Entropy, Probability and Atomism

Abstract

In Max Planck’s first lecture delivered at Columbia University in 1909, he explained how physical science was historically organized anthropomorphically—that is, according to man’s particular senses. Thus we had the sciences of optics (what the eye can perceive), acoustics (what the ear can hear) and heat (what the skin can feel). With new apparatus and measurement techniques, however, physical science has become less concerned with subjective sensory experience and more concerned with objective quantification. For example, radio antennae and bolometers have enabled scientists to measure the properties of electromagnetic radiation that lies far outside of the spectrum of visible light. Moreover, the laws of thermodynamics—and especially Clausius’ second law—has inspired a reorganization of physical science into just two classes of phenomena: those which are reversible and those which are irreversible. Unfortunately, according to Planck, this new classification scheme still has the (undesirable) mark of anthropomorphism. For the definition of irreversibility— and the associated concept of entropy—still relies on the skill of an experimenter in devising an efficient heat engine for the purpose of accomplishing useful work. In other words, the purely thermodynamic definition of entropy is based on the inclinations and limitations of man. Is there a better definition of entropy—one which is more objective? This is the question to which Planck now turns in his third lecture…

Nature prefers the more probable states to the less probable, because in nature processes take place in the direction of greater probability.

—Max Planck