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Is there a good classical description of a photon?

  1. Jun 8, 2015 #1
    The QED theories merely state that a photon has spin and momentum. Are there any reasonable mechanistic descriptions, perhaps in terms of variations of E and H beyond the infinite plane wave (which is also not helpful)?
     
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  3. Jun 8, 2015 #2

    jtbell

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    No. Photons are quintessentially quantum objects. Don't try to think of them as little "bullets" or spatially-localized wave packets. Especially not as wave packets of classical electric and magnetic fields.
     
  4. Jun 8, 2015 #3
    The optics of interference and diffraction are based on a model in which light is a plane wave. This model produces amazingly accurate results considering its complete lack of physicality. Now that experimentalists are producing Orbital Angular Momentum and Spatial Patterning in the lab, it would be nice to have a more realistic model for the E and H fields and it would save considerable effort if someone had previously made one -- say in 1920 or so. For instance, where would one have published such a model?
     
  5. Jun 9, 2015 #4
    I believe I am correct that these effects can only exist within a limited distance from the source, i.e. within the Radiation Near Field, roughly
    D^2/(2xlambda). As such, the two phenomena would in classical physics correspond to circular polarisation and to the use of an array to produce close-in hot spots in the pattern.
     
  6. Jun 10, 2015 #5
    You raise an interesting point about the adjustment between near field and far field. Apparently, at least in the case of spatial patterning, the reduction in propagation speed below c persists, and OAM is likely an enhancement to circular polarization. These interactions seem to be describable on a classical basis and a better model for the photon field could lead to the prediction of other forms of interaction such as better decoding of entanglement, although this is speculative. My interest is to review the models which have been put forward but I have not been able to find any except the plane wave "model".
     
  7. Jun 10, 2015 #6

    sophiecentaur

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    Only in simple cases. Even in dealing with the reflection from a curved mirror, that is no longer a valid or necessary assumption. Near field interference has to involve a spherical wave front; the sums are just a bit more complicated. (Fraunhofer vs Fresnel)

    How can there be? The whole reason for getting into QM is to explain phenomena that just don't stand up to Classical analysis so it is hardly likely that the quantum models that have been invented will be based on 'mechanistic' ideas. I'm afraid that you are avoiding biting the bullet and acknowledging that QM is totally outside the Classical world of Science. Sorry.
     
  8. Jun 10, 2015 #7
    Is there a QM description of the photon? The QM models I have seen are essentially correlations stating that a photon has spin h/ and momentum hf/c. A useful model should at least calculate the probability that two photons will collide to produce a particle/antiparticle pair.
     
  9. Jun 10, 2015 #8

    jtbell

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    Strictly speaking, QM does not include photons. For that, you have to move to quantum electrodynamics (QED). People do often use the term "QM" informally to cover both theories.
     
  10. Jun 10, 2015 #9

    sophiecentaur

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    You seem to be wanting a description in your own terms, that you can find familiar enough to satisfy you. Imo, stating the properties of the photon is sufficient description - when something is not actually 'like' anything else so there are no suitable metaphors for a conventional description so that's all you can expect.
     
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