The electrical neutrality of atoms and of bulk matter

The equality of the charges of the electron and the proton, and the charge neutrality of the neutron are of great significance in the fundamental theory of particles. This equality suggests a deep symmetry between leptons and quarks that is not yet revealed in other experiments. The electrical neutrality of bulk matter is a direct result of this characteristic of the fundamental charges, with important consequences for precise tests of fundamental physical laws and for electrical metrology. The question is of interest also in cosmology. In this paper, we discuss the experimental evidence for the equality of the fundamental electrical charges, its implications and the possibility of improved experiments.