The trouble with the "space travel will save us from overpopulation" argument is that, no matter what technology we come up with in the medium-term future, it i

The trouble with the "space travel will save us from overpopulation" argument is that, no matter what technology we come up with in the medium-term future, it is difficult to imagine ever solving overpopulation problems with emigration of any type - we just can't move enough people fast enough. As far as I know, in the entire history of the world, we have never moved enough of a population of healthy, established citizens of any region to alleviate any overpopulation issues. Anything even kind of like that mostly involves heavily threatened populations relocating under duress with little more than what they can carry. If they're lucky, they might manage to settle somewhere that will help them get back on their feet. There was an interesting passage in the Red Mars series about this. On their Earth, then had 11 (!) operational space elevators and a severe overpopulation problem. The numbers were all theoretical, of course, but they calculated that, even with 11 space elevators working full-tilt on sending people off the planet, they still wouldn't come close to making a dent in the world population. It's hard to imagine any kind of technology that could actually move and settle people off of Earth by the billions.