Was Sommerfeld wrong? (To the history of the appearance of spin in relativistic wave equations)

Abstract

Abstract This article presents a brief history of the appearance of electron spin in relativistic wave equations. Dirac derived his wave equation in 1928 with the intention to obtain an equation for the ‘simplest’ particle with spin zero. But, as Dirac later announced at the European Conference on Particle Physics (Budapest, 4–9 July 1977), it was a big surprise for him that the equation described the states of a particle with spin 1/2.