I'm seeing a lot of misinformation / misunderstanding in the comments. My PhD was primarily about nonequilibrium statistical physics, so let me try to give a si

I'm seeing a lot of misinformation / misunderstanding in the comments. My PhD was primarily about nonequilibrium statistical physics, so let me try to give a simple explanation of free energy and its relevance for biological systems. 1. The free energy is a concept from _equilibrium_ statistical physics. Most simply, it accounts for a balance between minimizing energy (what systems do at low temperature) and maximizing entropy (when systems become disordered, as happens at high temperatures). The interesting regime is at temperatures where the energetic and entropic contributions are both important. 2. In biology / biophysics, this is a heavily used concept. For example, the most likely configuration of a protein (that is, the arrangement of the atoms in the molecule) minimizes the free energy. Of course, there are fluctuations, and the "free energy surface" can have multiple minima, corresponding to different states. This is an approximation that usually works because on small scales, the environment of a protein can often be equilibrium like. 3. The idea that a biological systems maintain a nonequilibrium steady state (all living systems are out of equilibrium) by minimizing a free energy functional is kind of like the hidden variables hypothesis in quantum mechanics. Basically, the conjecture described in the articles is that there's some unknown free energy that you can write down (similar to a graphical model with hidden variables) that the cell is trying to minimize. 4. It should be emphasized that this perspective is attempting to map a nonequilibrium system onto an equilibrium system and there are many cases where such a correspondence is impossible (formally all equilibrium systems have a probability distribution called a boltzmann distribution and some nonequilibrium systems have statistics that simply cannot be captured by such a distribution). 5. To editorialize, because nonequilibrium steady states are fundamentally dynamical, I would not be willing to endorse this view. Ultimately, this "principle" asserts that there is some non-dynamical state function for the dynamical systems encountered in biology.