The Contributory Revolution

Appendix: Scientific and Philosophical Comments

A.1. The articulation between the concepts of entropy and (dis)order

In physics, the articulation between the concepts of entropy and (dis)order is a conceptual approximation that can be misleading and must be discussed with great care. In short, the increase of entropy in a physical system is the process of moving from less probable macroscopic states to more probable ones. It follows that the increase of entropy is the disappearance of unlikely initial characteristics and their replacement by more probable ones, i.e. the erasure of the past as far as energy constraints allow. In many situations – though not all – statistical mechanics defines probabilities by assuming that all states of the same energy have the same probability. In these situations, the increase in entropy is the dispersion of energy. However, it should be kept in mind that this dispersion occurs at the level of the phase space, describing the possible microscopic states and including both positions and velocities. Therefore, the increase in entropy cannot be confused with the simple disappearance of patterns in the system’s spatial configuration. Let us take an example. Water can be in a liquid state below 0°C, in a metastable state; this situation is called supercooling. Let us put this water in a completely insulated box: the energy is conserved according to the first principle and the entropy can only increase according to the second principle. What happens ...