The Fermi paradox or Fermi's paradox, named after Enrico Fermi, is the apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilizations, such as in the Drake equation, and the lack of evidence for such civilizations. The basic points of the argument, made by physicists Enrico Fermi (1901–1954) and Michael H. Hart (born 1932), are:

• The Sun is a typical star, and there are billions of stars in the galaxy, including many billions of years older than Earth.
• With high probability, some of these stars will have Earth-like planets, 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 about a million years.

According to this line of thinking, the Earth should already have been visited by extraterrestrial aliens. In an informal conversation, Fermi noted no convincing evidence of this, nor any signs of alien intelligence anywhere in the observable universe, leading him to ask, "Where is everybody?" There have been many attempts to explain the Fermi paradox, primarily suggesting that intelligent extraterrestrial life does not exist or occurs so rarely or briefly that humans will never make contact with it.