Standard Model

Except for detection of the Higgs boson, which particle physicists hope to achieve in the next decade or two, the Standard Model corresponds almost perfectly to experiment. However, it has several flaws and odd features that lead physicists to believe that it must eventually be absorbed into another, broader theory (possibly string theory).

First, it seems to list too many "fundamental" particles—several dozen of them. There are questions as to whether this really be the simplest possible account of physical reality.

Second, the Standard Model does not attempt to explain gravitation. (A gravitation-mediating boson, the graviton, is often listed along with the other bosons of the Standard Model, but is not actually predicted by the mathematics of the model.)

Third, the Standard Model relies on 19 numerical values that cannot be derived from its mathematics but must be determined by experiment. These values include the masses of various particles, the strengths of the strong and weak interactions, and more.

Again, most physicists argue that it does not seem plausible that a model with 19 adjustable parameters can really be the simplest possible. Thus, refinement of the Standard Model continues on several fronts, especially detection of the Higgs boson (or, possibly, bosons) and on the absorption of the Standard Model into a more comprehensive theory (possibly string theory) that explains gravitation as well as the strong, weak, and electromagnetic forces.