Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

First historical experiment disproving Ritz emission theory?

  1. Jul 7, 2011 #1


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Ritz proposed in 1908 that SR was wrong, and that the speed of light would depend on the speed of the source according to Galilean addition of velocities, c+v. The review linked to from PF's sticky on the experimental basis of SR has a nice section on this: http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html#moving-source_tests

    These results are typically described in terms of a limit on k, where the speed of light is c+kv, k=0 being SR and k=1 being the Ritz theory.

    Early tests such as de Sitter's in 1913 http://en.wikipedia.org/wiki/De_Sitter_double_star_experiment were later realized to be problematic because of optical extinction. The earliest test they list that disproves k=1 and is not subject to optical extinction or other issues is a pair of experiments in 1964.

    It seems impossible to believe that the Ritz theory was really viable until 1964. Of course nobody believed it by then, and it was indirectly inconsistent with a gazillion other experiments, but was there really no direct disproof of k=1 until 1964? Were the early tests such as de Sitter's sufficient to falsify k=1, even given extinction? (De Sitter claimed k<.002, but he didn't consider extinction.) Historically, what was the first direct test that ruled out the Ritz theory?
  2. jcsd
  3. Jul 8, 2011 #2
    Good question. I don't think I've seen any particular experimental test acknowledged in the literature which definitely rules out the Ritz theory. As you mention, it's typically reasoned away on the basis of additive velocities, De Sitter's reasoning (which I find pretty unconvincing) and lack of compliance with the Oseen extinction theory (which I find even less convincing).

    However, a full analysis of the Sagnac experiments (1913?) and all related ones including the Michelson-Miller experiment a couple of decades later very clearly shows that emission theories do not apply in the case where two light sources having different paths to the detector are compared. If the Ritz theory were correct no shift in phase of the 2 signals would occur, right?
    Last edited: Jul 8, 2011
  4. Jul 8, 2011 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    No, please take a more careful look at what I wrote in #1, and read the edu-observatory.org link. It was definitely directly disproved by experiments in 1964. The only question is whether it was directly disproved before then.

    No, that's not what I said.
  5. Jul 8, 2011 #4
    Ritz's original theory doesn't involve extinction effects, and therefore it was conclusively ruled out by DeSitter's double stars and the Sagnac effect, both in 1913.

    As regards the modified "extinction emission theory" (which wasn't discussed before the 1960ies), they were also conclusively ruled out after 1964 by a lot of experiments in vacuum (Sagnac type or with moving sources) and Brecher's modified version of DeSitter's experiments.

    However, if there were also relevant experiments before 1964 which were overlooked by Fox, I don't know.

    * Fox, J. G. (1962), "Experimental Evidence for the Second Postulate of Special Relativity", American Journal of Physics, Volume 30, Issue 4, pp. 297-300
    * Fox, J. G. (1965), "Evidence Against Emission Theories", American Journal of Physics 33 (1): 1–17
    * Fox, J. G. (1967), "Constancy of the Velocity of Light," J. Opt. Soc. Am. 57, 967-968

  6. Jul 8, 2011 #5


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Sorry, but I don't follow you here. Doesn't extinction exist regardless of whether you believe in SR or an emission theory?

    But it sounds like a good answer to my original question is simply that the Sagnac effect disproves emission theories, since the Sagnac effect occurs in vacuum, and you don't get extinction in a vacuum.

    I guess it's odd, though, that the edu-observatory.org page doesn't even mention the Sagnac effect in its discussion of moving source tests. Maybe that's because the waters are muddied by the existence of multiple versions of the emission theory that make different statements about what happens in reflection: http://en.wikipedia.org/wiki/Emission_theory#History


    [EDIT] Oh, I see, the Fox 1967 paper says that in Ritz's original formulation, he assumed that scattering would leave the velocity of the light unaffected. That seems bizarre to me, but I suppose there was never really any plausible set of physical mechanisms for the Ritz theory anyway.
    Last edited: Jul 8, 2011
  7. Jul 8, 2011 #6
    It sounds like the Wikipedia article compounds some confusion about extinction. According to the Ewald-Oseen extinction theory, incident radiation suffers extinction from any charge that is relatively free to move in response to the radiation within the specified spatial area regardless of whether its embedded in a vacuum or media (including the charges in the detector). Astronomers though, might be most focused on secondary extinction occurring in intervening matter while the light is in transit.

    But since the paths of light are circular in the Sagnac experiment (the mirrors are symmetrically situated), any possible extinction effects from the mirrors should cancel out.
    Last edited: Jul 8, 2011
  8. Jul 10, 2011 #7
    Yes I would think so. But we can trace the disprove of ballistic emission theories to much earlier in time, as I think Einstein understood before writing his 1905 paper. What many people (incl. Ritz?) seem to overlook is the Fizeau experiment that was meant to test the Fresnel drag coefficient. Not only the results were consistent with Fresnel's theory, at the same time the results rejected the whole class of ballistic emission theories.

    See also http://en.wikipedia.org/wiki/Fizeau_experiment

  9. Apr 21, 2012 #8
    I have a few questions regarding this topic:

    1) I would like to know a little bit more about these gazillion mentioned by bcrowell:
    What are some examples of these indirect experiments?

    2) I would also be interrested in the most recent experiences disproving the Ritz emission theory.

    3) Curious also about te most precise experiences disproving the Ritz theory.

    4) Finally, are there some recent experiences putting some opposite evidence, or some remaining doubts?


  10. Apr 22, 2012 #9
    One example was mentioned in the foregoing post. :wink:
    Perhaps ring laser gyroscopes?
    - http://en.wikipedia.org/wiki/Sagnac_effect
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook