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In quantum mechanics, it seems that nothing has exact positions, and in the pilot wave theory, things tend to travel like this?:

(Credit: Looking Glass Universe) pilot wave theory

and in other interpretations, it seems that there can be infinite many travel paths between measurements?

Did the measurements of speed of light take into account that things don't travel in straight paths?

Qmechanic
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frt132
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    Does this answer your question? What is the trajectory of a photon moving through a vacuum? – The Photon Dec 14 '19 at 00:14
  • Also the discussion on this question might be helpful. – The Photon Dec 14 '19 at 00:16
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    This kind of sum over paths is also present in the classical field description of light. As in the case of the quantum path integral, it doesn't matter, because the result of the sum is overwhelmingly propagation at the normal speed of light. – knzhou Dec 14 '19 at 00:29
  • @ThePhoton The answers given here and there seem to be kind of confusing. 'Photons don't travel, at all. A photon is an initial state prepared by a measurement and a final state of a second measurement. There are no "particles" between those states.' but photons do affect other things between measurements, photons with higher enough energy may even cause black holes, what does he want to imply by 'no particles' between measurements? ' the result of the sum is overwhelmingly propagation at the normal speed of light' - but it means theoretically one can get more 'accurate' speed by 'correction'. – frt132 Dec 14 '19 at 00:38
  • Why does this picture show the hairdryer sending whatevers through only one of the two openings? – G. Smith Dec 14 '19 at 01:04
  • @G.Smith Oh, the author didn't draw all the paths, but the other paths are likely too. – frt132 Dec 14 '19 at 01:08
  • @frt132 well at least draw countably infinite paths – user192234 Dec 14 '19 at 03:14

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In experiments measuring the speed of light, there is no need to consider any paths other than the straight one between the source and the detector.

Photons can be considered (at least according to the Feynman path integral approach) to be taking other paths (including crazy ones that go off to the Andromeda galaxy and back, faster than the speed of light), but such paths have a negligible effect on the propagation of light over macroscopic distances. The probability amplitudes of all the crazy paths tend to cancel, leaving only the contribution of the classical path.

Quantum physics is weird, but fortunately classical physics emerges from it in the macroscopic realm.

G. Smith
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  • Since the possibility of other paths is non-zero, one can still do a 'correction' to get more accurate speed of light? – frt132 Dec 14 '19 at 00:20
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    No, the observation already includes all the other paths. I do not believe we can measure any quantum spread in the speed of photons. I would be interested in others’ opinion whether this would be possible in principle at macroscopic scale with sufficiently precise equipment. – G. Smith Dec 14 '19 at 00:40
  • GR is emergent from QM might have happened but only in the future. Macroscopic realm opposed to microscopic realm will turn out to not be real, in the future. – user192234 Dec 14 '19 at 02:43
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    @user192234 Sorry, I have no idea what you are trying to say. I’m guessing that there might be translation issues. – G. Smith Dec 14 '19 at 06:23