A Grand Unified Theory (GUT) is a model in particle physics in which, at high energy, the electromagnetic force is merged with the other two gauge interactions of the Standard Model, the weak and strong nuclear forces. Many candidates have been proposed, but none is directly supported by experimental evidence. GUTs are often seen as intermediate steps towards a " Theory of Everything " (TOE), a putative theory of theoretical physics that fully explains and links together all known physical phenomena, and, ideally, has predictive power for the outcome of any experiment that could be carried out in principle. No such theory has yet been accepted by the physics community.