12. Why We Haven't Heard From "ET."
On page 97 of the book, there is a discussion about communications with extra-terrestrials. In 1961, astronomer Frank Drake devised an equation to estimate the number of advanced civilizations within our galaxy. He estimated there might be 10,000. Michael Shermer, publisher of Skeptic magazine, came up with a plausible reason for why we have been unable to detect any intelligent signal from one of these. It has to do with some of the variables in Drake's equation. The equation is as follows: N = R fp ne fl fi fc L
N is the number of communicating civilizations, R is the rate of formation for appropriate stars, fp is the number of stars with planets, ne is the number of Earth-like planets, fl is the number of planets with life, fi is the number of planets with intelligent life, fc is the number of planets that can communicate, and L is the lifetime of the communicating civilization.
The estimated number of civilizations varies widely among scientists. Carl Sagan estimated there might be as many as one million. If that number were correct, it seems unlikely that we would be unable to detect some kind of intelligent signal. Shermer points out that the huge variations for estimating the value for L (the lifetime of the civilization), is a chief cause for the widely differing estimates for N (the number of civilizations).
Shermer used the known history of the Earth to estimate his own value for L. He catalogued the duration of 60 civilizations, including Sumeria, Mesopotamia, Babylon, Egypt, Greece, Rome, China, Africa, India, Japan, Europe and the Americas. All 60 civilizations endured for a total of 25, 234 years. That would be an average of 420.6 years. Using this value for L in the Drake equation produces only 3.36 potential civilizations in our galaxy. We have to be realistic in realizing that we have only had the communication capability on Earth for a very short time. Even if ancient cultures had devised sophisticated communication devices, they would have to coincide with cultures that could receive their messages. As Shermer points out, history tells us that civilizations may rise and fall in cycles too brief to allow communication across the galaxy. (Scientific American, Aug. 2002, p. 33)
U.S. and European teams have recently (2004) discovered small Earthlike rocky planets orbiting distant stars. Up until now, all observed planets have been gas giants like Jupiter that are not likely to support life. The new discoveries hint that small life-supporting planets might be common. (US Finds Earthlike Planets at Other Stars, by Keary Davidson S.F. Chronicle, Wed. Sept. 1, 2004)