THE CODEBREAKERS

by DAVID KAHN

  Fortunately, “just in the most favored radio region,” Cocconi and Morrison pointed out, “there lies a unique, objective standard of frequency, which must be known to every observer in the universe.” This is the so-called radio emission line of neutral hydrogen, only discovered by man in 1951. For physical reasons, the axis of the spinning of the hydrogen electron around its nucleus wobbles, or precesses, at the rate of 1,420,405,752 times a second. Out in space, individual hydrogen atoms occasionally collide with one another. This gives them a bit of extra energy, which they later cast off in the form of an electromagnetic wave vibrating at the same rate as the precession of the spin axis. This is a radio wave of 1,420,405,752 cycles per second, or roughly 1,420 megacycles. Since all electromagnetic waves travel at the same speed, this frequency corresponds to a wavelength of 21 centimeters, or 8½ inches. Vast clouds of hydrogen float in the galaxy, and all the individual atomic emissions combine into a steady hum of radio noise at that frequency, or “station,” on the celestial dial. In a sense, this produces a homing beacon, a standard landmark in the radio range of the electromagnetic spectrum. “Therefore we think it most promising to search in the neighborhood of 1420 Mc/ sec,” the two physicists wrote. Not directly on the hydrogen emission line, for anyone foolish enough to send his signals right at that frequency would have them jammed by the hydrogen noise, but at frequencies nearby, or perhaps at double or half that frequency. The listening frequencies should be relatively free of cosmic radio noise, or static, which stars and nebula generate just as they generate light and heat in other parts of the electromagnetic spectrum.

  The next question to be faced in the process of narrowing down the potential channels is: Where are the broadcasts likely to come from? It is not practicable simply to tune a receiver to 1,420 megacycles and start listening for a signal from anywhere in the sky. Cosmic noise from all over space would drown it out. Rather, any searchers would have to direct their antennae at a possible sender to better pick up any signals—just as a portable radio plays louder when its antenna is pointed at the transmitter. The question of “where” really amounted to a consideration of the stars that were likely to have planets that may have evolved life. This meant long-lived, slow-turning stars rather like the sun. Naturally, the nearer stars would be considered first. Many of the 45 that lie within 16 light-years of the solar system must be excluded because they do not meet the conditions. The nearest star, Alpha Centauri, is actually a triple star—three stars revolving around one another—for which an orbit with a habitable life-zone seems most unlikely. In the neighborhood of the solar system, then, only a dozen or so stars met the requirements. Some of them, however, lay directly against a background of stars that produced a great deal of cosmic noise, which meant that it would be extra hard to detect any signals from them. Ruling these out left two nearby stars as the most likely contenders: Tau Ceti, in the constellation of the Whale, and Epsilon Eridani, in the constellation of the River Eridanus. Both are rather smaller than the sun, with one third its luminosity, but both, like the sun, are long-lived and slow-turning. These conclusions were reached independently by a number of theoreticians, including Drake, Cocconi and Morrison, and Su-Shu Huang, who first formulated the concept of habitable zones.

  Consequently, it was at Tau Ceti that Drake first aimed his 85-foot radio telescope on the morning of April 8, 1960. Because of the probable difficulty of isolating the possible intelligible signals from the constant background crackle of cosmic static, he had worked out several ingenious techniques to make any signal stand out more clearly. They resemble somewhat the electronic warfare techniques of electronic counter-countermeasures—and it may be significant that Drake spent three years of military service as electronics officer aboard the heavy cruiser U.S.S. Albany. They may also owe something to techniques developed to detect radar echoes from Venus that were extremely faint—one hundredth of a billionth of a billionth of a watt.

  In one of Drake’s techniques, the radio telescope looked alternately at the star and at a patch of sky near the star. The latter delivered to the telescope only general cosmic noise, without any emissions from the star, while the former delivered noise plus any emissions. Drake’s equipment compared the two and took note only of any emission from the star whose strength rose above the general noise level. This would be the signal. The other technique depended upon the fact that one potato more does not make much difference to a carload but does to a grocer weighing out a pound. Electronic equipment balanced two unequal incoming emissions: a very broad band of noise and a narrow band within it. The radio telescope listened on successive narrow bands within the broad one. If a signal were present in the broad band but not in the narrow one being listened to, its strength would be negligible compared with all the noise and so the emissions would remain balanced. But if the narrow band picked up the signal, the signal would concentrate all its weight in that band and would throw the two emissions out of balance. The difference between them would constitute the artificial signal.

  Drake called his effort “Project Ozma,” after the name of the queen of the imaginary land of Oz—“a place very far away, difficult to reach, and populated by exotic beings.” His equipment tuned automatically across 400,000 cycles of the radio spectrum, centered on the hydrogen frequency. The switch that automatically tuned the receiver from one 100-cycle band to the next after a minute’s observation was the last one he snapped on the historic morning of April 8, 1960, as man began his first major attempt to find life in other solar systems.

  Throughout the day the giant saucer of his radio telescope swiveled slowly as it followed Tau Ceti, its light invisible in the glare of the sun, across the sky. Only the hisses and buzzes of cosmic noise had come in on the loudspeaker, only the formless wiggles of its graphic representation on paper had been recorded. As Tau Ceti began setting in the west, Drake, who had been in and out of the control room during the day, decided to swing to Epsilon Eridani, his other possibility. No sooner had he done so than the pen, Drake said, “went bang off scale”—knocked there by some very powerful signal. With the volume turned down, the pen smoothly wrote a uniform series of pulses, eight to the second. They could only have been produced artificially, by some intelligence. There was, Drake said, “a moderate amount of pandemonium” in the control room. Checks of the equipment showed no flaws. And before the telescope could be moved to see if the signal remained strong from other directions of the sky, which would indicate a non-Epsilon Eridani source, it abruptly stopped.

  Drake strongly doubted that he had actually trapped an interstellar signal on his first try. The chances were much too remote. He said nothing about it, and two weeks later, when he heard the marching pulses again, he tested their origin by steering the antenna off the star. As he had suspected, the pulses continued, proving that they came from somewhere on Earth, probably as a result of some radar countermeasures work.

  Project Ozma continued for a total of about 150 hours of listening through July of 1960, without any evidence of interstellar signals. Then it was suspended, mainly because the telescope was needed in other projects, but also partly out of flagging interest in the face of no results. Drake had hoped to resume listening with a new 600-foot radio telescope that the Navy was then constructing, but this project was abandoned, and Ozma left in abeyance.

  Occasionally, during the public discussion of Ozma, a voice would be heard protesting against it. Perhaps, to the advanced creatures of another civilization, men might be nothing more than a tasty-looking herd of beef cattle. Why tempt fate? There were a number of answers to this. One was the immense distances to be covered and the unlikelihood that anyone would travel so far just for a steak. Another was the length of the voyage: by the time they arrived, Earth might well be able to protect itself. Another was that a civilization advanced enough to be able to contact Earth would probably have figured out its food supply problem for itself. All may be summarized in a single point of view: that the only thing worth traveling for (over grea
t distances) is information. It would not be worthwhile to mine diamonds or iron on Mars; synthetics made on Earth would be much cheaper. Nobel Prize winner Edward Purcell, discoverer of the hydrogen radio emission line, felt certain that “No one can threaten anyone else with objects,” and that interstellar conversation would be, “in the deepest sense, utterly benign.”

  What, some people asked, if everybody is listening and no one is sending? For example, Dr. Harrison S. Brown told Congressman Daddario during the hearings of the Committee on Science and Astronautics: “I would say that the success of Project Ozma will depend almost entirely upon how Congressmen in these other systems have behaved. Have they allocated the funds, the very substantial funds necessary to build the fantastically powerful transmitting systems which could be necessary? And here I am perhaps gloomy. I try to think how you gentlemen would react to a proposal to build at great expense a transmitter which would send signals which the inhabitants of another star may or may not hear in a few million years, and I believe that such a bill probably would receive somewhat less than enthusiastic attention.” Brown was probably politically right but technologically wrong. It seems possible that advanced civilizations could detect emerging ones by stray radio signals that leak out into the cosmos as part of the planet’s ordinary activities—radio broadcasting, high-powered military communications, satellite relay transmissions, and especially long-range radar. In the case of Earth, some wags, thinking of soap operas and disk jockeys, have remarked that this might deter more than invite.

  One of the most curious facts about any interstellar conversation will be the long delays it would involve. Since it takes radio waves traveling at the speed of light 20 years to reach a planet 20 light-years away, conversation would have to proceed at a leisurely pace. Obviously, men would not transmit a message, then do nothing for 40 years until a reply came back. Both sides would exchange continual streams of information. The answers would, in a sense, be a legacy for the inquirers’ children. And perhaps, Walter Sullivan suggests in his We Are Not Alone, just as children are a form of physical immortality for men, so knowledge might constitute a form of intellectual immortality for whole worlds. “Bertrand Russell has pointed out that ‘all the labours of the ages, all the devotion, all the inspiration, all the noonday brightness of human genius, are destined to extinction in the vast death of the solar system.’ Yet it seems that life, in a sense, may be eternal. Perhaps true wisdom is a torch—one that we have not yet received, but that can be handed to us by a civilization late in its life and passed on by our own world as its time of extinction draws near.”

  But how would we actually communicate? What would the language of the transmission be? No simple show-and-tell process will be possible.

  Many scientists think that other civilizations will hail us with a special calling signal. “We expect that the signal will be pulse-modulated with a speed not very fast or very slow compared to a second, on grounds of bandwidth and of rotations,” wrote Cocconi and Morrison. “For indisputable identification as an artificial signal, one signal might contain, for example, a sequence of small prime numbers of pulses, or simple arithmetical sums.” Nikola Tesla envisioned the same thing when he imagined that terrestrial astronomers would announce the first cosmic contact with the words: “Brethren! We have a message from another world, unknown and remote. It reads: one … two … three …”

  As for the language of the text, no one on Earth can make a useful guess. Probably the one overriding principle of the outer-spacelings will have been to make their message as clear as possible. It will be coded, but in a code designed for clarity and not for obscurity—a kind of cryptography in reverse, as Edward Purcell has said, an anticryptography. Will the skills of the cryptologist be required to help read it? His specialized knowledge of letter frequencies and Kerckhoffs superimpositions will naturally be useless and unnecessary on a plaintext in an unknown language. But his talent for seeing patterns in unfamiliar texts may well prove of vital assistance. Perhaps the cryptologist will attend the translation conference with the logician, the mathematician, the linguist, the biologist, the astronomer, the radio engineer. If so, it would mark the fitting summit of a career whose long road began more than 4,000 years earlier; for cryptology, it would be the ultimate solution.

  While it is impossible to predict what the language of the outer-spacelings’ message is likely to be, Russian linguist N. D. Andreyev of the Leningrad Academy of Sciences has recently proposed a method that he believes will enable men to decipher any language. Using what he calls “statistical-combinatory” analysis, he measures six different parameters in a text, such as the distance of one word from another in a sentence, to arrive at a semantic relationship between words. Testing this on human languages, he has ascertained the meaning of verbal symbols. “The data are uneven,” he wrote. “For several words their exact meanings are obtained; other words group themselves into clearly delimited and semantically homogeneous sets with a definite meaning in common (but without specifying individual notions belonging to single members of a set); some words reveal only their broad semantic class and do not permit any delimitative grouping.” His work on the problem has just begun, but it seems to show promise.

  But how will man reply? Here the thinking has been primarily that of logicians, mathematicians, and astronomers. Their proposals may be said to fall into two categories. One group bases its language primarily on mathematical logic. The other depends basically upon pictures.

  It is evident that no one is going to try to beam a message in Esperanto to the creatures of another world. That artificial language rests too directly upon those of Earth; it belongs to the type of artificial language called a posteriori because it is based upon existing tongues. But the logico-mathematical proposals for an interstellar language have in their background the other kind of artificial language, the kind called a priori, in which all experience is categorized logically and the language molded upon these categories. The first artificial languages were of these kind; it is the kind that Friedman thinks may lie under the mystery of the Voynich manuscript. Many different systems have been proposed. They arose early in the 1600s, as Latin, which had been the international language, fell into disuse in scholarship and governmental institutions. In a letter in 1629, Descartes urged the creation of a philosophical language in which simple ideas would be so denominated that they could be combined into more complex ones as are letters into words. Leibnitz likewise dreamed of such a language, which he hoped would avoid many philosophical problems based solely on linguistic confusions. Such languages were even worked out, the first by George Dalgarno. Bishop Wilkins followed with another, using signs and attached wiggles to indicate ideas and their relations. Some were almost bizarre, using numbers to build up a scheme of existence, as Timerio, in which “I love you” became 1-80-17, or using musical notes, like Solresol, in which “Domisol” signifies “God” and “Solmido” means “Satan.” Its inventor, Jean-Francois Sudre, noted that it could be sung or, if the seven notes were replaced by seven colors, painted.

  Near the end of the 19th century, the Italian mathematician Giuseppe Peano sought to reduce as much as possible of the language used in mathematics and logic to formulas. He tried to formalize not the subject of mathematical thought—the equations in the books—since this had been done long before, but mathematical thought itself, the running text that surrounds the equations. For this he created symbols for “and,” “or,” “not,” “implies,” “every,” and other logical terms that previously had to be expressed verbally. He hoped this would facilitate scientific thought in nonmathematical areas, just as mathematics did in quantitative areas. (Peano also invented a simplified Latin for ordinary discourse, which he described in a speech in Turin in 1903. He began in almost classic Latin, and as he explained his various simplifications he introduced them into his talk, ending up with his almost grammarless “Latino sine flexione.”) Peano’s ideas of a mathematical language were picked up by Alfred North Whitehe
ad and Bertrand Russell, whose revolutionary Principia Mathematica exposed the foundations of mathematics and showed those of logic to be identical. Today, mathematical logic, the outgrowth of their work, boasts a large vocabulary of syntactical terms with which to express relations between ideas.

  This syntax serves as the skeleton of the interstellar language based on logic. The flesh of the language is formed by its vocabulary, and this is the work of Dr. Hans Freudenthal, professor of mathematics at the University of Utrecht in the Netherlands. Freudenthal designed it more as an exercise in logical language than as a serious proposal for interstellar communication, though he believes that it could fulfill that function. He called his language “Lincos,” from “lingua cosmica.” Its sounds consist of radio signals of various lengths and frequencies; its word-divisions and punctuation consist of pauses of varying duration. Freudenthal did not specify what the actual radio signal will be for a given word, as this does not really matter; it can be left up to the technicians. In print, he often represented his words by abbreviations of Latin words meaning the same thing. Thus “Inq,” evidently deriving from the Latin “inquirere,” stands for whatever signal is used for “ask.”

  Lincos would have to be taught to the creatures of outer space before it could be used as a medium of communication, and Freudenthal proposed to do this by transmitting the statements of Lincos, which he hoped would be relatively self-evident, over and over again until the recipients catch on to their meaning.