Eavesdropping on Aliens: Could changing channels tune into alien civilizations?

A vast antenna farm in the Australian Outback may pick up the equivalent of talk radio and TV from other solar systems.

Astrophysicists are waiting for a message from space. The Harvard University physicists have decided to join the search for extraterrestrial intelligence (SETI). The effort, still considered somewhat suspect by some scientists, started in 1960. But, so far, nobody has heard a peep from the aliens.

Scientist hope that will change with the completion of the Murchison Wide-Field Array (MWA), a radio telescope under construction in Australia. Astronomers and cosmologists eagerly await the MWA because it will offer a new glimpse of conditions in the early universe. They also want to sift through MWA's flood of data for the telltale signs of other galactic civilizations.

The first search for alien civilizations, Project Ozma, started in 1960. Until now, most searches were designed to pick up deliberate "Anybody out there?" radio broadcasts sent by aliens. Instead, engineers propose to eavesdrop on stray signs of intelligence "leaked" accidentally into space from other civilizations.

Aliens may have already detected early radio and TV broadcasts from Earth. Maybe, engineers argue, we could pick up their stray signals, too. And just maybe, we might hear an extraterrestrial version of shock-jock radio, reality TV, or military radar. Such a signal would represent evidence of extraterrestrial intelligence.

Making contact

Harvard physicists aren't the first to contemplate eavesdropping on aliens. University of Washington astronomer Woodruff Sullivan has long urged the SETI community to listen for inadvertent radio emissions from other civilizations.

In 1978, Sullivan argued his case in the journal Science. "If we are at all typical" he wrote with two undergraduate coauthors, "then we should perhaps also be looking for unintentional signals from others at least as diligently as for intentional ones."

The late Carl Sagan also toyed with this idea in his 1985 novel Contact, later made into the 1997 feature film starring Jodie Foster. In Sagan's tale, astronomers decode an extraterrestrial signal, only to discover it's a broadcast of Adolf Hitler introducing the 1936 Olympic games in Berlin. The aliens, in other words, intercepted one of our earliest leaked transmissions and sent it back to tell us, "We know you're there."

Engineers began to embrace the new search strategy while brainstorming unorthodox ideas to pitch to the Foundational Questions Institute. The foundation supports inquiries on the frontiers of physics and cosmology.

Loeb wanted to propose a project that conventional funding sources, like NASA or the National Science Foundation, would never support. "We wanted something that no one else was thinking about, and if they did think about it, they'd probably object," physicist Loeb says. "It has to be something crazy," his colleague Zaldarriaga recalls telling Loeb. "What about your SETI idea?"

Wading into SETIs waters would be a radical departure for both of them. "I'm not a SETI person," Zaldarriaga insists. Still he considered the idea worth pursuing as a side project to MWAs main science mission.

Live from planet Omikron Perseii 8!

'Futurama' nostalgia setting in perhaps! Detecting Radio E.T. and distinguishing it from the background chatter will be a challenge, however. For one thing, our galaxy is noisy in the low-frequency radio spectrum. That noise has to be identified and filtered out. Humans are noisy, too. Our TVs, radios, radars, cell phones, and even computers all pump radiation in the same wavelength range as cosmic hydrogen.

The redshifted 21-centimeter hydrogen signal from the early universe falls within a range of 9 megahertz (MHz) to 200 MHz. We broadcast most radio energy in the range of 50 MHz and 400 MHz, so there's lots of overlap. As a result, when radio astronomers tune into hydrogen, they could get an earful of FM and TV broadcasts. Fortunately, Murchisons remoteness will shield the MWA from most human radio noise.

What would an alien signal sound like? The hypothetical radio-frequency "bump in the night" would have a few characteristics to distinguish it from natural sources. The signal would contain a relatively narrow range of frequencies that do not correspond to emissions from interstellar gas. "If you look at the FM dial on your radio, all the power is concentrated in very narrow frequency bands," Loeb explains.

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