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261 Extraterrestrials could visit our neighborhood for reasons that have nothing to do with us. In Arthur C. Clarke’s novel Rendezvous with Rama, a vast alien spacecraft passes through our solar system, using our Sun as a gravitational slingshot. Humans who land on its surface and explore its interior are observed by robotic tenders, but the great machine itself pro- ceeds on its way without stopping—or communicating.* Rees warned that if there are many other civilizations—especially if there are some that are much more advanced—the most epochal happen- ings on Earth would barely register in cosmic history. Our extinction might be a minor event.° In medieval Europe, the Earth was the center of the universe. Then it was our solar system, then our Galaxy. Each time, we turned out to be woefully wrong in our assessment of our self-importance. As Wickramas- inghe said, why should it be different this time?° Another common assumption is that contact is likely to occur during our own moment in time. This seems insensitive to the fact that the universe is vast not only in space but also in history. According to current estimates, the age of the universe is at least three times that of the Earth. Humans appeared only in the latest galactic instant, their radio communication technology only in the most recent nanosecond. Many assume that we will attract the attention of others at this point in our history because of three recent technological developments: radio, television, and radar signals that we radiate outward, nuclear weapons (particularly the electromagnetic pulse produced by an explosion), and spaceflight. However, the wave of significant electromagnetic signals is only about 50 light-years out, steadily weakening with distance. The issue is not only distance, but time. For the first 4 billion years of life on Earth, astronomer Dan Wertheimer pointed out, we did not leak radio at all. Then suddenly for 100 years or so we leak like crazy. Now, if we go digital, we will return to being radio quiet. That leaves a very narrow window for possible detection. The chances of locating alien beings who have just discovered radio are minimal.’ Extraterrestrial searchers would face the same problem. Ernst Mayr offered a fable in which another civilization, discovering the existence of the earth 4.5 billion years ago, began sending signals and continued until 1900 before giving up. They would have proven to their satisfaction that there was no intelligent life here. Our own eighteenth- century ancestors could not have detected twentieth-century television signals, even if they had been sent with the most powerful transmitters of our day.® Temporal Chauvinism Temporal Chauvinism