Typically, after a physical system is disturbed, it can gradually return toward a state of thermal equilibrium by exchanging heat with its surroundings. Thermal equilibrium is a state in which there is no net transfer of heat between the system and its surroundings.

One may assume that the further a disturbed system is from equilibrium, the longer it will take for it to settle. Under some conditions, however, the opposite occurs, and systems that start farther from equilibrium approach it faster than those that start closer. This counterintuitive phenomenon is known as the Mpemba effect.

In some cases, the Mpemba effect occurs because different components of a system’s initial disturbance fade at different rates, and if a system’s starting state does not contain the slowest-decaying components, it can approach equilibrium faster. This is the main idea behind the so-called strong Mpemba effect.