On Nov. 16, 1974, a few hundred astronomers, government officials and other dignitaries gathered in the tropical forests of Puerto Rico’s northwest interior, a four-hour drive from San Juan. The occasion was a rechristening of the Arecibo Observatory, at the time the largest radio telescope in the world. The mammoth structure — an immense concrete-and-aluminum saucer as wide as the Eiffel Tower is tall, planted implausibly inside a limestone sinkhole in the middle of a mountainous jungle — had been upgraded to ensure its ability to survive the volatile hurricane season and to increase its precision tenfold.
To celebrate the reopening, the astronomers who maintained the observatory decided to take the most sensitive device yet constructed for listening to the cosmos and transform it, briefly, into a machine for talking back. After a series of speeches, the assembled crowd sat in silence at the edge of the telescope while the public-address system blasted nearly three minutes of two-tone noise through the muggy afternoon heat. To the listeners, the pattern was indecipherable, but somehow the experience of hearing those two notes oscillating in the air moved many in the crowd to tears.
That 168 seconds of noise, now known as the Arecibo message, was the brainchild of the astronomer Frank Drake, then the director of the organization that oversaw the Arecibo facility. The broadcast marked the first time a human being had intentionally transmitted a message targeting another solar system. The engineers had translated the missive into sound, so that the assembled group would have something to experience during the transmission. But its true medium was the silent, invisible pulse of radio waves, traveling at the speed of light.
It seemed to most of the onlookers to be a hopeful act, if a largely symbolic one: a message in a bottle tossed into the sea of deep space. But within days, the Royal Astronomer of England, Martin Ryle, released a thunderous condemnation of Drake’s stunt. By alerting the cosmos of our existence, Ryle wrote, we were risking catastrophe. Arguing that ‘‘any creatures out there [might be] malevolent or hungry,’’ Ryle demanded that the International Astronomical Union denounce Drake’s message and explicitly forbid any further communications. It was irresponsible, Ryle fumed, to tinker with interstellar outreach when such gestures, however noble their intentions, might lead to the destruction of all life on earth.
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Today, more than four decades later, we still do not know if Ryle’s fears were warranted, because the Arecibo message is still eons away from its intended recipient, a cluster of roughly 300,000 stars known as M13. If you find yourself in the Northern Hemisphere this summer on a clear night, locate the Hercules constellation in the sky, 21 stars that form the image of a man, arms outstretched, perhaps kneeling. Imagine hurtling 250 trillion miles toward those stars. Though you would have traveled far outside our solar system, you would only be a tiny fraction of the way to M13. But if you were somehow able to turn on a ham radio receiver and tune it to 2,380 MHz, you might catch the message in flight: a long series of rhythmic pulses, 1,679 of them to be exact, with a clear, repetitive structure that would make them immediately detectable as a product of intelligent life.
In its intended goal of communicating with life-forms outside our planet, the Arecibo message has surprisingly sparse company. Perhaps the most famous is housed aboard the Voyager 1 spacecraft — a gold-plated audiovisual disc, containing multilingual greetings and other evidence of human civilization — which slipped free of our solar system just a few years ago, traveling at a relatively sluggish 35,000 miles per hour. By contrast, at the end of the three-minute transmission of the Arecibo message, its initial pulses had already reached the orbit of Mars. The entire message took less than a day to leave the solar system.
True, some signals emanating from human activity have traveled much farther than even Arecibo, thanks to the incidental leakage of radio and television broadcasts. This was a key plot point in Carl Sagan’s novel, ‘‘Contact,’’ which imagined an alien civilization detecting the existence of humans through early television broadcasts from the Berlin Olympic Games, including clips of Hitler speaking at the opening ceremony. Those grainy signals of Jesse Owens, and later of Howdy Doody and the McCarthy hearings, have ventured farther into space than the Arecibo pulses. But in the 40 years since Drake transmitted the message, just over a dozen intentional messages have been sent to the stars, most of them stunts of one fashion or another, including one broadcast of the Beatles’ ‘‘Across the Universe’’ to commemorate the 40th anniversary of that song’s recording. (We can only hope the aliens, if they exist, receive that message before they find the Hitler footage.)
In the age of radio telescopes, scientists have spent far more energy trying to look for signs that other life might exist than they have signaling the existence of our own. Drake himself is now more famous for inaugurating the modern search for extraterrestrial intelligence (SETI) nearly 60 years ago, when he used a telescope in West Virginia to scan two stars for structured radio waves. Today the nonprofit SETI Institute oversees a network of telescopes and computers listening for signs of intelligence in deep space. A new SETI-like project called Breakthrough Listen, funded by a $100 million grant from the Russian billionaire Yuri Milner, promises to radically increase our ability to detect signs of intelligent life. As a species, we are gathered around more interstellar mailboxes than ever before, waiting eagerly for a letter to arrive. But we have, until recently, shown little interest in sending our own.
Now this taciturn phase may be coming to an end, if a growing multidisciplinary group of scientists and amateur space enthusiasts have their way. A newly formed group known as METI (Messaging Extra Terrestrial Intelligence), led by the former SETI scientist Douglas Vakoch, is planning an ongoing series of messages to begin in 2018. And Milner’s Breakthrough Listen endeavor has also promised to support a ‘‘Breakthrough Message’’ companion project, including an open competition to design the messages that we will transmit to the stars. But as messaging schemes proliferate, they have been met with resistance. The intellectual descendants of Martin Ryle include luminaries like Elon Musk and Stephen Hawking, and they caution that an assumption of interstellar friendship is the wrong way to approach the question of extraterrestrial life. They argue that an advanced alien civilization might well respond to our interstellar greetings with the same graciousness that Cortés showed the Aztecs, making silence the more prudent option.
If you believe that these broadcasts have a plausible chance of making contact with an alien intelligence, the choice to send them must rank as one of the most important decisions we will ever make as a species. Are we going to be galactic introverts, huddled behind the door and merely listening for signs of life outside? Or are we going to be extroverts, conversation-starters? And if it’s the latter, what should we say?
Amid the decommissioned splendor of Fort Mason, on the northern edge of San Francisco, sits a bar and event space called the Interval. It’s run by the Long Now Foundation, an organization founded by Stewart Brand and Brian Eno, among others, to cultivate truly long-term thinking. The group is perhaps most famous for its plan to build a clock that will successfully keep time for 10,000 years. Long Now says the San Francisco space is designed to push the mind away from our attention-sapping present, and this is apparent from the 10,000-year clock prototypes to the menu of ‘‘extinct’’ cocktails.
The Interval seemed like a fitting backdrop for my first meeting with Doug Vakoch, in part because Long Now has been advising METI on its message plans and in part because the whole concept of sending interstellar messages is the epitome of long-term decision-making. The choice to send a message into space is one that may well not generate a meaningful outcome for a thousand years, or a hundred thousand. It is hard to imagine any decision confronting humanity that has a longer time horizon.
As Vakoch and I settled into a booth, I asked him how he found his way to his current vocation. ‘‘I liked science when I was a kid, but I couldn’t make up my mind which science,’’ he told me. Eventually, he found out about a burgeoning new field of study known as exobiology, or sometimes astrobiology, that examined the possible forms life could take on other planets. The field was speculative by nature: After all, its researchers had no actual specimens to study. To imagine other forms of life in the universe, exobiologists had to be versed in the astrophysics of stars and planets; the chemical reactions that could capture and store energy in these speculative organisms; the climate science that explains the weather systems on potentially life-compatible planets; the biological forms that might evolve in those different environments. With exobiology, Vakoch realized, he didn’t have to settle on one discipline: ‘‘When you think about life outside the earth, you get to dabble in all of them.’’
As early as high school, Vakoch began thinking about how you might communicate with an organism that had evolved on another planet, the animating question of a relatively obscure subfield of exobiology known as exosemiotics. By the time Vakoch reached high school in the 1970s, radio astronomy had advanced far enough to turn exosemiotics from a glorified thought experiment into something slightly more practical. Vakoch did a science-fair project on interstellar languages, and he continued to follow the field during his college years, even as he was studying comparative religion at Carleton College in Minnesota. ‘‘The issue that really hit me early on, and that has stayed with me, is just the challenge of creating a message that would be understandable,’’ Vakoch says. Hedging his bets, he pursued a graduate degree in clinical psychology, thinking it might help him better understand the mind of some unknown organism across the universe. If the exosemiotics passion turned out to be a dead end professionally, he figured that he could always retreat back to a more traditional career path as a psychologist.
During Vakoch’s graduate years, SETI was transforming itself from a NASA program sustained by government funding to an independent nonprofit organization, supported in part by the new fortunes of the tech sector. Vakoch moved to California and joined SETI in 1999. In the years that followed, Vakoch and other scientists involved in the program grew increasingly vocal in their argument for sending messages as well as listening for them. The ‘‘passive’’ approach was essential, they argued, but an ‘‘active’’ SETI — one targeting nearby star systems with high-powered radio signals — would increase the odds of contact. Concerned that embracing an active approach would imperil its funding, the SETI board resisted Vakoch’s efforts. Eventually Vakoch decided to form his own international organization, METI, with a multidisciplinary team that includes the former NASA chief historian Steven J. Dick, the French science historian Florence Raulin Cerceau, the Indian ecologist Abhik Gupta and the Canadian anthropologist Jerome H. Barkow.
The newfound interest in messaging has been piqued in large part by an explosion of newly discovered planets. We now know that the universe is teeming with planets occupying what exobiologists call ‘‘the Goldilocks zone’’: not too hot and not too cold, with ‘‘just right’’ surface temperatures capable of supporting liquid water. At the start of Drake’s career in the 1950s, not a single planet outside our solar system had been observed. Today we can target a long list of potential Goldilocks-zone planets, not just distant clusters of stars. ‘‘Now we know that virtually all stars have planets,’’ Vakoch says, adding that, of these stars, ‘‘maybe one out of five have potentially habitable planets. So there’s a lot of real estate that could be inhabited.’’
When Frank Drake and Carl Sagan first began thinking about message construction in the 1960s, their approach was genuinely equivalent to the proverbial message in a bottle. Now, we may not know the exact addresses of planets where life is likely, but we have identified many promising ZIP codes. The recent discovery of the Trappist-1 planets, three of which are potentially habitable, triggered such excitement in part because those planets were, relatively speaking, so close to home: just 40 light-years from Earth. If the Arecibo message does somehow find its way to an advanced civilization in M13, word would not come back for at least 50,000 years. But a targeted message sent to Trappist-1 could generate a reply before the end of the century.
Frank Drake is now 87 and lives with his wife in a house nestled in an old-growth redwood forest, at the end of a narrow, winding road in the hills near Santa Cruz. His circular driveway wraps around the trunk of a redwood bigger than a pool table. As I left my car, I found myself thinking again of the long now: a man who sends messages with a potential life span of 50,000 years, living among trees that first took root a millennium ago.
Drake has been retired for more than a decade, but when I asked him about the Arecibo message, his face lit up at the memory. ‘‘We had just finished a very big construction project at Arecibo, and I was director then, and so they said, ‘Can you please arrange a big ceremony?’ ’’ he recalled. ‘‘We had to have some kind of eye-catching event for this ceremony. What could we do that would be spectacular? We could send a message!’’
But how can you send a message to a life-form that may or may not exist and that you know nothing at all about, other than the fact that it evolved somewhere in the Milky Way? You need to start by explaining how the message is supposed to be read, which is known in exosemiotics as the ‘‘primer.’’ You don’t need a primer on Earth: You point to a cow, and you say, ‘‘Cow.’’ The plaques that NASA sent into space with Pioneer and Voyager had the advantage of being physical objects that could convey visual information, which at least enables you to connect words with images of the objects they refer to. In other words, you draw a cow and then put the word ‘‘cow’’ next to the drawing and slowly, with enough pointing, a language comes into view. But physical objects can’t be moved fast enough to get to a potential recipient in useful time scales. You need electromagnetic waves if you want to reach across the Milky Way.
But how do you point to something with a radio wave? Even if you figured out a way to somehow point to a cow with electromagnetic signals, the aliens aren’t going to have cows in their world, which means the reference will most likely be lost on them. Instead, you need to think hard about the things that our hypothetical friends in the Trappist-1 system will have in common with us. If their civilization is advanced enough to recognize structured data in radio waves, they must share many of our scientific and technological concepts. If they are hearing our message, that means they are capable of parsing structured disturbances in the electromagnetic spectrum, which means they understand the electromagnetic spectrum in some meaningful way.
The trick, then, is just getting the conversation started. Drake figured that he could count on intelligent aliens possessing the concept of simple numbers: one, three, 10, etc. And if they have numbers, then they will also very likely have the rest of what we know as basic math: addition, subtraction, multiplication, division. Furthermore, Drake reasoned, if they have multiplication and division, then they are likely to understand the concept of prime numbers — the group of numbers that are divisible only by themselves and one. (In ‘‘Contact,’’ the intercepted alien message begins with a long string of primes: 1, 2, 3, 5, 7, 11, 13, 17, 19, 23, and so on.) Many objects in space, like pulsars, send out radio signals with a certain periodicity: flashes of electromagnetic activity that switch on and off at regular rates. Primes, however, are a telltale sign of intelligent life. ‘‘Nature never uses prime numbers,’’ Drake says. ‘‘But mathematicians do.’’
Drake’s Arecibo message drew upon a close relative of the prime numbers to construct its message. He chose to send exactly 1,679 pulses, because 1,679 is a semiprime number: a number that can be formed only by multiplying two prime numbers together, in this case 73 and 23. Drake used that mathematical quirk to turn his pulses of electromagnetic energy into a visual system. To simplify his approach, imagine I send you a message consisting of 10 X’s and 5 O’s: XOXOXXXXOXXOXOX. You notice that the number 15 is a semi-prime number, and so you organize the symbols in a 3-by-5 grid and leave the O’s as blank spaces. The result is this:
If you were an English speaker, you might just recognize a greeting in that message, the word ‘‘HI’’ mapped out using only a binary language of on-and-off states.
Drake took the same approach, only using a much larger semiprime, which gave him a 23-by-73 grid to send a more complicated message. Because his imagined correspondents in M13 were not likely to understand any human language, he filled the grid with a mix of mathematical and visual referents. The top of the grid counted from one to 10 in binary code — effectively announcing to the aliens that numbers will be represented using these symbols.
Having established a way of counting, Drake then moved to connect the concept of numbers to some reference that the citizens of M13 would likely share with us. For this step, he encoded the atomic numbers for five elements: hydrogen, carbon, nitrogen, oxygen and phosphorous, the building blocks of DNA. Other parts of the message were more visually oriented. Drake used the on-off pulses of the radio signal to ‘‘draw’’ a pixelated image of a human body. He also included a sketch of our solar system and of the Arecibo telescope itself. The message said, in effect: This is how we count; this is what we are made of; this is where we came from; this is what we look like; and this is the technology we are using to send this message to you.
As inventive as Drake’s exosemiotics were in 1974, the Arecibo message was ultimately more of a proof-of-concept than a genuine attempt to make contact, as Drake himself is the first to admit. For starters, the 25,000 light-years that separate us from M13 raise a legitimate question about whether humans will even be around — or recognizably human — by the time a message comes back. The choice of where to send it was almost entirely haphazard. The METI project intends to improve on the Arecibo model by directly targeting nearby Goldilocks-zone planets.
One of the most recent planets added to that list orbits the star Gliese 411, a red dwarf located eight light-years away from Earth. On a spring evening in the Oakland hills, our own sun putting on a spectacular display as it slowly set over the Golden Gate Bridge, Vakoch and I met at one of the observatories at the Chabot Space and Science Center to take a peek at Gliese 411. A half moon overhead reduced our visibility but not so much that I couldn’t make out the faint tangerine glimmer of the star, a single blurred point of light that had traveled nearly 50 trillion miles across the universe to land on my retina. Even with the power of the Oakland telescope, there was no way to spot a planet orbiting the red dwarf. But in February of this year, a team of researchers using the Keck I telescope at the top of Mauna Kea in Hawaii announced that they had detected a ‘‘super-earth’’ in orbit around Gliese, a rocky and hot planet larger than our own.
The METI group aims to improve on the Arecibo message not just by targeting specific planets, like that super-earth orbiting Gliese, but also by rethinking the nature of the message itself. ‘‘Drake’s original design plays into the bias that vision is universal among intelligent life,’’ Vakoch told me. Visual diagrams — whether formed through semiprime grids or engraved on plaques — seem like a compelling way to encode information to us because humans happen to have evolved an unusually acute sense of vision. But perhaps the aliens followed a different evolutionary path and found their way to a technologically advanced civilization with an intelligence that was rooted in some other sense: hearing, for example, or some other way of perceiving the world around them for which there is no earthly equivalent.
Like so much of the SETI/METI debate, the question of visual messaging quickly spirals out into a deeper meditation, in this instance on the connection between intelligence and visual acuity. It is no accident that eyes developed independently so many times over the course of evolution on Earth, given the fact that light conveys information faster than any other conduit. That transmission-speed advantage would presumably apply on other planets in the Goldilocks zone, even if they happened to be on the other side of the Milky Way, and so it seems plausible that intelligent creatures would evolve some sort of visual system as well.
But even more universal than sight would be the experience of time. Hans Freudenthal’s ‘‘Lincos: Design of a Language for Cosmic Intercourse,’’ a seminal book of exosemiotics published more than a half-century ago, relied heavily on temporal cues in its primer stage. Vakoch and his collaborators have been working with Freudenthal’s language in their early drafts for the message. In Lincos, duration is used as a key building block. A pulse that lasts for a certain stretch (say, in human terms, one second) is followed by a sequence of pulses that signify the ‘‘word’’ for one; a pulse that lasts for six seconds is followed by the word for six. The words for basic math properties can be conveyed by combining pulses of different lengths. You might demonstrate the property of addition by sending the word for ‘‘three’’ and ‘‘six’’ and then sending a pulse that lasts for nine seconds. ‘‘It’s a way of being able to point at objects when you don’t have anything right in front of you,’’ Vakoch explains.
Other messaging enthusiasts think we needn’t bother worrying about primers and common referents. ‘‘Forget about sending mathematical relationships, the value of pi, prime numbers or the Fibonacci series,’’ the senior SETI astronomer, Seth Shostak, argued in a 2009 book. ‘‘No, if we want to broadcast a message from Earth, I propose that we just feed the Google servers into the transmitter. Send the aliens the World Wide Web. It would take half a year or less to transmit this in the microwave; using infrared lasers shortens the transmit time to no more than two days.’’ Shostak believes that the sheer magnitude of the transmitted data would enable the aliens to decipher it. There is some precedent for this in the history of archaeologists studying dead languages: The hardest code to crack is one with only a few fragments.
Sending all of Google would be a logical continuation of Drake’s 1974 message, in terms of content if not encoding. ‘‘The thing about the Arecibo message is that, in a sense, it’s brief but its intent is encyclopedic,’’ Vakoch told me as we waited for the sky to darken in the Oakland hills. ‘‘One of the things that we are exploring for our transmission is the opposite extreme. Rather than being encyclopedic, being selective. Instead of this huge digital data dive, trying to do something elegant. Part of that is thinking about what are the most fundamental concepts we need.’’ There is something provocative about the question Vakoch is wrestling with here: Of all the many manifestations of our achievements as a species, what’s the simplest message we can create that will signal that we’re interesting, worthy of an interstellar reply?
But to METI’s critics, what he should be worrying about instead is the form that the reply might take: a death ray, or an occupying army.
Before Doug Vakoch had even filed the papers to form the METI nonprofit organization in July 2015, a dozen or so science-and-tech luminaries, including SpaceX’s Elon Musk, signed a statement categorically opposing the project, at least without extensive further discussion, on a planetary scale. ‘‘Intentionally signaling other civilizations in the Milky Way Galaxy,’’ the statement argued, ‘‘raises concerns from all the people of Earth, about both the message and the consequences of contact. A worldwide scientific, political and humanitarian discussion must occur before any message is sent.’’
One signatory to that statement was the astronomer and science-fiction author David Brin, who has been carrying on a spirited but collegial series of debates with Vakoch over the wisdom of his project. ‘‘I just don’t think anybody should give our children a fait accompli based on blithe assumptions and assertions that have been untested and not subjected to critical peer review,’’ he told me over a Skype call from his home office in Southern California. ‘‘If you are going to do something that is going to change some of the fundamental observable parameters of our solar system, then how about an environmental-impact statement?’’
The anti-METI movement is predicated on a grim statistical likelihood: If we do ever manage to make contact with another intelligent life-form, then almost by definition, our new pen pals will be far more advanced than we are. The best way to understand this is to consider, on a percentage basis, just how young our own high-tech civilization actually is. We have been sending structured radio signals from Earth for only the last 100 years. If the universe were exactly 14 billion years old, then it would have taken 13,999,999,900 years for radio communication to be harnessed on our planet. The odds that our message would reach a society that had been tinkering with radio for a shorter, or even similar, period of time would be staggeringly long. Imagine another planet that deviates from our timetable by just a tenth of 1 percent: If they are more advanced than us, then they will have been using radio (and successor technologies) for 14 million years. Of course, depending on where they live in the universe, their signals might take millions of years to reach us. But even if you factor in that transmission lag, if we pick up a signal from another galaxy, we will almost certainly find ourselves in conversation with a more advanced civilization.
It is this asymmetry that has convinced so many future-minded thinkers that METI is a bad idea. The history of colonialism here on Earth weighs particularly heavy on the imaginations of the METI critics. Stephen Hawking, for instance, made this observation in a 2010 documentary series: ‘‘If aliens visit us, the outcome would be much as when Columbus landed in America, which didn’t turn out well for the Native Americans.’’ David Brin echoes the Hawking critique: ‘‘Every single case we know of a more technologically advanced culture contacting a less technologically advanced culture resulted at least in pain.’’
METI proponents counter the critics with two main arguments. The first is essentially that the horse has already left the barn: Given that we have been ‘‘leaking’’ radio waves in the form of ‘‘Leave It to Beaver’’ and the nightly news for decades, and given that other civilizations are likely to be far more advanced than we are, and thus capable of detecting even weak signals, then it seems likely that we are already visible to extraterrestrials. In other words, they know we’re here, but they haven’t considered us to be worthy of conversation yet. ‘‘Maybe in fact there are a lot more civilizations out there, and even nearby planets are populated, but they’re simply observing us,’’ Vakoch argues. ‘‘It’s as if we are in some galactic zoo, and if they’ve been watching us, it’s like watching zebras talking to one another. But what if one of those zebras suddenly turns toward you and with its hooves starts scratching out the prime numbers. You’d relate to that zebra differently!’’
Brin thinks that argument dangerously underestimates the difference between a high-power, targeted METI transmission and the passive leakage of media signals, which are far more difficult to detect. ‘‘Think about it this way: If you want to communicate with a Boy Scout camp on the other side of the lake, you could kneel down at the end of the lake and slap the water in Morse code,’’ he says. ‘‘And if they are spectacularly technologically advanced Boy Scouts who happened also to be looking your way, they might build instruments that would be able to parse out your Morse code. But then you whip out your laser-pointer and point it at their dock. That is exactly the order of magnitude difference between picking up [reruns of] ‘I Love Lucy’ from the 1980s, when we were at our noisiest, and what these guys want to do.’’
METI defenders also argue that the threat of some Klingon-style invasion is implausible, given the distances involved. If, in fact, advanced civilizations were capable of zipping around the galaxy at the speed of light, we would have already encountered them. The much more likely situation is that only communications can travel that fast, and so a malevolent presence on some distant planet will only be able to send us hate mail. But critics think that sense of security is unwarranted. Writing in Scientific American, the former chairman of SETI, John Gertz, argued that ‘‘a civilization with malign intent that is only modestly more advanced than we are might be able to annihilate Earth with ease by means of a small projectile filled with a self-replicating toxin or nano gray goo; a kinetic missile traveling at an appreciable percentage of the speed of light; or weaponry beyond our imagination.’’
Brin looks to our own technological progress as a sign of where a more advanced civilization might be in terms of interstellar combat: ‘‘It is possible that within just 50 years, we could create an antimatter rocket that could propel a substantial pellet of several kilograms, at half the speed of light at times to intersect with the orbit of a planet within 10 light-years of us.’’ Even a few kilograms colliding at that speed would make the asteroid that killed off the dinosaurs look like a meteor shower. ‘‘And if we could do that in 50 years, imagine what anybody else could do, completely obeying Einstein and the laws of physics.’’
Interestingly, Frank Drake himself is not a supporter of the METI efforts, though he does not share Hawking and Musk’s fear of interstellar conquistadors. ‘‘We send messages all the time, free of charge,’’ he says. ‘‘There’s a big shell out there now 80 light-years around us. A civilization only a little more advanced than we are can pick those things up. So the point is we are already sending copious amounts of information.’’ Drake believes that any other advanced civilization out there must be doing the same, so scientists like Vakoch should devote themselves to picking up on that chatter instead of trying to talk back. METI will consume resources, Drake says, that would be ‘‘better spent listening and not sending.’’
METI critics, of course, might be right about the frightening sophistication of these other, presumably older civilizations but wrong about the likely nature of their response. Yes, they could be capable of sending projectiles across the galaxy at a quarter of the speed of light. But their longevity would also suggest that they have figured out how to avoid self-destruction on a planetary scale. As Steven Pinker has argued, human beings have become steadily less violent over the last 500 years; per capita deaths from military conflict are most likely at an all-time low. Could this be a recurring pattern throughout the universe, played out on much longer time scales: the older a civilization gets, the less warlike it becomes? In which case, if we do get a message to extraterrestrials, then perhaps they really will come in peace.
These sorts of questions inevitably circle back to the two foundational thought experiments that SETI and METI are predicated upon: the Fermi Paradox and the Drake Equation. The paradox, first formulated by the Italian physicist and Nobel laureate Enrico Fermi, begins with the assumption that the universe contains an unthinkably large number of stars, with a significant percentage of them orbited by planets in the Goldilocks zone. If intelligent life arises on even a small fraction of those planets, then the universe should be teeming with advanced civilizations. And yet to date, we have seen no evidence of those civilizations, even after several decades of scanning the skies through SETI searches. Fermi’s question, apparently raised during a lunch conversation at Los Alamos in the early 1950s, was a simple one: ‘‘Where is everybody?’’
The Drake Equation is an attempt to answer that question. The equation dates back to one of the great academic retreats in the history of scholarship: a 1961 meeting at the Green Bank observatory in West Virginia, which included Frank Drake, a 26-year-old Carl Sagan and the dolphin researcher (and later psychedelic explorer) John Lilly. During the session, Drake shared his musings on the Fermi Paradox, formulated as an equation. If we start scanning the cosmos for signs of intelligent life, Drake asked, how likely are we to actually detect something? The equation didn’t generate a clear answer, because almost all the variables were unknown at the time and continue to be largely unknown a half-century later. But the equation had a clarifying effect, nonetheless. In mathematical form, it looks like this:
N= R* x ƒp x ne x ƒl x ƒi x ƒc x L
N represents the number of extant, communicative civilizations in the Milky Way. The initial variable R* corresponds to the rate of star formation in the galaxy, effectively giving you the total number of potential suns that could support life. The remaining variables then serve as a kind of nested sequence of filters: Given the number of stars in the Milky Way, what fraction of those have planets, and how many of those have an environment that can support life? On those potentially hospitable planets, how often does life itself actually emerge, and what fraction of that life evolves into intelligent life, and what fraction of that life eventually leads to a civilization’s transmitting detectable signals into space? At the end of his equation, Drake placed the crucial variable L, which is the average length of time during which those civilizations emit those signals.
What makes the Drake Equation so mesmerizing is in part the way it forces the mind to yoke together so many different intellectual disciplines in a single framework. As you move from left to right in the equation, you shift from astrophysics, to the biochemistry of life, to evolutionary theory, to cognitive science, all the way to theories of technological development. Your guess about each value in the Drake Equation winds up revealing a whole worldview: Perhaps you think life is rare, but when it does emerge, intelligent life usually follows; or perhaps you think microbial life is ubiquitous throughout the cosmos, but more complex organisms almost never form. The equation is notoriously vulnerable to very different outcomes, depending on the numbers you assign to each variable.
The most provocative value is the last one: L, the average life span of a signal-transmitting civilization. You don’t have to be a Pollyanna to defend a relatively high L value. All you need is to believe that it is possible for civilizations to become fundamentally self-sustaining and survive for millions of years. Even if one in a thousand intelligent life-forms in space generates a million-year civilization, the value of L increases meaningfully. But if your L-value is low, that implies a further question: What is keeping it low? Do technological civilizations keep flickering on and off in the Milky Way, like so many fireflies in space? Do they run out of resources? Do they blow themselves up?
Since Drake first sketched out the equation in 1961, two fundamental developments have reshaped our understanding of the problem. First, the numbers on the left-hand side of the equation (representing the amount of stars with habitable planets) have increased by several orders of magnitude. And second, we have been listening for signals for decades and heard nothing. As Brin puts it: ‘‘Something is keeping the Drake Equation small. And the difference between all the people in the SETI debates is not whether that’s true, but where in the Drake panoply the fault lies.’’
If the left-hand values keep getting bigger and bigger, the question is which variables on the right-hand side are the filters. As Brin puts it, we want the filter to be behind us, not the one variable, L, that still lies ahead of us. We want the emergence of intelligent life to be astonishingly rare; if the opposite is true, and intelligent life is abundant in the Milky Way, then L values might be low, perhaps measured in centuries and not even millenniums. In that case, the adoption of a technologically advanced lifestyle might be effectively simultaneous with extinction. First you invent radio, then you invent technologies capable of destroying all life on your planet and shortly thereafter you push the button and your civilization goes dark.
The L-value question explains why so many of METI’s opponents — like Musk and Hawking — are also concerned with the threat of extinction-level events triggered by other potential threats: superintelligent computers, runaway nanobots, nuclear weapons, asteroids. In a low L-value universe, planet-wide annihilation is an imminent possibility. Even if a small fraction of alien civilizations out there would be inclined to shoot a two-kilogram pellet toward us at half the speed of light, is it worth sending a message if there’s even the slightest chance that the reply could result in the destruction of all life on earth?
Other, more benign, explanations for the Fermi Paradox exist. Drake himself is pessimistic about the L value, but not for dystopian reasons. ‘‘It’s because we’re getting better at technology,’’ he says. The modern descendants of the TV and radio towers that inadvertently sent Elvis to the stars are far more efficient in terms of the power they use, which means the ‘‘leaked’’ signals emanating from Earth are far fainter than they were in the 1950s. In fact, we increasingly share information via fiber optics and other terrestrial conduits that have zero leakage outside our atmosphere. Perhaps technologically advanced societies do flicker on and off like fireflies, but it’s not a sign that they’re self-destructive; it’s just a sign that they got cable.
But to some METI critics, even a less-apocalyptic interpretation of the Fermi Paradox still suggests caution. Perhaps advanced civilizations tend to reach a point at which they decide, for some unknown reason, that it is in their collective best interest not to transmit any detectable signal to their neighbors in the Milky Way. ‘‘That’s the other answer for the Fermi Paradox,’’ Vakoch says with a smile. ‘‘There’s a Stephen Hawking on every planet, and that’s why we don’t hear from them.’’
In his California home among the redwoods, Frank Drake has a version of the Arecibo message visually encoded in a very different format: not a series of radio-wave pulses but as a stained-glass window in his living room. A grid of pixels on a cerulean blue background, it almost resembles a game of Space Invaders. Stained glass is an appropriate medium, given the nature of the message: an offering dispatched to unknown beings residing somewhere in the sky.
There is something about the METI question that forces the mind to stretch beyond its usual limits. You have to imagine some radically different form of intelligence, using only your human intelligence. You have to imagine time scales on which a decision made in 2017 might trigger momentous consequences 10,000 years from now. The sheer magnitude of those consequences challenges our usual measures of cause and effect. Whether you believe that the aliens are likely to be warriors or Zen masters, if you think that METI has a reasonable chance of making contact with another intelligent organism somewhere in the Milky Way, then you have to accept that this small group of astronomers and science-fiction authors and billionaire patrons debating semi-prime numbers and the ubiquity of visual intelligence may in fact be wrestling with a decision that could prove to be the most transformative one in the history of human civilization.
All of which takes us back to a much more down-to-earth, but no less challenging, question: Who gets to decide? After many years of debate, the SETI community established an agreed-upon procedure that scientists and government agencies should follow in the event that the SETI searches actually stumble upon an intelligible signal from space. The protocols specifically ordain that ‘‘no response to a signal or other evidence of extraterrestrial intelligence should be sent until appropriate international consultations have taken place.’’ But an equivalent set of guidelines does not yet exist to govern our own interstellar outreach.
One of the most thoughtful participants in the METI debate, Kathryn Denning, an anthropologist at York University in Toronto, has argued that our decisions about extraterrestrial contact are ultimately more political than scientific. ‘‘If I had to take a position, I’d say that broad consultation regarding METI is essential, and so I greatly respect the efforts in that direction,’’ Denning says. ‘‘But no matter how much consultation there is, it’s inevitable that there will be significant disagreement about the advisability of transmitting, and I don’t think this is the sort of thing where a simple majority vote or even supermajority should carry the day . . . so this keeps bringing us back to the same key question: Is it O.K. for some people to transmit messages at significant power when other people don’t want them to?’’
In a sense, the METI debate runs parallel to other existential decisions that we will be confronting in the coming decades, as our technological and scientific powers increase. Should we create superintelligent machines that exceed our own intellectual capabilities by such a wide margin that we cease to understand how their intelligence works? Should we ‘‘cure’’ death, as many technologists are proposing? Like METI, these are potentially among the most momentous decisions human beings will ever make, and yet the number of people actively participating in those decisions — or even aware such decisions are being made — is minuscule.
‘‘I think we need to rethink the message process so that we are sending a series of increasingly inclusive messages,’’ Vakoch says. ‘‘Any message that we initially send would be too narrow, too incomplete. But that’s O.K. Instead, what we should be doing is thinking about how to make the next round of messages better and more inclusive. We ideally want a way to incorporate both technical expertise — people who have been thinking about these issues from a range of different disciplines — and also getting lay input. I think it’s often been one or the other. One way we can get lay input in a way that makes a difference in terms of message content is to survey people about what sorts of things they would want to say. It’s important to see what the general themes are that people would want to say and then translate those into a Lincos-like message.’’
When I asked Denning where she stands on the METI issue, she told me: ‘‘I have to answer that question with a question: Why are you asking me? Why should my opinion matter more than that of a 6-year-old girl in Namibia? We both have exactly the same amount at stake, arguably, she more than I, since the odds of being dead before any consequences of transmission occur are probably a bit higher for me, assuming she has access to clean water and decent health care and isn’t killed far too young in war.’’ She continued: ‘‘I think the METI debate may be one of those rare topics where scientific knowledge is highly relevant to the discussion, but its connection to obvious policy is tenuous at best, because in the final analysis, it’s all about how much risk the people of Earth are willing to tolerate. . . . And why exactly should astronomers, cosmologists, physicists, anthropologists, psychologists, sociologists, biologists, sci-fi authors or anyone else (in no particular order), get to decide what those tolerances should be?’’
Wrestling with the METI question suggests, to me at least, that the one invention human society needs is more conceptual than technological: We need to define a special class of decisions that potentially create extinction-level risk. New technologies (like superintelligent computers) or interventions (like METI) that pose even the slightest risk of causing human extinction would require some novel form of global oversight. And part of that process would entail establishing, as Denning suggests, some measure of risk tolerance on a planetary level. If we don’t, then by default the gamblers will always set the agenda, and the rest of us will have to live with the consequences of their wagers.
In 2017, the idea of global oversight on any issue, however existential the threat it poses, may sound naïve. It may also be that technologies have their own inevitability, and we can only rein them in for so long: If contact with aliens is technically possible, then someone, somewhere is going to do it soon enough. There is not a lot of historical precedent for humans voluntarily swearing off a new technological capability — or choosing not to make contact with another society — because of some threat that might not arrive for generations. But maybe it’s time that humans learned how to make that kind of choice. This turns out to be one of the surprising gifts of the METI debate, whichever side you happen to take. Thinking hard about what kinds of civilization we might be able to talk to ends up making us think even harder about what kind of civilization we want to be ourselves.
Near the end of my conversation with Frank Drake, I came back to the question of our increasingly quiet planet: all those inefficient radio and television signals giving way to the undetectable transmissions of the internet age. Maybe that’s the long-term argument for sending intentional messages, I suggested; even if it fails in our lifetime, we will have created a signal that might enable an interstellar connection thousands of years from now.
Drake leaned forward, nodding. ‘‘It raises a very interesting, nonscientific question, which is: Are extraterrestrial civilizations altruistic? Do they recognize this problem and establish a beacon for the benefit of the other folks out there? My answer is: I think it’s actually Darwinian; I think evolution favors altruistic societies. So my guess is yes. And that means there might be one powerful signal for each civilization.’’ Given the transit time across the universe, that signal might well outlast us as a species, in which case it might ultimately serve as a memorial as much as a message, like an interstellar version of the Great Pyramids: proof that a technologically advanced organism evolved on this planet, whatever that organism’s ultimate fate.
As I stared at Drake’s stained-glass Arecibo message, in the middle of that redwood grove, it seemed to me that an altruistic civilization — one that wanted to reach across the cosmos in peace — would be something to aspire to, despite the potential for risk. Do we want to be the sort of civilization that boards up the windows and pretends that no one is home, for fear of some unknown threat lurking in the dark sky? Or do we want to be a beacon?