- Temperature is a measure of the average kinetic energy of a system particles. When temperature rises, the average kinetic energy of particles also increases.
- Temperature is the degree of hotness, a measure of heat intensity.
Absolute temperature is based on the Kelvin scale. Units on the Kelvin scale are called Kelvins (K) and no degree symbol is used.
The concept of an absolute zero of temperature evolved in connection with experiments with gases. When a fixed mass of gas is cooled at a constant pressure (volume), its volume (pressure) decreases with its temperature. A plot of the experimental values of volume (pressure) versus temperature can be extrapolated to cross the temperature axis when the volume (pressure) would be zero. The temperature is the absolute zero of temperature. It is -273.15 °C, or more approximately -273 °C.
What happens to the matter at absolute zero temperature?
At absolute zero temperature, it's the point at which particles have a minimum energy. Near absolute zero, the matter stops acting the way it should and starts exhibiting some strange properties. Some types of matter become superconducting, carrying electric current with absolutely no resistance, and some of them, like helium, become superfluid at this temperature, exhibiting absolutely no friction, becoming a Bose-Einstein Condensate (BEC). This means that a droplet of superfluid helium can rotate inside a container forever, as if it were in a vacuum.
So far, this temperature has never been achieved, and in theory it could never be achieved. In 1994, the NIST achieved a record cold temperature of 700 nK (billionths of a kelvin). In 2003, researchers at MIT eclipsed this with a new record of 450 pK (0.45 nK).