I wont go into any details because it is really not important. In class we handled a problem dealing with an incoming photon that crashes into an electron, the electron gains momentum and a new photon is emitted too. My first question is about Maxwellian E&M. I understand that according to classical EM an accelerating particle produces an EM wave. And according to the photon theory of light, the wavefront of any such wave is replete with bundles of energy called photons. So in this particle interaction I mentioned above, why has the electron emitted a single photon and not the massive amount of photons that an EM wave would predict? My second question deals with the mathematical construction of such interactions. It was assumed in this collision that the mass of the system was invariant in the before-after scenarios. This is not the typical assumption for nuclear disintegration, for example. The reason why I think the mass is assumed invariant is because the identity of the particle travelling is known in both cases. Namely, it is an "electron" and electrons have mass ##m##. This makes perfect sense, but is it known for a fact that all electrons have the exact same mass? In the case of protons and neutrons, I guess it is also assumed they all have the same mass (not implying here that m-proton=m-neutron). But I don't like this idea because it suggests that whenever I did problems on nuclear disintegration the mass difference (before vs after) was always a linear combination (with integer coefficients) of the masses of the proton and neutron. I think this is assuming too much, and perhaps not even true when I did in fact do such problems. Thanks for reading so far! Hehe.