Focus: Waves Will Be Waves  Published June 8, 1998  |  Phys.
Rev. Focus 1, 19 (1998)  |  DOI: 10.1103/PhysRevFocus.1.19  Wave
Optics in Reaction-Diffusion Systems  Joaquim Sainhas and Rui
Dilão  Published June 8, 1998 Figure 1  Chemical ripple tank.
Computer simulations of concentration waves generated at the top
left refract at the interface of two media according to Snell’s
law (from Phys. Rev. Lett. 80 , 5216).  Nature sometimes adds a
twist to the familiar type of diffusion where molecules simply
wander along through a medium, ignoring one another most of the
time. In reaction-diffusion systems, molecules react chemically
with each other when they collide, so a chemical wave can
propagate as the concentrations of the components change. These
chemical waves, claims a report in the 8 June issue of PRL,
conform to Snell’s law–the simple rule that dictates the angles
of reflection and refraction when light waves hit an interface.
The authors mathematically derive the phenomenon, which was
observed by others,