Fluctuations and Order

The volume that you have before you is the result of a growing realization that fluctuations in nonequilibrium systems playa much more important role than was 1 first believed. It has become clear that in nonequilibrium systems noise plays an active, one might even say a creative, role in processes involving self-organization, pattern formation, and coherence, as well as in biological information processing, energy transduction, and functionality. Now is not the time for a comprehensive summary of these new ideas, and I am certainly not the person to attempt such a thing. Rather, this short introductory essay (and the book as a whole) is an attempt to describe where we are at present and how the viewpoint that has evolved in the last decade or so differs from those of past decades. Fluctuations arise either because of the coupling of a particular system to an ex­ ternal unknown or "unknowable" system or because the particular description we are using is only a coarse-grained description which on some level is an approxima­ tion. We describe the unpredictable and random deviations from our deterministic equations of motion as noise or fluctuations. A nonequilibrium system is one in which there is a net flow of energy. There are, as I see it, four basic levels of sophistication, or paradigms, con­ cerning fluctuations in nature. At the lowest level of sophistication, there is an implicit assumption that noise is negligible: the deterministic paradigm.

This book is the result of a growing realization that fluctuations play an active, even creative, role in nonequilibrium processes such as self-organization, pattern formation, and information processing and energy transduction in biological systems. In contrast to the general notion that fluctuations represent an undesirable 'noise' in such systems-unimportant at best and undesirable or disruptive at worst-this book points toward a view in which fluctuations are fundamental aspects of the systems under study and frequently serve a constructive or stabilizing role in the dynamics. It includes contributions by prominent researchers in a great variety of disciplines, from theoretical cosmologists to experimental biologists, on such topics as stochastic resonance, noise in sensory nervous systems, mechanisms of intracellular transport, and kinetic theory of nonequilibrium systems.