Introduction

The aim of this chapter is to develop a quantum mechanical theory of electron dynamics that is consistent with special relativity. Such a theory is needed to explain the origin of electron spin (which is essentially a relativistic effect). Relativistic electron theory is also required to fully understand the fine structure of the hydrogen atom energy levels. (Recall, from Section 7.7, and Exercises 11 and 13, that the modification to the energy levels due to spin-orbit coupling is of the same order of magnitude as the first-order correction due to the electron's relativistic mass increase.)