The search for extraterrestrial intelligence (SETI) is a collective term for scientific searches for intelligent extraterrestrial life, for example, monitoring

electromagnetic radiation In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visible) li ...

for signs of transmissions from

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 on other planets. Scientific investigation began shortly after the advent of

radio Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmi ...

in the early 1900s, and focused international efforts have been ongoing since the 1980s. In 2015, Stephen Hawking and Israeli billionaire

Yuri Milner Yuri Borisovich (Bentsionovich) Milner (russian: Юрий Борисович (Бенционович) Мильнер; born 11 November 1961) is a Soviet-born Israeli entrepreneur, venture capitalist and physicist. He is a cofounder and former c ...

announced a project called

Breakthrough Listen Breakthrough Listen is a project to search for intelligent extraterrestrial communications in the Universe. With $100 million in funding and thousands of hours of dedicated telescope time on state-of-the-art facilities, it is the most comprehensi ...

History

Early work

There have been many earlier searches for extraterrestrial intelligence within the

Solar System The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...

. In 1896,

Nikola Tesla Nikola Tesla ( ; ,"Tesla"
''

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...

. In 1899, while conducting experiments at his Colorado Springs experimental station, he thought he had detected a signal from Mars since an odd repetitive static signal seemed to cut off when Mars set in the night sky. Analysis of Tesla's research has led to a range of explanations including: Tesla simply misunderstood the new technology he was working with, that he may have been observing signals from Marconi's European

experiments, and even speculation that he could have picked up naturally occurring radio noise caused by a moon of

Jupiter Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but slightly less than one-thousandth t ...

( Io) moving through the

magnetosphere of Jupiter The magnetosphere of Jupiter is the cavity created in the solar wind by the planet's magnetic field. Extending up to seven million kilometers in the Sun's direction and almost to the orbit of Saturn in the opposite direction, Jupiter's magnetosp ...

. In the early 1900s, Guglielmo Marconi,

Lord Kelvin William Thomson, 1st Baron Kelvin, (26 June 182417 December 1907) was a British mathematician, mathematical physicist and engineer born in Belfast. Professor of Natural Philosophy at the University of Glasgow for 53 years, he did important ...

and

David Peck Todd David Peck Todd (March 19, 1855 — June 1, 1939) was an American astronomer. He produced a complete set of photographs of the 1882 transit of Venus. Biography Todd was born in Lake Ridge, New York, the son of Sereno Edwards Todd and Rhoda (Pec ...

also stated their belief that radio could be used to contact

Martian Mars, the fourth planet from the Sun, has appeared as a setting in works of fiction since at least the mid-1600s. It became the most popular celestial object in fiction in the late 1800s as the Moon was evidently lifeless. At the time, the pr ...

s, with Marconi stating that his stations had also picked up potential Martian signals. On August 21–23, 1924, Mars entered an

opposition Opposition may refer to: Arts and media * ''Opposition'' (Altars EP), 2011 EP by Christian metalcore band Altars * The Opposition (band), a London post-punk band * '' The Opposition with Jordan Klepper'', a late-night television series on Com ...

closer to Earth than at any time in the century before or the next 80 years. In the United States, a "National Radio Silence Day" was promoted during a 36-hour period from August 21–23, with all radios quiet for five minutes on the hour, every hour. At the

United States Naval Observatory United States Naval Observatory (USNO) is a scientific and military facility that produces geopositioning, navigation and timekeeping data for the United States Navy and the United States Department of Defense. Established in 1830 as the Depo ...

, a radio receiver was lifted above the ground in a dirigible tuned to a

wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, t ...

between 8 and 9 km, using a "radio-camera" developed by Amherst College and Charles Francis Jenkins. The program was led by David Peck Todd with the military assistance of Admiral Edward W. Eberle ( Chief of Naval Operations), with

William F. Friedman William Frederick Friedman (September 24, 1891 – November 12, 1969) was a US Army cryptographer who ran the research division of the Army's Signal Intelligence Service (SIS) in the 1930s, and parts of its follow-on services into the 1950s. ...

(chief

cryptographer Cryptography, or cryptology (from grc, , translit=kryptós "hidden, secret"; and ''graphein'', "to write", or ''-logia'', "study", respectively), is the practice and study of techniques for secure communication in the presence of adver ...

of the United States Army), assigned to translate any potential Martian messages. A 1959 paper by

Philip Morrison Philip Morrison (November 7, 1915 – April 22, 2005) was a professor of physics at the Massachusetts Institute of Technology (MIT). He is known for his work on the Manhattan Project during World War II, and for his later work in quantum physi ...

and Giuseppe Cocconi first pointed out the possibility of searching the

microwave Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ra ...

spectrum. It proposed frequencies and a set of initial targets. In 1960,

Cornell University Cornell University is a private statutory land-grant research university based in Ithaca, New York. It is a member of the Ivy League. Founded in 1865 by Ezra Cornell and Andrew Dickson White, Cornell was founded with the intention to tea ...

astronomer

Frank Drake Frank Donald Drake (May 28, 1930 – September 2, 2022) was an American astrophysicist and astrobiologist. He began his career as a radio astronomer, studying the planets of the Solar System and later pulsars. Drake expanded his interests ...

performed the first modern SETI experiment, named "

Project Ozma Project Ozma was a search for extraterrestrial intelligence (SETI) experiment started in 1960 by Cornell University astronomer Frank Drake, at the National Radio Astronomy Observatory, Green Bank at Green Bank, West Virginia. The object of the e ...

" after the Queen of Oz in L. Frank Baum's fantasy books. Drake used a radio telescope in diameter at

Green Bank, West Virginia Green Bank is a census-designated place in Pocahontas County in West Virginia's Potomac Highlands inside the Allegheny Mountain Range. Green Bank is located along WV 28. Green Bank is home to the Green Bank Observatory and is also close to the ...

, to examine the stars

Tau Ceti Tau Ceti, Latinized from τ Ceti, is a single star in the constellation Cetus that is spectrally similar to the Sun, although it has only about 78% of the Sun's mass. At a distance of just under from the Solar System, it is a rela ...

and

Epsilon Eridani Epsilon Eridani ( Latinized from ε Eridani), formally named Ran, is a star in the southern constellation of Eridanus, at a declination of 9.46° south of the celestial equator. This allows it to be visible from most of Earth's surf ...

near the 1.420

gigahertz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that one he ...

marker frequency, a region of the radio spectrum dubbed the " water hole" due to its proximity to the

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...

and

hydroxyl radical The hydroxyl radical is the diatomic molecule . The hydroxyl radical is very stable as a dilute gas, but it decays very rapidly in the condensed phase. It is pervasive in some situations. Most notably the hydroxyl radicals are produced from the ...

spectral lines. A 400 kilohertz band around the marker frequency was scanned using a single-channel receiver with a bandwidth of 100 hertz. He found nothing of interest.

Soviet The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen nation ...

scientists took a strong interest in SETI during the 1960s and performed a number of searches with

omnidirectional antenna In radio communication, an omnidirectional antenna is a class of antenna which radiates equal radio power in all directions perpendicular to an axis (azimuthal directions), with power varying with angle to the axis ( elevation angle), declining ...

s in the hope of picking up powerful radio signals. Soviet astronomer

Iosif Shklovsky Iosif Samuilovich Shklovsky (russian: Ио́сиф Самуи́лович Шкло́вский; sometimes transliterated ''Josif, Josif, Shklovskii, Shklovskij'') (1 July 1916 – 3 March 1985) was a Soviet astronomer and astrophysicist. He ...

wrote the pioneering book in the field, ''Universe, Life, Intelligence'' (1962), which was expanded upon by American astronomer Carl Sagan as the best-selling book ''Intelligent Life in the Universe'' (1966). Wow signal

In the March 1955 issue of ''

Scientific American ''Scientific American'', informally abbreviated ''SciAm'' or sometimes ''SA'', is an American popular science magazine. Many famous scientists, including Albert Einstein and Nikola Tesla, have contributed articles to it. In print since 1845, it ...

'', John D. Kraus described an idea to scan the

cosmos The cosmos (, ) is another name for the Universe. Using the word ''cosmos'' implies viewing the universe as a complex and orderly system or entity. The cosmos, and understandings of the reasons for its existence and significance, are studied in ...

for natural radio signals using a flat-plane radio telescope equipped with a parabolic reflector. Within two years, his concept was approved for construction by

Ohio State University The Ohio State University, commonly called Ohio State or OSU, is a public land-grant research university in Columbus, Ohio. A member of the University System of Ohio, it has been ranked by major institutional rankings among the best publ ...

. With a total of US$71,000 () in grants from the

National Science Foundation The National Science Foundation (NSF) is an independent agency of the United States government that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National ...

, construction began on an plot in

Delaware, Ohio Delaware is a city in and the county seat of Delaware County, Ohio, United States. Delaware was founded in 1808 and was incorporated in 1816. It is located near the center of Ohio, is about north of Columbus, and is part of the Columbus, Ohio ...

. This Ohio State University Radio Observatory telescope was called "Big Ear". Later, it began the world's first continuous SETI program, called the Ohio State University SETI program. In 1971,

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the US federal government responsible for the civil List of government space agencies, space program ...

funded a SETI study that involved Drake,

Barney Oliver Bernard M. Oliver (May 17, 1916 – November 23, 1995), also known as Barney Oliver, was a scientist who made contributions in many fields, including radar, television, and computers. He was the founder and director of Hewlett Packard ( HP) ...

of Hewlett-Packard laboratories, and others. The resulting report proposed the construction of an Earth-based radio telescope array with 1,500 dishes known as "

Project Cyclops Project Cyclops is a 1971 NASA project that investigated how SETI should be conducted. As a NASA product the report is in the public domain. The project team created a design for coordinating large numbers of radio telescopes to search for Earth ...

". The price tag for the Cyclops array was US$10 billion. Cyclops was not built, but the report formed the basis of much SETI work that followed. The Ohio State SETI program gained fame on August 15, 1977, when Jerry Ehman, a project volunteer, witnessed a startlingly strong signal received by the telescope. He quickly circled the indication on a printout and scribbled the exclamation "Wow!" in the margin. Dubbed the ''

Wow! signal The Wow! signal was a strong narrowband radio signal detected on August 15, 1977, by Ohio State University's Big Ear radio telescope in the United States, then used to support the search for extraterrestrial intelligence. The signal appeared ...

'', it is considered by some to be the best candidate for a radio signal from an artificial, extraterrestrial source ever discovered, but it has not been detected again in several additional searches.

Sentinel, META, and BETA

In 1980, Carl Sagan, Bruce Murray, and Louis Friedman founded the U.S.

Planetary Society The Planetary Society is an American internationally-active non-governmental nonprofit organization. It is involved in research, public outreach, and political space advocacy for engineering projects related to astronomy, planetary science, a ...

, partly as a vehicle for SETI studies. In the early 1980s,

Harvard University Harvard University is a private Ivy League research university in Cambridge, Massachusetts. Founded in 1636 as Harvard College and named for its first benefactor, the Puritan clergyman John Harvard, it is the oldest institution of high ...

physicist Paul Horowitz took the next step and proposed the design of a

spectrum analyzer A spectrum analyzer measures the magnitude of an input signal versus frequency within the full frequency range of the instrument. The primary use is to measure the power of the spectrum of known and unknown signals. The input signal that most co ...

specifically intended to search for SETI transmissions. Traditional desktop spectrum analyzers were of little use for this job, as they sampled frequencies using banks of analog filters and so were restricted in the number of channels they could acquire. However, modern integrated-circuit digital signal processing (DSP) technology could be used to build autocorrelation receivers to check far more channels. This work led in 1981 to a portable spectrum analyzer named "Suitcase SETI" that had a capacity of 131,000 narrow band channels. After field tests that lasted into 1982, Suitcase SETI was put into use in 1983 with the Harvard/Smithsonian radio telescope at Oak Ridge Observatory in

Harvard, Massachusetts Harvard is a town in Worcester County, Massachusetts, United States. The town is located 25 miles west-northwest of Boston, in eastern Massachusetts. A farming community settled in 1658 and incorporated in 1732, it has been home to several ...

. This project was named "Sentinel" and continued into 1985. Even 131,000 channels were not enough to search the sky in detail at a fast rate, so Suitcase SETI was followed in 1985 by Project "META", for "Megachannel Extra-Terrestrial Assay". The META spectrum analyzer had a capacity of 8.4 million channels and a channel resolution of 0.05 hertz. An important feature of META was its use of frequency Doppler shift to distinguish between signals of terrestrial and extraterrestrial origin. The project was led by Horowitz with the help of the Planetary Society, and was partly funded by movie maker Steven Spielberg. A second such effort, META II, was begun in

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

in 1990, to search the southern sky. META II is still in operation, after an equipment upgrade in 1996. The follow-on to META was named "BETA", for "Billion-channel Extraterrestrial Assay", and it commenced observation on October 30, 1995. The heart of BETA's processing capability consisted of 63 dedicated fast Fourier transform (FFT) engines, each capable of performing a 2²²-point

complex Complex commonly refers to: * Complexity, the behaviour of a system whose components interact in multiple ways so possible interactions are difficult to describe ** Complex system, a system composed of many components which may interact with each ...

FFTs in two seconds, and 21 general-purpose

personal computers A personal computer (PC) is a multi-purpose microcomputer whose size, capabilities, and price make it feasible for individual use. Personal computers are intended to be operated directly by an end user, rather than by a computer expert or tec ...

equipped with custom digital signal processing boards. This allowed BETA to receive 250 million simultaneous channels with a resolution of 0.5 hertz per channel. It scanned through the microwave

spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors ...

from 1.400 to 1.720 gigahertz in eight hops, with two seconds of observation per hop. An important capability of the BETA search was rapid and automatic re-observation of candidate signals, achieved by observing the sky with two adjacent beams, one slightly to the east and the other slightly to the west. A successful candidate signal would first transit the east beam, and then the west beam and do so with a speed consistent with

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

's sidereal rotation rate. A third receiver observed the horizon to veto signals of obvious terrestrial origin. On March 23, 1999, the 26-meter radio telescope on which Sentinel, META and BETA were based was blown over by strong winds and seriously damaged. This forced the BETA project to cease operation.

MOP and Project Phoenix

In 1978, the NASA SETI program had been heavily criticized by Senator

William Proxmire Edward William Proxmire (November 11, 1915 – December 15, 2005) was an American politician. A member of the Democratic Party, he served as a United States Senator from Wisconsin from 1957 to 1989. He holds the record for being the longest-serv ...

, and funding for SETI research was removed from the NASA budget by Congress in 1981; however, funding was restored in 1982, after Carl Sagan talked with Proxmire and convinced him of the program's value. In 1992, the U.S. government funded an operational SETI program, in the form of the NASA Microwave Observing Program (MOP). MOP was planned as a long-term effort to conduct a general survey of the sky and also carry out targeted searches of 800 specific nearby stars. MOP was to be performed by radio antennas associated with the

NASA Deep Space Network The NASA Deep Space Network (DSN) is a worldwide network of American spacecraft communication ground segment facilities, located in the United States (California), Spain (Madrid), and Australia (Canberra), that supports NASA's interplanetary ...

, as well as the radio telescope of the National Radio Astronomy Observatory at Green Bank, West Virginia and the radio telescope at the Arecibo Observatory in Puerto Rico. The signals were to be analyzed by spectrum analyzers, each with a capacity of 15 million channels. These spectrum analyzers could be grouped together to obtain greater capacity. Those used in the targeted search had a bandwidth of 1 hertz per channel, while those used in the sky survey had a bandwidth of 30 hertz per channel. Arecibo Observatory Aerial View

MOP drew the attention of the

United States Congress The United States Congress is the legislature of the federal government of the United States. It is bicameral, composed of a lower body, the House of Representatives, and an upper body, the Senate. It meets in the U.S. Capitol in Washing ...

, where the program was ridiculed and canceled one year after its start. SETI advocates continued without government funding, and in 1995 the nonprofit

SETI Institute The SETI Institute is a not-for-profit research organization incorporated in 1984 whose mission is to explore, understand, and explain the origin and nature of life in the universe, and to use this knowledge to inspire and guide present and futu ...

Mountain View, California Mountain View is a city in Santa Clara County, California, United States. Named for its views of the Santa Cruz Mountains, it has a population of 82,376. Mountain View was integral to the early history and growth of Silicon Valley, and is the ...

resurrected the MOP program under the name of Project "Phoenix", backed by private sources of funding. Project Phoenix, under the direction of Jill Tarter, is a continuation of the targeted search program from MOP and studies roughly 1,000 nearby

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

-like stars. From 1995 through March 2004, Phoenix conducted observations at the Parkes radio telescope in Australia, the radio telescope of the National Radio Astronomy Observatory in Green Bank, West Virginia, and the radio telescope at the Arecibo Observatory in Puerto Rico. The project observed the equivalent of 800 stars over the available channels in the frequency range from 1200 to 3000 MHz. The search was sensitive enough to pick up transmitters with 1 GW

EIRP Effective radiated power (ERP), synonymous with equivalent radiated power, is an IEEE standardized definition of directional radio frequency (RF) power, such as that emitted by a radio transmitter. It is the total power in watts that would hav ...

to a distance of about 200 light-years. According to Prof. Tarter, in 2012 it costs around "$2 million per year to keep SETI research going at the SETI Institute" and approximately 10 times that to support "all kinds of SETI activity around the world".

Ongoing radio searches

Many radio frequencies penetrate Earth's atmosphere quite well, and this led to radio telescopes that investigate the cosmos using large radio antennas. Furthermore, human endeavors emit considerable electromagnetic radiation as a byproduct of communications such as television and radio. These signals would be easy to recognize as artificial due to their repetitive nature and narrow bandwidths. Earth has been sending radio waves from broadcasts into space for over 100 years. These signals have reached over 1,000 stars. Most Notably:

Vega Vega is the brightest star in the northern constellation of Lyra. It has the Bayer designation α Lyrae, which is Latinised to Alpha Lyrae and abbreviated Alpha Lyr or α Lyr. This star is relatively close at only from the Sun, a ...

Aldebaran Aldebaran (Arabic: “The Follower”, "الدبران") is the brightest star in the zodiac constellation of Taurus. It has the Bayer designation α Tauri, which is Latinized to Alpha Tauri and abbreviated Alpha Tau or α Tau. Alde ...

Barnard's Star Barnard's Star is a red dwarf about six light-years from Earth in the constellation of Ophiuchus. It is the fourth-nearest-known individual star to the Sun after the three components of the Alpha Centauri system, and the closest star in t ...

Sirius Sirius is the brightest star in the night sky. Its name is derived from the Greek word , or , meaning 'glowing' or 'scorching'. The star is designated α Canis Majoris, Latinized to Alpha Canis Majoris, and abbreviated Alpha CM ...

, and Proxima Centauri. Which are all in the Local Group of Stars near ours. If Alien Life exists on any orbiting planet of these nearby stars, these signals can be deciphered and heard; Even though some of the signal is garbled by the Earth's Ionosphere. (e.g., a broadcast from 1920 would have reached all of them.) Many international radio telescopes are currently being used for radio SETI searches, including the Low Frequency Array (LOFAR) in Europe, the

Murchison Widefield Array The Murchison Widefield Array (MWA) is a joint project between an international consortium of organisations to construct and operate a low-frequency radio array. 'Widefield' refers to its very large field of view (on the order of 30 degrees ac ...

(MWA) in Australia, and the

Lovell Telescope The Lovell Telescope is a radio telescope at Jodrell Bank Observatory, near Goostrey, Cheshire in the north-west of England. When construction was finished in 1957, the telescope was the largest steerable dish radio telescope in the world at ...

in the United Kingdom.

Allen Telescope Array

The SETI Institute collaborated with the

Radio Astronomy Laboratory The Radio Astronomy Lab (RAL) is an Organized Research Unit (ORU) within the Astronomy Department at the University of California, Berkeley. It was founded by faculty member Harold Weaver in 1958. Until 2012, RAL maintained a radio astronomy observ ...

at the Berkeley SETI Research Center to develop a specialized radio telescope array for SETI studies, something like a mini-cyclops array. Formerly known as the One Hectare Telescope (1HT), the concept was renamed the "Allen Telescope Array" (ATA) after the project's benefactor

Paul Allen Paul Gardner Allen (January 21, 1953 – October 15, 2018) was an American business magnate, computer programmer, researcher, investor, and philanthropist. He co-founded Microsoft Corporation with childhood friend Bill Gates in 1975, which ...

. Its sensitivity would be equivalent to a single large dish more than 100 meters in diameter if completed. Presently, the array under construction has 42 dishes at the Hat Creek Radio Observatory in rural northern California. The full array (ATA-350) is planned to consist of 350 or more offset- Gregorian radio dishes, each in diameter. These dishes are the largest producible with commercially available satellite television dish technology. The ATA was planned for a 2007 completion date, at a cost of US$25 million. The SETI Institute provided money for building the ATA while University of California, Berkeley designed the telescope and provided operational funding. The first portion of the array (ATA-42) became operational in October 2007 with 42 antennas. The DSP system planned for ATA-350 is extremely ambitious. Completion of the full 350 element array will depend on funding and the technical results from ATA-42. ATA-42 (ATA) is designed to allow multiple observers simultaneous access to the interferometer output at the same time. Typically, the ATA snapshot imager (used for astronomical surveys and SETI) is run in parallel with a

beamforming Beamforming or spatial filtering is a signal processing technique used in sensor arrays for directional signal transmission or reception. This is achieved by combining elements in an antenna array in such a way that signals at particular angles e ...

system (used primarily for SETI). ATA also supports observations in multiple synthesized pencil beams at once, through a technique known as "multibeaming". Multibeaming provides an effective filter for identifying false positives in SETI, since a very distant transmitter must appear at only one point on the sky. SETI Institute's Center for SETI Research (CSR) uses ATA in the search for extraterrestrial intelligence, observing 12 hours a day, 7 days a week. From 2007 to 2015, ATA has identified hundreds of millions of technological signals. So far, all these signals have been assigned the status of noise or radio frequency interference because a) they appear to be generated by satellites or Earth-based transmitters, or b) they disappeared before the threshold time limit of ~1 hour. Researchers in CSR are presently working on ways to reduce the threshold time limit, and to expand ATA's capabilities for detection of signals that may have embedded messages. Berkeley astronomers used the ATA to pursue several science topics, some of which might have turned up transient SETI signals, until 2011, when the collaboration between the University of California, Berkeley and the SETI Institute was terminated. CNET published an article and pictures about the Allen Telescope Array (ATA) on December 12, 2008. In April 2011, the ATA was forced to enter an 8-month "hibernation" due to funding shortfalls. Regular operation of the ATA was resumed on December 5, 2011. In 2012, new life was breathed into the ATA thanks to a $3.6M philanthropic donation by Franklin Antonio, co-founder and Chief Scientist of QUALCOMM Incorporated. This gift supports upgrades of all the receivers on the ATA dishes to have dramatically (2x - 10x from 1–8 GHz) greater sensitivity than before and supporting sensitive observations over a wider frequency range from 1–18 GHz, though initially the radio frequency electronics go to only 12 GHz. As of July, 2013 the first of these receivers was installed and proven. Full installation on all 42 antennas is expected in June, 2014. ATA is especially well suited to the search for extraterrestrial intelligence SETI and to discovery of

astronomical radio source An astronomical radio source is an object in outer space that emits strong radio waves. Radio emission comes from a wide variety of sources. Such objects are among the most extreme and energetic physical processes in the universe. History In 1932, ...

s, such as heretofore unexplained non-repeating, possibly extragalactic, pulses known as

fast radio burst In radio astronomy, a fast radio burst (FRB) is a transient radio pulse of length ranging from a fraction of a millisecond to 3 seconds, caused by some high-energy astrophysical process not yet understood. Astronomers estimate the average FRB rel ...

s or FRBs.

SERENDIP

SERENDIP (Search for Extraterrestrial Radio Emissions from Nearby Developed Intelligent Populations) is a SETI program launched in 1979 by the Berkeley SETI Research Center. SERENDIP takes advantage of ongoing "mainstream" radio telescope observations as a " piggy-back" or "

commensal Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit fro ...

" program, using large radio telescopes including the NRAO 90m telescope at Green Bank and the Arecibo 305m telescope. Rather than having its own observation program, SERENDIP analyzes deep space radio telescope data that it obtains while other

astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets and galaxies – in either ...

s are using the telescopes. The most recently deployed SERENDIP spectrometer, SERENDIP V.v, was installed at the Arecibo Telescope in June 2009. The digital back-end instrument was an FPGA-based 128 million-channel digital spectrometer covering 200 MHz of bandwidth. It took data commensally with the seven-beam Arecibo L-band Feed Array (ALFA). The program found around 400 suspicious signals, but there is not enough data to prove that they belong to

extraterrestrial intelligence 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 ...

Breakthrough Listen

''Breakthrough Listen'' is a ten-year initiative with $100 million funding begun in July 2015 to actively search for intelligent extraterrestrial communications in the

universe The universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development of the universe. ...

, in a substantially expanded way, using resources that had not previously been extensively used for the purpose. It has been described as the most comprehensive search for alien communications to date. The science program for Breakthrough Listen is based at Berkeley SETI Research Center, located in the Astronomy Department at the

University of California, Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public land-grant research university in Berkeley, California. Established in 1868 as the University of California, it is the state's first land-grant u ...

. Announced in July 2015, the project is observing for thousands of hours every year on two major radio telescopes, the

Green Bank Observatory The Green Bank Observatory (previously National Radio Astronomy Observatory, Green Bank) is an astronomical observatory located in the National Radio Quiet Zone in Green Bank, West Virginia, U.S. It is the operator of the Robert C. Byrd Green Ba ...

in West Virginia, and the

Parkes Observatory Parkes Observatory is a radio astronomy observatory, located north of the town of Parkes, New South Wales, Australia. It hosts Murriyang, the 64 m CSIRO Parkes Radio Telescope also known as "The Dish", along with two smaller radio telescopes. ...

in Australia. Previously, only about 24 to 36 hours of telescope per year were used in the search for alien life. Furthermore, the Automated Planet Finder at Lick Observatory is searching for optical signals coming from laser transmissions. The massive data rates from the radio telescopes (24 GB/s at Green Bank) necessitated the construction of dedicated hardware at the telescopes to perform the bulk of the analysis. Some of the data are also analyzed by volunteers in the SETI@home volunteer computing network. Founder of modern SETI

was one of the scientists on the project's advisory committee. In October 2019, Breakthrough Listen started a collaboration with scientists from the TESS team ( Transiting Exoplanet Survey Satellite) to look for signs of advanced extraterrestrial life. Thousands of new planets found by TESS will be scanned for

technosignature Technosignature or technomarker is any measurable property or effect that provides scientific evidence of past or present technology. Technosignatures are analogous to biosignatures, which signal the presence of life, whether intelligent or not. ...

s by Breakthrough Listen partner facilities across the globe. Data from TESS monitoring of stars will also be searched for anomalies.

FAST

China's 500 meter Aperture Spherical Telescope (FAST) lists ''detecting interstellar communication signals'' as part of its science mission. It is funded by the

National Development and Reform Commission The National Development and Reform Commission of the People's Republic of China (NDRC), formerly State Planning Commission and State Development Planning Commission, is a macroeconomic management agency under the State Council, which has b ...

(NDRC) and managed by the National Astronomical observatories (NAOC) of the Chinese Academy of Sciences (CAS). FAST is the first radio observatory built with SETI as a core scientific goal. FAST consists of a fixed diameter spherical dish constructed in a natural depression sinkhole caused by karst processes in the region. It is the world's largest filled-aperture radio telescope. According to its website, FAST could search out to 28 light-years, and would be able to reach 1400 stars. If the transmitter's radiated power is increased to 1000,000 MW, FAST would be able to reach one million stars. This is compared to the Arecibo 305 meter telescope detection distance of 18 light-years. 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. More recently, on 18 June 2022, Dan Werthimer, chief scientist for several

SETI The search for extraterrestrial intelligence (SETI) is a collective term for scientific searches for intelligent extraterrestrial life, for example, monitoring electromagnetic radiation for signs of transmissions from civilizations on other pl ...

-related projects, reportedly noted, “These signals are from radio interference; they are due to radio pollution from earthlings, not from E.T.”.

UCLA

Since 2016, UCLA undergraduate and graduate students have been participating in radio searches for technosignatures with the

Green Bank Telescope The Robert C. Byrd Green Bank Telescope (GBT) in Green Bank, West Virginia, US is the world's largest fully steerable radio telescope, surpassing the Effelsberg 100-m Radio Telescope in Germany. The Green Bank site was part of the National Radi ...

. Targets include the

Kepler Johannes Kepler (; ; 27 December 1571 – 15 November 1630) was a German astronomer, mathematician, astrologer, natural philosopher and writer on music. He is a key figure in the 17th-century Scientific Revolution, best known for his laws o ...

field, TRAPPIST-1, and solar-type stars. The search is sensitive to Arecibo-class transmitters located within 420 ly of Earth and to transmitters that are 1000 times more powerful than Arecibo located within 13,000 ly of Earth.

Community SETI projects

SETI@home

The SETI@home project uses

volunteer computing Volunteer computing is a type of distributed computing in which people donate their computers' unused resources to a research-oriented project, and sometimes in exchange for credit points. The fundamental idea behind it is that a modern desktop co ...

to analyze signals acquired by the SERENDIP project. SETI@home was conceived by David Gedye along with Craig Kasnoff and is a popular volunteer

project that was launched by the Berkeley SETI Research Center at the

, in May 1999. It was originally funded by

The Planetary Society The Planetary Society is an American internationally-active non-governmental nonprofit organization. It is involved in research, public outreach, and political space advocacy for engineering projects related to astronomy, planetary science, a ...

and Paramount Pictures, and later by the state of

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...

. The project is run by director David P. Anderson and chief scientist Dan Werthimer. Any individual can become involved with SETI research by downloading the

Berkeley Open Infrastructure for Network Computing The Berkeley Open Infrastructure for Network Computing (BOINC, pronounced – rhymes with "oink") is an open-source middleware system for volunteer computing (a type of distributed computing). Developed originally to support SETI@home, it beca ...

(BOINC) software program, attaching to the SETI@home project, and allowing the program to run as a background process that uses idle computer power. The SETI@home program itself runs signal analysis on a "work unit" of data recorded from the central 2.5 MHz wide band of the SERENDIP IV instrument. After computation on the work unit is complete, the results are then automatically reported back to SETI@home servers at University of California, Berkeley. By June 28, 2009, the SETI@home project had over 180,000 active participants volunteering a total of over 290,000 computers. These computers give SETI@home an average computational power of 617 teraFLOPS. In 2004

radio source SHGb02+14a SHGb02+14a is an astronomical radio source and a candidate in the Search for Extra-Terrestrial Intelligence (SETI), discovered in March 2003 by SETI@home and announced in ''New Scientist'' on September 1, 2004. Observation The source was origina ...

set off speculation in the media that a signal had been detected but researchers noted the frequency drifted rapidly and the detection on three SETI@home computers fell within random chance. As of 2010, after 10 years of data collection, SETI@home has listened to that one frequency at every point of over 67 percent of the sky observable from Arecibo with at least three scans (out of the goal of nine scans), which covers about 20 percent of the full celestial sphere. On March 31, 2020, the project stopped sending out new work to SETI@home users, bringing this particular SETI effort to an indefinite hiatus.

SETI Net

SETI Network is the only operational private search system. The SETI Net station consists of off-the-shelf, consumer-grade electronics to minimize cost and to allow this design to be replicated as simply as possible. It has a 3-meter parabolic antenna that can be directed in azimuth and elevation, an LNA that covers the 1420 MHz spectrum, a receiver to reproduce the wideband audio, and a standard

personal computer A personal computer (PC) is a multi-purpose microcomputer whose size, capabilities, and price make it feasible for individual use. Personal computers are intended to be operated directly by an end user, rather than by a computer expert or tec ...

as the control device and for deploying the detection algorithms. The antenna can be pointed and locked to one sky location, enabling the system to integrate on it for long periods. Currently the

area is being monitored when it is above the horizon. All search data are collected and made available on the Internet archive. SETI Net started operation in the early 1980s as a way to learn about the science of the search, and has developed several software packages for the amateur SETI community. It has provided an astronomical clock, a file manager to keep track of SETI data files, a spectrum analyzer optimized for amateur SETI, remote control of the station from the Internet, and other packages.

The SETI League and Project Argus

Founded in 1994 in response to the United States Congress cancellation of the NASA SETI program, The SETI League, Inc. is a membership-supported nonprofit organization with 1,500 members in 62 countries. This grass-roots alliance of amateur and professional radio astronomers is headed by executive director emeritus

H. Paul Shuch H. Paul Shuch (born May 23, 1946) is an American scientist and engineer who has coordinated radio amateurs to help in the search for extraterrestrial intelligence (SETI). Shuch, an aerospace engineer, microwave technologist, and radio amateur ...

, the engineer credited with developing the world's first commercial home satellite TV receiver. Many SETI League members are licensed radio amateurs and microwave experimenters. Others are digital signal processing experts and computer enthusiasts. The SETI League pioneered the conversion of backyard satellite TV dishes in diameter into research-grade radio telescopes of modest sensitivity. The organization concentrates on coordinating a global network of small, amateur-built radio telescopes under Project Argus, an all-sky survey seeking to achieve real-time coverage of the entire sky. Project Argus was conceived as a continuation of the all-sky survey component of the late NASA SETI program (the targeted search having been continued by the SETI Institute's Project Phoenix). There are currently 143 Project Argus radio telescopes operating in 27 countries. Project Argus instruments typically exhibit sensitivity on the order of 10⁻²³ Watts/square metre, or roughly equivalent to that achieved by the Ohio State University Big Ear radio telescope in 1977, when it detected the landmark "Wow!" candidate signal. The name "Argus" derives from the mythical Greek guard-beast who had 100 eyes, and could see in all directions at once. In the SETI context, the name has been used for radio telescopes in fiction (Arthur C. Clarke, ''" Imperial Earth"''; Carl Sagan, ''" Contact"''), was the name initially used for the NASA study ultimately known as "Cyclops," and is the name given to an omnidirectional radio telescope design being developed at the Ohio State University.

Optical experiments

While most SETI sky searches have studied the radio spectrum, some SETI researchers have considered the possibility that alien civilizations might be using powerful

laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The fi ...

s for interstellar communications at optical wavelengths. The idea was first suggested by R. N. Schwartz and

Charles Hard Townes Charles Hard Townes (July 28, 1915 – January 27, 2015) was an American physicist. Townes worked on the theory and application of the maser, for which he obtained the fundamental patent, and other work in quantum electronics associated wi ...

in a 1961 paper published in the journal ''

Nature Nature, in the broadest sense, is the physical world or universe. "Nature" can refer to the phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. Although humans are ...

'' titled "Interstellar and Interplanetary Communication by Optical Masers". However, the 1971 Cyclops study discounted the possibility of optical SETI, reasoning that construction of a laser system that could outshine the bright central star of a remote star system would be too difficult. In 1983, Townes published a detailed study of the idea in the United States journal ''

Proceedings of the National Academy of Sciences ''Proceedings of the National Academy of Sciences of the United States of America'' (often abbreviated ''PNAS'' or ''PNAS USA'') is a peer-reviewed multidisciplinary scientific journal. It is the official journal of the National Academy of Sci ...

'', which was met with widespread agreement by the SETI community. There are two problems with optical SETI. The first problem is that lasers are highly "monochromatic", that is, they emit light only on one frequency, making it troublesome to figure out what frequency to look for. However, emitting light in narrow pulses results in a broad spectrum of emission; the spread in frequency becomes higher as the pulse width becomes narrower, making it easier to detect an emission. The other problem is that while radio transmissions can be broadcast in all directions, lasers are highly directional. Interstellar gas and dust is almost transparent to near infrared, so these signals can be seen from greater distances, but the extraterrestrial laser signals would need to be transmitted in the direction of Earth in order to be detected. Optical SETI supporters have conducted paper studies of the effectiveness of using contemporary high-energy lasers and a ten-meter diameter mirror as an interstellar beacon. The analysis shows that an infrared pulse from a laser, focused into a narrow beam by such a mirror, would appear thousands of times brighter than the Sun to a distant civilization in the beam's line of fire. The Cyclops study proved incorrect in suggesting a laser beam would be inherently hard to see. Such a system could be made to automatically steer itself through a target list, sending a pulse to each target at a constant rate. This would allow targeting of all Sun-like stars within a distance of 100 light-years. The studies have also described an automatic laser pulse detector system with a low-cost, two-meter mirror made of carbon composite materials, focusing on an array of light detectors. This automatic detector system could perform sky surveys to detect laser flashes from civilizations attempting contact. Several optical SETI experiments are now in progress. A Harvard-Smithsonian group that includes Paul Horowitz designed a laser detector and mounted it on Harvard's optical telescope. This telescope is currently being used for a more conventional star survey, and the optical SETI survey is " piggybacking" on that effort. Between October 1998 and November 1999, the survey inspected about 2,500 stars. Nothing that resembled an intentional laser signal was detected, but efforts continue. The Harvard-Smithsonian group is now working with

Princeton University Princeton University is a private research university in Princeton, New Jersey. Founded in 1746 in Elizabeth as the College of New Jersey, Princeton is the fourth-oldest institution of higher education in the United States and one of the ...

to mount a similar detector system on Princeton's 91-centimeter (36-inch) telescope. The Harvard and Princeton telescopes will be "ganged" to track the same targets at the same time, with the intent being to detect the same signal in both locations as a means of reducing errors from detector noise. The Harvard-Smithsonian SETI group led by Professor Paul Horowitz built a dedicated all-sky optical survey system along the lines of that described above, featuring a 1.8-meter (72-inch) telescope. The new optical SETI survey telescope is being set up at the Oak Ridge Observatory in

. The University of California, Berkeley, home of SERENDIP and SETI@home, is also conducting optical SETI searches and collaborates with the NIROSETI program. The optical SETI program at Breakthrough Listen was initially directed by Geoffrey Marcy, an extrasolar planet hunter, and it involves examination of records of spectra taken during

extrasolar planet An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...

hunts for a continuous, rather than pulsed, laser signal. This survey uses the Automated Planet Finder 2.4-m telescope at the Lick Observatory, situated on the summit of Mount Hamilton, east of San Jose, California.Steven S. Vogt et al.,
APF - The Lick Observatory Automated Planet Finder
', 26 February 2014. The other Berkeley optical SETI effort is being pursued by the Harvard-Smithsonian group and is being directed by Dan Werthimer of Berkeley, who built the laser detector for the Harvard-Smithsonian group. This survey uses a 76-centimeter (30-inch) automated telescope at

Leuschner Observatory Leuschner Observatory, originally called the Students' Observatory, is an observatory jointly operated by the University of California, Berkeley and San Francisco State University. The observatory was built in 1886 on the Berkeley campus. For many ...

and an older laser detector built by Werthimer. In May 2017, astronomers reported studies related to laser light emissions from stars, as a way of detecting technology-related signals from an alien civilization. The reported studies included

Tabby's Star Tabby's Star (also known as Boyajian's Star and WTF Star, and designated KIC 8462852 in the Kepler Input Catalog) is an F-type main-sequence star in the constellation A constellation is an area on the celestial sphere in which a ...

(designated KIC 8462852 in the

Kepler Input Catalog The Kepler Input Catalog (or KIC) is a publicly searchable database of roughly 13.2 million targets used for the Kepler Spectral Classification Program (SCP) and ''Kepler''. Overview The Kepler SCP targets were observed by the 2MASS project ...

), an oddly dimming star in which its unusual starlight fluctuations may be the result of interference by an artificial megastructure, such as a Dyson swarm, made by such a civilization. No evidence was found for technology-related signals from KIC 8462852 in the studies. The SETI Institute also runs a program called ' Laser SETI' with an instrument composed of several cameras that continuously survey the entire night sky searching for millisecond singleton laser pulses of extraterrestrial origin.

Quantum communications

In a 2021 preprint, an astronomer described for the first time how one could search for

quantum communication Quantum information science is an interdisciplinary field that seeks to understand the analysis, processing, and transmission of information using quantum mechanics principles. It combines the study of Information science with quantum effects in p ...

transmissions sent by ETI using existing telescope and receiver technology. He also provides arguments for why future searches of ETI should also target interstellar quantum communication networks. A 2022 paper noted that interstellar quantum communication by other civilizations could be possible and may be advantageous, identifying some potential challenges and factors for detecting

s. They may use, for example, X-ray photons for remotely established

and quantum teleportation as the communication mode.

Search for extraterrestrial artifacts

The possibility of using interstellar messenger probes in the search for extraterrestrial intelligence was first suggested by Ronald N. Bracewell in 1960 (see

Bracewell probe A Bracewell probe is a hypothetical concept for an autonomous interstellar space probe dispatched for the express purpose of communication with one or more alien civilizations. It was proposed by Ronald N. Bracewell in a 1960 paper, as an alter ...

), and the technical feasibility of this approach was demonstrated by the British Interplanetary Society's starship study

Project Daedalus Project Daedalus (named after Daedalus, the Greek mythological designer who crafted wings for human flight) was a study conducted between 1973 and 1978 by the British Interplanetary Society to design a plausible uncrewed interstellar probe.Pro ...

in 1978. Starting in 1979,

Robert Freitas Robert A. Freitas Jr. (born 1952) is an American nanotechnologist. Career In 1974, Freitas earned a bachelor's degree in both physics and psychology from Harvey Mudd College, and in 1978, he received a Juris Doctor (J.D.) degree from Santa Clara ...

advanced arguments for the proposition that physical space-probes are a superior mode of interstellar communication to radio signals. See

Voyager Golden Record The Voyager Golden Records are two phonograph records that were included aboard both Voyager spacecraft launched in 1977. The records contain sounds and images selected to portray the diversity of life and culture on Earth, and are intended for ...

. In recognition that any sufficiently advanced interstellar probe in the vicinity of Earth could easily monitor the terrestrial

Internet The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, pub ...

, Invitation to ETI was established by Prof. Allen Tough in 1996, as a Web-based SETI experiment inviting such spacefaring probes to establish contact with humanity. The project's 100 Signatories includes prominent physical, biological, and social scientists, as well as artists, educators, entertainers, philosophers and futurists. Prof.

, executive director emeritus of The SETI League, serves as the project's Principal Investigator. Inscribing a message in matter and transporting it to an interstellar destination can be enormously more energy efficient than communication using electromagnetic waves if delays larger than light transit time can be tolerated. That said, for simple messages such as "hello," radio SETI could be far more efficient. If energy requirement is used as a proxy for technical difficulty, then a solarcentric Search for Extraterrestrial Artifacts (SETA) may be a useful supplement to traditional radio or optical searches. Much like the "preferred frequency" concept in SETI radio beacon theory, the Earth-Moon or Sun-Earth libration orbits might therefore constitute the most universally convenient parking places for automated extraterrestrial spacecraft exploring arbitrary stellar systems. A viable long-term SETI program may be founded upon a search for these objects. In 1979, Freitas and Valdes conducted a photographic search of the vicinity of the Earth-Moon triangular libration points and , and of the solar-synchronized positions in the associated halo orbits, seeking possible orbiting extraterrestrial interstellar probes, but found nothing to a detection limit of about 14th magnitude. The authors conducted a second, more comprehensive photographic search for probes in 1982 that examined the five Earth-Moon Lagrangian positions and included the solar-synchronized positions in the stable L4/L5 libration orbits, the potentially stable nonplanar orbits near L1/L2, Earth-Moon , and also in the Sun-Earth system. Again no extraterrestrial probes were found to limiting magnitudes of 17–19th magnitude near L3/L4/L5, 10–18th magnitude for /, and 14–16th magnitude for Sun-Earth . In June 1983, Valdes and Freitas used the 26 m radiotelescope at Hat Creek Radio Observatory to search for the tritium hyperfine line at 1516 MHz from 108 assorted astronomical objects, with emphasis on 53 nearby stars including all visible stars within a 20 light-year radius. The tritium frequency was deemed highly attractive for SETI work because (1) the isotope is cosmically rare, (2) the tritium hyperfine line is centered in the SETI waterhole region of the terrestrial microwave window, and (3) in addition to beacon signals, tritium hyperfine emission may occur as a byproduct of extensive

nuclear fusion Nuclear fusion is a reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles ( neutrons or protons). The difference in mass between the reactants and products is manife ...

energy production by extraterrestrial civilizations. The wideband- and narrowband-channel observations achieved sensitivities of 5–14 x 10⁻²¹ W/m²/channel and 0.7-2 x 10⁻²⁴ W/m²/channel, respectively, but no detections were made.

Technosignatures

Technosignatures, including all signs of technology, are a recent avenue in the search for extraterrestrial intelligence. Technosignatures may originate from various sources, from megastructures such as

Dyson sphere A Dyson sphere is a hypothetical megastructure that completely encompasses a star and captures a large percentage of its solar power output. The concept is a thought experiment that attempts to explain how a spacefaring civilization would meet ...

s and space mirrors or space shaders to the atmospheric contamination created by an industrial civilization, or city lights on extrasolar planets, and may be detectable in the future with large hypertelescopes. Technosignatures can be divided into three broad categories: astroengineering projects, signals of planetary origin, and spacecraft within and outside the

. An astroengineering installation such as a

, designed to convert all of the incident radiation of its host star into energy, could be detected through the observation of an infrared excess from a

solar analog Solar-type star, solar analogs (also analogues), and solar twins are stars that are particularly similar to the Sun. The stellar classification is a hierarchy with solar twin being most like the Sun followed by solar analog and then solar-type ...

star, or by the star's apparent disappearance in the visible spectrum over several years. After examining some 100,000 nearby large galaxies, a team of researchers has concluded that none of them display any obvious signs of highly advanced technological civilizations. Another hypothetical form of astroengineering, the

Shkadov thruster Stellar engines are a class of hypothetical megastructures used to control the motion of a star system. The concept has been introduced by Bădescu, Badescu and Cathcart. Some variants use this energy to produce thrust, and thus accelerate a star ...

, moves its host star by reflecting some of the star's light back on itself, and would be detected by observing if its

transit Transit may refer to: Arts and entertainment Film * ''Transit'' (1979 film), a 1979 Israeli film * ''Transit'' (2005 film), a film produced by MTV and Staying-Alive about four people in countries in the world * ''Transit'' (2006 film), a 2006 ...

s across the star abruptly end with the thruster in front.

Asteroid mining Asteroid mining is the hypothetical exploitation of materials from asteroids and other minor planets, including near-Earth objects. Notable asteroid mining challenges include the high cost of spaceflight, unreliable identification of asteroids ...

within the Solar System is also a detectable technosignature of the first kind. Individual extrasolar planets can be analyzed for signs of technology.

Avi Loeb Abraham "Avi" Loeb ( he, אברהם (אבי) לייב; born February 26, 1962) is an Israeli-American theoretical physicist who works on astrophysics and cosmology. Loeb is the Frank B. Baird Jr. Professor of Science at Harvard University. He h ...

of the Center for Astrophysics Harvard & Smithsonian has proposed that persistent light signals on the night side of an exoplanet can be an indication of the presence of cities and an advanced civilization. In addition, the excess infrared radiation and chemicals produced by various industrial processes or

terraforming Terraforming or terraformation ("Earth-shaping") is the hypothetical process of deliberately modifying the atmosphere, temperature, surface topography or ecology of a planet, moon, or other body to be similar to the environment of Earth to make ...

efforts may point to intelligence. Light and heat detected from planets need to be distinguished from natural sources to conclusively prove the existence of civilization on a planet. However, as argued by the Colossus team, a civilization heat signature should be within a "comfortable" temperature range, like terrestrial

urban heat islands An urban heat island (UHI) is an urban or metropolitan area that is significantly warmer than its surrounding rural areas due to human activities. The temperature difference is usually larger at night than during the day, and is most apparent ...

, i.e. only a few degrees warmer than the planet itself. In contrast, such natural sources as wild fires, volcanoes, etc. are significantly hotter, so they will be well distinguished by their maximum flux at a different wavelength. Other than astroengineering, technosignatures such as

artificial satellite A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioisoto ...

s around exoplanets, particularly such in geostationary orbit, might be detectable even with today's technology and data, and would allow, similar to fossiles on Earth, to find traces of extrasolar life from long ago. Extraterrestrial craft are another target in the search for technosignatures. Magnetic sail interstellar spacecraft should be detectable over thousands of light-years of distance through the synchrotron radiation they would produce through interaction with the interstellar medium; other interstellar spacecraft designs may be detectable at more modest distances. In addition, robotic probes within the Solar System are also being sought out with optical and radio searches. For a sufficiently advanced civilization, hyper energetic neutrinos from Planck scale accelerators should be detectable at a distance of many Mpc.

Fermi paradox

Italian physicist Enrico Fermi suggested in the 1950s that if technologically advanced civilizations are common in the universe, then they should be detectable in one way or another. (According to those who were there, Fermi either asked "Where are they?" or "Where is everybody?") The Fermi paradox is commonly understood as asking why extraterrestrials have not visited Earth,Ben Zuckerman and Michael H. Hart (editors), ''Extraterrestrials: Where Are They?'' Elsevier Science & Technology Books (1982), but the same reasoning applies to the question of why signals from extraterrestrials have not been heard. The SETI version of the question is sometimes referred to as "the Great Silence". The Fermi paradox can be stated more completely as follows: There are multiple explanations proposed for the Fermi paradox, ranging from analyses suggesting that intelligent life is rare (the " Rare Earth hypothesis"), to analyses suggesting that although extraterrestrial civilizations may be common, they would not communicate with us, would communicate in a way we have not discovered yet, could not travel across interstellar distances, or destroy themselves before they master the technology of either interstellar travel or communication. The German astrophysicist and radio astronomer Sebastian von Hoerner suggested that the average duration of civilization was 6,500 years. After this time, according to him, it disappears for external reasons (the destruction of life on the planet, the destruction of only rational beings) or internal causes (mental or physical degeneration). According to his calculations, on a habitable planet (one in 3 million stars) there is a sequence of technological species over a time distance of hundreds of millions of years, and each of them "produces" an average of 4 technological species. With these assumptions, the average distance between 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. ...

is 1,000 light years. Science writer

Timothy Ferris Timothy Ferris (born August 29, 1944) is an American science writer and the best-selling author of twelve books, including ''The Science of Liberty'' (2010) and ''Coming of Age in the Milky Way'' (1988), for which he was awarded the American ...

has posited that since galactic societies are most likely only transitory, an obvious solution is an interstellar communications network, or a type of library consisting mostly of automated systems. They would store the cumulative knowledge of vanished civilizations and communicate that knowledge through the galaxy. Ferris calls this the "Interstellar Internet", with the various automated systems acting as network "servers". If such an Interstellar Internet exists, the hypothesis states, communications between servers are mostly through narrow-band, highly directional radio or laser links. Intercepting such signals is, as discussed earlier, very difficult. However, the network could maintain some broadcast nodes in hopes of making contact with new civilizations. Although somewhat dated in terms of "information culture" arguments, not to mention the obvious technological problems of a system that could work effectively for billions of years and requires multiple lifeforms agreeing on certain basics of communications technologies, this hypothesis is actually testable (see below).

Difficulty of detection

A significant problem is the vastness of space. Despite piggybacking on the world's most sensitive radio telescope,

Charles Stuart Bowyer Charles Stuart Bowyer (August 2, 1934 – September 23, 2020) was an American astronomer and academic. He was a professor at the University of California. Early life and education Bowyer was born in Toledo, Ohio, to Howard and Elizabeth Bowyer. ...

said, the instrument could not detect random radio noise emanating from a civilization like ours, which has been leaking radio and TV signals for less than 100 years. For SERENDIP and most other SETI projects to detect a signal from an extraterrestrial civilization, the civilization would have to be beaming a powerful signal directly at us. It also means that Earth civilization will only be detectable within a distance of 100 light-years.

Post-detection disclosure protocol

The

International Academy of Astronautics The International Academy of Astronautics (IAA) is an independent non-governmental organization established in Stockholm (Sweden) on August 16, 1960, by Dr. Theodore von Kármán, and recognized by the United Nations in 1996. The IAA has electe ...

(IAA) has a long-standing SETI Permanent Study Group (SPSG, formerly called the IAA SETI Committee), which addresses matters of SETI

science Science is a systematic endeavor that Scientific method, builds and organizes knowledge in the form of Testability, testable explanations and predictions about the universe. Science may be as old as the human species, and some of the earli ...

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

, and

international policy International is an adjective (also used as a noun) meaning "between nations". International may also refer to: Music Albums * ''International'' (Kevin Michael album), 2011 * ''International'' (New Order album), 2002 * ''International'' (The T ...

. The SPSG meets in conjunction with the International Astronautical Congress (IAC) held annually at different locations around the world, and sponsors two SETI Symposia at each IAC. In 2005, the IAA established the SETI: Post-Detection Science and Technology Taskgroup (Chairman, Professor

Paul Davies Paul Charles William Davies (born 22 April 1946) is an English physicist, writer and broadcaster, a professor in Arizona State University and Director of BEYOND: Center for Fundamental Concepts in Science. He is affiliated with the Institute ...

) "to act as a Standing Committee to be available to be called on at any time to advise and consult on questions stemming from the discovery of a putative signal of extraterrestrial intelligent (ETI) origin." However, the protocols mentioned apply only to radio SETI rather than for METI (

Active SETI Active SETI (Active Search for Extra-Terrestrial Intelligence) is the attempt to send messages to intelligent extraterrestrial life. Active SETI messages are predominantly sent in the form of radio signals. Physical messages like that of the P ...

). The intention for METI is covered under the SETI charter "Declaration of Principles Concerning Sending Communications with Extraterrestrial Intelligence". In October 2000 astronomers

Iván Almár Iván Almár (born April 21, 1932 in Budapest) is a Hungarian astronomer. He proposed the San Marino Scale as a means of assessing risks related to extraterrestrial communication. Almár also serves on the Advisory Council of METI (Messaging ...

and Jill Tarter presented a paper to The SETI Permanent Study Group in Rio de Janeiro, Brazil which proposed a scale (modelled after the

Torino scale The Torino scale is a method for categorizing the impact hazard associated with near-Earth objects (NEOs) such as asteroids and comets. It is intended as a communication tool for astronomers and the public to assess the seriousness of collision pre ...

) which is an ordinal scale between zero and ten that quantifies the impact of any public announcement regarding evidence of extraterrestrial intelligence; the

Rio scale The Rio scale was proposed in 2000 as a means of quantifying the significance of a SETI detection. The scale was designed by Iván Almár and Jill Tarter to help policy-makers how likely, from 0 to 10, is that an extraterrestrial radio signal has ...

has since inspired the 2005

San Marino Scale The San Marino Scale is a suggested scale for assessing risks associated with deliberate transmissions from Earth aimed to possible extraterrestrial intelligent life. The scale evaluates the significance of transmissions from Earth as a function ...

(in regard to the risks of transmissions from Earth) and the 2010 London Scale (in regard to the detection of extraterrestrial life) The Rio scale itself was revised in 2018. The SETI Institute does not officially recognize the

as of extraterrestrial origin (as it was unable to be verified), although in a 2020 tweet the organization stated that ''an astronomer might have pinpointed the host star''. The SETI Institute has also publicly denied that the candidate signal

Radio source SHGb02+14a SHGb02+14a is an astronomical radio source and a candidate in the Search for Extra-Terrestrial Intelligence (SETI), discovered in March 2003 by SETI@home and announced in ''New Scientist'' on September 1, 2004. Observation The source was origina ...

is of extraterrestrial origin. Although other volunteering projects such as

Zooniverse Zooniverse is a citizen science web portal owned and operated by the Citizen Science Alliance. It is home to some of the Internet's largest, most popular and most successful citizen science projects. The organization grew from the original Gal ...

credit users for discoveries, there is currently no crediting or early notification by SETI@Home following the discovery of a signal. Some people, including Steven M. Greer, have expressed cynicism that the general public might not be informed in the event of a genuine discovery of extraterrestrial intelligence due to significant vested interests. Some, such as Bruce Jakosky have also argued that the official disclosure of extraterrestrial life may have far reaching and as yet undetermined implications for society, particularly for the world's

religion Religion is usually defined as a social- cultural system of designated behaviors and practices, morals, beliefs, worldviews, texts, sanctified places, prophecies, ethics, or organizations, that generally relates humanity to supernatural, ...

Active SETI

, also known as messaging to extraterrestrial intelligence (METI), consists of sending signals into space in the hope that they will be picked up by an alien intelligence.

Realized interstellar radio message projects

In November 1974, a largely symbolic attempt was made at the Arecibo Observatory to send a message to other worlds. Known as the Arecibo Message, it was sent towards the

globular cluster A globular cluster is a spheroidal conglomeration of stars. Globular clusters are bound together by gravity, with a higher concentration of stars towards their centers. They can contain anywhere from tens of thousands to many millions of membe ...

M13, which is 25,000 light-years from Earth. Further IRMs Cosmic Call, Teen Age Message, Cosmic Call 2, and A Message From Earth were transmitted in 1999, 2001, 2003 and 2008 from the Evpatoria Planetary Radar.

Debate

Physicist Stephen Hawking, in his book '' A Brief History of Time'', suggests that "alerting" extraterrestrial intelligences to our existence is foolhardy, citing humankind's history of treating its own kind harshly in meetings of civilizations with a significant technology gap, e.g., the extermination of Tasmanian aborigines. He suggests, in view of this history, that we "lay low". In one response to Hawking, in September 2016, astronomer Seth Shostak allays such concerns. Astronomer Jill Tarter also disagrees with Hawking, arguing that aliens developed and long-lived enough to communicate and travel across interstellar distances would have evolved a cooperative and less violent intelligence. She does think it is too soon for humans to attempt active SETI and that humans should be more advanced technologically first but keep listening in the meantime. The concern over METI was raised by the science journal ''Nature'' in an editorial in October 2006, which commented on a recent meeting of the

SETI study group. The editor said, "It is not obvious that all extraterrestrial civilizations will be benign, or that contact with even a benign one would not have serious repercussions" (Nature Vol 443 12 October 06 p 606). Astronomer and science fiction author

David Brin Glen David Brin (born October 6, 1950) is an American scientist and author of science fiction. He has won the Hugo,particle physicist at the

Fermi National Accelerator Laboratory Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a United States Department of Energy national laboratory specializing in high-energy particle physics. Since 2007, Fermilab has been operat ...

near

Chicago, Illinois (''City in a Garden''); I Will , image_map = , map_caption = Interactive Map of Chicago , coordinates = , coordinates_footnotes = , subdivision_type = Country , subdivision_name ...

, suggested that passive SETI could also be dangerous and that a signal released onto the Internet could act as a computer virus. Computer security expert

Bruce Schneier Bruce Schneier (; born January 15, 1963) is an American cryptographer, computer security professional, privacy specialist, and writer. Schneier is a Lecturer in Public Policy at the Harvard Kennedy School and a Fellow at the Berkman Klein Cente ...

dismissed this possibility as a "bizarre movie-plot threat". To lend a quantitative basis to discussions of the risks of transmitting deliberate messages from Earth, the SETI Permanent Study Group of the International Academy of Astronautics adopted in 2007 a new analytical tool, the

. Developed by Prof. Ivan Almar and Prof.

, the scale evaluates the significance of transmissions from Earth as a function of signal intensity and information content. Its adoption suggests that not all such transmissions are equal, and each must be evaluated separately before establishing blanket international policy regarding active SETI. However, some scientists consider these fears about the dangers of METI as panic and irrational superstition; see, for example, Alexander L. Zaitsev's papers. Biologist João Pedro de Magalhães also proposed in 2015 transmitting an invitation message to any extraterrestrial intelligences watching us already in the context of the Zoo Hypothesis and inviting them to respond, arguing this would not put us in any more danger than we are already if the Zoo Hypothesis is correct. On 13 February 2015, scientists (including Geoffrey Marcy, Seth Shostak,

and David Brin) at a convention of the American Association for the Advancement of Science, discussed

and whether transmitting a message to possible intelligent

extraterrestrials Extraterrestrial life, colloquially referred to as alien life, is life that may occur outside Earth and which did not originate on Earth. No extraterrestrial life has yet been conclusively detected, although efforts are underway. Such life might ...

in the

Cosmos The cosmos (, ) is another name for the Universe. Using the word ''cosmos'' implies viewing the universe as a complex and orderly system or entity. The cosmos, and understandings of the reasons for its existence and significance, are studied in ...

was a good idea; one result was a statement, signed by many, that a "worldwide scientific, political and humanitarian discussion must occur before any message is sent". On 28 March 2015, a related essay was written by Seth Shostak and published in ''

The New York Times ''The New York Times'' (''the Times'', ''NYT'', or the Gray Lady) is a daily newspaper based in New York City with a worldwide readership reported in 2020 to comprise a declining 840,000 paid print subscribers, and a growing 6 million paid d ...

''. Mark Buchanan argued – in the context of potentially detected extraterrestrial activity on Earth – that humanity needs to figure out whether it would be safe or wise to attempt to communicate with extraterrestrials and work on ways to handle such attempts in an organized manner.

Breakthrough Message

The Breakthrough Message program is an open competition announced in July 2015 to design a digital message that could be transmitted from Earth to an extraterrestrial civilization, with a US$1,000,000 prize pool. The message should be "representative of humanity and planet Earth". The program pledges "not to transmit any message until there has been a wide-ranging debate at high levels of science and politics on the risks and rewards of contacting advanced civilizations".

Criticism

As various SETI projects have progressed, some have criticized early claims by researchers as being too "euphoric". For example, Peter Schenkel, while remaining a supporter of SETI projects, wrote in 2006 that : " light of new findings and insights, it seems appropriate to put excessive euphoria to rest and to take a more down-to-earth view ... We should quietly admit that the early estimates—that there may be a million, a hundred thousand, or ten thousand advanced extraterrestrial civilizations in our galaxy—may no longer be tenable." Critics claim that the existence of extraterrestrial intelligence has no good Popperian criteria for

falsifiability Falsifiability is a standard of evaluation of scientific theories and hypotheses that was introduced by the philosopher of science Karl Popper in his book '' The Logic of Scientific Discovery'' (1934). He proposed it as the cornerstone of a s ...

, as explained in a 2009 editorial in ''

'', which said: : "Seti ... has always sat at the edge of mainstream astronomy. This is partly because, no matter how scientifically rigorous its practitioners try to be, SETI can't escape an association with UFO believers and other such crackpots. But it is also because SETI is arguably not a falsifiable experiment. Regardless of how exhaustively the Galaxy is searched, the null result of radio silence doesn't rule out the existence of alien civilizations. It means only that those civilizations might not be using radio to communicate." ''Nature'' added that SETI was "marked by a hope, bordering on faith" that aliens were aiming signals at us, that a hypothetical alien SETI project looking at Earth with "similar faith" would be "sorely disappointed" (despite our many untargeted radar and TV signals, and our few targeted Active SETI radio signals denounced by those fearing aliens), and that it had difficulties attracting even sympathetic working scientists and Government funding because it was "an effort so likely to turn up nothing". However, ''Nature'' also added, "Nonetheless, a small SETI effort is well worth supporting, especially given the enormous implications if it did succeed" and that "happily, a handful of wealthy technologists and other private donors have proved willing to provide that support". Supporters of the Rare Earth Hypothesis argue that advanced lifeforms are likely to be very rare, and that, if that is so, then SETI efforts will be futile. Revised edition (first published in 2000) However, the Rare Earth Hypothesis itself faces many criticisms. In 1993, Roy Mash stated that "Arguments favoring the existence of extraterrestrial intelligence nearly always contain an overt appeal to big numbers, often combined with a covert reliance on generalization from a single instance" and concluded that "the dispute between believers and skeptics is seen to boil down to a conflict of intuitions which can barely be engaged, let alone resolved, given our present state of knowledge". In 2012, Milan M. Ćirković (who was then research professor at the Astronomical Observatory of Belgrade and a research associate of the

Future of Humanity Institute The Future of Humanity Institute (FHI) is an interdisciplinary research centre at the University of Oxford investigating big-picture questions about humanity and its prospects. It was founded in 2005 as part of the Faculty of Philosophy and t ...

at the

University of Oxford , mottoeng = The Lord is my light , established = , endowment = £6.1 billion (including colleges) (2019) , budget = £2.145 billion (2019–20) , chancellor ...

) said that Mash was unrealistically over-reliant on excessive abstraction that ignored the empirical information available to modern SETI researchers.Ćirković (2012)
p166
/ref> George Basalla, Emeritus Professor of History at the

University of Delaware The University of Delaware (colloquially UD or Delaware) is a public land-grant research university located in Newark, Delaware. UD is the largest university in Delaware. It offers three associate's programs, 148 bachelor's programs, 121 ma ...

, is a critic of SETI who argued in 2006 that "extraterrestrials discussed by scientists are as imaginary as the spirits and gods of religion or myth", and has in turn been criticized by Milan M. Ćirković for, among other things, being unable to distinguish between "SETI believers" and "scientists engaged in SETI", who are often sceptical (especially about quick detection), such as

Freeman Dyson Freeman John Dyson (15 December 1923 – 28 February 2020) was an English-American theoretical physicist and mathematician known for his works in quantum field theory, astrophysics, random matrices, mathematical formulation of quantum m ...

(and, at least in their later years,

and Sebastian von Hoerner), and for ignoring the difference between the knowledge underlying the arguments of modern scientists and those of ancient Greek thinkers.Ćirković (2012)
p172
"It is Basalla, the critic of SETI and not its practitioners, who violates the spirit of Hull's dictum, for instance, when he writes that 'extraterrestrials discussed by scientists are as imaginary as the spirits and gods of religion or myth'. 4Second, the approach to this sociology of science criticism is obviously marred by Basalla's insistence on personal quirks and idiosyncrasies as the main motivation of scientific activity, an attitude that is not only demeaning to the many scientists mentioned, ..."

Massimo Pigliucci Massimo Pigliucci (; born January 16, 1964) is Professor of Philosophy at the City College of New York, former co-host of the '' Rationally Speaking Podcast'', and former editor in chief for the online magazine ''Scientia Salon''. He is a critic o ...

, Professor of Philosophy at CUNY- City College, asked in 2010 whether SETI is "uncomfortably close to the status of

pseudoscience Pseudoscience consists of statements, beliefs, or practices that claim to be both scientific and factual but are incompatible with the scientific method. Pseudoscience is often characterized by contradictory, exaggerated or unfalsifiable clai ...

" due to the lack of any clear point at which negative results cause the

hypothesis A hypothesis (plural hypotheses) is a proposed explanation for a phenomenon. For a hypothesis to be a scientific hypothesis, the scientific method requires that one can test it. Scientists generally base scientific hypotheses on previous obse ...

of Extraterrestrial Intelligence to be abandoned, before eventually concluding that SETI is "almost-science", which is described by Milan M. Ćirković as Pigliucci putting SETI in "the illustrious company of string theory,

interpretations of quantum mechanics An interpretation of quantum mechanics is an attempt to explain how the mathematical theory of quantum mechanics might correspond to experienced reality. Although quantum mechanics has held up to rigorous and extremely precise tests in an extraord ...

evolutionary psychology Evolutionary psychology is a theoretical approach in psychology that examines cognition and behavior from a modern evolutionary perspective. It seeks to identify human psychological adaptations with regards to the ancestral problems they evol ...

and history (of the 'synthetic' kind done recently by

Jared Diamond Jared Mason Diamond (born September 10, 1937) is an American geographer, historian, ornithologist, and author best known for his popular science books '' The Third Chimpanzee'' (1991); ''Guns, Germs, and Steel'' (1997, awarded a Pulitzer Priz ...

)", while adding that his justification for doing so with SETI "is weak, outdated, and reflecting particular philosophical prejudices similar to the ones described above in Mash and Basalla".Ćirković (2012)
p175
"However, in the second chapter, tellingly entitled 'Almost Science', the author (a distinguished philosopher, mainly involved in the philosophy of biology) devotes several subsections to the fields which are, in his opinion, neither pseudosciences, nor fully legitimate members of the scientific family. Here he puts SETI studies in the illustrious company of string theory, interpretations of quantum mechanics, evolutionary psychology and history (of the 'synthetic' kind done recently by Jared Diamond). While the club is fun to be in - and only a staunch conservative does not expect great breakthroughs to come out of one or more of these domains in the next few decades - the justification offered by Pigliucci in the case of SETI is weak, outdated, and reflecting particular philosophical prejudices similar to the ones described above in Mash and Basalla. 0

Ufology

Ufologist

Stanton Friedman Stanton Terry Friedman (July 29, 1934 – May 13, 2019) was an American nuclear physicist and professional ufologist who resided in New Brunswick, Canada. He was the original civilian investigator of the Roswell UFO incident. Early life Bor ...

has often criticized SETI researchers for, among other reasons, what he sees as their unscientific criticisms of Ufology, but, unlike SETI, Ufology has generally not been embraced by academia as a scientific field of study, and it is usually characterized as a partial or total

. In a 2016 interview, Jill Tarter pointed out that it is still a misconception that SETI and UFOs are related. She says that, "SETI uses the tools of the astronomer to attempt to find evidence of somebody else's technology coming from a great distance. If we ever claim detection of a signal, we will provide evidence and data that can be independently confirmed. UFOs—none of the above." The Galileo Project headed by Harvard astronomer

is one of the few scientific efforts to study UFOs or UAPs. Loeb criticized that the study of UAP is often dismissed and not sufficiently studied by scientists and should shift from "occupying the talking points of national security administrators and politicians" to the realm of science. The Galileo Projects finds that after the publication of the UFO Report by the U.S. Intelligence the

scientific community The scientific community is a diverse network of interacting scientists. It includes many " sub-communities" working on particular scientific fields, and within particular institutions; interdisciplinary and cross-institutional activities are als ...

needs to "systematically, scientifically and transparently look for potential evidence of extraterrestrial technological equipment".

References

External links

*
Harvard University SETI Program

University of California, Berkeley SETI Program

The eerie silence
Expanding the parameters of the search for technological and evolutionary footprints of extrasolar civilizations, beyond only radio signals. (

Physics World ''Physics World'' is the membership magazine of the Institute of Physics, one of the largest physical societies in the world. It is an international monthly magazine covering all areas of physics, pure and applied, and is aimed at physicists in ...

). March 2, 2010. *
Project Dorothy

Is it true that there could be intelligent life out there?
physics.org page about SETI *
The Rio Scale
a scale for rating SETI announcements.
Stephen Hawking and Russian tycoon Yuri Milner kick off new search for E.T.
$100 million funding to search star catalogue using SETI@home software, July 2015.
2012 Interview of SETI Pioneer

by astronomer Andrew Fraknoi {{DEFAULTSORT:Seti Astrobiology Distributed computing projects Radio astronomy Interstellar messages