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95 Others see the end as the collapse of a civilization, although they describe that differently. Diamond, for one, defined collapse as a drastic decrease in human population size over a considerable area for an extended time.° That is quite different from the annihilation of a sentient species. Other definitions refer to cultural or political collapse, a loss of morale, or absorp- tion by other civilizations. Our speculations about the longevity of civilizations—ours and others— have been influenced more by the circumstances of our time than by a long view of human history. The catalog of potential civilization-ending disas- ters is tied to our present or near future. Since our transition point of 1960, many commentators have adopted a Standard Pessimist Model, resting on a belief that the problems of our time are uniquely threatening. More advanced technological civilizations, it is assumed, must have passed through the same crisis. From the 1950s through the early 1990s, the threat of nuclear war weighed heavily on public opinion in many countries, provoking deep pes- simism about our near-term future. This strongly influenced those who speculated about extraterrestrial societies. Several argued that interstellar communication and transportation arise simultaneously with the means of extinction; the universe might be littered with the remnants of civilizations that failed to resolve that dilemma. For this rationale to work, commented Brin, there has to be an easily triggered mechanism for destroying civiliza- tions, such as a nuclear winter.’ Sagan claimed that if we find no other civilizations, the most likely explanation is that they destroy themselves before they are advanced enough to establish a high-powered radio-transmitting service. Shklovskii turned away from optimism about contact because he felt that nuclear war was inescapable. As Drake pointed out, this was a political calculation, not a scientific one.* Sagan and astrophysicist William Newman claimed that weapons of mass destruction force on every emerging society a behavioral discontinu- ity. If they were not “aggressive,” they probably would not have developed such weapons; if they do not quickly learn how to control that aggression, they rapidly self-destruct. Those who are as destructive as we are never make it to interstellar expansion, argued Von Hoerner. “They destroy each other before they can go anywhere. We have to solve the question of peace first.” Those who are aggressive would have killed each other or “blown up their planets;” those who survive would be more “gentle, peaceful, and reasonable.” The commentators most dubious about long civilizational lifetimes often have been preoccupied with “stability.” Oliver suggested that a major The Shadow of the Bomb The Shadow of the Bomb