Internal symmetry of a classical field theory
= Internal symmetry of a classical field theory
An internal symmetry changes field values while leaving spacetime coordinates fixed, preserving the <action>. A constant phase rotation of a <complex scalar field> is an example. This distinguishes internal charges from the spacetime translation charges in the <canonical stress-energy tensor>. Localizing the parameter generally requires gauge fields; a global internal symmetry is not automatically a gauge symmetry.