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Also called the "Equation of Life," the Drake Equation is
named for Dr. Frank Drake, one of the first astronomers to
think seriously about the factors that will influence our
chances of ever contacting other civilizations. Note that we
say contacting instead of visiting , since
the great distances between the stars makes interstellar
travel currently impractical. Our current preferred means of
communication is the sending and receiving of radio signals,
either beamed intentionally into space or "leaked" from
radio and TV broadcasts.
The Drake Equation represents a narrowing-down process,
or a process of elimination. The standards we set get more
and more specific as we narrow our possibilities, kind of
like an internet search or house-hunting in the newspaper
ads. There have been many forms of the equation, but here is
my favorite.
N = R* fp
nE fL fi fc
L
Note how all of the factors are multiplied together, so
if even one of them becomes very small, our chances of
contacting other civilizations becomes very slim. Here are
definitions of each of the factors:
- N -- This is the number of
civilizations in the Galaxy that we can communicate with.
Note how we don't even consider other galaxies, which are
too far away to even communicate with at the speed of
light!
- R* -- This is the rate of
star formation in our Galaxy. The Big Question here: How
many stars can we expect to form in our Galaxy in any
given year?
- fp -- This is the fraction
(number between zero and one) of stars that form their
own planetary systems. The Big Question: What is the
probability that a star will form planets?
- nE -- This is the number of
"Earthlike" planets in any given star's planetary system.
The Big Questions: What makes a planet "Earthlike?" How
many such planets can we expect to find, on average,
around any given star?
- fL -- This is the fraction
(number between zero and one) of "Earthlike" planets on
which life develops. The Big Questions: Given Earthlike
conditions, how likely is it that life will arise? How
easy is it for life to come to be?
- fi -- This is the fraction
(number between zero and one) of planets with life that
develop "intelligent" life. The Big Questions: What do we
mean by intelligence? Is intelligence such an
evolutionary "good deal" that it will arise in at least
one species on a planet?
- fc -- This is the fraction
(number between zero and one) of planets with intelligent
life, where those intelligent creatures develop the
technology to communicate with us. The Big Questions: Can
we reasonably expect an alien civilization to think and
develop the way we have? Will aliens look to the stars,
or look inward instead? How likely is it that alien races
will develop our "style" of technology, or is it more
likely they will go off in a direction we haven't even
dreamed of?
- L -- The "lifetime" of a civilization's "radio
phase," the time period during which that civilization
broadcasts and listens for radio waves from space. The
Big Questions: Are civilizations doomed to destroy
themselves through war, pollution, etc.? Will the dangers
of space (supernovae, meteors) wipe out a civilization
early in its history? Will civilizations quickly develop
better alternatives to using radio waves, as we have
replaced the telegraph with the telephone? Will
civilizations soon lose interest in (and government
funding for) searching the stars?
Multiply all these factors together, and you should get a
good estimate of the number of civilizations in the Galaxy
that we can communicate with. We make the (probably very
good) assumption that these civilizations are evenly
scattered across the Galaxy, and not all bunched up in one
corner. Thus, N would have to have a very large value in
order for a civilization to be even remotely close to us.
All in all, the prospects look grim... For a more
interactive experience, check out the Website for the Search
for Extra-Terrestrial Intelligence at
http://www.seti-inst.edu/drake-eq.html .
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Updated 7/7/06
By James
E. Heath