A theory of elementary forces that unites the weak, strong, electromagnetic, and gravitational interactions into one field theory and views the known interactions as low-energy manifestations of a single unified interaction. or grand unification theory (GUT) Theory that attempts to unify the electroweak force (see electroweak theory) with the strong force. The unification of all four fundamental interactions is sometimes called unified field theory. Such theories generally predict that a proton decays into lighter particles. So far, no successful GUTs have been devised