Extraterrestrial intelligence (often abbreviated ETI) refers to hypothetical intelligent extraterrestrial life. The question of whether other inhabited worlds might exist has been debated since ancient times. 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. 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.
The Copernican principle is generalized to the relativistic concept that humans are not privileged observers of the universe. Many prominent scientists, including Stephen Hawking 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.
Search for extraterrestrial intelligence
There has been a search for signals from extraterrestrial intelligence for several decades, with no solid results. 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.
Potential cultural impact of extraterrestrial contact
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. Some theories suggest that an extraterrestrial civilization could be advanced enough to dispense with biology, living instead inside of advanced computers. 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, an 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. 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). As an explanation for UFOs, ETI is sometimes contrasted with EDI (extradimensional intelligence), for example by Allen Hynek.
- Extraterrestrial life
- Extraterrestrials in fiction
- Messaging to Extra-Terrestrial Intelligence (METI or Active SETI)
- Plurality of Worlds: The Extraterrestrial life Debate from Democritus to Kant, by Steven Dick, Cambridge University Press 1984
- The Extraterrestrial Life Debate: 1750-1900, by Michael J. Crowe, Dover Publications, 2011
- Are we alone? Peter Spinks. May 21, 2013.
- Peacock, John A. (1998). Cosmological Physics. Cambridge University Press. p. 66. ISBN 0-521-42270-1.
- Hickman, Leo (25 April 2010). "Stephen Hawking takes a hard line on aliens". The Guardian. Retrieved 24 February 2012.
- Krauthammer, Charles (December 29, 2011). "Are we alone in the universe?". The Washington Post. Retrieved January 6, 2015.
- 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.
- 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.
- "The search for ET is a detective story without a body" by Nigel Henbest, New Scientist, March 9, 2013, p. 53.
- Larson, Phil (5 November 2011). "Searching for ET, But No Evidence Yet". White House. Retrieved 2011-11-06.
- Atkinson, Nancy (5 November 2011). "No Alien Visits or UFO Coverups, White House Says". UniverseToday. Retrieved 2011-11-06.
- 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. Bibcode:2011RSPTA.369..656H. doi:10.1098/rsta.2010.0229. Archived from the original (PDF) on 24 December 2012. Retrieved 5 April 2012.
- Kazan, Casey (1 August 2008). "The Impact of ET Contact: Europe's Scientists Discuss The Future of Humans in Space". Daily Galaxy. Retrieved 21 April 2012.
- Fuller, Curtis (1980). Proceedings of the First International UFO Congress. New York: Warner Books., pp. 157-63.