# Microstate (statistical mechanics)

## Specific microscopic configuration of a thermodynamic system / From Wikipedia, the free encyclopedia

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In statistical mechanics, a **microstate** is a specific configuration of a system that describes the precise positions and momenta of all the individual particles or components that make up the system. Each microstate has a certain probability of occurring during the course of the system's thermal fluctuations.

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In contrast, the **macrostate** of a system refers to its macroscopic properties, such as its temperature, pressure, volume and density.^{[1]} Treatments on statistical mechanics^{[2]}^{[3]} define a macrostate as follows: a particular set of values of energy, the number of particles, and the volume of an isolated thermodynamic system is said to specify a particular macrostate of it. In this description, microstates appear as different possible ways the system can achieve a particular macrostate.

A macrostate is characterized by a probability distribution of possible states across a certain statistical ensemble of all microstates. This distribution describes the probability of finding the system in a certain microstate. In the thermodynamic limit, the microstates visited by a macroscopic system during its fluctuations all have the same macroscopic properties.

In a quantum system, the microstate is simply the value of the wave function.^{[4]}