" To understand how then models are used in more detail one needs to distinguish from each other the various reference modes in which the investigator puts the model with respect to the original. The reference modes that perhaps are most important in computing are: (1) descriptive, i . e. , the model describes the original. If the deviation from model to original cannot be tolerated then the model has to be changed. Analysis models are in a descriptive reference mode to their originals. (2) prescriptive, i. Container Model Shipe. , the model prescribes the original. "

" Gravitons, the bosons believed to mediate the gravitational interaction, are not accounted for in the Standard Model. There are twelve different types, or "flavours", of fermions in the Standard Model. Amongst the proton, neutron, and electron, those fermions which constitute the vast majority of matter, the Standard Model considers only the electron a fundamental particle. The proton and neutron are aggregates of smaller particles known as quarks, which are held together by the strong interaction. The fundamental fermions in the Standard Model are given in the table. Table Left handed fermions in the Standard Model Fermion (Left-handed) Symbol Electric charge Weak charge* Weak isospin Hypercharge Color charge* Mass** Generation 1 Electron e -1 2 -1/2 -1/2 1 0. 511 MeV Electron neutrino νe 0 2 +1/2 -1/2 1 < 50 eV Positron ec 1 1 0 1 1 0. Model Part Ship511 MeV Electron antineutrino 0 1 0 0 1 < 50 eV Up quark u +2/3 2 +1/2 +1/6 3 ~5 MeV *** Down quark d -1/3 2 -1/2 +1/6 3 ~10 MeV *** Anti-up antiquark uc -2/3 1 0 -2/3 ~5 MeV *** Anti-down antiquark dc +1/3 1 0 +1/3 ~10 MeV *** Generation 2 Muon μ -1 2 -1/2 -1/2 1 105. 6 MeV Muon neutrino νμ 0 2 +1/2 -1/2 1 < 0. "