" The model does not describe the gravitational interaction. Since the completion of the Standard Model, many efforts have been made to address these problems . One attempt to address the first defect is known as grand unification. The so-called grand unified theories (GUTs) hypothesized that the SU(3), SU(2), and U(1) groups are actually subgroups of a single large symmetry group. At high energies (far beyond the reach of current experiments), the symmetry of the unifying group is preserved; at low energies, it reduces to SU(3)×SU(2)×U(1) by a process known as spontaneous symmetry breaking. The first theory of this kind was proposed in 1974 by Georgi and Glashow, using SU(5) as the unifying group. A distinguishing characteristic of these GUTs is that, unlike the Standard model, they predict the existence of proton decay. Model Air Plane Show In 1999, the Super-Kamiokande neutrino observatory reported that it had not detected proton decay, establishing a lower limit on the proton half-life of 6. 7× 1032 years. "

"6 MeV Muon antineutrino 0 1 0 0 1 < 0. 5 MeV Charm quark c +2/3 2 +1/2 +1/6 3 ~1. 5 GeV Strange quark s -1/3 2 -1/2 +1/6 3 ~100 MeV Anti-charm antiquark cc -2/3 1 0 -2/3 ~1. 5 GeV Anti-strange antiquark sc +1/3 1 0 +1/3 ~100 MeV Generation 3 Tau τ -1 2 -1/2 -1/2 1 1. 784 GeV Tau neutrino ντ 0 2 +1/2 -1/2 1 < 70 MeV Anti-Tau τc 1 1 0 1 1 1. 784 GeV Tau antineutrino 0 1 0 0 1 < 70 MeV Top quark t +2/3 2 +1/2 +1/6 3 173 GeV Bottom quark b -1/3 2 -1/2 +1/6 3 ~4. 7 GeV Anti-top antiquark tc -2/3 1 0 -2/3 173 GeV Anti-bottom antiquark bc +1/3 1 0 +1/3 ~4. Giant Model Plan Plane Scale7 GeV * - These are not ordinary Abelian charges which can be added together but labels of Group representations of Lie groups. ** - Mass is really a coupling between a left handed fermion and a right handed fermion. "