Hi, We're looking at the consequences of the Stern-Gerlach experiment which has lead us to the idea of spin orbit coupling in the hydrogen atom. In class, the coupling term of the Hamiltonian was derived by assuming the electron has a magnetic moment, then viewing the hydrogen atom in the electron's frame. We then said that the proton orbits the electron, which is effectively a current, thereby producing a magnetic field which interacts with the moment. Obviously, this idea of the proton having a circular trajectory is totally crap in quantum mechanics, but everyone I've asked hasn't been able to give me a different derivation. All I've gotten is that this is one of those cases where classical mechanics gives a result which happens to work in the quantum case. Anyone know how to get the result without this idea of an orbiting proton?