QED: Would atoms without electrons be visible? I have been reading a lot of QED books lately, and understand (as well as possible anyway) the interaction between electrons and photons. But I can't seem to get a clear indication of the interaction between photons and protons. It seems that normal light (not talking about high-energy levels or anything exciting, just the stuff that comes out of a light bulb) would be insufficient to really produce a reflection, but, so far, it depends upon who I ask.
That said, to boil down what I am really trying to determine: Would otherwise-normal atoms (or matter, really) with no electrons be visible? Would the protons take up the role normally provided by the electrons and cause a similar scattering of light, or would it really just mess things up?
 A: Ordinary light has far too little energy to significantly affect protons.
But gamma rays are the result of interactions between protons, neutrons and photons in an unstable nucleus (i.e., a radioactive atom).
Normal atoms without their electrons are positively charged and would not form ordinary matter but an exploding gas. Most ordinary experience would become invalid.
A: I will take the example of a proton beam in an accelerator. Your question becomes:

will light scatter off a proton beam

The answer is yes, though one would need very sensitive equipment to catch the scattered photons since the density of the beam is nowhere near the density of outer electrons on a surface. It is calculable, but people are not interested for the very low energy photons of the visible spectrum.
A: The main thing that makes electrons, rather than nuclei, be the primary interlopers with electromagnetic radiation in an atom is their much smaller mass. This is because for a given electric field, the acceleration on a nucleus will be far smaller than on the electron, so that to a very good approximation we can picture the nucleus as static.
Thus one alternative question you can ask (since we're doing counterfactual physics) is, what would atom-light interactions be like if the electron and proton masses were comparable? This is very tricky to answer on one hand because if the ratio $m_e/m_p$ were not small then the Born-Oppenheimer approximation breaks down completely and we would have to completely re-write all of atomic and molecular physics. 
On the other hand, at least in the lighter atoms (so the nucleus isn't 300 times heavier than electrons by dint of having so many nucleons), it is quite clear that the nucleus would also play an important role in the interaction dynamics. The way this would come about is in the calculation of atomic dipole moments, which would have to include an expectation value over the nuclear coordinates as well as the electronic ones (corresponding, physically, to the nucleus vibrating together with the electrons on atomic transitions). 
