Maximum entropy production

The maximum entropy production (MEP) principle is a proposed physical law stating that non-equilibrium thermodynamic systems evolve toward states that maximize the rate of entropy production, subject to the constraints imposed by boundary conditions and conservation laws. The principle is most often invoked in the context of planetary climate systems, where it has been argued that atmospheric and oceanic circulations self-organize into patterns that are not merely stable but entropy-production-maximizing.

The MEP principle was first proposed independently by Lars Onsager in the context of linear irreversible thermodynamics and later extended to nonlinear systems by Garth Paltridge in the 1970s. Paltridge showed that the observed meridional distribution of temperature and cloud cover on Earth is consistent with a state of maximum entropy production, suggesting that the climate system "selects" its own configuration from among the available stable states according to an extremum principle.

The principle remains controversial. Proponents argue that MEP is a genuine selection principle, analogous to the second law of thermodynamics, that explains why certain dissipative structures are observed rather than others. Critics argue that MEP is either tautological (systems that do not maximize entropy production are not observed because they are unstable) or unfalsifiable (the constraints can always be adjusted to make the observed state the maximizing state). The debate connects to broader questions in non-equilibrium thermodynamics, complex systems theory, and the foundations of statistical mechanics.