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34 merely looks at what is being accomplished. This definition also means that we don’t have to bother with the intelligence of individuals or even minor groups; the unit of definition is the species.* Jill Tarter refined the definition: The search for intelligent life is a search for a technology that is detectable by our technology. We are looking for a species’ ability to technologically modify its local environment in ways that can be detected over interstellar distances.* This may be only a tiny sampling of the Galaxy’s minds; more numerous examples may be beyond the reach of our detectors. Since the discrediting of Martian canals, the primary medium for detect- ing evidence of alien technology has been radio—first at the interplanetary scale, then at the interstellar. Inventors Nikola Tesla and Guglielmo Marconi not only foresaw the use of radio technology for communication beyond Earth; they believed they had actually detected signals of intelli- gent origin. Tesla was the first to publish this claim, in 1901. Marconi said that he often had received strong signals that seemed to come from some place outside the Earth and might have originated from the stars. He listened for signals from Mars during a transatlantic voyage on his yacht in 1922 and believed that he heard them.® Astronomer David Todd, who had suggested in 1909 that Martians might communicate with Earth by radio waves, organized amateur radio opera- tors to listen during Mars’ close approach to the Earth in August 1924. Although the U.S. Army and Navy declined his request for periods of radio silence, they did instruct radio operators to monitor and report any unusual signals. None were heard.’ In 1932, Karl Jansky of Bell Telephone Laboratories detected strange radio static that he could not attribute to any known source. A year later, he announced his interpretation: The radio emissions were coming from beyond the solar system. Although Jansky’s discovery made the front page of The New York Times, most professional astronomers ignored his pio- neering work.® Radio engineer Grote Reber, who built the first radio telescope dish in his back yard in the late 1930s, conducted the earliest systematic survey of cosmic radio waves. He reported in 1940 that virtually the entire Milky Way was a source of radio “noise.” Again, there was no immediate impact; for nearly a decade, Reber was the world’s only radio astronomer.’ Mind-Stretcher. What if Reber had detected a signal from extraterrestrial intelligence during that decade and sought to publish his findings in an appropriate journal? Given the lack of scientific interest in Jansky and Reber’s other findings, his discovery might have been ignored—even if a journal had agreed to print it. Wartime advances in radio and radar technologies made much more powerful radio telescopes possible, instruments capable of conducting Searching for Intelligence