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"Why ET Hasn't Called," by Michael Shermer. Scientific American, August 2002, page 33.
A formula proposed by astronomer Frank Drake in 1961 involves the multiplication of seven constants to estimate the number of technological civilizations in our galaxy. With the possible exception of one of the constants, the value of each constant -- for example, the fraction of planets with life --is mostly speculation. In his column "Skeptic," Shermer attempts to estimate one of the constants: L, the lifetime of communicating civilizations. He writes that the value of L may be one that we can determine with some accuracy by using data about civilizations on our planet. Using that historical data, Shermer estimates L to be far smaller than other published values and shows that we should expect no more than four technological civilizations in our galaxy. Carl Sagan's estimate was one million.
--- Mike Breen |
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