In thermodynamics, entropy is a quantity that represents the ability of a system to use its internal energy to do work, and because it is related to the number of possible microstates of the system, it is popularly used as a measure of "chaos" or "disorder". The Second Law of Thermodynamics guarantees that the total entropy of the Universe is always increasing, unlike most other physical quantities, which are conserved. As such, entropy is closely associated with time.
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