The Thomas Precession

This paper is intended to give a simple physical understanding of the kinematic effect referred to as the Wigner rotation or, when applied to an orbiting object, the Thomas precession. Since this is a kinematic effect it applies not only to particles with spin but to all physical bodies in which a direction can be defined. To aid in avoiding the usual pitfalls in working with these problems, a review is made of several different approaches to the problem of an infinitesimally extended accelerating physical object. The central problem is in taking successive Lorentz transformations between parallel coordinate systems and clearly distinguishing between physical rotations of the object and coordinate rotations. When accounting for the energy associated with the Thomas precession a simple physical explanation is given rather than the misleading description popularly presented.