The Drake Equation

[kl...@renoir.dec.com]

The following formula, affectionately known as the Drake Equation,
as it was created by Frank Drake (and Carl Sagan) in the 1960s, is set
up thusly:

N = R*fgfpneflfifaL

N - The number of advanced technological civilizations in the
Milky Way Galaxy.

R* - The mean birth rate of stars in the Milky Way Galaxy.

fg - The fraction of stars resembling the Sun which are not
members of binary or multiple star systems.

fp - The fraction of such stars with planetary systems.

ne - The number of Earth-like planets in each system orbiting
within the life-supporting zones of their stars.

fl - The fraction of these planets where life has arisen.

fi - The fraction of life-bearing planets on which life has
developed intelligence.

fa - The fraction of intelligent civilizations which have
developed an advanced technology.

L - The average lifetime of civilizations with advanced
technology.

Needless to say, this formula is comprised mostly of currently
unknown factors; depending on various estimates, there may be as many
as one million or as few as ten advanced civilizations in our galaxy.
This equation also does not take into account intelligent races which
may have developed in environments other than Earth-like worlds and do
not possess and/or use technologies recognizable to humans.

Larry Klaes kl...@wrksys.enet.dec.com
or - ...!decwrl!wrksys.enet.dec.com!klaes
or - klaes%wrksy...@decwrl.enet.dec.com
or - klaes%wrksys.en...@uunet.uu.net

"The Universe, or nothing!" - H. G. Wells

[Larry Wall]

In article <10...@shlump.nac.dec.com> kl...@renoir.dec.com writes:
: Needless to say, this formula is comprised mostly of currently

: unknown factors; depending on various estimates, there may be as many
: as one million or as few as ten advanced civilizations in our galaxy.

^^^

By some estimates there may be as few as one. We have too small a statistical
sample of planets on which life developed to say Anything Whatsoever about
the probability of life developing. Perhaps the probability is 1 in 10^28
and we just got lucky.

By other estimates there may be as few as zero advanced civilizations in
our galaxy... :-)

I suppose a case could even be made that there are -1 advanced civilizations
in our galaxy... :-) :-) :-)

Larry Wall
lw...@jpl-devvax.jpl.nasa.gov