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My book says that all interaction of light and matter can be reduced to the photoelectric effect, the Compton scattering and pair production. How true is this?

What about reflection and absorption and emission and blackbody radiation and all that stuff?

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    $\begingroup$ Write down the Feynman diagram for each and behold. $\endgroup$ – Cosmas Zachos Feb 15 '18 at 13:36
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    $\begingroup$ I guess this is technically true but a bit weird. It's true if you're considering any interaction of the form $\gamma + \text{charge} \to \gamma + \text{charge}$ to be "Compton scattering", though we usually reserve that phrase for when $\gamma$ is an X-ray and the charge is an electron. $\endgroup$ – knzhou Feb 15 '18 at 14:25
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    $\begingroup$ Then reflection is Compton scattering, absorption is photoelectric, emission is the same as absorption but backwards, blackbody radiation is the same as emission. $\endgroup$ – knzhou Feb 15 '18 at 14:25
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    $\begingroup$ You might want to comment on the domain the book covers. The word "all" may very well be intended to mean "everything in our domain of interest" rather than being unqualified and all-embracing. Knowing how to read that kind of intent is one of the soft skills that our developed by doing a systematic study of the field. $\endgroup$ – dmckee Feb 15 '18 at 17:02
  • $\begingroup$ Maybe you could mention the source of this assertion. The comment by @dmckee makes sense. $\endgroup$ – freecharly Feb 15 '18 at 18:43
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Your book's claim is correct: all light-matter interactions can be reduced, when expressed as QED perturbative expansions, to a small set of Feynman diagrams. (I'll leave it to a QED expert to validate the specific set in your book's claim, but it looks correct to me.) This is true for the processes you mentioned, reflection and absorption and emission and blackbody radiation, as well as the processes described in the existing (incorrect) answer, i.e. Rayleigh scattering, Mie scattering, Raman scattering, stimulated light emission, atomic light absorption, and any others you care to name.

As to whether that reduction is useful, that is really in the eye of the beholder. It's unlikely that any physicist will bat an eye at the suggestion that chemistry, biology, geology and ecology can be "reduced" to physics, despite the fact that those subjects require higher-level abstractions to begin to make sense to a human brain. The same is happening here, except that it's now atomic physics that gets the sharp end of the reductionism stick.

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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – dmckee Feb 19 '18 at 23:40
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There are many interaction processes of light with matter that are not included in the three interactions named Compton effect, photoelectric effect, pair production, to which all interactions can supposedly be reduced. For example, Rayleigh scattering, Mie scattering, Raman scattering, stimulated light emission, atomic light absorption, specular reflection, etc. In QED one might formally order photon-matter interactions in three classes to which the named three effects belong. But to reduce these QED interaction classes to the three cited effects is highly misleading.

In my opinion, such an reductionist classification of photon-matter interactions is a mere curiosity and at best useful for a few theorists studying QED. Even there, the classes of interactions should better not be named after these effects. For the general physicist, especially students, such a classification is mostly harmful. It doesn't help at all to understand, much less quantitatively describe, most of the important physical effects squeezed into it.

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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – rob Feb 19 '18 at 17:48

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