A physical system has chaotic dynamics, according to the dictionary, if its behavior depends sensitively on its initial conditions, that is, if systems of the same type starting out with similar sets of initial conditions can end up in states that are, in some relevant sense, very different. But when science calls a system chaotic, it normally implies two additional claims: That the dynamics of the system is relatively simple, in the sense that it can be expressed in the form of a mathematical expression having relatively few variables, and that the geometry of the system's possible trajectories has a certain aspect, often characterized by a strange attractor.

Chaos theory proper, it should be noted, has its home in classical physics (and other kinds of dynamics that share the relevant properties of classical physics). The extent to which chaotic mathematics is fruitful in understanding the quantum...