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310 calculations about expansion.'” The closer we are in space and in time, the more intense the competition may be. What we are likely to detect, Dyson speculated, may be a technology run wild rather than a technology firmly under control and supporting the rational needs of a superior intelligence. Assuming interstellar travel at moderate speeds, such a technological cancer could spread over a galaxy in a few million years. The Great Silence may be a warning that we live in a Darwinian universe, one in which only the stealthiest and most aggres- sive species survive.’ We can refine the issue further by eliminating the requirement that interstellar vehicles transport biological organisms. Intelligent machines not only would suffice, they may be preferred. What if Tipler is right in foreseeing relentless expansion throughout the Galaxy by machines programmed to act in their own self-interest? Several science fiction authors have portrayed deadly probes either deliberately or accidentally programmed to destructively home in on new civilizations after they become detectable by their radio transmissions. Although such machines may not be likely, they are in no way inconsistent with natural law. They also are quite consistent with the observed state of silence.'* Clarke dismissed interplanetary warfare as infinitely improbable; it would only arise in the unlikely event of encountering a civilization at a level of technological development similar to our own. “If ships from Earth ever set out to conquer other worlds,” he imagined, “they may find them- selves, at the end of their journeys, in the position of painted war canoes drawing slowly into New York Harbor.”!* The other side of that coin is that we might be unable to defend ourselves against a superior technology. If a race of superbeings moved in, warned philosophy professor Jan Narveson, the survival of mankind on terms at all agreeable to us will be a matter of sheer luck.'® Resistance indeed might be futile. This does not mean that conflict is inevitable among technological civilizations. It may or may not occur, depending on which choices are made. Communication between civilizations could influence those choices. We can hope that their historical experiences have imbued extraterres- trial cultures with the concept of enlightened self-interest, and that interac- tion at the interstellar level does not rest on social Darwinism. However, hope is not a plan. I want to show that we need not be afraid of interstellar contact, for unlike the primitive civilizations on Earth that were overpowered by more Assumptions: After Contact Distance Protects Us