Page Content (OCR)
165 series of calculations about the probability of Earth-like planets, the prob- ability of life arising on them, the probability of the evolution of higher life-forms and the evolution of technology—in effect, an early version of the Drake equation. According to some sources, Fermi came to the conclu- sion that we long ago would have been visited by extraterrestrials if any existed. Drake saw this differently, believing that Fermi had concluded that we don’t know enough to answer the question.’ In 1973, astronomer John Ball proposed a new version of Tsiolkovskii’s idea that we are in a reserve: Aliens have set us aside as part of a wilder- ness area, wildlife sanctuary, or zoo. This “zoo theory” predicted that we will never find them because they do not want to be found and have the technological ability to assure this. Ball added other possibilities: Extrater- restrial civilizations have not yet found us, or they may know we are here but are uninterested in us.° Others later raised objections to the zoo theory. Trefil thought that the odds against any sort of quarantine strategy are insuperably high; all it would take to ruin that strategy is one poacher. We can conceive of a single honest race capable of maintaining the solar system in isolation for ethical reasons, but not of a million other races doing the same thing.’ By the mid-1970s, debates about this question had been intensified by the growing credibility of two ideas: space colonization and interstellar flight. Princeton physicist Gerard O’Neill’s space colony concept, first published in 1974, showed how artificial, inside-out planets could draw on the resources of the Moon and the asteroids to construct new versions of themselves. O’Neill persuaded many people that expanding Humankind throughout the solar system was not only feasible, but economically justifi- able and possibly appealing.* Meanwhile, studies by scientists and engineers were suggesting that interstellar travel could be achieved by a civilization more technologically developed than our own. For some, the conjunction of these ideas strength- ened the belief that more advanced technological species could expand outward to colonize other solar systems. Older civilizations might have done this long ago, yet we see no evidence of their presence. These ideas fed into a backlash against the sweeping claims made by prominent SETI advocates—and the publicity they received. Some scien- tists began arguing that the search was a futile effort that did not merit public funding. To some extent, Casti suggested, this may have been a reaction against the euphoria emerging from the 1971 Byurakan meeting.” “Xenology” faced its first traumatic struggle, between those who seek optimistic excuses for the apparent absence of sentient neighbors and those The Great Debate The Great Debate