Search for Extraterrestrial Life Timeline

Ronald Bracewell proposed in 1960 that advanced civilizations might send autonomous interstellar probes to monitor and communicate with emerging societies, an alternative to radio-based communication (see Bracewell probe).

Image source: Bracewell probe

R. N. Schwartz and Charles Hard Townes published a 1961 paper in Nature titled "Interstellar and Interplanetary Communication by Optical Masers", proposing that lasers could be used for interstellar communication and detection.

The British Interplanetary Society's starship study Project Daedalus in 1978 demonstrated the technical feasibility of sending physical probes between stars, supporting the Bracewell probe approach to interstellar contact.

Image source: Project Daedalus

In 1979, Freitas and Valdes conducted a photographic search of the Earth-Moon triangular libration points L4 and L5 seeking possible orbiting extraterrestrial probes, finding nothing to a detection limit of about 14th magnitude; a second, more comprehensive search followed in 1982.

Image source: Robert Freitas

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 1983, Charles Hard Townes published a detailed study of optical SETI in the Proceedings of the National Academy of Sciences, which revived interest in laser-based searches within the SETI community.

Image source: Charles H. Townes

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 astronomical objects, with emphasis on 53 nearby stars including all visible stars within a 20 light-year radius.

In recognition that any sufficiently advanced interstellar probe near Earth could easily monitor the terrestrial Internet, 'Invitation to ETI' was established by Allen Tough in 1996 as a Web-based SETI experiment inviting spacefaring probes to establish contact with humanity.

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, renewing momentum for optical SETI searches.

In January 2020, two Pulsed All-sky Near-infrared Optical SETI (PANOSETI) project telescopes were installed in the Lick Observatory Astrograph Dome, designed to detect nanosecond optical pulses from across the sky.

In a 2021 preprint, astronomer Michael Hipke described for the first time how one could search for quantum communication transmissions sent by extraterrestrial intelligence using existing telescope and receiver technology.

A 2022 paper by Arjun Berera and Jaime Calderón-Figueroa noted that interstellar quantum communication by other civilizations could be possible and may be advantageous, identifying potential challenges and factors for detecting such technosignatures.

Image source: Timeline of quantum computing and communication

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

Image source: Iosif Shklovsky

In November 1974, a largely symbolic attempt was made at the Arecibo Observatory to send a message to other worlds, beaming a coded message toward the globular cluster M13.

Image source: Arecibo message

In 1978, the NASA SETI program was heavily criticized by Senator William Proxmire, and funding for SETI research was removed from the NASA budget by Congress in 1981; funding was restored in 1982 after Carl Sagan convinced Proxmire of the program's value.

Image source: SETI Institute

In 1980, Carl Sagan, Bruce Murray, and Louis Friedman founded The Planetary Society, which became a major advocate for space exploration and SETI research.

Image source: The Planetary Society

In 1993, philosopher Roy Mash stated that arguments favoring the existence of extraterrestrial intelligence nearly always contain an overt appeal to big numbers combined with covert reliance on generalization from a single instance, concluding the dispute boils down to a conflict of intuitions.

Founded in 1994 in response to the United States Congress cancellation of the NASA SETI program, The SETI League, Incorporated is a membership-supported nonprofit organization with 1,500 members in 62 countries promoting amateur participation through Project Argus stations.

Further interstellar radio messages — 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 toward nearby star systems.

In October 2000, astronomers Iván Almár and Jill Tarter presented the Rio scale to the SETI Permanent Study Group in Rio de Janeiro, an ordinal scale between zero and ten quantifying the impact of any public announcement regarding evidence of extraterrestrial intelligence; it inspired the San Marino Scale (2005) and London Scale (2010) and was revised in 2018.

George Basalla, Emeritus Professor of History at the University of Delaware, argued in 2006 that "extraterrestrials discussed by scientists are as imaginary as the spirits and gods of religion or myth", and was in turn criticized by Milan M. Ćirković.

Massimo Pigliucci 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 would cause the hypothesis of Extraterrestrial Intelligence to be abandoned, before eventually concluding SETI is "almost-science".

Image source: Massimo Pigliucci

In response to critics like Basalla and Mash, Milan M. Ćirković defended SETI's scientific legitimacy in 2012, arguing that the field's methodology and falsifiability place it firmly within mainstream science.

In 2012 it cost around $2 million per year to maintain SETI research at the SETI Institute and around 10 times that to support different SETI activities globally, highlighting how modestly funded the entire endeavor remained.

In a 2016 interview, Jill Tarter pointed out that it is still a misconception that SETI and UFOs are related, emphasizing that SETI searches for verifiable technological signals rather than unexplained sightings.

Image source: Jill Tarter

In September 2016, responding to Stephen Hawking's warnings about contacting alien civilizations, astronomer Seth Shostak sought to allay such concerns, arguing that fears of hostile extraterrestrials were overstated.

Image source: Seth Shostak

Following the publication of the 2021 UFO Report by the U.S. government, the Galileo Project was established to scientifically investigate unidentified aerial phenomena, taking a position distinct from traditional SETI while sharing rigorous scientific methods.

Image source: Galileo project

On May 24, 2023, a test extraterrestrial signal, in the form of a "coded radio signal from Mars", was transmitted to radio telescopes on Earth as part of the 'A Sign in Space' project, allowing the public and scientists to practice decoding a simulated alien transmission.

Image source: Percent sign

In June 2026, the International Academy of Astronautics ratified the first update to the protocol for announcing detections of extraterrestrial intelligence, following years of work by the SETI Permanent Study Group and deliberations at IAA meetings.

Image source: International Academy of Astronautics