Extraterrestrial intelligence

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Extraterrestrial intelligence (often abbreviated ETI) refers to hypothetical intelligent extraterrestrial life. No such life exists or has ever existed in the Solar System except for humans on Earth, and its existence on other star systems is still speculative.[1] The question of whether other inhabited worlds might exist has been debated since ancient times.[2] The modern form of the concept emerged when the Copernican Revolution demonstrated that the Earth was a planet revolving around the Sun, and other planets were, conversely, other worlds.[3] The question of whether other inhabited planets or moons exist was a natural consequence of this new understanding. It has become one of the most speculative questions in science and is a central theme of science fiction and popular culture.[4]


Intelligence is, along with the more precise concept of sapience, used to describe extraterrestrial life with similar cognitive abilities as humans. Another interchangeable term is sophoncy, first coined by Karen Anderson and published in the 1966 works by her husband Poul Anderson.

Sentience, like consciousness, is a concept sometimes mistakenly used to refer to the concept of extraterrestrial sapience and intelligence, since it does not exclude forms of life that are non-sapient.

The term extraterrestrial civilization frames a more particular case of extraterrestrial intelligence. It is the possible long-term result of intelligent and specifically sapient extraterrestrial life.


The Copernican principle is generalized to the relativistic concept that humans are not privileged observers of the universe.[5] Many prominent scientists, including Stephen Hawking[6] have proposed that the sheer scale of the universe makes it improbable for intelligent life not to have emerged elsewhere. However, Fermi's Paradox highlights the apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilization and humanity's lack of contact with, or evidence for, such civilizations.[7]

So far, as of 5 June 2023, there is no proof of extraterrestrial life, including intelligent extraterrestrial life.[8]

The Kardashev scale is a speculative method of measuring a civilization's level of technological advancement, based on the amount of energy a civilization is able to utilize.[9]

The Drake equation is a probabilistic argument used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way galaxy.[10]

Search for extraterrestrial intelligence[edit]

There has been a search for signals from extraterrestrial intelligence for several decades, with no solid results.[11] Active SETI (Active Search for Extra-Terrestrial Intelligence) is the attempt to send messages to intelligent extraterrestrial life. Active SETI messages are usually sent in the form of radio signals. Physical messages like that of the Pioneer plaque may also be considered an active SETI message.

Communication with extraterrestrial intelligence (CETI) is a branch of the search for extraterrestrial intelligence that focuses on composing and deciphering messages that could theoretically be understood by another technological civilization. The best-known CETI experiment was the 1974 Arecibo message composed by Frank Drake and Carl Sagan. There are multiple independent organizations and individuals engaged in CETI research.

The U.S. government's position is that "chances of contact with an extraterrestrial intelligence are extremely small, given the distances involved."[12][13] This line of thinking has led some to conclude that first contact will most likely be made with extraterrestrial artificial intelligence, rather than with biological beings.[14][15][16]

The Wow! signal remains the best candidate for an extraterrestrial radio signal ever detected.[17]

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.[18] More recently, on 18 June 2022, Dan Werthimer, chief scientist for several SETI-related projects, reportedly noted, “These signals are from radio interference; they are due to radio pollution from earthlings, not from E.T.”.[19]

Potential cultural impact of extraterrestrial contact[edit]

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.[20] Some theories suggest that an extraterrestrial civilization could be advanced enough to dispense with biology, living instead inside of advanced computers.[20] The medium through which humanity is contacted, be it electromagnetic radiation, direct physical interaction, extraterrestrial artefact, or otherwise, may also influence the results of contact. Incorporating these factors, various systems have been created to assess the implications of extraterrestrial contact.

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. Such meetings have generally led to the destruction of the civilization receiving contact (as opposed to the "contactor", which initiates contact), and therefore destruction of human civilization is a possible outcome.[21] However, the absence of any such contact to date means such conjecture is largely speculative.


The extraterrestrial hypothesis is the idea that some UFOs are vehicles containing or sent by extraterrestrial beings (usually called aliens in this context).[11] As an explanation for UFOs, ETI is sometimes contrasted with EDI (extradimensional intelligence), for example by Allen Hynek.[22]

See also[edit]


  1. ^ Bennett, Jeffrey (2017). Life in the universe. United States: Pearson. p. 3-4. ISBN 0-13-408908-1.
  2. ^ Plurality of Worlds: The Extraterrestrial life Debate from Democritus to Kant, by Steven Dick, Cambridge University Press 1984
  3. ^ The Extraterrestrial Life Debate: 1750-1900, by Michael J. Crowe, Dover Publications, 2011
  4. ^ Are we alone? Peter Spinks. May 21, 2013.
  5. ^ Peacock, John A. (1998). Cosmological Physics. Cambridge University Press. p. 66. ISBN 0-521-42270-1.
  6. ^ Hickman, Leo (25 April 2010). "Stephen Hawking takes a hard line on aliens". The Guardian. Retrieved 24 February 2012.
  7. ^ Krauthammer, Charles (December 29, 2011). "Are we alone in the universe?". The Washington Post. Retrieved January 6, 2015.
  8. ^ Kaufman, Marc (12 October 2022). "Life, Here and Beyond". NASA Astrobiology. Retrieved 3 February 2023. No life beyond Earth has ever been found; there is no evidence that alien life has ever visited our planet. It's all a story.{{cite web}}: CS1 maint: url-status (link)
  9. ^ Kardashev, Nikolai. "On the Inevitability and the Possible Structures of Supercivilizations", The search for extraterrestrial life: Recent developments; Proceedings of the Symposium, Boston, MA, June 18–21, 1984 (A86-38126 17-88). Dordrecht, D. Reidel Publishing Co., 1985, p. 497–504.
  10. ^ Zaun, Harald (1 November 2011). "Es war wie eine 180-Grad-Wende von diesem peinlichen Geheimnis!" [It was like a 180 degree turn from this embarrassing secret]. Telepolis (in German). Heise.
  11. ^ a b "The search for ET is a detective story without a body" by Nigel Henbest, New Scientist, March 9, 2013, p. 53.
  12. ^ Larson, Phil (5 November 2011). "Searching for ET, But No Evidence Yet". White House. Archived from the original on 24 November 2011. Retrieved 2011-11-06.
  13. ^ Atkinson, Nancy (5 November 2011). "No Alien Visits or UFO Coverups, White House Says". UniverseToday. Retrieved 2011-11-06.
  14. ^ Hollingham, Richard. "What if the aliens we are looking for are AI?". www.bbc.com. Retrieved 2020-11-24.
  15. ^ November 2016, Mike Wall 14 (14 November 2016). "Electronic E.T.: Intelligent Aliens Are Likely Machines". Space.com. Retrieved 2020-11-24.
  16. ^ ""Alien Artificial Intelligence is Out There" --And It's Billions of Years Old". The Daily Galaxy. 2019-01-01. Retrieved 2020-11-24.
  17. ^ "Was the Wow! Signal Alien?". Skeptoid. Retrieved 2019-02-06.
  18. ^ Byrd, Deborah (4 June 2022). "Has China's FAST telescope detected alien intelligence?". Earth & Sky. Retrieved 15 June 2022.
  19. ^ Overbye, Dennis (18 June 2022). "A Chinese Telescope Did Not Find an Alien Signal. The Search Continues. China's astronomers have been initiated into the search for extraterrestrial intelligence with the kind of false alarm that others in the field have experienced for decades". The New York Times. Retrieved 19 June 2022.
  20. ^ a b Harrison, A. A. (2011). "Fear, pandemonium, equanimity and delight: Human responses to extra-terrestrial life". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. 369 (1936): 656–668. Bibcode:2011RSPTA.369..656H. doi:10.1098/rsta.2010.0229. PMID 21220289.
  21. ^ Kazan, Casey (1 August 2008). "The Impact of ET Contact: Europe's Scientists Discuss The Future of Humans in Space". Daily Galaxy. Archived from the original on 15 May 2013. Retrieved 21 April 2012.
  22. ^ Fuller, Curtis (1980). Proceedings of the First International UFO Congress. New York: Warner Books. pp. 157–163.

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