I'm interested to know how they can be so sure that the change in distance between the two arms of LIGO is attributed to gravitational waves? I would of thought that miniscule movements in the Earth's crust would be a more likely culprit.
Ahh, just realised that there are two instruments located on either side of the states, so if both instruments register the same event then it is unlikely to be tectonic movement...
The LIGO mirrors and beam splitter are attached to Earth very loosely. They hang from towers of pendulums; when Earth moves, LIGO catches up eventually, but over the time it takes a gravity wave to oscillate the components might as well be in orbit.
That is one of the more routine feats of engineering involved.
