Classical Origin of Fermion Spin

The spin was postulated by Pauli from experimental evidence, but it was only with the arrival of the Dirac equation that the spin appears naturally. This leaded to many people to consider the spin as fundamentally "quantum". In the following paper we argue that the spin appears naturally from classical relativistic mechanics alone


W. E. Baylis, R Cabrera, J.D. Keselica, Quantum/Classical Interface: Classical Geometric Origin of Fermion Spin, Advances in Applied Clifford Algebras, 2010