This article is about the absence of evidence for extraterrestrial intelligence. For the type of estimation problem, see
Fermi problem.
A graphical representation of the
Arecibo message—Humanity's first attempt to use radio waves to actively communicate its existence to alien civilizations
The Fermi paradox or Fermi's paradox, named after physicist Enrico Fermi, is the apparent contradiction between the lack of evidence and high probability estimates, e.g., those given by the Drake equation, for the existence of extraterrestrial civilizations.[1] The basic points of the argument, made by physicists Enrico Fermi (1901–1954) and Michael H. Hart (born 1932), are:
- There are billions of stars in the galaxy that are similar to the Sun,[2][3] many of which are billions of years older than Earth.[4][5]
- With high probability, some of these stars will have Earth-like planets,[6][7] and if the Earth is typical, some might develop intelligent life.
- Some of these civilizations might develop interstellar travel, a step the Earth is investigating now.
- Even at the slow pace of currently envisioned interstellar travel, the Milky Way galaxy could be completely traversed in a few million years.[8]
According to this line of reasoning, the Earth should have already been visited by extraterrestrial aliens. In an informal conversation, Fermi noted no convincing evidence of this, leading him to ask, "Where is everybody?"[9][10] There have been many attempts to explain the Fermi paradox,[11][12] primarily suggesting either that intelligent extraterrestrial life is extremely rare, or proposing reasons that such civilizations have not contacted or visited Earth.