““We associate two different terms with this phenomenon: asymptotic freedom and infrared slavery. At one end of the scale, the short distances, the quarks barely affect one another; rather, they act like free particles. At the other end of the scale, the strength of the color interaction sees to it that the quarks remain enclosed inside their particles-the neutrons or protons for which they act as building blocks. This is what we call infrared slavery. When we try to separate one quark from another, the force with which they hold together increases. The energy expended for their separation will then be transformed into the creation of added particles according to Einstein's formula E=mc^2. What this means, in short, is that it is impossible to set a quark free.””
