Extraterrestrial Civilizations - Isaac Asimov [99]
Either way, it may be a narrow squeak. We may collapse, having almost saved ourselves. We may survive, after suffering agonies.
From this we might deduce (on the principle of mediocrity) that, on the whole, it is a narrow squeak for all civilizations. Through unpredictable accidents of history, or temperament, or even biology, some civilizations may have less chance than ours does, and some may have more.
If we view our own case as near the balance point, and think of ourselves as equally likely to fail or to survive, then we might suppose that half the civilizations that are established in the Galaxy will survive the kind of crisis we face today.
Of course, the present kind of crisis is not the only deadly crisis that may face a civilization. There may be external dangers—a supernova may explode within a few light-years of a civilization and radiation may seriously damage the gene pool. An asteroid may collide with the planet. The star it circles may have a spasm of instability.
There may be internal dangers, too, that we can’t easily predict since we have not yet reached the stage of civilization where we will be encountering them. For that matter, consider a civilization that has solved all its problems and reached a mild and secure plateau of security; that civilization may then fizzle to destruction out of sheer boredom.
It may be that sooner or later any civilization will come to an end no matter how many problems it solves.
In that case, what would the average duration of each civilization be?
For this question, we have no logical answer and no way of making any reasonable guess. We absolutely don’t know and can’t say.
We might argue that, from the fact that we have not been visited by any advanced civilization, the duration of civilizations must be short.
Before reaching that disheartening conclusion, we might make the experiment of assuming long duration and then seeing whether there can remain any logical reasons for our not having heard from our intellectual cousins among the distant stars. If there remains no reason, no reason at all, why we should not have heard from them, then we will be forced back to the short-duration-of-civilization hypothesis.
In pursuit of this experiment, let us say that the average civilization endures one million years before, for one reason or another, it comes to an end. Why a million years? Because it is a nice round figure and is both a long one in human terms and a short one in planetary terms.
Furthermore, is it fair to make the assumption, as I have been doing, that once a civilization comes to an end, it is a once-and-for-all collapse and that never again does a civilization appear on that planet?
Perhaps not. Even if humanity were to blow itself up and contaminate the land, water, and air with radioactivity, that radioactivity will dwindle with time. Some life may survive. As millions of years pass, the Earth may heal itself and geologic processes may reconcentrate its resources while evolutionary processes spread life outward in new and flourishing varieties. Eventually another intelligent species may arise and develop a civilization.
All the more would this be true if a humane, long-lived society ended its existence not in violence, but because of some social equivalent of old age.
We might easily suppose, then, that within a billion years, a second civilization would come into existence and live out its average lifetime of a million years. There might be, in short, second-generation civilizations, third-generation civilizations, and so on, up to perhaps tenth-generation civilizations before the planet’s star leaves the main sequence.
We have no evidence that this can be so. On Earth, there seems no doubt that our present civilization is a first-generation one. There are no signs whatever of an earlier, prehuman civilization,* and from what we know of the evolutionary history of life on the planet, we can’t see which prehuman living species could possibly have supported such a civilization.
Nevertheless, it is intuitively easy to believe