Anomalous cooling and heating - the Mpemba effect and its inverse

Under certain conditions, it takes a shorter time to cool a hot system than to cool the same system initiated at a lower temperature. This phenomenon - the "Mpemba Effect" - is well known in water, and has recently been observed in other systems as well. However, there is no single generic mechanism that explains this counter-intuitive behavior. Using the theoretical framework of non-equilibrium thermodynamics, we present a widely applicable mechanism for this effect, derive a sufficient condition for its appearance in Markovian dynamics, and predict an inverse Mpemba effect in heating: under proper conditions, a cold system can heat up faster than the same system initiated at a higher temperature. Our results suggest that it should be possible to observe the Mpemba effect and its inverse in a variety of systems, where they have never been demonstrated before.