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Still, statistically the probability that there are other thinking beings out there is good. Nobody knows how many stars there are in the Milky Way—estimates range from 100 billion or so to perhaps 400 billion—and the Milky Way is just one of 140 billion or so other galaxies, many of them even larger than ours. In the 1960s, a professor at Cornell named Frank Drake, excited by such whopping numbers, worked out a famous equation designed to calculate the chances of advanced life in the cosmos based on a series of diminishing probabilities.
不過，從統計角度來看，外層空間存在有思想的生物的可能性還是很大。誰也不清楚銀河系里有多少顆恒星--估計有1000億顆到4000億顆--而銀河系只是大約1400億個星系之一，其他許多比我們的銀河系還要大。20世紀60年代，康奈爾大學的一位名叫弗蘭克?德雷克的教授為這么巨大的數字所振奮，根據一系列不斷縮小的可能性，想出了一個著名的方程式，旨在計算宇宙中存在高級生命的可能性。
Under Drake's equation you divide the number of stars in a selected portion of the universe by the number of stars that are likely to have planetary systems; divide that by the number of planetary systems that could theoretically support life; divide that by the number on which life, having arisen, advances to a state of intelligence; and so on. At each such division, the number shrinks colossally—yet even with the most conservative inputs the number of advanced civilizations just in the Milky Way always works out to be somewhere in the millions.
按照德雷克的方程式，你把宇宙某個部分的恒星數除以恒星可能擁有行星系的數；再用那個商除以理論上能夠存在生命的行星系數；再用那個商除以已經出現生命，而且生命提高到了有智力的狀態的行星系數；如此等等。每這樣除一次，那個數字就大大縮小--然而，即使以最保守的輸入，僅在銀河系里，得出的高等文明社會的數字也總是在幾百萬個。
