Fig.1 is the setup at rest. The mirror at B is angled 45 deg to the path, and the mirror at C is angled 90 deg to the path. A light signal travels ABCBA. According to optics, the incidence angle equals the reflection angle, which is true in fig.1. To a viewer watching the setup move horizontally at speed v, it appears not to be true. In fig.2 the B mirror would have to rotate clockwise to reflect to C. In fig.3, the B mirror would have to rotate counterclockwise to reflect to A. The mirror can only have one position. What's the explanation? drawing
When light reflects from a moving boundary between two media, the angle of incidence is no longer equal to the angle of reflection.
In the frame comoving with the mirror the Snell law works as you would expect. In a frame moving with respect to the mirror several things happen: -the light rays are aberrated -the mirror appears rotated
Yes, length contraction means that the angle of mirror B will be different in the frame in which it is moving.
Thanks for all the answers. I checked the wiki reference and it seems a simple rule becomes very complex, as usual. If the experiment works in all frames (per 1st SR postulate), how so in the moving frame case?
