How Physicists Measure Gravitational Waves

Catching a glimpse of the weakest fundamental force in action isn't easy.

Sep 12 2015, 10:00am

LIGO. Image: Caltech

Of all the deep mysteries of astrophysics, gravitational waves often seem to get excluded from the spotlight. After all, we're supposed to understand gravity already—gravity is pretty much the foundational concept of astrophysics itself—at least compared to flashier topics like antimatter and dark energy.

We do understand well enough what gravity does and we can use that knowledge to explain the structures of the cosmos, but gravitational waves are an elusive quarry. The basic illustration is to imagine space-time as the canonical great big rubber sheet, with everything massive in the universe making dips in that sheet with depths according to the amount of mass they have. You've surely seen this illustrated.

Gravitational waves occur when something with mass (that is asymmetrical) accelerates. Because gravity is a tiny, tiny force—10 thousand billion billion billion billion times weaker than the electromagnetic force—most of these waves should be just plain undetectable. But sometimes really massive things accelerate, as in a binary star system, for example. We might be able to catch a glimpse of the resulting gravitational ripples. But it won't be easy.

In Physics World's latest 100 Second Science video, MIT physicist Nergis Mavalvala explains the theory behind the hunt. Enjoy.