rethermalize

Rethermalize refers to the process by which a system that has been driven out of thermal equilibrium returns to a thermal (or near-thermal) energy distribution. In classical and quantum contexts, this means the population of energy states evolves toward the appropriate equilibrium form, such as Maxwell-Boltzmann, Fermi-Dirac, or Bose-Einstein statistics, depending on the statistics obeyed by the particles involved.

In theoretical treatments, rethermalization is described by kinetic equations such as the Boltzmann equation or quantum kinetic formalisms. These frameworks encode conservation laws for energy, momentum, and particle number, and show how collisions or interactions redistribute energy and momentum among degrees of freedom, gradually erasing non-thermal features introduced by perturbations. The process can be influenced by factors such as dimensionality, interaction strength, and external constraints, and it may proceed through intermediate states or quasi-equilibria before full thermalization.

Mechanisms that drive rethermalization include elastic collisions that redistribute kinetic energy, inelastic processes that change internal states, and coupling to other degrees of freedom such as lattice vibrations or radiation fields. In quantum systems, effects like Pauli blocking and coherence can modify relaxation pathways and rates. The timescale for rethermalization varies widely—from microseconds to seconds in ultracold atomic gases, to femtoseconds or picoseconds in plasmas or solids—depending on density, cross sections, and available relaxation channels. Some systems exhibit prethermalization, reaching a long-lived quasi-equilibrium distribution before true rethermalization completes.

Rethermalization is a central concept in non-equilibrium statistical mechanics and experimental studies of relaxation dynamics, including ultracold gases, solid-state systems, and high-energy plasmas, helping to understand how complex many-body systems return to equilibrium after disturbance.