Experiment (a) and simulation (b) shows how identical red and green particles mix chaotically when gently tumbled in a cylindrical drum. The views correspond to the mixing patterns after 0, 0.25, 0.5, 0.75, and 1 full rotation of the tumbler. The fractal interface between the two populations grows with an unexpectedly high speed.
This research is reported by Troy Shinbrot et al. in Nature, 25 February 1999.