Science concerned with the production and maintenance of very low temperatures, and with the effects that occur under such conditions. Although it is impossible to reach absolute zero, a temperature as low as about one millionth of a degree on the Kelvin scale above absolute zero can be attained.

Low temperatures are achieved by removing energy from a substance. By using a succession of liquefied gases, a substance may be cooled to as low as 4.2°k, the boiling point of liquid helium.

Still lower temperatures may be reached by successive magnetization and demagnetization. Some unusual conditions, notably superconductivity and super fluidity, prevail at cryogenic temperatures.