makrostate

Makrostate, or macrostate, is a term used in thermodynamics and statistical mechanics to describe the macroscopic properties of a system while ignoring its microscopic details. A macrostate is specified by coarse-grained variables such as temperature, pressure, volume, energy, magnetization, or particle number. Many different microscopic configurations, or microstates, can realize the same macrostate.

The number of microstates compatible with a given macrostate is called its multiplicity. The Boltzmann relation S = k_B ln Ω links entropy to this multiplicity, where S is entropy, k_B is Boltzmann’s constant, and Ω is the number of microstates corresponding to the macrostate. At fixed energy, particle number, and volume, the system tends toward macrostates with larger multiplicity, i.e., higher entropy. In equilibrium statistical mechanics, macrostates are associated with probability distributions over microstates; ensembles such as the microcanonical, canonical, and grand canonical formalize these ideas.

An everyday illustration is an ideal gas in a rigid container with fixed N, V, and E. The macrostate is specified by these quantities, while the exact positions and momenta of all molecules are the microstate. Although the microstate is unknown, many microstates exist that realize the same macrostate, and macroscopic observables like temperature derive from the energy and particle distribution through the relation between S, E, and other variables.

In broader usage, macrostate can refer to the overall or large-scale state of a system, contrasted with its detailed microstructure. The term makrostate appears in several languages as a direct translation of macrostate, retaining the same fundamental meaning in scientific contexts.