According to Noether's theorem, each symmetry of a system is associated a conserved quantity. For example, the rotational invariance of a system implies the conservation of its angular momentum, or spacetime invariance implies the conservation of energy–momentum. In quantum field theory, internal symmetries also result in conserved quantities. For example, the U(1) gauge transformation of QED implies the conservation of the electric charge. Likewise, if a theory possesses an internal chiral or axial symmetry, there will be a conserved quantity, which is called the axial charge. Further, just as the motion of an electrically charged particle produces an electric current, a moving axial charge constitutes an axial current.