NOEL KING, HOST:
A couple years ago, a telescope here on Earth picked up a radio signal that seemed to be coming from a nearby star. Thus began a hunt for alien life. Here's NPR's Geoff Brumfiel.
GEOFF BRUMFIEL, BYLINE: The telescope was in Australia, a big dish that collected millions of potential signals. Those signals went to Shane Smith, an undergraduate intern with the University of California, Berkeley. Except in the summer of 2020, everyone was in pandemic lockdown. Smith wasn't at Berkeley. He was stuck at home in Hillsdale, Mich.
SHANE SMITH: I was in the basement of my house on my computer eight hours a day looking at data. I was listening to music.
(SOUNDBITE OF VULFPECK SONG)
SMITH: A lot of Vulfpeck, actually.
BRUMFIEL: While he looked at 8,000 of the most promising signals.
(SOUNDBITE OF VULFPECK SONG)
SMITH: You look by hand through those 8,000 - we call them events.
BRUMFIEL: Most turned out to be nothing.
SMITH: OK, that's not interesting.
BRUMFIEL: Until he found a signal that looked real.
(SOUNDBITE OF VULFPECK SONG)
SMITH: It passed all of our filters.
BRUMFIEL: And it sounded like this.
(SOUNDBITE OF RADIO SIGNAL)
BRUMFIEL: It seemed like it ticked all the boxes of an extraterrestrial transmission. So Smith showed it to his boss, Danny Price.
SMITH: Danny said it was really interesting. And he sent it along to some of the other researchers in the group.
BRUMFIEL: To see if anyone wanted to take a closer look.
SOFIA SHEIKH: I had just come off of a really kind of rough couple weeks of post-doc applications and was planning to take a break. And then I saw that signal and I was like, yeah, sure, I'll do it (laughter). Like, of course. That's really interesting.
BRUMFIEL: Sofia Sheikh is a scientist with the Berkeley Search for Extraterrestrial Intelligence Research Center. The signal came from the direction of the nearest star, Proxima Centauri, and it looked promising for several reasons.
SHEIKH: It was only appearing when the telescope was pointed toward Proxima Centauri. It was a narrow band.
BRUMFIEL: That just means the signal was in a narrow frequency range, kind of like it was coming from a radio station.
SHEIKH: And it was changing in frequency over the course of the observation.
BRUMFIEL: That last one is really important. On Earth, a station stays at one frequency, you know, 90.3 WPLN, that kind of thing. But when a signal comes from another star planet, the frequency will change as the Earth rotates. It's called the Doppler effect.
SMITH: Like a police car coming towards you with a siren, the pitch of the siren is going to be shifted.
(SOUNDBITE OF RADIO SIGNAL)
BRUMFIEL: So seemed to come from the direction of the star, very narrow frequency range, like a radio station, but shifting over time like it came from deep space.
SHEIKH: I really wasn't sure. With the information we had, it was consistent with an extraterrestrial signal, but it also could be consistent with other things.
BRUMFIEL: Because our modern world is awash with radio transmitters. Navigational beacons, television, Wi-Fi, even Bluetooth headphones - they all send out radio waves. The team went to work trying to eliminate some of the Earthly possibilities.
SMITH: You know, planes crossing overhead, satellites orbiting the Earth, you know, cars passing by on a nearby interstate.
BRUMFIEL: The signal wasn't coming from any of those sources, but further analysis also cast doubt on Proxima Centauri. Some of the features of the signal just didn't make sense if it was coming from the star. So Sheikh decided to look in a different way, by broadening out the search to see if they could find the signal somewhere else.
SHEIKH: Did we see it in any previous observations with this telescope, like, anywhere in the sky? Do we see it, like, the days before and after the detection?
BRUMFIEL: And when they tried this approach, they found a lot of signals just like it - copycats.
SHEIKH: All of these were fading in and out at different times, and one of them happened to match where it faded in when we looked towards Proxima Centauri and would fade out when we turned the telescope another way.
BRUMFIEL: A bunch of copycat signals is a sign of a problem from here on Earth. The phenomenon can happen sometimes when there's a fault in a transmitter.
SHEIKH: Maybe a wire comes loose.
BRUMFIEL: The transmitter can send out dozens of copies at different times and frequency. One copycat just happened to appear when the telescope was pointed to Proxima. Now, at this point, you might be wondering, Shane Smith, the intern, wasn't his one job to look at the signals? Didn't he spend weeks going through thousands of them? How did he miss all the copycats? Well, it turns out this wasn't Shane's fault. He was seeing a tiny slice of the picture. The telescope collected 4 million signals, but a computer filtered out most of them automatically. The 8,000 Shane had to review were just a small part of all those Bluetooth headphones and Wi-Fi routers sending out signals.
SMITH: Basically, I just wasn't seeing everything. I wasn't seeing the whole story, I guess.
BRUMFIEL: In fact, the team still isn't quite sure where the fake signal came from.
SHEIKH: I can tell you that it's probably within a couple kilometers of the telescope, that it's probably stationary on the ground, so maybe something like a cell tower.
BRUMFIEL: All that work, all those hours in the basement to discover a faulty cellphone tower. Well, Shane Smith doesn't mind.
SMITH: I wasn't ever, like, thinking or hoping that I'd find aliens with this whole experience.
BRUMFIEL: And neither does Sofia Sheikh.
SHEIKH: Even if it's a null result and we say we didn't see anything, that's information. That tells us where the aliens are not (laughter) if you'd like to put it that way.
BRUMFIEL: And it helped the team develop better methods for screening out all the noise. They published two papers in the journal Nature Astronomy about the signal and the lessons it taught them. And Sheikh, she says the team is even better prepared to find E.T.
SHEIKH: Even though this particular signal turned out to be human in origin, the next one might not be, or it might be, and you just kind of have to keep plugging along.
BRUMFIEL: Sooner or later, she says, she hopes they'll hear something worth listening to. Geoff Brumfiel, NPR News.
(SOUNDBITE OF JOHN WILLIAMS' "FLYING") Transcript provided by NPR, Copyright NPR.
