The Great Filter

By | April 29, 2008
2 Comments

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Via GeekPress, Nick Bostrom has a fascinating essay at Technology Review in which he lays out his case for hoping that we don’t find evidence that life ever existed on Mars or that it exists elsewhere in the universe. Why would we not want to find evidence of life?

According to Bostrom, the apparent silence of our galaxy — the lack of even one civilization which has advanced to the galactic colonization stage, which we ought to know about if it ever happened, because they would be here — is evidence either that there is no life out there or that life is in some way blocked from developing to that level. He talks in terms of a “great filter” that evolving life must pass through on the way to the galactic colonization stage. If life is evolving out there in the galaxy, and no aliens have ever shown up here, that suggests that no life anywhere has ever successfully made it through the filter. And if nobody else ever makes it through the filter, we have very little reason to hope that we ever will.

The filter could take many forms. It could be some stage in biological evolution that is just plain difficult to get through. For example, if life rarely makes it to the stage of producing multicellular organisms, and that’s the reason nobody is out there, then we’ve already passed through the filter and it would seem that we are in the clear.

Woo hoo! Let’s start colonizing the galaxy.

  • rjschwarz

    Maybe a Galactic empire is out there and maybe they’ve been trying to contact us using their special methods and someday we’ll figure out that method and find a series of answering machine messages getting increasingly irrate that we aren’t returning their calls.

  • http://www.jessemazer.com Jesse M.

    Have you read Robin Hanson’s version of the great filter argument? I particularly liked his “safecracker” analogy, suggesting that if there are a number of hard steps in the evolution of intelligence, we should expect that on the rare planets where all are achieved, they should be about equally spaced in time. Hanson offers some plausible candidates for equally-spaced hard steps in terrestrial evolution, with a spacing of about 300 million years. The safecracker analogy would also imply that if this is the spacing, then we should expect that intelligent life most likely evolved around 300 million years before the window of possibility on Earth closed forever…and interestingly, even though the Earth will probably be around for billions of years, there are suggestions that the gradual increasing of energy from the sun is driving down CO2 levels on the long term, and that this will make photosynthesis impossible in under a billion years (and the complexity of ecosystems may gradually go down until that point, perhaps making the evolution of intelligent life less and less likely). See here for details, and even more on Earth’s distant future can be found in the book The Life and Death of Planet Earth, by the same authors who wrote Rare Earth which is very relevant to the “great filter” problem.