Draconid Meteors Over Spain. Image Credit & Copyright: Juan Carlos Casado (TWAN), via NASA

For a long time I have bumbled blithely along with the sunny confidence that we are not alone in the universe. It’s been evident for a while now that it’s pretty common for stars to have planets around them, and what with the hundred billion stars in the galaxy and hundred billion galaxies in the observable universe, I thought there ought to be plenty of planets out there with life flourishing upon them. But yet. This article by Nick Bostrom of the Future of Humanity Institute at Oxford gives me pause on two counts: a) perhaps the fact that we haven’t yet discovered an extraterrestrial civilization means that there aren’t any, and b) if there aren’t any extraterrestrial civilizations, the implications for us are actually kind of terrible.

Part a) is what I want to know more about, but part b) is probably more interesting. On the subject of why we haven’t discovered any aliens (or why no aliens have come and visited us), I want to know more of the reasoning. The article argues forcefully that if advanced civilizations did develop in other parts of the galaxy then we ought to know about them because over astronomical time periods they would easily have been able to cross the galaxy, even at sub light speeds. We have already sent one spacecraft (Voyager 1, I think) outside the Solar System and if we wanted we could quite easily send another, perhaps carrying some human DNA and other specimens of life on Earth along with a pretty much arbitrary amount of information about our civilization. It might well be that in a hundred years we’ll develop technology that could take those building blocks and build a human colony on another planet. And the great thing about astronomical numbers is that if alien civilizations can exist, there’s bound to be enough of them that that idea would have occurred to them and they might have given it a crack. But yet: no evidence. Also no evidence of radio communications coming from elsewhere – although I don’t know if we could expect our own radio signals to be picked up at astronomical distances… Anyway. I am not completely convinced that we can be sure that alien civilizations don’t exist elsewhere in the galaxy, but to discuss part b) then we need to assume that.

Part b) is the scary bit: what it says is that if there are no alien civilizations elsewhere in the galaxy, either i) for life to arise on any planet is enormously improbable, meaning life here on Earth is completely unique. This puts us in an incredibly privileged position, astronomically speaking: the only civilization that the universe will ever see. It also means that our future possibilities are completely unbounded: maybe we will colonise the galaxy at some point. But the alternative, ii), is that life does arise relatively frequently, but something always prevents advanced civilizations from being able to explore space. If this is true, then the overwhelming likelihood is that we ourselves are doomed to destruction well before long-distance space travel becomes a possibility: if all other civilizations were destroyed, we surely will be as well. Some of the mechanisms by which this could happen are listed in the article: the old super-powerful weapon falling into the wrong hands possibility; pandemics; uh… other bad stuff.

As I say, I am not overwhelmingly convinced of part a), but if it’s true then part b) holds up pretty well. The conclusion is that we have to hope for option i) – i.e. that life itself is what is incredibly improbable – rather than ii), which is that it is incredibly improbable for civilizations to persist over astronomical time periods.