# Glouns, Color Charge, and Quark Confinement

In my reading about QCD, I’ve learned that quark confinement and asymptotic freedom (two properties unique to the strong force) are caused by the fact that glouns themselves have color charge, but I haven’t found any articles that I can understand that go any further. How, exactly, does the fact that the exchange particles themselves contain the color charge dictate the unique properties of quark confinement and asymptotic freedom?

The fundamental problem with attempting to explain the various quantum theories to a lay audience is that they don’t really have an English-language interpretation. The math says what it says, and that’s what the theory says.

Nevertheless, someone here might be able to offer some kind of explanation that’ll clear things up.

OK, here we go:

In QCD, the force arises from gluon exchange, just like electric force arises from photon exchange in QED, yes?

In perturbation theory, you have to add the Feynman diagrams for all possible interactions to the basic gluon-exchange diagram. There are two to worry about (at the 1 loop level):

1. Gluon splits into a quark-antiquark pair, then recombines into a gluon again.
2. Gluon splits into two gluons which recombine into a gluon again.
Apply the Feynman rules, and you find that diagram (1) increases the strength of the interaction, while (2) reduces it. It turns out that (2) wins out. Since the loop diagrams contribute more at higher energy, we deduce that the strength of the interaction decreases at higher energy.

Got that?

Note that in QED, process (2) cannot occur. There is no diagram that allows a photon to split into two photons. As a result, the electric force increases at higher energy.

There was a good QCD article in Scientific American sometime in the 70’s or 80’s. If you can’t find it, you’ll just have to wait for my forthcoming book, The Theory of Almost Everything.

There were quite a few actually. But there was a bit of a fashion in 70s popularisations to try to explain QCD using analogies with classical electromagnetism and I suspect this is the sort of approach athleticsabe is looking for. Two Scientific American articles from the period that get into these types of analogy are those on confinement by Nambu (November 1976) and Ken Johnson (July 1979).