So, an interferometer is the instrument used to measure gravitational waves. But, how do they do it?
Well, the interferometer is an ingenious invention created by Albert Michelson back in the 1880s. The concept is actually quite simple too. The design starts with a concentrated laser beam, like any good invention. Next, the laser beam hits a beam-splitting mirror at a 45 degree angle. Thus, half the beam travels straight through the mirror, and the other half is deflected at a 90 degree angle. Each beam separately travels down several mile long corridors to hit a solid mirror, and bounce directly back. Once the beams again meet up at the beam-splitting mirror they collide in perfectly opposite tandem, crests meet troughs, and the two laser halves destroy each other.
Wait... so then how does it measure a gravitational wave? Well, don't forget, these waves actually bend space-time. And, they do it cyclically, with one direction stretching while the other shrinks, and then swapping. So, when they meet the interferometer, they actually elongate one of the corridors, while shrinking the other. This shifts the laser out of phase, and the two halves no longer cancel perfectly. Thus, the now undistorted laser recombines in the beam-splitting mirror and continue on to hit a photosensitive device. However, gravitational waves oscillate, so the end result actually comes up as a strobe light. Scientists then take this flashing light in as data with a computer, and transfer it into sound waves to be more easily understood. After all that work, one of the most powerful events in the universe is finally reduced to a small beep. It is exactly this beep which scientists at the Advanced LIGO observatory heard on September 14, 2015 at 5:51 am.
Now, even more observatories are being put up all over the world in order to gain more accurate readings of these outlandish events. The soonest completed may be a new LIGO in India, and with this new observatory there will certainly be more gravitational wave sightings to come. With any luck, this outstanding discovery will lead to some excellent quantum mechanics and origin of the universe realizations.