Department of Physics and Materials Science

Gravitational Waves

Seeing gravity in a New Light

In Einstein's General Theory of Relativity, gravity is not considered a force,, but a distortion of both space and time (spacetime) by massive objects.

Much as a water waves are "ripples" that radiate away from some source, gravitational waves are ripples in spacetime that radiate away from large, accelerating masses like neutron stars and binary black holes.

These ripples can be detected by an interferometer similar to the one shown here (video above). Note how the laser is split into two beams in the middle. The two beams are then reflected and rejoin at the back of the cabinet. One beam travels a bit farther then the other, creating an interference pattern on the screen. The spacing of the bright lines (fringes) correlates to the length difference. Inserting the shutter blocks one beam, preventing an interference pattern from forming.

So what if the two paths had exactly the same length? In this case, the interference pattern would not form...unless space itself is different for each beam. This is what happens when a gravitational wave passes by!

The resulting length change is extremely small, so an interferometer must be huge to detect it. The Laser Interferometer Gravitational-wave Observatory (LIGO) uses interferometers that are over two miles wide to detect length changes a fraction of the width of a proton!