The entropy of a system, if left alone, will always increase: that is, a system will always relax from a ‘special’ (ordered) state to a less special (mixed-up) one. Physical systems unwind, cool down, and wear out. This is referred to as the second law of thermodynamics, and at its heart it is no more than a statement of statistical inevitability: if left alone, everything always eventually returns to a state of equilibrium.
