Throughout the 1960s Cocconi and Morrison, at Cornell University, employed radio telescopes tuned to the hydrogen frequency to search for an intelligent signal. A similar search was conducted by Frank Drake, head of Project Ozma, so named after the Wizard of Oz. Drake’s programme, which began in 1960, used a 26-metre Tatel radio telescope in the National Radio Astronomy Observatory (NRAO) in West Virginia. Project Ozma searched for radio signals near the hydrogen frequency from two nearby Sun-like stars, Epsilon Eridani (10.2 light years away) and Tau Ceti (11.9 light years away). There were no results after 400 hours listening. During the next thirty years over sixty searches, accumulating over 200,000 search hours, in the USA, the former Soviet Union, Australia, Canada, France, Holland, England, India, Japan and the Argentine, were conducted at various ‘magic’ frequencies. Of these about 90 per cent were conducted on the hydrogen line. One negative search during the 1970s of ten stars on the narrow band 21-cm wavelength was reported by Gerrit L. Verschuur (1980) of the NRAO, who suggested that advanced extraterrestrials might have instituted a series of protected bands for radio astronomy such as the 21-cm wavelength.
While several searches have been funded by governments, others have been financed by private means. Some, the ‘dedicated’ searchers, have diverted radio telescopes to pure SETI work, while other ‘parasitic’ searches have examined data supplied by conventional astronomic research; some have hooked up to disused early warning systems for detecting Soviet missile attacks, while others have relied upon portable receivers which they connect to radio telescopes whenever they can beg a few hours. None have reported contact. Although many searches have encountered many unexplained signals, none have been repeated or independently verified. Usually these unrepeated signals are dismissed as glitches in the receiving equipment. However, irregularities in the ionized gas between various stars can either depress or boost a narrow-band radio signal. Thus a signal that is depressed, and only momentarily boosted, would scarcely count as a repeatable event. If this were the case, then it is possible that many signals are being depressed and some of these one-off signals could be part of a continuous beacon. The only solution is to perform many thousands of repeated searches after a reported signal.
The state-funded Project CETI headed by Josef Shklovskii in the former Soviet Union made no progress after listening to 600 nearby stars, and the investigators eventually gave up. Political hostility in the USA prevented direct funding from NASA from the early days of SETI until 1982. Later, SETI’s status within NASA improved and the SETI Project Office became a fully fledged department. The longest full-time search to date has been undertaken by Bob Dixon of Ohio State University, who began, in the early 1970s, listening at the
1.42 GHz (hydrogen) frequency, also known as the ‘21-centimetre line’. Of significance in SETI’s history is the famous ‘Wow’ signal of August 1977 which was recoding by a technician at Ohio in response to an apparent signal. Unfortunately the signal was not repeated. Before the Ohio telescope was
terminated in 1998 Dixon had extended his search to cover the Waterhole, up to 1.7 GHz. Since 1983 Paul Horowitz, at Harvard, has been searching various ‘magic’ frequencies, but has split his frequencies into very narrow bands, about 0.05 hertz in width. The cost of his research was partly met by a grant from the film producer, Steven Spielberg. After five years of continuous sky survey this search found a handful of candidate radio signals with a narrow bandwidth which are not attributable to natural sources or interference. But they have not been repeated. While non-repeatable data is scientifically worthless it does indicate a need for a more comprehensive search. Horowitz is currently leading Project META (Megachannel Extraterrestrial Assay) at Harvard, which is supported by the Planetary Society.
Two assumptions can be discerned in these radio searches. First, the trans-mitting civilization will be more advanced than us; if they were not, then they would not have the appropriate technology. If they do have the technology, they are very likely to be more advanced as our communicative history is so short. Radio communication on Earth is less than 100 years old and has almost reached technical perfection – a state in which further technical refinements will not improve results. If radio communication can be as good as it can get within such a short time it is likely that other civilizations have either got it perfect or not at all. Second, the transmitting civilization, being more advanced than ours, would do their best to make it easy for us to listen. This is why they are likely to choose one of the various ‘magic’ frequencies in the noise-free area. This assumption provides a powerful heuristic limitation on the scope of the search.
Most proposals for radio searches are committed to receiving information rather than broadcasting messages. This is bound up with the belief that the transmitting civilization will be technologically superior. They will discover us, just as Columbus discovered America; the native Americans did not discover Europe. So instead of sending them signals we should await theirs. It is also more economical with resources to receive signals rather than broadcast. But if they are so much more advanced, what is their point in communicating? And could they communicate even if they are intelligent? They may be like the ancient Greeks; intelligent but lacking the technological means to communicate over long distances. Extraterrestrials outside of our technology threshold may be intelligent but we can have no way of confirming it if they have no access to a radio transmitter.
It should be stressed that persistence, despite repeated failure, is not a sign of dogmatic resistance to falsification. In this respect SETI could be described in Feyerabend’s terms as a research programme requiring breathing space. The technology is in its infancy and only a micro-fraction of the space has been searched. Nevertheless, SETI researchers do resemble the old panhandlers who persistently claimed that the valuable nuggets were to be found in the next search. And, like the panhandlers, they are aware that it will require only one verified find for them to be showered with reward. Drake (Drake and Sobel, 1993: 206) may have overstated resistance to falsification when he said: ‘No
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