Search for Extraterrestrial Intelligence (SETI) is a term most commonly used in connection with searches for artificial radio signals from intelligence beyond Earth using radio telescopes. Although early radio pioneers, including Nikola Tesla and Guglielmo Marconi, believed they had detected such signals, the modern scientific search began with Frank Drake's Project Ozma in April 1960. SETI became a small NASA research and development program during the 1970s–80s and was briefly operational for one year before Congress terminated it in 1993. The search continued in the twenty-first century in privately funded programs around the world.
Interest in SETI was fueled by rising belief in the possibility of extraterrestrial intelligence at the dawn of the space age. In 1959 Cornell physicists Giuseppe Cocconi and Philip Morrison published a seminal article “Searching for Interstellar Communications” in Nature. On technical grounds they suggested that such communications would most likely take place in the radio portion of the electromagnetic spectrum. They suggested further that searches should take place at 21 cm wavelengths, the 1420 MHz radio emission of neutral hydrogen, the most abundant element in the universe. This was the first of several “magic frequencies” that became prominent in the SETI literature of the twentieth century.
Frank Drake's first search, with an 85 ft radio telescope at the National Radio Astronomy Observatory in Green Bank, West Virginia, employed the 21 cm strategy. It was unsuccessful but precipitated a conference on the subject the following year at Green Bank, the first of many such conferences held throughout the following decades. In the Soviet Union, radio astronomer I. S. Shklovskii became the champion of SETI in the 1960s, and a group of Soviet astronomers began their own series of observations. Shklovskii and Carl Sagan's book, Intelligent Life in the Universe published in 1966, became the foundational book for SETI enthusiasts for the remainder of the century.
SETI as a research program took a major step forward with NASA's increasing interest in the 1970s. Led by John Billingham at NASA's Ames Research Center in California, NASA sponsored various studies on the problem, most notably those led by Bernard M. Oliver in 1971 and by Philip Morrison in 1975–76. Oliver and Billingham's Project Cyclops study laid much of the technical groundwork for SETI, while the landmark volume The Search for Extraterrestrial Intelligence, edited by Morrison et al., gave the field its name and, more important, provided the rationale for SETI as a NASA program.
With funding at the level of about $1.5 million per year, in 1983 NASA Ames Research Center and Jet Propulsion Laboratory (JPL) embarked on a program to build the instrumentation necessary for a systematic SETI effort. Ames concentrated on a “targeted search” of about 1,000 solar-type stars within 100 light-years, using the giant radio telescope at Arecibo, Puerto Rico, while JPL employed an “all-sky survey” approach, using the 34 m antennas of NASA's Deep Space Network. Ames proposed to cover the 1–3 GHz range of frequencies for its search, while JPL would cover 1–10 GHz. The central effort in searching these billions of channels was the construction of “multi-channel spectrum analyzers,” capable of covering millions of channels simultaneously and analyzing them for unusual signals. The NASA program became operational on 12 October 1992, symbolically the quincentennial of Columbus's landfall in the New World. Observations using both strategies continued for only one year, when Congress terminated the entire NASA SETI effort as part of budget cuts. NASA excluded SETI from its efforts in astrobiology.
The targeted search continued under the privately funded SETI Institute. Several other observational programs continued around the world, amid debate on the chances of success. Critics point out that no definitive signal has been received from the proposed extraterrestrials after 45 years of searching. Optimists insist that only a small portion of Earth's galaxy has been searched, and that a successful detection would be the greatest discovery in the history of science.
SETI has gone through several crises that have raised questions about the validity of its program and, beyond that, of humankind's place in the universe. Most notably is the so-called Fermi paradox, which points out that if extraterrestrial civilizations are widespread, and given the time scales of millions of years during which they could have undertaken interstellar travel, they should be here. They are not here (Unidentified Flying Object reports notwithstanding), therefore they do not exist. There are many answers to this paradox, but it is an argument that must be taken seriously. On such arguments hinge humankind's place and destiny in the cosmos, with implications for philosophy, religion, and other human endeavors.
See also: Astrobiology
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