Grand unified theory

Grand Unification, grand unified theory, or GUT is one of several very similar unified field theories or models in physics that unify what are considered three "fundamental" gauge symmetries: hypercharge, the weak force, and quantum chromodynamics (QCD). Grand unification is based on the idea that at extremely high energies, all symmetries have the same gauge coupling strength, which is consistent with the speculation that they are really different manifestations of a single overarching gauge symmetry. More specifically, GUTs predict that at energies above GeV, the electromagnetic, weak nuclear, and strong nuclear forces are fused into a single unified field. (Parker, B 1993, 'Overcoming some of the problems', pp.259-279)
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(GUT). Any quantum theory which attempts to show that the strong nuclear force, the weak nuclear force and electromagnetism are slightly different aspects of the same fundamental force: i.e. the grand unified force. The first step to GUT was the unification of the weak nuclear force and electromagnetism into the electroweak force. The electroweak force can be proved in particle accelerators but GUTs require too much energy to be provided, in order to prove them. GUTs require a virtual particle which can transform quarks into leptons. This gives rise to proton decay, which is being searched for at the moment because it would prove GUTs. Gravity must then be incorporated to provide a unified field theory.