Free Electron Paths from Dirac's Wave Equation Elucidating Zitterbewegung and Spin

Abstract: Despite the widespread belief that Dirac's wave equation does not exhibit electron paths, they are hiding in plain sight. The worldline of a free electron is revealed by applying Dirac's velocity operator to its wave function whose space-time arguments are expressed in a proper time by a Lorentz transformation. This motion can be decomposed into two parts: the electron's global motion of its inertia (or spin) center and an inherent local periodic motion about this point that produces the electron's spin. The latter has the ultra-high ZBW (zitterbewegung) frequency $\omega_0$ found by Schr\"{o}dinger in his operator analysis of Dirac's equation and so is appropriately called the \emph{zitter motion}. The decomposition corresponds to Gordon's decomposition of Dirac's current where the so-called polarization and magnetization currents are due to the zitter motion. In an inertial "rest"-frame fixed at the inertia center, Dirac's wave function corresponding to the electron spin in a specified direction implies that a free electron of mass $m$ moves in an inherent perpetual zitter motion at the speed of light $c$ in a circle of radius $c/\omega_0 = \hbar /(2mc)$ about the inertia center in a plane orthogonal to this spin direction. The electron continuously accelerates about the spin center without any external force because the inertia is effective at the spin center, rather than at its charge center where the electron interacts with the electro-magnetic potential. This analysis confirms the nature of ZBW directly from Dirac's equation, agreeing with the conclusions of Barut and Zanghi, Beck, Hestenes, Rivas and Salesi from their classical electron models. Furthermore, these five classical models are equivalent and express the same free electron dynamics as Dirac's equation.