Hard SF : Science Issues : Can Space Colonization Guarantee Human Survival?
Many people have argued that as long as humans live only on Earth, we have "all our eggs in one basket". They suggest we need space colonies to insure the future of the species.
There are many current and potential threats to the human race. However, considering the human source of many of the threats and the time-scales involved, I'm not sure that space colonization should be the top priority in preempting those threats.
To consider how well space colonization is likely to solve our problems we need to ask what the time-scales of sustainable, independent space colonies are. If, after disaster strikes Earth, Earth is still able to supplement the needs of space colonies, then those space colonies aren't necessarily essential to continuing the human race. We have to ask when space colonies would be functioning without need of any assistance from Earth. Truly independent space colonies must not simply provide bare nutrition, air, heat, and habitat repair for 100 years. They should have a non-traumatizing environment with enough people to protect against dangerous levels of inbreeding – able to last and progress indefinitely. There will also be a minimum number of people required for any space colony in order to provide needed manpower in various occupations (one person with multiple occupations doesn’t help if you need two of those occupations in different places at the same time).
How does that compare to the time-scales of threats from climate change, environmental crisis, nuclear / bio weapons and accidents, possible nanotech weapons or accidents, overpopulation, etc.? We also have to consider threats to the global economy, since an economic collapse would presumably at least interrupt efforts towards establishing space colonies. Economic crises also increase risks of war, which could have apocalyptic consequences.
Even assuming the ultimate solution of human survival is space colonization, we may need to find a way to extend the lifespan of human civilization and economy on Earth in order to have time to accomplish sustainable space colonization.
Consider the possible habitats. Space stations in orbit around Earth or at L5 have little natural resources at their location other than solar energy. The Moon has no atmosphere, a limited amount of water at best, which part of the Moon has access to solar energy varies during the month, and it's not considered one of the solar system's better sources of minerals. Venus is extremely hot, the atmosphere is dangerous and with the cloud cover I'm not sure how practical solar energy would be at the surface. Mars has too little atmosphere and accessible water is questionable, etc. Some of the outer planets' moons may have enough ice and raw materials, but are very cold, lack usable atmospheres and get limited solar energy. And so on.
We may be able to establish bases at some of these places in a realistically short amount of time, but not independent ones. Any colony that wants to get resources from post-apocalyptic Earth will need to have spaceships that can land on Earth and later achieve escape velocity from Earth while carrying cargo without help from Earth. Otherwise, the needed resources may not be available from a single astronomical body. That could require longer-distance travel between bodies - whether that's between asteroids, between moons, between planets or some other combination. Significant space travel ability may be essential. A colony would need an industrial base capable of extracting and refining raw materials, and making useful things from them.
Interstellar colonies and terraforming of planets in our solar system are longer-range goals. Colonies in any place other than an Earth-like planet will require a substantial infrastructure to allow humans to exist in an otherwise deadly environment. The colony needs to be able to maintain and repair that infrastructure...
There is a significant difference between an enormous disaster on Earth and one at any space colony we can expect for at least a century. Even something on the scale of a "dinosaur killer" asteroid impact won't necessarily kill all humans on Earth. (However, if the world economy / technology is set back too much it may not be possible to re-achieve a hi-tech civilization. We've extracted most minerals / fossil fuels that can be gotten without hi-tech, a post-disaster society may be left unable to get these.) It will be a long time before an independent space colony could grow to the point some of its people could survive after a major disaster.
Meanwhile, we have not yet solved the physical and psychological problems that develop during months of low gravity. Most of the physical issues may not be significant for those who never intend to return to Earth-type gravities. Psychological issues remain. Some physical issues may arise when dealing with years and decades in low gravity. Even in shorter spans of time, weakening bones may have serious consequences in low gravity situations. Weakened hip bones may be a problem for women giving birth in low gravity. Other stressful activities may also be problematic. We need to find out how low gravity will effect a fetus during pregnancy and child growth afterwards. Identifying and resolving all the issues is likely to take many years.
Currently, our society is not inclined to invest that much in either stopping global warming (and other threats) or space habitats. It strikes me as improbable that we will see a heavy investment in both of them at the same time in the next period of time. My impression is the best chance for human survival is focusing as much as possible on one or the other of the two paths, and that space colonization will not solve the problem within the limited time-frame.
Of course, if governments refuse to fund solutions to the environmental crisis, but budget money for space habitats we should use that money. Hopefully, governments will respond to the crisis before it’s too late and the problems will be brought under control and within safe limits. Then there will be no reason not to expand out into the universe.
For those who still believe space colonization should be the priority, I would like to suggest one piece of advice. The known threats to human survival in the next century or so are not vast earthquakes and volcanoes, asteroid impacts, supernovas or other natural disasters. Most of them are at least partly man-made. If the same problems are not to threaten survival of humans on space colonies, we either have to make humans on Earth act more responsibly to ensure survival before we colonize, or we need to know how to insure that those people who colonize are not so prone to make the same mistakes their Earthly brothers do. If space colonization ends up amounting to running away from our problems, we will not have changed the odds of human survival by much. Space colonies would need to be planned in a way to avoid this fate.