Number 72 (Story #3), March 23, 1992 by Phillip F. Schewe and Ben Stein CHEMICAL REACTIONS ON REDUCED-DIMENSIONALITY SURFACES , where diffusion processes are limited, do not conform to the classical laws of chemical kinetics. For example, when reactants meet on spatially-constrained (sometimes fractal) surfaces like microscopic pores or capillaries, they can, under certain non-equilibrium conditions, come to order spontaneously: instead of mixing, like reactants will aggregate while unlike reactants segregate. Convection currents, usually the predominant means for chemical mixing, have no room to form on these confined surfaces. At the March APS meeting, Raoul Kopelman of the University of Michigan described the first experimental evidence for this effect. In his experiment, he added two chemicals of contrasting colors to opposite ends of a gel-filled tube. When the chemicals met in the center and attempted to react on the gel surface, they formed two segregated regions, with the reaction rate between the chemicals actually diminishing in time. In addition to being understirred, chemicals on low-dimensional surfaces have a smaller probability of straying from their original positions and encountering atoms of different species. Kopelman says that reactions on low-dimensional surfaces occur in such processes as photosynthesis and photocatalysis, and play a role in population biology models and some theories of structure formation in the early universe.