I was reading "understanding light'' on this forum. If one wants to know what a photon is one first must ask, does one want to know what the physics is or does one want to know what the mathematics says. A physicist might ask a the question, "Are Maxwell's equations (the E,B fields) a representation (even if classical in nature) of the photon or are they a representation of the interaction between the photon and matter." in order to understand the physical process that is occuring. If the equations are an interaction theory (which I would suggest is the case) then one might want to suggest that matter reacts to the photon field(s?) with an E type interaction (reaction) as well as a B-type interaction (reaction-a spin related gyroscopic reaction?). For example, a single photon field could produce both type reactions. (Mathematically this is can be done using the A vector potential to represent a single field that can produce both E and B, but the same can be done physically using a directional rotating field.) Going down the road to the answer to the question "Are Maxwell's equations (the E,B fields) a representation (even if classical in nature) of the photon or are they a representation of the interaction between the photon and matter." also ask the question "What is matter." For example what is an electron or a proton, why do these particles that according to the SM are of such different construction both emit and absorb photons (how does the photon get emitted - what is the physics process of absorbtion not the mathematics) and behave the same toward light (given the SM view of the proton, the proton's composite quarks somehow must together react to absorb a photon) just like SM "point" electron (This forum "Does the electron have a makeup" - actually the only thing we realy know is that the experimental data indicates that one can describe the collisions of electrons as if the electron was a point. Objects with spin can act and react gyroscopically through the centerpoint of spin, i.e behave point like) Unfortunately, for the purely physical physicist (though not the mathematical physicist), the SM despite its elequent mathematical representation of the interaction behaviors of particles, does not give, from a physical perspective, a satisfying answer for the physic(s)al nature of massed particles nor the photon.