[thedoc (OP)]

Jeremy asked the Naked Scientists:
   I've been Googling this for an hour, and couldn't find anything answering my specific question:

How, exactly, does the Advanced LIGO instrument measure the gravitational waves? I understand the lasers return at different times, allowing the scientists to measure the change in length of the LIGO arms.

But how is that change in distance used? What does it tell us about the gravitational wave?
What do you think?