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, …