This story originally appeared in the December issue of Discover magazine as "Looking for Signs." Support our science journalism by becoming a subscriber.
Limits don’t sit well with Avi Loeb.
Loeb quickly reels some off to me over the phone (hands-free) during a drive home from work: About 25 billion stars, roughly one-quarter of those that reside in the Milky Way, have planets lying within a habitable zone. He rounds that down to an even 10 billion to keep the calculations simple. He rounds that down to an even 10 billion to keep the calculations simple. “And then there are about a trillion galaxies like the Milky Way,” he says, “which means there are about 1022 [10 billion trillion] planets in the observable universe that could potentially host life as we know it.” In other words, searches for extraterrestrial life have barely scratched the surface. “As in other areas of exploratory science,” Loeb says, “we should investigate thoroughly before making sweeping pronouncements.”
Most of the searching so far, he adds, has been in the radio range, where scientists have examined a tiny fraction of the possible frequencies in an equally tiny fraction of the possible search space. Surveys in optical wavelengths have been much less extensive. For any new technology we develop, Loeb says, we should consider whether, somewhere, an alien civilization might have developed it, too, possibly leaving behind some detectable traces. “As our technology improves, that can help us imagine things we haven’t imagined before and explore things we haven’t searched for before.”
