Radiating rumours
"It is so exciting if this really is the first clear detection, as we're expecting," Dr Carolin Crawford from Cambridge University told the BBC's Today programme. "It will really mark a new era for astronomy."
Gravitational waves are concentric ripples that squeeze and stretch the fabric of space-time. They are caused by the movement of mass, but most are so weak that they have no measurable effect.
For current technology to glimpse them, we need to find the waves - still incredibly subtle - that are radiating across the cosmos from extremely violent events, like explosions or collisions involving stars or black holes.
At each Ligo detector, a laser beam is split in two and sent down identical, perpendicular 4km tunnels - then reflected back again. The two arms work like rulers, at right angles, made of light.