Logic, methodology and philosophy of science VIII proceedings of the eighth international congress of logic, methodology and philosophy of science, and philosophy of science proceedings) ( PDFDrive ) 52

THE REDISCOVERY OF TIME 33 Fig Finite two-dimensional system of 5400 hard disks under the influence of a thermal gradient and an external force (gravitation) The figures show a typical velocity field: each arrow of the graph is an average over a cell of the velocities of the particles that belong to the cell (typically per cell) Picture (a) presents initial (random) mean velocity densities Picture (c) presents the same mean densities after a few thousand collisions; vortices corresponding to regular flows of particles can now be seen Picture (b) presents the same system under different external constraints; while whirlpools seem indeed to be present, there are no stable ordered structures as they show how the macroscopic instability is prepared by fluctuations Long-range correlations have also been shown recently to play a role in chemical systems, as shown by work under progress by M.Mareschal and A Amellal They lead to spectacular effects; for example, the fluctuation