In physics, absolute zero is a fundamental lower bound on the temperature of a macroscopic system. In practice it is believed to be unachievable but its existence has been inferred from extrapolation from observed physical phenomena and from kinetic theory.
Absolute zero is characterised as 0 kelvin or 0°Rankine (−273.15 °C or −459.67 °F).
History
A state of absolute zero was first proposed by Guillaume Amontons in 1702. Amontons was investigating the relationship between pressure and temperature in gases though he lacked accurate and precise thermometers. Though his results were at best semi-quantitative, he established that the pressure of a gas increases by roughly one-third between the temperatures of "cold" and the boiling point of water. His work led him to speculate that a sufficient reduction in temperature would lead to the disappearance of pressure.
Though absolute zero can be defined in this way, such a definition has practical and conceptual limitations as any real gas will liquefy before attaining a temperature of 0K.
In 1848, William Thomson, 1st Baron Kelvin proposed an absolute temperature scale in which equal reduction in measured temperature gave rise to equal reduction in the heat of a body. This freed the concept from the constraints of the gas laws and established an absolute zero as the temperature at which no further heat could be transfered from a body.
Source: Wikipedia
