  General equilibrium equations in economics play the same role with many-body
Newtonian equations in physics. Accordingly, each solution of the general
equilibrium equations can be regarded as a possible microstate of the economic
system. Since Arrow's Impossibility Theorem and Rawls' principle of social
fairness will provide a powerful support for the hypothesis of equal
probability, then the principle of maximum entropy is available in a just and
equilibrium economy so that an income distribution will occur spontaneously
(with the largest probability). Remarkably, some scholars have observed such an
income distribution in some democratic countries, e.g. USA. This result implies
that the hypothesis of equal probability may be only suitable for some "fair"
systems (economic or physical systems). From this meaning, the non-equilibrium
systems may be "unfair" so that the hypothesis of equal probability is
unavailable.
