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 The Copernican Revolution was the paradigm shift from the Ptolemaic model of the heavens, which described the cosmos as having Earth stationary at the center of the universe, to the heliocentric model with the Sun at the center of the Solar Sys ...

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.

Intelligence

Intelligence is, along with the more precise concept of

sapience Wisdom, sapience, or sagacity is the ability to contemplate and act using knowledge, experience, understanding, common sense and insight. Wisdom is associated with attributes such as unbiased judgment, compassion, experiential self-knowledge, ...

, 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 Poul William Anderson (November 25, 1926 – July 31, 2001) was an American fantasy and science fiction author who was active from the 1940s until the 21st century. Anderson wrote also historical novels. His awards include seven Hugo Awards and ...

. Sentience, like

consciousness Consciousness, at its simplest, is sentience and awareness of internal and external existence. However, the lack of definitions has led to millennia of analyses, explanations and debates by philosophers, theologians, linguisticians, and scien ...

, is a concept sometimes mistakenly used to refer to the concept of extraterrestrial sapience and intelligence, since it doesn't 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.

Probability

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. The

Kardashev scale The Kardashev scale ( Russian: Шкала Кардашева, ''Shkala Kardasheva'') is a method of measuring a civilization's level of technological advancement based on the amount of energy it is able to use. The measure was proposed by S ...

is a speculative method of measuring a

civilization A civilization (or civilisation) is any complex society characterized by the development of a state, social stratification, urbanization, and symbolic systems of communication beyond natural spoken language (namely, a writing system). ...

's level of

technological Technology is the application of knowledge to reach practical goals in a specifiable and reproducible way. The word ''technology'' may also mean the product of such an endeavor. The use of technology is widely prevalent in medicine, science, ...

advancement, based on the amount of

energy In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of hea ...

a civilization is able to utilize. The

Drake equation The Drake equation is a probabilistic argument used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way Galaxy. The equation was formulated in 1961 by Frank Drake, not for purposes of quantifying ...

is a probabilistic argument used to estimate the number of active, communicative extraterrestrial civilizations in the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. ...

galaxy.

Search for extraterrestrial intelligence

There has been a search for signals from extraterrestrial intelligence for several decades, with no solid results."The search for ET is a detective story without a body"
by

Nigel Henbest Nigel Henbest (born 1951) is a British astronomer, born in Manchester and educated in Northern Ireland and at Leicester University, where he studied physics, chemistry and astronomy. He did postgraduate research at the University of Cambridge b ...

, New Scientist, March 9, 2013, p. 53. 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." 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. The Wow! signal remains the best candidate for an extraterrestrial radio signal ever detected. On 14 June 2022, astronomers, working with China's Five-hundred-meter Aperture Spherical Telescope, 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. 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.”.

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, 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. However, the absence of any such contact to date means such conjecture is largely speculative.

UFOlogy

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

References

External links

An astrophysicist's view of UFOs
(Adam Frank; ''New York Times''; 30 May 2021) {{Authority control Extraterrestrial life Hypothetical objects