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I have a scenario where Aliens must escape their Star system because a star 5 light years away from them is going nova soon. They find humanity and learn all about them in a few years - our whole history, the biology of all animals, etc. Then they establish contact and send us gifts that improve our level of technology and seem to be very friendly. Without going into too much detail, they eventually tell our politicians about their master plan.

They plan to come to Earth and make it their second home. They are carbon-based and breathe Oxygen, but are quite different than humans - for example, our atmosphere is not breathable for them because of the different ratios of Oxygen/Nitrogen and the presence of some other gasses. So...they need to "terra" or rather "xenoform" our planet. They make a deal (and an ultimatum of sorts) with human politicians that infrastructure will be built in China, Mongolia, and a separate one around India (smaller) to give shelter and food for all of humanity, and humans will live there separated by a special barrier...and the rest of the planet will be heavily changed to fit the Alien biology.

Aliens are powerful enough to terraform other planets, but not enough to do it quickly and economically-and changing Earth will be much quicker and economical; they just need less Oxygen and tweak some other things. Since lifeforms are generally egoistic, they are not ready to Invest 100x of their time and resources when they have a beautiful planet like Earth here and now.

So now for the question: is it possible to fit all of humanity in China, India, and Mongolia? Knowing, of course, that we are talking about a society that can build city-sized buildings and skyscrapers, and that production of food is easier because of genetic engineering and certain megaprojects.

Also, feel free to comment on what kind of improvements can be made to this setup. Maybe this barrier I write about is not feasible, so building cities similar to Saudi Arabia's "Line" will be a better option.

EDIT:By "fit" I mean: could humans live "normally" like in some densely packed city and country,or would it be an instant catastrophe? Lets say that most people could have a small apartament like cheaper places in Tokyo,some groups (from the poorest countries) would live like the homeless in India and only richest of the richest would have really comfortable houses or luxury apartaments. Something like that.

Mishima
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    Gases mix freely. This is a very important difference between gases and liquids. The only way for one part of Earth's atmosphere to have a different mix of gases from the rest of the atmosphere is to keep it enclosed in an vessel, such as a glasshouse. Aside from the small engineering problem of building a glasshouse covering all of China, India and Mongolida, glasshouses have lots of problems, such as the need for active cooling and the need to regulate the atmosphere inside. The question is envisioning a technology level so much in advance that it is indistinguishable from magic. – AlexP May 04 '23 at 11:16
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    See also: How many fed per sq kilometre?. – Escaped dental patient. May 04 '23 at 11:25
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    Why would such an advanced civilization need do colonize Earth? Why would a nova even be a problem for them? They could build a barrier (thin mirrors would work wonders) between their solar system and that star, and that should be easier than terraforming Earth. Or they could prevent star from going nova via star-lifting. – Negdo May 04 '23 at 12:07
  • Saudia Arabia's "Line" is a terrible idea. – Daron May 04 '23 at 13:20
  • Please clarify what you mean by fit. If people are packed on the ground as closely as possible, they fit in Rhode Island, but I suspect that this isn't what you have in mind. – Mathaddict May 04 '23 at 16:40
  • @mathaddict Understood. I edited the question. – Mishima May 04 '23 at 17:11
  • I doubt that the aliens would be simplistic enough to assume that the whole of humanity could be shooed into China, Mongolia and India without catastrophic effects. Nobody would be willing or cooperative. And if by some means the people were simply beamed across I imagine conspiracy theories would run riot and there would be an orgy of killing. The Indians, Mongolians and especially the Chinese would not tolerate an invasion and the “invading force” would be killed as they arrived. – Slarty May 04 '23 at 17:40
  • Xenoforming something like Mars would be much, much easier than trying to force Earth's ecosystem into another pattern. Especially if you are already going to glass over most of Asia. Why not just glass over Mars? – Michael Richardson May 04 '23 at 17:44
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    @Slarty Unwilling and uncooperative would die due to terraforming, e.g. suffocate or eaten by alien frogs. Forced relocation is also an option. Aliens are capable of interstellar travel, certainly they can deal with Chinese government. Elites will get better deal than the masses, but advanced enough civilization could provide few billions of humans with all they need. If people had to chose between moving and death, they would move. Most of them anyway. These are finer details of the story, they are far beyond the scope of the question. – D'Monlord May 04 '23 at 17:53
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    @Michael Richardson "Xenoforming something like Mars would be much, much easier" - or not. It depends on what aliens want from a planet and what technologies they have. Both of which are unknown. – D'Monlord May 04 '23 at 17:55
  • @D'Monlord my point was that whatever happens billions are going to die in fighting alien frogs, the chinese, nuclear missiles, conventional wars, disease, starvation, riots etc etc so the question of if the current population could be fed and housed doesn't really arise. – Slarty May 04 '23 at 22:50
  • Somehow I feel that those aliens have better ways to adapt Earth to themselves, and also I feel that humanity would be able to survive outside that dome, if the oxygen PP would be high enough. And the question says aliens need MORE oxygen than humans, so the "xenoforming" might not be threatening to humanity as a whole. Also I wonder what would happen to algae and other plants at xenoforming. Also I wonder what "other gases" make aliens feel bad, there are only H2O, CO2 and Ar present with significant rate, Ar is inert and others are needed for carbon life to function. – Vesper May 05 '23 at 04:28

2 Answers2

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Easy. The main limiting factors are food, water, energy and shelter. All easily solved by high enough technology like space hydroponic farms, water desalinization, fusion reactors, megaskysrapers/underground cities. If humans and aliens have broadly similar needs in food and water, which seems likely, these problems would be solved by aliens anyway.

I would avoid the magical border thing as per AlexP comment. Just make aliens or humans xenophobic enough to make the idea of sharing the same space impossible. It might even work better for the story.

L.Dutch
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D'Monlord
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  • There's one other important limiting factor - sanitation. 8 billion humans crammed into an area of that size are going to produce a lot of waste, biological and otherwise. The proximity will also contribute to the rapid spread of any contagious diseases without strict enforcement of quarantines. – RisingZan May 04 '23 at 20:26
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    @RisingZan - nope. India and China are already home for ~35% of Earth population. Three times more wouldn't make much difference especially if aliens provide food - it would free up huge territory. An alien race capable of interplanetary travel would be able to process waste. "megaskysrapers/underground cities" mentioned above is the most efficient way to deal with the problem - you don't need to dig water supply and sewers to every little hut. – D'Monlord May 04 '23 at 20:48
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    This answer smells a bit too much like handwavium. Got a logistical problem? Solve it with futuristic tech. Where's the limit? Why not have energy be generated by deutero-null cold fusion reactors that are small enough to fit in a broom closet and generate enough energy to power an entire city for 1000 years with a single fuel cell? Why not have food and water be synthesized on demand and waste disposal powered by teleporters that warp everything directly to an incinerator, or even the Sun? – Abion47 May 05 '23 at 03:20
  • @Abion47 Humanity could fit in China, India, and Mongolia, they just would need better technology. Guess what, aliens who capable to move their entire population among stars do have vastly better technology than us. Assuming anything else would be strange. More efficient agriculture, better energy generators and better skyscrapers. Nothing is it is unobtainium. Water desalinization is existing technology, fusion reactors are always just 20 years away and the idea that our current agricultural or construction technology is the best that could ever exist is just plain dumb. – D'Monlord May 05 '23 at 08:06
  • @Abion47 please read the actual question again. OP wants a decent amount of handwaving. Like, handwaving the food requirement is explicitly spelled out. The building of the infrastructure itself? Also handwaved. And we already do full-cycle water recycling on the ISS, so it's not magical tech. It's just insanely expensive. But since the aliens provide all infrastructure to us (and even if they didn't), PLUS 0 spending on agriculture, this increased expense for living would be tolerable. – Hobbamok May 05 '23 at 08:37
  • @D'Monlord There's a big difference between "they give us the technology to do stuff more efficiently" and "they give us technology to do everything easily and magically". Efficiency is far from the only problem that housing 8+ billion people (or probably far more given OP's description of the timeline) within such a confined space. Logistically it would be a nightmare, even if we assumed that fusion reactors or hydroponics were common. And sure, we could say that eventually technology can advance to the point where anything is possible. It's just that that's also a major literary crutch. – Abion47 May 05 '23 at 14:38
  • @Hobbamok If OP wanted handwaving to that degree, then why even bother asking the question? The problem isn't knowing whether it's possible. The problem is explaining how it's possible satisfactorily enough that it wouldn't immediately break the suspension of disbelief for the reader. If it's enough of an issue to OP's story that they are concerned in how believable it is, then it would do them well to get answers that are actually believable and not simply technically true. (Also, water cycling on the ISS isn't 100% self-sufficient. They get replacement filters and stuff all the time.) – Abion47 May 05 '23 at 14:44
  • @D'Monlord Indeed,I choose India and China because of tbis reason:They already have a big population,but at the same time - in case of Mongolia and China especially-a lot of free space.I think that I will change this idea a litlle bit and add more "Human Zones" on every contnent. Im still thinking about it. – Mishima May 05 '23 at 15:36
  • Indeed,I think I will ask another question or questions about certain details about this,but big amount of handwavium is ok for now. But it is interesting to read your comments about it. – Mishima May 05 '23 at 15:39
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    @Abion47 You are right,but for now I wanted to concentrate on this particular topic. I do not know if so many people would even fit in those countries,and by that I do not mean "human as sardines" kind of scenario,but more comfortable.I know that high buildings and underground housing can solve everything,but I dont want to have 73638634 Burj Khalifas in my setting,that would be kinda dull.But some percent of ultra high skyscapers are welcome. – Mishima May 05 '23 at 15:46
  • @Mishima I don't know how tied to the idea you are, but another problem with choosing specifically China and India is that one of the largest mountain ranges in the world divides the two across nearly their entire shared border. Choosing these regions to deposit the entire population of the world is a guarantee that the factions will engage in tribalism and eventually go to war with each other. So even if the aliens don't kill many humans directly, it will still result in the deaths of millions if not billions. (Though maybe for story reasons, this is exactly what you were going for.) – Abion47 May 05 '23 at 16:11
  • (And, albeit to a much lesser degree, the Great Wall of China might serve as a similar barrier for the China-Mongolia border.) – Abion47 May 05 '23 at 16:14
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"Some like to assert that everybody on Earth could be fit into the State of Texas,..."

My quotations are from this source.

... using logic as follows. The area of Texas is about 262,000 mi2. Dividing this figure by the current human population of 7 billion leaves each person with less than 100 square meters, a small plot the size of a big room about 10 m x 10 m. Sounds plausible enough, right? Without going into the fact that almost half the State is desert, notice we have not allowed for any roads, shopping malls, schools, hospitals, football stadiums, prisons, sewage plants, rivers, lakes, reservoirs, golf courses, parks, and what else? How much land does it take to support a human being?

This beginning statement makes a good point. Removing all other considerations, what's the smallest amount of space a human could stand to live in? I suspect high-density locations like Japan would point out that a 10mx10m room would be more than adequate... but that's all you'd get. Nevertheless, let's continue the story.

Let's do the math again, but this time for the entire planet. The total land surface area of Earth is about 57,308,738 square miles, of which about 24% is mountainous and about 33% is desert. Subtracting this uninhabitable 57% (32,665,981 mi2) from the total land area leaves 24,642,757 square miles or 15.77 billion acres of habitable land.

Divide this figure by the current human population of 7 billion (that's 7,000 million people!) and you get just under one hectare (2.3 acres) per person. If all the habitable land on Earth were equally distributed among all human beings present on Earth, this is the per capita share of good land per person. Again, however, we have not allowed for any nice amenities such as roads, schools, hospitals, shopping malls, rivers, lakes, reservoirs, parks, golf courses, etc. Even so, could you live on 2.3 acres?

Efforts have been made to estimate the amount of land needed to sustain an average individual human (link). A person living the lifestyle of an average American requires almost 24 acres, ten times the world per capita share.

And that's the question, although the article author is being a bit dramatic (and very simplistic). That 24 acres can include space in desert areas (roads, hospitals...) and is shared with others for complex services (roads, hospitals...). While the vast majority of U.S. citizens would fit within this context, there are some (I live near some...) who entirely subsist off the energy grid and entirely provide food and shelter for themselves with less than an acre (it's all about efficiency... and a bit of modern technology). What they can't provide for themselves consistently is water.

EDIT: I need to step in and make couple of a clarifications because some commenters seem to have lost track of the OP's question. The above article is just one of many that have been done to demonstrate — pro or con — just how much of the Earth's surface today's population really needs. One such article I read some time ago used Hong Kong's population density to prove you could crush the world's population into New Jersey. But if you're inclined to argue about the efficiency of the above article, you've forgotten why I posted it. It's nothing more than a means of demonstrating that the OP's proposed circumstance (relocating all of humanity to China, India and Mongolia) is believable. My original answer is about to say this. Arguing that less space could be used is irrelevant.

The second half of this answer is a Frame Challenge that points out that building a world has little meaning if the people reading about, using, or gaming with the world can't understand or relate to it. As alien as the aliens may want to be, leaving your audience confused isn't a good thing. Worse, it's difficult to believe that some commonalities wouldn't exist between humanity and any alien race, not matter how evolutionarily distant from us they may be. The need for food, procreation, education, and science. Competition, whether it be sport, academic, professional, or military. Etc. As was pointed out by one commenter, an alien race that's utterly incomprehensible to us would be unlikely to find any interest in us or our planet — because at the very least, their interest in our planet is something we could understand. Thus, while stashing humanity on a mega-reservation is believable, that an alien race would cross vast tracts of space to do it without a purpose... isn't. And I can't see that purpose, nor was one presented. Anyway... cheers. END EDIT

What's the point I'm making?

What you're trying to do is believable, especially if the aliens are forthcoming with a bit of tech to improve the efficiency, but it's not practical.

  • Assuming humanity survived the inevitable "you're standing on my toes!" internal wars, they'd be looking for a way to oust the aliens from day #1.
  • Maybe... maybe... we could learn to overcome greed, bigotry, etc. fast enough not to tear ourselves apart (there is precedent, consider Turkey before the Bosnia and Herzegovina independence movement in the 90s), but I suspect the bedlam would be breathtaking.
  • If the aliens apply enough outside force to compel humanity into a small area, then your question is kinda irrelevant. You know... aliens with the tech to get to Earth, the tech to move all the humans, the tech to keep them there... can do pretty much anything.

But I would like to point out that your aliens are exhibiting a very odd psychology for conquerors who gobble up most of the planet for themselves.

  • Considering the suffering they'd cause among humanity and irritation they'd suffer themselves for as long as humans continued to breathe, such creatures (from a human perspective) would be far more likely to simply exterminate the humans. After all, if you have the power to force this condition upon humanity (8 billion people)... why share?

So, while I find your assertion to be believable from an implementation standpoint, I don't find it believable from a conceptual standpoint. You might think your aliens are trying to show some kind of mercy or something.... In reality, it would be much closer to wanting us to provide gladiatorial sport. Almost anything would be less cruel than to cloister humanity into a small area of their own planet with no hope of overcoming the technological advantage of the conquerors.

And we wouldn't have a hope. Allowing the hope would be a technology dichotomy. A space-faring species that could force us all into a limited area with enough efficiency to realistically stay there and survive would also have the technology to monitor almost every aspect of our society. They'd know if we were getting ahead of ourselves and stamp that out. And we're clever little monkeys... the aliens could be constantly putting out fires, so to speak.

Yeah... I'm having trouble swallowing this idea. Unless humanity was being stored away for slave labor or cannon fodder or some such, I don't understand why aliens would do this. I can't imagine a mix of desperation and compassion that would bring this situation to pass.

But, I'm unlikely to be creative/imaginative enough to justify that as a global assertion.

JBH
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    "your aliens are exhibiting a very odd psychology" - as they should, that's a huge part of what makes them aliens. Expecting human psychology from them is absurd. You are questioning the OP's premise based on idea that aliens are humans in disguise as it is often on TV. Aliens don't have to be that primitive. They are very likely to be a complete enigma with incomprehensible motivation. Full freedom for a writer. Even from humanity point of view their solution is far from being unbelievable. If humanity faced a choice between extinction and cruelty it would be cruel. – D'Monlord May 04 '23 at 15:21
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    @D'Monlord Yes and no. If the goal of this worldbuilding effort is to write a story, the alien psychology must be presented in terms that the reader can comprehend for the purposes of the story. Simply writing something sensless to humans off as "well... it's alien!" is a mark of a very poor writer. Worse, we humans can understand the motivations of cats, dogs, fish, insects... all of which are alien to humanity, just not alien to our world. The assumption that the ecology of an alien world would be incomprehensible is insensible. Even aliens need a good meal. So, no, I don't agree. – JBH May 04 '23 at 15:49
  • I didn't say a word about incomprehensible ecology, that's a straw man argument. I was clearly talking about psychology and motivation. "Aliens are just like us, just green" is a mark of a terrible writer with complete lack of imagination, yet this is what you advocate. Cats don't have religion, they are trivial to understand and we had centuries of observation. Aliens can have stuff humanity didn't even think about. In the same way they may not have a concept of religion and even a word for it, completely alien idea for them. Demanding aliens to obey your preconceptions is irrational. – D'Monlord May 04 '23 at 16:10
  • Thanks for your reply. I disagree with you. Even on Earth we have some situations that are (on a basic level) similar. For example,we have Animal preservation acts,and while some animals are very helpful for us (without cats there would be too many rats,et cetera) there is also the scientific and moral aspect to it.I dont want my aliens to be one-dimensional,like the ones that destroy all of humanity without any kind of negotation. They have moral values like we do,but at the same time their politicians are not idealistic-just like humans that try to negotiate but end up fighting a war. – Mishima May 04 '23 at 16:53
  • @D'Monlord Of course you did. "Expecting human psychology from them is absurd." How any creature thinks is a function of their evolution and place in the global ecology of their world. You're welcome to dismiss it as a straw man argument (you've dismissed a number of my explanations that way), but that doesn't matter to me. Quite frankly, if you believe my answer lacks merit or value to the OP, then you're welcome to down vote it - but demanding in your turn that I adhere to your beliefs and interpretation of worldbuilding and its purposes will fall on deaf ears. – JBH May 05 '23 at 02:44
  • @Mishima Thanks for your comment. I assume you're speaking about the second half of my answer and not the first, which supports your desire. I'm merely pointing out that the conditions you've described may require clever or insightful rationalization to be embraced as believable by your audience. Even if you disagree, which is certainly all right, I hope the answer gives you something to think about. – JBH May 05 '23 at 02:48
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    @D'Monlord The ecology argument is a valid one. For an alien species to have psychology that is incomprehensible to us, life itself would have to have evolved radically differently on their planet. Otherwise, things like survival of the fittest would be shared between us, which means on a certain level, we would be able to understand their reasoning if not their motivation or priorities. And that raises the question of if the aliens want to strip mine the planet or whatever, why not just be rid of us and be done with it if the alternative involves going through a lot of unnecessary trouble? – Abion47 May 05 '23 at 03:01
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    And if they are so vastly different from us as to be incomprehensible, that would also mean that we were incomprehensible to them. If that were the case, why would they value our existence at all? We would be something so utterly foreign to them as to be completely beyond any hope of understanding, so why go through the trouble of containing us as a collective species in a region on our own planet, gifting us the infrastructure and technology required to house billions of people in a megacity? Why not take a handful of us for zoos, pets, slaves, or scientific study, and then burn the rest? – Abion47 May 05 '23 at 03:05
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    How is invading a place and forcing its inhabitants into small areas of their former territory at all alien to even human psychology or history? – Obie 2.0 May 05 '23 at 03:24
  • @Obie2.0 You bring up a good point. U.S. expansion into native American territory is a good example. But some felt that was evil, some thought it was good, and some thought the only good Indian was a dead one. These three basic perspectives exist throughout human history - with genocides happening more often than most people realize (many who think native Americans undefiled by euopean colonialism lived entirely in harmony are disturbed to discover there were a fair number of genocides). (*Continued*) – JBH May 05 '23 at 03:57
  • ... Thus my concern: what's motivating the aliens to keep the humans? Humans killing humans disturbs other humans - but would aliens killing humans disturb aliens? What advantage is gained to the aliens by keeping all the humans on a reserve? And how would this be conveyed to the human readers of a story based in this world? – JBH May 05 '23 at 03:57
  • No one needs 10x10m room all by themselves. More realistically it would be one 10x10 room for 5 people to sleep, and another of same size as a living room/kitchen for all of them. That would leave 3/5 of the whole area for amenities. Then if that is not enough, just build higher buildings. – Boat May 05 '23 at 05:41
  • Just stack rooms is what I would also have said. We already do that anyway. – kutschkem May 05 '23 at 07:11
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    @JBH "The assumption that the ecology of an alien world would be incomprehensible is insensible" - your claim. I never did this assumption, that's classic strawman. "you've dismissed a number of my explanations that way" - blatant lie, your "arguments" were explicitly addressed. "but demanding in your turn" - I do not though, I just pointed out how ridiculous your demand that aliens must has the same psychology as us. "if they are so vastly different from us as to be incomprehensible" - I said they could be, and so demanding them to act as humans is dumb, see, it's that simple. – D'Monlord May 05 '23 at 08:23
  • That calculation COMPLETELY ignores any sort of verticality though. People can be quite happy sharing their 10m^2 Ground-area if that means they can have a 40+ sized flat. And that would already be achieved at 4 story high buildings. Build up to 5,10,20 stories and you have more than enough space for public transit (with that density, cars are a joke), amenities and even parks. – Hobbamok May 05 '23 at 08:33
  • @D'Monlord (Replying to the part of that comment that was directed at something I said.) That's the point, though. We would expect the aliens to act like humans, or, more accurately, to act in a way that, on a certain level, we would understand. To expect otherwise is to acknowledge that the aliens are so fundamentally different than us, they would effectively just be monsters to us and we would effectively just be dumb animals to them. And in that case, why they would bother to leave us alive, and how could that reason be conveyed to the reader in a way that doesn't feel like lazy writing? – Abion47 May 06 '23 at 03:29
  • @Boat You're not wrong. Many analyses like these have been done. One uses the population density of, if I remember correctly, Hong Kong. In that instance, the population (but not the land supporting it) would all fit in the U.S. state of New Jersey. The real issue isn't the population. It's the land needed to support it. Though technology can (and has) be used to improve, e.g., recycling and food density... it'll always be a lot. And it makes even less sense for the aliens to provide that tech to the humans in this scenario - unless there's an unstated need to keep us around. – JBH May 06 '23 at 03:43
  • @Hobbamok As I just said to Boat, there have been many analyses. Yes, you can crush population into less and less space, but the land needed to support the population is much less compressible. Yes, technology can improve that, but why would the aliens provide that? That's really the point of the second half of my answer. The point of the first half was nothing more than to point out that the OP's request was believable. – JBH May 06 '23 at 03:45