Broca's Brain: The Romance of Science

CHAPTER 17

FOR MUCH OF human history we could travel only as fast as our legs would take us-for any sustained journey, only a few miles an hour. Great journeys were undertaken, but very slowly. For example, 20,000 or 30,000 years ago, human beings crossed the Bering Strait and for the first time entered the Americas, gradually working their way down to the southernmost tip of South America, in Tierra del Fuego, where Charles Darwin encountered them on the memorable voyage of H.M.S. Beagle. A concerted and single-minded effort of a dedicated band to walk from the straits between Asia and Alaska to Tierra del Fuego might have succeeded in a matter of years; in fact, it probably took thousands of years for diffusion of the human population to carry it so far south.

The original motivation for traveling fast must have been, as the whiting’s plaint reminds us, to escape from enemies and predators, or else to seek enemies and prey. A few thousand years ago a remarkable discovery was made: the horse can be domesticated and ridden. The idea is a very peculiar one, the horse not having been evolved for humans to ride. If looked at objectively, it is only a little less silly than, say, an octopus riding a grouper. But it worked and-especially after the invention of the wheel and the chariot-horseback or horse-drawn vehicles represented for millennia the most advanced transportation technology available to the human species. One can travel as much as 10 or perhaps even 20 miles an hour with horse technology.

We have emerged from horse technology only very recently-as, for example, our use of the term “horsepower” to rate automobile engines clearly shows. An engine rated at 375 horsepower has very roughly the pulling capacity of 375 horses. A team of 375 horses would make a very interesting sight. Arrayed in ranks of five horses each, the team would extend for about two-tenths of a mile in length and would be astonishingly unwieldy. On many roads the front rank of horse would be out of sight of the driver. And, of course, 375 horses do not travel 375 times as fast as one horse. Even with enormous teams of horses the speed of transportation was only ten or so times faster than when we could depend upon only our legs.

Thus the changes of the last century in transportation technology are striking. We humans have relied on legs for millions of years; horses for thousands; the internal-combustion engine for less than a hundred; and rockets for transportation for a few decades. But these products of human inventive genius have enabled us to travel on the land and on the surface of the waters a hundred times faster than we can walk, in the air a thousand times faster, and in space more than ten thousand times faster.

It used to be that the speed of communication was the same as the speed of transportation. There were a few fast communication methods earlier in our history-for example, signal flags or smoke signals or even one or two attempts at arrays of signal towers with mirrors employed to reflect sunlight or moonlight from one to another. News of the recapture of the Fortress of Györ by Hungarian commandos from the Turks was apparently conveyed to the Hapsburg Emperor Rudolf II through such a device: the “moonbeam telegraph,” invented by the English astrologer John Dee, which apparently consisted of ten relay stations placed at intervals of forty kilometers between Györ and Prague. But with only a few exceptions, these methods proved impractical, and communications proceeded no faster than a man or a horse. This is no longer true. Communication by telephone and radio is now at the velocity of light-186,000 miles per second, or about two-thirds of a billion miles per hour. This is not simply the latest advance: it is the last advance. So far as we know, from Einstein’s Special Theory of Relativity, the universe is constructed in such a way (at least around here) that no material object and no information can be transmitted faster than the velocity of light. This is not an engineering barrier like the so-called sound barrier, but a fundamental cosmic speed limit built deeply into the fabric of nature. Still, two-thirds of a billion miles per hour is fast enough for most practical purposes.

What is remarkable is that in communications technology we have already reached this ultimate limit and have adapted to it so well. There are few people who emerge breathless and palpitating from a routine longdistance telephone call, astounded at the speed of transmission. We take this almost instantaneous means of communication for granted. Yet in transportation technology, while we have not achieved speeds at all approaching the velocity of light, we find ourselves colliding with other limits, physiological and technological:

Our planet turns. When it is midday at one spot on the Earth, it is the dead of night on the other side. The Earth has therefore been conveniently arranged into twenty-four time zones of more or less equal width, making strips of longitude around the planet. If we fly very fast, we create situations our minds can accommodate but our bodies can abide only with great difficulty. It is a commonplace today to fly in relatively short trips westward and arrive before we leave-for example, when we take less than an hour to fly between two points separated by one time zone. When I take a 9 P.M. flight to London, it is already tomorrow at my destination. When I arrive, after a five- or six-hour flight, it is late at night for me but the beginning of the business day at my destination. My body senses something wrong, my circadian rhythms go awry, and it takes a few days to get adjusted to English time. A flight from New York to New Delhi is, in this respect, even more vexing.

I find it very interesting that two of the most gifted and inventive science-fiction writers of the twentieth century-Isaac Asimov and Ray Bradbury-both refuse to fly. Their minds have come to grips with interplanetary and interstellar spaceflight, but their bodies rebel at a DC-3. The rate of change in transportation technology has simply been too great for many of us to accommodate conveniently.

Much stranger possibilities are now practical. The Earth turns on its axis once every twenty-four hours. The circumference of the Earth is 25,000 miles. Thus, if we were able to travel at 25,000/24 = 1,040 miles per hour, we could just compensate for the Earth’s rotation, and traveling westward at sunset, could maintain ourselves at sunset for the entire journey even if we circumnavigated the planet. (In fact, such a journey would also maintain us at the same local time as we journey westward from time zone to time zone, until we cross the international dateline and plunge precipitously into tomorrow.) But 1,040 miles per hour is less than twice the speed of sound and there are, worldwide, dozens of kinds of aircraft, chiefly military, that are capable of such speeds. [12]

Some commercial aircraft, such as the Anglo-French Concorde, have comparable capabilities. The question, I think, is not: Can we go faster? but Do we have to? There has been concern expressed, some of it in my view quite appropriately, about whether the conveniences supersonic transports provide can possibly compensate for their overall cost and their ecological impact.

Most of the demand for high-speed long-distance travel comes from businessmen and government officials who need to have conferences with their opposite numbers in other states or countries. But what is really involved here is not the transportation of material but the transportation of information. I think much of the necessity for high-speed transport could be avoided if the existing communications technology were better used. I have many times participated in government or private meetings in which there were, say, twenty participants, each of whom was paid $500 for transportation and living expenses merely to attend the meeting-the cost of which was therefore $10,000 just to get the participants together. But all the participants ever exchange is information. Video phones, leased telephone lines, and facsimile reproducers to transmit paper copies of notes and diagrams would, I believe, serve as well or even better. There is no significant function of such a meeting-including private discussions among the participants “in the corridor”-that cannot be performed less expensively and at least equally conveniently with communications rather than transportation technology.

There are certainly advances in transportation that seem to me promising and desirable: vertical takeoff and landing (VTOL) aircraft are a remarkable boon for isolated and remote communities in case of medical or other emergencies. But the recent advances in transportation technology that I find most appealing are rubber fins for snorkel and scuba diving and hang gliders. These are technological advances much in the spirit of those sought by Leonardo da Vinci in mankind’s first serious technological pursuit of flight in the fifteenth century; they permit an individual human being with little more than his own resources to enter-at a speed that is adequately exhilarating-another medium entirely.

WITH THE DEPLETION of fossil fuels I think it very likely that automobiles powered by internal-combustion engines will be with us for at most a few decades longer. The transportation of the future will simply have to be different. We can imagine quite comfortable and adequately speedy steam, solar, fuel-cell or electric ground vehicles, generating very little pollution and employing a technology comfortably accessible to the user.

Many responsible medical experts are concerned that we in the West-and increasingly even in developing countries-are becoming too sedentary. Driving an automobile exercises very few muscles. The demise of the automobile surely has many positive aspects when viewed in the long run, one of which is a return to the oldest transportation mechanism, walking, and to bicycling, which is in many ways the most remarkable.

I can easily imagine a healthy and stable future society in which walking and bicycling are the primary means of transportation; with pollution-free low-speed ground cars and railed public transportation systems widely available, and the most sophisticated transportation devices used relatively rarely by the average person. The one application of transportation technology that requires the most sophisticated technology is spaceflight. The returns in immediate practical benefits, scientific knowledge and appealing exploration provided by unmanned spaceflight are very impressive, and I would expect an increasing rate of space-vehicle launches by many nations in the next few decades, using more subtle forms of transportation, as described in the previous chapter. Nuclear electric, solar sailing and ion propulsion schemes have been proposed and are to some degree under development. As nuclear-fusion power plants are developed for Earth-bound applications in a few decades, there should be a development of fusion space engines as well.

The gravitational forces of planets have already been used to give velocities otherwise unobtainable. Mariner 10 reached Mercury only because it flew so close to Venus that Venus’ gravity provided a significant boost in speed. And Pioneer 10 was boosted into an orbit that will carry it out of the solar system entirely, only because of a close passage by the giant planet Jupiter. In a way Pioneer 10 and 11 and Voyager 1 and 2 are our most advanced transportation systems. They are leaving the solar system at a speed of roughly 43,000 miles per hour, carrying messages to anyone who may intercept them out there in the dark of the night sky from the people of the Earth-who, only a little while ago, could travel no faster than a few miles per hour.

CHAPTER 18

IT IS A LAZY afternoon in an exquisite New England autumn. In about ten weeks it will be January 1, 1900, and your diary, into which are committed the events and ideas of your young life, will never again bear an entry with a date in the 1800s. You have just turned seventeen. You are looking forward to being a sophomore in high school, but you are now at home, in part because your mother is seriously ill with tuberculosis and in part because of your own chronic stomach pains. You are bright, with a certain flair for the sciences, but no one has ever indicated that you might have an extraordinary talent. You are complacently viewing the New England countryside from the limb of a tall old cherry tree which you have climbed, when suddenly you are struck by an idea, an overpowering and compelling vision that it might be possible, in fact rather than in fancy, to voyage to the planet Mars.

When you descend from the cherry tree you know that you are a very different boy from the one who climbed it. Your life’s work is clearly set out for you, and for the next forty-five years your dedication never wavers. You have been smitten by the vision of flight to the planets. You are deeply moved and quietly awed by the vision in the cherry tree. The next year, on the anniversary of that vision, you climb the tree again to savor the joy and meaning of the experience; and forever after you make a point in your diary of calling the anniversary of that experience “Anniversary Day”-every October 19 until your death in the middle 1940s, by which time your theoretical insights and practical innovations have solved essentially all technological impediments to interplanetary flight.

Four years after your death a WAC Corporal mounted on the nose of a V-2 is successfully fired to an altitude of 250 miles, for all practical purposes to the threshold of space. All essential design elements of the WAC Corporal and the V-2, and the very concept of the multiple staging of rockets, have been worked out by you. A quarter of a century later, unmanned space vehicles will have been launched to all the planets known to ancient man; a dozen men will have set foot on the Moon; and two exquisitely miniaturized spacecraft named Viking will be on their way to Mars to attempt the first search for life on that planet.

ROBERT H. GODDARD never questioned or equivocated on the resolve he made in the cherry tree on the farm of his great-aunt Czarina in Worcester, Massachusetts. While there were others who had comparable visions-notably Konstantin Eduardovich Tsiolkovsky in Russia-Goddard represented a unique combination of visionary dedication and technological brilliance. He studied physics because he needed physics to get to Mars. He was for many years professor of physics and chairman of the physics department at Clark University in his hometown of Worcester.

In reading the notebooks of Robert Goddard, I am struck by how powerful his exploratory and scientific motivations were, and how influential speculative ideas-even erroneous ones-can be on the shaping of the future. In the few years surrounding the turn of the century, Goddard’s interests were profoundly influenced by the idea of life on other worlds. He was intrigued by the claims of W. H. Pickering, of the Harvard College Observatory, that the Moon has a perceptible atmosphere, active volcanism, variable frost patches, and even changing dark markings, which Pickering interpreted variously as the growth of vegetation or even as the migration of enormous insects across the floor of the crater Eratosthenes. Goddard was captivated by the science fiction of H. G. Wells and Garrett P. Serviss, particularly the latter’s Edison’s Conquest of Mars, which, Goddard reported, “gripped my imagination tremendously.” He attended and enjoyed lectures by Percival Lowell, who was an eloquent advocate of the proposition that intelligent beings inhabit the planet Mars. And yet, through all of this, while his imagination was intensely stimulated, Goddard managed to retain a sense of skepticism very rare in young people given to interplanetary epiphanies high up in cherry trees: “The actual conditions may be entirely different… from those which Professor Pickering suggests… The only antidote for fallacies is-in a word-to take nothing for granted.”

On January 2, 1902, we know from Goddard’s notebook, he wrote an essay on “The Habitability of Other Worlds.” The paper had not been found among Goddard’s writings, which seemed to me a great pity, since it might have given us a better understanding of the extent to which the search for extraterrestrial life was a prime motive in Goddard’s lifework. [13]

In his early postdoctoral years Goddard successfully pursued an experimental verification of his ideas on solid- and liquid-fueled rocket flight. In this endeavor he was supported principally by two men: Charles Greeley Abbott and George Ellery Hale. Abbott was then a young scientist at the Smithsonian Institution, of which he later became secretary, the quaint designation by which the executive officer of that organization is still known. Hale was the driving force behind American observational astronomy at the time; before he died he had founded the Yerkes, Mount Wilson and Mount Palomar observatories, each housing, in its time, the largest telescope in the world.

Both Abbott and Hale were solar physicists, and it seems clear that both had been captured by the young Goddard’s vision of a rocket sailing free above the obscuring blanket of the Earth’s atmosphere, able to view the Sun and stars unimpeded. But Goddard soared far beyond this daring vision. He talked and wrote of experiments on the composition and circulation of the upper atmosphere of the Earth, of performing gammaray and ultraviolet observations of the Sun and stars from above the Earth’s atmosphere. He conceived of a space vehicle passing 1,000 miles above the surface of Mars-by a curious historical accident just the low point in the orbits of the Mariner 9 and Viking spacecraft. Goddard calculated that a reasonably sized telescope at such a vantage point would be able to photograph features tens of meters across on the surface of the Red Planet, which is the resolution of the Viking orbiter cameras. He conceived of slow interstellar flight at velocities and time scales just equivalent to that of the Pioneer 10 and 11 spacecraft, our first interstellar emissaries.

Goddard’s spirit soared higher still. He conceived, not casually but quite seriously, of solar-powered spacecraft, and in a time when any practical application of nuclear energy was publicly ridiculed, nuclear propulsion for spacecraft over vast interstellar distances. Goddard imagined a time in the far distant future when the Sun has grown cold and the solar system become uninhabitable, when manned interstellar spacecraft would be outfitted by our remote descendants, to visit the stars-not merely the nearby stars, but also remote star clusters in the Milky Way Galaxy. He could not imagine relativistic spaceflight and so hypothesized a method of suspended animation of the human crew or-even more imaginative-a means of sending the genetic material of human beings which would automatically, at some very distant time, be allowed to recombine and produce a new generation of people.

“With each expedition,” he wrote, “there should be taken all the knowledge, literature, art (in a condensed form), and description of tools, appliances, and processes, in as condensed, light, and indestructible a form as possible, so that the new civilization could begin where the old ended.” These final speculations, entitled “The Last Migration,” were sealed in an envelope with instructions to be read “only by an optimist.” And that he surely was-not a Pollyanna who chooses to ignore the problems and evils of our times, but rather, a man committed to the improvement of the human condition and the creation of a vast prospect for the future of our species.

Goddard’s dedication to Mars was never far from his mind. In the wake of one of his first experimental successes, he was induced to write a press release on the details of his launch and its ultimate significance. He wished to discuss spacecraft to Mars but was dissuaded on the ground that this was too fantastic. As a compromise he talked about sending a quantity of magnesium flash powder which would make a visible bright flare on the Moon when it landed. This caused a sensation in the press. Goddard was for many years after disparagingly referred to as “the Moon Man,” and he remained rueful about his relations with the press ever after. (An editorial in the New York Times which criticized Goddard for having “forgotten” that a rocket will not work in the vacuum of space because it has nothing to push against may have contributed to his unease. The Times discovered Newton’s third law of motion and retracted its error only in the age of Apollo.) Goddard mused: “From that day, the whole thing was summed up, in the public mind, in the words ‘moon rocket’; and thus it happened that in trying to minimize the sensational side, I had really made more of a stir than if I had discussed transportation to Mars, which would probably have been considered as ridiculous by the press representative and doubtless never mentioned.”

Goddard’s notebooks are not filled with psychological insights. That was not, at least not very much, the spirit of the times in which he lived. [14] But there is a remark in Goddard’s notebooks that can be only a flash of poignant self-insight: “God pity a one-dream man.” That surely is what Goddard was. He knew great satisfaction in seeing the advances in rocket technology, but it must have been agonizingly slow. There are so many letters from Abbott urging faster progress, and so many responses from Goddard citing practical impediments. Goddard never lived to see the beginning of rocket astronomy and high-altitude meteorology, much less flights to the Moon or planets.

But all these things are happening because of what are very clearly the technological fruits of Goddard’s genius. October 19, 1976, was the 77th Anniversary Day of the Martian vision of Robert H. Goddard. On that day there were two functioning orbiters and two working landers on Mars, the Viking spacecraft whose origins can be traced with utter confidence back to a boy in a cherry tree in a New England autumn in 1899. Among its many other objectives, Viking had the task of checking out the possibility of life on Mars, the prospect that was so powerful a motivation for Goddard so many years before. Curiously, we are still not sure what the Viking biology results mean. Some think that microbial life may have been discovered; others think it unlikely. It is clear that a major program of future exploration of Mars will be required to understand just where in cosmic evolution this neighboring world lies and what its connection is with the state of evolution on our own planet.

From its earliest stages, rocket technology developed because of an interest in life on other worlds. And now that we have landed on Mars, obtained tantalizing and enigmatic biological results, the follow-on missions-roving vehicles and returned sample canisters-in turn require further developments in spacecraft technology, a mutual causality that I think Goddard would have appreciated.

CHAPTER 19

UNTIL RELATIVELY recently, astronomy suffered from a serious impediment and remarkable peculiarity: it was the only thoroughly nonexperimental science. The materials of study were all up there, and we and our machines were all down here.

No other science was so severely constrained. In physics and chemistry, of course, all is forged on the anvil of experiment, and those who doubt a given conclusion are free to perform a wide range of alternative manipulations of matter and energy in an attempt to extract contradictions or alternative explanations. Evolutionary biologists, even those of very patient temperaments, cannot afford to wait a few million years to observe one species evolve into another. But experiments on common amino acid sequences, enzyme structure, nucleic acid codes, chromosomal banding, and anatomy, physiology and behavior make a compelling case for the fact that evolution has occurred and clearly show which plant or animal groups (such as human beings) are related to which others (such as the great apes).

It is true that geophysicists, studying the deep interior of the Earth, cannot travel to the Wiechert discontinuity between core and mantle, or (just yet) to the Mohorovicic discontinuity between mantle and crust. But batholiths, extruded from the deep interior, can be found here and there on the surface and examined. The geophysicists have relied largely on seismic data, and here, like astronomers, they could not force the favors of nature but were compelled to await their voluntary bestowal-for example, in a seismic event situated on the other side of the Earth so that one of two nearby seismometers would be in the shadow of the Earth’s core and the other not. But impatient seismologists can and have set off their own chemical and nuclear explosions to ring Earth like a bell. And there are intriguing recent hints that it may be possible to turn earthquakes on and off. Those geologists intolerant of inferential reasoning could always go to the field and examine contemporary erosion processes. But there was no exact astronomical equivalent of the hard-rock geologist.

We have been restricted to the electromagnetic radiation reflected and emitted by astronomical objects. We have not been able to examine pieces of stars or planets [15] in our laboratories or to fly into such objects to examine them in situ. Ground-based passive observations have restricted us to a narrow fraction of the conceivable data on astronomical objects. Our position has been much worse than that of the fabled six blind men in pursuit of the nature of the elephant. It has been more like one blind man in a zoo. We were standing there for centuries stroking a left hind foot. It is not surprising that we did not deduce tusks, or notice that the foot did not belong to an elephant at all. If, by accident, the orbital plane of the double star was in our line of sight, we would see eclipses; otherwise not. We could not move to a position in space from which the eclipses could be observed. If we were observing a galaxy when a supernova was exploding, we could examine the supernova spectrum; otherwise not. We do not have the ability to perform experiments on supernova explosions-which is just as well. We could not examine in the laboratory the electrical, thermal, mineralogical and organic chemical properties of the lunar surface. We were restricted to inferences from the visible light reflected and the infrared and radio waves emitted by the moon, aided by occasional natural experiments such as eclipses and lunations.

But all that is gradually changing. Ground-based astronomers have, at least for nearby objects, an experimental tool: radar astronomy. At our convenience, at our choice of frequency, polarization, bandpass and pulse length, we can irradiate a nearby moon or planet with microwaves and examine the returned signal. We can wait for the object to rotate underneath the beam and illuminate some other place on its surface. Radar astronomy has delivered a host of new conclusions on the rotation periods of Venus and Mercury, and related problems in the tidal evolution of the solar system, on the craters of Venus, the fragmented surface of the Moon, the elevations of Mars, and the size and composition of the particles in the rings of Saturn. And radar astronomy is just beginning. We are still restricted to low altitudes, and for the outer solar system, to sun-facing hemispheres. But with the newly resurfaced Arecibo telescope of the National Astronomy and Ionosphere Center in Puerto Rico, we will be able to map the surface of Venus to a resolution of 1 kilometer-better than the best ground-based photographic resolution of the lunar surface-and obtain a host of new information on the asteroids, the Galilean satellites of Jupiter and the rings of Saturn. For the first time we are poking around in cosmic stuff, electromagnetically fingering the solar system.

A much more powerful technique of experimental (as opposed to observational) astronomy is spacecraft exploration. We can now travel into the magneto-spheres and atmospheres of the planets. We can land on and rove over their surfaces. We can collect material directly from the interplanetary medium. Our first preliminary steps into space have shown us a wide range of phenomena we never knew existed: the Van Allen trapped-particle belts of the earth; the mass concentrations beneath the circular maria of the moon; the sinuous channels and great volcanoes of Mars; the cratered surfaces of Phobos and Deimos. But what I am most struck by is that, before the advent of space vehicles, astronomers did very well-hamstrung though they were. The interpretations of the observations available to them were remarkably good. Space vehicles are ways of checking out the conclusions drawn inferentially by astronomers, a method of determining whether astronomical deductions on very distant objects-objects so far away as to be entirely inaccessible by space vehicles in the near future-should be believed.

ONE OF THE EARLIEST major debates in astronomy was on whether the Earth or the Sun was at the center of the solar system. The Ptolemaic and Copernican views explain the apparent motion of the Moon and planets to comparable precision. For the practical problem of predicting the positions of the Moon and planets as seen from the surface of the Earth, it hardly mattered which hypothesis was adopted. But the philosophical implications of the geocentric and heliocentric hypotheses were quite different. And there were ways of finding out which was right. In the Copernican view, Venus and Mercury should go through phases like the Moon. In the Ptolemaic view, they should not. When Galileo, using one of the first astronomical telescopes, observed a crescent Venus, he knew he had vindicated the Copernican hypothesis.

But space vehicles provide a more immediate test. According to Ptolemy, the planets are affixed to immense crystalline spheres. But when Mariner 2 or Pioneer 10 penetrated the locales of Ptolemy’s supposed crystal spheres, no impediment to their motion was detected; and, more directly, the acoustic and other micrometeorite detectors heard not even the faintest whisper of tinkling, much less the sound of smashed crystal. There is something very satisfying and immediate about this sort of test. There are probably no Ptolemaists in our midst. But there might be some with lingering doubts about whether Venus could not be made to go through phases in some modified geocentric hypothesis. Those people can now rest easy.

Before space vehicles, the German astrophysicist Ludwig Biermann was intrigued by the observations of the apparent acceleration of bright knots in the well-developed tails of comets passing through the inner solar system. Biermann showed that the radiation pressure of sunlight was inadequate to account for the observed acceleration and made the novel suggestion that there were charged particles streaming out from the Sun which, in interaction with the comet, produced the observed acceleration. Well, maybe. But could it not be equally due to, say, chemical explosions in the nucleus of the comet? Or some other explanation? But the first successful interplanetary spacecraft, Mariner 2, in the course of its fly-by of Venus, determined the existence of a solar wind with velocities and electron densities in just the range that Biermann had calculated would be necessary to accelerate his knots.

In the same period there was a debate on the nature of the solar wind. In one view, that of Eugene Parker of the University of Chicago, it was caused by hydro-dynamical flow out from the Sun; in another view, by evaporation from the top of the solar atmosphere. In the hydrodynamic explanation there should be no fractionation by mass; that is, the atomic composition of the solar wind should be the same as that of the Sun. But in the evaporation hypothesis, the lighter atoms escape the Sun’s gravity more easily, and heavy elements should be preferentially depleted in the solar wind. Interplanetary spacecraft have found that the ratio of hydrogen to helium in the solar wind is precisely that in the Sun, and have thereby provided convincing support for the hydrodynamic hypothesis of the origin of the solar wind.

In these examples from solar wind physics, we find that the spacecraft experiments provided the means for making critical judgments among competing hypotheses. In retrospect, we find that there were astronomers such as Biermann and Parker who were right for the right reasons. But there were others, equally bright, who disbelieved them and might have gone on disbelieving them had not the critical spacecraft experiments been performed. What is remarkable is not that there were alternative hypotheses which we now see to be incorrect, but rather that on the basis of the very meager data available anyone was smart enough to divine the correct answer-inferentially, using intuition, physics and common sense.

Before the Apollo missions, the uppermost layer of the lunar surface could be examined by visible, infrared and radio observations during both lunations and eclipses, and the polarization of sunlight reflected off the lunar surface had been measured. From these observations, Thomas Gold of Cornell University prepared a dark powder which, in the laboratory, reproduced the observed properties of the lunar surface very well. This “Golddust” can even be purchased for a modest price from the Edmund Scientific Company. A naked-eye comparison of lunar dust returned by Apollo astronauts with Golddust shows them to be almost indistinguishable. In particle-size distribution, and in electrical and thermal properties, they are a very close match. However, their chemical compositions are very different. Golddust is primarily Portland cement, charcoal and hairspray. The moon has a less exotic composition. But the observed lunar properties available to Gold before Apollo did not strongly depend on the chemical composition of the lunar surface. He was able to deduce very well that fraction of the lunar-surface properties which was relevant to pre-1969 observations of the Moon.

From the study of the available radio and radar data, we were able to deduce the high surface temperature and high surface pressures of Venus before the first Soviet Venera entry probe made in situ observations on the atmosphere, and subsequent Venera probes on the surface. Likewise, we correctly deduced the existence of elevation differences on Mars as great as 20 kilometers, although we were mistaken in thinking that dark areas were systematically at high elevations on the planet. [16]

Perhaps one of the most interesting such confrontations of astronomical inference with spacecraft observations is the case of the magnetosphere of Jupiter. In 1955 Kenneth Franklin and Bernard Burke were testing a radio telescope near Washington, D.C., intended for mapping galactic radio emission at a frequency of 22 Hertz. They noticed a regularly recurring interference on their records, which they at first thought was due to some conventional source of radio noise-such as a faulty ignition system on some nearby tractor. But they soon discovered that the timing of the interference corresponded perfectly well with transits overhead of the planet Jupiter. They had discovered that Jupiter was a powerful source of decameter radio emission.

Subsequently Jupiter was found to be a bright source at decimeter wavelengths as well. But the spectrum was very peculiar. At a wavelength of a few centimeters, very low temperatures of around 140°K were found-temperatures comparable to those uncovered for Jupiter at infrared wavelengths. But at decimeter wavelengths-up to one meter-the brightness temperature increased very rapidly with wavelength, approaching 100,000°K. This was too high a temperature for thermal emission-the radio radiation that all objects put out, simply because they are at a temperature above absolute zero.

Frank Drake, then of the National Radio Astronomy Observatory, proposed in 1959 that this spectrum implied that Jupiter was a source of synchrotron emission-the radiation that charged particles emit in their direction of motion when traveling close to the speed of light. On Earth, synchrotrons are convenient devices used in nuclear physics for accelerating electrons and protons to such high velocities, and it is in synchrotrons that such emission was first generally studied. Synchrotron emission is polarized, and the fact that the decimeter radiation from Jupiter is also polarized was an additional point in favor of Drake’s hypothesis. Drake suggested that Jupiter was surrounded by a vast belt of relativistic charged particles similar to the Van Allen radiation belt around the Earth, which had then just been discovered. If so, the decimeter emitting region should be much larger than the optical size of Jupiter. But conventional radio telescopes have inadequate angular resolution to make out any spatial detail whatever at the range of Jupiter. A radio interferometer can achieve such resolution, however. In the spring of 1960, very soon after the suggestion was made, V. Radhakrishnan and his colleagues at the California Institute of Technology employed an interferometer composed of two 90-foot-diameter antennas mounted on railroad tracks and separable by almost a third of a mile. They found that the region of decimeter emission around Jupiter was considerably larger than the ordinary optical disc of Jupiter, confirming Drake’s proposal.

Subsequent higher-resolution radio interferometry has shown Jupiter to be flanked by two symmetric “ears” of radio-wave emission with the same general configuration as the Van Allen radiation belts of the Earth. The general picture has evolved that on both planets electrons and protons from the solar wind are trapped and accelerated by the planetary magnetic dipole field and are constrained to spiral along the planet’s lines of magnetic force, bouncing from one magnetic pole to the other. The radio-emitting region around Jupiter is identified with its magnetosphere. The stronger the magnetic field, the farther out from the planet the boundary of the magnetic field will be. In addition, matching the observed radio spectrum from synchrotron emission theory specifies a magnetic field strength. The field strength could not be specified to very great precision but most estimates from radio astronomy in the late 1960s and early 1970s were in the range of 5 to 30 gauss, some ten to sixty times the surface magnetic field of the Earth at the equator.

Radhakrishnan and colleagues also found that the polarization of the decimeter waves from Jupiter varied regularly as the planet rotated, as if the Jovian radiation belts were wobbling with respect to the line of sight. They proposed that this was due to a 9-degree tilt between the axis of rotation and the magnetic axis of the planet-not very different from the displacement between the north geographic and the north magnetic poles of Earth. Subsequent studies of the decimeter and decameter emission by James Warwick of the University of Colorado and others suggested that the magnetic axis of Jupiter is displaced a small fraction of a Jupiter radius from the axis of rotation, quite different from the terrestrial case, where both axes intersect at the center of the Earth. It was also concluded that the south magnetic pole of Jupiter was in the northern hemisphere; that is, that a north-seeking compass on Jupiter would point south. There is nothing very bizarre about this suggestion. The Earth’s magnetic field has flipped its direction many times during its history, and it is only by definition that the north magnetic pole is in the northern hemisphere of the Earth at the present time. From the intensity of the decimeter and decameter emission, astronomers also calculated what the energies and fluxes of electrons and protons in the Jovian magnetosphere might be.

This is a very rich array of conclusions. But all of it is remarkably inferential. The whole elaborate superstructure was put to a critical test on December 3, 1973, when the Pioneer 10 spacecraft flew through the Jovian magnetosphere. There were magnetometers aboard, which measured the strength and direction of the magnetic field at various positions in the magneto-sphere; and there was a variety of charged-particle detectors, which measured energies and fluxes of the trapped electrons and protons. It is a stunning fact that virtually every one of the radio astronomical inferences was roughly confirmed by Pioneer 10 and its successor spacecraft, Pioneer 11. The surface equatorial magnetic field on Jupiter is about 6 gauss and larger at the poles. The inclination of the magnetic to the rotational axis is about 10 degrees. The magnetic axis can be described as apparently displaced about one quarter of a Jovian radius from the center of the planet. Farther out than three Jupiter radii, the magnetic field is approximately that of a dipole; closer in, it is much more complex than had been estimated.

The flux of charged particles received by Pioneer 10 along its trajectory through the magnetosphere was considerably larger than had been anticipated-but not so large as to inactivate the spacecraft. The survival of Pioneer 10 and 11 through the Jovian magnetosphere was more the result of good luck and good engineering than of the accuracy of pre-Pioneer magnetospheric theories.

In general, the synchrotron theory of the decimeter emission from Jupiter is confirmed. All those radio astronomers turn out to have known what they were doing. We can now believe, with much greater confidence than heretofore, deductions made from synchrotron physics and applied to other, more distant and less accessible comic objects, such as pulsars, quasars or supernova remnants. In fact, the theories can now be recalibrated and their accuracy improved. Theoretical radio astronomy has for the first time been put to a critical experimental test-and it has passed with flying colors. Of the many major findings by Pioneer 10 and 11, I think this is its greatest triumph: it has confirmed our understanding of an important branch of cosmic physics.

There is much about the Jovian magnetosphere and radio emissions that we still do not understand. The details of the decameter emissions are still deeply mysterious. Why are there localized sources of decameter emission on Jupiter probably less than 100 kilometers in size? What are these emission sources? Why do the decameter emission regions rotate about the planet with a very high time precision-better than seven significant figures-but different from the rotation periods of visible features in the Jovian clouds? Why do the decameter bursts have a very intricate (submillisecond) fine structure? Why are the decameter sources beamed-that is, not emitting in all directions equally? Why are the decameter sources intermittent-that is, not “on” all the time?

These mysterious properties of the Jovian decameter emission are reminiscent of the properties of pulsars. Typical pulsars have magnetic fields a trillion times larger than Jupiter’s; they rotate 100,000 times faster; they are a thousandth as old; they are a thousand times more massive. The boundary of the Jovian magneto-sphere moves at less than one thousandth of the speed of the light cone of a pulsar. Nevertheless, it is possible that Jupiter is a kind of pulsar that failed, a local and quite unprepossessing model of the rapidly rotating neutron stars, which are one end product of stellar evolution. Major insights into the still baffling problems of pulsar emission mechanisms and magnetosphere geometries may follow from close-up spacecraft observation of Jovian decameter emission-for example, by NASA’s Voyager and Galileo missions.

EXPERIMENTAL ASTROPHYSICS is developing rapidly. In another few decades at the very latest, we should see direct experimental investigation of the interstellar medium: the heliopause-the boundary between the region dominated by the solar wind and that dominated by the interstellar plasma-is estimated to lie at not much more than 100 astronomical units (9.3 billion miles) from the Earth. (Now, if there were only a local solar system quasar and a backyard black hole-nothing fancy, you understand, just little baby ones-we might with in situ spacecraft measurements check out the greater body of modern astrophysical speculation.)

If we can judge by past experience, each future venture in experimental spacecraft astrophysics will find that (a) a major school of astrophysicists was entirely right; (b) no one agreed on which school it was that was right until the spacecraft results were in; and (c) an entire new corpus of still more fascinating and fundamental problems was unveiled by the space vehicle results.

CHAPTER 20

THE WORD “ROBOT,” first introduced by the Czech writer Karel Čapek, is derived from the Slavic root for “worker.” But it signifies a machine rather than a human worker. Robots, especially robots in space, have often received derogatory notices in the press. We read that a human being was necessary to make the terminal landing adjustments on Apollo 11, without which the first manned lunar landing would have ended in disaster; that a mobile robot on the Martian surface could never be as clever as astronauts in selecting samples to be returned to Earth-bound geologists; and that machines could never have repaired, as men did, the Skylab sunshade, so vital for the continuance of the Skylab mission.

But all these comparisons turn out, naturally enough, to have been written by humans. I wonder a small self-congratulatory element, a whiff of human chauvinism, has not crept into these judgments. Just as whites can sometimes detect racism and men can occasionally discern sexism, I wonder whether we cannot here glimpse some comparable affliction of the human spirit-a disease that as yet has no name. The word “anthropocentrism” does not mean quite the same thing. The word “humanism” has been pre-empted by other and more benign activities of our kind. From the analogy with sexism and racism I suppose the name for this malady is “speciesism”-the prejudice that there are no beings so fine, so capable, so reliable as human beings.

This is a prejudice because it is, at the very least, a prejudgment, a conclusion drawn before all the facts are in. Such comparisons of men and machines in space are comparisons of smart men and dumb machines. We have not asked what sorts of machines could have been built for the $30-or-so billion that the Apollo and Skylab missions cost.

Each human being is a superbly constructed, astonishingly compact, self-ambulatory computer-capable on occasion of independent decision making and real control of his or her environment. And, as the old joke goes, these computers can be constructed by unskilled labor. But there are serious limitations to employing human beings in certain environments. Without a great deal deal of protection, human beings would be inconvenienced on the ocean floor, the surface of Venus, the deep interior of Jupiter, or even on long space missions. Perhaps the only interesting results of Skylab that could not have been obtained by machines is that human beings in space for a period of months undergo a serious loss of bone calcium and phosphorus-which seems to imply that human beings may be incapacitated under 0 g for missions of six to nine months or longer. But the minimum interplanetary voyages have characteristic times of a year or two. Because we value human beings highly, we are reluctant to send them on very risky missions. If we do send human beings to exotic environments, we must also send along their food, their air, their water, amenities for entertainment and waste recycling, and companions. By comparison, machines require no elaborate life-support systems, no entertainment, no companionship, and we do not yet feel any strong ethical prohibitions against sending machines on one-way, or suicide, missions.

Certainly, for simple missions, machines have proved themselves many times over. Unmanned vehicles have performed the first photography of the whole Earth and of the far side of the Moon; the first landings on the Moon, Mars and Venus; and the first thorough orbital reconnaissance of another planet, in the Mariner 9 and Viking missions to Mars. Here on Earth it is increasingly common for high-technology manufacturing-for example, chemical and pharmaceutical plants-to be performed largely or entirely under computer control. In all these activities machines are able, to some extent, to sense errors, to correct mistakes, to alert human controllers some great distance away about perceived problems.

The powerful abilities of computing machines to do arithmetic-hundreds of millions of times faster than unaided human beings-are legendary. But what about really difficult matters? Can machines in any sense think through a new problem? Can they make discussions of the branched-contingency tree variety which we think of as characteristically human? (That is, I ask Question 1; if the answer is A, I ask Question 2; but if the answer is B, I ask Question 3; and so on.) Some decades ago the English mathematician A. M. Turing described what would be necessary for him to believe in machine intelligence. The condition was simply that he could be in teletype communication with a machine and be unable to tell that it was not a human being. Turing imagined a conversation between a man and a machine of the following quality:

INTERROGATOR: In the first line of your sonnet which reads “Shall I compare thee to a Summer’s day,” would not “a Spring day” do as well or better?

WITNESS: It wouldn’t scan.

INTERROGATOR: How about “a Winter’s day”? That would scan all right.

WITNESS: Yes, but nobody wants to be compared to a Winter’s day.

INTERROGATOR: Would you say Mr. Pickwick reminded you of Christmas?

WITNESS: In a way.

INTERROGATOR: Yet Christmas is a Winter’s day, and I do not think Mr. Pickwick would mind the comparison.

WITNESS: I don’t think you’re serious. By a Winter’s day one means a typical Winter’s day, rather than a special one like Christmas.

No device of this sophistication has yet been built, although I am not sure how many humans would pass Turing’s human test. But the amount of effort and money put into artificial intelligence has been quite limited, and there are only about a half-dozen major centers of such activity in the world. One of the more striking results obtained in a very limited universe of discourse-that of children’s blocks-has come from the work of Terry Winograd, then at the Massachusetts Institute of Technology. Here is a dialogue between man and machine, the machine having been programmed by Winograd:

Q: What does the box contain?

A: The blue pyramid and the blue box.

Q: How many blocks are not in the box?

A: Four of them.

Q: Is at least one of them narrower than the one which I told you to pick up?

A: Yes, the red cube.

Q: Is there a steeple?

A: Sorry, I don’t know the word “steeple.”

Q: A steeple is a stack which contains two green cubes and a pyramid, for example.

A: I understand.

Q: Are there any steeples now?

A: No.

Q: Build one.

The machine does. It reaches out its mechanical hand, moves the cubes and builds the structure that has just been described.

Q: When did you pick up the pyramid?

A: While I was stacking up the red cube, the large red block and the large green cube.

Q: Why?

A: To get rid of it.

Q: Why did you clear off that cube?

A: To put it on the large green cube.

As another example, a machine psychiatrist has been developed by Joseph Weizenbaum, also at MIT. This is a much simpler program than Winograd’s, since it involves nondirective psychotherapy, which, generally speaking, requires extremely simple-minded computer programs. Here is a striking dialogue between a human being and a computer psychotherapist (There is certainly a selection effect here. Many other such machine/human psychiatric dialogues are not nearly so striking. But I suppose most human/human psychiatric dialogues are not very striking either.) In this interaction, in order to spell out clearly the respective roles of therapist and patient, the computer therapist types upper case while the patient types lower case:

men are all alike

IN WHAT WAY

they’re always bugging us about something or other

CAN YOU THINK OF A SPECIFIC EXAMPLE

well, my boy friend made me come here

YOUR BOY FRIEND MADE YOU COME HERE

he noticed that i’m depressed much of the time

I AM SORRY TO HEAR YOU ARE DEPRESSED

he’s right. I am unhappy

DO YOU THINK COMING HERE WILL HELP YOU NOT TO BE UNHAPPY

i need some help, that much is clear

WHAT WOULD IT MEAN TO YOU IF YOU GOT SOME HELP

perhaps i could learn to get along with my mother

TELL ME MORE ABOUT YOUR FAMILY

my mother takes care of me

WHO ELSE IN YOUR FAMILY TAKES CARE OF YOU

my father

YOUR FATHER

you are like my father in some ways

WHAT RESEMBLANCE DO YOU SEE

you are not very aggressive, but i don’t think you want me to notice that

WHAT MAKES YOU THINK I AM NOT VERY AGGRESSIVE

you don’t argue with me

WHY DO YOU THINK I DON’T ARGUE WITH YOU

you are afraid of me

DOES IT PLEASE YOU TO BELIEVE I AM AFRAID OF YOU

it pleases my father to think i am afraid of him

WHAT ELSE COMES TO MIND WHEN YOU THINK OF YOUR FATHER

bullies

DOES THAT HAVE ANYTHING TO DO WITH THE FACT THAT YOUR BOY FRIEND MADE YOU COME HERE

This astonishing-one is very tempted to say “perceptive”-response from the computer is, of course, preprogrammed. But, then, so are the responses of human psychotherapists. In a time when more and more people in our society seem to be in need of psychiatric counseling, and when time-sharing of computers is widespread, I can even imagine the development of a network of computer psychotherapeutic terminals, something like arrays of large telephone booths, in which, for a few dollars a session, we are able to talk to an attentive, tested and largely nondirective psychotherapist. Ensuring the confidentiality of the psychiatric dialogue is one of several important steps still to be worked out.

ANOTHER SIGN of the intellectual accomplishments of machines is in games. Even exceptionally simple computers-those that can be wired by a bright ten-year-old-can be programmed to play perfect tic-tac-toe. Some computers can play world-class checkers. Chess is of course a much more complicated game than tic-tac-toe or checkers. Here programming a machine to win is more difficult, and novel strategies have been used, including several rather successful attempts to have a computer learn from its own experience in playing previous chess games. Computers can learn, for example, empirically the rule that it is better in the beginning game to control the center of the chessboard than the periphery. The ten best chess players in the world still have nothing to fear from any present computer. But the situation is changing. Recently a computer for the first time did well enough to enter the Minnesota State Chess Open. This may be the first time that a non-human has entered a major sporting event on the planet Earth (and I cannot help but wonder if robot golfers and designated hitters may be attempted sometime in the next decade, to say nothing of dolphins in free-style competition). The computer did not win the Chess Open, but this is the first time one has done well enough to enter such a competition. Chess-playing computers are improving extremely rapidly.

I have heard machines demeaned (often with a just audible sigh of relief) for the fact that chess is an area where human beings are still superior. This reminds me very much of the old joke in which a stranger remarks with wonder on the accomplishments of a checker-playing dog. The dog’s owner replies, “Oh, it’s not all that remarkable. He loses two games out of three.” A machine that plays chess in the middle range of human expertise is a very capable machine; even if there are thousands of better human chess players, there are millions who are worse. To play chess requires strategy, foresight, analytical powers, and the ability to cross-correlate large numbers of variables and to learn from experience. These are excellent qualities in those whose job it is to discover and explore, as well as those who watch the baby and walk the dog.

With this as a more or less representative set of examples of the state of development of machine intelligence, I think it is clear that a major effort over the next decade could produce much more sophisticated examples. This is also the opinion of most of the workers in machine intelligence.

In thinking about this next generation of machine intelligence, it is important to distinguish between self-controlled and remotely controlled robots. A self-controlled robot has its intelligence within it; a remotely controlled robot has its intelligence at some other place, and its successful operation depends upon close communication between its central computer and itself. There are, of course, intermediate cases where the machine may be partly self-activated and partly remotely controlled. It is this mix of remote and in situ control that seems to offer the highest efficiency for the near future.

For example, we can imagine a machine designed for the mining of the ocean floor. There are enormous quantities of manganese nodules littering the abyssal depths. They were once thought to have been produced by meteorite infall on Earth, but are now believed to be formed occasionally in vast manganese fountains produced by the internal tectonic activity of the Earth. Many other scarce and industrially valuable minerals are likewise to be found on the deep ocean bottom. We have the capability today to design devices that systematically swim over or crawl upon the ocean floor; that are able to perform spectrometric and other chemical examinations of the surface material; that can automatically radio back to ship or land all findings; and that can mark the locales of especially valuable deposits-for example, by low-frequency radio-homing devices. The radio beacon will then direct great mining machines to the appropriate locales. The present state of the art in deep-sea submersibles and in spacecraft environmental sensors is clearly compatible with the development of such devices. Similar remarks can be made for off-shore oil drilling, for coal and other subterranean mineral mining, and so on. The likely economic returns from such devices would pay not only for their development, but for the entire space program many times over.

When the machines are faced with particularly difficult situations, they can be programmed to recognize that the situations are beyond their abilities and to inquire of human operators-working in safe and pleasant environments-what to do next. The examples just given are of devices that are largely self-controlled. The reverse also is possible, and a great deal of very preliminary work along these lines has been performed in the remote handling of highly radioactive materials in laboratories of the U.S. Department of Energy. Here I imagine a human being who is connected by radio link with a mobile machine. The operator is in Manila, say; the machine in the Mindanao Deep. The operator is attached to an array of electronic relays, which transmits and amplifies his movements to the machine and which can, conversely, carry what the machine finds back to his senses. So when the operator turns his head to the left, the television cameras on the machine turn left, and the operator sees on a great hemispherical television screen around him the scene the machine’s searchlights and cameras have revealed. When the operator in Manila takes a few strides forward in his wired suit, the machine in the abyssal depths ambles a few feet forward. When the operator reaches out his hand, the mechanical arm of the machine likewise extends itself; and the precision of the man/machine interaction is such that precise manipulation of material at the ocean bottom by the machine’s fingers is possible. With such devices, human beings can enter environments otherwise closed to them forever.

In the exploration of Mars, unmanned vehicles have already soft-landed, and only a little further in the future they will roam about the surface of the Red Planet, as some now do on the Moon. We are not ready for a manned mission to Mars. Some of us are concerned about such missions because of the dangers of carrying terrestrial microbes to Mars, and Martian microbes, if they exist, to Earth, but also because of their enormous expense. The Viking landers deposited on Mars in the summer of 1976 have a very interesting array of sensors and scientific instruments, which are the extension of human senses to an alien environment.

The obvious post-Viking device for Martian exploration, one which takes advantage of the Viking technology, is a Viking Rover in which the equivalent of an entire Viking spacecraft, but with considerably improved science, is put on wheels or tractor treads and permitted to rove slowly over the Martian landscape. But now we come to a new problem, one that is never encountered in machine operation on the Earth’s surface. Although Mars is the second closest planet, it is so far from the Earth that the light travel time becomes significant. At a typical relative position of Mars and the Earth, the planet is 20 light-minutes away. Thus, if the spacecraft were confronted with a steep incline, it might send a message of inquiry back to Earth. Forty minutes later the response would arrive saying something like “For heaven’s sake, stand dead still.” But by then, of course, an unsophisticated machine would have tumbled into the gully. Consequently, any Martian Rover requires slope and roughness sensors. Fortunately, these are readily available and are even seen in some children’s toys. When confronted with a precipitous slope or large boulder, the spacecraft would either stop until receiving instructions from the Earth in response to its query (and televised picture of the terrain), or back off and start in another and safer direction.

Much more elaborate contingency decision networks can be built into the onboard computers of spacecraft of the 1980s. For more remote objectives, to be explored further in the future, we can imagine human controllers in orbit around the target planet, or on one of its moons. In the exploration of Jupiter, for example, I can imagine the operators on a small moon outside the fierce Jovian radiation belts, controlling with only a few seconds’ delay the responses of a spacecraft floating in the dense Jovian clouds.

Human beings on Earth can also be in such an interaction loop, if they are willing to spend some time on the enterprise. If every decision in Martian exploration must be fed through a human controller on Earth, the Rover can traverse only a few feet an hour. But the lifetimes of such Rovers are so long that a few feet an hour represents a perfectly respectable rate of progress. However, as we imagine expeditions into the farthest reaches of the solar system-and ultimately to the stars-it is clear that self-controlled machine intelligence will assume heavier burdens of responsibility.

In the development of such machines we find a kind of convergent evolution. Viking is, in a curious sense, like some great outsized, clumsily constructed insect. It is not yet ambulatory, and it is certainly incapable of self-reproduction. But it has an exoskeleton, it has a wide range of insectlike sensory organs, and it is about as intelligent as a dragonfly. But Viking has an advantage that insects do not: it can, on occasion, by inquiring of its controllers on Earth, assume the intelligence of a human being-the controllers are able to reprogram the Viking computer on the basis of decisions they make.

As the field of machine intelligence advances and as increasingly distant objects in the solar system become accessible to exploration, we will see the development of increasingly sophisticated onboard computers, slowly climbing the phylogenetic tree from insect intelligence to crocodile intelligence to squirrel intelligence and-in the not very remote future, I think-to dog intelligence. Any flight to the outer solar system must have a computer capable of determining whether it is working properly. There is no possibility of sending to the Earth for a repairman. The machine must be able to sense when it is sick and skillfully doctor its own illnesses. A computer is needed that is able either to fix or replace failed computer, sensor or structural components. Such a computer, which has been called STAR (self-testing and repairing computer), is on the threshold of development. It employs redundant components, as biology does-we have two lungs and two kidneys partly because each is protection against failure of the other. But a computer can be much more redundant than a human being, who has, for example, but one head and one heart.

Because of the weight premium on deep space exploratory ventures, there will be strong pressures for continued miniaturization of intelligent machines. It is clear that remarkable miniaturization has already occurred: vacuum tubes have been replaced by transistors, wired circuits by printed circuit boards, and entire computer systems by silicon-chip microcircuitry. Today a circuit that used to occupy much of a 1930 radio set can be printed on the tip of a pin. If intelligent machines for terrestrial mining and space exploratory applications are pursued, the time cannot be far off when household and other domestic robots will become commercially feasible. Unlike the classical anthropoid robots of science fiction, there is no reason for such machines to look any more human than a vacuum cleaner does. They will be specialized for their functions. But there are many common tasks, ranging from bartending to floor washing, that involve a very limited array of intellectual capabilities, albeit substantial stamina and patience. All-purpose ambulatory household robots, which perform domestic functions as well as a proper nineteenth-century English butler, are probably many decades off. But more specialized machines, each adapted to a specific household function, are probably already on the horizon.

It is possible to imagine many other civic tasks and essential functions of everyday life carried out by intelligent machines. By the early 1970s, garbage collectors in Anchorage, Alaska, and other cities won wage settlements guaranteeing them salaries of about $20,000 per annum. It is possible that the economic pressures alone may make a persuasive case for the development of automated garbage-collecting machines. For the development of domestic and civic robots to be a general civic good, the effective re-employment of those human beings displaced by the robots must, of course, be arranged; but over a human generation that should not be too difficult-particularly if there are enlightened educational reforms. Human beings enjoy learning.

We appear to be on the verge of developing a wide variety of intelligent machines capable of performing tasks too dangerous, too expensive, too onerous or too boring for human beings. The development of such machines is, in my mind, one of the few legitimate “spinoffs” of the space program. The efficient exploitation of energy in agriculture-upon which our survival as a species depends-may even be contingent on the development of such machines. The main obstacle seems to be a very human problem, the quiet feeling that comes stealthily and unbidden, and argues that there is something threatening or “inhuman” about machines performing certain tasks as well as or better than human beings; or a sense of loathing for creatures made of silicon and germanium rather than proteins and nucleic acids. But in many respects our survival as a species depends on our transcending such primitive chauvinisms. In part, our adjustment to intelligent machines is a matter of acclimatization. There are already cardiac pacemakers that can sense the beat of the human heart; only when there is the slightest hint of fibrillation does the pacemaker stimulate the heart. This is a mild but very useful sort of machine intelligence. I cannot imagine the wearer of this device resenting its intelligence. I think in a relatively short period of time there will be a very similar sort of acceptance for much more intelligent and sophisticated machines. There is nothing inhuman about an intelligent machine; it is indeed an expression of those superb intellectual capabilities that only human beings, of all the creatures on our planet, now possess.

CHAPTER 21

THE WORLD has changed since 1899, but there are few fields which have changed more-in the development of fundamental insights and in the discovery of new phenomena-than astronomy. Here are a few titles of recent papers published in the scientific magazines The Astrophysical Journal and Icarus: “G240-72: A New Magnetic White Dwarf with Unusual Polarization,” “Relativistic Stellar Stability: Preferred Frame Effects,” “Detection of Interstellar Methylamine,” “A New List of 52 Degenerate Stars,” “The Age of Alpha Centauri,” “Do OB Runaways Have Collapsed Companions?,” “Finite Nuclear-size Effects on Neutrino-pair Bremsstrahlung in Neutron Stars,” “Gravitational Radiation from Stellar Collapse,” “A Search for a Cosmological Component of the Soft X-ray Background in the Direction of M31,” “The Photochemistry of Hydrocarbons in the Atmosphere of Titan,” “The Content of Uranium, Thorium and Potassium in the Rocks of Venus as Measured by Venera 8,” “HCN Radio Emission from Comet Kohoutek,” “A Radar Brightness and Altitude Image of a Portion of Venus” and “A Mariner 9 Photographic Atlas of the Moons of Mars.” Our astronomical ancestors would have extracted a glimmer of meaning from these titles, but I think their principal reaction would have been one of incredulity.

WHEN I WAS ASKED to chair the 75th Anniversary Committee of the American Astronomical Society in 1974, I thought it would provide a pleasant opportunity to acquaint myself with the state of our subject at the end of the past century. I was interested to see where we had been, where we are today, and if possible, something of where we may be going. In 1897 the Yerkes Observatory, then the largest telescope in the world, was given a formal dedication, and a scientific meeting of astronomers and astrophysicists was held in connection with the ceremony. A second meeting was held at the Harvard College Observatory in 1898 and a third at the Yerkes Observatory in 1899, by which time what is now the American Astronomical Society had been officially founded.

The astronomy of 1897 to 1899 seems to have been vigorous, combative, dominated by a few strong personalities and aided by remarkably short publication times. The average time between submission and publication for papers in the Astrophysical Journal (Ap. J.) in this period seems to be better than in Astrophysical Journal Letters today. The fact that a great many papers were from the Yerkes Observatory, where the journal was edited, may have had something to do with this. The opening of the Yerkes Observatory at Williams Bay, Wisconsin-which has the year 1895 imprinted upon it-was delayed more than a year because of the collapse of the floor, which narrowly missed killing the astronomer E. E. Barnard. The accident is mentioned in Ap. J. (6:149), but one finds no hint of negligence there. However, the British journal Observatory (20:393), clearly implies careless construction and a cover-up to shield those responsible. We also discover on the same page of Observatory that the dedication ceremonies were postponed for some weeks to accommodate the travel schedule of Mr. Yerkes, the robber-baron donor. The Astrophysical Journal says that “the dedication ceremonies were necessarily postponed from October 1, 1897,” but does not say why.

Ap. J. was edited by George Ellery Hale, the director of the Yerkes Observatory, and by James E. Keeler, who in 1898 became the director of the Lick Observatory on Mount Hamilton in California. However, there was a certain domination of Ap. J. by Williams Bay, perhaps because the Lick Observatory dominated the Publications of the Astronomical Society of the Pacific (PASP) in the same period. Volume 5 of the Astrophysical Journal has no fewer than thirteen plates of the Yerkes Observatory, including one of the powerhouse. The first fifty pages of Volume 6 have a dozen more plates of the Yerkes Observatory. The Eastern dominance of the American Astronomical Society is also reflected by the fact that the first president of the Astronomical and Astrophysical Society of America was Simon Newcomb, of the Naval Observatory in Washington, and the first vice presidents, Young and Hale. West Coast astronomers complained about the difficulties in traveling to the third conference of astronomers and astrophysicists at Yerkes and seem to have voiced some pleasure that promised demonstrations with the Yerkes 40-inch refractor for this ceremony had to be postponed because of cloudy weather. This was about the most in the way of interobservatory rancor that can be found in either journal.

But in the same period Observatory had a keen nose for American astronomical gossip. From Observatory we find that there was a “civil war” at the Lick Observatory and a “scandal” associated with Edward Holden (the director before Keeler), who is said to have permitted rats in the drinking water at Mount Hamilton. It also published a story about a test chemical explosion scheduled to go off in the San Francisco Bay Area and to be monitored by a seismic device on Mount Hamilton. At the appointed moment, no staff member could see any sign of needle deflection except for Holden, who promptly dispatched a messenger down the mountain to alert the world to the great sensitivity of the Lick seismometer. But soon up the mountain came another messenger with the news that the test had been postponed. A much faster messenger was then dispatched to overtake the first and an embarrassment to the Lick Observatory was, Observatory notes, narrowly averted.

The youth of American astronomy in this period is eloquently reflected in the proud announcement in 1900 that the Berkeley Astronomical Department would henceforth be independent of the Civil Engineering Department at the University of California. A survey by Professor George Airy, later the British Astronomer Royal, regretted being unable to report on astronomy in America in 1832 because essentially there was none. He would not have said that in 1899.

There is never much sign in these journals of the intrusion of external (as opposed to academic) politics, except for an occasional notice such as the appointment by President McKinley of T. J. J. See as professor of mathematics to the U.S. Navy, and a certain continuing chilliness in scientific debates between the personnel of the Lick and Potsdam (Germany) Observatories.

Some signs of the prevailing attitudes of the 1890s occasionally trickle through. For example, in a description of an eclipse expedition to Siloam, Georgia, on May 28, 1900: “Even some of the whites were lacking in a very deep knowledge of things ‘eclipse-wise.’ Many thought it was a money-making scheme and what I intended to charge for admission was a very important question, frequently asked. Another idea was that the eclipse could be seen only from the inside of my observatory… Just here I wish to express my appreciation of the high moral tone of the community, for, with a population of only 100, including the immediate neighborhood, it sustains 2 white and 2 colored churches and during my stay I did not hear a single profane word… As an unsophisticated Yankee in the Southland, unused to Southern ways, I naturally made many little slips that were not considered ‘just the thing.’ The smiles at my prefixing ‘Mr.’ to the name of my colored helper caused me to change it to ‘Colonel,’ which was entirely satisfactory to everybody.”

A board of visitors was appointed to resolve some (never publicly specified) problems at the U.S. Naval Observatory. A report of this group-which consisted of two obscure senators and Professors Edward C. Pickering, George C. Comstock and Hale-is illuminating because it mentions dollar amounts. We find that the annual running costs of the major observatories in the world were: Naval Observatory, $85,000; Paris Observatory, $53,000; Greenwich Observatory (England), $49,000; Harvard Observatory, $46,000; and Pulkowa Observatory (Russia), $36,000. The salaries of the two directors of the U.S. Naval Observatory were $4,000 each, and at the Harvard Observatory, $5,000. The distinguished board of visitors recommended that in a “schedule of salaries which could be expected to attract astronomers of the class desired,” the salary of directors of observatories should be $6,000. At the Naval Observatory, computers (exclusively human at the time) were paid $1,200 per annum, but at the Harvard Observatory only $500 per annum, and were almost exclusively women. In fact, all salaries at Harvard, except for the director’s, were significantly lower than at the Naval Observatory. The committee stated: “The great difference in salaries at Washington and Cambridge, especially for the officers of lower grade, is probably unavoidable. This is partly due to Civil Service Rules.” An additional sign of astronomical impecuniosity is the announcement of the post of “volunteer research assistant” at Yerkes, which had no associated pay but which was said to provide good experience for students with higher degrees.

Then, as now, astronomy was besieged by “paradoxers,” proponents of fringe or crackpot ideas. One proposed a telescope with ninety-one lenses in series as an alternative to a telescope with a smaller number of lenses of larger aperture. The British in this period were similarly plagued but in perhaps a gentler way. For example, an obituary in the Monthly Notices of the Royal Astronomical Society (59:226) of Henry Perigal informs us that the deceased had celebrated his ninety-fourth birthday by becoming a member of the Royal Institution, but was elected a Fellow of the Royal Astronomical Society in 1850. However, “our publications contain nothing from his pen.” The obituary describes “the remarkable way in which the charm of Mr. Perigal’s personality won him a place which might have seemed impossible of attainment for a man of his views; for there is no masking the fact that he was a paradoxer pure and simple, his main conviction being that the Moon did not rotate, and his main astronomical aim in life being to convince others, and especially young men not hardened in the opposite belief, of their grave error. To this end he made diagrams, constructed models, and wrote poems; bearing with heroic cheerfulness the continued disappointment of finding none of them of any avail. He has, however, done excellent work apart from this unfortunate misunderstanding.”

The number of American astronomers in this period was very small. The by-laws of the Astronomical and Astrophysical Society of America state that a quorum is constituted by twenty members. By the year 1900 only nine doctorates had been granted in astronomy in America. In that year there were four astronomical doctorates: two from Columbia University for G. N. Bauer and Carolyn Furness; one from the University of Chicago for Forest Ray Moulton; and one from Princeton University for Henry Norris Russell.

Some idea of what was considered important scientific work in this period can be garnered from the prizes that were awarded. E. E. Barnard received the Gold Medal of the Royal Astronomical Society in part for his discovery of the Jovian moon Jupiter 5 and for his astronomical photography with a portrait lens. His steamer, however, was caught in an Atlantic storm, and he did not arrive in time for the celebration ceremony. He is described as requiring several days to recover from the storm, whereupon the RAS hospitably gave a second dinner for him. Barnard’s lecture seems to have been spectacular and made full use of that recently improved audio-visual aid, the lantern slide projector.

In his discussion of his photograph of the region of the Milky Way near Theta Ophiuchus he concluded that “the entire groundwork of the Milky Way… has a substratum of nebulous matter.” (Meanwhile H. K. Palmer reported no nebulosity in photographs of the globular cluster M13.) Barnard, who was a superb visual observer, expressed considerable doubts about Percival Lowell’s view of an inhabited and canal-infested Mars. In his thanks to Barnard for his lecture, the president of the Royal Astronomical Society, Sir Robert Ball, voiced concern that henceforth he “should regard the canals in Mars with some suspicion, nay, even the seas [of Mars, the dark areas] had partly fallen under a ban. Perhaps the lecturer’s recent experiences on the Atlantic might explain something of this mistrust.” Lowell’s views were not then in favor in England, as another notice in Observatory indicated. In response to an inquiry on which books had most pleased and interested him in 1896, Professor Norman Lockyer replied, “Mars by Percival Lowell, Sentimental Tommy by J. M. Barrie. (No Time for Reading Seriously).”

Prizes in astronomy for 1898 awarded by the Académie Française included one to Seth Chandler for the discovery of the variation in latitude; one to Belopolsky, partly for studies of spectroscopic binary stars; and one to Schott for work on terrestrial magnetism. There was also a prize competition for the best treatise on “the theory of perturbations of Hyperion,” a moon of Saturn. We are informed that “the only essay presented was that by Dr. G. W. Hill of Washington to whom the prize was awarded.”

The Astronomical Society of the Pacific’s Bruce Medal was awarded in 1899 to Dr. Arthur Auwers of Berlin. The dedicatory address included the following remarks: “Today Auwers stands at the head of German astronomy. In him is seen the highest type of investigator in our time, one perhaps better developed in Germany than in any other country. The work of men of this type is marked by minute and careful research, untiring industry in the accumulation of facts, caution in propounding new theories or explanations, and, above all, the absence of effort to gain recognition by being the first to make a discovery.” In 1899 the Henry Draper Gold Medal of the National Academy of Sciences was presented for the first time in seven years. The recipient was Keeler. In 1898 Brooks, whose observatory was in Geneva, New York, announced the discovery of his twenty-first comet-which Brooks described as “achieving his majority.” Shortly thereafter he received the Lalande Prize of the Académie Française for his record in discovering comets.

In 1897, in connection with an exhibition in Brussels, the Belgian government offered prizes for the solutions of certain problems in astronomy. These problems included the numerical value ofred prizes for the solutions of certain problems in astronomy. These problems included the numerical value of the acceleration due to gravity on Earth, the secular acceleration of the Moon, the net motion of the solar system through space, the variation of latitude, the photography of planetary surfaces, and the nature of the canals of Mars. A final topic was the invention of a method to observe the solar corona in the absence of an eclipse. Monthly Notices (20:145) commented: “… if this pecuniary reward does induce anyone to solve this last problem or in fact any of the others, we think the money will be well spent.”

However, reading the scientific papers of this time, one gets the impression that the focus had shifted to other topics than those for which prizes were-being given. Sir William and Lady Huggins performed laboratory experiments which showed that at low pressures the emission spectrum of calcium exhibited only the so-called H and K lines. They concluded that the Sun was composed chiefly of hydrogen, helium, “coronium” and calcium. Huggins had earlier established a stellar spectral sequence, which he believed was evolutionary. The Darwinian influence in science was very strong in this period, and among American astronomers T. J. J. See’s work was notably dominated by a Darwinian perspective. It is interesting to compare Huggins’ spectral sequence with the present Morgan-Keenan spectral types:

HUGGINS’ STELLAR SPECTRAL SEQUENCE

Order of Increasing Age-Star (and modern spectral type in parentheses)-

Young-Sirius (A1V)

…

Altair (A7 IV-V)

Rigel (B8Ia)

Deneb (A2Ia)

…

…– Vega (A0V)

– Capella (G8, G0)

Arcturus (K1 III)

Aldebaran (K5 III)-Sun (G0)

Old-Betelgeuse (M2 I)-

Note: The modern stellar spectral sequence runs, from “early” to “late” spectral types, as O, B, A, F, G, K, M. Huggins was very nearly right.

We can see here the origin of the present terms “early” and “late” spectral type, which reflect the Darwinian spirit of late Victorian science. It is also clear that there is a reasonably continuous gradation of spectral types here, and the beginnings-through the later Hertzsprung-Russell diagram-of modern theories of stellar evolution.

There were major developments in physics during this period and readers of Ap. J. were alerted to them by the reprinting of summaries of important papers. Experiments were still being performed on the basic radiation laws. In some papers, the level of physical sophistication was not of the highest caliber, as, for example, in an article in PASP (11:18) where the linear momentum of Mars is calculated as the single product of the mass of the planet and the linear velocity of the surface. It concluded “the planet, exclusive of the cap, has a momentum of 183 and 3/8 septillion foot pounds.” Exponential notation for large numbers was evidently not in wide use.

In this time we have the publication of visual and photographic light curves, for example, of stars in M5; and experiments in filter photography of Orion by Keeler. An obviously exciting topic was time-variable astronomy, which must then have generated something of the excitement that pulsars, quasars and X-ray sources do today. There were many studies of variable velocities in the line of sight from which were derived the orbits of spectroscopic binaries, as well as periodic variations in the apparent velocity of Omicron Ceti from the Doppler displacement of H gamma and other spectral lines.

The first infrared measurements of stars were performed at the Yerkes Observatory by Ernest F. Nichols. The study concludes: “We do not receive from Arcturus more heat than would reach us from a candle at a distance of 5 or 6 miles.” No further calculations are given. The first experimental observations of the infrared opacity of carbon dioxide and water vapor were performed in this period by Rubens and Aschkinass, who essentially discovered the v₂ fundamental of carbon dioxide at 15 microns and the pure rotation spectrum of water.

There is preliminary photographic spectroscopy of the Andromeda nebula by Julius Scheiner at Potsdam, Germany, who concludes correctly that “the previous suspicion that the spiral nebulae are star clusters is now raised to a certainty.” As an example of the level of personal vituperation tolerated at this time, the following is an extract from a paper by Scheiner in which W. W. Campbell is criticized: “In the November number of the Astrophysical Journal, Professor Campbell attacks, with much indignation, some remarks of mine criticizing his discoveries… Such sensitiveness is somewhat surprising on the part of one who is himself given to severely taking others to task. Further, an astronomer who frequently observes phenomena which others cannot see, and fails to see those which others can, must be prepared to have his opinions contested. If, as Professor Campbell complains, I have only supported my views by a single example, I was only withheld by courteous motives from adding another. Namely, the fact that Professor Campbell cannot perceive the lines of aqueous vapor in the spectrum of Mars which were seen by Huggins and Vogel in the first place, and, after Mr. Campbell had called their existence in question, were again seen and identified with certainty by Professor Wilsing and myself.” The amount of water vapor in the Martian atmosphere that is now known to exist would have been entirely indetectable by the spectroscopic methods then in use.

Spectroscopy was a dominant element in late-nineteenth-century science. Ap. J. was busily publishing Rowland’s solar spectrum, which ran to 20,000 wavelengths, each to seven significant figures. It published a major obituary of Bunsen. Occasionally the astronomers took note of the extraordinary nature of their discoveries: “It is simply amazing that the feeble twinkling light of a star can be made to produce such an autographic record of substance and condition of the inconceivably distant luminary.” A major topic of debate for the Astrophysical Journal was whether spectra should be shown with red to the left or to the right. Those who favored red to the left cited the analogy of the piano (where high frequencies are to the right), but Ap. J. opted gamely for red to the right. Some room for compromise was available on whether, in lists of wavelengths, red should be at the top or at the bottom. Feelings ran high, and Huggins wrote to say that “any change… would be little less than intolerable.” But the Ap. J. won anyway.

Another major discussion in this period was on the nature of sunspots. G. Johnstone Stoney proposed that they were caused by a layer of condensed clouds in the photosphere of the Sun. But Wilson and FitzGerald objected to this on the ground that no conceivable condensates could exist at these high temperatures, with the possible exception of carbon. They suggested instead and very vaguely that sunspots are due to “reflection by convection streams of gas.” Evershed had a more ingenious idea. He thought that sunspots were holes in the outer photosphere of the Sun, permitting us to see to much greater and hotter depths. But why are they dark? He proposed that all the radiation would be moved from the visible to the inaccessible ultraviolet. This, of course, was before the Planck distribution of radiation from a hot object was understood. It was not at this time thought impossible that the spectral distributions of black bodies of different temperatures should cross; and some experimental curves of this period indeed showed such crossing-due, as we now know, to emissivity and absorptivity differences.

Ramsay had recently discovered the element krypton, which was said to have, among fourteen detectable spectral lines, one at 5570 Å, coincident with “the principal line of the aurora.” E. B. Frost concluded: “Thus it seems that the true origin of that hitherto perplexing line has been discovered.” We now know it is due to oxygen.

There were a great many papers on instrumental design, one of the more interesting being by Hale. In January 1897 he suggested that both refracting and reflecting telescopes were needed, but noted that there was a clear movement toward reflectors, especially equatorial coude telescopes. In a historical memoir, Hale mentions that the 40-inch lens was available to the Yerkes Observatory only because a previous plan to build a large refractor near Pasadena, California, had fallen through. What, I wonder, would the history of astronomy have been like if the plan had succeeded? Curiously enough, Pasadena seems to have made an offer to the University of Chicago to have the Yerkes Observatory situated there. It would have been a long commute for 1897.

AT THE END of the nineteenth century, solar system studies displayed the same mixture of future promise and current confusion that the stellar work did. One of the most notable papers of the period, by Henry Norris Russell, is called “The Atmosphere of Venus.” It is a discussion of the extension of the cusps of the crescent Venus, based in part on the author’s observations with the 5-inch finder telescope of the “great equatorial” of the Halsted Observatory at Princeton. Perhaps the young Russell was not yet considered fully reliable operating larger telescopes at Princeton. The essence of the analysis is correct by present standards. Russell concluded that refraction of sunlight was not responsible for the extension of the cusps, and that the cause was to be found in the scattering of sunlight: “… the atmosphere of Venus, like our own, contains suspended particles of dust or fog of some sort, and… what we see is the upper part of this hazy atmosphere, illuminated by rays that have passed close to the planet’s surface.” He later says that the apparent surface may be a dense cloud layer. The height of the haze is calculated as about 1 kilometer above what we would now call the main cloud deck, a number that is just consistent with limb photography by the Mariner 10 spacecraft. Russell thought, from the work of others, that there was some spectroscopic evidence for water vapor and oxygen in a thin Venus atmosphere. But the essence of his argument has stood the test of time remarkably well.

William H. Pickering’s discovery of Phoebe, the outermost satellite of Saturn, was announced; and Andrew E. Douglass of the Lowell Observatory published observations that led him to conclude that Jupiter 3 rotates about one hour slower than its period of revolution, a conclusion incorrect by one hour.

Others who estimated periods of rotation were not quite so successful. For example, there was a Leo Brenner who observed from the Manora Observatory in a place called Lussinpiccolo. Brenner severely criticized Percival Lowell’s estimate of the rotation period of Venus. Brenner himself compared two drawings of Venus in white light made by two different people four years apart-from which he deduced a rotation period of 23 hours, 57 minutes and 36.37728 seconds, which he said agreed well with the mean of his own “most reliable” drawings. Considering this, Brenner found it incomprehensible that there could still be partisans of a 224.7-day rotation period and concluded that “an inexperienced observer, an unsuitable telescope, an unhappily chosen eyepiece, a very small diameter of the planet, observed with an insufficient power, and a low declination, all together explained Mr. Lowell’s peculiar drawings.” The truth, of course, lies not between the extremes of Lowell and Brenner, but rather at the other end of the scale, with a minus sign, a retrograde period of 243 days.

In another communication Herr Brenner begins: “Gentlemen: I have the honor to inform you that Mrs. Manora has discovered a new division in the Saturnian ring system”-from which we discover that there is a Mrs. Manora at the Manora Observatory in Lussinpiccolo and that she performs observations along with Herr Brenner. Then follows a description of how the Encke, Cassini, Antoniadi, Strove and Manora divisions are all to be kept straight. Only the first two have stood the test of time. Herr Brenner seems to have faded into the mists of the nineteenth century.

AT THE SECOND CONFERENCE of Astronomers and Astrophysicists at Cambridge, there was a paper on the “suggestion” that asteroid rotation, if any, might be deduced from a light curve. But no variation of the brightness with time was found, and Henry Parkhurst concluded: “I think it is safe to dismiss the theory.” It is now a cornerstone of asteroid studies.

In a discussion of the thermal properties of the Moon, made independently of the one-dimensional equation of heat conduction but based on laboratory emissivity measurements, Frank Very concluded that a typical lunar daytime temperature is about 100°C-exactly the right answer. His conclusion is worth quoting: “Only the most terrible of Earth’s deserts where the burning sands blister the skin, and the men, beasts, and birds drop dead, can approach noontide on the cloudless surface of our satellite. Only the extreme polar latitudes of the Moon can have an endurable temperature by day, to say nothing of the night, when we should have to become troglodytes to preserve ourselves from such intense cold.” The expository styles were often fine.

Earlier in the decade, Maurice Loewy and Pierre Puiseux at the Paris Observatory had published an atlas of lunar photographs, the theoretical consequences of which were discussed in Ap. J. (5:51). The Paris group proposed a modified volcanic theory for the origin of the lunar craters, rills and other topographic forms, which was later criticized by E. E. Barnard after he examined the planet with the 40-inch telescope. Barnard was then criticized by the Royal Astronomical Society for his criticism, and so on. One of the arguments in this debate had a deceptive simplicity: volcanoes produce water; there is no water on the moon; therefore the lunar craters are not volcanic. While most of the lunar craters are not volcanic, this is not a convincing argument because it neglects the problem of possible repositories for water. Very’s conclusions on the temperature of the lunar poles could have been read with some profit. Water there freezes out as frost. The other possibility is that water might escape from the Moon to space.

This was recognized by Stoney in a remarkable paper called “Of Atmospheres upon Planets and Satellites.” He deduced that there should be no lunar atmosphere because of the very rapid escape to space of gases from the low lunar gravity, or any large build-up of the lightest gases, hydrogen and helium, on Earth. He believed that there was no water vapor in the Martian atmosphere and that Mars’ atmosphere and caps were probably carbon dioxide. He implied that hydrogen and helium were to be expected on Jupiter, and that Triton, the largest moon of Neptune, might have an atmosphere. Each of these conclusions is in accord with present-day findings or opinions. He also concluded that Titan should be airless, a prediction with which some modern theorists agree-although Titan seems to have another view of the matter (see Chapter 13).

In this period there are also a few breath-taking speculations, such as one by the Rev. J. M. Bacon that it would be a good idea to perform astronomical observations from high altitudes-from, for example, a free balloon. He suggested that there would be at least two advantages: better seeing and ultraviolet spectroscopy. Goddard later made similar proposals for rocket-launched observatories (Chapter 18).

Hermann Vogel had previously found, by eyeball spectroscopy, an absorption band at 6183 Å in the body of Saturn. Subsequently the International Color Photo Company of Chicago made photographic plates, which were so good that wavelengths as long as H Alpha in the red could be detected for a fifth-magnitude star. This new emulsion was used at Yerkes, and Hale reported that there was no sign of the 6183 Å band for the rings of Saturn. The band is now known to be at 6190 Å and is 6v₃ of methane.

Another reaction to Percival Lowell’s writings can be gleaned from the address of James Keeler at the dedication of the Yerkes Observatory:

It is to be regretted that the habitability of the planets, a subject of which astronomers profess to know little, has been chosen as a theme for exploitation by the romancer, to whom the step from habitability to inhabitants is a very short one. The result of his ingenuity is that fact and fancy become inextricably tangled in the mind of the layman, who learns to regard communication with the inhabitants of Mars as a project deserving serious consideration (for which he may even wish to give money to scientific societies), and who does not know that it is condemned as a vagary by the very men whose labors have excited the imagination of the novelist. When he is made to understand the true state of our knowledge of these subjects, he is much disappointed and feels a certain resentment towards science, as if it had imposed upon him. Science is not responsible for these erroneous ideas, which, having no solid basis, gradually die out and are forgotten.

The address of Simon Newcomb on this occasion contains some remarks which apply generally, if a little idealistically, to the scientific endeavor:

Is the man thus moved into the exploration of nature by an unconquerable passion more to be envied or pitied? In no other pursuit does such certainty come to him who deserves it No life is so enjoyable as that whose energies are devoted to following out the inborn impulses of one’s nature. The investigator of truth is little subject to the disappointments which await the ambitious man in other fields of activity. It is pleasant to be one of a brotherhood extending over the world in which no rivalry exists except that which comes out of trying to do better work than anyone else, while mutual admiration stifles jealousy… As the great captain of industry is amoved by the love of wealth and the politician by the love of power, so the astronomer is moved by the love of knowledge for its own sake and not for the sake of its application. Yet he is proud to know that his science has been worth more to mankind than it has cost… He feels that man does not live by bread alone. If it is not more than bread to know the place we occupy in the universe, it is certainly something that we should place not far behind the means of subsistence.

AFTER READING through the publications of astronomers three-quarters of a century ago, I felt an irresistible temptation to imagine the 150th Anniversary Meeting of the American Astronomical Society-or whatever name it will have metamorphosed into by then-and guess how our present endeavors will be viewed.

In examining the late-nineteenth-century literature, we are amused at some of the debates on sunspots, and impressed that the Zeeman effect was not considered a laboratory curiosity but something to which astronomers should devote considerable attention. These two threads intertwined, as if prefigured, a few years later in G. E. Hale’s discovery of large magnetic field strengths in sunspots.

Likewise we find innumerable papers in which the existence of a stellar evolution is assumed but its nature remains hidden; in which the Kelvin-Helmholtz gravitational contraction was considered the only possible stellar energy source, and nuclear energy remained entirely unanticipated. But at the same time, and sometimes in the same volume of the Astrophysical Journal, there is acknowledgment of curious work being done on radioactivity by a man named Becquerel in France. Here again we see the two apparently unrelated threads moving through our few-years snapshot of late-nineteenth-century astronomy and destined to intertwine forty years later.

There are many related examples-for instance, in the interpretation of series spectra of nonhydrogenic elements obtained at the telescope and pursued in the laboratory. New physics and new astronomy were the complementary sides of the emerging science of astrophysics.

Accordingly, it is difficult not to wonder how many of the deepest present debates-for example, on the nature of quasars, or the properties of black holes, or the emission geometry of pulsars-must await an intertwining with new developments in physics. If the experience of seventy-five years ago is any guide, there will already be people today who dimly guess which physics will join with which astronomy. And a few years later, the connection will be considered obvious.

We also see in the nineteenth-century material a number of cases where the observational methods or their interpretations are clearly in default by present standards. Planetary periods deduced to ten significant figures by the comparison of two drawings made by different people of features we now know to be unreal to begin with is one of the worst examples. But there are many others, including a plethora of “double-star measurements” of widely separated objects, which are mainly physically unconnected stars; a fascination with pressure and other effects on the frequencies of spectral lines when no one is paying any attention to curve of growth analysis; and acrimonious debates on the presence or absence of some substance based solely upon naked-eye spectroscopy.

Also curious is the sparseness of the physics in late-Victorian astrophysics. Reasonably sophisticated physics is almost exclusively the province of geometrical and physical optics, the photographic process, and celestial mechanics. To make theories of stellar evolution based on stellar spectra without wondering much about the dependence of excitation and ionization on temperature, or attempting to calculate the subsurface temperature of the Moon without ever solving Fourier’s equation of heat conduction seems to me to be less than quaint. In seeing elaborate empirical representations of laboratory spectra, the modern reader becomes impatient for Bohr and Schrödinger and their successors to come along and develop quantum mechanics.

I wonder how many of our present debates and most celebrated theories will appear, from the vantage point of the year 2049, marked by shoddy observations, indifferent intellectual powers or inadequate physical insight. I have the sense that we are today more self-critical than scientists were in 1899; that because of the larger population of astronomers, we check each other’s results more often; and that, in part because of the existence of organizations like the American Astronomical Society, the standards of exchange and discussion of results have risen significantly. I hope our colleagues of 2049 will agree.

The major advance between 1899 and 1974 must be considered technological. But in 1899 the world’s largest refractor had been built. It is still the world’s largest refractor. A reflector of 100-inch aperture was beginning to be considered. We have improved on that aperture only by a factor of two in the intervening years. But what would our colleagues of 1899-living after Hertz but before Marconi-have made of the Arecibo Observatory, or the Very Large Array, or Very Long Baseline Interferometry (VLBI)? Or checking out the debate on the period of rotation of Mercury by radar Doppler spectroscopy? Or testing the nature of the lunar surface by returning some of it to Earth? Or pursuing the problem of the nature and habitability of Mars by orbiting it for a year and returning 7,200 photographs of it, each of higher quality than the best 1899 photographs of the Moon? Or landing on the planet with imaging systems, microbiology experimentation, seismometers and gas chromatograph/mass spectrometers, which did not even vaguely exist in 1899? Or testing cosmological models by orbital ultraviolet spectroscopy of interstellar deuterium-when neither the models to be tested nor the existence of the atom that tests it were known in 1899, much less the technique of observation?

It is clear that in the past seventy-five years American and world astronomy has moved enormously beyond even the most romantic speculations of the late-Victorian astronomers. And in the next seventy-five years? It is possible to make pedestrian predictions. We will have completely examined the electromagnetic spectrum from rather short gamma rays to rather long radio waves. We will have sent unmanned spacecraft to all of the planets and most of the satellites in the solar system. We will have launched spacecraft into the Sun to do experimental stellar structure, beginning perhaps-because of the low temperatures-with the sunspots. Hale would have appreciated that. I think it possible that seventy-five years from now, we will have launched subrelativistic spacecraft-traveling at about 0.1 the speed of light-to the nearby stars. Among other benefits, such missions would permit direct examination of the interstellar medium and give us a longer baseline for VLBI than many are thinking of today. We will have to invent some new superlative to succeed “very”-perhaps “ultra.” The nature of pulsars, quasars and black holes should by then be well in hand, as well as the answers to some of the deepest cosmological questions. It is even possible that we will have opened up a regular communications channel with civilizations on planets of other stars, and that the cutting edge of astronomy as well as many other sciences will come from a kind of Encyclopaedia Galactica, transmitted at very high bit rates to some immense array of radio telescopes.

But in reading the astronomy of seventy-five years ago, I think it likely that, except for interstellar contact, these achievements, while interesting, will be considered rather old-fashioned astronomy, and that the real frontiers and the fundamental excitement of the science will be in areas that depend on new physics and new technology, which we can today at best dimly glimpse.

CHAPTER 22

THROUGH ALL of our history we have pondered the stars and mused whether humanity is unique or if, somewhere else in the dark of the night sky, there are other beings who contemplate and wonder as we do, fellow thinkers in the cosmos. Such beings might view themselves and the universe differently. Somewhere else there might be very exotic biologies and technologies and societies. In a cosmic setting vast and old beyond ordinary human understanding, we are a little lonely; and we ponder the ultimate significance, if any, of our tiny but exquisite blue planet. The search for extraterrestrial intelligence is the search for a generally acceptable cosmic context for the human species. In the deepest sense, the search for extraterrestrial intelligence is a search for ourselves.

In the last few years-in one-millionth the lifetime of our species on this planet-we have achieved an extraordinary technological capability which enables us to seek out unimaginably distant civilizations even if they are no more advanced than we. That capability is called radio astronomy and involves single radio telescopes, collections or arrays of radio telescopes, sensitive radio detectors, advanced computers for processing received data, and the imagination and skill of dedicated scientists. Radio astronomy has in the last decade opened a new window on the physical universe. It may also, if we are wise enough to make the effort, cast a profound light on the biological universe.

Some scientists working on the question of extraterrestrial intelligence, myself among them, have attempted to estimate the number of advanced technical civilizations-defined operationally as societies capable of radio astronomy-in the Milky Way Galaxy. Such estimates are little better than guesses. They require assigning numerical values to quantities such as the numbers and ages of stars; the abundance of planetary systems and the likelihood of the origin of life, which we know less well; and the probability of the evolution of intelligent life and the lifetime of technical civilizations, about which we know very little indeed.

When we do the arithmetic, the sorts of numbers we come up with are, characteristically, around a million technical civilizations. A million civilizations is a breath-takingly large number, and it is exhilarating to imagine the diversity, lifestyles and commerce of those million worlds. But the Milky Way Galaxy contains some 250 billion stars, and even with a million civilizations, less than one star in 200,000 would have a planet inhabited by an advanced civilization. Since we have little idea which stars are likely candidates, we will have to examine a very large number of them. Such considerations suggest that the quest for extraterrestrial intelligence may require a significant effort.

Despite claims about ancient astronauts and unidentified flying objects, there is no firm evidence for past visitations of the Earth by other civilizations (see Chapters 5 and 6). We are restricted to remote signaling and, of the long-distance techniques available to our technology, radio is by far the best. Radio telescopes are relatively inexpensive; radio signals travel at the speed of light, faster than which nothing can go; and the use of radio for communication is not a short-sighted or anthropocentric activity. Radio represents a large part of the electromagnetic spectrum, and any technical civilization anywhere in the Galaxy will have discovered radio early-just as in the last few centuries we have explored the entire electromagnetic spectrum from short gamma rays to very long radio waves. Advanced civilizations might very well use some other means of communication with their peers. But if they wish to communicate with backward or emerging civilizations, there are only a few obvious methods, the chief of which is radio.

The first serious attempt to listen for possible radio signals from other civilizations was carried out at the National Radio Astronomy Observatory in Greenbank, West Virginia, in 1959 and 1960. It was organized by Frank Drake, now at Cornell University, and was called Project Ozma, after the princess of the Land of Oz, a place very exotic, very distant and very difficult to reach, Drake examined two nearby stars, Epsilon Eridani and Tau Ceti, for a few weeks with negative results. Positive results would have been astonishing because as we have seen, even rather optimistic estimates of the number of technical civilizations in the Galaxy imply that several hundred thousand stars must be examined in order to achieve success by random stellar selection.

Since Project Ozma, there have been six or eight other such programs, all at a rather modest level, in the United States, Canada and the Soviet Union. All results have been negative. The total number of individual stars examined to date in this way is less than a thousand. We have performed something like one tenth of one percent of the required effort.

However, there are signs that much more serious efforts may be mustered in the reasonably near future. All the observing programs to date have involved quite tiny amounts of time on large telescopes, or when large amounts of time have been committed, only very small radio telescopes could be used. A comprehensive examination of the problem was recently made by a NASA committee chaired by Philip Morrison of the Massachusetts Institute of Technology. The committee identified a wide range of options, including new (and expensive) giant ground-based and spaceborne radio telescopes. It also pointed out that major progress can be made at modest cost by the development of more sensitive radio receivers and of ingenious computerized data-processing systems. In the Soviet Union there is a state commission devoted to organizing a search for extraterrestrial intelligence, and the large RATAN-600 radio telescope in the Caucasus, recently completed, is devoted part-time to this effort. Hand in hand with the recent spectacular advances in radio technology, there has been a dramatic increase in the scientific and public respectability of the entire subject of extraterrestrial life. A clear sign of the new attitude is the Viking missions to Mars, which are to a significant extent dedicated to the search for life on another planet.

But along with the burgeoning dedication to a serious search, a slightly negative note has emerged which is nevertheless very interesting. A few scientists have lately asked a curious question: If extraterrestrial intelligence is abundant, why have we not already seen its manifestations? Think of the advances by our own technical civilization in the past ten thousand years and imagine such advances continued over millions or billions of years more. If only a tiny fraction of advanced civilizations are millions or billions of years more advanced than ours, why have they not produced artifacts, devices or even industrial pollution of such magnitude that we would have detected it? Why have they not restructured the entire Galaxy for their convenience?

Skeptics also ask why there is no clear evidence of extraterrestrial visits to Earth. We have already launched slow and modest interstellar spacecraft. A society more advanced than ours should be able to ply the spaces between the stars conveniently if not effortlessly. Over millions of years such societies should have established colonies, which might themselves launch interstellar expeditions. Why are they not here? The temptation is to deduce that there are at most a few advanced extraterrestrial civilizations-either because statistically we are one of the first technical civilizations to have emerged or because it is the fate of all such civilizations to destroy themselves before they are much further along than we.

It seems to me that such despair is quite premature. All such arguments depend on our correctly surmising the intentions of beings far more advanced than ourselves, and when examined more closely I think these arguments reveal a range of interesting human conceits. Why do we expect that it will be easy to recognize the manifestations of very advanced civilizations? Is our situation not closer to that of members of an isolated society in the Amazon basin, say, who lack the tools to detect the powerful international radio and television traffic that is all around them? Also, there is a wide range of incompletely understood phenomena in astronomy. Might the modulation of pulsars or the energy source of quasars, for example, have a technological origin? Or perhaps there is a galactic ethic of noninterference with backward or emerging civilizations. Perhaps there is a waiting time before contact is considered appropriate, so as to give us a fair opportunity to destroy ourselves first, if we are so inclined. Perhaps all societies significantly more advanced than our own have achieved an effective personal immortality and lose the motivation for interstellar gallivanting, which may, for all we know, be a typical urge only of adolescent civilizations. Perhaps mature civilizations do not wish to pollute the cosmos. There is a very long list of such “perhapses,” few of which we are in a position to evaluate with any degree of assurance.

The question of extraterrestrial civilizations seems to me entirely open. Personally, I think it far more difficult to understand a universe in which we are the only technological civilization, or one of a very few, than to conceive of a cosmos brimming over with intelligent life. Many aspects of the problem are, fortunately, amenable to experimental verification. We can search for planets of other stars, seek simple forms of life on such nearby planets as Mars, and perform more extensive laboratory studies on the chemistry of the origin of life. We can investigate more deeply the evolution of organisms and societies. The problem cries out for a long-term, open-minded, systematic search, with nature as the only arbiter of what is or is not likely.

If there are a million technical civilizations in the Milky Way Galaxy, the average separation between civilizations is about 300 light-years. Since a light-year is the distance that light travels in one year (a little under 6 trillion miles), this implies that the one-way transit time for an interstellar communication from the nearest civilization is some 300 years. The time for a query and a response would be 600 years. This is the reason that interstellar dialogues are much less likely-particularly around the time of first contact-than interstellar monologues. At first sight, it seems remarkably selfless that a civilization might broadcast radio messages with no hope of knowing, at least in the immediate future, whether they have been received and what the response to them might be. But human beings often perform very similar actions as, for example, burying time capsules to be recovered by future generations, or even writing books, composing music and creating art intended for posterity. A civilization that had been aided by the receipt of such a message in its past might wish similarly to benefit other emerging technical societies.

For a radio search program to succeed, the Earth must be among the intended beneficiaries. If the transmitting civilization were only slightly more advanced than we are, it would possess ample radio power for interstellar communication-so much, perhaps, that the broadcasting could be delegated to relatively small groups of radio hobbyists and partisans of primitive civilizations. If an entire planetary government or an alliance of worlds carried out the project, the broadcasters could transmit to a very large number of stars, so large that a message is likely to be beamed our way, even though there may be no reason to pay special attention to our region of the sky.

It is easy to see that communication is possible, even without any previous agreement or contact between transmitting and receiving civilizations. There is no difficulty in envisioning an interstellar radio message that unambiguously arises from intelligent life. A modulated signal (beep, beep-beep, beep-beep-beep…) comprising the numbers 1, 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31-the first dozen prime numbers-could have only a biological origin. No prior agreement between civilizations and no precautions against Earth chauvinism are required to make this clear.

Such a message would be an announcement, or beacon signal, indicating the presence of an advanced civilization but communicating very little about its nature. The beacon signal might also note a particular frequency where the main message is to be found, or might indicate that the principal message can be found at higher time resolution at the frequency of the beacon signal. The communication of quite complex information is not very difficult, even for civilizations with extremely different biologies and social conventions. Arithmetical statements can be transmitted, some true and some false, each followed by an appropriate coded word (in dahs and dits, for example), which would transmit the ideas of true and false, concepts that many people might guess would be extremely difficult to communicate in such a context.

But by far the most promising method is to send pictures. A repeated message that is the product of two prime numbers is clearly to be decoded as a two-dimensional array, or raster-that is, a picture. The product of three prime numbers might be a three-dimensional still picture or one frame of a two-dimensional motion picture. As an example of such a message, consider an array of zeros and ones which could be long and short beeps or tones on two adjacent frequencies, or tones of different amplitudes, or even signals with different radio polarizations. In 1974 such a message was transmitted to space from the 305-meter antenna at the Arecibo Observatory in Puerto Rico, which Cornell University runs for the National Science Foundation. The occasion was a ceremony marking the resurfacing of the Arecibo dish, the largest radio/radar telescope on the planet Earth. The signal was sent to a collection of stars called M13, a globular cluster comprising about a million separate suns which happened to be overhead at the time of the ceremony. Since M13 is 24,000 light-years away, the message will take 24,000 years to arrive there. If any responsive creature is listening, it will be 48,000 years before we receive a reply. The Arecibo message was clearly intended not as a serious attempt at interstellar communication, but rather as an indication of the remarkable advances in terrestrial radio technology.

The decoded message says something like this: “Here is how we count from one to ten. Here are the atomic numbers of five chemical elements-hydrogen, carbon, nitrogen, oxygen and phosphorus-that we think are interesting or important. Here are some ways to put these atoms together: the molecules adenine, thymine, guanine and cytosine, and a chain composed of alternating sugars and phosphates. These molecular building blocks are in turn put together to form a long molecule of DNA comprising about four billion links in the chain. The molecule is a double helix. In some way this molecule is important for the clumsy-looking creature at the center of the message. That creature is 14 radio wavelengths, or about 176 centimeters, high. There are about four billion of these creatures on the third planet from our star. There are nine planets altogether-four little ones on the inside, four big ones toward the outside and one little one at the extremity. This message is brought to you courtesy of a radio telescope 2,430 wavelengths, or 306 meters, in diameter. Yours truly.”

With many similar pictorial messages, each consistent with and corroborating the others, it is very likely that almost unambiguous interstellar radio communication could be achieved even between two civilizations that have never met. Our immediate objective is not to send such messages because we are very young and backward; we wish to listen.

The detection of intelligent radio signals from the depths of space would approach in an experimental and scientifically rigorous manner many of the most profound questions that have concerned scientists and philosophers since prehistoric times. Such a signal would indicate that the origin of life is not an extraordinary, difficult or unlikely event. It would imply that, given billions of years for natural selection, simple forms of life evolve generally into complex and intelligent forms, as on Earth; and that such intelligent forms commonly produce an advanced technology, as has also occurred here. But it is not likely that the transmissions we receive will be from a society at our own level of technological advance. A society only a little more backward than ours will not have radio astronomy at all. The most likely case is that the message will be from a civilization far in our technological future. Thus, even before we decode such a message, we will have gained an invaluable piece of knowledge: that it is possible to avoid the dangers of the period through which we are now passing.

There are some who look on our global problems here on Earth-at our vast national antagonisms, our nuclear arsenals, our growing populations, the disparity between the poor and the affluent, shortages of food and resources, and our inadvertent alterations of the natural environment-and conclude that we live in a system that has suddenly become unstable, a system that is destined soon to collapse. There are others who believe that our problems are soluble, that humanity is still in its childhood, that one day soon we will grow up. The receipt of a single message from space would show that it is possible to live through such technological adolescence: the transmitting civilization, after all, has survived. Such knowledge, it seems to me, might be worth a great price.

Another likely consequence of an interstellar message is a strengthening of the bonds that join all human and other beings on our planet. The sure lesson of evolution is that organisms elsewhere must have separate evolutionary pathways; that their chemistry and biology and very likely their social organizations will be profoundly dissimilar to anything on Earth. We may well be able to communicate with them because we share a common universe-because the laws of physics and chemistry and the regularities of astronomy are universal. But they may always be, in the deepest sense, different. And in the face of this difference, the animosities that divide the peoples of the Earth may wither. The differences among human beings of separate races and nationalities, religions and sexes, are likely to be insignificant compared to the differences between all human and all extraterrestrial intelligent beings.

If the message comes by radio, both transmitting and receiving civilizations will have in common at least a knowledge of radiophysics. The commonality of the physical sciences is the reason that many scientists expect the messages from extraterrestrial civilizations to be decodable-probably in a slow and halting manner, but unambiguously nevertheless. No one is wise enough to predict in detail what the consequences of such a decoding will be, because no one is wise enough to understand beforehand what the nature of the message will be. Since the transmission is likely to be from a civilization far in advance of our own, stunning insights are possible in the physical, biological and social sciences, in the novel perspective of a quite different kind of intelligence. But decoding will probably be a task of years and decades.

Some have worried that a message from an advanced society might make us lose faith in our own, might deprive us of the initiative to make new discoveries if it seemed that others had made those discoveries already, or might have other negative consequences. This is rather like a student dropping out of school because his teachers and textbooks are more learned than he is. We are free to ignore an interstellar message if we find it offensive. If we choose not to respond, there is no way for the transmitting civilization to determine that its message was received and understood on the tiny distant planet Earth. The translation of a radio message from the depths of space, about which we can be as slow and cautious as we wish, seems to pose few dangers to mankind; instead, it holds the greatest promise of both practical and philosophical benefits.

In particular, it is possible that among the first contents of such a message may be detailed prescriptions for the avoidance of technological disaster, for a passage through adolescence to maturity. Perhaps the transmissions from advanced civilizations will describe which pathways of cultural evolution are likely to lead to the stability and longevity of an intelligent species, and which other paths lead to stagnation or degeneration or disaster. There is, of course, no guarantee that such would be the contents of an interstellar message, but it would be foolhardy to overlook the possibility. Perhaps there are straightforward solutions, still undiscovered on Earth, to problems of food shortages, population growth, energy supplies, dwindling resources, pollution and war.

While there will surely be differences among civilizations, there may well be laws of development of civilizations which cannot be glimpsed until information is available about the evolution of many civilizations. Because of our isolation from the rest of the cosmos, we have information on the evolution of only one civilization-our own. And the most important aspect of that evolution-the future-remains closed to us. Perhaps it is not likely, but it is certainly possible that the future of human civilization depends on the receipt and decoding of interstellar messages from extraterrestrial civilizations.

And what if we make a long-term, dedicated search for extraterrestrial intelligence and fail? Even then we surely will not have wasted our time. We will have developed an important technology, with applications to many other aspects of our own civilization. We will have added greatly to our knowledge of the physical universe. And we will have calibrated something of the importance and uniqueness of our species, our civilization and our planet. For if intelligent life is scarce or absent elsewhere, we will have learned something significant about the rarity and value of our culture and our biological patrimony, painstakingly extracted over 4.6 billion years of tortuous evolutionary history. Such a finding will stress, as perhaps nothing else can, our responsibilities to the dangers of our time: because the most likely explanation of negative results, after a comprehensive and resourceful search, is that societies commonly destroy themselves before they are advanced enough to establish a high-power radio-transmitting service. In an interesting sense, the organization of a search for interstellar radio messages, quite apart from the outcome, is likely to have a cohesive and constructive influence on the whole of the human predicament.

But we will not know the outcome of such a search, much less the contents of messages from interstellar civilizations, if we do not make a serious effort to listen for signals. It may be that civilizations are divided into two great classes: those that make such an effort, achieve contact and become new members of a loosely tied federation of galactic communities, and those that cannot or choose not to make such an effort, or who lack the imagination to try, and who in consequence soon decay and vanish.

It is difficult to think of another enterprise within our capability and at a relatively modest cost that holds as much promise for the future of humanity.