I was watching a science channel series about colonizing other planets. While most shows were about different bodies in our solar system (Venus! Titan!), one was about going to other stars, and they brought up the idea, long discussed in science fiction circles, of generation ships that take multiple human lifetimes to reach their destination. This proposal has always seemed quite naive to me. If you had the technology to support a population, indeed a society, in a large structure in space, and the experience of walking around on a planet was beyond living memory, what could motivate these people to deliberately enter a gravity well just because their great-grandparents had escaped from one? By the time they got to the new star, assuming they stopped, they’d probably keep living on the ship as they had always done and seek to bring resources to the ship, or perhaps even to build another similar structure, rather than to leave the only home they’d ever known. Indeed, if you could build something like that in our solar system, why bother putting a huge engine on it? It’s incredibly parochial to assume that living on a planet is the only way to thrive and exploit new resources after you prove just the opposite on the way to your goal. If Einstein was right and faster-than-light travel is impossible, a truly space-faring civilization must be a space-dwelling civilization, and the notion of returning to a planetary surface might appeal only to a few adventurers, not to the vast majority. If the human species survives long enough, our descendants will colonize our planets and asteroids for millennia before anyone seriously thinks about going to another star.