Quantum chromodynamics

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See also the article Standard Model.

In particle physics, quantum chromodynamics (abbreviated as QCD) is a specific kind of quantum field theory which supposes that fundamental particles or hadrons (such as protons and neutrons) are made up of quarks and gluons which interact while they also have a kind of charge named colour charge, which is not the same at all as real colours).

For the quarks, three colour charges are distinguished; red, green and blue. The colour charge of a quark's anti-particle partner is called anti-red, anti-green or anti-blue.

Free particles are combinations of these fundamental particles with no net colour. Examples of such particles are mesons, which could then be described as a combination of a quark and an anti-quark, or baryons, which are, according to QCD, combinations of three quarks, one of each colour charge.

Another specific property of QCD is that the force between the quarks increases as the distance between them becomes larger. This is known as asymptotic freedom.

Since the 1950s, experimental tests have been carried out which have confirmed many aspects of QCD.


  • Hawking, S. & Mlodinow, L. The Grand Design: New Answers To The Ultimate Question of Life, Bantam Press, 2010.