New Criticals

Being a dissipative structure implies some formal criteria for the entropy production of a system.  Remember that the second law says that irreversible processes must always be accompanied by an increase in entropy. For an isolated system that cannot exchange matter or energy with its surroundings, this results in the boring prediction that the system will evolve into the state with the highest possible entropy and then do nothing. For an open system, however, which is capable of exchanging matter and energy with its environment, we may split the entropy change term into one term representing the entropy change as a result of processes internal to the system and another term representing the entropy change as a result of flows into and out of the system, like so:

∆S = ∆Si + ∆Se

The second law requires that ∆Si, the entropy change due to irreversible processes internal to the system, be positive. It is thus a measure of the energetic cost of maintaining a particular non-equilibrium organization. But the second law places no constraint on the sign of ∆Se, the term for the entropy exchanged with the environment. Schrodinger’s “What is life?” (1944) is generally considered to be the first modern work of biophysics, and it contains a number of vague insights which provided the basis for the mathematical formalization of these ideas in the work of Prigogine and Morowitz. Schrodinger understood that life could not be violating the second law, despite naive appearances, but the connections between entropy and organization were far from understood at this point. Schrodinger knew, however, that the act of eating and breathing was a way of “concentrating a stream of order", or "negative entropy” upon the organism.

So for any system that can exchange matter or energy with its surroundings, the possibility arises that ∆Se is negative and greater in magnitude than ∆Si, rendering the overall entropy change of the system negative. Such a system will be spontaneously driven into higher energy states by flows of matter and energy seeking to dissipate the potential difference between the external source and sink. These dissipative flows through the system represent its internal organization. So that’s what is meant by the term “non-equilibrium organization.” We will revisit this topic when we discuss the chemistry of eating and breathing (oxidative phosphorylation) in depth.