A U G U S T 1 9 8 8
by Gregg Easterbrook
ON a promising day in 1960 scientists at the National Radio Astronomy Observatory, in Green Bank, West Virginia, tuned a radio telescope to a frequency they had reason to believe alien beings would use to contact Earth. Then they pointed the telescope toward Epsilon Eridani, a nearby star similar to the sun. "Almost immediately we picked up a signal that seemed exactly what we were looking for," says the astronomer Frank Drake, who ran the effort, which was nicknamed Project Ozma, after the ruling princess of Oz. "No one had ever done this, so we had no idea what to expect. For all we knew, every solar system in the galaxy was populated. "
Ozma team members wondered if they stood witness to a pivotal moment of human history. But after analyzing the signal and making inquiries, they realized that Ozma had stumbled on an Earth-based signal, which they surmised was a classified test of military communication jammers. The searchers returned to their task, training the telescope on another star and trying other frequencies. When they heard nothing, Project Ozma ended.
Since 1960 there have been almost fifty other efforts at what is now called SETI, for "search for extraterrestrial intelligence." Projects have been undertaken in many countries, using progressively more sophisticated equipment. The summaries read like this: "Searched 674 nearby stars, found nothing." "Searched five closest galaxies, found nothing." "Searched all sky, found nothing."
"Searched, found nothing" is the mantra of SETI. Does this mean we are alone?
THE fanciest alien-snooping apparatus in the world today is located on a ridgeline above a picturesque little New England town about an hour west of Boston.
There the physicist Paul Horowitz, of Harvard University, has wired up a radio telescope with a signal analyzer comparable in power to a Cray supercomputer; the machine monitors 8.4 million space radio channels simultaneously. It breaks down the radio spectrum into extremely narrow bands; the narrower a radio signal, the more likely it is to be artificial. In the five years he and his team have been listening, Horowitz jokes, "we've discovered the sun twice." But nothing more.
Scientists assume that contact with any extraterrestrial civilizations that may exist is most likely to occur by radio; therefore SETI is primarily a vocation of radio astronomy. But because it is possible to monitor only a small portion of the vast number of space radio frequencies, those who wish to tune in the heavens must select a channel. In 1959 Philip Morrison and Giuseppe Cocconi, two physicists at Cornell University, argued that because hydrogen is the most common substance in the universe and naturally emits radio waves in a relatively noise-free portion of the radio spectrum, it would be logical to listen there for a signal from intelligent beings. Most SETI researchers have accepted this reasoning and, since the frequency of the hydroxyl radical, which combines with hydrogen to make water, is close to the hydrogen frequency, this prime search area was later dubbed "the water hole." Paul Horowitz's superanalyzer listens to several frequency bands in the water hole.
Early searches like Project Ozma assumed that an alien civilization somehow knew about Earth and was aiming a powerful message transmitter directly at us. But since Earth and any extraterrestrial radio transmitter are moving relative to each other, any signal would probably have been changed by Doppler shifts (just as the pitch of an ambulance's screeching siren changes depending upon whether it is speeding toward you or racing away) and would have become too scrambled for computers of the day to understand. The Harvard superanalyzer has a more refined ear. It corrects for the Doppler shifts, which are the composite result of many different motions, and listens on many adjacent frequencies at once, so it could identify an extraterrestrial radio beacon sweeping the galaxy like a lighthouse beam.
Paul Horowitz got his start in the alien-seeking business when he designed a "suitcase SETI," a portable signal analyzer that could be hooked up to telescopes engaged in conventional radio astronomy. In 1982 he obtained permission to attach this machine to the world's largest radio telescope, a U.S. facility in Arecibo, Puerto Rico. The Arecibo dish, which spans a small valley, then listened in on the regions around some 250 near-by stars. Researchers heard nothing.
Later Horowitz started the superanalyzer effort. This and a system at Ohio State University are the only full-time SETI listening posts in operation. Russian, French, Dutch, West German, Australian, and other projects run intermittently. An additional SETI bastion is NASA's Ames Research Center, in northern California.
In the 1970s, when many NASA space probes were being launched, U.S. scientists took the lead. Carl Sagan won his early celebrity by advocating space-directed "exobiology" and by supervising the design of coded messages about Earth that were etched on the sides of some NASA probes in case the little spacecraft were ever found by other beings. Popular culture, which had traditionally presented extraterrestrials as sinister invaders, began to embrace the notion that aliens would be nice guys, even cute. The robust space program, rapid advances in astronomy equipment, and the simple fact that no one knew whether other star systems were vacant or teeming with life made SETI chic.
But as the search hours have mounted and nothing has been found, the spotlight has dimmed. Career considerations have reduced SETl's place in science. Scientists fund their research mainly through grants, and to justify grants they must produce results. When several rounds of SETI investment failed to generate results, most foundations lost interest. Horowitz had such trouble finding conventional underwriting for the Harvard project that the movie producer Steven Spielberg contributed $100,000 to build the superanalyzer.
The hope of fame, too, has faded. During the early years of SETI researchers were keenly aware that whoever recorded the first alien transmission would be widely acclaimed. That promise still holds, but thirty years of frustration at scanning the skies for life has persuaded most scientists that they might as well make a steady living juggling numbers in more humdrum pursuits. And so the mantle of SETI has been passed from Sagan and other big shots to workers like Horowitz and Robert Dixon, the director of the Ohio State project. Both are shy, soft-spoken scholars who exhibit the fidgety demeanor associated with too much time in a windowless lab. Both, like most scientists, would die a thousand deaths on a talk show.
The SETI true believers who remain are bound together by two forces: first, a craving to know what may be out there, and whether humanity's ultimate fate lies far beyond current horizons; second, an almost devout belief that man simply cannot be alone.
In the Milky Way, where we live, there are at least 100 billion suns. Within range of current detection instruments are 10 billion other galaxies, many larger than our own. Beyond them may lie a gigantic number of galactic islands -- perhaps an infinite number, and corresponding to that, an infinity of suns. Intuition would seem to demand that in such a vast firmament many hearts would beat.
"I feel nearly certain the galaxy will turn out to be rich with life, of many shapes and sizes, and that any civilization we contact will be far wiser than we," Horowitz says. "To think we are the best the universe could manage -- the mediocrity of it all!"
Their speculations about alien life lead SETI researchers to study many beguiling topics: how planets form, how life began, whether interstellar travel is possible, whether evolutionary outcomes are inevitable, what extraterrestrial beings may be like. These topics -- the ones this article will address -- are what keep the second generation of SETI researchers going.
The prospect that SETI will never encounter anything does not deter true believers. Rather, it, too, drives them on, because failure to find the expected can be as significant as discovery of the unforeseen. An eventual scientific determination that there are no other beings would have immense social and political significance, conveying to the world's quarrelsome governments an urgent message about their obligations not just to present citizens but to life itself.
ON October 10, 1986, the Harvard system logged a signal that, Horowitz says, "looked for all the world like the real thing." The supercomputer signal analyzer would not be tricked by unusual man-made transmissions. Horowitz felt something that SETI researchers have learned, the hard way, to resist -- a quiver of excitement. But when Horowitz re-aimed the telescope's antenna to the coordinates suggested by the reading, only static greeted him. Four times the Harvard system has picked up a non-random possibly intelligent transmission: each time the trace was never repeated.
Other researchers have had the same experience. Benjamin Zuckerman, an astronomer at the University of California at Los Angeles, and Patrick Palmer, a colleague from the University of Chicago, examined 700 nearby solar systems for life signals over four years in the early 1970s using the Green Bank radio telescope, which Project Ozma had used. During that time they recorded ten instances of vexing, possibly artificial readings that did not repeat. Though astronomers for career reasons often jealously guard the coordinates of stellar regions where something unusual resides, after Zuckerman and Palmer abandoned their search they gave others the locations from which their mystery readings appeared to emanate. These systems have since been further inspected, without results.
At Ohio State there was the "WOW!" incident. A researcher poring over data from the previous day's sky scan found a readout so apparently alien in character that he scrawled "WOW!" across the margin. For months the team panned the telescope back and forth across the patch of sky whence "WOW!" had come. But the source was not found again. "It's very puzzling," Dixon says. "Occasionally we see things that we can't explain. But when we go back to look again, it's never there."
To understand the vastness of the task before SETI, it's necessary to know a little about radio -- by which scientists mean everything in the radio spectrum, including television, microwaves, and radar. Radio is effective only when the correct frequency and antenna position are known. For example, if a person stood next to the broadcast tower for station WGAG ("Playing the Music You've Tried to Forget") but kept his radio tuned to a different station, he'd never guess that WGAG existed. Or if he wanted to pick up television from Chicago but pointed the set's antenna toward St. Louis, he would hardly get great reception.
Another fact about radio waves is that they pass through many objects in their path -- this is the reason that radios and televisions work indoors -- and are large enough to dance completely around small objects. These properties mean that radio messages can travel immense distances without being absorbed or scattered by dust clouds in their way, and still be intelligible at the other end. The transmitter on the Pioneer 10 space probe, which left the solar system in 1983, radiates only eight watts of power, yet its signal can still be heard on Earth. Keeping in touch with Pioneer 10 is practical, however, only because NASA knows exactly where it is and what channel it broadcasts on.
Combine the multitude of usable space frequencies with 100 billion stars to point radio-telescope antennas toward, and the fact that SETI has not yet heard anything becomes melancholy but inconclusive. "We have eliminated the possibility that the sky is teeming with signals directed at us, which is something many scientists used to believe," Horowitz says. "But I think that's all we have eliminated. Everything else remains speculation."
Needless to say, there is no way to know if the waterhole frequencies, which seem to us a logical place to direct our efforts, would seem logical to anyone else. Some have suggested that SETI listen on the frequencies of tritium, an isotope used in thermonuclear bombs which is quite rare and thus is associated with technological advancement. Horowitz, frustrated by five years of cosmic silence, recently switched the Harvard receiver over to the second harmonic of hydrogen -- a frequency that has no natural counterpart, and so is free of background noise. Any signal logged there would almost have to be artificial.
Ideally, the entire sky spectrum would be monitored by receivers akin to colossal police radio scanners. In 1971 a study group of scientists convened at Ames proposed building a gigantic array of radio telescopes, called Cyclops, able to scan multiple frequencies with extraordinary sensitivity. The price tag was close to $10 billion. Cyclops was derided as a boondoggle, and a formal proposal was never made. Recently the agency has been considering a more economical search, using existing radio telescopes, which would monitor the 1,000 sunlike stars closest to Earth, and would also sweep the entire sky for very strong signals.
Because the odds are against stumbling across alien chatter by chance, most scientists believe that another civilization will be detected only if it is sending out a signal designed to be noticed: one that sweeps the cosmos in a distinctive pattern, using a frequency that could be deduced logically. "If someone is trying to hide, it's very unlikely we will find them," says Philip Morrison, who is now a professor at the Massachusetts Institute of Technology.
Conceivably, a sophisticated detector like the Harvard system could pick up extraterrestrial "leakage," meaning everyday radio and television transmissions that escaped another planet inadvertently: Another World from another world, as it were. That is a long shot, however. The source planet would have to be nearby, and the telescope would have to point precisely at it by chance.
By the same token, it is considered unlikely that an alien civilization could learn of our existence unless we chose to declare ourselves by constructing beacons. Radio has been in use for almost a century, but most of the signals have been too weak to escape the atmosphere. Only since the coming of television transmission, which is powerful enough to leak into space, have Earthlings begun contributing to galactic static. But the Milky Way is 100,000 light-years wide: the region blessed with emanations of Mr. Ed and other human cultural achievements represents far less than one percent of that expanse. A millennium will pass before any noteworthy portion of the galaxy may have the pleasure of tuning in network talk shows.
But maybe we are being wiretapped. If interstellar travel proves as arduous as some scientists now suppose, an advanced civilization might have to content itself with sending robot probes to solar systems containing planets with the potential to support life. The probes would conduct observations and listen patiently, perhaps over many epochs, for radio and television broadcasts, which would be amplified and beamed back home for analysis.
Scientists have suggested that if our solar system were being wiretapped, good places to plant the bug would be at the L points in nearby space, where the gravity of Moon and Earth cancel each other out, or in the asteroid belt, where the thousands of irregular objects could provide cover. Since 1979 the L points have been examined with radio telescopes, optical telescopes, and radar. Apparently nothing is there. In 1983 NASA orbited an infrared-sensing telescope called IRAS (infrared astronomical satellite). IRAS scanned the asteroid belt and discovered many thousands of new asteroids, but nothing that was clearly an artificial heat source -- nothing that might have been the power pack of an alien probe or the engines of a starship.
Other trails have been followed. Jill Tarter, an astronomer at the Ames Research Center, has examined the center of the galaxy for strong pulsating signals. Another team inspected nearby stars for indications of emissions caused by dumped waste material from nuclear reactors. Freeman Dyson, a Princeton physicist, has suggested that an advanced civilization might dismantle one or more of the planets in its solar system and use the debris to build a gargantuan shell that would capture solar energy, making a vast zone around its sun habitable. Stars surrounded by "Dyson spheres" would exhibit properties that ought not to occur naturally; U.S. and Russian astronomers have scanned many stars for hints of such construction projects, and found nothing.
There is in theory no limit to the range of radio transmission. Horowitz estimates that a device the size of the Arecibo radio telescope, equipped with an adequate transmitter (it would have to be stronger than any in existence today but could be built using current technology), could communicate with a similar unit anywhere in the galaxy, assuming the proper frequency and antenna direction were known. Conversation would be excruciatingly desultory, however. In 1974 Sagan and some colleagues used Arecibo to beam a coded message toward the Great Cluster, a star group some 25,000 light-years from Earth. Radio waves travel at the speed of light: should that message be received and understood, a total of 50,000 years would pass before the reply arrived.
Radio is not the only technique by which extraterrestrials could alert others to their presence. A civilization that mastered a potent energy source might build very bright beacons, perhaps using lasers. Spotting such optical phenomena would require no guesswork regarding frequencies, and there would be no mistaking that the viewer was beholding a product of intelligence. Extraterrestrials with large amounts of power at their disposal might also draw attention to themselves by hanging out a sign consisting of light, microwave, or other generators arranged in an unnatural pattern, dike a square. Yet man, watching the sky since prehistoric times, first with the eye and later with the telescope, has beheld no sight not of his own or nature's making.
SHORTLY after Project Ozma shut down, Frank Drake convened a conference of physicists and astronomers. There he proposed what has come to be known as the Drake equation, a mathematical model for predicting whether aliens exist. To this day the Drake equation dominates scientific discourse on the question of whether we are alone.
At the 1960 conference Drake, who is now the dean of natural science at the University of California at Santa Cruz, used his equation to predict that there are about a million extraterrestrial civilizations scattered across our galaxy. Many of the scientists in attendance supported this conclusion.
The trouble is, "everything we have learned since 1960 tends to reduce the likelihood of success under the Drake equation," according to James Trefil, a physicist at George Mason University. Drake concedes that when he runs his own equation today, he gets an estimate of 10,000 intelligent civilizations in the Milky Way, down considerably from a million. When Trefil runs the Drake equation, he gets an estimate of one -- us.
A critical variable in the equation is the number of other planets. In 1960 it was assumed that planets would be prevalent throughout the galaxy. But so far no planet outside this solar system has been detected.
Four years ago a group of astronomers announced that they had found a "brown dwarf," an object of a type halfway between sun and planet, previously only hypothesized, orbiting a star called van Biesbrock 8. This announcement elicited considerable excitement, but subsequent attempts to sight the object proved futile. In early 1987 astronomers from Cornell and the California Institute of Technology detected a thick disk of matter turning about the star HLTauri: such disks are thought to be the antecedents of planets. Most recently another possible brown dwarf, revolving around a star called Giclas 29-38, was spotted by Benjamin Zuckerman and a colleague. Astronomers are now attempting to confirm this discovery.
The fact that no "extrasolar" planet has yet been observed does not discourage astronomers. Because planets produce no light and little heat, they are far more difficult to detect than stars. Merely finding one close by can be a challenge. Scientists continue to debate whether there is a tenth planet on the perimeter of our own solar system. Astronomers search for distant planets by inference -- for instance, examining stars to see if they "wobble" in a way that would indicate the gravitational influence of an unseen companion. This is a painstaking form of inquiry.
Some thinkers have postulated that living beings might not need to have solid bodies -- that intelligence could exist as pure thought, as patterns of magnetism within the burning fury of a star, or in other strange genres. For the moment, however, the only kind of life that we know exists is corporeal and carbon-based. Familiarity dictates that this is the type to search for first, which makes other planets a prerequisite to other life. Assuming that extrasolar planets are eventually found, the first priority will be to analyze atmospheric readings for signs of oxygen. Oxygen is crucial to the higher organic life we know of, and organic life is crucial to maintaining an oxygen atmosphere. This is because oxygen strongly tends to combine with other elements -- for example, with iron, to form rust -- and so unless a living process constantly replenished a planet's oxygen supply, the gas would be gobbled up by chemical reactions.
Earth's primordial atmosphere was probably composed mainly of nitrogen and carbon dioxide. About three billion years ago plants appeared, and they laboriously consumed carbon dioxide and produced oxygen. Two billion years of this toil caused the atmosphere to become oxygenated, capable of sustaining the form of biological internal combustion that provides animals with enough energy to roam about. Sure enough, around a billion years ago the first animals appeared. Take note of the implication: if extraterrestrial astronomers have looked this way, they could have identified Earth as a living planet as much as a billion years ago.
If thinking beings require an extremely long time to come into being and then almost immediately learn how to wipe themselves out, life may be an on-again off-again phenomenon and the universe a place where every few eons a fleeting call for help or companionship echoes out of existence, unheard.
By present estimates the genesis of the universe occurred roughly 15 billion years ago. Many mental tricks can be played with such a monumental expanse of time. Express it as a single year and the first reptile appears on Christmas Eve. Suffice it to say that the historical period of mankind, about 10,000 years, represents 0.00006 percent of the approximate age of the universe.
Also by present estimates the sun and the earth formed about five billion years ago. This means that our solar system did not come into existence until the universe was already 10 billion years old. That, in turn, is why SETI optimists believe that aliens would be more advanced than we. Supposing that Earth's 3.8-billion-year cycle of life development represents a "typical" case, creatures on planets pre-dating Earth could have evolved, flourished, and built galactic civilizations while our place of origin was still a whirl of ethereal lint.
Some astronomers doubt that planets pre-dating Earth are likely, however. Most of the heavy elements necessary to form planetary core and mantle are thought to have been produced not during the Big Bang but by the detonation of supernovas: observations of supernova 1987A appear to confirm this. The primordial cosmos was rich with supernovas, but just how many had to explode before space contained enough metallic elements to forge planets is a matter of conjecture. So, too, are related issues -- for example, how much time passed before matter accumulated in our galaxy and others structured like it.
Thus the formation of large solid objects like Earth might be a relatively recent phenomenon. In fact, Earth might be a trendsetter: because supernova detonations have steadily increased the volume of heavy elements available to the planetary blacksmith, solar systems may have been rare for stars preceding our sun's "generation" but may become common for those that form in ages to come. Bear in mind that the creation of stars, far from being a miracle confined to the eons of genesis, is an ongoing event. Young stars continue to coalesce out of cosmic dust clouds and light up, some right in our neighborhood. Nobody knows how long the creation of stars will continue; estimates range from billions of years to indefinitely.
When Earth formed, it had no atmosphere or oceans: the light elements that make up air and water were trapped inside the core. As the planet contracted, volcanos and geysers erupted, carrying air and water to the surface. And the first of many majestic coincidences began.
Unless a planet reaches a certain mass, any surface air will gradually escape. But if the planet grows too big, its internal temperature will tend to convert surface water into vapor. Earth's mass turned out to be ideal for holding an atmosphere yet preserving liquid water.
Next, Earth chose a star of exactly the right size. Had Earth condensed near a big star, you would not be reading this. Big stars burn violently and explode into supernovas so quickly that any planets around them would have insufficient time to cool, let alone produce life. Little stars shine for long periods; astronomers can only guess how long, because the universe has not existed long enough for any little stars to burn out yet. But in order for a planet to draw warmth from a little star, it would have to orbit very close to the solar surface. Theoretically, a planet bound in such a tight orbit would not rotate relative to the star, just as the moon always shows the same side to the earth. One side would eternally sizzle while the other knew perpetual night.
Thus big and little stars are unlikely to serve as benefactors of life. The many multiple stellar systems (with two or more stars orbiting each other) can also be disqualified: astronomers theorize that such systems will have no planets. And if there's life associated with exotic stellar furnaces like quasars, it won't be anything we recognize.
That leaves average stars, like the sun. They shine for billions of years and, during their "main sequence" -- what the sun has been in since life appeared -- burn at admirably consistent temperatures. A large fraction of the Milky Way is average stars, meaning that there could be many multitudes of potentially habitable solar systems. And roughly half the distant galaxies appear structurally similar to our galaxy, suggesting a gigantic number of viable locales throughout the universe. But it turns out that orbiting the right star is just the beginning.
Hart's most unnerving calculation involves what he calls the "continuously habitable zone." Had Earth spun in an orbit only five percent closer to the sun, Hart says, it would have experienced a runaway greenhouse effect, creating unbearable surface temperatures and evaporating the oceans. Venus provides evidence for this: 28 percent closer to the sun, that planet has a nearly opaque atmosphere high in carbon dioxide and 900-degree surface temperatures. And had Earth been positioned just one percent farther out, Hart believes, it would have experienced runaway glaciation, locking its surface water in ice for eternity. Recently other scientists have endorsed Hart's concept of such a zone but have proposed that it must be wider, perhaps extending as far as the orbit of Mars for an Earth-like planet.
Arguments like this concern whether the elements that form the basis of organic chemistry would do so under other conditions. An intriguing aspect of the universe is that as far as can be seen in every direction, the physical laws and elements appear to be the same. That suggests that there may be no alternative forms of chemistry around which to structure a type of life that would not require something like terrestrial conditions. Although there appears to be water on Mars, it's frozen and probably always has been. Ice may as well be granite as far as life is concerned -- it cannot be used in living interactions like growing and feeding a cell. Astronauts found no hint of organic activity on the moon, and the Viking probes that landed on Mars drew similar blanks. In the two places that have been inspected firsthand for life independent of oxygen, water, and moderate climes, none has been found.
Although there is no generally agreed-upon definition of life, one area of consensus is that living things must have a system for storing and duplicating information about their structure. For terrestrial organisms that system is DNA and RNA. The key ingredient in both is carbon, which is one reason we describe ourselves as a carbon-based life form.
Carbon has a subatomic quirk that allows it to form astonishingly complicated molecules that happen to be excellent for storing detailed information such as the secrets of life. The helical strands of human DNA have more than six billion distinct molecular components, each composed of carbon assemblies that are themselves complex. Amino acids, sugars, fats, and other building blocks of organic life also rely on carbon's quirk.
Below freezing, carbon-based molecules cannot obtain the liquid water they need to operate biologically. And above a few hundred degrees Fahrenheit, the precious life-coding chains break down; eventually they burn. So carbon can probably be the chemical foundation of life only under conditions approximating Earth's.
Now, here's the rub. There are very few elements like carbon. Silicon has the same subatomic quirk, which is why science-fiction writers speculate about silicon-based life. But silicon, like carbon, could form sophisticated information-storing molecules only under a fairly narrow range of temperatures and pressures. All remaining elements with the quirk seem to be quite uncommon in the universe, compared with carbon and silicon.
Thus even if there are billions of planets, only a relatively tiny number are likely to be exactly the right size and drifting in a magic, continuously habitable zone. Which leads to the next question: When proper conditions do exist, what makes life begin?
In 1953 two scientists, Harold Urey and Stanley Miller, performed one of the most striking experiments of the twentieth century. In a pressure vessel they mixed simple molecules simulating the primordial atmosphere of Earth. Then they zapped the vessel with electricity to simulate lightning bolts. Without further assistance the contents formed amino acids and sugars.
Other researchers later achieved the same results by zapping atmospheric elements with ultraviolet and other ionizing radiation, to simulate the solar and cosmic rays that fell on Earth more intensely in earlier periods.
The notion that biological substances could arise from a purely natural process made scientists cheer and gave the clergy chills. But on reflection, less had happened than met the eye. Though the goo in Urey and Miller's beaker contained ingredients used by life, it did not come to life. It was just interesting goo. Now as then, nobody has any idea what makes chemicals start living. The origin of life is perhaps the leading unknown of contemporary science.
Optimists, citing events like the Urey-Miller experiment, believe that the fundamental character of physical law favors life. Organisms will spring up anywhere conditions permit, as they have spread into every available nook of Earth; and because the mechanisms of natural selection reward brainpower, thinking beings will probably follow. The life we know of has survived ice ages, cosmic radiation, the nuclear-winter-like aftermaths of the impacts of comets and meteors, and the application of its own intelligence to the technology of mass slaughter. On Earth, at least, life has proved adaptable and enduring.
Pessimists focus on the stupendous unlikelihood that molecules as complex as, say, the nucleic acids of DNA would assemble spontaneously. Michael Hart has estimated the odds that a functional piece of DNA would ever assemble itself as one in a ten followed by thirty zeros. The odds are also against the possibility that any given subatomic particles would assemble into nuggets of gold, lead, or any given heavy element. But we know of one inanimate process -- the supernova -- that serves as a catalyst for the formation of heavy elements, whereas no inanimate process has ever been observed to make molecule chains that live. Extremely high odds like those given by Hart do not rule something out; no poker player can rule out drawing a full house on each of a hundred consecutive hands. But Hart's odds suggest great rarity -- say, one living planet per galaxy.
Obviously, the jump from non-living to living can be made; it's been made here. But not even Darwinists can say how. The origin of life isn't a subject that draws much in the way of research grants, since -- on the surface, at least -- the answer would seem to have no practical applications. Scientists tend to pursue this question in their off hours, after the rent has been paid by teaching and applied research, using thought experiments rather than lab tests -- the same way Einstein pursued the theories of relativity. An answer might have similarly profound results.
Four general types of hypotheses are being pursued by researchers: that life arose through some process affiliated with natural selection, that life was divinely created, that life began elsewhere and was transferred to Earth, and "X" -- that life began in some other manner. Let's have a look.
AT its chemical crux, life is self-duplicating information. Nature unquestionably can produce information without guidance. And if some mechanism like a gene can store and reproduce that information, then knowledge can seem to arise from "nothing."
Edward Argyle, a Canadian astronomer, has estimated that the maximum number of bits of information that interacting chemicals can produce by sheer random trial is about 200. By Argyle's calculation, making a single-cell organism requires about 6 million bits of information. Making a human being entails about 240 million bits.
This is one of the objections to naming evolution as the creator of life. Darwinian mechanics almost certainly govern the way organisms adapt to changes in their environments: the evidence is overwhelming. But Darwinian theory tells little about how life is created, since its logical precepts concern organisms that are already alive.
According to Gerald Soffen,a NASA biologist, who directed the life-seeking experiments of the Viking probes, the early milestones of life are these: the development of organic compounds; the self-replication of those compounds; the appearance of cells, to isolate the compounds from their chemical environment; photosynthesis, to enable cells to use the sun's energy for motion and growth; and the assembly of DNA. "It's really hard to imagine how these things could have happened," Soffen said at a recent conference. "Once you reach the point of a single-cell organism with genes, I am comfortable that evolution takes command. But the early leaps -- they're very mysterious."
Here's the ultimate test: If the spark of life was struck without guidance, Homo sapiens should eventually be able to create life too. Why should the spontaneous origin of life be some kind of one-time event that could happen in the dim past but cannot happen now? Such a creation would have to be so easy that a natural system containing no knowledge could accomplish it. And if that system could create life once, why can it not do so again and again?
Biologists argue that a re-enactment of the origin of life might require the flawless simulation of prehistoric conditions and, the first spark being an event chance was weighted against, might require innumerable fruitless tries. These are fair points. But knowledge of prehistoric conditions is improving. And surely science, aided by accumulated learning, can reduce the odds against an event it supposes nature once staged without volition in conditions of pandemonium. Until biologists can create life at will, temporal forces alone cannot explain our origin.
SCIENTISTS are fond of spontaneous-life theories for personal as well as analytical reasons. Such theories assign a central role in both biology and ontology to the gene, a structure so uncannily like a computer that scientists feel a deep affinity for it. And natural selection places logic, pristine and unemotional, at the forefront of worldly forces. Logic is what scientists are good at; professional communities naturally advance the point of view that reflects favorably on their own importance. It's a mistake, for instance, to scoff at Darwinian mechanics as "random." The individual mutations that propel evolutionary tides do occur at random, but everything else about the system seems beautifully reasoned and subtle. Good genes are preserved while bad ones are discarded; organisms become more sophisticated; thinking beings are eventually produced, and they figure it all out.
If we suppose that the origin of life is divine, this does not, as might be assumed, mean that God could place any kind of creature anywhere. Unless billions of years of natural history are an elaborate sham -- right down to phony constellations, simulated radioactive-decay rates of rocks, and fraudulently layered fossils at the bottom of the sea -- God must have employed the very forces scientists now define and document. If God created man by setting in motion a four-billion-year process of evolution -- a possible divine explanation for the origin of life -- this would suggest that God, elsewhere in the cosmos, would be constrained by approximately the same natural limitations that appear to constrain life. If it turns out that the underlying chemistry of life requires conditions at least approximating those found on Earth, then divine interventions and guidance aimed at nurturing life would employ principles little different from those being investigated by science; they would not be fundamentally at odds with science, as the current debate over creationism tends to assume.
One puzzling aspect of interviewing SETI scientists, unusually forward-thinking men and women probing a question of profound spiritual sign)ficance, was that not one of them speculated about such matters. If they had, their colleagues would probably hoot them down. The dominance during this century of rational over sublime thought may be fair recompense for religion's past bias against science. In any case, to polarize debate by pitting science against spirit, as though the two forces could not conjoin, seems a formula for postponing enlightenment.
BECAUSE science is at a loss to explain how life began here, some thinkers simply conclude that it must have begun elsewhere. This theory is called panspermia, and it is reinforced by some of the oddest discoveries of contemporary science.
Until this century chemists believed that most carbon-based molecules could be grown only by living creatures. When spectroscopic astronomy was devised, this theory went out the window. More than 150 simple carbon compounds have been identified floating about the heavens, sometimes in clouds of gigantic proportions. A parallel discovery is that one class of meteor contains some of the base substances of DNA.
This supposition, which at first blush may sound nutty, was originally proposed around the turn of the century by Svante Arrhenius, a Nobel Prize-winning chemist from Sweden. More recently, related theories have won respectable support, notably from Francis Crick, one of the pioneers of DNA research, and Fred Hoyle, a prominent British astronomer. Crick came to his view because, he says, DNA is just too complicated to have evolved unassisted in a mere 3.8 billion years. Hoyle has suggested that sudden plagues of disease might be explained by Earth's passing through a cloud of sporelike molecules. Neither scientist has evidential support for his view; these are strictly theories. But they should not be shunned merely because they smack of late-night movies. Nor should "directed panspermia" -- the suggestion that life was actively transplanted here by an alien race.
A fundamental doctrine of natural selection is that all life on Earth has a single ancestor: a single molecule or string of chemicals that made the jump from inert to animate. There is evidence for common ancestry: for example, the fact that although many thousands of amino acids are possible, most living things on Earth share the same twenty.
The evidence favoring common ancestry is often advanced as a proof of Darwin's procession: a way to show that amoebas can become fish, fish can become mammals, and so on. But the tidiness of the design of living things might as easily be an argument for sacred influence: there would have been no need for God to re-invent the amino acid endlessly. And it might be an argument that the origin of life was orchestrated by other beings, who brought an existing system of living chemistry to Earth.
Arthur C. Clarke, a scientist and a writer, once supposed that a civilization could seed a galaxy by launching small automated probes containing genetic stews to be released into the atmospheres of planets. Such "spacecraft," others have suggested, might be no more than pellets of chemicals, fired off at nominal expenditure of labor and money.
Panspermia theories, of course, beg the question of how life began at whatever place originated the spreading of life. The theories' advocates reply that when we find the extraterrestrial wellspring, we'll find the answer.
Finally, there is the prospect that life began in yet another way. The current leading contender for such an "X" explanation is a theory proposed by a Scottish chemist named Graham Cairns-Smith. Cairns-Smith, acknowledging the difficulty of imagining how carbon-based organisms could have catapulted into being, has suggested that life began in a form based on the small, flat crystals found in clay. These crystals exhibit some rudimentary qualifications for life: they assemble themselves and, by duplicating their own structure, pass along a very simple form of inherited information. Clays sometimes contain structures roughly like cells which might have protected pre-animate molecules from being washed away by the many mediocre chemicals adjacent.
Cairns-Smith suggests that living chemistry first appeared directed by these extremely simplistic crystalline memories. When the precursors of DNA began to develop, they staged a "genetic takeover," expropriating control of the semi-living loam. This theory has inconsistencies that can be skipped here. What's important is that it has occasioned great scientific excitement, if for no other reason than that plausible explanations for the origin of life are so hard to come by.
ONE objection to the notion that extra-terrestrial civilizations exist is that other beings would not stay put on their home planet but would explore and colonize many worlds. That ought to make them much easier to find than if SETI were a search for a needle in a 100-billion-star haystack. In fact, they might end up here -- not as unconfirmed UFOs but in the flesh.
Enrico Fermi, one of the inventors of the atomic bomb, proposed that the absence of extraterrestrials on Earth is the strongest argument that extraterrestrials do not exist. Indeed, Fermi's simple question -- "Where are they?" -- has become the rallying cry of SETI skeptics within the scientific community. This question still carries considerable weight. The answer may turn on whether interstellar travel is possible.
Cosmic dimensions are measured in light-years. The closest companion to our sun, Proxima Centauri, lies about four and a half light-years away. This is a typical gap between stars in the Milky Way. Andromeda, the nearest galaxy similar to ours, is about two million light-years from us.
What do such ranges mean in practical terms? Light moves at 186,000 miles per second. The fastest man-made object, Pioneer 10, achieved a top speed of twenty-five miles per second, far below one tenth of one percent of light speed. At that speed Pioneer 10 would require 33,000 years to reach Proxima Centauri, 744 million years to cross our galaxy, and 15 billion years -- as long as the universe has existed -- to traverse the intergalactic wasteland that separates the Milky Way from Andromeda.
One of Einstein's hypotheses is that nothing can move faster than the speed of light. Numerous determined scientific attempts to refute this constraint have failed: Hollywood whimsies like hyperspace and warp drive have no grounding in even the most speculative branches of physics. Another Einsteinian precept says that the faster an object moves, the greater its mass. As an object's speed approaches that of light, its mass approaches infinity and phenomenal amounts of energy are required to make the object go even a tiny bit faster. Thus even a hypothetical matter-anti-matter drive system -- the most intense power source imaginable under known laws of physics, because it would convert virtually all of the fuel's mass to energy -- could not propel a starship beyond the speed of light.
Pushing a starship to even a respectable percentage of the speed of light would require not the sparkling dilithium crystals depicted on Star Trek but fuel stores of immense bulk. Computations for a perfectly efficient antimatter drive, whose specific engineering features can scarcely be envisioned even in outline, indicate that an interstellar round trip in a ship the size of the space shuttle at 99 percent of the speed of light would require about two and a half million tons of anti-matter -- the weight of two dozen aircraft carriers.
Today anti-matter can be made only a few subatomic particles at a time, rendering it in effect priceless. Predictions are that in the twenty-first century anti-matter will be attainable at a cost of perhaps $10 million a milligram, which works out to $9.1 quadrillion a ton. (That's the fuel surcharge only -- starship extra.) There are many other potential drawbacks to anti-matter as well. So even if future technical breakthroughs bring the cost of anti-matter within bounds, unless there is some fundamental feature of the universe about which we know nothing, such as warps or other dimensions, space transportation at a speed approaching that of light may always be infeasible. (Smallscale anti-matter engines may, however, someday make travel within our solar system quite practical.)
Many researchers assume that velocities of about 10 percent of the speed of light will eventually be feasible for starships. Eric Jones, an astrophysicist at the Los Alamos National Laboratory, has calculated that accelerating a large starship to this relatively slow speed would require the equivalent of 25,000 times as much energy as the entire Earth now consumes in a year. This may seem mindboggling, but considering the rate at which energy production has escalated during the industrial era, Jones presumes that the mission will someday be accomplished. At 10 percent of the speed of light the relativity problem is avoided -- only to be replaced by the time problem. A trip to Proxima Centauri would take forty years.
ONE type of space expedition may be thinkable in "slow" starships: a one-way trip, for colonization. If your intention were to travel to another solar system and never come back, a forty-year passage might not be out of the question, especially if suspended animation had become possible.
The somewhat gloomy current outlook regarding the prevalence and suitability of planets beyond our solar system does not bar the prospect of space expansionism. Fairly rare temperate circumstances may be necessary for life to begin. But once life reaches the thinking stage and technology is developed, whole new vistas are opened. Today man operates under the arctic icepack, in orbit, and in many other places where he could not have evolved. It is possible that mankind will someday colonize Mars and other lifeless bodies of this solar system (such as the moons of Saturn and Jupiter, though not the planets themselves). A favorite saying among space-program optimists goes, "Is there life on Mars? No, but there will be." And scientists speak of eventually being able to "terraform" inhospitable planets -- changing them to suit our tastes, using space mirrors and lenses to warm them, giant processors to alter their atmospheres, and so on. Presumably, sophisticated aliens could do the same for themselves. Thinking beings and their mechanized creations might serve the natural scheme nicely in that respect, spreading life to places nature unaided could not have put it.
The idea that space could be colonized makes SETI true believers very nervous, because the apparent absence of settlements in our section of the galaxy becomes another argument that aliens don't exist. Any advanced extraterrestrials whose civilization predates humanity would have had ample time to turn the Milky Way into a franchise operation. As far as can be told, no one has done so.
This is not to say that the idea of eventual human settlement of space should be discounted. It is almost certain that over the centuries to come life expectancy will increase. Some optimistic biologists now put the "natural" human lifespan at 110 years, assuming that advances in medicine, nutrition, and fitness continue. What's more, some believe that there is no fundamental reason why the body must deteriorate. Genetic engineering may eliminate many typical aging processes, and enable people to live several centuries.
For our longer-lived descendants, lengthy space trips may be tolerable: colonists in the past have accepted many hardships in return for opportunity in a new world of their own making. If the future holds environmental breakdown, nuclear conflict, or another calamity for Earth, the stimulus to colonize space might be great.
Jones has calculated that using colony vessels moving at 10 percent of the speed of light, and adopting a star-hopping pattern -- each successful colony later dispatching more settlers -- humanity could populate the entire galaxy in less than 50 million years. That seems a preposterous length of time to us, but it is modest by the yardstick of the cosmos.
Ponder for a moment what a colonized galaxy might be like. The human being has advanced from a quizzical primate using sharp rocks for tools to the more-or-less intelligent creature of today in about two million years. Provided we don't slaughter ourselves or go mad, what will we have evolved to 50 million years hence?
Let's assume for the sake of argument that genetic engineering is used only in constructive ways. As colonists settle planets with conditions different from Earth's, they will alter genes to adapt to new environments. A visitor arriving in our galaxy after eons of such transitions might see a vast diversity of worlds populated by many "different" races and find it hard to believe that all descended from the same human root.
Consider another aspect. If the speed of light is indeed an absolute barrier, space colonies will for all intents and purposes be independent of earthly authority. The most significant implication is that settlements will lie beyond the scope of earthly combat. "If you're planning to destroy human life with a nuclear war, better do it soon, because once we start spreading out to deep space, human life will become impossible to destroy," Michael Hart predicts.
To date it seems that technology more often than not pushes civilization in the direction of oblivion. Suppose instead that technological development channels society through a period of extreme risk (the period we are in now) and then unfolds an era in which technology shields rather than imperils life -- for instance, by scattering it across huge distances. That would be a great ray of hope for humanity. It would also render all the more eerie the apparent absence of others who have made the same breakthrough.
SHOULD we one day awake to find a silver saucer floating over the White House, Earthlings would have little choice but to pay heed. But if an alien contact occurred by radio, humanity would face the momentous choice of whether to reply. The decision could turn on speculation about what the other beings were like.
We know from science fiction that all extraterrestrials speak English, with a midwestern accent, that the men wear flowing metallic robes and the women wear brass bikinis, and that not a single alien in the entire expanse of the galaxy can shoot straight. SETI researchers, though, have another article of faith: that extraterrestrials will not be hostile. "SETI is a screening mechanism," Horowitz says. "Civilizations that don't acquire the wisdom to control war will destroy themselves long before they can take to space, so the ones who are trying to contact you would be, by definition, no longer menacing."
Drake points out that even rudimentary radio conversations with alien beings could be of tangible benefit. "A simple yes or no answer to the question of whether fusionenergy research should be pursued would be worth tens of billions of dollars to the governments of Earth," he says.
The SETI specialists' hopeful stance turns partly on the depth of their conviction about the unbreakability of the light barrier. In fact, this is something a SETI proponent must believe: otherwise, activities like beaming messages toward the Great Cluster might be irresponsible, for they might draw conquerors down on Earth. Regrettably, the one example we have -- human history -- does not bear out an assertion that technical progress and social wisdom are natural partners. Our technology has grown in almost magical fashion over the past 2,000 years, but foreign policy is still practiced pretty much as it was during the Roman Empire.
Contact with an alien civilization might be cause for celebration merely because it could demonstrate that nuclear knowledge can be acquired without setting in motion Armageddon. But the alternatives to Armageddon aren't automatically blissful. An alien civilization might avoid self-destruction by means abhorrent: global dictatorship, mind control, any number of unpleasant possibilities.
Suppose we receive an alien message that is deciphered as warm greetings and petitions for peace. How could we know whether the sentiments were genuine or pretense? Whether the noble government that had sent them a thousand years before had been deposed by warlike fanatics? Furthermore, there is no reason to assume that any other planet would have cohesive single governments whose word would be bond. Earth doesn't. An extraterrestrial emissary approaching our world would have grave difficulty just figuring out whom to deal with. The United States, which claims to be No. 1? The United Nations, which claims to be in charge? China, the largest nation? Each of some 160 sovereign governments on an equal basis? Contact with an alien civilization might be similarly perplexing, composed of many conflicting attestations from sources whose veracity we could not assess.
There may also be more than one thinking species per planet. That Earth has a lone intelligent presence doesn't establish this as a rule, or even mean that affairs will remain so here. What if we hear from a planet with several competing intelligent creatures, each with a different story to tell?
James Trefil, of George Mason University, has cautioned that if evolution functions approximately the same way on other worlds that it has functioned here -- conferring survival upon the fittest -- advanced extraterrestrials might still be aggressive, territorial, and quick to reach for the sword. In that case, counting on poor alien marksmanship might not be prudent. Even if a message arrived from a great distance, we might for defensive reasons be compelled to assume that the senders knew something about the speed-of-light barrier that we didn't, and withhold our reply.
The most disquieting aspect of natural selection as observed on Earth is that it channels intellect to predators. Most bright animals are carnivores: stalking requires tactics, pattern recognition, and, for social animals, coordinated action, all incubators of brainpower. Though the martial heritage of mankind has been exaggerated in popular fiction (there's no proof, for example, that our Cro Magnon ancestors waged war against the vanished Neanderthals), it's reasonably certain that the forebears of modern Homo sapiens were hunters, and it's definite that man has been savage during the historical era. This isn't much of a testimonial to "intelligence."
Can we hope that on other worlds creatures other than predators have proved dominant? Yes. Not all selection pressures favor predation. The beaver has highly evolved dam-building talents designed to make habitats, not corner prey; the transcontinental migratory skills of some birds are unrelated to killing. An extraterrestrial intelligence descended from a herding beast, whose ancient instinctual imperative was to sacrifice for the common defense rather than to attack, might find a notion like mutually assured destruction as curious as military tacticians find the Amish.
In other ways, though, the thought that natural selection might function on other worlds as it has on ours is comforting, for this would imply that "human" nature was something deeper even than we know. Aliens, far from being alien in the original sense of the word, might exhibit many recognizable traits: curiosity, desire for companionship, love of laughter, pleasure in art and culture, and respect for the sanctity of life.
Speculation about alien contact usually centers on culture shock, invasion scares, and technological secrets that might be unlocked. A stock assumption is that the first question we would send to an extraterrestrial radio operator would be something like "How do you build a 10,000-megajoule charged-particle beam?" Consider the ramifications if instead the question were "Have you seen God?"
Many religions expound variations on what Christians call the kingdom of God -- the idea that human travails and celestial sufferance of evil are a transitory state of affairs, to be replaced by perfect justice when God manifests Himself and takes active control of events. Judaism, Islam, and Christianity all teach that this full revelation of God will occur. So if any long-lived alien race we might contact testifies that it has walked the cosmos for thousands of millennia without encountering God or obtaining divine grace, a lot of air would rush out of the faiths we Earthlings practice.
If, on the other hand, the aliens have met the absolute and will tell us the specifics, human society will shake to its foundations.
HERE, then, are the possibilities with respect to life on other worlds:
We have company. The scientific search for extraterrestrial beings, which is mathematically unlikely to succeed in a short time, may simply not have looked in the right place yet. There may be many populated planets -- some trying to make contact with us, others avoiding contact. Once communication is established, exchanges will probably be confined to radio conversations interrupted by very long pauses -- unless there exists some way around the speed-of-light barrier to space travel and radio messages, in which case anything might happen.
We had company. Perhaps thinking beings are common, but so is the sorrow that civilizations acquire weapons more readily than wisdom. Life comes and goes: the final frontier could be littered with outposts where populations arose and then flashed into oblivion.
In this event, contact of a sort might remain a possibility. Any radio messages sent by extinct civilizations would travel the galaxy for many thousands of years. A dying civilization might leave a "monument" -- an archive and a warning against folly -- with a signal to draw others to it. "When you read an old book, it doesn't matter that the author has died, or even that his entire culture no longer exists," Robert Dixon, of Ohio State, says. "If the book is valuable, the reader still benefits."
We are alone in this galaxy. Maybe the skeptics are right: the odds against life are so fantastic that one viable planet per galaxy is the best that can be hoped for. If so, then the Milky Way is ours -- ours to ruin or to make flower.
There could be preternatural logic to allocating thinking beings one per galaxy. Given humanity's record of slaughter and bigotry against its own kind, perhaps it would not be possible for numerous highly developed races that considered each other "alien" to abide in harmony. Eternal conflict might be destiny unless the potential combatants were separated by gulfs so vast that no device they could ever invent would allow them to strike at one another. The sheer extremity of the distances between galaxies -- chasms unbridgeable even at the speed of light -- represents to some philosophers a weird enigma. Maybe it's less weird than it seems.
We are alone, period. Perhaps there is no sound of breathing on any other world, no matter how many stars stretch out to the barricade of existence. And there never will be.
This prospect assigns to our existence two poles of possible meaning. One is that life is a fluke -- attractive but without inherent significance, like a splatter of paint that forms a pretty pattern. The other is that human life is precious beyond words. If Earth is the sole home to life, then the cosmic enterprise can be invested with higher purpose only if we prosper and learn to treat one another properly. If we blow ourselves up, the whole of creation will be rendered pointless.
We are the first. Because the universe is ancient, man assumes he must be a latecomer. We expect that other beings could be to us as the greatest teacher is to the lowliest student. But by its own measure, creation glistens with morning dew. Stars are still forming. The universe may exist ten times longer, or a hundred times, or forever. Supposing that life arose by a thoughtless process, it might not be surprising that 15 billion years would pass before the first success was recorded. Supposing that God is running the show, who can say what His timetable calls for?
In either case, if we are first, we will someday be the sage old beings expected to wander the cosmos righting wrongs and pointing others the way.
THE radio telescope of Ohio State University, larger than two football fields, sits in a wooded glade off a dirt road near the town of Lewis Center, Ohio. Since 1973, when the big machine began listening for voices among the stars, scientists, students, and occasionally local citizens have visited the site to bend their ears to the sound of the universe.
On natural frequencies the universe makes a sort of a whoosh, like faraway wind. Because the Ohio State equipment is sensitive, a trained ear can discern tiny fluctuations in the whoosh when disruptions occur, such as an airplane passing nearby. If a person stood on the reflector while the telescope was operating, natural radio emissions from his body would drive every needle on the monitors right off the scale.
The laboratory where the signals are received is quiet, the kind of place a scientist would go to concentrate. Crickets can be heard calling out to each other, and in the distance the sigh of a freight train greets the Ohio countryside. From the stars comes only silence.