The first particles that show an interesting symmetry are actually the nucleon and the proton. This symmetry is reinforced by the discovery that the interactions between nucleon (p and n) is i...The first particles that show an interesting symmetry are actually the nucleon and the proton. This symmetry is reinforced by the discovery that the interactions between nucleon (p and n) is independent of charge, they only depend on the nucleon character of these particles – the strong interactions see only one nucleon and one pion. The symmetry that was proposed (by Wigner) is an internal symmetry like spin symmetry called isotopic spin or isospin.
