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Chapter 3: Philosophy

Solving the Drake Equation

Dear Dr. SETI:
I read about the Drake Equation, but I find itīs pure guesswork to predict anything specific about the number of existing technological civilizations in our neighbourhood. I guess it is rather a matter of belief, and one guess can be about as good as another even if they ar wildly different. Am I completely wrong about that?

Jan, Denmark

The Doctor Responds:
Not at all, Jan! The importance of the Drake Equation is not in the solving, but rather in the contemplation. It was written not for purposes of quantification at all, but rather as the agenda for the world's first SETI meeting, in Green Bank WV in 1961. It was quite useful for its intended application, which was to summarize all the various factors which scientists must contemplate when considering the question of other life.

It is interesting that when the Equation was first written, the only factor which we had any basis to estimate with reasonable accuracy was the first, the rate of stellar formation. In the four decades since, we have learned something about extra-solar planets, so we can now estimate the second factor. We also have direct evidence as to the existence of two planets in their star's habitable zones, so (though the sample size is small) we can roughly estimate the third factor. At this rate, we should have three more factors nailed down by the middle of the next century! A value for the seventh will probably always elude us.

For the record, I consider the Drake Equation to be a marvelous tool for quantifying our ignorance. But in case you'd like to have a go at solving it, here's a downloadable spreadsheet which will let you plug in your own estimates for each of the seven factors, and see what results from your assumptions.

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