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119 What Are We Looking for? As is often the case for exploration, SETI is based on fragmentary knowledge. A group of experts acknowledged that the search is fraught with uncertainties and assumptions. For what evidence are we searching? When and where should we look? Some answers are based on science; what kinds of signals travel well across the Galaxy? Some are based on technology; what is the rela- tive effort of sending spacecraft as compared to signals? Some are based on the supposed behavior of the alien civilization; should we look for something they have deliberately sent us or for unintentional by- products of their technology? All of these questions require at least provisional answers before we can search.** Journalist Joel Achenbach may have overstated the case when he con- cluded that the alien question is likely to remain a matter of “infinite pos- sibilities and zero certainties.” We have narrowed some of the parameters; although many unknowns remain, researchers will continue to chip away at the uncertainty surrounding them. To Sagan, uncertainty served a higher purpose: It drove us to accumulate better data. “Someone has to propose ideas at the boundaries of the plau- sible,” he told an interviewer, “in order to so annoy the experimentalists or observationalists that they’ll be motivated to disprove the idea.”*° Although deliberate searches for evidence of intelligent life will remain the preferred method, a discovery might be serendipitous. Radio signals from space were first discovered inadvertently. The cosmic microwave background was detected by researchers looking for something entirely different; pulsars too were found by accident. As telescope designer Roger Angel saw it, unexpected astronomical discoveries often occurred when observers were pushing new equipment to its limits to accomplish a highly focused goal unrelated to the actual discovery. George Pimentel of the U.S. National Science Foundation highlighted the role of serendipity in the first Congressional hearings on SETI, held in 1978. If extraterrestrial life is found, it will occur in the course of other activities of our best astronomers. The chances of hearing messages are probably best enhanced by devoting as much of our scientific resources as we can afford to the best astronomy of the day, and giving serendipity its chance.*” In this context, it would seem useful to periodically remind astronomers that unusual phenomena might be evidence of alien techno- logical activity. Uncertainty, Ambiguity, and Serendipity Uncertainty, Ambiguity, and Serendipity