The fundamental physical constant, often denoted as k and equal to 1.38 x 10-23 J/K, is called Boltzmann's constant. This constant plays an important role in statistical mechanics. In the late nineteenth century Austrian physicist Ludwig Eduard Boltzmann first recognized the important connection between entropy and probability. He began studies investigating the relationship between the temperature and the energy distribution of molecules in a gas. During these studies he laid the foundations of statistical mechanics by applying the laws of mechanics and the theory of probability to the motions of atoms.

The kinetic theory of gases pictures a gas as composed of a very large number of molecules whose size is small compared with the average distance between molecules. The molecules move rapidly and freely through space. From 1870 to 1910 a controversy raged between two groups of scientists, the Energetics and the Atomists regarding the...