![]() It was the first systematic search for signals from communicative extraterrestrial civilizations. ![]() Seven months after Cocconi and Morrison published their article, Drake began searching for extraterrestrial intelligence in an experiment called Project Ozma. This calculation arrives at the estimated figure of 100 million worlds where life has been forged by evolution." Only one in a million million has the right combination of chemicals, temperature, water, days and nights to support planetary life as we know it. Two months later, Harvard University astronomy professor Harlow Shapley speculated on the number of inhabited planets in the universe, saying "The universe has 10 million, million, million suns (10 followed by 18 zeros) similar to our own. This is the wavelength of radio emission by neutral hydrogen, the most common element in the universe, and they reasoned that other intelligences might see this as a logical landmark in the radio spectrum. Such messages, they suggested, might be transmitted at a wavelength of 21 cm (1,420.4 MHz). Cocconi and Morrison argued that radio telescopes had become sensitive enough to pick up transmissions that might be broadcast into space by civilizations orbiting other stars. In September 1959, physicists Giuseppe Cocconi and Philip Morrison published an article in the journal Nature with the provocative title "Searching for Interstellar Communications". R ∗ = the average rate of star formation in our Galaxy f p = the fraction of those stars that have planets n e = the average number of planets that can potentially support life per star that has planets f l = the fraction of planets that could support life that actually develop life at some point f i = the fraction of planets with life that actually go on to develop intelligent life (civilizations) f c = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space L = the length of time for which such civilizations release detectable signals into space History which are on the current past light cone) N = the number of civilizations in the Milky Way galaxy with which communication might be possible (i.e. The Drake equation is: N = R ∗ ⋅ f p ⋅ n e ⋅ f l ⋅ f i ⋅ f c ⋅ L It is more properly thought of as an approximation than as a serious attempt to determine a precise number.Ĭriticism related to the Drake equation focuses not on the equation itself, but on the fact that the estimated values for several of its factors are highly conjectural, the combined multiplicative effect being that the uncertainty associated with any derived value is so large that the equation cannot be used to draw firm conclusions. ![]() The equation summarizes the main concepts which scientists must contemplate when considering the question of other radio-communicative life. The equation was formulated in 1961 by Frank Drake, not for purposes of quantifying the number of civilizations, but as a way to stimulate scientific dialogue at the first scientific meeting on the search for extraterrestrial intelligence (SETI). The Drake equation is a probabilistic argument used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way Galaxy.
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