Cosmos - Carl Sagan [165]
My colleague William Newman and I have calculated that if a million years ago a spacefaring civilization with a low population growth rate emerged two hundred light-years away and spread outward, colonizing suitable worlds along the way, their survey starships would be entering our solar system only about now. But a million years is a very long period of time. If the nearest civilization is younger than this, they would not have reached us yet. A sphere two hundred light-years in radius contains 200,000 suns and perhaps a comparable number of worlds suitable for colonization. It is only after 200,000 other worlds have been colonized that, in the usual course of things, our solar system would be accidentally discovered to harbor an indigenous civilization.
What does it mean for a civilization to be a million years old? We have had radio telescopes and spaceships for a few decades; our technical civilization is a few hundred years old, scientific ideas of a modern cast a few thousand, civilization in general a few tens of thousands of years; human beings evolved on this planet only a few million years ago. At anything like our present rate of technical progress, an advanced civilization millions of years old is as much beyond us as we are beyond a bush baby or a macaque. Would we even recognize its presence? Would a society a million years in advance of us be interested in colonization or interstellar spaceflight? People have a finite lifespan for a reason. Enormous progress in the biological and medical sciences might uncover that reason and lead to suitable remedies. Could it be that we are so interested in spaceflight because it is a way of perpetuating ourselves beyond our own lifetimes? Might a civilization composed of essentially immortal beings consider interstellar exploration fundamentally childish? It may be that we have not been visited because the stars are strewn abundantly in the expanse of space, so that before a nearby civilization arrives, it has altered its exploratory motivations or evolved into forms indetectable to us.
A standard motif in science fiction and UFO literature assumes extraterrestrials roughly as capable as we. Perhaps they have a different sort of spaceship or ray gun, but in battle—and science fiction loves to portray battles between civilizations—they and we are rather evenly matched. In fact, there is almost no chance that two galactic civilizations will interact at the same level. In any confrontation, one will always utterly dominate the other. A million years is a great many. If an advanced civilization were to arrive in our solar system, there would be nothing whatever we could do about it. Their science and technology would be far beyond ours. It is pointless to worry about the possible malevolent intentions of an advanced civilization with whom we might make contact. It is more likely that the mere fact they have survived so long means they have learned to live with themselves and others. Perhaps our fears about extraterrestrial contact are merely a projection of our own backwardness, an expression of our guilty conscience about our past history: the ravages that have been visited on civilizations only slightly more backward than we.