Fermi paradox

apparent contradiction between the lack of evidence and high probability estimates for the existence of extraterrestrial civilizations

probabilistic argument to estimate the number of alien civilizations in our galaxy

hypothesis that complex extraterrestrial life is a very improbable phenomenon and likely to be extremely rare

hypothesis that alien life has not been discovered because alien civilizations are silent and very cautious

theory regarding lack of alien contact

whatever prevents non-living matter from undergoing abiogenesis and later becoming spacefaring.

idea that any intelligent life is destroyed by aliens

thumb|right|200px|Gamma-ray bursts might have regulated the advent of intelligent life Neocatastrophism is the hypothesis that life-exterminating events such as gamma-ray bursts have acted as a galactic regulation mechanism in the Milky Way upon the emergence of complex life in its habitable zone. It is one of several proposed solutions to the Fermi paradox since it provides a mechanism which would have delayed the advent of intelligent beings in local galaxies near Earth.

British physicist

hypothesized solution to the Fermi paradox that alien civilizations are storing energy and hibernating till the universe cools to make better use of stored energy to do tasks

solution to the Fermi paradox by holding that our astronomical observations represent an illusion

the idea that an absence of detectable Von Neumann probes is contrapositive evidence that no intelligent life exists outside of the Solar System

idea that humanity is the first intelligent life