Details

In this model, a "microstate" at time is characterized by quantities: the color (black or white) of balls sitting on each of the sites. A "macrostate" at time is characterized by a single coarse-grained quantity: the difference between the numbers of white and black balls, relative to the total number . The microscopic dynamics are reversible [2] and recurrent [3] (the microstate repeats itself after time steps). However, under a molecular chaos assumption (the fraction of white balls just about to cross a tunnel is assumed to be at any time) [4], the irreversible evolution equation is expected to be correct in the limit .

In this Demonstration, all the balls are white initially. You can control the total number of sites , the fraction of bonds with a tunnel and the time range to display. You can choose to follow the temporal evolution of the macrostate or the microstate.

References

[1] G. A. Gottwald and M. Oliver, "Boltzmann's Dilemma: An Introduction to Statistical Mechanics via the Kac Ring," SIAM Review, 51(3), 2009 pp. 613–635. doi:10.1137/070705799.

[2] Wikipedia. "Loschmidt's Paradox." (Oct 3, 2016) en.wikipedia.org/wiki/Loschmidt's_paradox.

[3] Wikipedia. "Poincaré Recurrence Theorem." (Oct 3, 2016) en.wikipedia.org/wiki/Poincaré_recurrence_theorem.

[4] Wikipedia. "Molecular Chaos." (Oct 3, 2016) en.wikipedia.org/wiki/Molecular_chaos.