The theoretical temperature at which molecular motion vanishes and a body would have no heat energy; the zero point of the Kelvin and Rankine temperature scales. Absolute zero may be interpreted as the temperature at which the volume of a perfect gas vanishes or, more generally, as the temperature of the cold source that would render a Carnot cycle 100 percent efficient. The value of absolute zero is not estimated to be -273. 15° Celsius, -459. 67° Fahrenheit, 0° Kelvin, and 0° Rankine.