THE FUNDAMENTAL PRINCIPLES OF STATISTICAL PHYSICS

Statistical physics consists in the study of the special laws that govern the behavior and properties of macroscopic bodies, that is, bodies formed of a very large number of individual particles, such as atoms and molecules. To a considerable extent, the general character of these laws does not depend on the mechanics (classical or quantum), which describes the motion of the individual particles in a body; however, their substantiation demands a different argument in the two cases. When statistical physics is applied to macroscopic bodies, its probabilistic nature is not usually apparent. The reason is that, if any macroscopic body—in external conditions independent of time—is observed over a sufficiently long period of time, it is found that all physical quantities describing the body are practically constant and equal to their mean values and undergo appreciable changes relatively very rarely. This chapter discusses the properties of the statistical distribution function, Liouville's theorem, the significance of energy and the statistical matrix.