# Wave direction in an interferometer

1. Jul 5, 2012

### ith

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?

Last edited by a moderator: May 6, 2017
2. Jul 5, 2012

### ghwellsjr

It would be a lot easier to illustrate if you showed the trajectory of a single photon as it traced out two diagonal paths, the outbound one going up and to the right and the inbound one going up and to the left. Then it would be easy to see how this photon will be able to travel through the tube without hitting the walls. Once you see it that way, you can imagine successive photons traversing their own diagonal paths each one above the previous one. Then, if you want, you can draw other illustrations to show how other photons emitted in different directions don't make it through the tube.

3. Jul 6, 2012

### ith

Perhaps I kow already. The direction should be diagonal, because the pipe moves.

4. Jul 6, 2012

### ith

I purposedly wanted to draw the wave, and not photons.

Let the source moves relatively to some observer.
Photons in other images are shown as little balls, that follow their source. So they move diagonally, relatively to the observer. Why waves would do so? Is the bottom image correct for the observer? Would the wave front lag behind the source or move with it just as these "photon balls"?

What if the circles were not wave fronts, but instead bursts of photons. Would not they lag behind? Would they behave differently that wave fronts?