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29 Jan 09

Drake equation - Wikipedia, the free encyclopedia

  • The Drake equation states that:



    N = R^{\ast} \times f_p \times n_e \times f_{\ell} \times f_i \times f_c \times L \!


    where:



    N is the number of civilizations in our galaxy with which communication might be possible;


    and



    R* is the average rate of star formation in our galaxy

    fp is the fraction of those stars that have planets

    ne is the average number of planets that can potentially support life per star that has planets

    fℓ is the fraction of the above that actually go on to develop life at some point

    fi is the fraction of the above that actually go on to develop intelligent life

    fc is the fraction of civilizations that develop a technology that releases detectable signs of their existence into space

    L is the length of time such civilizations release detectable signals into space.
  • By plugging in apparently "plausible" values for each of the parameters above, the resultant expectant value of N is often (much) greater than 1. This has provided considerable motivation for the SETI movement. However, we have no evidence for extraterrestrial civilizations. This conflict is often called the Fermi paradox, after Enrico Fermi who first asked about our lack of observation of extraterrestrials, and motivates advocates of SETI to continually expand the volume of space in which another civilization could be observed.
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