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Center for Nonlinear Studies |
Although macroscopic irreversibility was explained by Boltzmann as being due to a probabilistic evolution toward more probable states, he did not explain how it actually happens. In classical statistical mechanics, irreversibility is closely related to chaotic particle evolution. However, it is difficult to explore this dynamics experimentally, because it is usually impossible to reverse the velocities of particles or fluid elements. However, a direct experimental test is in fact possible in fluids at low Reynolds number. In this talk I will describe this experiment, which shows that irreversibility has a surprising threshold behavior if the fluid contains particles (suspensions). Numerical simulations allow us to connect the irreversibility to the chaotic dynamics of interacting particles.[1] A second example of irreversibility shows how the mixing or chemical reaction of two stirred fluids actually takes place.[2] [1] This work was done jointly with D.J. Pine, J. Brady, and A. Leshansky; Nature 04380 (2005) plus subsequent unpublished work.. [2] P.E. Arratia and J.P. Gollub Predicting the progress of diffusively limited chemical reactions...", Phys. Rev. Lett. 96, 024501 (2006). Supported by NSF DMR-0405186
Host: Robert Ecke, T-CNLS