You are very unlikely to spend your retirement years on a space station parked at L5. Or L4 or L1 for that matter.
And even if, theoretically, we did create such space colonies, it wouldn't solve Earth's overpopulation problem.
Watch the fascinating 5-minute NASA video from 1975 on space colonization below. Nate Berg at The Atlantic notes that this film was "the product of a 10-week NASA program in the summer of 1975 that pulled together engineers, scientists, architects and students to imagine convincing ideas about how humans might be able to live in space for long periods of time on a large scale." "Taurus" was conceived as a one mile diameter, doughnut shaped (i.e torus-shaped - hence "Taurus", get it?) space station that could permanently house 10,000 and was situated in L5 orbit, a gravitationally stable sweet spot in between the Earth and the moon. It would be constructed from lunar-mined ore, powered by solar energy, and its colonists nourished by a 100-acre farm.
Such grand deep space colonies didn't happen for reasons I outline below. Space colonization as a solution to global overpopulation - which is part of what sparked such ideas back in the day - isn't viable. One day, probably a very long time from now, we may create O'Neill Cylinders with thousands of people living in them - but if we do it won't be to solve an overpopulation problem on Earth.
As the world hit 4 billion people in 1975, a great number of people worried about Stanford biologist Paul Ehrlich's warnings in the late 1960s that the looming world "population bomb" would inevitably result in the starvation and deaths of "hundreds of millions of people" by the end of the decade.
Obviously that Malthusian catastrophe didn't happen (fortunately!); Ehrlich and others failed to appreciate the major increases in agricultural output brought about by Green Revolution technologies. Agricultural research began in the 1940s and 1950s to develop new high-yield varieties of wheat, rice, corn and other crops, combined with increased availability and adoption of irrigation technology, fertilizers and pesticides. Beginning in the late 1960s, that research started to pay off. By the mid-1980s, global crop yields had more than doubled, thus staving off the predicted famines. (Side note: all of those advances - from research to irrigation infrastructure to fertilizer - were greatly facilitated by Western aid subsidies to developing countries.)
But the eventual success of the green revolution wasn't immediately apparent back in the mid-1970s. Fears of a Malthusian catastrophe, combined with the amazing success of the Apollo program, sparked the notion that perhaps the only solution to global overpopulation was to build self-sufficient (or what we now call "closed loop life support") space colonies. These ideas were popularized by Princeton physicist and space activist Dr. Gerard O'Neill. Oh, the optimism of the day. But these were were not just ahead of their time; they were also quite unnecessary, as global economic and agricultural growth since that time has shown.
But here's the but. Roger Martin from Population Matters notes a quote from Norman Borlaug, who won the Nobel peace prize in 1970 for his critical contributions to the Green Revolution. In his Nobel acceptance speech Borlaug said, "I have only bought you a 40-year breathing space to stabilise your populations."
In an essay noting our reaching the 7 billion person mark last month, New Yorker writer Elizabeth Kolbert wrote that:
[Bill Gates and others] have pointed out [that] just to keep per-capita food production constant in the coming decades will require a second “green revolution.” (The first one increased global grain yields by roughly two per cent a year from 1950 to 1990.) This will have to be accomplished under increasingly trying circumstances. An analysis in Science concluded that rising temperatures have already begun to depress global corn and wheat production. Another analysis, published in the Proceedings of the National Academy of Sciences of the United States, warned that, owing to global warming, corn and soybean crops in the U.S. could decline by as much as eighty per cent by the end of the century.
Part of what made the first green revolution possible was a sharp increase in the use of phosphorus-rich fertilizers. Thanks to this increased use, experts say, reserves of phosphorus are now being exhausted. Foreign Policy has called this “the gravest natural resource shortage you’ve never heard of.” Other essential commodities that could similarly run short include oil, water, and arable land. Jamais Cascio, a research fellow at the Institute for the Future, an offshoot of the RAND Corporation, put it this way recently on the Times Web site: getting to ten billion “would be a sign of successful navigation of this century’s problems.”
Many writers make the inarguable point that Malthus (and Ehrlich) were wrong. They were, in the sense that they underestimated technological advances that allowed the population curve to continue its upward trajectory for far longer than they imagined. But their basic point is correct: given limited resources and relatively fixed technological constraints, there is an upper limit to how many people the Earth can support. And even the original green revolution can't continue, since increasing water scarcity, salinization, soil loss, input shortages (such as phosphorus) and other problems put limits on even the best of current technology.
The planet has a carrying capacity. Whether the number is 8 billion, 10 billion, 15 billion or more is probably not something that would be wise to test.
We're gonna need a bigger boat. But that's not possible. And not only that - there are no life rafts, either. Space colonies aren't going to solve our problems. Earth is the only spaceship the vast, vast majority of us will know.
I think space technology might be critical to solving many problems here on Earth. But as a solution to overpopulation - no. Space technology can, maybe, help us address certain resource shortages. (If somebody finds economically viable amounts of phosphorus on the moon, that might really be something to write home about.) [Added 12/12/11: I'm being facetious; phosphorus is not found in great quantities on the moon.] Mining the moon for Helium-3 has applications for medical imaging devices as well as a source of possible aneutronic nuclear fusion. Dennis Wingo has written about the abundance of platinum group metals. And finally, there are rare earth elements.
But even beyond possible space resource utilization, it may be that the sustainable living technologies that the world will need to allow several billion Chinese and Indians who expect, demand, and can afford American standards of affluence, will have to be developed through space programs. Technology doesn't necessarily develop just because there is a theoretical need for it; often there must be an external catalyst to make it possible. But more on that idea later.
Gerard O'Neill was an impressive visionary, but he lived a hundred years ahead of his time. And while I like and respect many modern-day O'Neillians, such visions are at best premature. But perhaps more importantly for current space policy, their message is not one that will advance space exploration. People want tangible benefits from space - back on Earth.
But orbiting massive space colonies are a nice fantasy.