Extraterrestrial intelligence

Extraterrestrial intelligence (ETI) refers to hypothetical intelligent extraterrestrial life. No such life has ever been verifiably observed to exist.^[1] The question of whether other inhabited worlds might exist has been debated since ancient times.^[2] The modern form of the concept emerged when the Copernican Revolution demonstrated that the Earth was a planet revolving around the Sun, and other planets were, conversely, other worlds.^[3] The question of whether other inhabited planets or moons exist was a natural consequence of this new understanding. It has become one of the most speculative questions in science and is a central theme of science fiction and popular culture.^[4]

An alternative name for it is "Extraterrestrial Technological Instantiations" (ETI). The term was coined to avoid the use of terms such as "civilizations" "species" and "intelligence", as those may prove to be ambiguous and open to interpretation, or simply inapplicable in its local context.^[5]