It is argued that the spin-orbit forces on a Dirac electron implied by the usual interpretation of the theory are inconsistent with the currently accepted result of classical electrodynamics. The two theories can be reconciled by reidentifying the position and momentum operators for a spinning system in the limit of low translational velocities. Some thoughts on the significance of this result are presented.

• Received 23 July 1973

DOI:https://doi.org/10.1103/PhysRevD.8.3492