  Noether's theorem has gained outstanding importance in theoretical particle
physics, because it leads to basic conservation laws, such as the conservation
of momentum and of angular momentum. Closely related to this theorem, but
unnoticed so far, is a complementary law, which requires the (virtual) exchange
of momentum between the particles of a closed multi-particle system. This
exchange of momentum determines an interaction. For a two-particle system
defined by an irreducible representation of the Poincare group, this
interaction is identified as the electromagnetic interaction. This sheds new
light on the particle interactions described by the Standard Model. It resolves
long-standing questions about the value of the electromagnetic coupling
constant, and about divergent integrals in quantum electrodynamics.
