The search for extraterrestrial intelligence (SETI) is a collective term for scientific searches for intelligent

extraterrestrial life 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 ...

, for example, monitoring electromagnetic radiation for signs of transmissions from civilizations on other planets. Scientific investigation began shortly after the advent of radio in the early 1900s, and focused international efforts have been ongoing since the 1980s. In 2015, Stephen Hawking and Israeli billionaire Yuri Milner announced a project called Breakthrough Listen.

History

Early work

There have been many earlier searches for extraterrestrial intelligence within the Solar System. In 1896, Nikola Tesla suggested that an extreme version of his wireless electrical transmission system could be used to contact beings on Mars. 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 radio experiments, and even speculation that he could have picked up naturally occurring radio noise caused by a moon of Jupiter ( Io) moving through the magnetosphere of Jupiter. In the early 1900s,

Guglielmo Marconi Guglielmo Giovanni Maria Marconi, 1st Marquis of Marconi (; 25 April 187420 July 1937) was an Italians, Italian inventor and electrical engineering, electrical engineer, known for his creation of a practical radio wave-based Wireless telegrap ...

, Lord Kelvin and David Peck Todd also stated their belief that radio could be used to contact Martians, with Marconi stating that his stations had also picked up potential Martian signals. On August 21–23, 1924, Mars entered an opposition 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, a radio receiver was lifted above the ground in a

dirigible An airship or dirigible balloon is a type of aerostat or lighter-than-air aircraft that can navigate through the air under its own power. Aerostats gain their lift from a lifting gas that is less dense than the surrounding air. In early ...

tuned to a wavelength between 8 and 9 km, using a "radio-camera" developed by

Amherst College Amherst College ( ) is a private liberal arts college in Amherst, Massachusetts. Founded in 1821 as an attempt to relocate Williams College by its then-president Zephaniah Swift Moore, Amherst is the third oldest institution of higher educatio ...

and

Charles Francis Jenkins Charles Francis Jenkins (August 22, 1867 – June 6, 1934) was an American engineer who was a pioneer of early cinema and one of the inventors of television, though he used mechanical rather than electronic technologies. His businesses incl ...

. The program was led by David Peck Todd with the military assistance of Admiral

Edward W. Eberle Edward Walter Eberle (August 17, 1864 – July 6, 1929) was an Admiral (United States), admiral in the United States Navy, who served as List of Superintendents of the United States Naval Academy, Superintendent of the United States Naval Aca ...

(

Chief of Naval Operations The chief of naval operations (CNO) is the professional head of the United States Navy. The position is a statutory office () held by an admiral who is a military adviser and deputy to the secretary of the Navy. In a separate capacity as a memb ...

), with William F. Friedman (chief cryptographer of the United States Army), assigned to translate any potential Martian messages. A 1959 paper by Philip Morrison and

Giuseppe Cocconi Giuseppe Cocconi (1914–2008) was an Italian physicist who was director of the Proton Synchrotron at CERN in Geneva. He is known for his work in particle physics and for his involvement with SETI where he wrote, " e probability of success is d ...

first pointed out the possibility of searching the microwave spectrum. It proposed

frequencies Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...

and a set of initial targets. In 1960, Cornell University astronomer Frank Drake performed the first modern SETI experiment, named " Project Ozma" after the

Queen of Oz ''Queen of Oz'' is an upcoming British television sitcom developed by and starring Catherine Tate as the scandalous Princess Georgiana, a disgraced member of a fictional British Royal Family sent to rule Australia. The first series, consisting ...

L. Frank Baum Lyman Frank Baum (; May 15, 1856 – May 6, 1919) was an American author best known for his children's books, particularly ''The Wonderful Wizard of Oz'' and its sequels. He wrote 14 novels in the ''Oz'' series, plus 41 other novels (not includ ...

's fantasy books. Drake used a radio telescope in diameter at Green Bank, West Virginia, to examine the stars Tau Ceti and Epsilon Eridani near the 1.420 gigahertz marker frequency, a region of the radio spectrum dubbed the " water hole" due to its proximity to the hydrogen and hydroxyl radical 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 scientists took a strong interest in SETI during the 1960s and performed a number of searches with omnidirectional antennas in the hope of picking up powerful radio signals. Soviet astronomer Iosif Shklovsky wrote the pioneering book in the field, ''Universe, Life, Intelligence'' (1962), which was expanded upon by American astronomer

Carl Sagan Carl Edward Sagan (; ; November 9, 1934December 20, 1996) was an American astronomer, planetary scientist, cosmologist, astrophysicist, astrobiologist, author, and science communicator. His best known scientific contribution is research on ext ...

as the best-selling book ''Intelligent Life in the Universe'' (1966). Wow signal

In the March 1955 issue of '' Scientific American'',

John D. Kraus John Daniel Kraus (June 28, 1910 – July 18, 2004) was an American physicist known for his contributions to electromagnetics, radio astronomy, and antenna theory. His inventions included the helical antenna, the corner reflector antenna, a ...

described an idea to scan the cosmos for natural radio signals using a flat-plane radio telescope equipped with a parabolic

reflector Reflector may refer to: Science * Reflector, a device that causes reflection (for example, a mirror or a retroreflector) * Reflector (photography), used to control lighting contrast * Reflecting telescope * Reflector (antenna), the part of an ant ...

. Within two years, his concept was approved for construction by Ohio State University. With a total of

US$ The United States dollar (symbol: $; code: USD; also abbreviated US$ or U.S. Dollar, to distinguish it from other dollar-denominated currencies; referred to as the dollar, U.S. dollar, American dollar, or colloquially buck) is the official ...

71,000 () in grants from the National Science Foundation, construction began on an plot in Delaware, Ohio. This

Ohio State University Radio Observatory The Ohio State University Radio Observatory was a Kraus-type (after its inventor John D. Kraus) radio telescope located on the grounds of the Perkins Observatory at Ohio Wesleyan University in Delaware, Ohio from 1963 to 1998. Known as Big Ear, th ...

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 funded a SETI study that involved Drake, Barney Oliver 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". 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 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 ...

, 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'', it is considered by some to be the best candidate for a radio signal from an artificial,

extraterrestrial Extraterrestrial refers to any object or being beyond ( extra-) the planet Earth ( terrestrial). It is derived from the Latin words ''extra'' ("outside", "outwards") and ''terrestris'' ("earthly", "of or relating to the Earth"). It may be abbrevia ...

source ever discovered, but it has not been detected again in several additional searches.

Sentinel, META, and BETA

In 1980,

, Bruce Murray, and

Louis Friedman Louis Dill Friedman (born July 7, 1941) is an American astronautics engineer and space spokesperson. He was born in New York and raised in the Bronx. Dr. Friedman was a co-founder of The Planetary Society with Carl Sagan and Bruce C. Murray. E ...

founded the U.S. Planetary Society, partly as a vehicle for SETI studies. In the early 1980s, Harvard University physicist

Paul Horowitz Paul Horowitz (born 1942) is an American physicist and electrical engineer, known primarily for his work in electronics design, as well as for his role in the search for extraterrestrial intelligence (see SETI). Biography At age 8, Horowitz ac ...

took the next step and proposed the design of a spectrum analyzer 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 Digital signal processing (DSP) is the use of digital processing, such as by computers or more specialized digital signal processors, to perform a wide variety of signal processing operations. The digital signals processed in this manner are ...

(DSP) technology could be used to build

autocorrelation Autocorrelation, sometimes known as serial correlation in the discrete time case, is the correlation of a signal with a delayed copy of itself as a function of delay. Informally, it is the similarity between observations of a random variable ...

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 The Oak Ridge Observatory (ORO, code: 801), also known as the George R. Agassiz Station, is located at 42 Pinnacle Road, Harvard, Massachusetts. It was operated by the Center for Astrophysics Harvard & Smithsonian as a facility of the Smiths ...

in Harvard, Massachusetts. 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 The Doppler effect or Doppler shift (or simply Doppler, when in context) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who d ...

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 Steven Allan Spielberg (; born December 18, 1946) is an American director, writer, and producer. A major figure of the New Hollywood era and pioneer of the modern blockbuster, he is the most commercially successful director of all time. Spie ...

. A second such effort, META II, was begun in Argentina 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 A fast Fourier transform (FFT) is an algorithm that computes the discrete Fourier transform (DFT) of a sequence, or its inverse (IDFT). Fourier analysis converts a signal from its original domain (often time or space) to a representation in th ...

(FFT) engines, each capable of performing a 2²²-point complex FFTs in two seconds, and 21 general-purpose personal computers equipped with custom

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 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'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, and funding for SETI research was removed from the NASA budget by Congress in 1981; however, funding was restored in 1982, after

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, as well as the radio telescope of the

National Radio Astronomy Observatory The National Radio Astronomy Observatory (NRAO) is a federally funded research and development center of the United States National Science Foundation operated under cooperative agreement by Associated Universities, Inc. for the purpose of radio a ...

at Green Bank, West Virginia and the

radio telescope A radio telescope is a specialized antenna and radio receiver used to detect radio waves from astronomical radio sources in the sky. Radio telescopes are the main observing instrument used in radio astronomy, which studies the radio frequency ...

at the

Arecibo Observatory The Arecibo Observatory, also known as the National Astronomy and Ionosphere Center (NAIC) and formerly known as the Arecibo Ionosphere Observatory, is an observatory in Barrio Esperanza, Arecibo, Puerto Rico owned by the US National Science F ...

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, 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 of Mountain View, California resurrected the MOP program under the name of Project "Phoenix", backed by private sources of funding. Project Phoenix, under the direction of

Jill Tarter Jill Cornell Tarter (born January 16, 1944) is an American astronomer best known for her work on the search for extraterrestrial intelligence (SETI). Tarter is the former director of the Center for SETI Research, holding the Bernard M. Oliver Cha ...

, is a continuation of the targeted search program from MOP and studies roughly 1,000 nearby Sun-like stars. From 1995 through March 2004, Phoenix conducted observations at the

Parkes radio telescope Parkes may refer to: * Sir Henry Parkes (1815–1896), Australian politician, one of the earliest and most prominent advocates for Australian federation Named for Henry Parkes * Parkes, New South Wales, a regional town * Parkes Observatory, a radi ...

Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

, the radio telescope of the

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 to a distance of about 200

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s. 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

s 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, Aldebaran, Barnard's Star, Sirius, and

Proxima Centauri Proxima Centauri is a small, low-mass star located away from the Sun in the southern constellation of Centaurus. Its Latin name means the 'nearest tarof Centaurus'. It was discovered in 1915 by Robert Innes and is the nearest-kno ...

. 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 The ionosphere () is the ionized part of the upper atmosphere of Earth, from about to above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays an ...

. (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 The Low-Frequency Array, or LOFAR, is a large radio telescope, with an antenna network located mainly in the Netherlands, and spreading across 7 other European countries as of 2019. Originally designed and built by ASTRON, the Netherlands Institu ...

(LOFAR) in Europe, the Murchison Widefield Array (MWA) in Australia, and the Lovell Telescope in the United Kingdom.

Allen Telescope Array

The SETI Institute collaborated with the Radio Astronomy Laboratory at the

Berkeley SETI Research Center The Berkeley SETI Research Center (BSRC) conducts experiments searching for optical and electromagnetic transmissions from intelligent extraterrestrial civilizations.Paul Allen. 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 The Hat Creek Radio Observatory (HCRO) is operated by SRI International in the Western United States. The observatory is home to the Allen Telescope Array designed and owned by the SETI Institute in Mountain View, CA. Location Hat Creek Radio ...

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 Interferometry is a technique which uses the ''interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber op ...

output at the same time. Typically, the ATA snapshot imager (used for astronomical surveys and SETI) is run in parallel with a beamforming 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 ''CNET'' (short for "Computer Network") is an American media website that publishes reviews, news, articles, blogs, podcasts, and videos on technology and consumer electronics globally. ''CNET'' originally produced content for radio and televi ...

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 sources, such as heretofore unexplained non-repeating, possibly extragalactic, pulses known as fast radio bursts 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 The Berkeley SETI Research Center (BSRC) conducts experiments searching for optical and electromagnetic transmissions from intelligent extraterrestrial civilizations.

-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.

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, 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

Transiting Exoplanet Survey Satellite Transiting Exoplanet Survey Satellite (TESS, Explorer 95 or MIDEX-7) is a space telescope for NASA's Explorer program, designed to search for exoplanets using the transit method in an area 400 times larger than that covered by the ''Kepler' ...

) to look for signs of advanced extraterrestrial life. Thousands of new planets found by TESS will be scanned for technosignatures 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 (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 Dan Werthimer is co-founder and chief scientist of the SETI@home project and directs other UC Berkeley SETI searches at radio, infrared and visible wavelengths, including the Search for Extra-Terrestrial Radio Emissions from Nearby Developed Int ...

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

UCLA

Since 2016, UCLA undergraduate and graduate students have been participating in radio searches for technosignatures with the Green Bank Telescope. Targets include the Kepler 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 to analyze signals acquired by the

SERENDIP SERENDIP (Search for Extraterrestrial Radio Emissions from Nearby Developed Intelligent Populations) is a Search for Extra-Terrestrial Intelligence (SETI) program originated by the Berkeley SETI Research Center at the University of California, Berke ...

project. SETI@home was conceived by David Gedye along with Craig Kasnoff and is a popular volunteer volunteer computing project that was launched by the

Berkeley SETI Research Center The Berkeley SETI Research Center (BSRC) conducts experiments searching for optical and electromagnetic transmissions from intelligent extraterrestrial civilizations. 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 ''Imperial Earth'' is a science fiction novel by British writer Arthur C. Clarke, published in 1975 by Gollancz Books. The plot follows the protagonist, Duncan Makenzie, on a trip to Earth from his home on Titan, in large part as a diplo ...

"''; Carl Sagan, ''"

Contact Contact may refer to: Interaction Physical interaction * Contact (geology), a common geological feature * Contact lens or contact, a lens placed on the eye * Contact sport, a sport in which players make contact with other players or objects * ...

"''), 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 lasers for interstellar communications at optical wavelengths. The idea was first suggested by R. N. Schwartz and Charles Hard Townes in a 1961 paper published in the journal '' Nature'' 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'', 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 "

piggyback Piggyback, piggy-back, or piggybacking may mean: Transport * Piggyback (transportation), something that is riding on the back of something else Art, entertainment, and media * Splash cymbal piggybacking, mounting a cymbal on top of an already ...

ing" 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 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

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

in Harvard, Massachusetts. The University of California, Berkeley, home of

and SETI@home, is also conducting optical SETI searches and collaborates with the

NIROSETI The NIROSETI (Near-InfraRed Optical Search for Extraterrestrial Intelligence) is an astronomical program to search for artificial signals in the optical (Visible spectrum, visible) and near infrared (NIR) wavebands of the electromagnetic spectrum. ...

program. The optical SETI program at Breakthrough Listen was initially directed by

Geoffrey Marcy Geoffrey William Marcy (born September 29, 1954) is an American astronomer. He was an early influence in the field of exoplanet detection, discovery, and characterization. Marcy was a professor of astronomy at the University of California, Berk ...

, an extrasolar planet hunter, and it involves examination of records of spectra taken during extrasolar planet hunts for a continuous, rather than pulsed, laser signal. This survey uses the

Automated Planet Finder The Automated Planet Finder (APF) Telescope a.k.a. Rocky Planet Finder, is a fully robotic 2.4-meter optical telescope at Lick Observatory, situated on the summit of Mount Hamilton, east of San Jose, California, USA.Steven S. Vogt et al., APF - ...

2.4-m telescope at the

Lick Observatory The Lick Observatory is an astronomical observatory owned and operated by the University of California. It is on the summit of Mount Hamilton, in the Diablo Range just east of San Jose, California, United States. The observatory is managed by th ...

, 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

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 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 (designated KIC 8462852 in the Kepler Input Catalog), 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 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 ...

, 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 Laser SETI is an instrument that could continuously survey the entire night sky for brief laser pulses. The instrument can look everywhere simultaneously. The technology, which consists of a robust assembly of straightforward optical and mec ...

' 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 In academic publishing, a preprint is a version of a scholarly or scientific paper that precedes formal peer review and publication in a peer-reviewed scholarly or scientific journal. The preprint may be available, often as a non-typeset versio ...

, an astronomer described for the first time how one could search for quantum communication 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 technosignatures. They may use, for example, X-ray photons for remotely established quantum communication 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 Ronald Newbold Bracewell Order of Australia, AO (22 July 1921 – 12 August 2007) was the Lewis M. Terman Professor of Electrical Engineering of the Space, Telecommunications, and Radioscience Laboratory at Stanford University. Education B ...

in 1960 (see Bracewell probe), and the technical feasibility of this approach was demonstrated by the British Interplanetary Society's starship study Project Daedalus in 1978. Starting in 1979, Robert Freitas advanced arguments for the proposition that physical space-probes are a superior mode of interstellar communication to radio signals. See Voyager Golden Record. In recognition that any sufficiently advanced interstellar probe in the vicinity of Earth could easily monitor the terrestrial Internet,

Invitation to ETI Invitation or The Invitation may refer to: Films * ''Invitation'' (1952 film), an MGM film starring Dorothy McGuire and Van Johnson * ''The Invitation'' (1973 film), a Swiss film * ''The Invitation'' (2003 film), an American film starring Lance H ...

was established by Prof.

Allen Tough Allen Tough (January 6, 1936 – 27 April, 2012) was a Canadian educator and researcher. Widely known as a futurist, scientist, and author, Tough was Professor Emeritus at the University of Toronto at the time of his death. He made major contri ...

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. H. Paul Shuch, executive director emeritus of

The SETI League ''The'' () is a grammatical article in English, denoting persons or things already mentioned, under discussion, implied or otherwise presumed familiar to listeners, readers, or speakers. It is the definite article in English. ''The'' is the m ...

, 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 In lunar astronomy, libration is the wagging or wavering of the Moon perceived by Earth-bound observers and caused by changes in their perspective. It permits an observer to see slightly different hemispheres of the surface at different tim ...

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 A waterhole is a depression in the ground in which water can collect, or a more permanent pool in the bed of an ephemeral river. Waterhole or water hole may refer to: * Water hole (radio), an especially quiet region of the electromagnetic spect ...

of the terrestrial microwave window, and (3) in addition to beacon signals, tritium hyperfine emission may occur as a byproduct of extensive nuclear fusion 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 spheres 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 Engineering on an astronomical scale, or astronomical engineering, ''i.e.'', engineering involving operations with whole astronomical objects (planets, stars, etc.), is a known theme in science fiction, as well as a matter of recent scientific r ...

projects, signals of planetary origin, and spacecraft within and outside the Solar System. An astroengineering installation such as a Dyson sphere, 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 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, moves its host star by reflecting some of the star's light back on itself, and would be detected by observing if its transits across the star abruptly end with the thruster in front. Asteroid mining 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 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 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, 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 satellites around

exoplanet 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 ...

s, particularly such in

geostationary orbit A geostationary orbit, also referred to as a geosynchronous equatorial orbit''Geostationary orbit'' and ''Geosynchronous (equatorial) orbit'' are used somewhat interchangeably in sources. (GEO), is a circular geosynchronous orbit in altitud ...

, might be detectable even with today's technology and data, and would allow, similar to

fossile A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in ...

s on Earth, to find traces of extrasolar life from long ago. Extraterrestrial craft are another target in the search for technosignatures.

Magnetic sail A magnetic sail is a proposed method of spacecraft propulsion that uses a static magnetic field to deflect a plasma wind of charged particles radiated by the Sun or a Star thereby transferring momentum to accelerate or decelerate a spacecraft. ...

interstellar spacecraft A starship, starcraft, or interstellar spacecraft is a theoretical spacecraft designed for traveling between planetary systems. The term is mostly found in science fiction. Reference to a "star-ship" appears as early as 1882 in '' Oahspe: A Ne ...

should be detectable over thousands of light-years of distance through the

synchrotron radiation Synchrotron radiation (also known as magnetobremsstrahlung radiation) is the electromagnetic radiation emitted when relativistic charged particles are subject to an acceleration perpendicular to their velocity (). It is produced artificially in ...

they would produce through interaction with the

interstellar medium In astronomy, the interstellar medium is the matter and radiation that exist in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as dust and cosmic rays. It fills interstella ...

; 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 Enrico Fermi (; 29 September 1901 – 28 November 1954) was an Italian (later naturalized American) physicist and the creator of the world's first nuclear reactor, the Chicago Pile-1. He has been called the "architect of the nuclear age" and ...

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 In planetary astronomy and astrobiology, the Rare Earth hypothesis argues that the origin of life and the evolution of biological complexity such as sexually reproducing, multicellular organisms on Earth (and, subsequently, human intelligenc ...

"), 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 Sebastian Rudolf Karl von Hoerner (15 April 1919 – 7 January 2003) was a German astrophysicist and radio astronomer. He was born in Görlitz, Lower Silesia. After the end of World War II he studied physics at University of Göttingen. He obtain ...

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 is 1,000 light years. Science writer Timothy Ferris 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 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

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

presented a paper to The SETI Permanent Study Group in

Rio de Janeiro, Brazil Rio de Janeiro ( , , ; literally 'River of January'), or simply Rio, is the capital of the state of the same name, Brazil's third-most populous state, and the second-most populous city in Brazil, after São Paulo. Listed by the GaWC as a b ...

which proposed a scale (modelled after the Torino scale) 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 has since inspired the 2005 San Marino Scale (in regard to the risks of transmissions from Earth) and the 2010

London Scale London is the capital and largest city of England and the United Kingdom, with a population of just under 9 million. It stands on the River Thames in south-east England at the head of a estuary down to the North Sea, and has been a major se ...

(in regard to the detection of extraterrestrial life) The Rio scale itself was revised in 2018. The SETI Institute does not officially recognize the Wow! signal 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 is of extraterrestrial origin. Although other volunteering projects such as Zooniverse 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 Steven Macon Greer (June 28, 1955) is an American ufologistLewis-Kraus, Gideon (April 30, 2021How the Pentagon Started Taking U.F.O.s Seriously ''The New Yorker''. Retrieved on July 5, 2021. who founded the Center for the Study of Extraterrestria ...

, 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 Bruce Martin Jakosky (born December 9, 1955) is a professor of Geological Sciences and associate director of the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado, Boulder. He has been involved with the Viking prog ...

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 religions.

Active SETI

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 The Arecibo message is an interstellar radio message carrying basic information about humanity and Earth that was sent to the globular cluster Messier 13 in 1974. It was meant as a demonstration of human technological achievement, rather than a ...

, it was sent towards the globular cluster M13, which is 25,000 light-years from Earth. Further IRMs

Cosmic Call Cosmic commonly refers to: * The cosmos, a concept of the universe Cosmic may also refer to: Media * ''Cosmic'' (album), an album by Bazzi * Afro/Cosmic music * "Cosmic", a song by Kylie Minogue from the album '' X'' * CosM.i.C, a member of ...

Teen Age Message The Teen Age Message (TAM) was a series of interstellar radio transmissions sent from the Yevpatoria Planetary Radar to six solar-type stars during August–September 2001. The structure of the TAM was suggested by Alexander Zaitsev, Chief Scie ...

Cosmic Call 2 Cosmic commonly refers to: * The cosmos, a concept of the universe Cosmic may also refer to: Media * ''Cosmic'' (album), an album by Bazzi * Afro/Cosmic music * "Cosmic", a song by Kylie Minogue from the album '' X'' * CosM.i.C, a member of ...

, and

A Message From Earth Gliese 581c (Gl 581c or GJ 581c) is a planet orbiting within the Gliese 581 system. It is the second planet discovered in the system and the third in order from the star. With a mass at least 5.5 times that of the Earth, it is classified as a s ...

were transmitted in 1999, 2001, 2003 and 2008 from the

Evpatoria Yevpatoria ( uk, Євпаторія, Yevpatoriia; russian: Евпатория, Yevpatoriya; crh, , , gr, Ευπατορία) is a city of regional significance in Western Crimea, north of Kalamita Bay. Yevpatoria serves as the administrative ...

Planetary Radar.

Debate

Physicist Stephen Hawking, in his book ''

A Brief History of Time ''A Brief History of Time: From the Big Bang to Black Holes'' is a book on theoretical cosmology by English physicist Stephen Hawking. It was first published in 1988. Hawking wrote the book for readers who had no prior knowledge of physics. I ...

'', 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 Seth Shostak (born July 20, 1943) is an American astronomer and author, and is currently the senior astronomer for the SETI Institute. Shostak hosts SETI's weekly radio show/podcast ''Big Picture Science'', has played himself numerous times in TV ...

allays such concerns. Astronomer

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 International Academy of Astronautics 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 has expressed similar concerns. Richard Carrigan, a

particle physicist Particle physics or high energy physics is the study of Elementary particle, fundamental particles and fundamental interaction, forces that constitute matter and radiation. The fundamental particles in the universe are classified in the Standa ...

at the Fermi National Accelerator Laboratory near Chicago, Illinois, suggested that passive SETI could also be dangerous and that a signal released onto the Internet could act as a

computer virus A computer virus is a type of computer program that, when executed, replicates itself by modifying other computer programs and inserting its own code. If this replication succeeds, the affected areas are then said to be "infected" with a compu ...

. Computer security expert Bruce Schneier 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 San Marino Scale. Developed by Prof.

Ivan Almar Ivan () is a Slavic male given name, connected with the variant of the Greek name (English: John) from Hebrew meaning 'God is gracious'. It is associated worldwide with Slavic countries. The earliest person known to bear the name was Bulgari ...

and Prof. H. Paul Shuch, 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 Aleksandr Leonidovich Zaitsev (russian: Александр Леонидович Зайцев; 19 May 1945 – 29 November 2021) was a Russian and Soviet radio engineer and astronomer from Fryazino. He worked on radar astronomy devices, near-Ear ...

's papers. Biologist

João Pedro de Magalhães Joao Pedro Lourenco Rocha De Magalhaes is a Portuguese microbiologist. He studies aging through both computational and experimental approaches. His ultimate goal is to cure human aging. In 1999, he obtained his degree in Microbiology from Escola ...

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

, Seth Shostak, Frank Drake and David Brin) at a convention of the

American Association for the Advancement of Science The American Association for the Advancement of Science (AAAS) is an American international non-profit organization with the stated goals of promoting cooperation among scientists, defending scientific freedom, encouraging scientific respons ...

, discussed Active SETI and whether transmitting a message to possible intelligent extraterrestrials in the Cosmos 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''.

Mark Buchanan Mark Buchanan (born October 31, 1961 in Cleveland, Ohio) is an American outreach physicist and author. He was formerly an editor with the international journal of science ''Nature'', and the popular science magazine ''New Scientist''. He has been a ...

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 Breakthrough Initiatives is a science-based program founded in 2015 and funded by Julia and Yuri Milner, also of Breakthrough Prize, to search for extraterrestrial intelligence over a span of at least 10 years. The program is divided into multiple ...

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 Sir Karl Raimund Popper (28 July 1902 – 17 September 1994) was an Austrian-British philosopher, academic and social commentator. One of the 20th century's most influential philosophers of science, Popper is known for his rejection of the cl ...

criteria for falsifiability, as explained in a 2009

editorial An editorial, or leading article (UK) or leader (UK) is an article written by the senior editorial people or publisher of a newspaper, magazine, or any other written document, often unsigned. Australian and major United States newspapers, suc ...

in '' Nature'', 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 In planetary astronomy and astrobiology, the Rare Earth hypothesis argues that the origin of life and the evolution of biological complexity such as sexually reproducing, multicellular organisms on Earth (and, subsequently, human intelligenc ...

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 Milan M. Ćirković (born 11 March 1971 in Belgrade) is a Serbian astronomer, astrophysicist, philosopher and science book author. He has worked in the fields of astrobiology, global catastrophic risks and future of humanity where he also co-author ...

(who was then research professor at the Astronomical Observatory of Belgrade and a research associate of the Future of Humanity Institute at the University of Oxford) said that Mash was unrealistically over-reliant on excessive abstraction that ignored the

empirical Empirical evidence for a proposition is evidence, i.e. what supports or counters this proposition, that is constituted by or accessible to sense experience or experimental procedure. Empirical evidence is of central importance to the sciences and ...

information available to modern SETI researchers.Ćirković (2012)
p166
/ref>

George Basalla George Basalla (born 1928 in Altoona, Pennsylvania) is an American history of science, historian of science and emeritus, professor emeritus at the University of Delaware. Education and career Basalla completed his Ph.D. in the history of science ...

Emeritus ''Emeritus'' (; female: ''emerita'') is an adjective used to designate a retired chair, professor, pastor, bishop, pope, director, president, prime minister, rabbi, emperor, or other person who has been "permitted to retain as an honorary title ...

Professor of History at the University of Delaware, 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 (and, at least in their later years, Iosif Shklovsky 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, Professor of

Philosophy Philosophy (from , ) is the systematized study of general and fundamental questions, such as those about existence, reason, knowledge, values, mind, and language. Such questions are often posed as problems to be studied or resolved. Some ...

CUNY , mottoeng = The education of free people is the hope of Mankind , budget = $3.6 billion , established = , type = Public university system , chancellor = Fél ...

City College City college may refer to: In the United States * Community college, a type of educational institution sometimes called a ''junior college'' or a ''city college'' in the United States * City College of New York ** 137th Street – City College (IR ...

, asked in 2010 whether SETI is "uncomfortably close to the status of pseudoscience" due to the lack of any clear point at which negative results cause the hypothesis 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 In physics, string theory is a theoretical framework in which the point-like particles of particle physics are replaced by one-dimensional objects called strings. String theory describes how these strings propagate through space and interac ...

, interpretations of quantum mechanics, evolutionary psychology and history (of the 'synthetic' kind done recently by Jared Diamond)", 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 Ufology ( ) is the investigation of unidentified flying objects (UFOs) by people who believe that they may be of extraordinary origins (most frequently of extraterrestrial alien visitors). While there are instances of government, private, and f ...

Stanton Friedman 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 pseudoscience. In a 2016 interview,

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 Avi Loeb 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 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). 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
Frank Drake by astronomer

Andrew Fraknoi Andrew Fraknoi (born 1948) is a retired professor of astronomy recognized for his lifetime of work using everyday language to make astronomy more accessible and popular for both students and the general public. In 2017 Fraknoi retired from his po ...

{{DEFAULTSORT:Seti Astrobiology Distributed computing projects Radio astronomy Interstellar messages