The entropy of an isolated system will always increase (more precisely, it will never decrease).

To illustrate this principle, first of all, let's say the second law of thermodynamics in another way: all spontaneous processes of isolated systems are developing in a more disorderly direction, and it is impossible to restore the system to its original orderly state unless the outside world does work on it. In addition, the more chaotic the microscopic state, the greater the entropy value of the system, and vice versa. Therefore, the entropy of isolated systems will increase forever.

Entropy increasing principle: In an isolated system, all irreversible processes are bound to go in the direction of entropy increasing, which is the entropy increasing principle.

The principle of entropy increase is another expression of the second law of thermodynamics, which points out the direction of irreversible process more generally than Kelvin and Clausius. At the same time, it is pointed out that the second law of thermodynamics is a statistical law of random motion of a large number of molecules, so it is only applicable to the system composed of a large number of molecules, not to the system composed of a single molecule or a small number of molecules.