On the Statistical Viewpoint Concerning the 2nd Law of Thermodynamics a   Reminder on the Ehrenfests' Urn Model
  In statistical thermodynamics the 2nd law is properly spelled out in terms of conditioned probabilities. As such it makes the statement, that `entropy increases with time' without preferring a time direction. In this paper I try to explain this statement--which is well known since the time of the Ehrenfests--in some detail within a systematic Bayesian approach. 
Domenico Giulini