SETI

The search for extraterrestrial intelligence (SETI) is the scientific search for intelligent extraterrestrial life, 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 going on since the 1980s.

When Fermi asked "Where is everybody?" this became the basis of the Fermi Paradox, which refers to the high probability estimates for the existence of extraterrestrial intelligence (ETI) and the apparent lack of evidence.

The first scientific meeting of the SETI institute had 10 attendees including Frank Drake and Carl Sagan who used the Drake Equation to speculate that the number of civilizations was roughly between 1,000 and 100,000,000 civilizations in the Milky Way galaxy. Conversely, Frank Tipler and John Barrow used pessimistic numbers and speculated that the average number of civilizations in a galaxy is much less than one.

Arthur C. Clarke proposed looking for large bands of satellites called Clarke Belts in distant star systems, considered “technomarkers” (the analogues of “biomarkers”, which indicate the presence of life). This is similar to a Dyson Sphere or other forms of megastructures.

Nikolai Kardashev talked extensively of extraterrestrial intelligence and supercivilizations, thinking that a large unification of civilizations over an extent of one to ten billion light-years with concentration in a certain region has a probability of 60%.

A Bracewell probe is an autonomous interstellar spacecraft with a high level of artificial intelligence designed for communication with one or more alien civilizations. The advantage is that it can communicate with alien cultures more efficiently than a radio message exchange might, but communications protocols would not be able to be quickly updated by their "base of operations". A self-replicating device would greatly speed up a Bracewell probe's search for alien civilizations. Such a probe may outlive the civilization which created and launched it.

Breakthrough Listen is an active SETI with $100 million funding begun in 2015. Founder of modern SETI Frank Drake is one of the scientists on the project's advisory committee. It has a collaboration with TESS (Transiting Exoplanet Survey Satellite) to scan for technosignatures.

SERENDIP (Search for Extraterrestrial Radio Emissions from Nearby Developed Intelligent Populations) is a SETI program that analyzes deep space radio telescope data that it "piggy-backs" off other astronomers using the telescopes.

SETI@home uses distributed computing to analyze signals acquired by the SERENDIP project.

Trivia
The ancients had similar thoughts when looking up to the heavens. Metrodorus of Chios said in the 4th century B.C.: "It seems impossible, in a large field only one shaft of wheat to grow, and in an infinite universe to have only one living world."