I was reading that one of the successes of the Dirac equation was that it was able to account for the fine structure of some of the differences in the spectrum of the hydrogen atom. But the Dirac equation is about subatomic particles moving at relativistic velocities. But an electron around the hydrogen atom is in a superposition state. It's not supposed to have a velocity, does it? And if it does, is it really at relativistic velocities? What kind of numbers are we talking about here?