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| | Modern Particle Theory timeline |
 | | By the mid-1960's, physicists realized that their previous understanding, where all matter is composed of the fundamental protons, neutrons, and electron, was insufficient to explain the myriad new particles being discovered. |
 | | Over the last thirty years, the theory that is now called the Standard Model of particles and interactions has gradually grown and gained increasing acceptance with new evidence from new particle accelerators. |
 | | They suggested that mesons and baryons are composites of three quarks or antiquarks, called up, down, or strange (u, d, s) with spin 0.5 and electric charges 2/3, -1/3, -1/3, respectively (it turns out that this theory is not completely accurate). |
| pdg.web.cern.ch /pdg/cpep/history/smt.html (950 words) |
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