There is no reliable or reproducible evidence that
aliens have visited
Earth. No transmissions or evidence of
intelligent extraterrestrial life have
been observed anywhere other than
Earth in the
universe. This runs counter to the knowledge that the universe is filled with a very large number of planets, some of which likely hold the conditions hospitable for life. Life typically expands until it fills all available niches. These contradictory facts form the basis for the
Fermi paradox, of which the firstborn hypothesis is one proposed solution.
Avi Loeb, an astrophysicist and cosmologist, has suggested that Earth may be a very early example of a life-bearing planet and that life-bearing planets may be more likely trillions of years from now. He has put forward the view that the Universe has only recently reached a state in which life becomes possible and this is the reason humanity has not detected extraterrestrial life. ==Relationship to other proposed Fermi paradox solutions ==