by Bryan Walsh
Aliens, of course, could be classified as an existential threat themselves. That’s what fiction teaches us, from H. G. Wells’s Victorian-era story The War of the Worlds to the mid-century thriller The Body Snatchers to the 2018 blockbuster film A Quiet Place. As different as these narratives are, each emblematic of the cultural fears of their moment, they share common themes. Advanced extraterrestrials come to conquer Earth—whether secretly or in force—and humans band together to repel them. But in any extraterrestrial intelligence that possesses the technological capability to cross the stars for Earth and the hostile intentions to attack it would almost certainly crush us, as quickly and as efficiently as a malevolent superintelligent AI. If such ETs exist and they’re angry, then aliens would be an existential threat—albeit one we could do little to counter. If they exist.
But do they? That’s the question that really matters for existential risk—not military plans to track UFOs or panicked tales about alien abduction. If intelligent aliens live, if they have ever lived, then they hold out the possibility of another experiment, another attempt on a distant star to survive and thrive in a universe so often hostile to life. If they’ve managed to outlast the same kind of existential threats that we face, then they offer us a strand of hope that we too can make it, that our destiny isn’t death. Perhaps they may even be able to guide us, as many of the scientists who launched the first searches for extraterrestrial intelligence so fervently hoped. “We are at a very dangerous moment in human history,” said Carl Sagan in 1978. “We are not certain that we will be able to survive this period of what I like to call technological adolescence. Were we to receive a message from somewhere else, it would show that it’s possible to survive this kind of period. And that’s a useful bit of information to have.”3
If they don’t exist, however, then we face another question. If we are truly as alone in the universe as we now appear, then perhaps intelligent life is an unlikely accident of cosmic fate, and we really are one in a 100 billion—the number of stars in the Milky Way. If so, our fate is even weightier, for Homo sapiens would become the cosmos’s sole conscious observers. Or worse, perhaps intelligent life has arisen elsewhere in the galaxy, only we see no evidence because aliens have been destroyed over and over, or have destroyed themselves. Maybe every time the experiment of intelligence has been conducted, it has failed. If that is the case—if the apparent lack of intelligent life in the galaxy is the product of repeated cosmic catastrophes that destroyed alien civilizations, as we ourselves are in danger of being destroyed—then are we too doomed to extinction?
We should be worried. The Search for Extraterrestrial Intelligence, or SETI, has been under way for decades, and a new wave of science has shown that our galaxy may be far more hospitable to life than we first suspected. Yet we have found nothing. Not a scrap of evidence of extraterrestrial intelligence, not even the slightest hint of an alien microbe, the sort of foundational life that has existed on our planet for billions of years. So far, at least, it’s all quiet on the interstellar front.
It’s a big galaxy and an even bigger universe. Jill Tarter, the doyenne of SETI and the inspiration for Jodie Foster’s alien hunter in the film Contact, has said that all our attempts to search for alien life amount to plunging a single glass into the world’s oceans.4 But the longer our searches are met with silence, the more we will ask a question that first occurred to the physicist Enrico Fermi decades ago: where is everybody? And the answer—if it ever comes—could be the most important we will ever receive.
In 1961, an eclectic band of scientists and engineers met to talk alien hunting in Green Bank, West Virginia. Green Bank is nestled in the Allegheny Mountains, amid some of the most beautiful land in the United States, but the scientists didn’t choose the town for its scenery. A couple of years earlier, the physicists Giuseppe Cocconi and Philip Morrison had published a paper in Nature that laid out what would become the fundamental strategy for the search for intelligent life.5 They knew that unless extraterrestrial life showed up on our doorstep, chances were that our telescopes would never actually catch a visual glimpse of aliens. Cocconi and Morrison argued that we should instead try to listen for the signals that aliens might send, just as an amateur radio enthusiast might scan the radio-frequency spectrum hoping to find someone to talk to. The best tool to search for such signals on a cosmic scale was a radio telescope, an antenna and a receiver that can catch radio waves from the stars. And it just so happened that the National Radio Astronomy Observatory (NRAO) had recently been built in none other than Green Bank.
One of the attendees at the Green Bank meeting was a young astronomer named Frank Drake. The year before Drake had launched the first SETI search, using Green Bank’s new radio telescope and employing Cocconi and Morrison’s methods. But Drake’s biggest contribution to the hunt for alien life came not at the controls of a radio telescope, but at a blackboard. The 1961 meeting—which included Cocconi and Morrison among others, as well as Sagan—aimed to codify the nascent science of SETI. If you’re going to hunt something, it helps to have some idea of what’s out there, and how common your target is. So Drake created a variable-filled equation estimating just how many alien civilizations might exist in our galaxy. Here it is:
N = R* x fp x ne x fl x fi x fc x L6
N equals the number of “broadcasting civilizations”—extraterrestrial intelligences that have reached the point of being able to transmit radio signals that we might be able to detect on Earth. That’s the target for SETI. To find that number, the Drake equation multiples the average rate of star formation, times the fraction of those stars that have planets, times the number of planets per solar system that could support life, times the fraction of habitable planets that do support life, times the fraction of life-bearing planets where intelligence arises, times the fraction of those alien civilizations that go on to develop broadcasting technology, times the average broadcasting life span of those civilizations.
It’s a lot more succinct in the math.
As theories go, the Drake equation is brilliant. If we knew the value of all of the variables that the equation lays out, we would know how many other civilizations are out there, possibly broadcasting to Earth. The problem is that other than the first variable—the average rate of star formation—everything else in the equation was largely unknown when Drake wrote it, so somewhat educated guesses were used to fill in the rest. The group at the 1961 meeting estimated that there were between 1,000 and 100 million civilizations in the galaxy—an optimistic hypothesis even at its more pessimistic end, and one that gave the search for intelligent life plenty to search for. And SETI is nothing if not optimistic.
Hopes that humans would rapidly make contact came to nothing, however. From the start SETI was hampered by skeptical mainstream scientists and by government officials who viewed the search for little green men as a waste of money. SETI never fully overcame the “giggle factor” that initially hobbled the study of other unlikely existential risks like asteroid impacts, and while it enjoyed a vogue through the far-out 1960s and into the 1970s, Congress eventually forced NASA to cut all funding for SETI research in 1993.7 Public funding has never been restored.
Since then, the SETI Institute has been forced to make do with what philanthropic funding it can scrounge up, grabbing observation time on university-run radio telescopes. In 2007 the Allen Telescope Array—named after its benefactor, Microsoft cofounder Paul Allen—finally went online in Northern California as a radio telescope dedicated to SETI searches. But that project had to be downsized when operating funding couldn’t be secured from the National Science Foundation. The number of antennas was limited to 42—which, as fans of The Hitchhiker’s Guide to the Galaxy series know, is the supposed answer to life, the universe, and everything.8 (SETI researchers slip more fan service into their work than the directors of a Marvel movie.)
SETI was at risk of petering out, another relic of a time when Americans were more hopeful and more adventurous. But recent sci
entific discoveries—and new deep-pocketed benefactors—gave fresh life to the search for alien life. The Kepler Space Telescope, launched by NASA in 2009, was designed to locate Earth-like planets orbiting other stars, and it succeeded far beyond what its mission planners could have hoped. By the end of its nine-year life in deep space, Kepler had discovered more than 2,600 exoplanets—planets outside our own solar system—30 of which are less than twice the size of Earth while falling within their star’s so-called Goldilocks zone, the orbital region where liquid water could pool on a planet’s surface.9 (Our sun’s own Goldilocks zone—not too hot, not too cold—includes Earth, of course, but also Mars.) Astronomers have now found more than 3,500 exoplanets, with more being added to the list all the time.10
This has obvious ramifications for SETI. While Drake had to estimate the number of stars with planets, we now know that planets are everywhere, and that it is far more common for a star system to have planets than to lack them. By one estimate, there may be tens of billions of potentially habitable planets in our galaxy.11 That means plenty of possible places where at least basic life as we know it could arise, and eventually develop into broadcasting civilizations. “This has changed the whole perspective that scientists and astronomers have about the possibility of life in the universe,” Andrew Siemion, director of the Berkeley SETI Research Center at the University of California, told me. “We now know for certain that all the necessary conditions for life to flourish exist ubiquitously, which has sharpened the questions for SETI and astrobiology.”
SETI has undergone a revolution of its own. In July 2015 the Russian-Israeli tech entrepreneur Yuri Milner launched Breakthrough Listen, a $100 million, ten-year program to accelerate SETI efforts to search for radio signals from extraterrestrial civilizations. Milner’s funding, which is channeled through the Berkeley SETI Research Center, is securing thousands of hours of searching time on radio telescopes at Green Bank in West Virginia and the Parkes Observatory in Australia. Breakthrough will scan the nearest 1 million stars, a search radius 700 light-years across.12 That’s about as far as light emanating from Earth carrying evidence of our own technological development should have reached, meaning that any aliens in the territory Breakthrough is searching may already be aware of our existence. (A key point: interstellar distances are far away in space and time. Light that reaches us from a place a thousand light-years away was emitted a thousand years ago, and vice versa for any potential aliens observing Earth.)
Breakthrough and the SETI Institute—a Silicon Valley–based nonprofit research group that has long steered the search for alien life—are together conducting the broadest-ever SETI missions, with telescopes now covering frequencies between 1,000 and 15,000 megahertz.13 Breakthrough will also scan the Milky Way’s galactic plane—the slice of space where most of the galaxy’s mass exists—and scores of the nearest galaxies. And Breakthrough will employ optical SETI searches at the Automated Planet Finder at the Lick Observatory in California, looking for laser signals from distant worlds—the interstellar equivalent of the beacon towers that were once used to pass messages along the Great Wall of China. A single day of work at Breakthrough is equal to a full year of any other search that has ever been performed, according to Siemion.14
Couple that with rapid growth in the same kind of machine learning that is improving surveillance of near-Earth objects like asteroids, and you can see why SETI experts are confident that contact is just a matter of time. SETI has long defended its failure to find evidence of extraterrestrial intelligence by citing—fairly—how little of the sky humans have yet been able to search. But we’re getting better and better at looking. “I bet everybody a cup of Starbucks that we’ll find ET within a couple of decades,” Seth Shostak, senior astronomer at the SETI Institute, told me on a visit to his overstuffed office in Mountain View, California. “And when that day comes, it will be the biggest story of all time.”
So exciting is the possibility of contacting aliens that there are those who don’t want to wait around for aliens to contact us. They want to shout “Hello” into the cosmos, carrying out what is known as active SETI or messaging extraterrestrial intelligence (METI). But that impatience creates an existential risk of its own.
SETI is a passive search. The hope is that there are extraterrestrial intelligences out there trying to message us, and we just need to be ready with our radio telescopes to hear. Listening isn’t just a search method, though, but a philosophy. Early SETI advocates like Sagan took it for granted that any alien civilization we might come into contact with would be more advanced than us, likely far more advanced, technologically and even ethically. (The universe, after all, had been around for nearly 14 billion years before human beings showed up.15) Given our assumed place as a young species in the cosmic hierarchy—and given all that we might hope to learn from our alien betters—a core SETI belief is that we should listen before we speak. Shouting into the cosmos, Sagan said, was “deeply unwise and immature,”16 the act of a toddler calling attention to themselves.
Proponents of messaging, however, believe it’s a mistake to assume that any technologically mature alien civilization will automatically take the first step to establish contact with us. If we’re not signaling, after all, maybe they won’t signal first either. It’s possible that extraterrestrials are no longer using radio, and that sifting through radio waves while searching for alien life is like trying to find evidence of other people in 2018 by looking for smoke signals. Perhaps they assume our silence is a sign that we just don’t want to talk, which means it would be up to us to start the conversation.
In truth SETI has often included the occasional effort to send a message into space. The first known attempt was undertaken by Soviet scientists in 1962 at the Unique Korenberg Telescope Array. Using Morse code, they transmitted the words “MIR,” “LENIN,” and “SSSR” to Venus, on the assumption that any advanced life-form would obviously be communist and would get their references.17 Laugh now, but that’s really no different than Carl Sagan assuming alien civilizations would have the same values as Carl Sagan.
The Soviet attempt was interplanetary, but Frank Drake himself was responsible for sending the first deliberate interstellar message, on November 16, 1974. To commemorate the rechristening of the Arecibo Observatory in Puerto Rico, then the largest radio telescope in the world, Drake blasted 168 seconds of two-tone sound toward the star system M13. It was noise to the listeners in Puerto Rico, but any aliens who happened to receive it might have noticed a clear, repetitive structure indicating its origin was non-natural. Also encoded in the message were the numbers 1 to 10, the atomic numbers of several basic elements on Earth, and a graphic of the solar system indicating the planetary origin of the transmission.18
Given that M13 is 25,000 light-years away from Earth, it’s going to take thousands upon thousands of years before Drake’s message ever reaches its destination, and at least another 25,000 years before a reply would ever reach us. Yet just days after the message was transmitted, Martin Ryle, then Britain’s Astronomer Royal, sent an angry letter to Drake. It was “very hazardous to reveal our existence and location to the Galaxy,” Ryle wrote. “For all we know, any creatures out there might be malevolent—or hungry.”19
To this day, mainstream SETI has eschewed active messaging in part out of the concern, however remote, that something malevolent or hungry might be on the receiving end. The editorial board of the journal Nature has cautioned that “the risk posed by active SETI is real,”20 and in 2006, when the International Academy of Astronautics convened a committee on SETI but refused to push for a ban on active messaging, two prominent members resigned.21 Before his death, Stephen Hawking was on record saying he didn’t think it was a very good idea to invite extraterrestrials to come calling. “I imagine they might exist in massive ships… having used up all the resources from their home planet,” he said. “Such advanced aliens would perhaps become nomads, looking to conquer and colonize whatever planets they can reach.”22
But those fears haven’t stopped a breakaway group of space scientists from launching the new group METI, led by the former SETI staffer Douglas Vakoch. Milner’s Breakthrough Initiative also has a Breakthrough Message component, with a crowdsourced competition to devise a letter to the stars. The interest in METI is in part a product of the exoplanet revolution. With so many potentially life-supporting planets out there, the thinking goes, why not target them and begin beaming out messages of greetings? If Drake’s Arecibo message was like shouting at random in the middle of a forest, METI can direct signals to where there’s a chance of life, including some planets that are as few as 100 light-years away. Given the vastness of space, METI advocates believe, anything that increases the chances that we might make contact is worth trying. And they argue that the risk of active messaging is overstated. After all, for decades humans have been leaking radio and TV signals into space that could be picked up by sufficiently advanced extraterrestrial intelligence, so it’s not as if we’ve been keeping quiet.
The deeper debate about METI isn’t necessarily the act of messaging, but the content. If there really are ETs out there silently listening, the signal from METI or one of the other active messaging groups may be the first thing they ever hear from Earthlings. That’s an enormous responsibility. Why should any single group get to decide how Earth says hello—or whether it says anything at all? “What’s just so interesting is the assumption of the right to do this,” Kathryn Denning, an anthropologist at York University in Canada who studies the strange tribe of alien hunters, told me. “To make these choices on behalf of all humanity. And a refusal to look carefully at the potential consequences. The idea is that all innovation is good, and let history sort it out.”