A theory of strong interaction is called quantum chromodynamics (QCD). Particles interacting strongly are supposed to have color charge, for example quarks appear in three "mutations" - red, green and blue. A hadron composed of quarks has to be white, for example baryons - three quarks in RGB mutations resulting in white or mesons - pair of quark-antiquark (color + anti-color is considered to be white).

My question are:

  • Who coined the term chromodynamics?
  • Why colors are used and not simply numbers or some characters?

The use of color to refer to the "color charge" characteristic of QCD is present in Gell-Mann, Fritzsch and Bardeen's original work from 1972. This terminology was apparently due to Gell-Mann:

"They had actually begun exploring this possibility in their earlier paper at the Tel Aviv conference. Now, working with Bardeen, they elaborated on the idea. What Nambu called "charm" Murray started calling "color" The three flavors of quarks—up, down, and strange-would also come in three different colors-red, white, and blue. Feeling cosmopolitan there in Geneva, Murray picked the arbitrary labels in honor of the French flag. It was a natural choice of terminology. Gell-Mann and Feynman had used "color" for years at Caltech as a fanciful name for new particle properties-there were red and blue neutrinos, for example. (But it was not an original notion. An Indiana University physicist had written about "color" in a textbook published in 1970. And other physicists had used the term as well.) Like Neapolitan ice cream, every baryon would consist of three differently colored quarks. A delta would be made from a red up, a white up, and a blue up, each would have different quantum numbers, and the Pauli principle would be saved." – Strange Beauty by George Johnson [Random House, 2011]

The later switch from red-white-blue to red-green-blue was apparently due to Fritzsch:

"Initially Gell-Mann liked to use the French national colors red, white, and blue since he lived in a house not far from the village of Gex, in the Jura mountains near Geneva. But Fritzsch preferred the colors red, green, and blue, because white is not a primary color. When one mixes red, green, and blue, one obtains white, and that turned out to be very useful later." – The Fundamental Constants by Harald Fritzsch [World Scientific, 2009]

According to his New York Times obituary, "it was Dr. Gell-Mann who named the theory quantum chromodynamics", a term which follows naturally from his choice of metaphor (chromo = color, dynamics = the study of forces).

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