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The radiation field is used as an example for functional integration calculations. Calculations of fluctuations of both thermal and quantum origin are given. The Landau-Ginzburg functional is used to define the concept of mean function. Fluctuations about the mean functions are discussed. The formal notation of functional integration is used to obtain the statistical-mechanics analog of Noether's theorem. The approach is heuristic, rather than rigorous, throughout.
M. Revzen (Fri,) studied this question.