The Great Filter

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This article is about the lack of observation of intelligent extra-terrestial life. For the music album by Tub Ring, see The Great Filter (album).

The Great Filter is an implication of the failure to observe any extraterrestial life, despite considerable effort (the Fermi paradox). One possible explanation is that there is something, the Great Filter, which acts to reduce the great number of potential sites to the tiny number actually observed. It might work either by one or more barriers to the evolution of intelligent life, or a high probability of self-destruction. [1][2]. The main counter-intuitive conclusion of this observation is The easier it was for life to evolve to our stage, the bleaker our future chances probably are.

[edit] Main argument

The main argument is that we have not yet observed extraterrestial intelligent life, even though we observe a great number of stars. Therefore, the whole process must be unlikely (the Great Filter). This implies in turn that some step in the evolution of communicating intelligent life must be unlikely. Hanson listed the likely steps as:

  • 1. The right star system (including organics)
  • 2. Reproductive something (e.g. RNA)
  • 3. Simple (prokaryotic) single-cell life
  • 4. Complex (archaeatic & eukaryotic) single-cell life
  • 5. Sexual reproduction
  • 6. Multi-cell life
  • 7. Tool-using animals with big brains
  • 8. Colonization explosion

At least one of these steps must be improbable. If it's not 1-7, then the implication is that our future is bleak, since of the many civilization that made it to step 7, none have made it to step 8 (or the galaxy would be full of colonies), and the only thing that appears likely to keep us from step 8 is some sort of catastrophe. So by this argument, finding multi-cellular life on Mars (provided it evolved independently) would be very bad news, since it would imply steps 1-6 are easy, and hence only 7 or 8 could be the big problem.

[edit] References

  1. ^ Robin Hanson (1998). The Great Filter — Are We Almost Past It?.
  2. ^ Nick Bostrom (May/June 2008). Where Are They? Why I hope the search for extraterrestrial life finds nothing. MIT Technology Review.