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We are restricted to remote signaling and, of the long-distance techniques available to our technology, radio is by far the best. Radio telescopes are relatively inexpensive; radio signals travel at the speed of light, faster than which nothing can go; and the use of radio for communication is not a short-sighted or anthropocentric activity. Radio represents a large part of the electromagnetic spectrum and any technical civili
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zation anywhere in the Galaxy will have discovered radio early -- just as in the last few centuries we have explored the entire electromagnetic spectrum from short gamma rays to very long radio waves. Advanced civilizations might well use some other means of communication with their peers. But if they wish to communicate with backward or emerging civilizations, there are only a few obvious methods, the chief of which is radio.
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The first serious attempt to listen for possible radio signals from other civilization was carried out at the National Radio Astronomy Observatory in Greenbank. It was organized by Frank Drake, now at Cornel University, and was called Project Ozma, a place very exotic, very distant and very difficult to reach. Drake examined two nearby stars for a few weeks with negative results. Positive results would have been astonishing b
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ecause as we have seen, even rather optimistic estimates of the number of technical civilization in the Galaxy imply that several hundred thousand stars must be examined in order to achieve success by random stellar selection. Since Project Ozma, there have been six or eight other such programs, all at a rather modest level, in the United States, Canada and the Soviet Union. All results have been negative. The total number of
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individual stars examined to date in this way is less than a thousand. We have performed something like one tenth of one percent of the required effort. However, there are signs that much more serious efforts may be mustered in the reasonably near future. Besides, hand in hand with the recent spectacular advances in radio technology, there has been a dramatic increase in the scientific and public respectability of the entire s
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ubject of extraterrestrial life. A clear sign of the new attitude is the Viking missions to Mars, which are to a significant extent dedicated to the search for life on another planet. But along with the burgeoning dedication to a serious search, a slightly negative note has emerged which is nevertheless very interesting. A few scientists have lately asked a curious question: If extraterrestrial intelligence is abundant, why ha
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ve we not already seen its manifestations? Skeptics also ask why there is no clear evidence of extraterrestrial visits to Earth. We have already launched slow and modest interstellar spacecraft.
