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In electromagnetic interaction the Coulomb's inverse square law becomes increasingly inadequate at small separation between the two charges because they begin to penetrate the virtual electron-positron shield as shown in part (a) of Figure 15-07 and 15-08. A parallel phenomenon exists in strong interaction. However, there is the additional virtual gluon shielding, which has the opposite effect and produce the apparent strength of the colour charge as shown in part (b) of Figure 15-08. It shows that the interaction strength falls off with decreasing separation. At very small separation the quarks appear as free -- not interacting with each other. Thus at small separation, the methods of perturbation theory is applicable again to calculate quantities of physical interest. |