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SETI::Drake - Estimate the number of interstellar communicating civilizations


  use SETI::Drake;
  $d = SETI::Drake->new(
      R  => $stars,
      fp => $planets,
      ne => $support,
      fl => $life,
      fi => $intelligence,
      fc => $communication,
      L  => $lifespan,
  $n = $d->N;
  printf 'You are ' .
    ($n > $threshold ? 'opt' : 'pess') .
    "imistic: %0.2f\n", $n;


A SETI::Drake object answers the question, "How many detectible, intelligent, interstellar communicating civilizations might be out there, in the galaxy?" by providing a single method, N(), which is a prediction based on the product of seven factors. In other words, this module does nothing more than multiply seven numbers together.

According to NOVA, Drake's values were:

  R  => 5,     # Number of stars formed per year.
  fp => 0.5,   # Fraction of those stars that form planets.
  ne => 2,     # Average number of those planets that can support life.
  fl => 1,     # Fraction of those planets that actually do develop life.
  fi => 0.2,   # Fraction of those planets that then evolve intelligence.
  fc => 1,     # Fraction of those planets that develop interstellar communication.
  L  => 10000, # Average lifetime (in years) of an interstellar communicating civilization.

According to Wikipedia, Drake's values were:

  R  => 10,  # Annual rate of star creation in our galaxy.
  fp => 0.5, # Fraction of those stars which have planets.
  ne => 2,   # Average number of these planets that can potentially support life.
  fl => 1,   # Fraction of the above that develop life.
  fi => 0.1, # Fraction of the above that develop intelligent life.
  fc => 0.1, # Fraction of the above that communicate.
  L  => 10,  # Expected lifetime (in years) of such a civilisation.

On Cosmos, Carl Sagan computes it this way:

  R  => 400_000_000_000,  # Number of stars in the Milky Way.
  fp => 1/4,  # Fraction of stars that have planets.
  ne => 2,    # Worlds suitable for sustaining life per system.
  fl => 1/2,  # Fraction of suitable worlds in which life does arise
  fi => 1/10, # Fraction of worlds where intelligent life evolves.
  fc => 1/10, # Fraction of worlds that produce a technical civilization.
  L  => 1/100_000_000, # Chance that we might destroy ourselves tomorrow.



  my $d = SETI::Drake->new($arguments);

Return a new SETI::Drake instance. If no equation variables are provided, Frank Drake's choices (from his 2004 chalkboard video interview on Nova) are used.


  $N = $d->N;

Return the value of the Drake equation:

  N = R* x fp x ne x fl x fc x L


Use Math::BigRat.

SEE ALSO ^ - Carl Sagan explains it.


Copyright 2004, Gene Boggs, All Rights Reserved

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.



Gene Boggs <>

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