- #1

Peter Morgan

Gold Member

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## Main Question or Discussion Point

*[Moderator's note: This thread is spun off from a previous thread since it was getting into material too technical for the original thread. The quote at the top of this post is from the previous thread.]*

Field quantization doesn't require a photon picture. A measurement device that creates a record that corresponds to the Planck spectrum just has to be modeled by an operator that has (in the given state) that probability distribution associated with its continuous spectrum (or else by a POVM). That doesn't require a photon picture.He starts with the Planck spectrum of black-body radiation which rightfully needs field quantization, i.e., the photon picture. Then he uses the naive billiard-ball photon picture all the time although in a very beautiful section he writes all the arguments against it, including the point that both Compton and photoelectric effects are explainable through the semiclassical approximation and explicitly (and rightly!) stating that both effects do not necessarily prove the necessity of field quantization. So, why the heck is he using the wrong intuitions although obviously knowing much better?

That some operators have a discrete (or continuous) spectrum does not mean that the world is discrete (or continuous). Sometimes measurement results are discrete, which have to be modeled as discrete, and sometimes measurement results are continuous, which have to be modeled as continuous, and there are tools available for both (of course, because otherwise we would use a different mathematics). Where there is always continuity is in the evolution of probability densities over time for an operator that has a given spectrum, or, for one example, as we move a screen behind a double slit backward and forward so that an interference pattern changes, and I take it to be the dominance of that continuity that leads us to model using a (quantum) field theory.

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