“ET, ET, where are you? We are searching just for you.”
That human beings are ‘special’ (or, to put it differently, the world is anthropocentric) is a proposition that is becoming increasingly difficult to accept as the evidence of our insignificant existence piles up. Development of modern astronomy, and radio astronomy in particular, has enabled us to explore hitherto unknown parts of the universe that are invisible to the naked eye and our optical telescopes. Part of the excitement of our “insignificance” in the vast expanse of the universe is the possible existence of other intelligent and sentient beings elsewhere in the universe. Confirmation of extraterrestrial intelligence has long been an elusive goal. While the naysayer may consider it a futile search (many, in fact, consider it “fringe science”), there’s one simple idea that drives this search: that ‘absence of evidence is not evidence of absence’, attributed to Carl Sagan, one of the pioneers in this search.
While many authors and filmmakers have written novels and made movies on extraterrestrial intelligence, the origins of our first scientific and genuine attempt to search the cosmos for extraterrestrial signals date back to the year 1959. In this year two physicists from Cornell University, Giuseppe Cocconi and Philip Morrison, proposed the Morrison-Cocconi Conjecture* – that the most likely frequencies at which to search for extraterrestrial signals are around 1420 MHz (corresponding to the 21 cm line of the neutral hydrogen spectrum or the HI line), which is a very ‘quiet’ part of the spectrum and should be known as a universal marker to a sufficiently advanced civilisation doing radio astronomy. Frank Drake, a Cornell astronomer, conducted the first experimental search in 1960 at the National Radio Astronomy Observatory (NRAO) at Green Bank, West Virginia. It was called Project Ozma. No extraterrestrial signals were detected. Drake later (1961) conceived a method to estimate the number of communicating civilizations that might exist. This statistical method came to be known as the Drake Equation.
Another SETI project was Project Cyclops. Even though the project was never carried out because of the costs, the report – prepared in 1971 by Bernard Oliver and John Billingham – became an important document in SETI literature. The report identified a radio frequency band, called the Water Hole, in which there is minimal noise from natural radio sources and which is, therefore, the band in which to search for intelligent signals from outer space. This is the band between 1420 MHz (Hydrogen line, H, 21 cm) and 1662 MHz (Hydroxyl line, OH, 18 cm), thus the name “Water” Hole. Many projects were carried out in the period from 1972 – 1990, notable amongst them being: the Ohio State University’s Big Ear Observatory in Delaware, Ohio, which detected the famous (and unexplained) “WOW!” signal from the Sagittarius constellation; Interstellar Messages were sent aboard Pioneer 10 and 11 space probes (1972-1973), and then Voyager 1 and 2 space probes (1977). In 1984, the SETI Institute was founded, initially supported by NASA. However, the US Congress withdrew funding for the NASA SETI Targeted Search in 1993.
In 1995, the SETI Institute launched Project Phoenix, funded entirely by private donations. Phoenix used the 210-foot Parkes telescope in Australia, the 140-foot Greenbank Telescope, West Virginia and the 300-metre Arecibo Telescope in Puerto Rico. The project carried out a targeted search of the sky, observing about 800 stars up to about 240 lightyears. No ET signals were found. Efforts such as Optical SETI and [email protected] were also undertaken. The latest in the SETI Institute’s efforts is the Allen Telescope Array (ATA), a joint project of the SETI Institute and the Radio Astronomy Laboratory at the University of California, Berkeley. A large part of the funding is from Paul Allen (the co-founder of Microsoft), hence the name, ‘Allen Telescope Array’.
True, we haven’t found any extraterrestrial signals yet. Does that mean we should give up the search? As the SETI Institute puts it,
“Christopher Columbus did not turn around simply because he failed to find any new lands during his first few days at sea.”
*‘Searching for Interstellar Communications’, GIUSEPPE COCCONI & PHILIP MORRISON, Nature 184, 844-846 (19 September 1959)