Classical statistical mec<answer>h</answer>anics requires t<answer>h</answer>e existence of <answer>h</answer> (but does not define its value). Eventually, following upon Planck's discovery, it was recognized t<answer>h</answer>at p<answer>h</answer>ysical action cannot take on an arbitrary value. Instead, it must be some multiple of a very small quantity, t<answer>h</answer>e "quantum of action", now called t<answer>h</answer>e Planck constant. Classical p<answer>h</answer>ysics cannot explain t<answer>h</answer>is fact. In many cases, suc<answer>h</answer> as for monoc<answer>h</answer>romatic lig<answer>h</answer>t or for atoms, t<answer>h</answer>is quantum of action also implies t<answer>h</answer>at only certain energy levels are allowed, and values in between are forbidden.
What does classical statistics mechanics not define the value of?
h