The search for extraterrestrial intelligence (SETI) is the collective name for a number of activities people undertake to search for intelligent extraterrestrial life. Some of the most well known projects are run by the SETI Institute. SETI projects use scientific methods to search for intelligent life on other planets. For example, electromagnetic radiation is monitored for signs of transmissions from civilizations on other worlds. The United States government contributed to early SETI projects, but recent work has been primarily funded by private sources.
There are great challenges in searching across the cosmos for a first transmission that could be characterized as intelligent, since its direction, spectrum and method of communication are all unknown beforehand. SETI projects necessarily make assumptions to narrow the search, the foremost being that electromagnetic radiation would be a medium of communication for advanced extraterrestrial life.
As early as 1896, Nikola Tesla suggested that radio could be used to contact extraterrestrial life. In 1899 while investigating atmospheric electricity using a Tesla coil receiver in his Knob Hill lab, Tesla observed repetitive signals, substantially different from the signals noted from storms and Earth noise, that he interpreted as being of extraterrestrial origin. He later recalled the signals appeared in groups of one, two, three, and four clicks together. Tesla thought the signals were coming from Mars. Analysis of Tesla's research has ranged from suggestions that Tesla detected nothing, he simply was misunderstanding the new technology he was working with, to claims that Tesla may have been observing naturally occurring Jovian plasma torus signals. In the early 1900s, Guglielmo Marconi, 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.
Founded in 1994 in response to the US 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 Prof. H. Paul Shuch, 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.
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