Page "Theory of everything" Paragraph 19

Several Grand Unified Theories ( GUTs ) have been proposed to unify electromagnetism and the weak and strong forces.

Grand unification would imply the existence of an electronuclear force ; it is expected to set in at energies of the order of 10 < sup > 16 </ sup > GeV, far greater than could be reached by any possible Earth-based particle accelerator.

Although the simplest GUTs have been experimentally ruled out, the general idea, especially when linked with supersymmetry, remains a favorite candidate in the theoretical physics community.

Supersymmetric GUTs seem plausible not only for their theoretical " beauty ", but because they naturally produce large quantities of dark matter, and because the inflationary force may be related to GUT physics ( although it does not seem to form an inevitable part of the theory ).

Yet GUTs are clearly not the final answer ; both the current standard model and all proposed GUTs are quantum field theories which require the problematic technique of renormalization to yield sensible answers.

This is usually regarded as a sign that these are only effective field theories, omitting crucial phenomena relevant only at very high energies.