Though here on Earth it is considered impolite to eavesdrop, Avi Loeb actively encourages it on an interstellar scale. Indeed, Loeb, of the Harvard-Smithsonian Center for Astrophysics, considers eavesdropping to be the next step in the search for extra-terrestrial intelligence (SETI). Though astronomers have been tuning in to the sky for decades, until now they have been listening for powerful signals that could only be intentionally beamed out by civilizations far more advanced than ours. In a recent paper, Loeb and colleague Matias Zaldarriaga show the feasibility of listening for everyday broadcast waves from a "twin civilization"—that is, one on technological par with our own—at least on planets orbiting the nearest thousand stars. Though that number is small, universally speaking, scientists are building instruments that would eventually tune us in to some 100 million stars. Critics of SETI initiatives consider them quixotic and costly. But Loeb points out that astronomers will soon be collecting low-frequency readings of space anyway, for various non-SETI projects. All the eavesdropping endeavor would need is software to analyze these readings, looking for telltale radiation patterns from an intelligent civilization communicating with itself. As for matters of politeness, Loeb is unrepentant. "It is better to be impolite than remain ignorant," he says, adding that eavesdropping is "the only safe method to learn more about the universe without taking a risk at revealing our own existence." Should our neighbors be belligerent, it’s better to give them our ear, but not our voice. Earth has been broadcasting for 50 years, Loeb says, meaning that an alien scientist who beat Loeb to his idea might currently be eavesdropping on us. Click here to watch a video of Loeb explaining his plans for SETI.