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Allen Telescope Array
The SETI Institute’s Allen Telescope Array, used to search for any signals that might come from extraterrestrial intelligences. A debate is brewing in the SETI community about whether broadcasting is a wide approach. (credit: SETI Institute)

Who speaks for Earth, and does it really matter?


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For more than half a century, astronomers have—intermittently, and usually with minimal support—tuned radio telescopes to seek signals of extraterrestrial intelligence. Those efforts, to date, have come up empty, but that lack of detection has not dissuaded a core group of scientists who believe that the search for extraterrestrial intelligence (SETI) is still in its early phases in terms of both where and how they’ve searched.

The controversy over SETI, which arguably reached its apex in the early 1990s when Congress voted to eliminate the modest amount of NASA funding that went towards search efforts, has largely died down. Contemporary SETI projects are funded, for better or for worse, privately, negating any taxpayer angst about such work.

“A worldwide scientific, political and humanitarian discussion must occur before any message is sent,” said a recent declaration about Active SETI.

However, there is a controversy, albeit at a much smaller scale, about another aspect of SETI, called messaging to extraterrestrial intelligence (METI) or Active SETI. As the names suggest, this is not about listening for alien signals but broadcasting our own deliberate messages into the cosmos. After all, if everyone is listening but no one is broadcasting, what is there to detect?

Some, though, worry that Active SETI could be a threat to us: if we broadcast signals and alert any extraterrestrial civilizations to our presence, we should not assume they would be benevolent. In recent years, Stephen Hawking has warned that any contact with an extraterrestrial intelligence would likely not end well for us, so why let them know we’re here?

Last month, a group of scientists and others issued a statement warning against Active SETI efforts without some kind of global consultation on what message we should send to an extraterrestrial intelligence (ETI). “ETI’s reaction to a message from Earth cannot presently be known,” the statement argued. “We know nothing of ETI’s intentions and capabilities, and it is impossible to predict whether ETI will be benign or hostile.”

“Intentionally signaling other civilizations in the Milky Way Galaxy raises concerns from all the people of Earth, about both the message and the consequences of contact,” the statement concluded. “A worldwide scientific, political and humanitarian discussion must occur before any message is sent.”

The statement carried the names of a number of scientists who work in astrobiology or related fields, although Hawking was not among them. The statement’s signatories also included science fiction author David Brin and, perhaps most intriguingly, Elon Musk, who has warned about the development of artificial intelligence here on Earth but has been less outspoken about extraterrestrial intelligence.

The statement was released just before a session about Active SETI at the annual meeting of the American Association for the Advancement of Science (AAAS), held in mid-February in San Jose, California. At a press conference the day before the session, proponents and opponents of Active SETI argued their cases.

“This is the only really important scientific field without any subject matter,” Brin said. “It’s an area where opinion rules, and everyone has a very fierce opinion.”

Brin said that he and others “have felt that that tendency towards trying to ease the way to this endeavor of Active SETI or METI has not been handled well,” he said. “We have, for instance, been characterized as being paranoid about expecting invasions of slathering Cardassian invaders. None of us have mentioned such things, ever.”

He argued at the press conference that the debate about Active SETI was based solely on opinion. “This is the only really important scientific field without any subject matter,” he said. “It’s an area where opinion rules, and everyone has a very fierce opinion.”

Any effort to send messages into the universe, he said, “should be discussed worldwide” and not be left to a small group. It’s the same, he said, as the moratorium in generic engineering research in the 1990s to discuss best practices to protect the public.

“I don’t understand why these guys don’t want it,” he said, referring to Active SETI proponents’ opposition to such a discussion. “Half a billion people would probably tune in. It would be exciting, it would be fascinating, it would be instructive, and it would probably draw an awful lot of new donations to SETI.”

Brin, in his comments, dismissed the notion that any ETIs could already detect the radio “leakage” from the Earth in the form of radio and television programming, military radars, and other signals unintentionally broadcast into the universe. Those signals, he argued, are far too weak for any advanced civilization to detect at interstellar distances.

SETI researcher Seth Shostak disagrees. It’s true, he notes, that our current SETI systems would not be able to detect such signals at a “nominal distance” of 100 light-years: they are two to six orders of magnitude—a factor of 100 to one million—too weak.

“But what about a society advanced enough to ruin your whole day, or at least threaten to ruin your whole day?” he asked. “They are at least centuries beyond where we are technologically.” In our civilization, our systems are getting more sensitive by about two orders of magnitude per century, he said. If that holds true over extended periods, he concluded that such an advanced civilization could easily detect our radio leakage.

“If you’re going to worry about this, don’t worry about this, because it’s too late to worry about that,” Shostak concluded.

He was also dismissive of proposals for international consultations on what messages to send. “I don’t know what the decision metric is,” he said, regarding how you would determine if its permissible to engage in Active SETI, let alone what message to send.

Moreover, any effort to reduce radio leakage could “hamstring every future generation” that wants to use high-power radio transmissions on Earth or elsewhere in the solar system, he said. “To me, that’s a price I’m not willing to pay.”

“If you’re going to worry about this, don’t worry about this, because it’s too late to worry about that,” Shostak said of other civilizations detecting our transmissions.

That discussion at the AAAS press conference, though, suggests that the debate about Active SETI may be much ado about nothing. If radio technology does continue to advance at the rate Shostak and others argue, civilizations “millions of years more advanced than us,” to use the language of last month’s declaration, should have the ability to detect our radio leakage even at large distances. And, if they are too far away to detect them even with their advanced technology, then perhaps they are also too far away to pose much of a risk—or benefit—to us.

Current SETI searches assume that other civilizations are actively transmitting, said the SETI Institute’s Douglas Vakoch at the press conference, but that need not always be the case as our own technologies improve.

“At this point, in our passive SETI searches, we require the other civilization to be sending an intentional signal more powerful than our leakage radiation,” he said. “But that would change in about two or three centuries.”

There’s also the issue of how to conduct any sort of international consultation, including the requirement in the declaration for a “worldwide consensus” before sending any signals. Society is not very good at developing a worldwide consensus on any issue, and if we were able to develop one regarding SETI, would that really be representative of the fractious nature of our civilization? Brin’s hope that such a consultation might attract half a billion people—an audience usually reserved for a few major global sporting or entertainment events—seems difficult to justify.

And, for all the discussion about Active SETI, there is very little activity. “There have been all sorts of stunts in the last 20 years,” Brin said, but few that have used “really substantial instruments” that produce signals that could be detected at great distances.

Those small-scale efforts, Vakoch said, may be analogous to the origins of SETI in the 1960s. He suggested a more focused effort might use the Arecibo radio telescope to broadcast messages to a targeted group of relatively nearby (within about 25 parsecs) stars, perhaps tacked on to ongoing use of Arecibo for planetary radar studies.

And why do it? “If you’re going to conduct SETI experiments where you’re trying to look for putative alien broadcasts, it may be very instructive to have to construct a transmitting project,” Shostak suggested. “You walk a mile in the Klingon’s shoes, assuming they have them.”

Brin said he has no problem with developing messages, not for transmission but to better understand how to interpret them. That includes a project to construct a message to be transmitted not to another star system, but to NASA’s New Horizons spacecraft, which will store the message in its onboard flash memory after its completed its science mission in the Kuiper Belt and its heading beyond the solar system. Hypothetically, that message could be found by aliens—much like those on the Pioneer and Voyager spacecraft—but it’s really more about us, and figuring out what we want to say about our civilization.

“We are learning so much so fast,” Brin said, citing the explosion of exoplanet discoveries over the last two decades. He wonders why, for example, there’s no evidence of extraterrestrial life on the Earth even though it was “prime real estate” for supporting life for two billion years. “There is a mystery. Let’s embrace it. Let’s discuss it. It’s fascinating.”

“This is an incredible time for the adventure,” Brin said. Of that, at least, there is little debate.


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