Extraterrestrial Civilizations (29 page)

Consequently, when the time comes where the weapons the intelligent species develops are so powerful and destructive that they outstrip the capacity of the species to recover and rebuild—the civilization automatically comes to an end.

Homo sapiens
has, it would seem, run the full gamut and now faces a situation whereby a full-scale thermonuclear war could end civilization—perhaps forever.

Even if we avoid a thermonuclear war, the other concomitants of a developing technology that has been allowed to expand without sufficiently intelligent and thoughtful guidance could do us in. An endlessly expanding population combined with dwindling reserves of energy and material resources would inevitably bring about a period of increasing starvation, which might lead to the desperation of thermonuclear war.

The pollution of the environment may diminish the viability of the Earth—by poisoning it with radioactive wastes from our nuclear power plants, or with chemical wastes from our factories and automobiles, or with something as unremarkable as the carbon dioxide from our burning coal and oil (which may induce a runaway greenhouse effect).

Or civilization may just break down in internal violence without the thermonuclear horror, as the constraints of civilization simply fall apart under the strains of increasing populations and the decline in living standards. We see this already in the rising tide of terrorism.

Well, then, suppose that that is how it always is on any world. A civilization arrives, technological advance accelerates until it reaches
the nuclear bomb level, and then civilization dies with a bang, or possibly with a whimper.

Let us further take ourselves as average and say that on every habitable planet with a total potential life-bearing duration of 12 billion years, an intelligent species comes into being after 4,600,000,000 years, and in the course of 600,000 years builds a civilization slowly and ends it quickly—ruining the planet, in the process, to the point where no further civilization can arise upon it.

Since 600,000 is 1/20,000 of 12 billion, we can divide the 650 million habitable planets in our Galaxy by 20,000 and find that only 32,500 of them would be in that 600,000-year period in which a species the intellectual equivalent of
Homo sapiens
is expanding in power.

Judging by the length of time human beings have spent at different stages in their development and taking that as the average, we could suppose that 540 habitable planets bear an intelligent species that, at least in the more advanced parts of the planet, are practicing agriculture and living in cities.

In 270 planets in our Galaxy, intelligent species have developed writing; in 20 planets modern science has developed; in 10 the equivalent of the industrial revolution has taken place; and in 2 nuclear energy has been developed, and those 2 civilizations are, of course, near extinction.

Since our 600,000 years of humanity occur near the middle of the Sun’s lifetime, and since we are taking the human experience as average, then all but 1/20,000 of the habitable planets fall outside that period, half earlier and half later. That means that on about 325 million such planets no intelligent species has as yet appeared, and on 325 million planets there are signs of civilization in ruins. And nowhere is there a planet with a civilization not only alive but substantially farther advanced than we are.

If all this is so, then even though our earlier analysis of hundreds of millions of civilizations arising in our Galaxy is correct, it is no wonder that we haven’t heard from them.

Yet this analysis, while depressing, is perhaps not completely compelling. Contentiousness is not the only factor to be considered in
human beings. There is also an element of cooperation and even selflessness.

If the intelligence of a human being makes it possible for him to remember grievances and to labor to avenge them, it also makes it possible for him to sympathize with the feelings of others, to understand and forgive. Even with a completely hard heart, a human being may appreciate, for purely selfish motives, the advantages of cooperation.

After all, though an instant blow may fell a competitor and make it possible for you to eat all the food immediately present, sharing the supply and combining talents in the search for additional food may improve the long-term chances of fending off starvation.

There are countless examples in human history of unselfish devotion to family, friends, tribe, and even to abstract ideals. Countless men and women have placed any number of considerations ahead of immediate satisfaction of desires—even ahead of life.

And if the unselfish have always represented a minority in human history, their influence has been out of proportion to their numbers.

Even that most contentious of all human activities, organized warfare, could not be carried on at any level beyond the free-for-all melee were it not certain that soldiers would defend each other and routinely risk their lives on behalf of each other.

The result is that, on the whole, the political units of humanity (societies within which violence is placed under severe constraint and is visited with organized punishment) have tended to increase in size and population with time.

The hunting tribes of a few hundred individuals gave way to farming communities, to city-states, to empires of increasing extent. One-sixth of the land area of the world is now under the centralized rule of the Soviet government in Moscow. One-fifth of the world’s population is under the rule of the Chinese government in Peking. One-third of the world’s wealth is under the control of the American government in Washington.

One might suppose that the natural development is toward a political unit that will include the entire planet and all its population and wealth.

There seems precious little sign of this at the moment. The nations of the world recognize no law higher than their own will and may freely go to war with each other if they choose—and some do choose. What’s more, the inner constraints may fail, and civil war or anarchic terrorism at various levels can occur.

It remains a clearly visible fact, though, that since the coming of the nuclear bomb, there has been a growing reluctance to chance war. There have been no wars between major powers since 1945; and no minor war has been allowed to embroil the major powers in active combat.

Again, there is increasing appreciation of the fact that overpopulation, pollution, resource depletion, and human alienation are dangers that affect the entire globe, and that the solutions will have to be undertaken on a global scale. The thought seems to go against the grain, and one can almost hear the grinding of collective teeth in frustration as the peoples of the world face the annoying necessity of having to forget their grievances and suspicions in order that they might learn to cooperate.

Humanity may fail. The forces of violence may overcome those of cooperation; or else we have waited too long and even though we attempt cooperation with all our heart, we can no longer prevent civilization from collapsing under the gathering pressures. However, even if we lose out, it will not be an inevitable or unopposed loss; we will put up a fight.

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 that such a succession of generations could exist. It might even be that a dying civilization might provide for its own succession, either by the genetic engineering of some near-intelligent species, or by the creation of artificial intelligence.

Counting in all the successive civilizations existing on a planet, we might suppose that the average total duration of civilization upon a planet, during the course of its star’s stay on the main sequence, is perhaps 10 million years.

This is a conservative enough estimate. It means that civilization would be present on a planet like Earth for only 1/740 of the time the planet will endure as a home for life after the first civilization has arisen. That means that only one star out of 570,000 shines down on civilization that is now existing.

Remembering our calculation that 390 million civilizations have come into being, we now have a thirteenth figure:

Even a consideration of the mortality of civilizations leaves us with over half a million of them now existing in our own Galaxy. We must, therefore, still ask the question: Where is everybody?

And yet, just because these half-million advanced civilizations are in our own Galaxy, let us not overestimate their closeness to us. They are not our next-door neighbors by any means.

Here on the outskirts of the Galaxy (where we have decided the civilizations must exist) the distance between two neighboring stars that are not connected gravitationally in the form of multiple-star systems is about 7.6 light-years.

If only one star out of 570,000 shines down upon an advanced civilization now existing, the average separation of two civilizations is 7.6 light-years multiplied by the cube root of 570,000. This comes to about 630 light-years.

This is a long distance, and it may be that of all the reasons I have so far advanced as possibly explaining the lack of visits from other civilizations the impracticality of negotiating such distances is the most nearly compelling.
^*
It may well be that every civilization, no matter how advanced, is isolated in its own planetary system and that visits among them are out of the question.

Nevertheless, it is possible to take the view that interstellar travel seems difficult to us only at our present level of technology. A hundred years ago it might have seemed to us that reaching the Moon was a matter of insuperable difficulty; that jet planes and television were mad fantasies. Yet such things are now so common we give them no thought.

Give us another hundred years—or another thousand of the prospective million-year-existence of our civilization—and might not interstellar travel become commonplace and easy?

We’ll discuss the pros and cons later, but for now let us assume that interstellar travel is a reality for the half-million civilizations of the Galaxy and that traveling from planetary system to planetary system offers no difficulties. If that is so, why haven’t they visited us?