Life is hard

Slashdot linked to this article, an interesting take on the possibility of finding life on Mars by Nick Bostrom. What I’m most struck by is that his thinking is much like mine, but he takes the reasoning another step. An AI researcher would be proud, though: he uses good, probabilistic reasoning.

His main point is that because SETI has never found any signs of intelligent life, there’s probably some evolutionary step that’s improbable. Not just unlikely, but so terribly unlikely that it’s got only a one-in-a-billion chance of happening on any given planet. With odds like that, it would be easy to see why there are no other civilizations broadcasting radio waves into space–we were simply outrageously lucky to be here at all. He calls this unlikely event the “Great Filter”.

Nick puts forward the two obvious candidates for his Great Filter: the two evolutionary advances that took the longest time to occur. They are the origin of the first unicellular life (which admittedly sounds unlikely, right?) and the transition from prokaryotes (cells like bacteria, which don’t have all the complicated structure ours do, such as nuclei and mitochondria) to eukaryotes (which are much like ours). Eukaryotes took about 1.8 billion years to evolve–that’s an outrageously long time. But it happening even that fast might be unlikely. What if the average time that step takes to happen is a trillion years? Then we’re very lucky, and we’re unlikely to have neighbors.

So, that’s the sort of thing that had already occurred to me (and indeed, that I pontificated on to Megan not so long ago). But Nick takes that reasoning farther than I did–you should read the article to find out how.

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