Patience is bitter, but its fruit is sweet.
Jean-Jacques Rousseau, Emile
In 1991, Drake wrote about his hopes for detecting signals from an ETC: "This discovery, which I fully expect to witness before the year 2000, will profoundly change the world."130 Ten years on, much has happened in SETI research. The field is thriving. But the discovery has not been made. Perhaps Drake was simply being impatient. Perhaps the answer to the Fermi paradox is that ETCs are out there, communicating with each other and maybe even attempting to communicate with us, but that we simply have not listened long enough for our search to bear fruit.
This is the position SETI enthusiasts take, and for good reason. Consider, for example, some of the difficulties the Arecibo telescope has in receiving a signal from an ETC. One is that the Arecibo receiving beam area covers only a small patch of sky at any particular time, so there are millions of slightly different directions in which astronomers can point the telescope. Another is that for each patch of sky there are billions of frequencies to check. Yet another difficulty is that a signal might take the form of a burst rather than a continuous beacon; to detect a burst, Arecibo has to be pointing there at the right time. In short, to detect a radio signal from an ETC, our telescopes must be pointing in the right direction at the right time and tuned to the right frequency. There are trillions of possible combinations of these parameters, of which we have checked only a fraction. If ETCs chose to chatter at each other using lasers, then it is extremely unlikely that Earth would be in the path of any of the beams; billions of civilizations could be out there, talking to each other, and we would not hear them. It seems not unreasonable, then, to say we have not searched long enough. Perhaps we simply have to be patient.131
Some people, however, believe this to be an unsatisfactory resolution of the Fermi paradox. In a sense, the crux of the paradox is that we have been "waiting" for evidence of extraterrestrials for billions of years: they themselves, or their probes, or at least their signals, should already be here. Evidence of their existence, whatever form such evidence might take, should have been here long before mankind began to wonder if other species were out there. Spending a few more decades observing, with admittedly much more powerful technology, is missing the point.
Let us consider it another way. How many ETCs presently inhabit the Galaxy? Sagan and Drake suggested there might be 106 ETCs in our Galaxy at or beyond our present level of technological development (so on average there should be an ETC within 300 light years of Earth).132 A more conservative estimate by Horowitz is there might be 103 advanced ETCs in our Galaxy (so, if they are randomly distributed through space, there will be an ETC within 1000 light years of Earth). If these 103 to 106 civilizations are long-lived — perhaps billions of years old — then they must surely have a Clarke-level of technology (one that, to us, is indistinguishable from magic). Even if they do not want to travel, or find it impossible to travel, surely such civilizations could make it easy for us to see them; why don't they? Alternatively, these civilizations might be short-lived. (Many authors often set parameters in the Drake equation in such a way they arrive at the relation N = L. In other words, the number of civilizations out there right now is equal to their average lifespan.) If there are 1000 civilizations now, and if the rate of formation of technological civilizations has been more or less constant over the history of the Galaxy, then about 10 billion civiliza tions will have lived and died in our Galaxy alone. Is it likely that not one ETC left any record of their hopes, their achievements, their existence? (If true, it is an almost unbearably sad thought.)
We return to the question: where are they — either their craft or their probes or their signals? We should not have to wait for evidence of their existence — the evidence should already be here.
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