The Fermi paradox is the apparent conflict between the fact that humans have found no evidence of intelligent extraterrestrial life despite the probablity that it exists, given what we know about the universe. The word paradox means a statement that contains conflicting ideas, in this case something like: Extraterrestrials likely exist and travel through space but we have not seen them.
The probability of intelligent extraterrestrial civilizations is based on the knowledge that there are 400 billion stars in our galaxy, many of which are likely to have planets with conditions that support life as we know it. Because many stars are billions of years older than our solar system, it seems probable that intelligent life would have developed on some of these planets and that those civilizations would be advanced enough to develop technology for interstellar travel. And yet – at least according to conventional sources of information – we have found no evidence of extraterrestrial civilizations.
A corollary to the Fermi paradox is the idea that, since efforts to detect intelligent extraterrestrial civilizations have been futile, we should not devote further resources to this search. Critics of the search have proposed reducing funding for such efforts, such as SETI (Search for Extraterrestrial Intelligence). However, E.T. may be like black swans – thought non-existent until they appear.
The Fermi paradox is named for physicist Enrico Fermi. The concept developed out of a comment Fermi made when he and other scientists were discussing a New Yorker cartoon depicting aliens landing in New York City. Fermi reportedly asked, “Where is everyone?” His comment has been interpreted to mean, “If E.T. exist, why aren’t they here?”