13—The number of planets in our Galaxy on which a technological civilization is now in being = 530,000.

  EXPLORATION

  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?

  Can it be that as one civilization after another ventures out into space, there is intersection and conflict? Even granted that each civilization, in order to get out into space, develops a planetwide political unit, might there not nevertheless be wars among the worlds?

  If we want to wax dramatic, we can imagine civilizations killing each other off with devices that explode whole planets or induce stars to leave the main sequence.

  Yet that seems wrong to me. Civilizations that had managed to suppress undue violence on their home worlds would have learned the value of peace. Surely they would not forget it lightly, once off their planet.

  Besides, it is not likely that the struggle would be so even that, like the fabled Kilkenny cats, the various civilizations would destroy each other until none was left. Those that were more advanced might win out and establish sway over broader and broader sections of the Galaxy. Indeed, the oldest civilizations, intent on imperial growth, might take over scores, hundreds, thousands of habitable planets before those could develop native civilizations, aborting those civilizations forever.

  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 the gap between intelligent species and, however small the portion so transmitted and received, each species is the better and wiser for it. In fact, such cross-fertilization may increase the life expectancy of each civilization that participates.

  VISITS

  And if extraterrestrial civilizations have visited Earth and have, on principle, left us to develop freely and undisturbed, might they have visited Earth so recently that human beings had come into existence and were aware of them?

  All cultures, after all, have tales of beings with supernormal powers who created and guided human beings in primitive days and who taught them various aspects of technology. Can such tales of gods have arisen from the dim memory of visits of extraterrestrials to Earth in ages not too long past? Instead of life having been seeded on the planet from outer space, could technology have been planted here? Might the extraterrestrials not merely have allowed civilization to develop here, but actually helped it?* It is an intriguing thought, but there is no evidence in its favor that is in the least convincing.

  Certainly, human beings need no visitors from outer space in order to be inspired to create legends. Elaborate legends with only the dimmest kernels of truth have been based on such people as Alexander the Great and Charlemagne, who were completely human actors in the historical drama.

  For that matter, even a fictional character such as Sherlock Holmes has been invested with life and reality by millions over the world, and an endless flood of tales is still invented concerning him.

  Secondly, the thought that any form of technology sprang up suddenly in human history, or that any artifact was too complex for the humans of the time, so that the intervention of a more sophisticated culture must be assumed is about as surely wrong as anything can be.

  This dramatic supposition has received its most recent reincarnation in the books of Eric von Däniken. He finds all sorts of ancient works either too enormous (like the pyramids of Egypt) or too mysterious (like markings in the sands of Peru) to be of human manufacture.

  Archeologists, however, are quite convinced that even the pyramids could be built with not more than the techniques available in 2500 B.C., plus human ingenuity and muscle. It is a mistake to believe that the ancients were not every bit as intelligent as we. Their technology was more primitive, but their brains were not.

  Then, too, all that von Däniken finds mysterious and therefore suggestive of extraterrestrial influence archeologists are convinced they can explain, much more convincingly, in a thoroughly earthly manner.

  The conclusion, therefore, is that while there is nothing inconceivable about visits to Earth by extraterrestrial civilizations in the past, even in the near past, there is no acceptable evidence that it has happened, and the evidence deduced for the purpose by various enthusiasts is, as far as we can tell, utterly worthless.

  Yet even the visits of ancient astronauts are not the most dramatic suggestions of the sort. There are endless reports of Earth being visited by extraterrestrial civilizations now.

  Such reports are usually based on the sighting of something that the sighters cannot explain and that they (or someone else on their behalf) explain as representing an interstellar spaceship—often by saying “But what else can it be?” as though their own ignorance is a decisive factor.

  As long as human beings have existed, they have experienced things they could not explain. The more sophisticated a human being is, the more widely experienced, the more likely he or she is to expect the inexplicable and to greet it as an interesting challenge to be investigated soberly, if possible, and without jumping to conclusions. The rule is to seek the simplest and most ordinary explanation consistent with the facts and to allow one’s self to be driven (with greater and greater reluctance) to the more complex and unusual when nothing less will do. And if one is left with no likely explanation at all, then it must be left there; the sophisticated observer has usually learned to live with uncertainty.

  Unsophisticated human beings with limited experience are impatient with puzzles and seek solutions, often pouncing on something they have vaguely heard of if it satisfies an apparently fundamental human need for drama and excitement.

  Thus, mysterious lights or sounds, experienced by people living in a society in which angels and demons are commonplace beliefs, will invariably be interpreted as representing angels and demons—or spirits of the dead, or whatever.

  In the nineteenth century, they were described as airships on occasion. In the days after World War II, when talk of rocketry reached the general public, they became spaceships.

  Thus began the modern craze of “flying saucers” (from an early description in 1947) or, more soberly, “unidentified flying objects,” usually abbreviated as UFOs.

  That there are such things as unidentified flying objects is beyond dispute. Someone who sees airplane lights and has never seen airplane lights before has seen a UFO. Someone who sees the planet Venus, with its image distorted near the horizon or by a mist, and mistakes it for something much closer, has seen a UFO.

  There are thousands of reports of UFOs each year. Many of them are hoaxes; many of them are honest, but capable of a prosaic explanation. A very few of them are honest and entirely mysterious. What of these?

  The honestly mysterious sightings are mysterious usually only in that information is insufficient. How much information can someone gather who sees something he cannot understand and sees it without warning and briefly—and grows excited or frightened in the process?

  Enthusiasts, of course, consider these mysterious sightings to be evidence of extraterrestrial spaceships. They also consider sightings that are by no means mysterious, but are clear mistakes or even hoaxes, to be evidence of extraterrestrial spaceships. Some of them even report having been on board extraterrestrial spaceships.

  There is, however, no reason so far to suppose that any UFO report can represent an extraterrestrial spaceship. An extraterrestrial spaceship is not inconceivable, to be sure, and one may show up tomorrow and will then have to be accepted. But at present there is no acceptable evidence for one.

  Those UFO reports that seem to be most honest and reliable report only mysterious lights. As the reports grow more dramatic, they also grow more unreliable, and all accounts of actual “encounters of the second or third kind” would seem utterly worthless.

  Any extraterrestrials reported are always described as essentially human in form, which is so unlikely a possibility that we can dismiss it out of hand. Descriptions of the ship itself and of the scientific devices of the aliens usually betray a great knowledge of science fiction movies of the more primitive kind and no knowledge whatever of real science.

  In short, then, once we allow the practicality of easy interstellar travel, we are forced to speculate that Earth is being visited or has been visited, is being helped or at least left alone by a Federation of benevolent civilizations.

  Well, perhaps, but none of it sounds compelling. It seems safer to assume that interstellar travel is not easy or practical

  The final conclusion I can come to at the end of the reasoning in this chapter, then, is that extraterrestrial civilizations do exist, probably in great numbers, but that we have not been visited by them, very likely because interstellar distances are too great to be penetrated.

  *This statement must be modified in view of the discovery of Pluto’s satellite. Charon, in 1978. Charon has 1/10 the mass of Pluto, so that Pluto/Charon are much more nearly a double planet than Earth/Moon are. Pluto and Charon are, however, quite small bodies, and the line of argument in this section may still be valid if applied to bodies large enough to be Earthlike.

  *I must stress that the “evidence on hand” is fragmentary and uncertain. At any timetomorrow, perhaps-new evidence may break the chain of logic in this book at any point.

  *It always yields ludicrously short intervals of time when we try to calculate how long it would take a virus, a bacterium, a pair of flies, a pair of mice, a pair of human beings, even a pair of elephants, to produce offspring equal in mass to the entire Earth-assuming free reproduction, unlimited food, and no deaths but by old age. In the case of human beings, if we start with one pair and multiply them at an overall rate of 3.3 percent a year-easily within human capacity the descendants of that one pair will be equal in mass to the entire Earth in 1,600 years

  * Even if we accept tales such as that of Atlantis, we would be dealing with only a slightly earlier version of human civilization.

  * I will discuss the difllcultles of interstellar travel in some detail in the next chapter.

  * This was the central motif of the science fiction movie 2001: A Space Odyssey.

  CHAPTER 11

  Space Exploration

  THE NEXT TARGETS

  If the key to the paradox of the existence of many civilizations in a Universe in which to all appearances we are alone, rests with the presumed difficulty of space exploration, let us examine that problem more closely.

  After all, human beings managed to place the first object in orbit, thus initiating the “Space Age,” only on October 4, 1957. Before the Spage Age was a dozen years old, human beings stood on the Moon. That is a rather promising beginning. Surely we can go farther now.

  In a way, we already have. Instruments have been soft-landed on the surface of Venus and Mars, and photographs and other data have been sent back to Earth. Probes have, without landing, skimmed by the surfaces of Mercury and Jupiter and have, again, returned photographs and other data. As I write, probes are on the way to Saturn and beyond.

  This far penetration of human instruments without the involvement of human beings themselves does not, however, have the glorious ring of accomplishment that we associate with the mystique of exploration. Can human beings themselves, as distinct from their inanimate instruments, move to worlds beyond the Moon?

  Unfortunately, the Moon is not a particularly hopeful precedent. It is so close to Earth that it can’t help but give us a false confidence; it lures us on to underestimate the distances involved in space exploration.

  The Moon, after all, is so close to Earth that it takes only 3 days to reach it, as compared with the 7 weeks it took Columbus to cross the Atlantic Ocean.

  In reaching the Moon, we have made only the most microscopic dent in the true vastness of space. Indeed, we have not really left Earth, since the Moon is as much a slave to Earth’s gravitational influence as an apple on a tree—something Isaac Newton perceived three centuries ago.

  To be sure, there are small bodies that occasionally come to within a few million kilometers of the Earth, 10 to 50 times the distance of the Moon—an occasional asteroid or comet. The nearest sizable body other than the Moon, however, is the planet Venus.

  Even when Venus is at its closest to Earth, it is 40 million kilometers (25 million miles) away in a straight line, and is 105 times the distance of the Moon.