ABSTRACT
Perhaps the most powerful symmetry principle in physics associated with the non-gravitational interactions is gauge invariance. It forms the foundation of our understanding of the Standard Model and all of its generalizations. Its origins emerged in the 1820s with the discovery of electromagnetism and the first theory of electrodynamics. Over a period of several decades of experimental study and theoretical refinement, physicists realized that different forms of the vector potential result in the same observable forces. James Clerk Maxwell formulated the equations of electromagnetism that embody the first known gauge principle, though the nomenclature “gauge” was not used then and the equations were written in a rather obscure way that many people found hard to understand. The presence of a conserved current indicates the presence of a symmetry.
