The Varieties of Scientific Experience: A Personal View of the Search for God

by Carl Sagan

  So there's nobody to talk to except ourselves, and we hardly do that very well. In that case, if you believe that argument, it would be foolish to make a massive or expensive search for extraterrestrial intelligence because even if this number L were a few decades, the number of civilizations would be only a few, and therefore the distance to the nearest one would be enormously far away.

  Now let's take another route, the optimistic one. And that is, it seems perfectly possible that we are able to solve the issues of technological adolescence that confront us. And even if there's only a small chance of doing that, say, 1 percent, 1 percent of all those civilizations in the Galaxy living for very long periods of time implies a very large number. Suppose that 1 percent of civilizations lived for evolutionary or geological or stellar evolutionary timescales-say, billions of years. If there's only 1 percent that do that, then the average lifetime would be 1 percent of 109 which is 107, so 10 million years would be the value for L. Multiply that by a tenth and the answer would be a million, 106 civilizations in the galaxy, a vastly different story.

  So you can see that while there are significant uncertainties for each of these factors, by far the largest uncertainty, the place we have the least experience (none whatever, as a matter of fact) is in the average lifetime of a technical civilization. And it is this connection of L with the number of civilizations and the distance to the nearest one that in a remarkable way binds up this quite outre subject of extraterrestrial intelligence with the most pressing human concerns. Because it means that the receipt of a message, never mind being able to decode it, from elsewhere would say that L is probably a large number, that someone has been able to survive technological adolescence. It would be knowledge very much worth having.

  If there are a million technical civilizations in the Galaxy, then you can readily calculate to first order, just extracting a cube root, the distance to the nearest civilization. If they are randomly distributed through the Galaxy, and we know how many stars there are in a galaxy, how far to the nearest one? And the answer is, it's just a few hundred light-years away. It's next door. It's not next door as far as visiting, but it's next door as far as radio communication.

  Now, even a few hundred light-years away means that we must not imagine much in the way of dialogue. It's more monologue. They talk, we listen, because otherwise they would say, let us imagine, "Hello. How are you?" and we would say, "Fine, thank you, and you?" and that exchange would take, say, six hundred years. It's not what you might call a snappy conversation.

  On the other hand, it's very clear that one-way transmission of information is something that can be enormously valuable. Aristotle talks to us. We do not, except for spiritualists, talk to Aristotle. And I have grave doubts about the spiritualists. (Although Aristotle is almost never on their list of contacts.)

  Now, let's therefore say a few more words about this idea of radio communication. What we imagine is that beings on a planet of another star know that emerging civilizations will stumble upon radio. It's part of the electromagnetic spectrum; it is, as I will show you in a moment, a clear channel through the Galaxy. The technology is relatively simple and inexpensive. Radio waves travel at the speed of light, faster than which nothing can go, so far as we know. The information that can be transmitted is enormous, not just "Hello, how are you?" Put another way, if an identical system were at the center of the Galaxy and we were here using our present detection technology, we could pick up that signal coming from thousands of light-years away. It gives you an idea of the remarkable power of this technology, which has in fact been only lately brought up to its actual capabilities.

  There is a question of frequency. What channel would you listen on? There's an enormous number of possible radio frequencies. We have here the radio frequency spectrum in gigahertz, thousands of millions of cycles per second, against the noise background from various sources in degrees absolute. And what we see is that at the low frequencies there is a background from charged particles in magnetic fields in the Galaxy, the galactic background. It's noise. And it gets to be very substantial noise.

  This is not where you would want to transmit or receive. At the high-frequency end, there is another source of noise, intrinsic to the quantum nature of radio detectors. And in the middle there is a broad region where the noise is low, and this is the window in which it makes sense to transmit. In this window there are certain spectral lines, for example, of atomic hydrogen, the most abundant atom in the universe, at specific frequencies. So for this reason there is now a very sophisticated search program going on at Harvard, in Massachusetts, a cooperative project with Harvard University and the Planetary Society, a hundred-thousand-member worldwide organization, and it is remarkable that dues and contributions to a private organization are able to maintain by far the most sophisticated search for extraterrestrial intelligence yet attempted. [4]

  fig. 33

  This illustration might convey a sense of how a success would be noted. The slanting line indicates a very weak signal from an extraterrestrial source. You listen at many frequencies for a while and see if there's anything happening. The Planetary Society system was recently upgraded, so that 8.4 million separate channels are being listened to simultaneously. The antenna points to some part of the sky. And some places have peaks. They may be due to radio interference on the Earth, satellites in Earth orbit, automobile ignitions, diathermy machines. But each of those has a particular kind of signature, and it is possible to imagine signals that don't look like any of those things, which the computer immediately would cull out of the noise, leaving no doubt that this was an artificial signal of extraterrestrial origin, even if we had no opportunity, no ability, to understand what it meant.

  Now, as I said, the expectation is that they send and we, newly emerged, the youngest communicative civilization in the Galaxy, we listen. Not the other way around.

  Let me stress that this is the one respect in which our civilization is probably unique in the Galaxy. No one even slightly more ignorant can communicate at all. Let me say this in a better way: A civilization only a few decades behind us would not have radio astronomy and therefore could not tumble to this technique. Or maybe they could tumble to it, but they couldn't manifest it. And anyone, therefore, whom we hear from is likely to be ahead of us, because if they're even a little bit behind us, they can't communicate at all.

  So the most likely situation is communications from beings vastly more advanced than us. And this therefore raises the ques-

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  tion, could we possibly understand what they're saying? What we have to remember here is that if this is an intentional message from them to us, then they can make it easy. They can make allowances for civilizations. And if they do not choose to do that, then we will not understand the message.

  Maybe you would say advanced civilizations communicate with each other by zeta waves. And I'd say, "What is a zeta wave?" And you reply, "It is something fantastic for communication that I can't give you any details about, because it won't be invented for another five thousand years." Well, that's wonderful, and if those fellows can communicate with zeta waves, that's terrific. But if they wish to communicate with us, they will have to wheel out some ancient, creaking radio telescope from the technology museum and use it, because that is all that young civilizations will be able to understand and detect.

  Now, suppose we get a message. What would it be like? Here is a possibility: There would be a powerful beacon or announcement signal, something that makes it very clear that we are unambiguously receiving a message from an advanced civilization. It might, for example, be highly monochromatic; that is, a very narrow radio frequency band pass, and/or it might be a sequence of pulses that could not possibly be of natural origin. For example, a sequence of prime numbers, numbers divisible only by 1 and themselves-1, 2, 3, 5, 7, 11, 13, 17, 19, and so on. There is no natural process that could produce such numbers.

  Then, having established unambiguously that the message was f
rom intelligent beings in space, it is perfectly possible to imagine a vast amount of additional information conveyed in ways that we can understand. For example, it is perfectly possible to transmit pictures. In fact, it's done by radio all the time. That's what your television set does. It is possible to send mathematics. It's very easy. I mean, suppose they set out the numbers-beep, that's one; beep beep, that's two; beep beep beep, that's three-and so on. And then they do (I'm just going to make this up) beep glagga beep wonk beep beep. Well, a few more like that and you decide a glagga means "plus" and wonk means "equal." But suppose they now do beep glagga beep beep wonk beep beep? And then there's some symbol after that. That symbol, that new symbol must mean "false." And you can immediately see that abstract concepts like true and false could be communicated very quickly. And between these two modes-the use of mathematics, which we would, of course, share in common, and the transmission of pictures-it is possible that a very rich message could be conveyed. What that message would be, clearly none of us are in a position to say.

  Now, I would like you to just think about contrasting this open-minded, experimental approach, which consists of some plausibility arguments that no one takes too seriously, with the more traditional approach to intelligent life in space: the one in which there are no experiments, in which there is no withholding of opinion until the evidence is in, in which we are asked merely to take it on faith. The contrast is, in my opinion, very stark. There is quite a different approach in method. And I remind you about how powerfully we were fooled by the Martian canal situation, where passions and emotions were heavily engaged.

  What do they look like? There is a standard Hollywood convention that extraterrestrials look just like us. Well, maybe they have pointy ears or antennae or green skin, but those are minor cosmetic variations. Extraterrestrials and humans are fundamentally the same. Why should that be? Look at the long sequence of stochastic random events that led to our evolution. I mentioned the extinction of the dinosaurs. That's one. Take another: We have ten fingers. And that's why we use base-ten arithmetic. Nothing special about one, two, three, four, five, six, seven, eight, nine, and then one-zero, except we count on our fingers. Why do we have ten fingers? Because we evolved from a Devonian fish that had ten phalanges in its fins. If we evolved from a Devonian fish that had twelve phalanges, then we'd all be doing base-twelve arithmetic, and base-ten arithmetic would be considered only by mathematicians.

  This is true at every level, including biochemical levels, to such an extent that I think it is fair to say-never mind some other planet-if you started the Earth out again and let just these random factors operate, such as when a cosmic ray would strike a chromosome, producing a mutation in the hereditary material, you might wind up with intelligent beings after some thousands of millions of years. You might wind up with creatures of high ethical and artistic or theological accomplishment, But they would not look anything like human beings. We are the products of a unique evolutionary sequence. Unique doesn't mean better; it just means unique. Elsewhere, different environment, different necessity to adapt to changing conditions, a different sequence of random events, including random genetic events, and we should not expect anything like a human being.

  Now, what about religion? What about the idea that we are all made in God's image? Is that also a failure of the imagination? What do we mean when we say we are made in God's image? Do we, for example, imagine that God has nostrils and breathes? If so, what does He breathe? Air? Where is the air? Air with oxygen in it? No other planet in the solar system has oxygen except the Earth. Why restrict God to very few places? Why would He need nostrils? What about a navel? Would God have a navel? What about hair? What about a vermiform appendix? What about toes? Toes are clearly the result of our ancestors' life in the canopy of the high forest, swinging from branch to branch. Very good to have four limbs that can hold on to trees. We just happened to have the toes in this particular transitional moment. Big toe is good for balance; little toe is not good for very much at all. It's just an evolutionary accident. Vermiform appendix? Likewise good for nothing. It's just on its way out.

  Arthur Clarke has said that Christian orthodoxy is too narrow and timid for what is likely to be found in the search for extraterrestrial intelligence. He has said that the doctrine of man made in the image of God is ticking like a time bomb at Christianity's base, set to explode if other intelligent creatures are discovered. I don't in the least agree. I think that the only sense that can be put on the phrase "made in God's image" is that there is a sense of intellectual affinity between us and higher organisms, if such there be.

  The same laws of physics apply everywhere. If we imagine those extraterrestrial beings sending us radio messages, we and they have something in common. We must. The very act of receiving the message means that we have radio technology in common. We have quantum mechanics. We have atomic physics. We have Newtonian gravitation. We can see that those laws of nature apply everywhere in the universe. It's not a question of what your biology is like. It's not a question of the sequence of events that led to you getting a technical civilization. The mere fact that you have a technical civilization means that you have come to grips to some extent with the universe as it really is. And so it is in that sense and in that sense alone, I believe, that it makes sense to talk about such an affinity between advanced beings and ourselves.

  Five

  EXTRATERRESTRIAL

  FOLKLORE: IMPLICATIONS FOR

  THE EVOLUTION OF RELIGION

  I consider the idea of extraterrestrial intelligence a subject of philosophical, scientific, and even historical importance. If we were so lucky as to receive some sign of extraterrestrial intelligence, I think there is little doubt that it would be an extremely significant historical event. And if, on the other hand, we were to make a detailed and comprehensive search to no avail, that would also be something worth knowing It would say something about the rarity and preciousness of intelligent life and again, I believe, would have extremely important and beneficial social consequences. Therefore the search for extraterrestrial life is one of those few circumstances where both a success and a failure would be a success by all standards.

  So I am hardly opposed to the idea of extraterrestrials visiting us. If we ourselves are poking around our solar system, if we are capable, as we are, of sending our own spacecraft not just to the other planets in our solar system but beyond our solar system to the stars, then surely other civilizations, if they exist, thousands or millions of years more advanced than ours, ought to be able to achieve interstellar spaceflight much more readily, much more swiftly.

  And I don't for a moment deny this as a possibility. I would stress that the economy of effort is far greater for radio communication than direct communication by interstellar spacecraft. I would argue that you can broadcast to millions or thousands of millions of worlds simultaneously, speedily, inexpensively, in a way that even for a very advanced civilization would be much more difficult and costly to do via interstellar spacecraft. However, I certainly could not exclude the possibility that the Earth is now or once was visited. But precisely because the stakes in the answer are high, precisely because this is an issue that engages powerful emotions, we would in this case demand only the most scrupulous standards of evidence.

  I want tonight to discuss two modern hypotheses that I think are proper to call folklore, the ancient astronaut hypothesis and the UFO or unidentified flying object hypothesis, and then attempt to connect them with the history of slightly more conventional religions.

  The ancient astronaut hypothesis was popularized most effectively by a Swiss hotelier named Erich von Daniken. And his works, the first of which was called Chariots of the Gods? (the question mark becoming suppressed in subsequent printings), were huge bestsellers in the late 1960s, early 1970s, selling worldwide tens of millions of copies, an enormously successful set of books.

  The fundamental hypothesis of von Daniken was that there is impressed in the archaeology and fol
klore and myth of many civilizations on Earth certain indications of past contact with the Earth by extraterrestrial beings. This is not an absurd proposition on the face of it, but how acceptable the hypothesis is depends on how good the evidence is. And, unfortunately, the standards of evidence were extremely poor, in many cases nonexistent. So to give an example (and I promise I am not burlesquing the argument as I describe it), here is von Daniken's approach to the pyramids of Egypt: The pyramids of Egypt, he said, are constructed of individual blocks, rectangular paral-lelopipeds, each of which weighs twenty tons or thereabouts. "Twenty tons," he said. That's extremely heavy. Individual persons could not lift a twenty-ton block, much less many of them, to make a pyramid. Therefore modern construction equipment is necessary, and in 2000 to 3000 B.C., that could only be of extraterrestrial manufacture. Hence extraterrestrials exist.

  Now, we can recognize that this argument neglects certain facts. If we knew nothing of Egyptian archaeology, we could nevertheless imagine ways in which large numbers of people could build massive edifices. (The Bible, after all, refers to ambitious construction projects, for example the enormous Tower of Babel.) And then when we look at the internal evidence, or even read Herodotus, who alluded to Egyptian pyramid-construction techniques, we find that there is an entirely self-consistent and perfectly natural explanation. In fact, there are many, some of which involve sending rafts up the Nile, and rollers to move the blocks, and the removal of underlying material. There were even inscriptions on a few key blocks that say the equivalent of "My goodness, we did it!" signed "Tiger Team Eleven," which seems an unlikely delight in modest construction by some being who had effortlessly traveled through interstellar space. And we know that the first pyramid that was ever constructed fell down and that the second pyramid, halfway through construction, had the angle of the sides dramatically pared, because they had learned from the example of the first one that fell down. Again, an error of exceeding the angle of repose was unlikely to be made by an extraterrestrial spacefaring civilization.