The Fermi paradox (or Fermi’s paradox) is the apparent contradiction between high estimates of the probability of the existence of extra-terrestrial civilization and humanity’s lack of contact with, or evidence for, such civilizations. The basic points of the argument, made by physicists Enrico Fermi and Michael H. Hart, are:
• The Sun is a young star. There are billions of stars in the galaxy that are billions of years older;
• Some of these stars likely have Earth-like planets which, if the Earth is typical, may develop intelligent life;
• Presumably some of these civilizations will develop interstellar travel, as Earth seems likely to do;
• At any practical pace of interstellar travel, the galaxy can be completely colonized in just a few tens of millions of years.
According to this line of thinking, the Earth should have already been colonized, or at least visited. But no convincing evidence of this exists. Furthermore, no confirmed signs of intelligence elsewhere have been spotted, either in our galaxy or the more than 80 billion other galaxies of the observable universe. Hence Fermi’s question “Where is everybody?”.
Other common names for the same phenomenon are Fermi’s question (“Where are they?”), the Fermi Problem, the Great Silence,and silentium universi (Latin for “silence of the universe”).
The Fermi paradox is a conflict between an argument of scale and probability and a lack of evidence. A more complete definition could be stated thus:
The apparent size and age of the universe suggest that many technologically advanced extraterrestrial civilizations ought to exist.However, this hypothesis seems inconsistent with the lack of evidence to support it.