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Introduction works or signals of alien minds, their claims were discredited. Finding no confirmed evidence of other intelligences nearby, we have extended our search to the stars. The way we search has been limited to the technical means available at the time. In each phase, observers have been operating at the limits of those technologies; initial results, and extrapolations from them, often proved to be incorrect. This is not unusual in astronomy. Edwin Hubble, speaking in the 1930s, described the uncertainty of exploring the universe with telescopes. Although we know our immediate neighborhood rather intimately, our knowledge fades rapidly with increasing distance. “Eventually, we reach the dim boundary—the utmost limits of our telescopes. There, we measure shadows, and we search among ghostly errors of measurement for land- marks that are scarcely more substantial.”!” At different times, scientific findings and theories have supported or diminished the probability of extraterrestrial life and intelligence. Stars with planets were assumed to be common, then rare, and again common. The complexity and uncertainty of biological evolution was seen by some as making alien life and intelligence highly unlikely; others argued that the universality of physical processes, including evolution, made them aoe noe a probable. These differences are reflected in a prevailing division between those who believe extraterrestrial intelligence exists and those who do not: believers and deniers. As we do not yet have sufficient evidence to prove either case, these views are opinions. Another body of opinion, the agnostics, may lie between, but they are much less likely to be heard. Many advocates of the search are eager to find extraterrestrial intelli- gence, as if contact were sure to change our future in a positive way; one detects a hint of transcendental aspiration. The searchers persist, even in the knowledge that the first detection may not take place in their lifetimes. Others do not want scientists to search for alien intelligence. Particularly striking is the strenuous resistance by some critics to government financing of any search programs, even though the amounts actually sought have been a tiny percentage of public funding for science. Reacting to the pub- licity surrounding the first modern search for alien radio signals, astrono- mer Otto Struve concluded that this effort had divided his colleagues into two camps: those who are all for it and those who regard it as the worst evil of our generation." Since the early years of the Space Age, searching for alien life has been politically accepted as legitimate science. Searching for alien intelligence remains far more controversial. This has not been just a matter of degree, in whicha compromise could be reached. More is at stake than a zero-sum Lee dane budget rivalry. ,