Stability in the dissipative steady state

Stability questions arise in a number of different ways. At the simplest level we can ask about the stability of a particle in a force field. It is stable if any deviations of the particle from its initial location cause it to be exposed to forces returning it back to the initial point. With time, however, “stability” has taken on a broader meaning. We find references to the stability of an orbit, of a laser's mode of oscillation, or of a set of biological populations. Harry L. Swinney and Jerry P. Gollub recently discussed the stability of liquid flow patterns in PHYSICS TODAY (August, page 41). In all of these cases there are questions about the persistence of an initial behavior pattern.