[5] Intelligence is, along with the more precise concept of sapience, used to describe extraterrestrial life with similar cognitive abilities as humans.
[7] Many prominent scientists, including Stephen Hawking[8] have proposed that the sheer scale of the universe makes it improbable for intelligent life not to have emerged elsewhere.
[11] The Drake equation is a probabilistic framework used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way galaxy.
The best-known CETI experiment was the 1974 Arecibo message composed by Frank Drake and Carl Sagan.
The U.S. government's position, in line with that of most relevant experts, is that "chances of contact with an extraterrestrial intelligence are extremely small, given the distances involved.
[19] On 14 June 2022 astronomers working with China's FAST telescope reported the possibility of having detected artificial (presumably alien) signals, but cautions that further studies are required to determine if some kind of natural radio interference may be the source.
[20] On 18 June 2022 Dan Werthimer, chief scientist for several SETI-related projects, reportedly noted that “These signals are from radio interference; they are due to radio pollution from earthlings, not from E.T.”[21] The potential changes from extraterrestrial contact could vary greatly in magnitude and type, based on the extraterrestrial civilization's level of technological advancement, degree of benevolence or malevolence, and level of mutual comprehension between itself and humanity.
The implications of extraterrestrial contact, particularly with a technologically superior civilization, have often been likened to the meeting of two vastly different human cultures on Earth, a historical precedent being the Columbian Exchange.