Unanswered Questions

Beyond the Proton, Neutron, and Electron

What are the properties of quarks?

The American physicist Murray Gell-Man (1929-) has written that he gave the particles the name “quark” from the phrase “Three quarks for Muster Mark” in Finnegan’s Wake by James Joyce. Flavor and color have nothing to do with their traditional meanings. The names up and down are associated with a property of protons and neutrons central to an earlier theory. While some people believe that using ordinary words in a very technical context suggests that physicists are not serious about the particles, others believe that their use suggests a whimsical approach to physics that invites people into the discussion rather than erecting barriers to keep others out.

The quarks are fractionally charged, that is their charges are either 2/3 or -1/3 the charge of the proton. They have been given the names “up” and “down” respectively. The proton is composed of two up quarks and one down quark while the neutron is composed of one up and two down quarks. You can check to see that the charges of the quarks add up correctly. Up and down quarks are said to be two different quark “flavors.” Because the quarks have half-integral spin (like electrons and neutrinos) there cannot be two identical quarks that have the same quantum properties. Quarks have additional property called color charge that can be red, green, or blue. A proton or neutron must have quarks with one of each of the colors so that they add to white, just like ordinary colors do.


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