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Light implying consistency between QM and SR

  1. Aug 12, 2010 #1
    Hi All,

    Let me see if I can put my doubt in words appropriately...

    Imagine a source of EM radiation, say a laser beam, and suppose you are running against the laser's direction, i.e., photons go to positive x and you to negative x direction, for instance.

    From the POV of SR, light does not change its velocity, but there is Doppler effect and the transfer of momentum and energy (from light to you) increases.

    From the POV of QM, there is also Doppler effect and Planck's equation E = hv introduces also an increase in the energy and momentum of the photon.

    I am considering that there is conservation of number of photons produced by the source in this context.

    Do these two effects rest harmonically on the top of the same physicist's desk?

    In other words, if photons are to be considered roughly packets of EM radiation, whose number are conserved in going from one reference frame to another, and if its velocity does not change in going from one reference frame to another so it must be that the energy ought to increase with the frequency. Does it make sense?

    Best wishes

    Last edited: Aug 12, 2010
  2. jcsd
  3. Aug 15, 2010 #2
    Yes, it makes sense.
    So what is your question?
  4. Aug 17, 2010 #3
    My question is:

    Does Relativity in itself imply the increase of energy of radiation with its frequency ?

    And perhaps we should go beyond classical Doppler effect. Does relativistic Doppler effect accounts for the correct increase (with the frequency) in the energy of photons (EM packets of radiation) ?
    Best wishes

    Last edited: Aug 17, 2010
  5. Aug 18, 2010 #4
    yes, it does

    yes, it does
  6. Aug 18, 2010 #5
    It seems quite strange, for if Relativity could have offered support to Planck's equation, E = hv, Planck, himself, wouldn't have said that his equation was just a hint that was capable to provide an answer to the black body problem. Do you know some reference to this result ?

    Thank you in advance,

    Best wishes

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