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Sunday, February 22, 2015

What is Equal Apriori Probability?

A fundamental postulate of statistical mechanics is that a macroscopic system in equilibrium is equally likely to be in any of its accessible microscopic states satisfying macroscopic conditions of system. It is called the postulate of equal apriori probability.

According to this postulate, the probability of finding the phase point for given system in any region of phase space is identical with that for any other region of equal extension or volume. This may also be stated as for a system in equilibrium, all accessible microstates corresponding to a given microstate are equally probable.

The basis for the postulate of Equal Apriori Probability is ergodic hypothesis. The constancy of volume element in phase space with time indicate validity of postulate of Equal Apriori Probability.