Relativity holds that energy and mass are equivalent via the equation $E=mc^2$ also I know in quantum mechanics we talk about electrons jumping into bigger orbitals if they gain just the right amount of energy, or electrons emitting light and cascading down into lower energy levels, as in the laser phenomenon of population inversion. Either way the energy of the electrons is changing which changes its relativistic mass.
Back in relativity we have nuclear reactions converting mass into radiation and vice versa. So both theories seem to be talking about the same thing. Some how or other the massless photon is able to condense into ordinary matter. What I'm interested in is what that looks like. Is matter just a bunch of dead photos? Are they perhaps waves that somehow got tangled up and they are interfering with each other photon in the nucleus so that they sort of orbit each other?
Another thing that's always confused me is when to use what theories where. My chemistry teachers seem to switch back and forth arbitrarily between relativity and QM to explain various phenomenon.
