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Hello! I have recently been working on a paper that suggests a way of disproving the first postulate of the theory of relativity, as well as the equivalence principle. The mechanism that I am proposing is as follows: Imagine that you are in a large box. You don't know if you are moving at constant velocity or if you are at rest. According to the first postulate of relativity, it is impossible to figure out if you are moving uniformly or if you are at rest. Regardless, you try to build a mechanism of distinguishing between constant motion and rest. You design the following mechanism: Knowing that the speed of light is constant, you shoot a photon from one wall of your box to the other, and measure the time it took the photon to reach the second wall. You calculate how long the trip should take (at rest) and how much longer it should take if your box had some forward velocity. Then you compare your calculations to your observations. You assume it should take longer for light to reach the second wall if your box is moving because the speed of light is a constant and because of some principles of simultaneity of relativity. The theory is, if the box is moving, light (being like an arrow - and its speed independent of the speed of the box) would take longer to hit the target (the second wall) because it moves forward during the time light is travelling to hit it. So light catches up to hit it at a time slightly longer than it would take if the "target" did not move. From that info it becomes easy to distinguish if you are at rest or moving; and at what speed you may be moving. Of course, this is relative to the speed of light, but light speed is a universal constant, so I dont think that poses a problem to the theory. Is the assumption that you make correct? Would this be a way in which one could disprove the first postulate of the theory of relativity, as well as the equivalence principle? Can I excpect to receive a Nobel prize anytime soon?! :-) :-) I'd love to hear your opinion. And if it turns out that I'm correct, I'd be glad to send you a copy of my paper as soon as I complete it, for review. If I'm not correct, then at least I'll understand relativity better. Talk to you soon!
Question Date: 2010-04-21
Answer 1:

This experiment has been done (in fact, this IS the Michaelson-Morely experiment if my memory serves me right), and no, special relativity holds up. Here's how it works:

If the box is moving, then so are you, and so is the emitter you are using to emit your photon. This does three things: (1) the clock you are using to measure how long it takes your photon to make it to the opposite wall is subject to time dilation, (2) the entire box experiences Lorentz Contraction, making the distance to the opposite side of the box shorter, and (3) your photon experiences a relativistic blueshift as it is emitted toward the wall, and then, because the wall is receding, it experiences a redshift as it is reflected away, only to get blueshifted again when it reaches your detector. In the end, the combination of redshifting and blueshifting will cause the photon to have the same wavelength upon its return as when it left your emitter.

The time dilation and Lorentz Contraction alone will cause you to measure the same speed of light as if you were "at rest". The redshifting and blueshifting will stop you if you try to watch the wavelength of the photon knowing the frequency with which it was emitted.

Nice thought, though, about the experiment. Actually, there is one already known problem with special relativity in the context of your experiment, and that is this: you did say PHOTON, not BEAM. A photon is a quantum of light, the position of which is described by a wave form. Relativity is not a quantum theory; it is a classical theory. If space and time were also quantized, how would they change as you changed velocity (velocity would have to be quantized too, of course). How quantum mechanics and relativity fit together is one of the big problems in theoretical physics. Solve that one and I guarantee you WILL get the Nobel Prize!

Answer 2:

The main flaw with your conclusion lies in the basic tenet of relativity:
namely, the speed of light is constant in ANY inertial reference frame.Things will proceed as you describe them, but only for people in a frame of reference outside the box looking in. For the person inside the box, the speed of light is constant in the box's frame of reference. So events will proceed exactly as they would in a box at rest...because the box IS at rest in this frame (by definition)!

Relativity thus predicts some weird things, like the loss of simultaneity (e.g., the lights in your question turn on at the same time in the box's reference frame, but at different times in the outside reference frame) and time dilation (like your light clocks would show). But these things have been measured and shown to be spot on.

So, if you are okay with the speed of light being a constant in any inertial reference frame, and okay with all inertial reference frames being equal, then one has to be okay with the loss of simultaneity and all the other weird (and cool) things special relativity predicts!!

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