Have aliens visited our planet? I have a simple answer, but only if I reframe the question as a simple question.
If by aliens you mean any life forms that originated off earth, it has been suggested that microscopic life forms seeded the earth from somewhere else, perhaps space itself. We may be our own Martians. But I don’t think that is what most people mean by the question. I think they mean something like “Have people from other worlds come to earth?” People? Some would argue that aliens are people too. Certainly Star Trek represents other intelligent life forms as people 99% of the time, in the sense that human actors can play the parts, but I don’t rule out the possibility that intelligent life forms may be very different from us. The English Astronomer, Sir Arthur Eddington said “Not only is the universe stranger than we imagine, it is stranger than we can imagine.” I believe the same is true of life, including intelligent life, on other worlds.
So I ask instead, “Has any extraterrestrial intelligence reached Earth?” I do not refer to intelligent “life,” because I don’t want to rule out artificial intelligence. Are intelligent robots, even self-replicating robots, living or not? Does it matter? It may well be that artificial intelligence is the norm in the universe as a whole and intelligent life forms are only the preliminary.
When I was a nineteen-year-old college student in 1959, I sent the same letter to both Nashville papers. I said that Sputnik was a science fiction challenge too. I questioned how writers could continue speculating about intelligent life in nearby star systems, much less planets in our own solar systems, when we, on the verge of space travel ourselves, had never had any confirmed visits from outer space. It was deemed the best letter of the day in one paper and the best letter of the week in the other.
I did not know at the time that I was raising Fermi’s question:
In 1950 the physicist Enrico Fermi, questioning generous estimates of the number of civilizations in our galaxy famously asked his fellow scientists “Where are they?” Several writers have jumped right from “We are not alone in the universe,” to “Aliens have visited earth.” Actually, there are several steps in between. It is quite possible that intelligent species or their intelligent inventions are common in absolute numbers, since the universe is so vast, yet rare enough that two such groups never, or almost never, meet.
One answer to the question “where are they?” is they have been here, but they have kept themselves well hidden. Yet they seem to have left abundant evidence behind for believers, such as Eric von Daniken in Chariots of the Gods. Another answer is that they are here, but we don’t recognize them because they are so different from us. I doubt that. I believe it is difficult to overlook an intelligence capable of space flight unless it is deliberately hiding.
The simplest explanation for why we can’t find them is that we are alone in our little corner of the universe, but the simplest explanation never completely rules out bizarre alternatives. I will say, though, that for reasons I will mention later, if such a hidden intelligence does exist, or ever existed on earth, it owns the whole galaxy. It originated from one source and we exist only at its sufferance, possibly as its creations. I think it just doesn’t exist. That may be a statement of faith, but it’s the same statement of faith as the belief that if I flip a coin into the air, it will land flat instead of on edge.
Traditional science fiction speaks in awe of men from outer space thousands of years ahead of us. Everything they do is totally mysterious to us. In the words of Arthur C. Clarke, “Any sufficiently advanced technology is indistinguishable from magic.” In the words of the soulless Borg of Star Trek, “resistance is futile” (rhymes with tile). The Borg are typical of belligerent advanced aliens. Often aliens thousands of years ahead of us are depicted as benevolent and condescending.
Thousands of years? Try millions. If the universe is 20 billion years old, could intelligent life have evolved one percent sooner somewhere else than it did here? That would be 200 million years ago. What about one percent later? The earth has been through a lot of changes in 200 million years but if we could go back to the earth of that time, we would find everything we needed to colonize it. The earth of 200 million years from now, without human influence, would no doubt also be eminently habitable. But since we’re here, changing that earth, we may find our continued existence depends on expanding out into space.
If we ever realize Carl Sagan’s dream of contact with intelligences beyond earth, its origin is statistically more likely to be millions of years ahead of ours than thousands. (It could also be millions of years behind ours, but then it would not have developed yet.) I do not assume that every civilization will develop interstellar travel. Still I see no reason that any civilization that does need have a life span less than the life span of the Universe.
Astronomer Sebastian von Hoerner disagrees. Why? Because it is “entirely inconceivable.” This is the argument from personal incredulity, the same argument creationists use when they argue that complex structures like the eye could not have emerged via evolution. The Soviet Astronomer I. S. Shklovskii and the American Carl Sagan collaborated on the book Intelligent Life in The Universe in 1966. Sagan and Shklovskii use von Hoerner’s mathematical model, among others, to calculate the number of civilizations in our galaxy, somewhere between 50,000 and a million.
In the words of Enrico Fermi, “Where are they?” If the lifetime of a civilization from the time it becomes able to communicate across space is measured in thousands of years and the distance between such civilizations is measured in hundreds of light years, perhaps they have simply not had time to reach us. But why haven’t we at least heard their radio signals?
Sagan and Shklovskii both believed it was possible in principle for a civilization to persist indefinitely. Shklovskii believed this was possible only if the civilization were organized on Communist principles. Sagan was able to visualize other alternatives. Yet neither scientist followed this assumption to its logical conclusion.
If there are, by the more “conservative” estimate, 50,000 civilizations in our galaxy, and if only one civilization in 10,000 achieves immortality through interstellar travel, whichever civilization got here first would own the galaxy by now, considering that they would be not thousands but hundreds of millions of years ahead of us.
I am aware that there is a lot of space to occupy, but if a population expands in a sphere around the home star, doubling every thousand years, it could expand a trillion fold in just forty thousand years. Migrating at one per cent of the speed of light, in that time it would occupy a sphere with a radius of 400 light years. It would not even be necessary to find (to them) habitable planets as they go; with a sufficiently advanced technology, they could remake planets to their liking. It has even been suggested that, within the next fifty thousand years, we could remake Jupiter into three hundred earth-like planets. The (to us) aliens might instead choose to live in migrating space habitats, as proposed by Gerald K O’Neil in The High Frontier.
I remember reading that a Soviet astronomer had proposed that the moons of Mars were hollow artificial satellites. A nut case, I thought. Surely if the Martians were putting satellites in orbit millions of years ago they would have been all over our planet by now. (The higher gravity would be a minor inconvenience to such an advanced civilization.) If there were two intelligent life forms in the same solar system then surely, under the assumption of mediocrity, the galaxy must be swarming with civilizations capable of interstellar flight. We would find ourselves in an occupied galaxy.
Then I found out that that nut case was Shklovskii himself. His and Sagan’s book contains a chapter on the assumption of mediocrity. He should have known that artificial satellites around Mars were incompatible with that principle. His speculation has since been disproved.
Rereading von Daniken’s Chariots of the Gods I was struck by his disdain for establishment science. The world is full of unexplained mysteries: the pyramids (How did they build them? Why did they build them?) maps based on continental outlines presumably unknown at the time they were drawn, legends of Gods coming from the sky; he has traveled the earth to find many others. Von Daniken accounts for a wide variety of unanswered questions with a single hypothesis: We have been visited (invaded?) by space aliens. He believes that archaeologists, historians, geologists, etc. have tried to force the facts to fit pre-existing theories when, he impatiently points out, it is obvious that only the bold assertion of alien intervention can account for them. I can see why his book became a best seller in a society obsessed with flying saucers at a time when the youth culture was questioning the establishment in every way.
Yes, bold new ideas have broken us through many a scientific maze, but only if they led down the right path. Far more ideas, bold or not, have lead to dead ends. Carl Sagan rightly pointed out that extraordinary claims require extraordinary proof. Sagan, like most scientists (stodgy old men?) rebukes von Daniken’s claims, but he does not rule out the possibility that aliens have visited us in the past. I do.
My quarrel with von Daniken is not with his imagination but with his lack of imagination. He imagines aliens separated from us by a paper-thin margin of thousands of years when millions are more plausible. He imagines occasional voyages when I believe the norm for space exploration is settlement, consolidating territory, and moving on-the same pattern by which humans occupied the earth. He imagines evidence of such visits in the form of a few bizarre artifacts when I imagine a cacophony of radio signals across the galaxy. He imagines that parallel evolution in alien environments has led to humanoids enough like us, or our recent ancestors, to cross-breed whether in a planned eugenic program or the haphazard manner of white explorers rediscovering lands already occupied by other branches of the human species. Well, he’s got me there. I can’t imagine that. But he also lacks the imagination to understand the endless human ability to create new artifacts, fashion esoteric religions, and depict odd-looking space creatures without alien intervention.
I don’t believe von Daniken’s hypothesis, and similar speculations by UFO enthusiasts and others, can be salvaged. I admit, with Carl Sagan, that “absence of evidence is not evidence of absence,” but I believe that if the enthusiasts were right, the space travelers would be abundant enough and close enough that evidence of their presence would be overwhelming. In that case, the cosmos would be largely closed to us. I believe the human species itself is intelligent enough and strange enough to account for all manner of weird phenomena. It is we who will be the aliens establishing our presence on nearby worlds around neighboring stars.