I'm struggling to understand a hopefully silly implication about light clocks on trains. The train is in motion. SR and all that. Bob is on the side of the tracks watching. We're going to get super specific and say that the emitter for the light clock is an LED with a collimator.
Problem 1: The light beam leaves the LED, passes through the collimator, strikes the reflector on the ceiling of the train, and returns to the clock. Bob sees the clock tick. Bob must conclude that the beam of light traveled at an angle relative to his reference frame. Yet the laws of optics must still be obeyed.
Proposed solution to problem 1: Bob figures out that the LED emitted light in many directions. While the light was traveling to the collimator, the collimator was traveling with the train. So the light that made it through the collimator was moving at the proper angle relative to Bob's coordinates for it to hit the reflector on the far side of the train. The optics works from Bob's perspective, and the beam travels at the "correct angle". Do I have that right? (I think a similar argument could be made for a laser by recognizing that the lasing cavity is moving. The photons that are coherent are the ones that are moving "correctly" to the cavity.)
Problem 2: We replace the mirror at the top of the train with a retroreflector. Now Bob is completely baffled (and so am I). The clock still ticks, but that implies that the angle of reflection was equal to the angle of incidence. Yet, that's a retroreflector at the top of the train. The light should have reflected back along the incident beam. How did it make it back to the light clock? The laws of optics must still be obeyed.
The retroreflector can be considered (in the classic 2D case) to be a pair of mirrors at right angels to each other. All I can imagine is that if I were to carefully trace out a beam striking one of the mirrors and work out the time and locations of the reflections from the two mirrors in Bob's frame, it wouldn't behave like a retroreflector anymore, but rather like a plane mirror. Is that really the result? Or is there something else going on that I'm missing?