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263 begun reaching out to the stars long before intelligent life emerged on the Earth. The Clarks suggested comparing two stretches of time. The first is from the earliest era that extraterrestrial intelligence could have arisen in our Galaxy to our present. The second stretches from the present to the maximum realistic planning horizon, say 200 years. The first stretch is 10 million times as long as the second. If we assume that the chance per year of being visited by extraterrestrials is constant, we are 10 million times as likely to have been visited in the past as we are to be visited in the immedi- ate future.’ One frequent theme in SETI literature is that we are passing through a crucial historical threshold. As Sagan put it, this is the first time that our technology has reached the precipice of self-destruction, but it also is the first time that we can postpone or avoid destruction by going somewhere off the Earth. These two capabilities make our time extraordinary in con- tradictory ways." O’Neill, too, argued that our moment in time is distinctive. We have arrived within the past few decades at a point where we are able to use radio communication. Within a few more decades, we will be able to spread human presence into the Galaxy. However, O’Neill carried the argument farther: This conjunction of events gives us a very distorted view of what is practical and possible. These capabilities do not ensure that contact will take place in our time." Some SETI literature suggests a sense of urgency, implying that we need to make contact now. The desire for an encounter in one’s own lifetime is understandable. Laser pioneer Charles Townes commented that he would be much more interested in learning of life 5 or 10 light-years away so that there would be some chance of communication during his lifetime than in finding life 100,000 light-years away.'* However, this personal sense of urgency does not change our place in time. Some assume that extraterrestrial intelligences that detected us would share this urgency, acting immediately to make contact. We have no factual basis for this assumption other than our emotions of the moment. If another - a: on a oe civilization discovers us by detecting our signals or by scanning us from its probes, there could be a significant delay between that discovery and our becoming aware of the alien society. The length of that delay would depend on the distance between them and us and on the actions they choose to take. Even the most eager extraterrestrials may not be able to overcome the light speed barrier, either with signals or with machines. Delay might be deliberate. Masterful aliens may wait and observe, particularly if they or their probes are sentient machines, patient and unhurried. The super-Copernican principle, physicist John Wheeler told us, rejects now-centeredness as firmly as Copernicus rejected here-centeredness."° Temporal Chauvinism