Fermi’s Paradox

The Fermi paradox, named after Italian-American physicist Enrico Fermi, is the apparent contradiction between the lack of evidence for extraterrestrial life and various high estimates for their probability. The following are some of the facts and hypotheses that together serve to highlight the apparent contradiction: • There are billions of stars in the Milky Way similar to the Sun. • With high probability, some of these stars have Earth-like planets in a circumstellar habitable zone. • Many of these stars, and hence their planets, are much older than the Sun. If the Earth is typical, some may have developed intelligent life long ago. • Some of these civilizations may have developed interstellar travel, a step humans are 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.