Absolute zero

Absolute zero, temperature (0°K [kelvin]/-273.15°C/-459.67°F) at which all substances have zero thermal energy and thus, theoretically, the lowest possible temperature. Originally conceived as the temperature at which an ideal gas at constant pressure would contract to zero volume, absolute zero is of great significance in thermodynamics and is used as the fixed point for the absolute, or kelvin, temperature scale. In practice the absolute zero temperature is unattainable, although temperatures within a few millionths of 0°K have been achieved in cryogenics laboratories.

See also: Gas; Temperature.