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About Photon as an independent entity

  1. May 30, 2010 #1
    Hi All

    I was re-reading the first pages of the book from Mr Claude Cohen-Tannoudji ,... (Quantum Mechanics) and something called my attention.
    In commenting the appearence , in 1905, of the photon notion in Albert Einstein's paper on photelectric effect, he (Mr. Claude) says that only in 1920, with the Compton effect, was the photon proved to be an independent entity.

    My question thus is concerned with this criteria.

    Why photoelectric effect is less capable of demonstrating the photon's independent nature as a physical entity than Compton's effect?

    Best Wishes

  2. jcsd
  3. May 30, 2010 #2


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    Science Advisor

    I think in the early days of quantum mechanics, the interpretation of the photoelectric effect was that electromagnetic waves contain a continuous amount of energy, but that the energy could only be added and subtracted in "chunks" of magnitude h*nu. However, the Compton effect shows that the interaction of a free electron with an electromagnetic wave is correctly analyzed by treating both the electron and the EM wave as free particles and conserving energy and momentum. This is not consistent with the earlier interpretation, and makes it clearer that the photon is a true "entity". Afterwards, it became clear that all particles have both wave and particle characteristics, which is the interpretation we have today.
  4. May 31, 2010 #3
    Thank you Phyzguy

    Best Regards,

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