Introduction
The Standard Model is a model (or theory) that serves as the basis of the modern understanding of particle physics by incorporating the known elementary particles and forces. Agreeing with both quantum mechanics and special relativity, the Standard Model is a quantum field theory that primarily deals with bosons and fermions. Unfortunately, many faults and inconsistencies plague the Standard Model; most prominent is its inability to describe gravity.
History and Development
The Standard Model was developed in the 1960s and 1970s in order to accurately describe the existence and activity of the elementary particles in particles physics. Three physicists, namely American Steven Weinberg and Pakistani Abdus Salam with the previous work of American Sheldon Glashow on the electromagnetic and weak forces in 1967, developed the general version of the Standard Model. Although this model was NEITHER comprehensive NOR complete (it still is not complete), the three physicists were awarded the 1979 Nobel Prize in Physics. At the time, only Generation I and Generation II particles were known; however, the Standard Model did in fact predict the existence of a Generation III, as well as the charm quark (both have since been discovered). Soon after that 1979 commendation, additions were made to the Standard Model to create a more extensive model. An important event occurred in 1983 when the W and Z bosons were discovered by Italian Carlo Rubbia. Still, scientists search for elusive particles that have not yet been discovered in hope of completing the Standard Model.
Fermions
Fermions, which are particles that contain half-integral spins and adhere to the Pauli exclusion principle, include three families or generations, which each contains a combination of quarks and leptons. These generations are categorized based upon the particles mass; the particles otherwise behave in much the same fashion in all three generations. The first family is the constituent for basic and ordinary matter and is comprised of the up and down quarks, the electron, and the electron neutrino. The electron and electron neutron (and their associated particles in other generations) are specifically designated as beings leptons, which signifies that they do not contain a “color” that is present in all other fermions. This lack of color results in weakening interactions with increased distance. The up and down quarks make up protons (two up quarks and one down quark) and neutrons (two down quarks and one down quark), and these two subatomic particles are known as nucleons because they inhabit the nucleus. The other two families or generations of fermions do not comprise ordinary matter, but they are formed in particle accelerators. The second generation contains the charm quark, strange quark, muon, muon neutrino, and the appropriate antiparticle to the aforementioned particles. The third generation contains the top quark, bottom quark, tau, tau neutrino, and the appropriate antiparticle to each particle.
Bosons
On the other hand, bosons have integral spins and do not adhere to the Pauli exclusion rule. Bosons include the eight types of gluons, the photon, W and Z bosons, and Higgs bosons. Gluons are responsible for the strong nuclear force and come in pairs of “colors” and “anti-colors.” The photon, which is essentially a packet of light, is involved in electromagnetic interactions. W and Z bosons, in contrast with gluons, control the weak nuclear force. The Higgs boson is a predicted particle that has zero spin and an large mass. Higgs bosons are thought to carry the Higgs field, which may be crucial in creating mass. The final and most controversial particle of the Standard Model is the graviton, which many physicists to be the elementary particle of the gravity though there is a lack of experimental affirmation.
Faults and Challenges
One main loophole in the theory is the lack of any mention of gravity. 
Like with most theories in the scientific community, the Standard Model has not been immune from numerous and serious challenges. One main loophole in the theory is the lack of any mention of gravity (the graviton has not been confirmed experimentally). Additionally, the nineteen parameters used in calculations cannot be separately determined and are considered rather inconsistent. Finally, the Standard Model does not effectively combine both the strong and electroweak forces. The remedy to these inconsistencies in the Standard Model lies in Grand Unification Theories and ultimately, the Theory of Everything (string theory?).
Sources and Links
- “Standard Model.” Wikipedia.org. Viewed: July 2004. http://en.wikipedia.org/wiki/Standard_Model.
- “Standard Model.” Microsoft Encarta Encyclopedia Standard 2001. CD –ROM. Viewed: July 2004.