There Are At Least 36 Intelligent Alien Civilizations In Our Galaxy, Say Scientists
Published today in The Astrophysical Journal, the new paper examines the likely number of Communicating Extra-Terrestrial Intelligent (CETI) civilizations in the Milky Way. It assumes that intelligent life comes to occur on other planets much as it has done on our own planet. A key assumption is that it takes around five billion years for intelligent life to form on other planets, as it does on Earth. Another is that a technological civilization will last at least 100 years—as ours has, thus far. After all, it took 4.5 billion years of evolution before a technological civilization arose on Earth, and was capable of communicating.