Extraterrestrial Civilizations - Isaac Asimov [101]
The half-million habitable worlds might all bear civilizations indeed, but all of those civilizations might belong to any of but a dozen different “Galactic nations,” so to speak, maintaining an uneasy peace among themselves. Perhaps the oldest or the mightiest might have managed to take over all the worlds—aborting those civilizations not yet begun, destroying or enslaving those that had gotten a late start—and established a “Galactic Empire.”
But if that is so, why haven’t we been aborted, taken over, enslaved, destroyed? Where are these Galactic Imperial horrors?
Perhaps they are on their way. The Galaxy is so huge that they just haven’t got to us yet.
Surely, that is not very likely. The Galaxy was formed 15 million years ago. Really large stars don’t shine for very many million years before exploding, so that by the time the Galaxy was a billion years old or so, there must have been a growing number of second-generation Sunlike stars in the outskirts. Add another 4 billion years for civilizations to develop, and it is possible that some of them have been out in space and expanding now for 10 billion years.
The Galaxy is about 315,000 light-years in circumference, so to go from any point to the antipodes, even the long way round at the very rim, in either direction, will be a little over 150,000 light-years. That means an expanding civilization would have to travel (on the average) just about the distance from the Earth to the Sun every year, no farther than that, in order to make it around the Galaxy in 10 billion years.
That’s just one civilization; as others are added, the rate of colonization from a growing number of nuclei grows. Even supposing no very great speeds, every corner of the habitable portions of the Galaxy must have been thoroughly explored—provided there has been the development of a practical method for interstellar voyaging.
Then why haven’t they come here?
Can it be they have just overlooked us—somehow missed us in the crowds of stars?
Not very likely. Our Sun is, of course, a Sunlike star, and I doubt if in 10 billion years of looking, a single such star anywhere in the Galaxy would have been overlooked.
Well, then, if interstellar travel is a practical possibility, we must have been visited; and since Earth has not been taken over and settled and our own independent civilization has in no way been interfered with, it cannot have been by Galactic Imperialists.
Civilizations expanding outward may be far more benign. They may, on principle, allow all habitable planets to develop life in their own way. They may, on principle, establish their bases and seek their resources in those planetary systems that lack habitable planets, making use instead of Marslike or Moonlike worlds.
The different civilizations may have formed a Galactic Federation and our planetary system may be a ward of the Federation, so to speak, until such time as a native civilization appears and advances to the point where it qualifies for membership.
Starships may have us under observation, for all we know. The Austrian-born astronomer Thomas Gold (1920–) has suggested, probably in jest, that the first observation vessels may have landed on Earth when it was a new and still sterile planet, and that from the bacterial content of the garbage or wastes left behind, life on Earth began. This is a kind of reincarnation of Arrhenius’s suggestion of the seeding of Earth from extraterrestrial spores.
Is all this possible? Could we imagine civilizations so concerned with other civilizations, and not “taking over”?
Perhaps we might reason that half a million civilizations would approach the Universe in half a million different ways, produce half a million sets of cultures, half a million lines of scientific developments, half a million bodies of arts and literatures and amusements and varieties of communications and understandings. Some of all these may be capable of transmission and reception across