Allosteric regulation in proteins has been studied for more than 25 years but the fundamental mechanisms of allosteric signalling and the time scales of their propagations remain elusive. Here I describe allostery in the PDZ3 domain stressing the role of side chain atoms with lower degrees of freedom. Interactions are due to concerted (cooperative) motions involving changes in dihedral angles of the side chains. While Brownian motion studies usually emphasize the path taken by the large particle within a solvent bath. I focus instead on the collision event itself: Particle motion is impelled by surrounding molecules moving in a chaotic milieu (high dimensional specification of this motion). When the rare but certain collision event occurs, the particle moves in a linear jump (low dimensional specification of that motion). The multiple time scales are evident because the particle motion is a very rare event compared to the extremely fast motions of the surrounding smaller molecules. I argue that protein side chain interactions involve a similar generation of motion in atoms with lower degrees of freedom due to the action of atoms with higher degrees of freedom starting with the solvent itself.