macrostaat

In physics, a macrostate (Dutch: macrostaat) describes the macroscopic, observable properties of a system as used in thermodynamics and statistical mechanics. It is specified by variables such as the total energy E, the number of particles N, and the volume V, along with any other conserved quantities or macroscopic constraints (for example magnetization in a magnetic material). A macrostate characterizes what can be measured with ordinary instruments, without reference to the detailed microscopic configuration.

A macrostate does not uniquely determine the system's microscopic arrangement. Many different microstates—specific positions and momenta of all particles—are compatible with the same macrostate. The set of all microstates consistent with a given macrostate is called its degeneracy or multiplicity, often denoted Omega.

The link to entropy is given by Boltzmann's principle: S = k_B ln Omega, where k_B is Boltzmann's constant. Higher Omega means higher entropy. Thermodynamic quantities such as temperature and pressure can be derived from these macroscopic variables and from the dependence of Omega on energy and volume. In large systems, the macroscopic properties fluctuate only weakly around their most probable values.

Statistical ensembles formalize these ideas: the microcanonical ensemble fixes E, N, and V; the canonical ensemble fixes N and V while allowing E to fluctuate around a mean determined by the temperature T. The macrostate concept remains the same across ensembles: it is the emergent, coarse-grained description that governs observable behavior.

The term macrostaat is used in Dutch-language physics literature as an equivalent to macrostate.