Cryogenics is the science of dealing with the production of and effects of very low temperatures. However, there’s some debate over how low ‘low temperature’ must be to qualify as cryogenic. Some say lower than -1000C. Others, such as NIST, put it at below -1500C. At these temperatures most gases become liquid, which gives them some interesting uses. Cryogenic temperatures are mostly produced through the Joule-Thomson effect, which takes advantage of the relationship between pressure, temperature, and volume.