, Volume 29, Issue 6, pp 621-635

Level I theory of large deviations in the ideal gas

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LetX 1,X 2,... be i.i.d. random elements (the states of the particles 1,2,...). Letf be an ℝd-valued, measurable function (an observable) and letB ⊂Rdbe a convex Borel set. DenoteS n=f(X1)+f(X2)+...+f(Xn). Using large-deviation theory, it may be shown that, under certain regularity conditions, there exists a point υB (the dominating point of B) so that, givenS n/nε B, actually Sn/n→υ B in probability as n→∞. Having this conditional weak law of large numbers as our starting point, we consider physical systems of independent particles, especially the ideal gas. Given an observed energy level, we derive convergence results for empirical means, empirical distributions, and microcanonical distributions. Results are obtained for a closed system with a fixed number of particles as well as for an open particle system in the space (a Poisson random field). Our approach is elementary in the sense that we need not refer to the abstract “level II” theory of large deviations. However, the treatment is not restricted to the so-called discrete ideal gas, but we consider the continuous ideal gas.