Doomsday and Fermi

From: Keith M. Elis (zarathustra_winced@yahoo.com)
Date: Thu Apr 24 2003 - 09:41:22 MDT

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    Here's a thought that must have been raised by someone, but I haven't the
    breadth of experience to know.

    The Doomsday argument concludes, as it must, that the sum total of humans
    who will live is not much larger than the number of humans who have already
    lived. By Bayes' theorem, we must update our beliefs to incorporate the
    statistical likelihood that our civilization's end is in sight. On another
    track, the Fermi paradox suggests that either life is very uncommon in the
    universe, or we are relatively advanced as a technological civilization.

    In short, the two propositions 'life is common in the universe' and 'we are
    a typical civilization' are not compatible. As Fermi asked, if life is
    common, where is it? We must conclude that if life is common, most life is
    not technologically advanced enough to be detectable. If this is true, we
    are atypical.

    One can also approach it from the other direction. If we are a typical
    civilization, then most life in the universe is detectable. As we have not
    yet detected any other life, then we must conclude that detectable life is
    relatively uncommon.

    This is simplified reasoning and not entirely contiguous, but it does relate
    the empirical data of evolution to a Doomsday Counter-Argument. If evolution
    does happen as quickly and easily as it appears to have on this planet, then
    we should assume that this typical in the universe. Thus, life is common in
    the universe. If so, then detectable life is atypical, and we cannot be said
    to be a typical civilization. If it's true we are an atypical civilization
    in any one respect, then otherwise airtight statistical conclusions (such as
    the conclusions of the Doomsday argument) break apart.

    Keith

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