High Temperature (a)

Low Temperature (b)

Fig 21.20.

Spontaneous symmetry breaking in a ferromag-net. (a) High temperature, above the critical temperature. Each arrow shows one iron atom's magnetic dipole orientation. Each is randomly oriented, so there is no preferred direction. (b) Low temperature. Now all the dipoles line up, so there is one preferred direction.

Each flavor of quark comes in each of the three colors. The six antiquarks come in corresponding anticolors.

The rule for combining quarks is that we can have only colorless combinations, like those shown in Fig. 21.21. One way of having a colorless combination is to have a quark of one color and an

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