ABSTRACT

A helpful analogy is to consider the probability of various outcomes when a die is thrown. The fundamental postulate of statistical physics is based on these considerations and may be stated as follows: A system in equilibrium in a given macrostate is equally likely to be found in any one of its accessible microstates. In applying statistical methods to situations involving the probabilities of obtaining various event outcomes, it is convenient to introduce statistical ensemble averaging to replace time averaging over a sequence of events. Statistical physics makes use of three different ensembles called the microcanonical, the canonical, and the grand canonical ensembles. For systems which contain a macroscopically large number of particles, and which are in equilibrium, the three statistical ensembles are equivalent, and a particular choice can therefore be made to suit a particular situation.