Gravitational waves

It's not every day that Physics is front page news or the main item on the BBC Six O'Clock News. But here we are a week after the big announcement. I have posted before about Einstein's view of space-time as like a stretched out rubber sheet http://wigtonphysics.blogspot.co.uk/2013/10/playing-with-space-time.html The gravitational waves idea is that massive objects cause ripples that travel through space-time like they would across a stretched rubber sheet. The equipment involves two very long laser beams at 90 degrees to each other. The beams are supposed to run in phase. If one arm gets stretched by the gravitational waves, the laser beams will be out of step when  they meet. This can be detected. I was interested in the idea that the ones detected came from colliding black holes. I was surprised they could claim the device had much directionality. However, I see that they detected the same pattern using two devices on opposite sides on the American continent with a short time delay between them. That's how they could postulate a direction.