“A sad spectacle!” exclaimed Thomas Carlyle, contemplating the possibility that millions of planets circle other suns. “If they be inhabited, what a scope for pain and folly; and if they be not inhabited, what a waste of space!”

Much more is now known about the universe than in Carlyle’s time, but the question of whether ETI (a fashionable new acronym for Extraterrestrial Intelligence) exists is as open as it ever was. However, one incredible new fact has entered the picture. For the first time in history we have the technology for maybe answering the question. This mere possibility is so overwhelming in its implications that a new science called “exobiology” has already been named even though its entire subject matter may not exist.

We do know that our Milky Way galaxy contains more than 200 billion suns, and that there are billions of other galaxies. Are there other planets? Fifty years ago the two most popular theories about the origin of the solar system each made such planetary systems so unlikely that top astronomers believed that ours was the only one in the galaxy. After flaws were found in both theories, astronomers returned to a model proposed by Immanuel Kant (later by Laplace) in which solar systems are so likely that most of the Milky Way’s stars must have them. The wobblings of a few nearby suns suggest big planets close to them, but no one really knows.

If solar systems are plentiful, our galaxy could contain billions of planets earthlike enough to support carbon-based life. Biologists have a strong case for confining life to carbon compounds (silicon and boron are the next best bets), but no one has any notion of how earthlike a planet must be to permit carbon life to arise. Our two nearest neighbors, Venus and Mars, were probably formed the same time the earth was, yet their atmospheres are strikingly different from each other and from ours. Even if a planet goes through an early history exactly like our earth’s, no one knows the probability that life on its surface can get started. If it does start, no one knows the probability that it will evolve anything as intelligent as a fish.

Our probes of Mars have been great disappointments in SETI (Search for ETI). I can still recall the tingling of my spine when as a boy I read on the first page of H.G. Wells’s War of the Worlds:

Yet across the gulf of space, minds that are to our minds as ours are to those of the beasts that perish, intellects vast and cool and unsympathetic, regarded this earth with envious eyes, and slowly and surely drew their plans against us.

Not even Wells guessed how quickly the Martians would vanish from science fiction.

If we can trust recent polls, half of America believes that ETIs are regularly visiting the earth in UFOs, but this is no more than part of the big upsurge of enthusiasm for parascience and the occult. It is not taken seriously by the vast majority of scientists, least of all by Carl Sagan who has repeatedly said that there is not one scintilla of evidence that ETIs have ever visited us. His arguments have had the same notable absence of effect on UFO buffs as his demolition of Velikovsky’s crank theories has had on Velikovsky and his admirers.

Nevertheless Sagan is the most tireless of all exobiologists in his efforts to persuade fellow scientists and the government that ETI is an idea whose time has come. A few years ago his book The Cosmic Connection was a lyrical outburst of a firm belief that our galaxy teems with ETI. Murmurs of Earth, to which Sagan contributes a lively preface, essay, and epilogue, is a collection of essays by the six persons most responsible for a remarkable LP recording placed on each of the Voyager spacecraft launched last fall. After photographing Jupiter next year, they will proceed to Saturn. One may be diverted toward Uranus, but both are destined to leave the solar system to wander through the galaxy, making a round trip every quarter billion years.

SETI (the Search for…) must be distinguished from CETI (Communication with…). The search began with a historic paper by the physicists Philip Morrison and Giuseppe Coconni, “Searching for Interstellar Communications,” in Nature, 1959. There are good reasons to suspect, the authors argued, that ETIs exist. If so, the probability seems high that many are far ahead of us in both brain power and technology. We now have the means to send radio messages to other stars, therefore so do they. Perhaps they are doing just this. Since we have the ability to detect such messages, a systematic search seems desirable. “The probability of success is difficult to estimate,” the authors concluded, “but if we never search, the chance of success is zero.”


The first search for ETI was made by the astronomer Frank Drake in 1960, using radio telescopes he had assembled at Green Bank, West Virginia. The effort was minor and no signals were detected. Drake’s initial thoughts about CETI concerned pulsed codes that would begin with simple arithmetical facts such as the sequence of prime numbers. It is assumed by all exobiologists that on any planet where there are “things” that keep their identities (pebbles, fingers, stars…), two things plus two things make four things. (No one doubts this except a small group of extreme cultural relativists with a meager grasp of logic and mathematics.) By starting with simple theorems about counting numbers, it is possible slowly to construct a scientific language by which we could communicate with aliens across interstellar distances. A Yale mathematician, Hans Freudenthal, wrote an entire book to show how this can be done.

There is an easier way. It occurred to Drake early in the game (he writes about this in Sagan’s book) that excellent pictures can be transmitted in pulsed codes simply by drawing a rectangular matrix of cells and coloring each cell black or white. After a few preliminary explanations, one would proceed to send pictures in a binary code that used, say, 1 for black, 0 for white. Any ETI capable of detecting the message would surely be able to figure out how to scan the matrix, and in this way enormous amounts of information could be quickly transmitted.

But do ETIs have eyes? It seems likely. An organ sensitive to electromagnetic waves is by far the most efficient way for an intelligent creature to map its environment. On earth, for instance, the eye has independently evolved three times: on vertebrates, insects, and mollusks. An octopus has excellent eyes, yet evolution produced them entirely apart from those of insects and vertebrates. Even if ETIs are eyeless and explore their world by other senses, a picture composed of two kinds of cells would still be meaningful in terms of whatever senses they use. A cube has the same structure to a blind man’s touch that it has for one who sees it.

Although radio is by far the best way to contact ETIs, it occurred to several scientists that it might be worthwhile to add a visual message to Pioneer 10 and 11 when they were launched in 1971 and 1972. These spacecraft have already taken spectacular pictures of Jupiter. After photographing Saturn next year they will leave the solar system to travel for eons, like the Voyager craft, around the galaxy. Each Pioneer carries a metal plate designed by Sagan. It bears a picture of a nude man and woman, drawn by Sagan’s wife, Linda, as well as some basic information about our solar system. It was the first visual message fired from earth into space.

When Sagan was asked by NASA to prepare a more elaborate message for the Voyagers, he vowed to squeeze into it as much information as he could. His first step was to seek the advice of distinguished consultants, including Morrison, who started it all, and three SF writers: Isaac Asimov, Arthur Clarke, and Robert Heinlein.

The Voyager message finally took the form of a gold-plated copper record in an aluminum cover containing instruments for playing. It is an aural not a visual message. Sagan is under no illusions about the probability that ETIs will intercept the craft and play the record. The chances are infinitesimal. However, the Voyager message will become available to earthlings (first in the book under review, later as a record), so its main function is public relations—to arouse among people the expectation of ETI contact and to cushion the violent cultural shock that is sure to follow if such contact is made.

Murmurs of Earth is an eloquent account of this recording, how it got made, why it was made, and what it contains. Linda Sagan somehow managed to write a delightful essay about the record’s weakest aspect, a section in which short inane greetings to aliens are spoken in almost sixty languages. Burma asks, “Are you well?” Indonesia’s message is, “Good night, ladies and gentlemen. Goodbye and see you next time.” Turkey sends: “Dear Turkish-speaking friends, may the honors of the morning be upon your heads.” East China: “Friends of space, how are you? Have you eaten yet? Come and visit us if you have time.” (To eat us?)

Delegates to the Outer Space Committee of the UN also recorded greetings. The French delegate read a poem by Baudelaire. The Australian delegate decided to speak in Esperanto. The Nigerian delegate said, “…as you probably know, my country is situated on the west coast of the continent of Africa….”


Kurt Waldheim, the UN’s Secretary General, read a statement about how we step “into the universe seeking only peace and friendship.” If we are capable of saying this, in the light of our history, should we not beware of similar statements from ETI? Jimmy Carter’s message speaks of earth as “rapidly becoming a single global civilization,” and hoping someday “to join a community of galactic civilizations. A strange message from an evangelical Baptist, who, if he accepts New Testament prophecy, must believe with Billy Graham that our world is going to get worse and worse until finally—for Billy soon!—world history will end in the thunder and lightning of the Second Coming and the final overthrow of Satan.

It was wise of Sagan and his friends to put nothing on the disk about major religions—there was just no way to include one without the others—but was it cricket to omit all hints of earthly war, famine, disease, crime, and poverty? No inquisitions, no pogroms, no holocausts, no Hiroshima or Nagasaki! The only merit I can see in this decision is that it will alert us to similar lapses in case we start getting messages. ETIs may consider us a nuisance, the way our colonists regarded native Indians, or lowgrade organisms to slaughter for some desired protein the way we kill turtles to get oil for beauty creams.

Sir Martin Ryle, the Royal Astronomer of England, has vigorously opposed sending any kind of message into space. However, as Sagan and Morrison often have said, the distances between us and the most likely nearest ETI are so great that there is almost no chance of personal contact. A “cosmic quarantine” ensures only dialogue at safe distances. Also, as Drake points out, our presence has already been announced to ETIs by the expanding sphere of our radio and radar transmissions, and by the infrared heat generated by our technology. This provides, of course, other ways we can detect them. We, too, can eavesdrop.

Sagan’s disk carries in aural form 116 pictures that advanced ETIs should have no difficulty in reconstructing. All are in the book with an accompanying essay by Jon Lomberg. The first picture is simply a circle, a clever suggestion of Morrison’s to show the ETIs they have hit on the proper way to make the pictures. The rest are photographs, mostly black and white silhouettes, though some are in color. The color photos are recorded in red, blue, and green separations that can be superimposed to give a full color range. The photographs were carefully selected to represent such diverse aspects of earth as our companion planets, DNA, cell division, human anatomy, conception, birth, rivers, sand dunes, flowers, animals, houses, cities, factories, bridges, cars, trains, planes, and other familiar things.

Most of the record is devoted to sounds and music. Ann Druyan writes about the sounds: earthquakes, volcanoes, thunder, wind, rain, surf, crickets, frogs, birds, hyenas, elephants, dogs, chimps, whales, footsteps, heartbeats, laughter, infant cries, even a kiss that NASA gave strict orders to keep heterosexual. The music section, discussed by Timothy Ferris, includes twenty-seven pieces and runs a full ninety minutes. Bach, Mozart, Beethoven, and Stravinsky supply the Western classics. Louis Armstrong blows “Melancholy Blues.” There are pygmy songs, African drums, Japanese bamboo flutes, bagpipes, and other forms of ethnic music.

No one expects the Voyagers to reach any ETIs until after a few tens of millions of years; even then the craft may fly unnoticed by inhabited planets. However, in his epilogue Sagan injects a more optimistic note. There is a Red Dwarf star called AC p2= 79 3888 that the craft could reach in only 60,000 years. When one Voyager is about to leave the solar system we could make a firing adjustment that would direct it toward this dwarf. It just might have planets that just might have intelligent life, and they just might….

Nigel Calder’s latest book, Spaceships of the Mind, is written from a viewpoint almost the opposite of Sagan’s. Not that Sagan isn’t gung ho for exploring the solar system, landing astronauts on Mars, and starting colonies in space. It’s just that Sagan has confined his attention to SETI, CETI, and ETI, on the assumption that the ETIs really are out there. It may surprise the reader to learn that there is a growing body of respectable scientific opinion that ETIs may not be there at all.

To begin with, some astronomers, unhappy with accepted models of solar system history, are considering new models in which planets again are exceptional. Secondly, most biologists are persuaded that life is impossible without proteins, and this entails an exceedingly narrow range of conditions on a planet before life can even get started. Finally, if life does begin they see its evolution on earth as a sequence of such unlikely events that there is a large probability against the rise of intelligence.

The physicist John Wheeler has carried this view to its ultimate. In his cosmic vision an infinite number of big bangs are constantly taking place in “superspace,” and with each explosion random factors produce different physical constants. As a result, every universe has its peculiar set of mathematically consistent particles and laws. In most of these universes the formation of suns, let alone planets, is not possible. The universe has to be “finely tuned” to permit planets, still more finely tuned to permit life. As Wheeler sees it, billions upon billions of lifeless universes are being produced. Since they contain no creatures to “observe” them, there is a Berkeleyan sense—which Wheeler, Eugene Wigner, and a few other physicists believe to be supported by quantum mechanics—in which they do not even exist. (So far as I know, Wheeler and Wigner have never followed Bishop Berkeley in restoring existence to unobserved objects by allowing God to observe them.* ) When chance elements form a universe that permits it, life barely squeaks through on one planet. “Chances are overwhelming,” Wheeler wrote in 1973, “that earth is the sole outpost of life in the universe.”

Cosmologists have coined a new phrase called the “anthropic principle.” As the physicist P.C.W. Davies explains in “The Tailor-Made Universe” (The Sciences, May 1978), the principle’s essence is that “we observe the world that we do because we are here. This is not meant to imply that our existence causes the observed features to arise, only that it crucially depends on their having arisen.” The most surprising aspect of the principle is that it permits answering certain questions about cosmology and microphysics by considering the nature of life. Instead of asking what sort of life can evolve in a universe, we turn it around and ask what laws of a universe allow us to exist. Why are our laws what they are? Because if they were otherwise we wouldn’t be here to discover them!

Nigel Calder, England’s leading popularizer of science, discloses in Spaceships of the Mind that he favors this new view and is inclined, therefore, to think we are the galaxy’s only ETIs. It is, as Calder admits, a minority opinion, but one likely to grow if it turns out that Mars is totally barren of life, and if no radio messages from the stars are detected in the next few decades. It is amusing that the pendulum seems to be swinging back to a point of view that dominated Western thought for centuries before Bruno was incarcerated for (among other things) suggesting that the cosmos swarms with inhabited worlds!

Spaceships of the Mind, based on a TV series that Calder presented on the BBC, is concerned mainly with humanity’s great leap into uninhabited space. The book surveys what Calder calls the “Big Ideas” about this leap, the wild extrapolations. Will we soon be building “Santa Claus machines”—automatic factories in space that take material from the moon, planets, or asteroids and process it to make the substances needed for a space colony? Will we at some future date be constructing “Dyson spheres” (proposed by the physicist Freeman Dyson)—space cities that cluster in a massive shell around a star to make maximum use of the star’s energy? Will we colonize large asteroids, explore the moons of Saturn, rendezvous with comets? Will spaceships obtain economical thrust from ion engines that eject electrified atoms? Will they unfurl huge metal-foil sails to catch the feeble pressure of sunlight and tack around the solar system?

A chapter in Calder’s book is devoted to the Big Ideas of Gerard O’Neill, a former Princeton physicist now at the center of a thriving counterculture space cult dedicated to the planning of gigantic space settlements. It produces books, issues a periodical, and runs workshops. The Crystal Palace is one of O’Neill’s smaller ideas. Imagine an enormous structure that resembles a dozen bicycle tires stacked together inside a thick cylinder to provide shielding from deadly cosmic rays. Inside the tubes: atmosphere, soil for farms, and housing for 6,000 colonists. The whole thing rotates to generate pseudogravity.

Calder’s book is on the borderline between science and fantasy, but no matter. What came to mind as I marveled at its lurid illustrations was the favorite magazine of my boyhood, Hugo Gernsback’s Science and Invention. Its cover pictures, on gold paper to symbolize the golden age of science, were a crazy mixture of hits and misses. One big miss was a marvelous cover showing what a Martian should look like. Other covers were amazingly prophetic. My guess is that fifty years from now Calder’s book will seem the same quaint mixture of hits and misses. But Calder knows his science, and between discussions of outrageous plans there are solid facts about the universe, and informed speculation about the awesome possibilities that lie ahead as population pressures and energy needs propel us into what O’Neill calls the High Frontier.

At the close of The Great Gatsby, F. Scott Fitzgerald imagines that “enchanted moment” when the old Dutch sailors held their breath in the presence of the new continent, “face to face for the last time in history with something commensurate to…[humanity’s] capacity for wonder.” The paragraph is beautifully written, but how provincial it now seems! Let us not fault Fitzgerald for scientific ignorance. As late as 1931 a widely used astronomy text by Forest Ray Moulton ridiculed tales about travel to the moon and Mars. “Only those who are unfamiliar with the physical forces involved,” wrote Moulton, “believe that such adventures will ever pass beyond the realm of fancy.”

In the Center of Immensities, by Sir Bernard Lovell, the eminent British radio astronomer, is the most scholarly book of the three. It is essentially a history of cosmology, written with wisdom and grace, with a sound knowledge of the history of science and philosophy, and from the perspective of today’s preparation for the Big Jump.

Lovell, too, favors the anthropic principle. Our presence on earth, he believes, is the outcome of events that have near zero probability. “It seems that the chances of the existence of man on Earth today, or of intelligent life anywhere in the Universe, are vanishingly small.” Even the expansion rate of the cosmos has to be just so to permit life.

If the rate had been less by an almost insignificant amount in the first second [after the primeval bang], then the Universe would have collapsed long before any biological evolution could have taken place. Conversely, if the rate had been marginally greater, then the expansion would have reached such magnitudes that no gravitationally bound systems (that is, galaxies and stars) could have formed.

We Are Not Alone is the title of a book on ETI by the science writer Walter Sullivan. We are alone say Wheeler and Lovell and Calder. Sagan’s Voyager message will be heard only by ourselves. Who is right? Is the new revival of this ancient notion sad and lonely, or should we greet it with elation? I don’t know.

This Issue

November 23, 1978