Kenneth Chang, "Scientists Hope to Listen for Potential ‘Friends’ Elsewhere in the Universe" (2007)

When it turns on in a couple of years, a field of what looks like oversized television antennas in western Australia will begin listening for gurgles of the early universe from billions of years ago.

Worthy as that goal may be, a couple of scientists wondered if this giant instrument, inelegantly known as the Low-Frequency Demonstrator of the Mileura Wide-Field Array, could also act as rabbit ears to tune in to something like “I Love Lucy” from a not-too-distant alien civilization.

To date, almost all searches for extraterrestrial civilizations have listened for deliberate radio beacons from beings reaching out for someone else. But there is no guarantee that aliens next door would want to broadcast their presence to the universe.

The Mileura Wide-Field Array is designed to hear the sounds of “reionization,” when ultraviolet radiation from the first quasars and galaxies blew apart interstellar hydrogen atoms. But, to the frustration of cosmologists, those electromagnetic signals would be roughly the same wavelengths as television and radio broadcasts. The array of 8,000 antenna is being built in a sparsely populated swath of Australia where scientists hope to be able to separate Earth noise from the cosmological data.

As Avi Loeb and Matias Zaldarriaga of the Harvard-Smithsonian Center for Astrophysics, members of the array project, worked on the problem of filtering out Earth noise, a thought came to them: could a variation of the technique also eavesdrop on any alien broadcasts?

“Maybe as a side project, we could put limits on emissions from other places,” Dr. Zaldarriaga said.

Their calculations, presented yesterday at a meeting of the American Astronomical Society in Seattle, show that the antenna array will be too weak to pull in interstellar television or radio shows. But by staring at the sky for a month, it could detect pulses of any powerful military radar out to a distance of 30 light-years. Some 1,000 stars lie within that distance.

Future, larger antenna arrays could detect Earth-like signals from several hundred light-years away, an expanse that would include 100 million stars, and perhaps could be powerful enough to start pulling in some cosmic reruns.