The Fermi paradox (or Fermi's paradox) 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 and Michael H. Hart, are: The Sun is a typical star, and there are billions of stars in the galaxy that are billions of years older. 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 though Fermi saw no convincing evidence of this, nor any signs of alien intelligence anywhere in the observable universe, leading him to ask, ""Where is everybody?""