In this post I’d like to begin shifting focus from general thermodynamic considerations to a more detailed discussion of the emergence of life, but let’s begin with an overview of how the laws of thermodynamics both constrain and enable the possibilities of living organizations.
Some jargon: A living organism is an informed, autocatalytic, non-equilibrium organization. Each of these words expresses specific enabling constraints related to the conditions of energy flow through organisms. In this post I treat the catalytic and the non-equilibrium aspects and briefly introduce the concept of information. The next post will discuss more detailed aspects of information and complexity, as well as the meaning of autocatalysis (self-making). But we begin with the most central concept: an organism is a non-equilibrium organization.
What this expresses is the simple fact that any living system is in a higher energy state than the corresponding material in a non-living state would be. Simply put, you are hotter than the room, and one really crude way of telling how long someone has been dead is to check their temperature. So we have an intuition that life depends on the maintenance of this higher energy state, and our experience first reveals this dependence to us a constraint: We have to keep eating and breathing and we have to stay warm. To understand why, however, we have to understand what this constraint enables: All non-equilibrium distributions of matter are to some extent more organized than the corresponding equilibrium distribution would be. This is the converse of the classical version of the second law. Our classical understanding of entropy was based on the fact that the microscopically random motions of heat flow cannot ever be completely converted into directed motion, which we call “work.” So it basically said that no process can be 100% efficient. Well for exactly the same statistical reasons, no process can be 100% inefficient either. You can’t have heat flow through a system without, at the very least, having higher average kinetic energies near the source (hot thing) than the sink (cold thing). This idea comes from H. J. Hamilton.