Brace yourselves for gravitational waves

[Alex K]

I always understood that part(more or less, your example helped me think about it in a yet another way, though, so thanks). What I don't understand is the purpose of the odd positioning of the paths the two beams of light are supposed to travel and how can they possibly cancel each other out if they meet at a right angle, rather than a flat one.

Oh, very good question! They indeed wouldn't cancel if they just met at a right angle - they come in at a right angle but hit something like a semipermeable mirror, and so on the other side of that you have one direction where both returning waves are added (or subtracted depending on design) and *in parallel* again, and that's where you see the cancellation (where it says detector in the pic)



Note the half arrows showing the directions of the beams