Editing Unified field theory (section)

=== Modern progress ===
In 1963, American physicist [[Sheldon Glashow]] proposed that the [[weak nuclear force]], electricity, and magnetism could arise from a partially unified [[electroweak theory]].  In 1967,  Pakistani [[Abdus Salam]] and American [[Steven Weinberg]] independently revised Glashow's theory by having the masses for the [[W particle]] and [[Z particle]] arise through [[spontaneous symmetry breaking]] with the [[Higgs mechanism]].  This unified theory modelled the [[electroweak interaction]] as a force mediated by four particles: the photon for the electromagnetic aspect, a neutral Z particle, and two charged W particles for the weak aspect. As a result of the spontaneous symmetry breaking, the weak force becomes short-range and the W and Z bosons acquire masses of 80.4 and {{val|91.2|u=GeV/c<sup>2</sup>}}, respectively. Their theory was first given experimental support by the discovery of weak neutral currents in 1973.  In 1983, the Z and W bosons were first produced at [[CERN]] by [[Carlo Rubbia]]'s team. For their insights, Glashow, Salam, and Weinberg were awarded the [[Nobel Prize in Physics]] in 1979. Carlo Rubbia and [[Simon van der Meer]] received the Prize in 1984.

After [[Gerardus 't Hooft]] showed the Glashow–Weinberg–Salam electroweak interactions to be mathematically consistent, the electroweak theory became a template for further attempts at unifying forces. In 1974, Sheldon Glashow and [[Howard Georgi]] proposed unifying the strong and electroweak interactions into the [[Georgi–Glashow model]], the first [[Grand Unified Theory]], which would have observable effects for energies much above 100 GeV.

Since then there have been several proposals for Grand Unified Theories, e.g. the [[Pati–Salam model]], although none is currently universally accepted. A major problem for experimental tests of such theories is the energy scale involved, which is well beyond the reach of current [[particle accelerator|accelerators]]. Grand Unified Theories make predictions for the relative strengths of the strong, weak, and electromagnetic forces, and in 1991 [[Large Electron-Positron Collider|LEP]] determined that [[Minimal Supersymmetric Standard Model|supersymmetric]] theories have the correct ratio of couplings for a Georgi–Glashow Grand Unified Theory.

Many Grand Unified Theories (but not Pati–Salam) predict that [[proton decay|the proton can decay]], and if this were to be seen, details of the decay products could give hints at more aspects of the Grand Unified Theory. It is at present unknown if the proton can decay, although experiments have determined a lower bound of 10<sup>35</sup> years for its lifetime.