than the Tsar Bomb. Repeat the calculations you get the following figures: $2$ miles $-$ $6 \times 10^{15} $ joules $3$ miles $-$ $2 \times 10^{16} = 20 \times 10^{15}$ joules $4$ miles $-$ $5 \times 10^{16} = 50 \times 10^{15}$ joules $5$ miles $-$ $9 \times 10^{16} = 90 \times 10^{15}$ joules $6$ miles $-$ $1.65 \times 10^{17} = 165 \times 10^{15}$ joules $6.5$ miles $-$ $2.1 \times 10^{17} = 210 \times 10^{15}$ joules So you can certainly get at least $6.5$ miles. Is that enough for you? ]

[Question] [ [Monomolecular wire](https://en.wikipedia.org/wiki/Monomolecular_wire) weapons are a somewhat common element in science-fiction. Including in this this [*fantastic* image](http://www.consortium-horizon.com/wiki/Fichier:EclipsePhaseCoverPanopticon_1500px.png) I found while looking into this:  Is the only infeasible thing in this image that the octopus would need bones to stand like that, or is the monomolecular whip also not feasible? Let's assume that we have the ability to construct a monomolecular wire from any real material. That uses up the hand waving allowed for this question. Which material would we use, and how effective would it be for use as a blade or whip? (*I have seen blades described as either rigid or a taught wire strung in a open frame. I don't care which one is used.*) To qualify as working or feasible, I'm interested in the wire not breaking while cutting through something of various densities, like a *human arm*. The effort required to do so, tensile strength, sharpness, etc seem all to factor into that one metric. Limb amputation. Let's call it *amputationility*. **So, can I cut off an arm with a monomolecular wire made of real materials?** If no real material would work, what minimum properties of a real material would need to be modified and to what value? --- *Note: I considered tagging this as hard-science. But given the possible requirement of a fantasy material I've left it off. However, I want answers to be as scientific as possible. An answer of "the material needs very high tensile strength" is not satisfactory, I want to know how high the tensile strength needs to be. Numbers people, show me some numbers.* [Answer] Graphene is what you're looking for. With a tensile strength of 130000 MPa, it has (IIRC) the highest tensile strength in the world. So lets make a wire-thin sword! I envision it to probably end up looking something like this: ``` >----------------------------------------------<| ||||||| | L_______________________________________________| ``` where the `-------` represent the blade, and the `<|` the tip that the other end of the blade is connected to, and the `||||>` represents a handle. It's important to note that the wire is being pulled taut by the `<|` piece at the end of the blade. The `L____|` represents a structure similar to that of a hacksaw, in order to hold the wires tightly. This is a **slashing/chopping** weapon. How/Why does this work? The "Graphene wire" is really a **Graphene ribbon** Graphene itself contains elastic properties, which helps with the above concept of cutting. Even if the Graphene doesn't cut right away, the elasticity will help it to continue cutting as you swing the blade through your target. "Graphene sheets (with thicknesses of between 2 and 8 nm) had spring constants in the region of 1-5 N/m and a Young’s modulus (different to that of three-dimensional graphite) of 0.5 TPa." Graphene also has amazing shear strength. Shear modulus of graphite was reported to be ~0.44 TPa. To give you some context, the shear strength of a carbon diamond structure is ~93 GPa. 1 TPa is 1000 GPa. **To answer your question: Yes, you can.** Unfortunately, because the human body is so variable, I can't find any actual numbers regarding how much force is required to tear off a limb - however, we should note that this blade doesn't apply force the same way a sword does. A sword cuts and splits the target because it "wedges" it apart. In this case, however, because we have a monomolecular ribbon that's completely flat, we should be able to pass through the entire target (irrelevant of what the target is made of, but assuming you gave it a good chop with no deviation in blade angle) extremely easily, since all we're severing are molecular bonds. Forces at the molecular level are at the pico-Newton level (1pN = $10^{-12}$ N); what we exert on anything using anything at any given time exerts more force than what's required. Here's some more context: One pound of force gives us 43.62 Newtons. Even a toddler could exert one pound of force by accident - so if you gave this thing to a baby and he accidentally swung it through you, good luck. Thank you to Samuel for pointing out some numbers for me: "the shear strength of the Graphene ribbon is maybe 4200 piconewtons / angstrom, while fibers in the skin, like collagen, have a shear strength of only 5.5 piconewtons / angstrom." These numbers show that along the same area, the ribbon has a shear strength of over 750 times that of collagen. Skin seems easy to cut though. What about bone? Luckily for us, most of bone's elasticity comes from the collagen in it, which means we cut bone just as easily as we do skin. For an adult? It cuts anything, and everything, better than warm butter. Once you finish slicing, the limb will only be held on by suction and surface tension. Any movement, and it simply slides/pops off. **However, even regarding the above saying that it is possible in theory, this tool is much better suited to a hospital setting requiring quick amputations than a battle situation.** Strictly speaking, this would work as an amputation device, but would be sorely suited for battle if the opponents also had access to similar weapons. In that scenario, please refer to Ville Neimi's answer (2 to 4th paragraph) regarding why it would suck as a weapon. Note that in normal use, the Graphene should be strong enough to be reused over and over again. The hexagonal structure of the Graphene ribbon means that even if any edge atoms are lost, it doesn't matter - No matter which atoms you lose, you will always have a suitable cutting edge. --- **References:** R. R. Nair, M. Sepioni, I-Ling Tsai, O. Lehtinen, J. Keinonen, A. V. Krasheninnikov, T. Thomson, A. K. Geim, I. V. Grigorieva. Spin-half paramagnetism in graphene induced by point defects. Nature Physics, 2012; DOI: 10.1038/nphys2183 <http://www.graphenea.com/pages/graphene-properties#.VYCbRkZ8ork> <https://en.wikipedia.org/wiki/Graphene#Thermal_conductivity> <http://poplab.stanford.edu/pdfs/PopVarshneyRoy-GrapheneThermal-MRSbull12.pdf> <https://web.engr.illinois.edu/~aluru/Journals/APL11.pdf> <https://en.wikipedia.org/wiki/Bone> [Answer] I'll assume you mean "monomolecular" literally. In that case the answer is "**No**", you can't make practical melee weapons from monomolecular wire. You could build tools or missiles using monomolecular wire and those could have significant amputationility. The basic issue is that a melee weapon needs to sustain repeatedly hitting the target and, most likely, armor, other weapons and coincidental objects. When that happens the atoms of the weapon will collide with the atoms of whatever is hit. No matter how hard your weapon is this will result in some of the atoms being ablated. Most weapons are hard enough for the loss to be insignificant, maybe requiring occasional resharpening of the edge. A monomolecular weapon **needs** all of its atoms for its structure. Even if the material has some redundancy so it doesn't simply go "poof" or break on first impact it will be locally weakened. So repeated impacts will result in the weapon losing strength until it suddenly breaks. Probably just at the moment you are fighting for your life. At this point it is simpler to add redundancy by making the impact point a composite of multiple molecules or crystals, just like conventional weapons are. A thin wire of "conventional" metal maybe reinforced with nanotubes or graphene gets the job done and is more robust and much simpler to engineer. For practical monomolecular weapon you need something where the fragility and unpredictable robustness do not matter. A single use weapon such as a missile you throw away or shoot. A specialized tool used for assassination that unless you mess up you only use a single time and then dispose of. A weapon that can recover from being broken by simply producing more of the blade or whip. The last is probably closest to what is wanted. A whip with an electric charge or a super science force field such as in the picture adding rigidity for pseudo inertia on impact could cause significant damage. And while it would almost certainly break on impact, it would be a simple matter for a microcontroller to detect the length of the whip was reduced from the change in capacitance and extrude enough new material to keep the length constant. A monomolecular whip has very little mass for a certain length so you'd probably run out of power before replacement material. But even then it would be much easier to use a conventional material instead of an exotic monomolecular one. More robust and probably cheaper. As noted in comments, the practicality of even this limited class of monomolecular weapons is still much less than that of more conventional weapons due to marginal benefits over much more reliable solutions, so nobody would use them. Practical in theory, but not in practice. Which I am not sure even makes sense. [Answer] I think, just like your cool picture suggests, that a whip-like weapon is what you're looking for. Consider a whip, i.e. a strand of something (and yes, we'll use carbon-nanotubes here, because they are really, really cool!) with a handle. Add some barbs to the end. Keep in mind that anything that is thin enough and does not move out of the way is actually a cutting edge. Now, you hit your opponent. The strand of carbon nanotubes will be wound around your opponent's arm, and you pull back hard. The thinness of the strand, together with the force you apply by pulling it back, and assisted by the barbs at the end, that will get hooked into your opponent's armour, clothing or flesh, result in the loop around the limb trying to get smaller, and thus cutting tissue that is in the way. The only question remaining is: can you pull hard enough to cut through the bone? That is where it really helps if your enemy is an armed octopus: They have no bones, which will make the limb removing business a lot easier. The downside: your octopus still has plenty of remaining limbs to make it very, very clear what he thinks about that. [Answer] As a starting point, I used [How does a knife cut things at the atomic level?](https://physics.stackexchange.com/questions/134119/how-does-a-knife-cut-things-at-the-atomic-level) from Physics Stack Exchange, specifically, [lemon's answer](https://physics.stackexchange.com/questions/134119/how-does-a-knife-cut-things-at-the-atomic-level/134137#134137). lemon1 talked about something called [nanoindentation](http://en.wikipedia.org/wiki/Nanoindentation), which is typically used as a laboratory testing technique. For now, I'll use some of Wikipedia's equations to work this out. The [Young's modulus](http://en.wikipedia.org/wiki/Young%27s_modulus) of the thing being cut, $E$, is related to the stiffness of the contact, $S$ and the indentation depth, $h$, by $$E=\frac{1}{\beta}\frac{\sqrt{\pi}}{2}\frac{S}{\sqrt{A(h)}}\tag{1}$$ where $$A(h)=\sum\_{n=0}^{n=7}C\_nh^{2^{-(n-1)}}$$ Doing some re-arranging, $$A(h)=\left(\frac{S\sqrt{\pi}}{E\beta2}\right)^2$$ Setting these two equal gives us $$\left(\frac{S\sqrt{\pi}}{E\beta2}\right)^2=\sum\_{n=0}^{n=7}C\_nh^{2^{-(n-1)}}$$ Let's solve for $S$: $$S=\frac{2E\beta}{\pi}\sqrt{\sum\_{n=0}^{n=7}C\_nh^{2^{-(n-1)}}}\tag{2}$$ If we say that $C\_0=C\_1=C\_2=. . .=24.5$, and $h$, the thickness of the human arm, is about 0.1 meters, and $E$ is about 14, then, for one tip, I find that the stiffness needed is . . . $\approx$ 1,196,000 Newtons/meter; the force needed is 196,000 Newtons. That's only if one tip is used. Add on more tips on a smaller scale, and this could be feasible. You would get smaller tips, and so smaller identations for each one, but it *could* work. Perhaps. The important thing to gain from this is that the types of tips used in nanoindentation can be quite effective. [A (paywalled) study](http://www.sciencedirect.com/science/article/pii/S0927025605003289) also mentioned in lemon's answer showed that the different types of nanoindenters used in the process can produce slightly different results. Fortunately, [the Wikipedia page on the devices](http://en.wikipedia.org/wiki/Nanoindenter) produces a nice starting point for research . . . which led me nowhere. Curses. What was I even trying to get at? Consider a long piece of barbed wire. Now make the barbs tiny - really tiny - and lined on every piece of the wire. Then turn each barb into something like a nanoindenter. Now you've got quite the weapon. The reason I covered nanoindenters was that I wanted to see if it would be possible to pick a design such that the shape would be more important that the composition. In any event, the resulting weapon would look like this: ``` || --------|| ||---x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x --------|| || ``` The tip of each "x", though, would be in the shape of a nanoindenter. --- 1 Note to any potential editors: the username is all lowercase. [Answer] No way. The positive answer(er)s all fail to take into account a) how exceedingly small a molecule is, b) how many molecules there are in a body (and how much they interact with one another) c) how a chain has to weather the sum of all forces acting on it and d) that a force acting perpendicularly on a chain can not simply be colinearized as is, but will lead to a colinear force many times the former magnitude. Have a breaking strength of 1TP like one answer gave for graphene: One Pascal is one Newton of force (100 grams in earth gravity) on one square meter. So 1TP means **10^12 Newtons per square meter**! Yay! But consider the cross section of a molecule: Let's be generous and set it to 2nmx2nm - thats (2\*10^-9)^2. So the breaking force for that single molecule is: 4\*10^-6 Newtons ... the force gravity exerts on four tenths of a milligram of mass. You could lift four fruitflies with that! (Yay?) Any molecule encountered by the "whip" on it's way through flesh will need to be acted upon by a force - shear intermolecular-bonds, shove it out of the way, resist adhesive forces... and at any one time, the whip traversing something as small as the human finger would encounter (lowballing) 10^5 molecules - so any of those molecules could be acted upon by (in the mean) 4\*10^-11 Newtons - that's just about ten times the force needed to break a hydrogen bond (weakest bond there is <http://www.picotwist.com/index.php?content=smb&option=odg>) and just a fourth of the force need to break a noncovalent bond. And we haven't even begun figuring in the multiplicators coming into play because the "whip" has these forces acting perpendicular to itself. The "whip" will drift towards its target, strike with undetectable force, and then break at the first tug. Possibly there is a papercut along the way. ]