Thermalize

Thermalize is a verb meaning to bring a system into thermal equilibrium, or to allow it to reach a state in which its macroscopic properties are described by a single temperature. In thermodynamics, a system thermalizes when it exchanges energy with its surroundings or among its parts until a uniform temperature is established throughout and no net energy flows between the system and its environment.

In classical many-particle systems, thermalization occurs through repeated interactions and collisions that redistribute energy among degrees of freedom, driving the system toward the Maxwell-Boltzmann distribution. In an isolated system this progression defines a thermal equilibrium state; when the system is in contact with a heat bath, the equilibrium is defined by the bath temperature.

In quantum systems, thermalization refers to approaching a thermal (Gibbs) state as described by statistical mechanics. The eigenstate thermalization hypothesis suggests that energy eigenstates encode thermal properties for typical superpositions, explaining how closed, non-integrable systems can thermalize. Conversely, integrable systems or those exhibiting many-body localization may fail to thermalize, retaining memory of initial conditions.

Timescales for thermalization depend on interaction strength, particle density, dimensionality, and coupling to environments. Examples include a gas in a sealed container reaching a uniform temperature, ultracold atomic gases equilibrating after perturbation, and plasmas exchanging energy with surrounding matter.

The term also appears in experimental and applied contexts, where reaching a designated temperature or steady-state is part of a measurement or process. Overall, thermalization describes the process by which a system evolves toward a common temperature and a state describable by equilibrium thermodynamics.