Does macroscopic disorder imply microscopic chaos?

TL;DR

This paper critiques previous claims linking macroscopic disorder to microscopic chaos, clarifying the concept of chaos in extended systems and arguing that macroscopic disorder does not necessarily imply microscopic chaos.

Contribution

It challenges the interpretation of chaos in extended systems and clarifies the distinction between macroscopic disorder and microscopic chaos.

Findings

Macroscopic disorder does not imply microscopic chaos.

The notion of chaos in infinite systems requires clarification.

Some systems without local instabilities can still be considered chaotic.

Abstract

We argue that Gaspard and coworkers [Nature 394, 865 (1998)] do not give evidence for microscopic chaos in the sense in which they use the term. The effectively infinite number of molecules in a fluid can generate the same macroscopic disorder without any intrinsic instability. But we argue also that the notion of chaos in infinitely extended systems needs clarification: In a wider sense, even some systems without local instabilities can be considered chaotic.