by Ben Bova
By 1974 Drake was a professor of astronomy at Cornell. Together with Sagan, who by then headed Cornell’s Laboratory for Planetary Studies, he used the Arecibo telescope to beam a simple message at the globular star cluster M13, which contains more than 100,000 stars. The The British astronomer and Nobel laureate Sir Martin Ryle strongly objected, arguing that no signals should be sent out because they can show possibly hostile and dangerous aliens where we are. Sagan, who grew up reading science fiction, pointed out that since M13 is 25,000 light-years away, even if there are evil aliens intent on conquest, they could not possibly trouble us for at least 50,000 years.
DYSON SPHERES AND CYCLOPS
Freeman Dyson, one of the most original thinkers of the twentieth century, suggested another variation of SETI based on the concept that civilizations might be categorized by the amounts of energy they have access to. We on Earth’s surface depend on sunlight, but the Earth receives only a tiny fraction of the total energy that the Sun is emitting. An advanced civilization might make use of all the energy its central star is emitting by building a shell that completely encloses the star. Dyson estimated that there is enough raw material in the gas giant planets to build such a shell around the Sun at the distance of the Earth’s orbit, 1 AU.
A civilization that had built such a Dyson sphere (as the idea was quickly dubbed) would live on the inner surface of its shell and have all its star’s energy available to it. It might not be beaming out radio signals, but the shell itself would be radiating infrared energy as it got rid of the waste heat it was absorbing. Dyson suggested searching for objects in deep space that were about an astronomical unit in radius and glowing sullenly at infrared frequencies.
NASA, meanwhile, jumped on the SETI bandwagon in a major way. The space agency proposed building a gigantic array of as many as 1,000 100-meter dish-shaped antennas over an area of some 10 kilometers across, which would be capable of detecting far fainter signals than even the Arecibo telescope. Called Cyclops, the program would be able to make substantial contributions to the field of radio astronomy, as well as to SETI. Like many NASA proposals, however, its billion-dollar price tag gave Washington a bad case of sticker shock.
THE COUNTERATTACK
Despite the bright hopes and hard work of the SETI researchers, dozens of radio telescope facilities working over several decades found no repeated signals, no signs of intelligent life.
Politicians found SETI an easy target and a good way to make headlines. In the 1970s, Senator William Proxmire of Wisconsin postured as a guardian of the taxpayer’s purse by awarding a “Golden Fleece” award to government programs that he thought were wasting tax money. In 1978, he awarded a Golden Fleece to SETI, deriding the scientists who, his news release claimed, were searching for “Martians.”
Proxmire’s attacks on scientific research and individual scientists eventually resulted in a libel suit. Yet he prevailed, as far as SETI was concerned. By 1981, when the proposed NASA budget included $2 million to support SETI (million, not billion), Proxmire led the campaign in the Senate to forbid NASA from spending any money on SETI.
Sagan visited Proxmire and, by showing that SETI efforts were leading to much more sophisticated electronic equipment that would have an impact on many industries, he got Proxmire to back off somewhat. (The impending libel suit by a scientist the senator had publicly ridiculed may have also been a factor.)
But the handwriting was on the wall. To the politicians, SETI’s lack of results meant failure. Together with Viking’s disappointing search for life on Mars, Washington’s interest in SETI and space exploration shriveled like a leaky balloon.
Moreover, there was a scientific counterattack against SETI going on, as well.
“WHERE IS EVERYBODY?”
In 1950, at lunch with fellow scientists at the Los Alamos National Laboratory, Nobel laureate Enrico Fermi (1901–1954) asked a simple question: If there are intelligent extraterrestrials, where is everybody? Why haven’t we seen evidence of them?
The obvious answer was that, if they exist, the distances between their worlds and ours are so vast that the only hope we have of finding evidence for them lies in radio searches. Hence SETI.
But by 1975, after some fifteen years of radio searches, two scientists published papers that proposed something close to heresy, as far as the SETI researchers were concerned. American Michael Hart and David Viewing of Britain independently came to the conclusion that the reason no intelligent signals have been found is that there are no intelligent creatures out there. Planets like Earth are so rare, they argued, that we should not expect to find a similar world or intelligent life.
In 1980, Tulane University mathematician Frank Tipler claimed that the universe is only capable of hosting one intelligent species, and we are it. Tipler is not a hidebound conservative nor a chalk-dust-dry academic. His work has included ideas on how to build time machines. Yet, he concluded that there are no other intelligent species in the entire universe.
Tipler made a practical argument for the nonexistence of extraterrestrials. The Milky Way galaxy is at least twice as old as our solar system. There are billions of stars that have existed for billions of years longer than we have. If intelligence has arisen on even a few of these ancient stars, those alien civilizations would be far older and far more knowledgeable than we. Their technological capabilities would immensely exceed our own.
Such a civilization would be able to colonize the entire galaxy, Tipler suggested. It need not send its own people into space, it could send self-replicating machines that move from one star to another, colonizing any planets they find, then using those planets’ natural resources to build more copies of themselves and move on to the next stars.27 In effect, such machines would be like a virus spreading from star to star, planet to planet. If their spacecraft could achieve velocities of only 10 percent of the speed of light (something that we should be able to do before this century is out), they could spread exponentially across the entire Milky Way in less than a million years, a small fraction of the Milky Way’s multibillion-year existence.
The fact that Earth has not been visited by these mechanical representatives of a superior civilization, Tipler concluded, is proof that no such civilizations exist.
Howls of protest greeted Tipler’s pessimistic argument. The SETI optimists pointed out that his conclusions rest on enormous assumptions. For example, could such ancient civilizations exist? The oldest stars are metal-poor; they might not have contained the proper elements for life or a technologically sophisticated civilization to arise around them. Or if such very old and wise civilizations do exist, perhaps they would have no interest in colonizing the galaxy. Then, of course, there are plenty of people who claim quite ardently that we have indeed been visited by aliens. More on them in the next chapter.
GALACTIC GEOBIOLOGY
Despite accounts of alien visitations, no credible evidence for intelligent life beyond the Earth has so far been found by SETI researchers. Perhaps if we consider the composition and history of the Milky Way galaxy, we may gain a better insight into the reasons why we have not located intelligent life elsewhere.
The Milky Way is a vast pinwheel of at least 100 billion stars, with enough loose gas and dust to build hundreds of billions more.
According to accepted cosmological understanding, the universe began between 10 and 15 billion years ago, as the result of a titanic burst of energy commonly called the Big Bang. All the matter and energy in the universe today originated in that Big Bang. The matter was almost entirely hydrogen, the simplest atom of them all, with a few percent of helium and a trace of lithium, the next two lightest elements.
Billions of galaxies began to take shape, enormous aggregations of stars and clouds of gas and dust. Our Milky Way is one of them. The earliest stars to form were built from the only elements then available: hydrogen, helium, and lithium. Any planets that grew around them were also composed of hydrogen, helium, and lithium. There were no other elements in existenc
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Those earliest worlds could not support life. There was as yet no oxygen, no carbon, no nitrogen or calcium or potassium or any element heavier than lithium. Not even water existed yet, because there was not yet any oxygen to combine with the abundant hydrogen. The Milky Way was lifeless.
The stars are nuclear factories that cook up heavier elements. Inside their dense, million-degree-hot cores, hydrogen is fused into helium. Eventually, helium begins fusion processes that produce carbon, oxygen, and neon. As a star ages, its core becomes ever hotter and denser, and it produces ever-heavier elements. When massive stars finally explode, these heavier elements are spewed out into interstellar space.
The next generation of stars had a richer mix of raw materials to build with. Planets circling such stars had iron, aluminum, silicon, oxygen, carbon, nitrogen, and many other elements in them. The elements of life were available to them.
Moreover, the galaxy itself has a “habitable zone.” The Milky Way is a spiral galaxy, a vast pinwheel of stars and loose clouds of gas and dust. Our Sun and solar system exist in one of the galaxy’s spiral arms, about 30,000 light-years from its core. The central regions of the Milky Way are thick with stars—and drenched in hard radiation that apparently is emanating from a black hole at the galaxy’s heart. Stars near the galactic core are jostled by orbital instabilities caused by the gravitational perturbations from stars that are literally too close together for comfort. The radiation levels are probably lethal, as well.
The Sun orbits about the Milky Way’s center in about 200 million years, safely within the habitable zone in which stable orbits can be maintained and life can develop.
As we have seen, the Sun is about 4.5 billion years old, less than half the age of the first stars in the Milky Way. The Sun is a “metal-rich” star. That is, the Sun—and its retinue of planets—contain more elements heavier than helium than the earlier stars did. We know that on at least one planet circling the Sun, life has arisen. Over the 4.5 billion years of Earth’s history, life has evolved at least one intelligent species, who now searches the universe for other life, other intelligence.
Perhaps our solar system is one of the first that has had sufficient amounts of heavy elements to generate life and intelligence. And technology, as well. Without copper and iron, our technological civilization could never have gotten started. Perhaps we are the oldest and wisest organisms in our stellar neighborhood!
HOW RARE IS OUR EARTH?
By the year 2000, the various arguments against the existence of intelligent aliens were summarized by paleontologist Peter D. Ward and astronomer Donald Brownlee in their book, Rare Earth. Basically, they refined the idea that complex life (meaning multicelled organisms) is so rare in the universe that we may be the only example in the entire galaxy. While microbial life may exist elsewhere, intelligent life might be unique to our special planet.
Moreover, biologists were awakening to the idea that intelligence is neither a necessary nor inevitable consequence of life. Most of us still hold in our minds the concept of a Tree of Life (or perhaps a Ladder of Life) that starts with very simple organisms and culminates, at the top, with an intelligent species: Homo sapiens. We tacitly assume that wherever life exists, intelligence will eventually arise, given enough time. But is that true? The modern biological view of life resembles a thick, wild bush more than a tree or a ladder. Intelligence is merely one evolutionary tactic, an adaptation that helps a species to survive, little different from developing a shaggy coat of fur or sharp-focusing eyes or wings or gills or any of myriad of adaptations.
Life adapts in every way it can, and intelligence—which we regard as the high point of it all—is most likely just another adaptation that has helped our species to survive, but it may eventually push us into extinction as our weaponry or heedlessness exceeds our ability to control our passions.
Harvard paleobiologist Stephen Jay Gould (1941–2002) put it this way: “Humans [and intelligence] are here by the luck of the draw, not the inevitability of life’s direction or evolution’s mechanism.”
In other words, it is not inevitable that there are other intelligent species out there to communicate with us. We may indeed be alone. On the other hand, intelligence might be such a useful trait that the universe is teeming with intelligent species. We simply do not know.
CONGRESS STRIKES AGAIN
Scientists argued these points back and forth. The politicians in Washington acted on them. In 1992, Congress again forbade NASA from spending a penny on SETI. Proxmire was long gone from the Senate, but Senator Richard Bryan of Nevada echoed his sentiments:
The Great Martian Chase has finally come to an end. As of today, millions have been spent and we have yet to bag a single little green fellow. Not a single martian has said take me to your leader, and not a single flying saucer has applied for FAA approval.
Notwithstanding the fact that SETI had nothing to do with Mars or UFOs, NASA was prohibited from working on SETI.
Long before that, Sagan and others began to realize that SETI, and space science in general, needed widespread public support if it was to survive the butcher knives of Washington. By 1970 he and Bruce Murray, then the director of the Jet Propulsion Laboratory (where most of NASA’s planetary exploration programs were based), created a public support group, the Planetary Society. Using his immensely popular television series, Cosmos, to help publicize the organization, Sagan saw the Planetary Society swiftly grow to 100,000 members.
The Planetary Society raised money to continue SETI without government funding. Harvard physicist Paul Horowitz had developed a compact electronics system he called Suitcase SETI, capable of scanning 65,000 narrow-wavelength channels. As portable as its name implied, Suitcase SETI was used at Arecibo and elsewhere before Congress cut off NASA’s funding for SETI. The Planetary Society funded Horowitz’s work, dubbing it Project Sentinel.
By 1985 Horowitz had developed an even better electronics system, META (Megachannel ExtraTerrestrial Assay), capable of scanning 8 million channels. With a donation of $100,000 from filmmaker Steven Spielberg, the Planetary Society was able to get Harvard University to allow Horowitz to use the 18.3-meter radio telescope in the town of Harvard, Massachusetts, exclusively for SETI observations. Horowitz later improved his system into BETA, capable of scanning a billion radio frequencies.
The Planetary Society also organized SETI@home, in which ordinary citizens can devote their home computers when they are ordinarily idle to analyzing data coming in from the University of California, Berkeley’s Project Serendip, a privately funded effort that uses the Arecibo radio telescope. With funding help from Paramount Pictures, producers of Star Trek, SETI@home has attracted more than 1 million volunteers who allow their home computers to help analyze incoming Serendip data in the hopes of detecting a signal from an intelligent civilization. Anyone with a home computer can join, and they can use incoming Serendip data as “wallpaper.”
Meanwhile, Drake left Cornell and, with former NASA scientist Jill Tarcher and others, formed the SETI Institute in California. SETI carried on, despite Washington’s disinterest. Raising money privately, they continued SETI’s radio telescope searches, dubbing their work Project Phoenix after the mythical bird that rises newborn out of its own ashes.
Directed by Tarter, Project Phoenix uses the giant Arecibo dish and is budgeted at about $1 million per year, all the money donated by private individuals.
In 2000, Drake announced that philanthropist Paul G. Allen, a cofounder of Microsoft Corporation, and former Microsoft executive Nathan P. Myhrvold had pledged $12.5 million for developing an array of hundreds of 6-meter-wide radio telescope dishes, somewhat of a “smaller, faster, cheaper” version of NASA’s old Project Cyclops. The new array will be far less expensive, since it will take advantage of the fact that commercial manufacturers have been building similar dish antennas for private homes to receive television signals from satellites. Such mass production has brought down the price of steerable dish antennas. Th
e facility will be sited at the Hat Creek Observatory, some 400 kilometers north of San Francisco. It will be called the Allen Telescope Array; the primary laboratory supporting the array will be named after Myhrvold.
Drake points out that, “The Allen Array will be the world’s most powerful instrument designed to seek out signals from civilizations elsewhere in our galaxy.”
Yet, despite continued searches and increasingly sophisticated scanning technology, radio telescopes have found nothing to date. If there are intelligent aliens scattered among the stars, perhaps they are doing precisely what we are: listening but not sending deliberate signals of greeting out to the stars. Not at radio frequencies, it seems.
Nor have radio astronomers been able to detect radio emissions from a civilization’s ordinary day-to-day chatter. No alien version of I Love Lucy has been picked up by SETI researchers.
Could radio be the wrong medium? After all, the chances are that any civilization that we can contact will be considerably advanced beyond our technology. Radio is already almost a century old here on Earth; most likely the extraterrestrials (if they exist) stopped using such primitive technology ages ago.