by Carl Sagan
The information in the upper right-hand portion of the cover is designed to show how pictures are to be constructed from the recorded signals. The top drawing shows the typical signal that occurs at the start of a picture. The picture is made from this signal, which traces the picture as a series of vertical lines, similar to ordinary television (in which the picture is a series of horizontal lines). Picture lines 1, 2, and 3 are noted in binary numbers, and the duration of one of the “picture lines,” about 8 milliseconds, is noted. The drawing immediately below shows how these lines are to be drawn vertically, with a staggered “interlace” to give the correct picture rendition. Immediately below this is a drawing of an entire picture raster, showing that there are 512 vertical lines in a complete picture. Immediately below that is a replica of the first picture on the record to permit the recipients to verify that they are decoding the signals correctly. A circle was used in this picture to insure that the recipients use the correct ratio of horizontal to vertical height in picture reconstruction.
The drawing in the lower left-hand corner of the cover is the pulsar map previously sent as part of the plaques on Pioneers 10 and 11. It shows the location of the solar system with respect to 14 pulsars, whose precise periods are given. The drawing containing two circles in the lower right-hand corner is a drawing of the hydrogen atom in its two lowest states, with a connecting line and digit 1 to indicate that the time interval associated with the transition from one state to the other is to be used as the fundamental time scale, both for the time given on the cover and in the decoded pictures.
Electroplated onto the record’s cover is an ultra-pure source of uranium-238 with a radioactivity of about 0.00026 microcuries. The steady decay of the uranium source into its daughter isotopes makes it a kind of radioactive clock. Half of the uranium-238 will decay in 4.51 billion years. Thus, by examining this two-centimeter diameter area on the record plate and measuring the amount of daughter elements to remaining uranium-238, an extraterrestrial recipient of the Voyager spacecraft could calculate the time elapsed since a spot of uranium was placed aboard the spacecraft. This should be a check on the epoch of launch, which is also described by the pulsar map on the record cover.
Despite these and other impediments, the Voyager record project has attracted and continues to attract substantial interest, most of it favorable. An article in Science News by Jonathan Eberhart began:
Describe the world. Not just that multi-colored ball in the spacecraft photos, but the world—its place in space, its diverse biota, its wide-ranging cultures with their lifestyles, arts and technologies—everything, or at least enough to get the idea across. And do it on one long-playing record.
Oh, there’s one stipulation: Assume not only that your audience doesn’t speak your language, but that it has never even heard of the Earth or the rest of the solar system. An audience that lives, say, on a planet orbiting another star, light-years away from anything you would recognize as home.
After a detailed and entirely accurate account of the record contents Eberhart concluded: “Try it. Make your own list. Or imagine: If you, as an alien, got this message, what would you think?”
Very large numbers of people wrote to ask if a commercially available version of the record might be in the offing. We are still hopeful that such a nonprofit two-record album may be made, even though CBS Records is understandably unsure of how to estimate the sales of such an album.
Most of the comments in the Voyager record project—in the press and in hundreds of letters—were positive and supportive, and encouraged us to think that we had succeeded in communicating something of our vision of the project’s purpose. As with Pioneer 10 and 11, a few individuals were worried that the record would “give away” our position in the Galaxy, as a preliminary to some dire interstellar invasion. But at least for the next million years or so the trajectory of the spacecraft itself will quite clearly indicate that it is from the Sun, to say nothing of the sobering fact that our military radar and commercial television indicate the Earth to be an abode of some form of possibly intelligent life—and these signals travel at the speed of light.
Colman S. von Keviczky, the director of something he calls “The International UFO Galactic Spacecraft-Research and Analytic Network,” is convinced that we already have clear evidence of extraterrestrial visitation and is concerned that our visitors may be confused by our sending greetings into interstellar space. In a letter to the UN Secretary General, a copy of which von Keviczky was kind enough to send to me, he writes: “The world’s military powers have been classified [sic] the UFOs strategic survey as espionage, endangering the national security! In light of these accurate military attitudes, the NASA’s attempt to seek communication with ‘possible’ extraterrestrial intelligence is not only brazen inconsistency but seems to be sheer hypocrisy.”
Technicians mounting the interstellar record on the instrument bay of the Voyager spacecraft.
A few writers also criticized us for presenting only the favorable circumstances of mankind and chided us for not including scenes of famine, devastation, ravaged cities, and nuclear weapons explosions. This is an issue we debated long and hard during our deliberations on repertoire. There is no question that destruction is a characteristic aspect of what we are pleased to call human civilization. But such a message content might be misinterpreted. Might a photo of a thermonuclear explosion be considered by an extraterrestrial civilization as a pathetically feeble but still palpably nasty attempt at threat? Bernard Oliver had the nice idea of showing a human being with arms outstretched to a galaxy, symbolizing our wish to embrace our fellow creatures among the stars. But a comparable ambiguity seemed to me possible here as well; the gesture could be interpreted by an uncharitable recipient as an intent of galactic aggrandizement. Besides, is it a mistake to put our best face to the cosmos? We tried to send our best music. Why not a hopeful rather than a despairing view of humanity and its possible future?
By the middle of June the deadline John Casani had given us had expired—as well as about ten days he had hidden in his hip pocket, knowing there would be last-minute emergencies. The music had been mixed and a master magnetic tape prepared, which contained all the nonpictorial contents of the record. This was combined at CBS with the pictorial information on two wax masters, which Timothy Ferris then hand-carried to Los Angeles where the copper mothers were prepared. So there would be something done directly by the human hand, Ferris had an inscription etched directly on the record, circumscribing the interior ungrooved portion where the record label ordinarily would be. It reads: “To the makers of music, all worlds, all times.” And in place of the label we have photoengraved a photograph of Earth taken from space, to which is added the words “United States of America, Planet Earth.”
The bonded pairs of records on each space vehicle are not heavy, but they have a substantial heft. They glisten, golden, in the sunlight. Encased in aluminum cocoons, they were affixed to the flight spacecraft with, in each case, the stylus and cartridge nearby. Each record in fact consists of two one-sided copper mothers, each 0.02 inches thick, bonded back to back with a 0.01-inch bonding thickness, so that the total thickness of the record is 0.05 inches. It weighs about 1.25 pounds. The record, cover, spider support and mounting bracket weigh about 2.4 pounds. The stylus and cartridge are bracketed to the underside of the spider support. The rendezvous of record and spacecraft occurred at the John F. Kennedy Spaceflight Center at Cape Canaveral, Florida, and is shown in the photograph on this page.
Once the spacecraft were mounted on the top of their Titan III-E Centaur launch boosters they were put through a series of electronic tests to be sure that all was still in working order. All tests were passed, and the day came, August 20, 1977, when the first Voyager was ready to be launched to the planets and the stars. First to leave Earth was Voyager 2. Because of the intricacies of the interplanetary trajectories Voyager 1, although launched later, would arrive at Jupiter earlier. All the authors of this book and
many others connected with the Voyager record were at Cape Canaveral on that day for the launch. It had been an arduous and sometimes thankless task, but a supremely satisfying one as well. We had pushed at immobile bureaucracies and let our many other responsibilities slide. Perhaps the Voyagers would never be recovered by some extraterrestrial society. But making the record had provided us with a unique opportunity to view our planet, our species and our civilization as a whole, and to imagine the moment of contact with some other planet, species and civilization. The Voyager 2 launch was flawless, and it was with a sense of exhilaration mixed with many other emotions that we saw it gracefully penetrate the cloud cover and vanish into the blue sky and the black of space beyond. We kissed and embraced, and many of us cried.
Our concern with time and our sense of the Voyager message as a time capsule is expressed in many places on the record—greetings in Sumerian, Hittite and !Kung, photographs of Kalahari Bushmen, music from New Guinea and from Australian aborigines, and the inclusion of the composition “Flowing Streams,” whose original structure antedates Pythagoras and perhaps goes back to the time of Homer. The Chinese musicologist Chou Wen Chung had hesitated not one moment in selecting from the 5,000-year-old tradition of Chinese music “Flowing Streams” as the single most important piece for inclusion on Voyager. The record itself is an act of preservation of its musical, pictorial and spoken contents.
In researching “Kinds of Flowers” we came upon a charming and powerful tradition about Javanese gamelan music: there is, it is said, a kind of spirit music in the world, continuously but silently playing. When a gamelan orchestra performs, it is merely making audible the present movement of the music of eternity. Perhaps all of the Voyager record can be viewed similarly—as a local and momentary expression of cosmic discourse, an exchange of greetings and music and information among diverse galactic species that has been in progress for billions of years.
Billions of years from now our sun, then a distended red giant star, will have reduced Earth to a charred cinder. But the Voyager record will still be largely intact, in some other remote region of the Milky Way galaxy, preserving a murmur of an ancient civilization that once flourished–perhaps before moving on to greater deeds and other worlds—on the distant planet Earth.
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1 A further discussion of reaction to this aspect of the Pioneer plaques is contained in my earlier book The Cosmic Connection.
References
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von Hoerner, Sebastian, “Universal Music?” Psychology of Music, Vol. 2 (1974), pp. 18-23.
Morrison, Philip, ed., The Search for Extraterrestrial Intelligence: SETI. Washington, D.C.: National Aeronautics and Space Administration, 1977.
Sagan, Carl, ed., Communication with Extraterrestrial Intelligence (CETI). Cambridge, Mass.: M.I.T. Press, 1973.
—–, The Cosmic Connection: An Extraterrestrial Perspective. New York: Doubleday, 1973.
—–, and Frank Drake, “The Search for Extraterrestrial Intelligence,” Scientific American, Vol. 232 (1975), 80-89.
Shklovskii, I. S., and Carl Sagan, Intelligent Life in the Universe. San Francisco: Holden-Day, 1966.
So deep is the conviction that there must be life out there beyond the dark, one thinks that if they are more advanced than ourselves they may come across space at any moment, perhaps in our generation. Later, contemplating the infinity of time, one wonders if perchance their messages came long ago, hurtling into the swamp muck of the steaming coal forests, the bright projectile clambered over by hissing reptiles, and the delicate instruments running mindlessly down with no report.
—Loren Eiseley
The Voyager record, like its celestial chariot, is one more step toward a very great intellectual and technical goal: contact with an extraterrestrial civilization. How we would communicate with extraterrestrial intelligent life and what we might expect from “Them” are topics that have long obsessed the thinkers of exobiology. Ideas about other worlds have filled the air like confetti. Already the earliest thoughts from the primitive era of, yes, the early 1960’s now seem naive. As time has passed, we have seen the power of proposed communication techniques grow explosively. The Voyager record is the ultimate of our “messages”—so far. Even though it has yet to “round the horn” at Jupiter, it too has shown us how to do much better still.
The development of interstellar message techniques began soon after the start of the modern age of the search for extraterrestrial intelligence (SETI). That era began in 1959 with two independent events. At Cornell University, two physicists, Philip Morrison (later to advise on the Voyager record) and Giuseppe Coconni, wondered if perhaps cosmic rays could be used as effective interstellar messengers. While studying the problem, they realized that cosmic rays held little promise after all, but that radio waves could be very effective for interstellar contact. Not only that, they were tremendously excited by their calculation that the developing radio transmission systems and radio telescopes of earth, circa 1959, could communicate over interstellar distances to similar equipment. Recognizing the remarkable threshold in human evolution on which we stood, they published a classic paper in Nature, “Searching for Interstellar Communications,” calling attention to mankind’s abilities. It ended with a statement which still can bring goose pimples: “If signals [interstellar] are present, the means of detecting them is now at hand. Few will deny the profound importance, practical and philosophical, which the detection of interstellar communications would have. We therefore feel that a discriminating search for signals deserves a considerable effort. The probability of success is difficult to estimate; but if we never search, the chance of success is zero.”
Meanwhile, at the National Radio Astronomy Observatory, I had independently made those same calculations, showing that the radio telescopes we were then constructing could detect reasonable signals from the nearest stars. I had already started to assemble the special equipment needed to provide high sensitivity to interstellar signals. This equipment was used in 1960, at Green Bank, West Virginia, in a search for signals from two stars, Tau Ceti and Epsilon Eridani. Both this search, called Project OZMA, and the Morrison/Coconni paper received a great deal of publicity and started considerable ferment in the scientific community. Most people supported the search programs, while a few thought that SETI was premature.
Enough interest was generated that in November 1961 a now-famous conference on SETI was held at Green Bank under the auspices, surprisingly, of the prestigious National Academy of Sciences. Attending was virtually every scientist with a serious interest in SETI—all eleven of them! Not many, perhaps, but they were all very good scientists. So good, in fact, that in the middle of the conference the Nobel Prize was awarded to one attendee, Melvin Calvin. The etiquette for celebrating when a visitor gets the Nobel Prize is not well established, but we took a fling at it. Having been tipped off that this might happen, we had stashed away a supply of champagne in the dormitory basement—no mean task in West Virginia, then a semi-dry state. Emily Post would have been pleased, because it turned out that the celebration, which reverberated through the mountains, was just the right thing. Other attendees at that special occasion included Carl Sagan, Philip Morrison, and Barney Oliver, all of whom much later came to play various roles in the making of the Voyager record.
This was the conference where the equations that remain basic to the SETI problem were first written down. It was calculated that the nearest civilizations might be as far as a thousand light-years away and that almost any we could contact would be far more advanced than we. Interest in the intelligence of dolphins was then at a high pitch thanks to the work of John Lilly, one of the attendees. Lilly astonished and stimulated the assembled scientists with his anecdotes concerning the behavior and wit of dolphins. We were impressed with how diverse intelligent life must be. In fact, so fascinating were the dolphin experiments that when the conference was over, the attendees formed an informal group called the Order of the Dolphin and planned to
keep in contact and exchange ideas on SETI. Eighteen years later, the Order of the Dolphin is still in existence.
There was some discussion about possible means for constructing a message intended to permit easy communication between civilizations that had had no prior contact. Some ideas, seemingly profound at the time, were to transmit such esoterica as the value of π carried to some very large number of decimal points, or perhaps a sequence of prime numbers (numbers that can be divided only by themselves and by the number one). We thought that such messages would be recognized as evidence of intelligent origin and moreover would give a measure of our intelligence by showing how smart we were to be able to calculate such enormous numbers. In retrospect, I must say that these were bad ideas, because the existence of the transmission itself is already sufficient evidence of the existence of an intelligent civilization.
About this time Lingua Cosmica, a book on interstellar codes, was published by Hans Freudenthal, a Yale mathematician. It contained an ingenious method to construct a language by utilizing simple mathematics to establish simple rules and concepts. For example, an equation such as 2 + 3 = 5 and another equation such as 4 + 5 = 9 can be used to establish the meaning of the plus sign and the equal sign. The numbers themselves, of course, can be established by representing them as simply as a series of dots equal to their value. Some of these concepts were used in the early part of the picture sequence of the Voyager record. Freudenthal showed that by using such mathematical equations one could develop quite a sophisticated language—in fact, even an ability in the end to express emotions. As ingenious as it was, Lingua Cosmica was a rather risky method for interstellar communication, because it assumed that the recipients have brains and logic very similar to ours. More than that, if anywhere along the way a lesson in logic was not understood, all subsequent lessons would be gibberish and the correct coding systems would never be established or understood. A simpler unambiguous method was called for.