Hello, I would like to understand the Michelson–Morley interferometer, but with the laser being an omnidirectional photon source and a pipe. http://img822.imageshack.us/img822/6520/interferometer.png [Broken] There are two pipes, but only one transmits light. The other absorbs the light, because the wave direction is not parallel to the pipe. One of the images shows the interferometer as seen by the stationary observer. Now, what about the moving observer? I have a problem understanding the case. Is the wave direction bent for him, relatively to the stationary observer? If yes, how he interprets, that still the same pipe transmits light? If not, what about the direction of the output beam, which should be diagonal for the moving observer in order to hit the mirror?