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Let me stress, TERRESTRIAL EXPERIMENT, as distinct from astronomical observations of the transverse Doppler effect, stellar aberration and so on.

To clarify what I mean by 'thrown sideways'. Supposing a source of light is moved in a straight line at 300 metres per second in a direction orthogonal to the direction of propagation. Would the photons inherit the source's lateral movement so that they would take a path deviated by one part per million in the direction of the source's motion, from the direction they would have taken with the source stationary?

There are four possible answers to this question.

  1. Yes. The result was null. Light can not be thrown sideways.
  2. Yes. The result was positive. Light can be thrown sideways.
  3. Yes, but practical difficulties prevented any definitive results from being obtained.
  4. No. It is considered unnecessary to conduct such an experiment for the following reasons . . .

Which is it please?

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  • $\begingroup$ @AlNejati That looks like it should be an answer $\endgroup$ – David Z Oct 16 '18 at 6:04
  • $\begingroup$ Your experiment as described cannot be done. An experiment that will show the light-gravity interaction is proposed here since 2006 phys.uconn.edu/~mallett/Mallett2006.pdf , but I did not find that anybody has tried to do it."This paper has shown that the gravitational field produced by the cir- culating light beam of a ring laser results in the rotation of the plane of polarization of an electromagnetic wave. A laboratory arrangement has been suggested" $\endgroup$ – anna v Oct 16 '18 at 6:19
  • $\begingroup$ While your question is experimental (and so I will leave the answer to the experts), it is based on the assumptions that challenge two most established theories, special relativity and quantum field theory. In relativity, the speed or direction of light does not depend on the movement of the source (only the energy does). In QFT, photons don't travel as particles on a definite path, but as waves of probability taking every available path at the same time. Thus your question is equivalent to asking if special relativity and QFT have been sufficiently tested and therefore is moot. $\endgroup$ – safesphere Oct 16 '18 at 6:29
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Foucault's apparatus uses a fast-rotating mirror to 'throw' light slightly sideways. The known rotational speed of the mirror plus the known distance that the light travelled was used to determine the speed of light.

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  • $\begingroup$ would the accuracy of the experiment allow detecting gravitational effects? $\endgroup$ – anna v Oct 16 '18 at 6:22
  • $\begingroup$ @annav Faraday rotation? $\endgroup$ – Al Nejati Oct 16 '18 at 6:31
  • $\begingroup$ just gave a link on the OP on a proposed experiment , in a comment $\endgroup$ – anna v Oct 16 '18 at 6:39
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On terrestrial length scales, any effect like that is so small that very special equipment is needed to measure it. However, the size of the effect can be greatly magnified by using distant stars instead of a light beam on earth. In this case, the "sideways propagation" effect can easily be measured with telescopes of the sort which have been available for the last 100 years. It is named "stellar aberration"and has been extensively documented.

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