The Michelson Interferometer

http://soundracer.deviantart.com/art/Waves-wallpaper-118672151

The Mechanics: Visualized

Why can we see an interference pattern?

When the distance between the reflected beam and the beam that passes through mirror 1 is the same, the waves are perfectly in phase:

But when the distance is slightly off, for instance, by a half of a wavelength, the two light waves are perfectly out of phase:

How about the rings?Away from the very very centre of the light beam, the distance of the light beam is increased slightly at the edges of the beam (because of a slight angle from the source), resulting in an in-and-out of phase behaviour from the edges of the beam:

Still confused? Think of when you use a flashlight—the very edges of the light beam usually fades off into the dark. This is analogous to the edges of the light beam from the interferometer—it’s just at a much smaller scale.

//Note that other than the rays at the very very centre of the beam, the other rays are at a slight angle(not perfectly perpendicular to the receiving surface).

How can we use this?An application of this actually magnifies this interferometer to a much much larger scale—in fact, 4 km long “arms”, or distances between the mirrors and the beam splitter (mirror 2).

Update/Bummer alert: They haven’t found anything yet from the first North American observatory, from 2002-2010. They’ve built a new one in Hanford, Washington that’s expected to be much better/sensitive.

Source: https://www.youtube.com/watch?v=RzZgFKoIfQI

Einstein proposed that gravitational waves result from the collision of two great masses, and the Laser Interferometer Gravitational-Wave Observatory was built in search of the evidence of gravitational waves. Basically, the fact that the arms are so far apart are supposed to detect very, very, very slight changes in distance as the result of pulling and stretching from gravitational waves.

https://www.ligo-wa.caltech.edu/