Thanks for the replies everyone!
I was always thinking in my head that the timer would be at the source, and somehow never thought that the information that the photon hit the detector would have to travel back (in the same apparent fashion as the opposite beam is traveling) to the source...
This is my first time posting so it's nice to meet everyone!
I'm not trained in physics, but lately I've been very interested in and reading a lot about both Relativity and Quantum Mechanics. With regard to relativity, I found the topic of relativity of simultaneity very interesting. The...