Re: extraterrestrial life

[Roger Freedman <airboy@PHYSICS.UCSB.EDU>]

Yvon Jean <phys@NTL.SYMPATICO.CA> writes:

> What is the formula for calculating the probability  of Extra-Terrestrial
> life out there?

The formula in question is called the Drake equation (it is originally due
to the astronomer Frank Drake). You'll find an extensive discussion of this
equation in an article by G. Schilling entitled "The Chances of Finding
Aliens: Reevaluating the Drake Equation" in the December 1998 issue of Sky
& Telescope. The Drake equation itself is:

N = R* fp ne fl fi fc L

   N  = the number of technologically advanced civilizations
        in the Galaxy whose messages we might be able to detect
   R* = the rate at which solar-type stars form in the Galaxy
   fp = the fraction of stars that have planets
   ne = the number of planets per solar system suitable for life
   fl = the fraction of those habitable planets on which life actually arises
   fi = the fraction of those life forms that evolve into intelligent species
   fc = the fraction of those species that develop adequate technology
        and then choose to send messages out into space
   L  = the lifetime of that technologically advanced civilization


+++++++++++++++++++++++++++++++++++++++++++++++++++++++

Roger A. Freedman
Department of Physics and College of Creative Studies
University of California, Santa Barbara

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