Cosmic Connection

by Carl Sagan

  We have been describing a search for signals beamed in our general direction by civilizations interested in communicating with us. We ourselves are not beaming signals in the direction of some specific other star or stars. If all civilizations listened and none transmitted, we would each reach the erroneous conclusion that the Galaxy was unpopulated, except by ourselves. Accordingly, it has been proposed–as an alternative and much more expensive enterprise–that we also “eavesdrop”; that is, tune in on the signals that a civilization uses for its own purposes, such as domestic radio and television transmission, radar surveillance systems, and the like. A large radio telescope devoting half time to a rigorous search for intelligent extraterrestrial signals beamed our way would cost tens of millions of dollars (or rubles) to construct and operate. An array of large radio telescopes, designed to eavesdrop to a distance of some hundreds of lightyears, would cost many billions of dollars.

  In addition, the chance of success in eavesdropping may be slight. One hundred years ago we had no domestic radio and television signals leaking out into space. One hundred years from now the development of tight beam transmission by satellites and cable television and new technologies may mean that again no radio and television signals would be leaking into space. It may be that such signals are detectable only for a few hundred years in the multibillion-year history of a planet. The eavesdropping enterprise, in addition to being expensive, may also have a very small probability of success.

  The situation we find ourselves in is rather curious. There is at least a fair probability that there are many civilizations beaming signals our way. We have the technology to detect these signals out to immense distances–to the other side of the Galaxy. Except for a few back-burner efforts in the United States and the Soviet Union, we–that is, mankind–are not carrying out the search for extraterrestrial intelligence. Such an enterprise is sufficiently exciting and, at last, sufficiently respectable that there would be little difficulty in staffing a radio observatory designed for this purpose with devoted, capable, and innovative scientists. The only obstacle appears to be money.

  While not small change, some tens of millions of dollars (or rubles) is, nevertheless, an amount of money well within the reach of wealthy individuals and foundations. In fact, there is in astronomy a long and proud history of observatories funded by private individuals and foundations: The Lick Observatory, on Mount Hamilton, California, by Mr. Lick (who wanted to build a pyramid, but settled for an observatory–in the base of which he is buried); the Yerkes Observatory in Williams Bay, Wisconsin, by Mr. Yerkes; the Lowell Observatory in Flagstaff, Arizona, by Mr. Lowell; and the Mount Wilson and Mount Palomar Observatories in Southern California, by a foundation established by Mr. Carnegie. Government money will probably be forthcoming for such an enterprise eventually. After all, it costs about the same as the replacement costs of U.S. aircraft shot down over Vietnam in Christmas week, 1972. But a radio telescope designed for communication with extraterrestrial intelligence and an attached institute of exobiology would make a very fitting personal memorial for someone.

  30. If We Succeed

  In considering the problem of interstellar communication, some people are worried. What if a civilization we come into contact with is more advanced than we?

  The history of contact between advanced and backward technological civilizations on Earth is a sorry one. The technically less advanced societies–although they may have superior mathematics or astronomy or poetry or moral precepts–get wiped out. If this is a law of societal natural selection here, why not elsewhere? And in that case, should we not keep quiet?

  There are those who predict a dire catastrophe if we broadcast our presence to another star. The extraterrestrials will come and–eat us, or something equally unpleasant. (Actually, if we are especially tasty, they need only sample one of us, determine what sequence of our amino acids makes us appetizing, and then reconstruct the relevant proteins on their own planet. The high freightage makes us economically, if not gastronomically, unappetizing.) The message aboard Pioneer 10 was criticized by a few because it “gave away” our position in the Galaxy. I very much doubt if we pose any threat to anybody out there. We are the most backward possible civilization able to engage in communication, and the vast spaces between the stars are a kind of natural quarantine, preventing us at any time in the near future from messing around out there.

  But, in any case, it is too late. We have already announced our presence. The initial radio broadcasts, starting with Marconi and reaching significant intensity in the 1920s, have leaked through the ionosphere and are expanding at the velocity of light in a spherical wavefront centered around the Earth. And in that wavefront, an advanced technical civilization can pick up the tinny transmissions of Enrico Caruso arias, the Scopes trial, the 1928 election returns, the big jazz bands. These are the harbingers of the cultures of Earth, our first emissaries to the stars.

  If there are technical civilizations some fifty light-years out, they will just now be detecting these strange, primitive signals. Even if they are poised to respond instantly with the fastest spaceship possible, it will be at least another fifty years before we hear from them. Pioneer 10 will take a million years to cover the same distance.

  It is too late to be shy and hesitant. We have announced our presence to the cosmos–in a backward and groping and unrepresentative manner, to be sure–but here we are!

  The vast distances between the stars imply that there will be no cosmic dialogues by radio transmission. Suppose we receive a signal from a civilization at some likely distance for first contact, such as three hundred light-years. The message says, perhaps, “Hello, you guys; how are you?” Having long been prepared for this moment, we immediately reply, let us say, “Fine, how are you?” The total round-trip communication time would be six hundred years. It’s not what you’d call a snappy conversation.

  Six hundred years ago, the Black Death stalked Europe, the Ming dynasty was just founded, Charles the Wise sat on the French throne, Gregory XI was Pope, and the Aztecs were hanging those who polluted the water and the air. Six hundred years is a long time on Earth. Interstellar radio communication will not be a dialogue. It will be a monologue. The dumb guys hear from the smart guys, as if the astrologer of Charles the Wise were to receive a message from us.

  While the time for radio signals to travel a distance of three hundred light-years is three hundred years, the amount of information that can be conveyed is enormous. In fact, with instrumentation not very much more advanced than our own, essentially all the important insights of our civilization could be transmitted in a few days. It would take three hundred years to get there, but only a few days to be transmitted. But the more lively transmission is in the other direction, from the smarts (them) to the dumbs (us) (see Chapter 31). It is possible that there is a breath-taking repository of galactic knowledge being beamed from several directions at Earth at this moment, advanced text interspersed with primers, so we can learn Galactic, the language of transmission. But we will not hear it if we do not listen for it.

  But how could we possibly decode such a message? European scholars spent more than a century in entirely erroneous attempts to decode Egyptian hieroglyphics before the discovery of the Rosetta Stone and the brilliant attack on its translation by Young and Champollion. Some ancient languages, such as the glyphs of Easter Island, the writings of the Mayas, and some varieties of Cretan script, remain completely undecoded to the present time. Yet they were languages of human beings like ourselves, with common biological instincts and encodings, and distant from us in time by only a few hundreds to a few thousands of years. How can we expect that a civilization vastly more advanced than we, and based entirely upon different biological principles, could ever send a message we could understand?

  The differences in the two cases are intent and intelligence. The objective of the Easter Island glyphs was not to communicate to twentieth-century scientists. It was to communicate to other Easter Island inhabit
ants, or, possibly, to the gods. The idea of a code, at least in the usual military intelligence application, is to make a message difficult to read. But the situation we are considering is the opposite. We are considering not cryptography, but anticryptography, the design by a very intelligent civilization of a message so simple that even civilizations as primitive as ours can understand it.

  The message will be based upon commonalities between the transmitting and receiving civilizations. Those commonalities are, of course, not any spoken or written language or any common, instinctual encoding in our genetic materials, but rather what we truly share in common–the universe around us, science and mathematics. There are schemes in which mathematical propositions are transmitted, conveying such concepts as addition and equality and negation and then working up to more sophisticated concepts. There are schemes in which radio messages are sent, which, from the number of constituent bits, are clearly pictures; when reconstructed as pictures, they can be clearly understood. The plaque on Pioneer 10 is an example of a sort of picture which, transmitted as an object on a spacecraft or as a picture by radio transmission, would be reliably understood by an advanced extraterrestrial civilization. Likewise, similar messages, coming our way, will be understood by us, if we have the wit to listen.

  Some individuals find the absence of a dialogue distressing–as if meaningful dialogues were commonplace on this planet. Philip Morrison, of the Massachusetts Institute of Technology, has pointed out that such cultural monologues are entirely common in the history of mankind; that, for example, the entire cultural patrimony of classical Greece, which has influenced our civilization in a profound way, has traveled in only one direction in time. We have not sent our wisdom to the Greeks. The Greeks have sent their wisdom to us–on paper and parchment, and not by radio waves, but the principle is the same.

  The scientific, logical, cultural, and ethical knowledge to be gained by tuning into galactic transmissions may be, in the long run, the most profound single event in the history of our civilization. There will be information in what we will no longer be able to call the humanities–because our communicants will not be human. There will be a deparochialization of the way we view the cosmos and ourselves. There will be a new perspective on the differences we perceive among ourselves once we grasp the enormous differences that will exist between us and beings elsewhere–beings with whom we have nonetheless a serious commonality of intellectual interest.

  But, at the same time, it is not likely to result in discontinuous change. The information may flutter one day into our radio telescopes at a breathtaking rate of information transfer. The decoding of the message, the understanding of the contents, and the extremely cautious application of what we are taught might take decades or even centuries.

  The cultural shock from the content of the message is likely, in the short run, to be small. The main impact will be the receipt of the message itself. Landing of men on the Moon is now considered, at least in the United States, as such a commonplace and relatively uninteresting occurrence that I think we can say the receipt of a message from an extraterrestrial civilization, a message that will take a long time to decode and understand, will not be very much more disorienting to the average man.

  Eventually, we may wish to respond.

  Why should an advanced society wish to expend the effort to communicate such information to a backward, emerging, novice civilization like our own? I can imagine that they are motivated by benevolence; that during their emerging phases, they were themselves helped along by such messages and that this is a tradition worthy of continuance. There are some science-fiction stories in which the contents of the message are malevolent, in which we receive instructions for the construction of a machine, which we then dutifully build and it then dutifully takes over the Earth. But no one will blindly construct such a machine. No one will implement the instructions contained in an extraterrestrial message until the full theoretical underpinnings and scientific bases of the instructions are well understood. This is one reason why the short-term cultural shock of a message will be small. I do not believe that there is any significant danger from the receipt of such a message, provided the most elementary cautions are adhered to.

  It has been suggested that the contents of the initial message received will contain instructions for avoiding our own self-destruction, a possibly common fate of societies shortly after they reach the technical phase. There are certainly enough nuclear weapons on our planet today to destroy every man, woman, and child many times over. It is proposed that advanced extraterrestrial civilizations, motivated either by altruism or through a selfish interest in maintaining a stimulating set of communicants, convey the information for stabilizing societies. I do not know if this is possible; historical differences between organisms and societies with billions of years of independent evolution would be enormous. But it is a possibility not worth ignoring, this feedback hypothesis that the existence of interstellar communication enlarges the number of civilizations and may be the agency of our own survival. There is another way in which such a feedback process works, even if there are no specific instructions on how to avoid destroying ourselves. There is the matter of time scale. Governments on Earth rarely plan more than five years into the future. Individuals ordinarily make detailed plans for only much shorter times. Even an unsuccessful search for extraterrestrial intelligence, which may take decades or centuries, is a useful example of long-range planning. But think of the consequences of receiving a message that was transmitted three hundred years ago, and a discussion of which will take another six hundred years. Awaiting the answer to our reply requires a continuity of purpose unusual in human institutions. Much of the current ecological catastrophe is due to a grasp of short-term gains and an awesome blindness to long-term disasters. The time scale of interstellar civilizations and discourse with them provides a sense of historical continuity vital for the continuance of our own civilization.

  31. Cables, Drums, and Seashells

  In almost all scientific descriptions of contact between Earth and an extraterrestrial civilization, the extraterrestrial civilization is described as advanced.

  Why advanced? Why aren’t there any primitive civilizations out there, backward fellows poking around, fumbling over interstellar debris, constantly botching things up? Why are we obsessed with advanced civilizations?

  The answer is very simple: The primitive ones don’t talk to us. (The really smart ones may not talk to us, either, but that is a point I’ll come to in a moment.)

  Let us consider contact using radio astronomy. Radio astronomy on Earth is a by-product of the Second World War, when there were strong military pressures for the development of radar. Serious radio astronomy emerged only in the 1950s, major radio telescopes only in the 1960s. If we define an advanced civilization as one able to engage in long-distance radio communication using large radio telescopes, there has been an advanced civilization on our planet for only about ten years. Therefore, any civilization ten years less advanced than we cannot talk to us at all.

  Even rather optimistic estimates of the rate at which advanced technical civilizations emerge in the Galaxy are lower than one every ten years (see Chapter 28). If this is correct, it means that of all the civilizations in the Galaxy able to communicate by radio, there is none as dumb as we. There may be millions of civilizations less advanced than we, but we have no way to make contact with them: They lack the technology to receive or transmit. Objections that the Pioneer 10 message may be too difficult for the recipients to decipher ignores the fact that the recipients must be able to acquire this tiny bit of space debris in interstellar space–a task vastly beyond our present capabilities. If they are advanced enough to capture Pioneer 10 in the dark between the stars, they will, I think, be smart enough to make out its message, which can be read without special hinting by many physicists on as backward a planet as Earth (although, to be sure, those physicists share some genetic and cultural biases and chauvinisms with the authors of t
he message).

  But what about civilizations vastly in advance of our own? The amount of technical progress we have made in the past few hundred years is startling. Not only have entire new technologies developed, but entire new laws of physics and entire new ways of examining the universe have evolved. This intellectual and technological development is continuing. If Earth’s civilization survives, the advance of science and technology will also continue.

  Civilizations hundreds or thousands or millions of years beyond us should have sciences and technologies so far beyond our present capabilities as to be indistinguishable from magic. It is not that what they can do violates the laws of physics; it is that we will not understand how they are able to use the laws of physics to do what they do.

  It is possible that we are so backward and so uninteresting to such civilizations as not to be worthy of contact, or at least of much contact. There may be a few specialists in primitive planetary societies who receive master’s or doctor’s degrees in studying Earth or listening to our raspy radio and television traffic. There may be amateurs–Boy Scouts, radio hams, and the equivalent–who may be interested in developments on Earth. But a civilization a million years in our future is unlikely, I believe, to be very interested in us. There are all those other civilizations a million years in our future for them to talk to.

  Communications between two very advanced civilizations will likely use a science and a technology inaccessible to us. We therefore have no prospect for tuning in on such communications traffic, either accidentally or on purpose.