The Standard Model of Particle Physics is a theory that describes the fundamental particles and forces of nature. It classifies all known elementary particles and describes three of the four known fundamental forces in the universe: electromagnetic, weak, and strong interactions. The model was developed in stages throughout the latter half of the 20th century, through the work of many scientists worldwide, with the current formulation being finalized in the mid-1970s upon experimental confirmation of the existence of quarks.
The Standard Model consists of two types of particles: fermions and bosons. Fermions are the building blocks of matter, and there are 12 fermions, split into six quarks and six leptons. Bosons are force carriers, and there are five bosons: the photon, W and Z bosons, and the gluon and Higgs boson.
The Standard Model has been tested with exquisite precision and has demonstrated some success in providing experimental predictions. It has predicted various properties of weak neutral currents and the W and Z bosons with great accuracy. Although the Standard Model is believed to be theoretically self-consistent and has demonstrated some success in providing experimental predictions, it leaves some physical phenomena unexplained and so falls short of being a complete theory of fundamental interactions.
For example, the Standard Model does not fully explain baryon asymmetry, incorporate the full theory of gravitation as described by general relativity, or account for the universe’s accelerating expansion as possibly described by dark energy. The model does not contain any viable dark matter particle that possesses all of the required properties deduced from observational cosmology. It also does not incorporate neutrino oscillations and their non-zero masses.
The development of the Standard Model was driven by theoretical and experimental particle physicists alike. The Standard Model is a paradigm of a quantum field theory for theorists, exhibiting a wide range of phenomena, including spontaneous symmetry breaking, anomalies, and non-perturbative behavior. It is used as a basis for building more exotic models that incorporate hypothetical particles, extra dimensions, and elaborate symmetries (such as supersymmetry)
