The branch of physics that studies the phenomena that occur at very low temperatures; SYN. cryogeny.
Measurement of temperature at extremely low values, i.e., below -200C.
Study of effects of extremely low temperatures.
Science of very low temperatures (approaching absolute zero), including the production of very low temperatures and the exploitation of special properties associated with them, such as the disappearance of electrical resistance (superconductivity).
Low temperatures can be produced by the Joule–Thomson effect (cooling a gas by making it do work as it expands). Gases such as oxygen, hydrogen, and helium may be liquefied in this way, and temperatures of 0.3K can be reached. Further cooling requires magnetic methods; a magnetic material, in contact with the substance to be cooled and with liquid helium, is magnetized by a strong magnetic field. The heat generated by the process is carried away by the helium. When the material is then demagnetized, its temperature falls; temperatures of around 10-3K have been achieved in this way. A similar process, called nuclear adiabatic expansion, was used to produce the lowest temperature recorded: 2 × 10-9K, produced in 1989 by a team of Finnish scientists. At temperatures near absolute zero, materials can display unusual properties. Some metals, such as mercury and lead, exhibit superconductivity. Liquid helium loses its viscosity and becomes a “superfluid” when cooled to below 2K; in this state it flows up the sides
Of its container. Cryogenics has several practical applications. Cryotherapy is a process used in eye surgery, in which a freezing probe is briefly applied to the outside of the eye to repair a break in the retina. Electronic components called Josephson junctions, which could be used in very fast computers, need low temperatures to function. Magnetic levitation (maglev) systems must be maintained at low temperatures. Food can be frozen for years, and freezing eggs, sperm and pre-embryos is now routine.