Microstate (statistical mechanics)

A macrostate describes in thermodynamics and statistical physics, a system with many degrees of freedom ( ie, for example, a gas consisting of 1 mol ~ single particle is ) by a few state variables, such as energy, temperature, volume, pressure, chemical composition or magnetization.

In mechanics can be a system of particles described completely by each particle, one associates a position and velocity vector. This is called a microstate. This can be represented by a point in phase space.

However, many particles (), it is practically impossible to determine the initial state or a microscopic to solve the equation of motion for the system. In chaotic systems, the determination of the orbit of the system is also impossible in principle, since small changes in initial conditions lead to arbitrarily large deviations.

However, the microscopic solution of the equation of motion is also not necessary, since the macroscopic properties depend only on a few parameters.

At any given macrostate, which is determined by a few macroscopic state variables, many microstates are possible. These form a continuous whole distributed in phase space. The macro state is thus determined by a statistical concept ( probability distribution of microstates ). The fluctuations of the macroscopic quantities are negligible due to the high particle numbers.

With macroscopic quantities can be set up as macroscopic, deterministic laws. If one knows, for example, for a gas, the macroscopic state variables volume, temperature and number of particles, so the pressure can be clearly calculated ( Thermal equation of state of ideal gases ).