The above abstract definition of a volume is required as the appropriate setting for definitions of ergodicity in physics. Consider a container of liquid, or gas, or plasma, or other collection of atoms or particles. Each and every particle formula_85 has a 3D position, and a 3D velocity, and is thus described by six numbers: a point in six-dimensional space formula_86 If there are formula_39 of these particles in the system, a complete description requires formula_88 numbers. Any one system is just a single point in formula_89 The physical system is not all of formula_90, of course; if it's a box of width, height and length formula_91 then a point is in formula_92 Nor can velocities be infinite: they are scaled by some probability measure, for example the Boltzmann–Gibbs measure for a gas. None-the-less, for formula_39 close to Avogadro's number, this is obviously a very large space. This space is called the canonical ensemble.