irreversibility

Definition: The property of a system that precludes a change to the system from being a reversible process. The paradox that although the equations describing the bodies in a system, such as Newton's laws of motion, Maxwell's equations, or Schrödinger's equation are invariant under time reversal, events involving systems made up of large numbers of these bodies are not reversible. The resolution of this paradox requires the concept of entropy using statistical mechanics.