A laser is fed into the machine and its light is split along two paths
The separate beams bounce back and forth between damped mirrors
Eventually, the two light paths are recombined and sent to a detector
Gravitational waves passing through the lab should disturb the set-up
Theory holds they should very subtly stretch and squeeze its space
This ought to show itself as a change in the lengths of the light arms
The photodetector is designed to capture this signal in the recombined beam
Crucially, because they travel straight through matter, nothing can obscure the source of these waves - there are no shadows. And they could offer an unparalleled "view" of objects that don't emit light, like black holes.
This is why gravitational astronomy has been described as listening to, rather than looking at, the cosmos.
Tuck Stebbins, from Nasa's Goddard Space Flight Center, told the AFP news agency that gravitational waves could even be a window - in fact, the only possible window - on the origin of the universe.
"These waves are streaming to you all the time and if you could see them, you could see back to the first one trillionth of a second of the Big Bang," he said.