altergnostic

You are welcome. The zigzag path is supposed to help us visualize the reason for the expected fringe displacement, and it is based on the expected variation of the speed of light relative to the interferometer - although the animation is completely off on that matter, specially concerning the x-axis beam, but it depicts the beams as having varying speeds relative to the aether, which is nowhere near the original assumptions. But your points are correct regarding MM's own assumptions. What concerns me the most now, after I have read Michelson, is his use of a distance measured in a stationary interferometer's frame (moving aether) divided by a speed measured from the stationary aether frame (moving interferometer).

Well, from Michelson's book you can read that the beam should miss the receptor (at great enough speeds). That can only mean that they expected that the beam would be "left behind" as the interferometer moves to the right in an stationary aether. In other words, if the interferometer moves to the right, the beam would zigzag to the left: there would be no velocity component gained from the velocity of the interferometer. "The speed of light is c relative to the aether regardless of the speed of the source". There should be a zigzag as observed from the interferometer's frame, not from the aethers frame (which is what the animation shows). If the background is stationary (and the interferometer moves) then beam would describe a straight line up and down while the interferometer moves to the right. From the point of view of the interferometer, the aether moves to the left, so the aether "wind" should force the beam in the same direction.

If the light moves to the right, it has gained the speed of the interferometer relative to the aether, if the interferometer moves and the light stays behind it has maintained c relative to the aether, just like any other wave in a medium. Very straightforward. And the experiment was not at considerable speeds, but the animation is. The interfereometer obviously travels at a good fraction of the speed of light in the animation. If it depicted the actual speeds of the experiment, the beams would complete the two-way trip before any noticeable displacement of the interferometer at all. Either way, the photon should never have a horizontal component like that, it would move straight up while the interferometer moves to the right and, considering the speeds shown in the animation, it would completely miss the interferometer upon return. That's what Michelson himself said, did you read his original paper?

The speed of light was c relative to the aether in all frames. In the lab frame, you are moving relative to the aether at v and the light is moving relative to the aether at c, so the light is moving relative to you at c+-v, not relative to the background. If the interferometer is moving to the right in a stationary aether, the aether moves to the left in a stationary interferometer's frame. You can't move both the interferometer and the light to the right. That is adding the speed of the source to the speed of light in the aether stationary frame! Again, Michelson said it with all the words, that the beam would indeed miss the detector at considerable speeds. The op is correct and the animation at wiki is not.

You are correct. In his original paper, Michelson clearly states that the beam should miss the mirror at a considerable speed, but that this effect would be too subtle to matter at the speeds actually involved. At the speeds shown in the animation, the beam should miss the mirror or the detector. Also, the return speed for the photon in the x axis should be greater than the outgoing speed, relative to the interferometer.

We can't bring length contraction to this thread because this would be a post hoc solution, and the op seems concerned about the expectations at the time of the experiment, even before the experiment was even performed. I have to agree with the crticism... It seems that the animation doesn't follow from the assumption that light travels at c relative to the aether. Here is the original paper from Michelson: http://www.aip.org/history/gap/Michelson/Michelson.html On page 5, I think we can find where the problem comes from. There we find the times being calculated by dividing the distance (as measured from the interferometer's frame) over the addition of velocities (as measured from the aether's frame). They were conflating numbers from different frames! The distance D should be a distance as seen from the aether, which should be D +- Vt !!! Holy s***!

Actually farsight has a point. In 1905, Einstein was careful to define time operationaly, and not as a property of nature. Later he created the mathematical abstraction known as spacetime, which was then taken to have a physical meaning, but if you look at Einstein's first writings, he was concerned with the concept of time because we can only measure time indirectly: what we actually measure is the change of something in space - be it the position of a pendulum or the state of a subatomic particle. Hence, physically and operationally speaking, time is strictly the measurement of a change of matter/energy in space. If a clock reads less elapsed time, it must mean that it underwent less cycles when compared to the reading of another clock. So of course the "speed of time" is just a mathematical abstraction and can only have a concrete physical meaning if considered to be "the speed of the rate of change of a cyclic change of state", since time is "the speed of cyclic change of state". Thinking about it... the speed of time sounds like an acceleration!

Of course in SR you can't ask Q.B because you can't calculate it, and that is because light is never an observer, it is only the tool with which the observer observes other things: light is the c in v/c while what is being observed is the v in v/c. But you can always ask interesting questions and use logic to answer them. Then, logically, one photon would be moving at 2c relative to the other. The only thing you must remember is that this is not observed by either photon: you need a photon being directly detected to observe something. In this case, a third photon being emitted at the surface of one photon and reaching the other directly, else one won't even know the other exists at all. Only the source knows it emited 2 photons and only the source is physically able to determine their relative velocities. An observer at the point of emission can always place two mirrors at x and -x and wait for both photons to return, measure each photon's velocity for the round-trip and calculate the relative speed between them.

The gif to the right would be true if there was an aether. That was the expectation. That is not what occured. Both beams described their paths at c as if the setup was at rest, like the gif to the left. Both beams were detected at the same instant, so they described their paths at the same speed relative to the detector, not relative to some hypothetical aether, hence different aether theories had to be proposed until Einstein (and others) showed that we didn't need an aether at all. The animation to the right is a false visualization.