The search for extraterrestrial intelligence, or SETI, is a numbers game — and bigger numbers are better. The more places you look for alien beings — the more expansive your search — the greater the chance you’ll turn up proof of their existence. So it’s notable that Breakthrough Listen, a privately funded, decade-long research project based at the University of California, Berkeley, just announced a significant number of new observations. And while the researchers didn't uncover any signals from extraterrestrials, they’ve taken a major step forward in the search.
The basic premise of SETI — that we live in a galaxy festooned with brainy societies — rests upon the hypothesis that there must be many habitats in the Milky Way where complex biology has had a chance to evolve and thrive. There are about a trillion planets in the Milky Way. If you represented each planet with a marble and laid them all out on the ground cheek by jowl, they’d cover an area larger than Washington, D.C. It doesn’t take an outsize imagination to expect that at least some fraction of this multitude are home to clever inhabitants.
But how many is “some?” Even Nostradamus would struggle to come up with a precise answer. So let’s say one planet in a million, which doesn’t sound terribly brash (and we’re not even counting moons!). In that case, our galaxy has spawned roughly a million societies. Even if this estimate is hundreds or thousands of times too optimistic, there could still be plenty of aliens to find.
But if this straw-man argument suggests that extraterrestrials are out there, it also suggests that detecting them will require a lot of searching. The new results from Breakthrough Listen — an examination of roughly 1,300 nearby stars — has approximately doubled the tally of reconnoitered real estate. This was not a trivial effort; it took scientists three years of heavy-duty work using large antennas in West Virginia and Australia. For each of these star systems, they carefully sifted through several billion radio channels, looking for a signal of the type that only a radio transmitter can produce.
The bottom line of the new observations? No extraterrestrial radio emissions were detected. Sure, there were plenty of signals, but all could be ascribed to human activity — either transmitters here on Earth or orbiting satellites.
If that surprises or disappoints you, get a grip. Those 1,300 stars represent only a minuscule sample of the total planetary population.
It’s also worth noting that the new observations were reviewed only by the Breakthrough Listen team. Maybe they missed something. Others might apply their own signal-decoding algorithms and do their own analyses of this massive thicket of numbers and find something interesting. The Berkeley folks have made their data publicly accessible online just in case others want to try their personal favorite algorithm.
Still, it’s clear that SETI so far has failed to come home with a kewpie doll. Neither Breakthrough Listen nor any other SETI project has picked up a compelling narrow-band radio signal — one that’s at a single spot on the radio dial — that clearly originates from a source beyond our solar system. But Breakthrough Listen at least has refined the equipment, developed the software and trained a half-dozen grad students, all with the intention of continuing and expanding the search.
Indeed, the Breakthrough Listen team is thinking big. Their long-term goal is to target a million star systems — exceeding by hundreds of times the total number of targets scrutinized by SETI since the birth of the field 60 years ago.
Examining a million stellar environments might sound impractical, but it’s not. While it took three years to add 1,300 to the list of observed systems, the speed of the search is increasing. It won’t take a century or two to add a million more. The actual timescale is closer to a decade. That should buoy readers who hope to be among the first humans to learn whether aliens really exist.
Sure, there are no guarantees, and SETI rests upon a hypothesis that’s impossible to falsify. It may be that there is an abundance of inhabited worlds but that 21st century SETI technology — mostly listening for alien radio signals — is incapable of detecting them. But such caveats are no reason to stop trying, any more than we should abandon efforts to find a cure for the common cold just because none has yet been found.
SETI has always butted up against the fact that the universe is very large and mostly empty — and that exploring large chunks of it takes a long time. But there’s both hope and expectation that, as the numbers grow, so too will the chance that one day we’ll find a scratchy signal — one that will change all future history.
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