How To Catch The Biggest Wave In The Universe

Aug 17, 2016
Originally published on August 30, 2016 10:38 am

When it comes to waves, it doesn't get much bigger than the gravitational variety. Einstein predicted that huge events — like black holes merging — create gravitational waves. Unlike most waves we experience, these are distortions in space and time. They roll across the entire universe virtually unimpeded.

Einstein first predicted the existence of gravitational waves in 1916, but none were spotted until recently. Given their incredible power, why did it take a century to locate them?

To find out, I went to see where the detection finally occurred. It's just off Interstate 12 in Livingston Parish, La. To get there you head through town, past the "Gold and Guns" pawn shop and up a country road. Turn onto an empty lane and eventually some low buildings emerge from a forest of gangly pine trees.

This is the Laser Interferometer Gravitational-Wave Observatory. That's kind of a mouthful, so scientists just call it LIGO.

Physicist Joe Giaime of Louisiana State University in Baton Rouge runs this detector. He says measuring waves in space-time might sound complicated, but the basic concept is pretty simple.

"The thing we're measuring is length," he says. "Everybody kind of knows what length is."

Because gravitational waves warp space, they literally change how long things are. LIGO is basically the world's most complicated tape measure.

We walk up a little hill overlooking the machine. A drab concrete pipe stretches off toward the flat Louisiana horizon. Giaime explains that this is one of the LIGO's two arms.

The machine is in the shape of a giant letter L. When a gravitational wave passes by, one arm of the machine gets a little shorter and the other one gets a little longer. The machine measures the difference in length. And that's all there is to it.

At least, in theory.

In practice, making those measurements is a lot tougher. By the time gravitational waves get to Earth, they stretch and shrink dimensions by less than a thousandth of the width of a subatomic particle. And on Earth there are lots of bigger waves that can drown them out — seismic waves from earthquakes, for example. A big quake anywhere on the planet can set the whole machine shaking.

"We just stop and wait it out," Giaime says.

This machine is so sensitive that it can feel the vibrations from passing trucks, falling trees and even storms in faraway oceans.

Overcoming all this background noise is the real trick to LIGO. To see how that works, Giaime and I hop into his car and set off on a road alongside the concrete tube. As we drive, he explains that inside the tube is a laser. The laser beam travels 2.5 miles to the end of the tunnel, where there's a mirror. The narrow beam of light then bounces off the mirror and goes back. In this way, the laser constantly monitors the length of the tube for any space-time distortions.

At the end of the arm, there's a little building with the mirror inside. We head in. We have to wear hair nets and booties over our shoes because these mirrors are perfectly adjusted and carefully controlled.

"Contamination can ruin all those things," Giaime says.

After donning our protective gear, we walk through a second door into a room with a big steel tank. The mirror is inside. It hangs in a vacuum, isolated from the noisy world, just waiting for a gravitational wave to stretch the tube.

The search started more than a decade ago. But for a long time, LIGO didn't see anything.

"Up until last year, we would give tours to little kids, and at the end of the tour, they would say, 'So what have you seen, what have you measured?' " Giaime says. "And the answer was, 'Nothing! Nothing yet.' "

Giaime began to get nervous. "I can personally say I was wondering if there was some sort of misunderstanding about what was out there in the universe," he says.

But he and the rest of the team kept at it. Upgrading the lasers and tweaking the mirrors. Finally, on Sept. 14, 2015, at 5:51 in the morning, a wave passed through this detector and the machine vibrated — like a giant tuning fork listening to space and time.

Moments later, an identical detector in the state of Washington picked it up, too. The signal was real.

It was all that was left of the massive wave created when two black holes collided billions of years ago. The wave is small now, but at the moment of the merger, the power released was greater than all the stars combined.

It truly was the biggest wave in the universe.

Science reporters at NPR are exploring all sorts of waves this summer. Find more of our favorites here.

Copyright 2016 NPR. To see more, visit http://www.npr.org/.

DAVID GREENE, HOST:

This being summertime, our colleagues at NPR's science desk are going with the flow, with a series on waves.

(SOUNDBITE OF MUSIC)

GREENE: Nice. Today, it is gravitational waves. Now, Einstein predicted that these waves must roll across the entire universe. But as NPR's Geoff Brumfiel reports, it took 100 years to actually find one.

GEOFF BRUMFIEL, BYLINE: In February, the announcement finally came, and it made headlines around the world.

(SOUNDBITE OF ARCHIVED RECORDING)

DAVID REITZE: Ladies and gentlemen, we have detected gravitational waves. We did it.

(APPLAUSE)

BRUMFIEL: The waves came from two black holes, which collided long ago. The ripples fanned out across the fabric of space and time, distorting the very dimensions we live in. Now, fact is most of us didn't notice. So how did scientists detect them? To find out, I went to see where they did it. It's just off Interstate 12, in Livingston Parish, La. To get there, you head through town, past the Gold and Guns pawn shop and up a country road.

There's a rusted, old pickup truck and another rusted, old pickup truck, even more rusted than the first one.

Turn onto an empty lane lined with pine trees, and keep going. Oh, I think I see some buildings up ahead.

This is the Laser Interferometer Gravitational-Wave Observatory That's kind of a mouthful, so scientists just call it LIGO. Physicist Joe Giaime is in charge here. He says measuring waves in space-time might sound complicated, but the basic concept is pretty simple.

JOE GIAIME: The thing we're measuring is length. Everybody kind of knows what length is.

BRUMFIEL: Because gravitational waves warp space, they literally change how long things are. And LIGO is basically the world's most complicated tape measurer. We walk up a little hill overlooking the machine. A drab, concrete pipe stretches off towards the flat Louisiana horizon. Giaime explains that this is one of LIGO's two arms.

GIAIME: And the other one is - juts off from the main building at a - at a right angle from the one we're on.

BRUMFIEL: So it's a giant L?

GIAIME: It's a giant L. That's right.

BRUMFIEL: When a gravitational wave passes by, one arm of the L gets a little shorter. The other one gets a little longer. The machine measures the difference. That's all there is to it, at least in theory. In practice, it's a lot tougher. By the time gravitational waves get to Earth, they stretch and shrink dimensions by less than a thousandth of the width of a subatomic particle. And on Earth, there are lots of bigger waves that can drown them out, like seismic waves from earthquakes. A big quake anywhere on the planet can set this whole machine shaking.

GIAIME: And so we just stop and wait it out.

BRUMFIEL: The machine is so sensitive, it can feel the vibrations from passing trucks, falling trees, even storms in faraway oceans. Overcoming all this background noise is the real trick to LIGO. And to see how they do that, we get into Giaime's car and set off on a road alongside the concrete tube. As we drive, he explains that inside the tube is a laser. The beam travels two-and-a-half miles to the end of the tunnel, where there's a mirror. Then, the laser bounces off the mirror and goes back.

GIAIME: So it's pretty boring what's going on here in the middle.

BRUMFIEL: The light's just going back and forth and back and forth, basically?

GIAIME: That's right.

BRUMFIEL: The laser light constantly monitors the length of the tube. We reach the end of the arm. There's a little building with a mirror inside. We head in. We have to wear hairnets and booties over our shoes. That's because these mirrors are perfectly adjusted and carefully controlled.

GIAIME: Contamination can ruin all those things.

BRUMFIEL: So basically don't touch anything.

GIAIME: Well, you won't get anywhere near it. Don't worry about that (laughter).

BRUMFIEL: We go through a second door. In this room, there's a big, steel tank. The mirror is inside.

GIAIME: The mirror weighs about 100 pounds, I guess.

BRUMFIEL: It hangs in a vacuum, isolated from the noisy world, just waiting for a gravitational wave to stretch the tube. The search started over a decade ago, but for a long time, LIGO didn't see anything.

GIAIME: Up until last year, you know, we would give tours here to little kids, who, at the end of the tour, would look us in the eye and say, you know, so what have you seen? What have you measured? And the answer is nothing - nothing yet.

BRUMFIEL: And Giaime began to get nervous. He had moments of doubt.

GIAIME: I can certainly say, personally, that I was wondering whether maybe there was some misunderstanding about - about what was out there in the universe.

BRUMFIEL: But he and the rest of the team kept at it, upgrading the lasers, tweaking the mirrors. And finally, on September 14 at 5:51 a.m., a wave passed through the detector. The whole machine vibrated, like a giant tuning fork listening to space and time.

(SOUNDBITE OF CHIRP)

BRUMFIEL: That's it. That weird, little chirp is the space-time distortion changing the length of LIGO's tunnels. Moments later, an identical detector in Washington state picked it up, too.

(SOUNDBITE OF CHIRP)

BRUMFIEL: That's all that's left of the massive wave created when the two black holes collided billions of years ago. It's small now, but at the moment of the merger, the power released was greater than all the stars combined. It truly was the biggest wave in the universe. Geoff Brumfiel, NPR News. Transcript provided by NPR, Copyright NPR.