Chapter 9: Fundamental Physics

Section 14: Elementary Particles

Charge quantization

It is an observed fact that the electric and other charges of all particles are simple rational multiples of each other. In the context of electromagnetism alone, there would be no particular reason to expect this (unless magnetic monopoles exist). But as soon as different particles are related by a non-Abelian symmetry group, then the discreteness of the representations of such a group immediately implies that all charges must be rational multiples of each other.

From Stephen Wolfram: A New Kind of Science [citation]