# How did Planck use the concept of statistical entropy in trying to understand the meaning of his own law?

I was reading Introducing Quantum Theory: A graphic guide (by J.P.McEvoy & Oscar Zarate) and came across Planck's predicament of understanding his very own law that accurately explained the blackbody radiation. It says (in the voice of Planck):

... From the very day I formulated the radiation law, I began to devote myself to the task of investigating it with true physical intuition. After trying every possible approach using traditional classical applications of laws of thermodynamics, I was desperate. But forcefully I was compelled to consider statistical version of the second law $$S = k .\log{W}$$ that I rejected and hated the most. After some of the most intense weeks of my life, the light began to appear to me ... The light was energy is not continuous but discrete in nature.

That was hard indeed! But why did he hate the Boltzmann's version of entropy??

Nevertheless, my question is: How did Mr. Planck use the entropy concept to come to the revolutionary conclusion that energy is discrete ? Please give me a math-free explanation.

• I've added the history tag to your interesting question. I am assuming you would like a citation or quote that both validates Planck's opinion and also records the reasons why he felt as he did. Nov 27, 2014 at 7:29