The [[second law of thermodynamics]] predicts that such entropy should increase until equilibrium. But under the theory of statistical mechanics there would always be a nonzero probability that the entropy of an isolated system will spontaneously decrease. The fluctuation theorem precisely quantifies such probability under the theory of statistical mechanics. | The [[second law of thermodynamics]] predicts that such entropy should increase until equilibrium. But under the theory of statistical mechanics there would always be a nonzero probability that the entropy of an isolated system will spontaneously decrease. The fluctuation theorem precisely quantifies such probability under the theory of statistical mechanics. |