Measuring disorder in the quantum realm is creating a bit of a mess. A mathematical study found that three different definitions of entropy that were previously thought to be equivalent don’t always ...

Understanding this properly, it turns out, is not so easy. Our intuitions about entropy mostly come from experience with systems having short-range interactions. Take a dilute gas, for example.

The second law of thermodynamics, which says that a system can never move to a state with lower entropy, or order, is one of ...