The Great Filter

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The Great Filter describes the possible unlikelihood of advanced civilised life (beyond our questionable own) being prevalent in our galaxy and in the universe at large. It is a prime contender as a resolution to Fermi's Paradox which asks why we get no radio signals from interstellar civilisations even though many seem likely to exist according to some estimates. Most of the optimistic hopes for a thriving universe rely on the Drake Equation which yields very positive estimates. The Great Filter might be seen as the pessimistic antithesis of the Drake Equation.

[edit] Premise

Formulated by Robin Hanson, the initial premise of the Great Filter can be inadequately summarised by the following bullet points:

  • Life will naturally advance, via significant "steps", to the point where interstellar travel and galactic colonisation is inevitable.
  • In the context of our civilisation, any one step might be in the past, such as the Precambrian explosion or development of big brains and hands.
  • There may also be future hurdles - "steps" we are yet to encounter - to technological advances that need to be overcome without effecting a civilisation's own annihilation (I'm looking at you Earth - Sincerely, The Universe).
  • For any sufficiently advanced civilisation, and fuel efficiency be damned, such civilisations will have developed the grunt to propel themselves at near light speed.
  • Such a civilisation will therefore colonise a galaxy at near light speed and, if not by themselves at first, by use of drones to prepare the way

[edit] Conclusions

The conclusions are outlined in the following lazy bullet points:

  • Our radio antennas don't even hear a peep from alien Carl Sagans let alone there ever having been a (fortuitous) blitzkrieg on Capitol Hill by a mammoth trash can lid. This suggests that galactic colonisation has never happened (though the anthropomorphic[wp] assumption that a totally alien life form's communications technology would proceed along lines basically equivalent to our own is a leap unto itself.)
  • Extraterrestrial civilisations may possibly have made it as far as we have in terms of technology but never made it any further which is bad news for us. Their technology develops to our point but they inevitably screw themselves back to the stone age or worse.
  • Extraterrestrial civilisations may never have even arisen due to failure in achieving one of the the various "steps" required from simple unicellular life to galactic colonists and we are the lucky ones...so far (see previous point). This is closely related to the "rare Earth" hypothesis.
  • Even if the evil alien drones missed our bountiful solar system, there should be plenty of spectroscopic evidence of stellar scale industrial activity that is necessary for interstellar colonisation. (This would currently be somewhat difficult to pick up, present or not, due to the ways in which exoplanets[wp] are detected, but coming technology like the ATLAST[wp] telescope should make it possible to observe those planets more directly.)

Naturally, like the Drake Equation, the entire concept relies on nested assumptions. But unlike the Drake Equation, the Great Filter better explains why our planet is dominated by a bunch of great apes rather than super intelligent alien cyborgs.

[edit] External links

  • For a more detailed and challenging read, see Hanson's original work.
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