— the origin of the absolute temperature; is at $273.16$ K below the triple point of water. Temperature equal to absolute zero, characterizes the ground state of many-particle systems, ie the state with the lowest possible energy (see zero energy), in which atoms and molecules is carried out so-called «zero» oscillations. At absolute zero all substances other than helium are solid crystalline state. From Ernst theorem implies that, in practice, absolute zero is unattainable.