Murmurs of Earth

by Carl Sagan

  The double helix winds into the head of a human being, indicating a relationship with the intelligent creature. Various attempts were made to make a better unisex version of the human, but the next-best version looked as much like a gorilla as a human, and so I had to settle for this rather masculine-appearing person. That the DNA is important to us is clear. Of equal importance, a large number placed within the DNA molecule tells of the number of nucleotide pairs, or code bits, in the typical human DNA molecule. This expressed something that couldn’t be described otherwise in such simple artwork—the level of our evolution, and some measure of the level of our intelligence.

  To the creature’s right is a measure of its size, given in terms of the wavelength on which the message was transmitted, 12.6 centimeters. To the creature’s left is a large number giving the population of humans on earth. Below the human is a sketch of the solar system, including the sun and all nine planets, and showing at least the relative sizes of the planets. Planet 3 is offset from the rest toward the human, showing that there is something special about it, that it is, in fact, the home of the human race. Finally, below the solar system and “up” with respect to the Earth is a sketch of a telescope, a reflector focusing rays to a point. Just below this is a number giving the size of the telescope, about 1,000 feet, again in wavelengths. This is both the size of the telescope that sent the message, the Arecibo radio telescope, and the size of the largest radio telescope on Earth. Thus, we described the state of advancement of our technology. Note that if the message is sent over and over, it will seem to flow out of the telescope, making the point that this is the one that is sending the message.

  Carl knew I was constructing this message, and since he was very interested in it, he volunteered to be a proxy extraterrestrial. So one day we went off to the campus faculty club and had a long lunch while I silently laid out the rough drawing of the message in front of him. He cogitated over it, and having grasped the first part of the message, the hardest part, with effort, he proceeded to plow successfully through the whole thing. He had a few suggestions for improvements, but the message worked. I felt full of confidence this time as the computers at Arecibo went to work constructing the commands needed to control the radio transmitters.

  The message was successfully sent on November 16, 1974, at 1:00 AST (Atlantic standard time) as approximately two hundred people watched. It was directed toward the great globular cluster of stars in the constellation Hercules known as Messier 13, some 25,000 light-years away. It will take the message 25,000 years to reach the 300,000 stars of Messier 13, passing perhaps 30 other stars along the way. As the audience looked at the huge transmitting structure 500 feet above them, shimmering in the tropical sun, many sensed that there was something very special about the eerie whine, the sound of a message being transmitted to the stars for the first time. It took 169 seconds to send, and as the warbling of the message changed to the steady tone that marked the end of the message, the emotional impact on many of the audience was evident—there were tears in many eyes and sighs to be heard. Brighter than the fires of our own sun, the message was on its way. The first bits of the message were already passing the orbit of Mars. Only seven hours later the message had passed the orbit of Pluto and was plunging at the speed of light into the darkness of the interstellar space. It is now farther from Earth than the distance to the nearest star.

  Figure 8

  The first written plan of the Voyager message, prepared in Hawaii in January 1977. Note how few pictures we then thought were possible, and how the first guess was that it would take several minutes to send each picture.

  The Arecibo message provoked only two major protests. One was from a few scientists who worried that we hadn’t corrected for the speed of the Earth in space in launching the message. Just as a football quarterback must correct the direction he throws a pass to compensate for his own movement, so we must correct for the fact that we are launching the message from a moving platform, Earth. We are moving about 150 miles a second because of our orbital motion around the center of the Milky Way (our motion around the sun gives us just a measly 18.5 miles a second). This speed is enough to divert the course of the message significantly, through an angle about one-tenth the diameter of the moon. We should correct for this. But we don’t know our speed through space sufficiently accurately to make a very exact correction. In this case, it doesn’t matter because the angular size of Messier 13 is larger than that of the moon, and so the message will arrive at Messier 13 even though we didn’t launch it in quite the right direction.

  The other protest was a serious one, made by Sir Martin Ryle, a Nobel laureate and the Astronomer Royal of England. He wrote with great anxiety that he felt it was very hazardous to reveal our existence and location to the galaxy. For all we know, any creatures out there were malevolent or hungry, and once they knew of us, they might come to attack or eat us. He strongly recommended that no messages of this sort be sent again and even asked the Executive Committee of the International Astronomical Union to approve a resolution condemning such messages. Many other less knowledgeable people had the same concerns.

  The fact is, for better or for worse, we have already announced our presence and location to the universe, and continue to do so every day. There is a sphere of radio transmissions about thirty light-years thick expanding outward at the speed of light, announcing to every star it envelops that the earth is full of people. Our television programs flood space with signals detectable at enormous distances by instruments not much greater than our own. It is a sobering thought that the first news of us may be the outcome of the Super Bowl.

  Our radar transmissions similarly spread the signs of human activity to the far corners of the galaxy. Whether or not Sir Martin Ryle is justified in his anxieties about revealing the location of our civilization is of course a debatable subject. Even so, it is too late to worry about it, so we might as well try to be friendly.

  Finally, it became Voyager’s turn to carry the news of our existence to the cosmos. As we contemplated this message, all the lessons of the past were in our minds. The need for absolute clarity had been learned from the first messages. The fear of sexual content and anxiety about prejudice had surfaced when the Pioneer plaque was unveiled. We heard the calls for ecumenism among the preparers of messages. The pleas that we give special concern to expressing friendship in messages still rang in our ears.

  In late January 1977 there was a meeting of the American Astronomical Society, this time in Honolulu, and I had the pleasure of sharing a delightful cottage with Carl and his family at the Kahala Hilton Hotel. In fact, Carl had reserved this cottage many months earlier because the cottage opened out onto a large pool in which two highly trained dolphins were kept. The cottage is known as the Kawabata Cottage because the Japanese Nobel laureate of that name resided there once. There was something inspiring about sleeping in that cottage with the windows open—one could hear our old friends the dolphins slowly swimming by, breathing, playing with one another. Somehow one had the feeling that they weren’t just some sea creatures but some very witty and intelligent beings living in the next room.

  We were all worrying about the make-up of the Voyager message, because time was short. It had occurred to Carl that perhaps we should just send near duplicates of the Pioneer plaques, thus avoiding any new criticism and the tough problem of selecting a group to construct a brand-new message. We knew that no matter how the group was made up, there would be complaints that someone or some source of wisdom had been neglected. But that seemed a cop-out and an opportunity wasted.

  Carl was very interested in sending some music. In fact, Barney Oliver had suggested sending a tape recording that would make this possible. However, we believed a tape recording wouldn’t have the required longevity.

  Due to our earlier experiences, I was very partial to pictures; they seemed to me the best way to express sophisticated and interesting information clearly. An engraved plaque, as on the Pioneers, is very durable,
but it also is very limited. Maybe just one or two pictures—but what could one say about Earth in just two pictures?

  Then it occurred to me that we could have our cake and eat it too. A phonograph record is an engraved plaque that can carry sounds. But a television picture is just a collection of signals at various frequencies, just as sound is. If we could translate those picture frequencies to ones that could successfully be recorded on a phonograph record, then we could record pictures too. We could have sound and pictures, and in fact combine them to increase greatly the information content of the “plaque.”

  The potential information content was enormous. Our first message had contained something like 1,000 characters. The Pioneer plaques could hold as much as 100,000 characters, although we didn’t use nearly that many. One side of a long-playing phonograph record can hold 10 million characters!

  Thinking this was a good solution, I put together a suggested table of contents for a record. I thought then that we might use one side of a record, and a quick estimate showed that a television picture might take three minutes to send. It seemed a good idea to have a mix of pictures of humans and other aspects of Earth, the sounds that went with the pictures, and some examples of music. This first suggested table of contents, from which the Voyager record grew, is shown in Figure 8.

  One of the most remarkable things about the Voyager record is how we found ways to increase greatly its information content. In the end, as described in the previous essay, it was a two-sided record running at half the normal speed, so that we had two hours of playing time. The television pictures took only four seconds each to play (twelve seconds for color photographs). What started out to be about ten pictures ended up being a hundred and eighteen; and there was a whole catalogue of terrestrial voices and sounds and an hour and a half of music. It would have been a lot easier to choose the pictures if we had been limited to ten! It is tantalizing that the 10 million or so characters of the Voyager record are only as many characters as can be sent in a few seconds on a normal television channel. How rich radio interstellar messages could be!

  Carl liked the idea of a record and successfully sold it to NASA officials. But we had to wait for weeks while all the necessary people in NASA gave approval to the project. By then it was very late, and the construction of the record became a crash project.

  Carl divided up the responsiblities. He carried the ball in arranging the music selections with Tim Ferris; Ann Druyan took over the sounds of earth, and Linda Sagan, the group of greetings in many languages. I quickly assembled as ecumenical and knowledgeable a group as I could, to put together the very challenging picture sequence. Jon Lomberg played a key role in assembling a countless array of candidate pictures from an unbelievable variety of sources including, for example, the Cornell libraries, the libraries of Toronto, the National Geographic Society, and the United Nations, among many others. He helped make selections and did original artwork as necessary. Wendy Gradison helped provide candidate pictures as well as taking care of the onerous task of getting permissions for the use of each individual photograph selected. Amahl Shakhashiri assisted in finding pictures, taking them in some cases, and choosing the ones finally to be used on the record. Herman Eckelmann, our staff photographer, worked as long as needed day after day, both to take special pictures and to make the required prints and slides.

  Valentin Boriakoff played a very special and key role in the success of the picture-sequence recording. When we got right down to it, we found to our surprise that the world just didn’t make machines that would convert the signals of television pictures to the much lower frequency signals which could be recorded on a phonograph record. Although intellectually the idea was simple, the electronics to carry out the operation didn’t seem to exist. Even the vast array of computers we operate at the Arecibo Observatory couldn’t cope with the task. The television industry itself had never had a need for such a capability, and so hadn’t dealt with the problem.

  Valentin is one of our star electronics designers, and we threw the problem to him. Somehow he found a small company in Colorado named Colorado Video, Inc., that had just developed a machine to make the required transformations. They had figured that someday someone would need a machine to send television pictures over telephone lines and the like, and had built the special-purpose computer required. Fortunately their device worked well, and they wanted very much to share in the Voyager record project. They donated the use of their machine and personnel. And so the pictures were successfully recorded at Colorado Video, with Valentin’s help, and in only eight seconds each. Without the work of CVI, the information content of the record, the grand pictures of our earth, would have been very much more limited.

  The short time available to assemble the record caused a regrettable flaw in the end product. The sounds, music, and pictures are all recorded separately instead of being interrelated. How much better it would be if the human voices were next to the appropriate picture, the sound of a motor next to a picture of a car, or the picture of a violin next to the sound of its music. If ever there are recipients of the Voyager record, they will recognize that we certainly are clever enough to arrange such a helpful combination of sounds and pictures. They may also recognize that the lack of such a mix means one thing: those ancient artists who gave them this record (are any of the artists in the pictures?), now dead a billion years, just didn’t have time. Too rushed, no time to organize. Other demands, other commitments. Interstellar messages aren’t the most important things in the civilization of this era. Not yet, anyway. This They will know. Perhaps this will be nothing new to Them. Perhaps there will be a motion we wouldn’t recognize, to Them a nod, as They realize that a billion years before there had been a civilization little different from Theirs.

  References

  * * *

  1. “The Search for Extraterrestrial Intelligence” by Carl Sagan and Frank Drake, Scientific American, Vol. 232, No. 5 (May 1975), pp. 80-89.

  2. “The Arecibo Message of November 1974” by the staff of the National Astronomy and Ionosphere Center, Icarus, Vol. 26 (1975), pp. 462-466.

  3. “On Hands and Knees in Search of Elysium” by Frank Drake, Technology Review, Vol. 78, No. 7 (June 1976), pp. 22-29.

  4. “A Message from Earth” by Carl Sagan, Linda Salzman Sagan, and Frank Drake, Science, Vol. 175 (February 25, 1972), pp. 881-884.

  5. Interstellar Communication: Scientific Perspectives, edited by Cyril Ponnamperuma and A. G. W. Cameron. Boston: Houghton Mifflin, 1974.

  “I think an extraterrestrial message will be much more like a discipline of learned study than like a series of headlines.”

  Philip Morrison

  When Carl Sagan first mentioned the Voyager record to me, I didn’t expect to end up constructing a pictorial message for extraterrestrials. I had written a paper a few years earlier entitled “Some Thoughts on Art, Extraterrestrials, and the Nature of Beauty,” which was printed and distributed by the National Air and Space Museum of the Smithsonian Institution. Referring to the work of various philosophers and aestheticians (such as Pythagoras and Gustav Fechner), I had suggested that some of the aesthetic principles of human art forms, especially music, were based on physical constants and the mathematical order of nature. Thus different intelligent species, observing the same universe, might produce art forms with some similar characteristics. In particular, I had speculated that certain highly ordered structures like fugues (especially those of Bach) might be accessible to minds all though the inhabited galaxy, if they could hear them.

  Sagan, sensing my enthusiasm for a project that actually involved sending music into interstellar space (my excited response to his proposed plan for Voyager took approximately one nanosecond to manifest itself) said, “Consider yourself co-opted,” and asked me to submit ideas and proposals.

  As it turned out, I had a hand in the design of three areas of the record: the choice of music (mostly in the classical selections, especially the Bach and Mozart pieces), the sound mont
age (having worked for some years in the production of radio montages on scientific topics for the Ideas program of the Canadian Broadcasting Corporation, I submitted a proposed montage that suggested and outlined an evolutionary sound sequence—a sequence that was in part incorporated into the sound essay produced by Ann Druyan) and the picture package, where most of my efforts were directed.

  When Frank Drake had decided that a metal phonograph record would be more efficient for information storage than an engraved plaque (such as the Pioneer 10 plaque), he thought that a few pictures might be encoded on the record. The original idea was to have six pictures. It was thought that we might show Earth, the DNA molecule, and a few shots of humans and animals. Since I am a painter with a longstanding professional interest in interstellar communication, Sagan suggested to Frank Drake that my ideas might be useful.

  I arrived at Cornell in early May 1977. In previous weeks, Frank and Carl had contacted various members of the CETI1

  “brain trust,” including such scientists as Philip Morrison, Bernard Oliver, Leslie Orgel and A. G. W. Cameron, men who had been thinking about interstellar communication for a long time. The question was, Which pictures of Earth and humanity should be sent? By comparing responses and seeing what common suggestions were made independently, Drake compiled a list of subjects. At this point, no actual photographs had been selected or even submitted—just general subjects. Frank said to me, “Your job is to find the photographs and construct diagrams if necessary.”