by David Toomey
In fifty-odd years, there have been more than a few honest mistakes, one hoax, and one possible signal, the last never repeated but still unexplained.* The searches have made broad but reasonable assumptions about the signals’ senders. Some searches were targeted at stars, with the implicit supposition that the senders would live in a solar system. Others, called “sky surveys” or “all-sky surveys,” allowed that the senders may have set up shop in the vast reaches of interstellar space.
Natural sources of radio waves (like our galaxy and the Earth’s atmosphere) broadcast over a broad range of frequencies. SETI searches assume that a civilization wishing to communicate via radio would use a signal clearly distinguishable from such sources. Accordingly, most searches have tried to detect narrowband signals lying in a range of frequencies that is mostly quiet—a sliver of the microwave region of the electromagnetic spectrum between the emission line at the 21-centimeter hydrogen wavelength and, just a tweak of the dial away, the 18-centimeter emissions of OH, the hydroxyl radical. There may be another reason for the choice, not strictly scientific. It so happens that hydrogen and hydroxyl can be combined to make water. People who listen for messages from the stars can be a fairly romantic lot, and Barnard Oliver, a leading figure in SETI since its beginnings, called the sliver “an uncannily poetic place for water-based life to seek its kind.”3 He and others after him began to call it the “water hole.” If the medium isn’t quite the message, so their thinking goes, it can at least tell us where to look for the message.
Most searches have assumed that the first signal detected will not be the transmission itself but the “carrier” that underpins that transmission. It would be a simple sustained tone or a series of short, intense pulses conveying no information beyond its self-evident artificial nature. The transmission—the actual message—would be far weaker, and to receive it we would need to develop more sensitive receivers.
In the half century since the meeting at Green Bank, much has happened to SETI. Funding has disappeared and reappeared, and serious doubts have been raised as to the existence of extraterrestrial civilizations. Yet two factors of the Drake Equation—the rate of formation of stars that might host planets, and the fraction of stars that do host planets (both unknowns in 1961)—have come within the scope of observation. Astronomers now estimate that between ten and twenty stars that might host planets are born every year, and astrophysicist Geoff Marcy, whose research group has discovered the majority of extrasolar planets, believes that between half and three-quarters of all stars are accompanied by a retinue of planets. NASA’s Kepler space observatory mission team is conducting a survey that will fully address the second term and partly address the third term of the Drake Equation—the fraction of stars with planets and the fraction of those planets that are Earthlike, respectively. And now SETI itself is old enough to have a history, and its own historical places. At Green Bank, in the meeting room where Drake first scribbled his equation, there is a commemorative plaque.
Might any of the assumptions made by SETI cause a search to overlook intelligent weird life? Probably not. Although the chemistry and biochemistry of intelligent weird life might differ, its physics would be our physics.* A technical civilization of weird life would recognize the advantages of communicating via radio waves or light pulses as easily as we do, and although its radio transmitters and lasers might be manufactured with a metallurgy derived from a rather exotic chemistry, they would work as well as ours. Certain sorts of intelligent weird life—those that, say, grew thirsty for liquid methane—might not regard Oliver’s water hole as particularly poetic (assuming of course, they knew what poetry was), but they would nonetheless recognize it as the best range of wavelengths for sending and receiving signals.
THE CHANCES FOR INTELLIGENT WEIRD LIFE
Another question arises—rather nearer our interests here: What are the chances that intelligent extraterrestrials would have a biology radically different from our own? We can guess. Certainly it is easy enough to dust off the Drake Equation again and rejigger it for weird life. The third unknown in the equation—the fraction of planets that are Earthlike (that is, having an environment suitable for life as we know it)—might be altered (narrowly) to represent the fraction of planets that are, say, Triton-like if we’re looking for nitrogen drinkers or Titan-like if we’re looking for methane drinkers. As we saw in Chapter 5, planetary scientist Jonathan Lunine makes this point regarding Titan in particular: “A positive answer would force the third term in the Drake Equation—ne—traditionally defined in terms of the environment of our own Earth, to be radically expanded.”4 As it happens, an expanded definition of that term yields something else: an answer to what SETI calls the “where are they?” question.
The question, which arose some twenty years after SETI began, challenged one of its central assumptions. Distances between stars are great, faster-than-light travel is impossible in the universe Einstein gave us, and travel at speeds approaching the speed of light would be prohibitively expensive in terms of energy. For these reasons, most SETI practitioners had assumed it unlikely that any civilization, no matter how advanced, would practice routine interstellar travel, and this assumption justified the emphasis on communication with radio telescopes and lasers. Physicist and Nobel laureate Edward Purcell was speaking for many when he remarked, “All this stuff about travelling around the universe in space suits . . . belongs back where it came from, on the cereal box.”5 But it seemed that the ingenuity given to breakfast product packaging was, in the view of some anyway, lacking as regards ideas for the possible varieties of interstellar travel.
Although the distances between the stars are vast, it is also true that the galaxy is old, and there are Sun-like stars 5 billion years older than the Sun. There is the possibility of Earthlike planets of the same age. What this means is that there has already been ample time for a star-faring civilization—even a slowly moving one—to colonize the galaxy many times over. In the mid-1970s, scientists Michael Hart and David Viewing took another look at the energy requirements and concluded that slower interstellar travel might be managed with nuclear propulsion at a cost that, for the civilizations they were imagining, would be reasonable.6
Hart calculated that civilizations with the ability to travel at a relatively modest velocity of one-tenth the speed of light could have spread through the entire galaxy in only 1 million years. He acknowledged any number of reasons such civilizations might not do so. Perhaps some preferred a more contemplative lifestyle; perhaps some simply lacked the interest; perhaps some destroyed themselves before they had a chance. But SETI was postulating thousands of civilizations, and hundreds of thousands over time. If only one of them had spread out across the Milky Way, the evidence would be unmistakable—if not a family of squamous purple ovoids moving into the apartment downstairs, then at least detectable radiation from a spacecraft’s drive, or an artifact on Earth or the Moon. SETI researchers, discounting the claims of authors like Whitley Strieber and Erich von Däniken as unable to withstand rigorous proofs, agree that there is no such evidence. That we see no evidence, so argued Hart, means there is none, and that we are probably here alone.
The thinking was reasonable, and for SETI practitioners, the conclusion sobering. The “where are they?” question pushed SETI to what one practitioner called “a major crisis of identity and purpose.”7 The crisis led in turn to an intellectual housecleaning, forcing the formulation of new ideas and the clarification of old ones.8 The strongest argument against Hart and Viewing’s conclusion (and the best answer to the question) was one of the simplest. Phillip Morrison suggested that extraterrestrials had not colonized the galaxy simply because “something limits every growth.”9 In other words, we could not know exactly what prevented the colonization, but we could be sure that something did, and we could be sure that something always would.
But there were other arguments too. A civilization might have colonized the galaxy and still be invisible to us, if members of that civiliz
ation were a certain kind of weird. Recall Lunine’s conjecture that there may be many, many more Titans than Earths, and consequently much more Titan-like life than Earthlike life in the galaxy. If we jump over one or two other unknowns in the Drake Equation, we might conclude that there is a greater possibility for a civilization to arise on a Titan-like planet (or moon) orbiting a red dwarf star than on an Earthlike planet orbiting a Sun-like star. We might further suppose that intelligent beings that had evolved on such a world and were interested in interstellar colonization would, like many a colonist, seek the familiar. So one answer to “where are they?” is that they are (or were) in red dwarf star systems.
The Drake Equation could also be altered (widely) to represent that rather larger fraction of planets and moons and comets that would support any and all weird life. We could argue in general terms that if the arrangement of matter in our Solar System is typical—that is, with most of the real estate farther out from its sun and well outside the traditional habitable zone—then “cold” weird life has more places to get a foothold, in fact about a million times more. If the other factors in the equation remain unchanged, there is a correspondingly greater chance that the signal will be from a weird intelligence. Of course, all the other factors probably do not remain unchanged.
SHOSTAK
The most ambitious SETI project at present is privately funded, and conducted jointly by UC Berkeley and the SETI Institute in Mountain View, California. The senior astronomer at the SETI Institute is Seth Shostak. He has been involved with SETI for more than twenty years, and since 2003 he has served as chair of the SETI Permanent Committee aligned with the International Academy of Astronautics. Shostak has probably given more time to thinking seriously about extraterrestrials than has anyone else alive. He is the one the news outlets call when someone reports a signal, and if and when a signal is detected, he will in all likelihood be the one you’ll see on the talk shows explaining narrowband frequencies and drift scans.
Shostak, now in his sixties, has the relaxed and cheerful manner of a man who long ago made peace with any doubts about his career choice. He can answer skeptics in sound bites and statistic-laden twenty-minute lectures, and he can do either with an ease that suggests he knows something they don’t. In fact, he probably does. It has to do with the chances of detecting a signal.
Until the UC Berkeley–SETI Institute collaboration, the most ambitious SETI effort was Project Phoenix. It lasted nine years and listened for signals from stars inside an imaginary bubble centered on Earth and extending outward 150 light years—750 stars in all. But there are 200–400 billion stars in the Milky Way galaxy. Consider Frank Drake’s estimate that distributed randomly among those stars there are 10,000 communicating civilizations. If we sifted through the static at Project Phoenix’s rate, we would expect to spend about 98,000 years before finding a signal. But—and this is a point Shostak makes often—the speed at which signals can be processed increases along with computing power, and in accordance with Moore’s law,* computing power doubles every eighteen months. Assuming the trend will continue (and there’s no reason to think it won’t), then in the next twenty years the Allen Telescope Array, with regular upgrades, can be expected to have examined 1 million stars. If Drake’s estimate is right, then odds are good that by 2030, SETI will have detected at least one extraterrestrial civilization.
THE NATURE OF EXTRATERRESTRIAL CIVILIZATIONS
What might that civilization be like? Shostak suspects that although we cannot predict the “macroscopic structure and general demeanor” of the extraterrestrials who send a signal, we can make an educated guess as to their nature.10 First, he thinks, the senders of any signal will have a technology that is thousands, perhaps millions, of years ahead of ours. To understand his reasoning, we need to back up a bit.
Cosmologists put the age of the universe at 13.7 billion years. Shrink that span to a single calendar year, and the galaxies form in May, the Sun and its planets form in mid-September, one-celled organisms appear on Earth in early October, and a month later the atmosphere begins to oxidize. The first dinosaurs hatch on December 24, and for several days they reign as Earth’s largest land-dwelling organisms. On December 30, the first small warm-blooded animals scurry through the underbrush. Early on New Year’s Eve, Homo erectus appears and disappears, and Neanderthal comes into view and vanishes. The rise and fall of civilizations; the vast migrations of peoples; the discoveries of continents; the struggles of nations and empires; the creation of art, philosophy, and religion; the development of science and technology; all that has been accomplished by human civilizations—everything that we call recorded history—appears in the final ten seconds of the year, roughly the time it took you to read this sentence. Of course, the clock doesn’t stop here, and assuming that human civilization survives for another ten seconds on the calendar, we might reasonably suppose that its technology will advance as far beyond ours as ours is advanced beyond the reed boats of Mesopotamia.
For the sake of argument, let’s define the current stage in human history—from radio in the 1930s to the present globally networked computer technology and communication, unmanned spaceflight to the nearer planets, and so on—as lasting for the last one-tenth of a second on the cosmic calendar year. Since we have only one example to work with, we can’t know how long it takes for life to arise, intelligence to develop, and civilizations to emerge. But let’s be conservative and suppose that no civilization anywhere in the galaxy could have arisen earlier than 200 million years ago, the moment on Earth when mammals first appeared. In other words, let’s suppose that all civilizations in the galaxy arose after that moment. On the calendar, that’s December 26—six days ago. The odds of any civilization beginning at a random moment in the previous six days and reaching a stage of development equivalent to the current stage in human history at precisely the same one-tenth of a second are (the word is inescapable) astronomical. Thus does the calendar in a single stroke dismiss the densely populated universes of much science fiction. The notion of scores of interstellar civilizations spread halfway across the galaxy—all with roughly similar technologies, warring with each other on bad days, and on better days negotiating treaties and trading recipes—is a fantasy, and likely to remain one.
The truth is likely to be far stranger. And lonelier. There may be civilizations that winked on and off in a few seconds on the calendar, civilizations that reached their height when Earth’s most complex organisms were trilobites. They were too early for us, and we are too late for them. There is very little chance that a signal will come from a civilization that just lit up in the same tenth of a second we did. Any civilizations that might exist at this moment, and so any we are likely to hear from, have been lit for a while, and stayed lit. They will be much older than us and, we may assume, much more advanced technologically.
What can we say about such beings, and such civilizations? Shostak, for one, suspects they will be machines. His reasoning is based on predictions of our own future, and the assumption that most technological civilizations created by biological beings will reach a point in their history at which they will cede their power to artificial beings. We might add here that there is every reason to expect that beings with a weird biology—say, beings with a biochemistry based on silicon and ammonia (as long as they had an aptitude for technology)—would do the same.
In 1994, artificial intelligence pioneer Marvin Minsky penned a piece entitled “Will Robots Inherit the Earth?”—a rhetorical question, which the piece answered more or less in the affirmative. Experts in artificial intelligence expect that members of the human generation now in its twenties will live to see the day when computers match the computational power of the human brain. Since computer power increases exponentially, only fifty years after that day there will be computers or computer networks with the computational power of everyone on Earth. In any measurable way, they will be a lot smarter than we are, and we would be wise to admit it. If our past is any guide to our future,
we probably will.
Many of us long ago ceded spelling and multiplication to the better judgment of software programs. If you checked my math a few paragraphs back, you probably did not use a pencil and paper. Stand on a busy street corner and look around at the pedestrians studying their iPhones and Blackberrys, and at the automobiles with drivers using GPS navigation, and you might well conclude that we’ve already become cyborgs, and we’ve managed to do it without subcutaneous computer chip implants. All of which is to say that insofar as there was a war with the machines, it was bloodless. The humans lost, and most of us don’t seem to care. As individuals, we relinquish our choices of restaurants (and best routes to get to those restaurants) to software programs. As a society, we relinquish our judgment on matters of greater consequence, like health care and finance, to programs and databases. There is no obvious reason we will not continue this practice; in fact, most likely we’ll extend and enlarge it, sooner or later allowing computer networks to manage agriculture, trade, economic, and environmental policies—that is, everything on Earth that can be managed.
Both milestones cited in the preceding paragraphs (the development of a computer with the computational power of a human brain and the development of a network with the computational power of everyone living) are human centered, and there is no reason to expect computer development to stop or pause to acknowledge either. The rather more relevant marker, at least as described in 1993 by mathematician Vernor Vinge, is the moment when all networked computers exchange information at such a rate that they become self-aware. Then, Vinge said, they will begin to adopt motives and goals that the smartest among us simply won’t understand.11 The train will have left the station, and we’ll be standing on the platform, wondering if they’ll ever write home. Meanwhile, our electronic progeny will design their own progeny from scratch, and natural selection will give way to a Lamarckian, self-directed evolution that will be very, very fast, with generations succeeding generations in seconds and then milliseconds, its individuals fashioned with genetics, robotics, and nanotechnology for any and all purposes and any and all environments. And because they will be able to replace parts and download and upload memory as necessary, for most intents and purposes they will be immortal.