With the recent discovery of what may be water on Mars, the question of whether there may be intelligent alien life out there somewhere surfaces again. Water on a world something like Earth suggests that there may be lots of scope for it, as does the almost daily discoveries of more and more exoplanets.

And yet… I’ve been running the Seti@home program on my computer on and off for years – and it has found no aliens yet! And neither has anyone else’s. Of course, there could be lots of reasons for that, but with, certainly, hundreds of billions of stars and hundreds of billions of galaxies out there in the observable Universe, one would think that aliens (the ‘intelligent’ sort – like us I mean) would be out there somewhere. Furthermore, since there has been billions of years in which it could have evolved, it should not only be out there, it should be right here too: if even one civilization developed over the past, say, 5 billion years, and decided to colonise our galaxy, it would have done so by now.

So… no aliens around here, then. Unless we’re them, of course. But there is ample evidence that we evolved right here and are not, well, aliens. I’ve written about alien life before, and my arguments still apply, but some numbers can be updated a bit – the number of planets, for example, can be increased dramatically: it seems about one star in three, at least, has planets. So the probability of intelligent, space-faring life probably has to be reduced… almost to zero.

Probes are going to Mars, at some point. If they find life related to life on Earth, it could mean that the hypothesis that life on Earth began on Mars and got here by way of being splashed from Mars after collisions – or vice-versa – is possibly right. And it tells us nothing about how easy it is to evolve life elsewhere in the Universe. If there is life there, but it is not related to life on Earth (it uses a different chemical basis altogether), then primitive life is presumably easy to evolve and the entire Universe will probably be littered with various forms of it.

According to Nick Bostrom, this would be bad news. Because if life is easy to evolve, yet intelligent life is not out there, then intelligent life must be either a) almost impossible to evolve from primitive life; or b) almost certain not to survive long enough to colonise space.

In the case of b), which seems most likely of the two possibilities (because we are, after all, here – but then, we would be if we were asking this question), that means that there is a “Great Filter” in our future: something in our future waiting to exterminate us. Maybe some nuclear holocaust, super-military-disease, nanotech disaster, AI terminator doom… you name it, is waiting for us, and has waited for all other intelligent civilisations. Or hostile predatory aliens, I suppose. But if they exist, the odds are vastly on the side of them having colonised this planet millions of years ago, if colonising planets was their habit. And the point is, it would be somebody’s habit. Only one needs to do it, over billions of years. And they don’t seem to have done so. There is no sign of them anywhere: the Universe is full of white noise; no stars or galaxies seem to be having their energy mined in mysterious ways; vast resource fields of rock and gas are out there, apparently untouched. The place is pristine.

We are alone. And it is probably just as well, as we would be bacterium, almost certainly, in comparison to what could have evolved if the odds were in favour of it.

But if that’s so, what are we to make of this? Credible-seeming witnesses who are all cranks, liars and dupes? Surely not… [90m]


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