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The Drake Equation

It is conventional practice in the SETI community to parse this imposing number of possible sites for life by application of the Drake Equation. First proposed by Frank Drake in 1961, this simple formula sets out the factors that determine the number of contemporary broadcasting societies in our own galaxy (this latter limitation is mere parochialism. One could easily consider the rest of the universe, but signals from far-away galaxies are clearly more difficult to detect.) The Drake Equation estimates the number of suitable stars, multiplies this by the fraction with habitable planets, then by the fraction of those planets that have developed technologically sophisticated life. The resulting product is then multiplied by the fraction of the galaxy’s lifetime during which such a technologically civilization is active (this incorporates the famous “L” term, which is the lifetime of a technological civilization).

While a reasonable approach, the Drake Equation makes the assumption that “they” are like “us”: evolved upon, and living on (or near) a biologically suitable planet. This is also the assumption made by both Hollywood and by my esteemed opponent.

Contributed by: Dr. Seth Shostak

Cosmic Questions

Are We Alone? Topic Index
The Outlook for Cosmic Company

The Drake Equation

A Rare Intelligence?
The Possibilities of a Signal
Human Dispersion
Living Machines
The Fermi Paradox
Doing the Experiment


Seth Shostak

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