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  • diffraction and c

    From RichD@21:1/5 to All on Sat Oct 5 01:17:52 2019
    On another board, during some discussion of relativity,
    it was claimed that a test of relativistic Doppler shift
    could be performed via frequency combs (a recent tool)
    and diffraction gratings; i.e. v = fλ

    Then, someone objected, dismissing the argument as
    circular, since the diffraction grating model itself
    depends on assuming a constant speed of light, c, as
    per Einstein's second postulate.

    I don't recall this. Anyone here wish to comment?

    --
    Rich

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  • From torty5737@gmail.com@21:1/5 to All on Wed Oct 16 10:23:15 2019
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  • From whit3rd@21:1/5 to RichD on Sun Nov 10 18:05:35 2019
    On Saturday, October 5, 2019 at 1:17:53 AM UTC-7, RichD wrote:
    On another board, during some discussion of relativity,
    it was claimed that a test of relativistic Doppler shift
    could be performed via frequency combs (a recent tool)
    and diffraction gratings; i.e. v = fλ

    Then, someone objected, dismissing the argument as
    circular, since the diffraction grating model itself
    depends on assuming a constant speed of light, c, as
    per Einstein's second postulate.

    A 'diffraction grating' is a physical object, held together by electrical forces.
    If you alter the laws of electricity and magnetism on a cosmological scale,
    it could change the object in question.
    The speed of light in vacuum is derived from those laws of electricity and magnetism.

    Yes, there's a certain circularity involved.

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