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231 global warming, and the extinction of species. We need more effort to plan centuries and millennia ahead.“ The search may reveal a multitude of other civilizations of very different ages, with some having histories that reach far back into the galactic past. Norris calculated that the median age of an extraterrestrial intelligent species is about 1 billion years; if there is a confederation of more advanced societies, Oliver speculated, it will have existed for a billion years or more.”! To encompass the possible age of other societies, we would need to embrace geological and astrophysical time. The other side of this coin is that the apparent crises of the moment may seem smaller. One scientist found the present increase in carbon dioxide emissions from burning fossil fuels “irrelevant” on geological timescales.” The Clock of the Long Now Daniel Hillis of the Thinking Machines Corporation proposed a giant mechanical clock, perhaps the size of Stonehenge, that would record time for 10 thousand years by ticking once a year. This monumental timepiece, to be built in the American desert, would be intended to direct people away from current dangerously short attention spans and toward long-term awareness and responsibilities. If a message comes to us from a great distance, we will be learning about the other civilization’s past, not its present. Lago saw astronomers as cosmic archaeologists, digging through the ruins of a previous universe. We see the nearest star system, Alpha Centauri, as it was 4 years ago, the Androm- eda galaxy as it was 25 million years before our time. The whole of the past, from minutes ago to billions of years ago, exists simultaneously. The past travels to us. Any species that tries to communicate across space is also trying to communicate across time. Its message probably will not be heard by its contemporaries, but only by individuals yet unborn. The living can only eavesdrop on the past and call out to a future they will never see. Civiliza- tions can only look into each other’s yesterdays, meeting each other’s ancestors. They can only send messages to the other’s descendants. Extra- terrestrials will learn that, far away and long, ago, on a planet that called itself Earth, there lived a generation of humans who called out to the stars. All this changes, of course, if contact is direct. An Opening into Deep Time