Theoretical physicist Stephen Hawking's public statements this year have been decidedly unusual, even weird. In April, he emphatically argued that humans should not try to contact aliens, for fear of being conquered. A week later he released a 3,000-word guide to building and using a time machine.

His more recent declaration is tame by comparison, but still noteworthy. Hawking says that "our only chance of long-term survival" is to launch ourselves, as a species, into space. He's not knocking climate scientists' attempts to figure things out on Earth--he's just thinking long term. "There have been a number of times in the past when our survival has been touch-and-go," explains Hawking at Big Think, mentioning the Cuban Missile Crisis, and "the frequency of such occasions is likely to increase in the future. ... Our population and our use of the finite resources of the planet earth are growing exponentially along with our technical ability to change the environment for good or ill," while "our genetic code still caries our selfish and aggressive instincts." Taken together, he reasons, "it will be difficult enough to avoid disaster in the next hundred years, let alone the next thousand or million. Our only chance of long-term survival is not to remain inward-looking on planet earth, but to spread out into space." This, concludes Hawking, is precisely why he is "in favor of manned ... space flight."

Lest you be downcast, fear not: Hawking proclaims himself an "optimist," saying that if we can just "avoid disaster for the next two centuries our species should be safe," as we head out to other planetary homes. Striking out into the universe is not simply a matter self-preservation, but a moral duty. "If we are the only intelligent beings in the galaxy," he says, "we should make sure we survive and continue." Of course, the suggestion that we are the only intelligent life forms for a few trillion miles seems to raise the question: so why worry about alien attacks?