Subatomic Particles The basic conception of a subject now known as subatomic particle physics dates back to 500 BC when the Greek philosopher Leucippus and his pupil Democritus suggested that matter consists of small, indivisible particles, which they called atoms. For more than 2000 years after this, the notion of atoms lay in obscurity. For quite a long time, people believed that all matter consisted of four elements: earth, fire, air, and water. We now know that atoms do exist, and that some particles smaller than atoms also exist. These subatomic particles are divided into two main groups, the leptons and the hadrons. The best known lepton ("light" particle) is the electron. In order to account for the emission of electrons from the nucleus, the neutrino, an essentially massless neutral particle was postulated. The muon and the tau, both much more massive than the electron, comprise the rest of the lepton family. The hadrons are divided into two groups, the mesons and the baryons. Protons and neutrons are baryons. Mesons and baryons are made of smaller particles called quarks. There are six different quarks: up, down, charmed, strange, top, and bottom. While these are cool names, they convey nothing about the distinct properties of the quark. Each quark comes in three different colors: red blue and green. Again, the color label has nothing to do with the quark's appearance. Baryons are composed of three quarks, mesons are composed of a quark and an antiquark. Now that <b>...</b>
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