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Valencia, Spain, Oct. 6, 2006. After four long days, the 57th International Astronautical Congress draws to a close, and two prominent members of the Search for Extraterrestrial Intelligence (SETI) Permanent Committee decide to resign in protest.

One is Michael Michaud, an author and former U.S. diplomat who helped establish the first SETI protocol—a set of rules, published in 1989, that delineate what to do should we detect an extraterrestrial signal. He sought to create a second protocol on whether SETI should move to a new phase. Instead of just passively listening for signals from other civilizations, should we send out a signal of our own? The question roiled the small, cerebral, and normally collegial community of SETI scientists. “That gradually got testy,” Michaud says. “People got confrontational. The tone of the debate deteriorated, and by the 2000s it was clear that we did not have consensus on the issue.”

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If another species wants to annihilate or enslave us, they already have all the information they need.

In Valencia, the debate spills out into public. The SETI committee passes a resolution allowing people to transmit from Earth even without “appropriate international consultations.” Michaud resigns along with John Billingham, a towering figure in SETI research who led NASA’s earlier search. Nature publishes a damning editorial, and before long even Stephen Hawking advocates a wary silence.

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Scientists are no closer to consensus today, and the question is more urgent than ever. New SETI technologies are greatly expanding the scope of the search; if aliens are out there and are sending radio or light signals, we could hear from them within a decade. We need to decide whether we would respond to an extraterrestrial message. Moreover, the very success of the search may hinge on our willingness to communicate. A number of SETI scientists think the reason we may not have heard from aliens yet is that they’re waiting for us to reach out to them first.

Those who think we should stay mum point out that not even Will Smith could defend Earth from an extraterrestrial foe. Our only real protection, they argue, is to stay hidden. “We have to realize that we know almost nothing about ET,” says John Gertz, a former chair of the SETI Institute board of trustees and a Hollywood producer. “We don’t know how advanced they are, we don’t know what their intentions are—whether they’ll be hostile or friendly or, in my opinion as a businessman, simply want to barter or trade with us. But if their intentions are hostile, their abilities to do us harm can be absolute.”

HELLO OUT THERE: The Evpatoria Deep Space Center in Crimea has sent messages, including music, to several known planetary systems.ESO/José Francisco Salgado
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He and others think we should take a cue from the “Great Silence”—the fact that we haven’t found evidence of extraterrestrial civilizations even though they have had billions of years to colonize the galaxy. Perhaps aliens are silent because they’re petrified of some threat we’re too primitive to perceive or even contemplate.

Many skeptics are not categorically opposed to sending a transmission, but just want to make sure the decision reflects broad agreement among humanity. “I don’t regard this as an issue of fear,” Michaud says. “Our purpose is not to prevent communication. It’s to say, let’s make a rational decision.” That means a grand international dialogue mediated by, say, the U.N. Security Council.

“Why rush off and start screaming our presence to the universe now?”

Scientists who favor Active SETI, or METI—Messaging to Extraterrestrial Intelligence—think it’s too late to hide. We’ve been broadcasting our presence into space since the 1930s. “Any civilization slightly more advanced than we are could pick up I Love Lucy going off into space,” says astronomer Douglas Vakoch, who founded METI International, an organization dedicated to researching active approaches to SETI. If another species wants to annihilate or enslave us, they already have all the information they need. A deliberate communication does not add to our risk, but might win us friends. Vakoch and others read a hopeful lesson into the Great Silence. According to an idea known as the zoo hypothesis, civilizations may be watching us for a sign we want to engage them in conversation.

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Advocates of Active SETI see the skeptics’ insistence on due international process as laudable but unrealistic. “While that’s nice in principle, it’s almost impossible to enforce,” Vakoch says. “And there’s little chance we’d reach a consensus about what we would say.” In fact, once the news of an incoming message broke, anyone with access to a transmitter could send whatever reply they wanted.

Of course, all these arguments are hotly contested. Seth Shostak, an astronomer who has championed Active SETI, estimated in 2010 that our first radio transmissions have already reached around 15,000 star systems and that extraterrestrials with an antenna the size of Chicago could pick up our leakage from a few hundred light-years away. “Certainly any society that could threaten you by sending space ships to New York,” he says, “have big antennas that could pick up our broadcasts.” They could probably also build advanced versions of the Hubble Space Telescope capable of observing the lights of our cities.

But not everyone agrees that any potentially threatening alien already knows we’re here. Billingham co-authored a 2010 paper pointing out that not only would alien receivers have to be massive to detect radiation from Earth—Shostak’s Chicago-sized antenna would tax the resources even of an advanced civilization—but they would also have to be pointed in our direction for unrealistically long periods of time. According to Billingham’s calculations, even a deliberate transmission sent in 1999 from one of our largest radio telescopes, located in Crimea, would be picked up as a coherent message only out to 19 light-years away—and only if the alien civilization had a multi-telescope array with a total collecting area of 1 square kilometer.

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If we’re already barely whispering, Gertz asks, “why rush off and start screaming our presence to the universe now?” To try a different approach and to declare our intentions to join an interstellar conversation, Vakoch might shoot back.

In the end—for all the disputing theories on how advanced an extraterrestrial civilization may be, what intentions it might harbor toward us, or how we might craft a message should we manage to agree on a unified dispatch—this debate says more about us than it says about the alien subjects of the conversation. Do we fear contact or welcome it? Do we see our own history of intercultural exchange, which includes humanity’s worst evils as well as its highest achievements, as a net positive or negative? Can we find common ground for true international collaboration? “It’s like a cosmic ink blot test,” Vakoch says. “What we interpret may be a reflection of our desires and hopes and fears, not having much to do with what the extraterrestrials are trying to tell us.”

And if there’s one thing scientists from both sides of the argument can agree on, it’s that, from detecting thousands of exoplanets to figuring out new ways to search for life—by examining the chemistry of the atmosphere of remote planets, by building larger and more powerful telescopes—we’re making technological progress in the field of SETI in leaps and bounds. “It’s the perfect time,” Michaud says, “to have this debate again.”

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Jordana Cepelewicz is an editorial fellow at Nautilus. 

Lead image courtesy of ESO/José Francisco Salgado

This article was originally published on Nautilus Cosmos in December 2016.

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