Page Content (OCR)
114 The authors of the SETI 2020 report reached exactly the opposite con- clusion in 2002. Estimates of the chance of success, based on the Drake equation, have become more optimistic in the last half-decade, particularly because of the discovery of extrasolar planets and the growing evidence for possible life elsewhere in our solar system.’ In that document, Jill Tarter reviewed how premises had changed since AL Nenia ne Cela ene NTO. Planetary systems are now the rule, not the exception. The scientific view of potential habitats for unknown kinds of life has expanded. More than one hundred different interstellar molecules have been detected, possibly including the simplest amino acid. The process of evolution that led to intelligent life on Earth was more episodic and random than we had believed. One can argue that we were particularly slow in our evolutionary history; elsewhere life may have evolved to intelligence on a shorter timescale, or it may not have evolved at all. While there is a stronger case today for the prevalence of life elsewhere, the scientific community is strongly divided over whether intelligence will always, or even often, accompany the origin of life. Intelligence may be the inevitable result of predator—prey relationships, or it may be a fluke. We are less optimistic now about the longevity of a technological civilization as a radio-transmitting technology. As our sample size is one (ourselves) and we do not know the longevity of that sample, we can only get answers by making assumptions.* Consider the challenges that radio searches face: the vast number of stars to be surveyed and the wide range of possible frequencies on which a signal might be transmitted. Even the best SETI programs are limited in their coverage; no system looks for everything. The vast majority of search space remains unexplored. Search space does not just mean the three-dimensional volume of the Galaxy. As the Jet Propulsion Laboratory’s Michael Klein explained, it is a multidimensional space that includes source location, signal frequency, power level, time of arrival, signal modulation, and polarizations.’ The NASA program, if it had been carried to its planned conclusion, would have explored only one ten-billionth of the cosmic haystack. That haystack is so immense, said Drake, that no theory, no amount of dedica- tion, no endless hours at the typical radio telescope is going to produce a thorough search."” Jill Tarter reminded us of the scale. “We’re going out now 155 light years in a galaxy that’s one hundred thousand light-years in diameter. It’s way too early to get discouraged.”"! A thorough search would mean surveying the entire sky over the plau- sible microwave band. This would require national-level resources, particu- larly if one insists on continuous coverage. Noting that history is littered Should We Continue the Search? the Project Cyclops ‘report of 1972: