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Patience 115 with grand enterprises that tried to plan too much too early, Paul Horowitz argued that this applies to SETI; we know too little.” Searches have looked for continuously present signals; powerful but occasional pulses in the radio band would be undetected by all existing radio telescopes. The NASA search would have missed signals that pulsed on and off or that significantly varied in frequency during observations."* Current SETI systems are not sensitive enough to be able to detect radio and television leakage from the Earth at the distance of the nearest star to the Sun, 4.3 light-years. We could detect early warning radars out to 15 light-years, although we would need at least 100 times more sensitivity to extract the message from the signal."* As scenarios of detection increase in plausibility, they also increase in difficulty.'* The easiest signals to find—beacons—may be the least likely. The most likely—the local communications of a remote civilization—are the hardest to detect. The radio search assumes that a technological civilization will be located nearby only if the number of such civilizations is very large. Yet, there are orders of magnitude of uncertainty in estimates of the average distance between communicative civilizations in our Galaxy. Depending on the assumptions that one plugs into the Drake equation, the nearest commu- nicative civilization is within or beyond our present capability." Clarke thought that it was ridiculously optimistic to expect immediate success in such a search. He wanted to see the whole debate given a decade or two of benign neglect while radio astronomers sift through the torrents of noise pouring down from the sky."” Patience There is reason for long-term optimism. If there are extraterrestrials radi- ating significant radio signals, the probability of our detecting them will continue to improve. The sensitivity of radio telescopes has been doubling every 3 years. Within the next two decades, said Shostak, we'll check out not a few thousand, but two million stars.'* Like politics, searching for others is the art of the possible. Any given phase of the search will use one technology and one strategy to examine one part of the electromagnetic spectrum. If those searches fail, research- ers might reasonably argue that we should move on to another part of the spectrum, perhaps using a different strategy and possibly a different tech- nology. “We should not limit our searching to approaches which seem plausible only in the light of our current technological prowess,” argued Drake. “We should search, where affordable, for almost any physically possible variety of signal . . . the costs of doing business have become much greater.”