Distant Wanderers

If they chose radio, they could easily overcome the universal cacophony of background noise in the electromagnetic microwave region (1,000 to 100,000 megahertz). Just above the terrestrial TV and FM bands, it is relatively quiet. There, only a trace of background radiation from the Big Bang remains. (This is an effect anyone can hear in the form of soft constant static when flipping the dials on an FM radio.) However, the pursuit of ET in the radio spectrum has a short history. Although decades, even centuries earlier, there were many ideas about how to signal or find extraterrestrial civilizations, the genesis of modern SETI really began only some 40 years ago.

In a paper published in Nature in 1959, the Cornell University physicists Giuseppe Cocconi and Philip Morrison suggested that the most effective way of communicating across galactic distances had to be via radio waves. At about the same time, Frank Drake, a young radio astronomer at the National Radio Astronomy Observatory in Green Bank, West Virginia, was working on a pet project named Ozma. (The name came from the mythical Princess Ozma, featured in L. Frank Baum's fabled Land of Oz: a place far, far away, populated with strange and exotic beings.)

NRAO and Associated Universities Inc. The 26 metre (85 foot) Tatel Radio Telescope which was built in 1958.

Drake became the first radio astronomer to attempt to detect interstellar radio transmissions from an extraterrestrial intelligence. On April 8, 1960, he used the novel combination of sensitive new receivers and a 26-metre radio telescope to survey several nearby stars, the first of which was Tau Ceti, an early-morning star in the Cetus constellation some 3.3 parsecs (a parsec being a distance of approximately 3.26 light years) from Earth. Drake picked up a strong signal almost as soon as he began scanning with his single, 100-hertz receiver at the 21-centimetre emission line (1,420 megahertz), which is the emission frequency of cold hydrogen from interstellar space. Yet some weeks later, Drake learned that the "signal" was really terrestrial interference from a secret U.S. military project.

Despite this frustrating experience with radio frequency interference (RFI), Drake's efforts prompted a request from the National Academy of Sciences asking that he organize a 1961 meeting to discuss the budding Search for Extraterrestrial Intelligence, or SETI and shortly thereafter the institute was founded.

As University of Arizona astronomer Neville Woolf points out, looking for evidence of ETI in the radio spectrum could well be futile, because the ETI may have long moved on to more advanced forms of communication, which our own technologically primitive civilization has yet to realize. "Radio SETI is a noble search", says Woolf. "Yet, if we were to look for ETI technologies by looking for giant steam engines, people would laugh because they would say that's old technology. But what's old on the scale of a Universe that's 10 billion years old?