The Fermi paradox is the apparent contradiction between the high probability of the existence of extraterrestrial civilizations and the lack of evidence for, or communication with, such civilizations.
The paradox is based on the assumption that there are billions of stars in the galaxy that are similar to our sun, and that some of these stars should have Earth-like planets orbiting them. With so many potential habitable planets, it seems likely that there should be many other intelligent life forms in the universe, yet we have not observed any evidence of their existence.
Various hypotheses have been proposed to explain the Fermi paradox, including the possibility that intelligent life may be rare, that civilizations may self-destruct, or that they may have advanced technology that we cannot detect. The paradox remains an unsolved mystery in the search for extraterrestrial life.