Home Alone in the Universe?

As I first learned at a dinner table surrounded by new acquaintances, questioning people’s belief in extraterrestrial intelligence (ETI) is like questioning their religious faith. Doubts are met with gasps. The fierce stares say not just, “We disagree,” but “You have blasphemed.”

Don’t get me wrong. I have nothing against curing cancer, heart disease, and AIDS, which advanced aliens could presumably do. I’d be fascinated to hear an alien’s perspective on the meaning and purpose of life. I’m all for immediate solutions to our war/crime/ poverty problems, which a mature society is supposed to have solved. I even think that receiving all these blessings from above may follow logically from contact with a civilization that’s survived for millions of years. But I also think that astronomers are now in a position to know that our chance of achieving such contact is very small.

Nothing drives ETI faith like the Copernican Principle, the idea that we do not occupy a privileged position in the universe. Many regard this as a necessary axiom for the continued success of the scientific enterprise. The practice of science begins, we are told, with the assumption that we are typical, not exceptional. We can’t scientifically study a sampling of one, after all. Moreover, history suggests that Copernicus began an unstoppable progression: the world’s greatest modern thinkers proposed and then proved that the Earth is not the center of the universe, that the Sun is not the center, that our galaxy is not the center, and finally, that there is no center.

Copernicus gave us the theory to take the first step, and Galileo demonstrated its truth. Einstein gave us the theory to take the last steps, and Edwin Hubble’s observations of distant galaxies convinced the world.

Astronomer Robert Jastrow, founder of NASA’s Goddard Institute, calls Hubble’s achievement “the last great step in the revolution of thought regarding mankind’s place in the cosmos that had been initiated by Copernicus.” But today’s Copernican Principle proposes, not only that the universe does not revolve around the Earth, but that the universe does not revolve around us, either literally or figuratively.

Having proved that our planet, sun, and galaxy are typical, science has yet to settle the question about whether we ourselves are typical. We lack absolute certainty that we are not, in the most important sense, the center”until someone confirms the existence of intelligent beings elsewhere in the universe.

Yes, if you put it that way, Robert Jastrow agrees: the final step in the Copernican revolution has yet to be taken. But in my talks with him during the 1990s, he insisted that we are on the verge of taking it.

“I think that mankind is on the threshold of entering a larger, cosmic community,” he told me during a visit to his home and then to California’s Mt. Wilson Observatories, where he serves as Director. His words carried a kind of ecclesiastical authority, seeming to reverberate from the seven-story dome above him, the observatory he calls a “cathedral dedicated to mankind’s quest for understanding of the Cosmos.” Less loftily, he added, simply, “We’ll be hearing from those guys soon.”

Taking a seat on the wicker chair that Edwin Hubble had sat upon almost eighty years before, I pondered this possibility”and then promptly forgot it while playing with the controls that split open the ceiling to the night sky, that slued the 100-ton telescope across the room, that spun the entire cavernous structure around me.

Sitting there a mile above Los Angeles at the focus of the world’s largest telescope, positioned at the helm of the entire scientific enterprise, Hubble felt tremendous power. Oddly, he was simultaneously struck with a sensation of puniness, of being the first to fully understand how diminutive our place is in this enormous universe. While tweaking the controls over hundreds of cold nights through the early 1920s, Hubble provided photographic proof that our galaxy is but one of many. The nebulas, then understood to be wisps of gas among the Milky Way’s stars, turned out to be more distant galaxies containing billions of stars of their own.

Now, having entered a new millennium, we’re poised to make the final test of the Copernican Principle. And why should Robert Jastrow think our generation will be the lucky one to finally make contact, aside from the fact that his generation of astronomers can’t die in peace until it happens? For one thing, new SETI (Search for Extra-Terrestrial Intelligence) telescopes and computers are being built with greatly enhanced sensitivity and coverage.

But Dr. Jastrow was thinking more about the signals we’ve been sending than those we hope to receive. “We’re a very conspicuous part of the universe right now,” he explained. “The TV and FM broadcasts”and the radar from our defense installations”are sending out a signal that there is life on this planet.”

The SETI Institute’s Robert Arnold agreed, saying: “These electromagnetic artifacts of daily commerce, entertainment, and defense give the Earth a distinct radio frequency signature that is brighter than the Sun.”

According to Jastrow, “That started in intensity, at the million-watt level, about thirty years ago, in the 1960s.” Jack Parr and I Love Lucy are at a wave front, he said, that’s spreading out into the cosmos. “Within thirty light-years there are some dozens of stars. And if they got the word thirty years ago, they would be sending a reply back to us. And those who are only fifteen light-years away will have sent a message back fifteen years ago, which should just about be reaching us today.”

Other astronomers belonging to Dr. Jastrow’s generation recall the same kind of enthusiasm, but new concerns have since dampened it. “I used to rather enjoy thinking that the early civilizations would have set up an intercommunicating system,” said Senior Astronomer Emeritus Eric Carlson of Chicago’s Adler Planetarium. “Maybe laser beams or something full of information about all the other civilizations in the past history of the galaxy, and that this is all circulating . . . from star to star around the galaxy, and all we have to do is tap into it.”

The actual likelihood that we’ll hear back from anyone that close, of course, depends upon just how densely packed our galaxy is with civilizations”and upon how long those civilizations last. Today Carlson frets about what might happen to any civilization in the course of a ten-billion-year-old galaxy. What will be left of human culture in a billion years, or even a million? “I tend to get this sense of a galaxy as being sort of like a garden,” says Carlson. “You have the early spring flowers, and then you have the late spring flowers and so on, and you have life with consciousness springing up here and there for a while. And whether it’s ever in contact at the same time, I just don’t know.”

The next generation of cosmologists might still say that the existence of extraterrestrial civilizations is “extremely likely,” as cosmologist George Smoot (Lawrence Berkeley Laboratories) told me. “But I think the chances of there being life near to us is pretty low,” he cautioned, “and whether there’s life in our own galaxy, besides ourselves, I don’t know.”

Among the youngest astronomers to make a name for himself is Charles Steidel, the Caltech leader of an international team to discover ways of viewing thirteen-billion-year-old baby galaxies. His thoughts reflect the addition of twenty-first-century biological understanding to the equation: “The chance of there being life with which we would be capable of communicating, I think, is fairly low, because there are so many ways that things could develop.”

Even Robert Jastrow, who has proved more relentlessly upbeat about alien civilizations than any other astronomer with whom I’ve spoken, appears to have had some second thoughts. When I was about to go to press with a book on modern cosmology, he asked me to make a small addition to a statement he had made in my chapter about SETI. Instead of saying, “We’ll be hearing from those guys soon,” he wanted me to change it to, “If life is common, we’ll be hearing from those guys soon.”

Most people are oblivious to recent evidence bearing upon the ETI question, both pro and con. But the Copernican principle is firmly embedded in popular culture, understood in terms of “the awful waste of space” if aliens aren’t out there. Any chatty taxi driver can tell you that there are billions of galaxies and billions of stars within each. The sheer numbers demand that there be millions of habitable planets in our galaxy alone, even if the percentage of tenantable star systems is small. To say otherwise is to expose one’s lack of scientific education.

Contact is assumed to be not a matter of if, but when. Our movies have given us progressively better special effects to prepare us for a day when the Earth will stand still, when we’ll experience Close Encounters of the Third Kind, or when SETI will help us make Contact. Generation X and following have been entertained by more extraterrestrials than cowboys, Indians, and soldiers combined. It’s probably not an overstatement to say that no movies have had greater influence on men under age thirty-five than the Star Wars films.

Infatuation with extraterrestrials further increased in the last decade. The Rockford Files became The X-Files. Mob-fighting Untouchables turned into alien-fighting Men in Black, also spun into a children’s cartoon series. The biggest hit in late night radio is a national show that frequently features guests offering firsthand accounts of their close encounters with aliens or their spacecraft.

For some people, real life is apparently taking too long to catch up to their media-led expectations”and they aren’t going to wait any longer. During the 1990s, psychologists estimated that in the U.S. alone 900,000 people claimed to have been abducted by aliens, and the trend was increasing. In his book Close Encounters of the Fourth Kind, C. D. B. Bryan reported “the emergence of a new psychological disorder,” observed in people who have been conditioned to look to “alien saviors” who might give them the fulfillment they aren’t finding on terra firma.

Theoretical physicist Paul Davies claims that people are looking to extraterrestrials as “a conduit to the Ultimate.” For many, the prospect of ETI has come to meet a need once met by religion. Even the SETI scientists say they are motivated by a nobler goal than the mere search for intelligence. Imagine, they say, the boost in knowledge, in morality, and maybe even in spirituality, to be gained from a billion-year-old civilization.

Robert Jastrow imagines what it might do to our present religions. “When we make contact with them, it will be a transforming event,” he says. “I do not know how the Judeo-Christian tradition will react to this development, because the concept that there exist beings superior to us in this universe, not only technically, but perhaps spiritually and morally, will take some rethinking, I think, of the classic doctrines of Western religion.”

Any signals we detect, according to SETI astronomer Jill Tarter, will come from long-lived civilizations. This fact, combined with the fact that religions cause so many wars on this planet, means that our first detected signals will come from beings “who either never had, or have outgrown, organized religion,” she said at a recent science/religion meeting sponsored by the Templeton Foundation and held in the Bahamas.

Other scientists and theologians at the Nassau meeting thought that pantheistic religions could survive an alien encounter, but most assumed that Western religion would certainly meet its fate when meeting extraterrestrials. Science historian Steven Dick called SETI “a religious quest” that might help to reconcile science and religion. But he assumed this would occur at the expense of Christianity, which could not accommodate the implications of ETI.

It strikes me that today’s scholars may be too quick to pronounce last rites over the faith that actually engendered most early ETI enthusiasts. Throughout the Middle Ages, well-read people believed that a “plurality of worlds” was impossible, following Aristotle’s arguments. In 1277, a council of bishops in France condemned this position, officially opening the way for many to take other worlds seriously.

Whether encouraged or discouraged by their churches, prominent Christians became the most prominent ETI promoters. These included Giordano Bruno and Nicholas of Cusa (fifteenth century), Johannes Kepler (sixteenth century), American Puritan divine Cotton Mather (seventeenth century), and Yale president/minister Timothy Dwight (eighteenth century).

Whether aliens will deliver a knockout blow to any particular religion depends, of course, upon exactly what aliens have to tell us about God. Materialists have traditionally assumed that Jews, Christians, and Muslims, believing in a transcendent God, will receive bad news. And the Christian belief in Jesus’ death for human sin seems particularly problematic to them. How could we reconcile Jesus’ death for all with the existence of other intelligent creatures in the universe?

Christian ETI enthusiasts, however, have a variety of responses to the skeptics:

Who can tell what other cradle,
High above the Milky Way,
Still may rock the King of Heaven
On another Christmas Day?

Most ETI believers remain blissfully foggy about the best evidence to support their faith. Here are some of the recent scientific discoveries and trends I’d be sure to mention if I were to argue for the existence of ETI at my next dinner party.

• Exoplanets. The Copernican Principle came through once again by predicting that we should find planets orbiting Sun-like stars. Waiting all their lives for this discovery, astronomers finally received word of it in 1995.

Until very recently, no extrasolar planet had been observed directly, but rigorous measurements of the wobble in their host stars assured planet-hunters of their presence. The first exoplanets discovered appeared to belong to freakish solar systems, not only because the pinpointed planets were huge”as expected, since these are easiest to measure”but also because they were orbiting close to their parent stars, which was very unlike our expectation of finding solar systems like ours, with large, gaseous planets farther out. Our solar system is beginning to look like the freakish one.

Astrophysicist Virginia Trimble (University of California, Irvine) typified the consensus before these discoveries, writing: “It is not a coincidence that the solid-surfaced, terrestrial planets are close to the Sun and warm enough for liquid water, while the jovian (gas-giant) planets are in the outer, frigid reaches of the solar system.” Using “common sense and computer models,” she calculated that “the Milky Way probably still contains at least 10 10 [that’s ten billion] stars that could have harbored habitable, terrestrial planets for more than five billion years.” Our actual observation of unexpectedly different planetary systems now forces us to rethink our views on the commonness of earthlike planets.

Exobiologists have dubbed the habitable belt where water can exist in liquid form around a star “the Goldilocks zone,” because it’s neither too hot nor too cold for life. Those exoplanets that have been observed spending any time in the Goldilocks zone merely pass through it. Their orbits are extremely elliptical, meaning surface temperatures fluctuate from hotter than Venus to colder than Mars. The very fact that these massive planets cut through the habitable zone in their elongated orbits ensures there can be no smaller, more hospitable planets in this system, since the giants would destabilize their orbits.

Teachers and students learned from Science News : “Recent discoveries of giant planets orbiting within spitting distance of their stars have upset a central tenet of astronomers”that Earth’s solar system, where large planets orbit far from the Sun, provides the model for planetary development everywhere.”

Of course, it’s too early to tell by these methods just how rare our earth is. The technique is not yet refined enough to find smaller planets. Over the next two decades, NASA’s Origins Program will be developing a series of space-based telescopes, hoping not only to detect the wobble produced by small, Earth-sized planets (2009’s Space Interferometry Mission), but to measure the chemical signature of life itself (2012’s Terrestrial Planet Finder).

In short, exoplanet discoveries probably provide the most important scientific gain in recent years to favor ETI existence, but this good news came at a price: the Copernican Principle cannot be applied so neatly to our own star system. Our solar system does not appear to be typical, and those that permit life, if they exist, must be the exception, not the rule”even among Sun-like stars.

• SETI Strides. New search instruments coming on line in the near future may dwarf all previous attempts to pick up signals from distant civilizations. The argument can be made that earlier searches just didn’t have the coverage required”either in sensitivity, frequencies, or number of examined stars. And these shortcomings will shortly be remedied with instruments that are making great leaps in capability.

The SETI Institute of Mountain View, California, calls its main search Project Phoenix, the best-funded search ever. Unlike others, this project carefully searches star by star, listening only to the likeliest candidates within a radius of two hundred light-years. Project Phoenix has shuttled its Targeted Search System back and forth between the largest radio dishes in the world.

In September 2000, Microsoft’s cofounder Paul Allen and his associate Nathan Myhrvold pledged $12.5 million dollars to the SETI Institute for the development of the Allen Telescope Array (ATA), a specially designed radio telescope that will be dedicated to the search for ETI. A small prototype is complete, and the full ATA, comprised of hundreds of backyard-type satellite dishes working together, is scheduled to come online in 2005. In the time it now takes Project Phoenix to survey 1,000 stars, ATA will examine 100,000, and might eventually scrutinize a million stars a year, looking out to 1,000 light-years or more.

“This telescope will do it,” SETI astronomer Seth Shostak told me. According to Shostak, the ATA will scan so many stars with such speed that “even if we use the most conservative estimates about the number of civilizations out there, I think we’ll find their signals within the next couple of decades.”

Not wanting to wait that long, over three million volunteer enthusiasts are also partaking in the pursuit, either by joining a “distributed computing” network called SETI@Home, or by building their own radio telescopes as members of the amateur SETI League.

“It gets the heart pounding,” says Shostak, anticipating the fact that we may soon be listening to alien wisdom. It’s an experience several Silicon Valley legends are giving tens of millions of dollars to have. And amateurs are giving tens of millions of hours to try to bring us the experience sooner.

Some analysts of SETI projects argue that Project Phoenix is wasting its considerable resources on an outdated strategy. Nathan Cohen and Robert Hohlfeld, scientists at Boston University, point out that targeted search strategies assume that ET civilizations are much more abundant than recent observations allow. They favor scanning larger, star-rich areas of the sky, betting on the numbers rather than the long-shot chance of finding ETIs via nearby, star-by-star searches.

“Unless ETs truly infest the stars like flies (very unlikely),” write Cohen and Hohlfeld, “the first signals we can detect will come from very rare, very powerful transmitters very far away. The 1971 model, which lent too much weight to nearby stars, turns out to be a naive case, the best that could be calculated at the time.”

• Slow Strides in Space Travel. Each new problem for space travel is a problem solved for SETI enthusiasts. Easy progress in our ability to zip around the solar system might imply our eventual ability to travel between the stars”and the ability of advanced aliens to do so. In that case, we shouldn’t have to go looking for them; they should already be here.

But here we are, already past 2001, the year when, according to Arthur C. Clarke’s trend-setting classic of science fiction, humankind would make contact with more highly evolved beings (or at least one of their artifacts). At the very least, by this time we were supposed to be doing manned missions to Jupiter’s moons. Clarke’s expectation in the 1960s was not unrealistic, considering the fact that our new space program went from putting the first man in orbit to the first man on the moon in just seven years.

So why was that first small step for man the last great leap to be made in twentieth-century space exploration? Each passing year that delays the planning of a manned Mars mission reminds us of the exponentially greater distances”and difficulties”as we try to reach objects beyond our Earth-Moon system. And so these difficult-to-cross distances may explain why we haven’t been visited.

If the public knows little about the best reasons to believe in intelligent extraterrestrials, it knows even less about the new reasons to doubt.

• Fermi’s Paradox”Back in Style. Fermi’s Paradox, a SETI-challenge that was tried and found wanting in the 1950s, has been given a retrial. This time, expert witnesses on propulsion technologies have been called in, claiming that if life sprung up in our galaxy many millions of years ago, then our galaxy should have been entirely colonized by now.

It all started over a Los Alamos lab lunch in the summer of 1950, when renowned Italian physicist Enrico Fermi had one of those napkin-scribbling epiphanies. His conclusion stemmed from the indisputable premise that there are billions of stars in our galaxy that are older than our sun, and that life routinely develops under favorable conditions.

Exhausted planet resources and dying stars would provide good motives for exploration and homesteading. Some cultures, like our own, would find other motives for colonizing, and it would only take one enterprising population to begin exponential expansion. Fermi showed that, even assuming modest speeds, every habitable star system in the galaxy should have been colonized within mere millions, not billions, of years. Complete colonization could take place in the relative twinkling of a cosmic eye, many times over, in a ten-billion-year-old galaxy like the Milky Way. “So,” asked Fermi, “where are they?”

Astronomers immediately developed solutions to the paradox, but as the years passed, each of these explanations has become problematic. Some suggested that perhaps the distances between stars are just too great for biological creatures ever to cross. But today, while still in our space age’s infancy, physicists and engineers at NASA envision propulsion strategies that should reach 10 to 20 percent of the speed of light, making trips to the stars feasible, even for short-lived biological beings like us.

Figuring on a cruising speed of 10 percent that of light and periods of four hundred years’ settling time between migrations, astronomers say it would take just five million years for one colonizing group to reach every star system across the Milky Way’s 100,000 light-years.

In the 1970s, four astrophysicists”Michael Hart, David Viewing, Frank Tipler, and Ronald Bracewell”independently published studies concluding that the Fermi Paradox was difficult to escape. Today, as NASA lays the groundwork for new propulsion strategies, the thought that older cultures should have developed these long ago lends added weight to Fermi’s argument. “The implication is clear,” wrote British astronomer Ian Crawford last year: “The first technological civilization with the ability and the inclination to colonize the galaxy could have done so before any competitors even had a chance to evolve.”

In the past, alien defenders turned to sociological factors that might have prevented interstellar travel. Perhaps aliens just don’t like traveling. Perhaps civilizations routinely blow themselves up after achieving nuclear capabilities. Or perhaps, according to the “zoo hypothesis,” our solar system has been set aside as a primitive nature preserve, not to be touched.

But even SETI Institute astronomer Seth Shostak is skeptical about these scenarios, writing in his book Sharing the Universe : “It isn’t that we can resolve the Fermi paradox by arguing that most alien societies self-destruct or lose interest in expansion. Every single one of them must do so, for otherwise representatives of at least one society would be in our neighborhood.”

Some of them, if not all, would have ample motivation to move when their host stars ran out of hydrogen and died. Hundreds of millions of solar-type stars in our Milky Way have already suffered this fate, turning any surrounding paradises into hells by puffing up into red giants or compacting into white dwarfs.

What are SETI proponents to do? Most have returned to pointing out the physical challenges of interstellar trekking. During the 1950s, astronomer Frank Drake decided that energy costs might make interstellar travel not just high-priced, but impossibly so. There’s no guarantee that better propulsion systems are physically possible or that less costly energy sources can be tapped for higher speeds.

It’s exactly here that believers in advanced ETI exacerbate the paradox. They invariably assume that the space-travel technology and energy resources of advanced technological civilizations will also be highly developed. After all, Carl Sagan and other SETI pioneers classified these advanced civilizations according to their abilities to harness the power of entire stars or galaxies. It doesn’t sound like insufficient energy production would be the thing to hold back such societies from powering greatly increased transit speeds. In our own history, the cost of raw materials and fuels, relative to wages, has been dropping exponentially for the past 150 years. In 1983 Carl Sagan himself predicted that this trend would likely continue for another millennium.

• New Analysis of SETI Results. Recent analyses of radio search findings have only tended to put severe constraints on the numbers and types of possible alien civilizations.

At the first SETI conference in 1961, Frank Drake proposed a list of factors to quantify the technological populations expected to inhabit our galaxy. Drake’s associates assigned values to the rate of star formation, the fraction of stars with planetary systems, the number of planets suitable for life, the fraction of planets where life develops, and the fraction where technological civilizations develop. By multiplying the terms together, they determined that there should be about one million societies using radio waves in our galaxy. The scientists assumed, conservatively, that perhaps 1 percent of the civilizations would not blow themselves up shortly after achieving nuclear capabilities. Others have since assigned higher values to this and other factors, and have arrived at an even higher number.

Drake’s first project to search for extraterrestrial radio signals became the forerunner of more than seventy grander radio searches by teams around the world, using the world’s largest radio telescopes and most sophisticated computer programs to analyze the data.

However, after what has now been forty years of null SETI results, astronomers are reexamining each of the factors making up the Drake Equation, concerned that the values of some may have been grossly overestimated. Charting the distances and radio powers that SETI projects have checked to date, Massachusetts physicist Andrew LePage has already determined which kinds of civilizations can be ruled out. These include nearby civilizations slightly more advanced than ours (called type I), as well as those at greater distances that are yet more advanced (called types II and III). “These are not trivial results,” writes LePage. “Before scientists began to look they thought that type II or III civilizations might actually be quite common. That does not appear to be the case.”

• The Rare Earth Equation. Today the Drake Equation is being superseded by the Rare Earth Equation, as it was named by geologist Peter Ward and astronomer Donald Brownlee, both at the University of Washington in Seattle. Since the Drake Equation depends upon the number of Earth-like planets orbiting Sun-like stars, Ward and Brownlee used the latest data to revise previous estimates concerning both”and to add many once-neglected factors, now known to be critical, to the equation.

These include the fraction of stars in a galaxy’s habitable zone, the fraction of metal-rich planets, the fraction of planets with a large moon, the fraction of planets where complex animals arise (as opposed to bacteria or algae), and the fraction of planets with a critically low number of mass extinction events. In their 2000 book, Rare Earth”Why Complex Life Is Uncommon in the Universe, Ward and Brownlee remind their readers: “When any term of the equation approaches zero, so too does the final result.” And they conclude: “It appears that Earth indeed may be extraordinarily rare.” Here’s why:

• Special Gas Giant. Jupiter-like planets that orbit close to their host stars, or that orbit eccentrically, refuse to politely share their space with smaller, life-harboring planets. Habitable planets need to make circular orbits within the “Goldilocks zone.” Gas giants making eccentric orbits will eject smaller neighbors out of the system or send them crashing into their sun.

Well-behaved gas giants, like Jupiter and Saturn, keep circular orbits at a respectful distance. In that position, they actually serve the necessary function of cosmic vacuum sweeper, drawing comets and asteroids to themselves, rather than allowing them