The theoretical temperature at which all molecular motion ceases. "Absolute zero" may be interpreted as the temperature which the volume of a perfect gas vanishes, or more generally as the temperature of the cold source which would render a Carnot cycle 100 percent efficient. The value of absolute zero is now estimated to be -273.16° Celsius (Centigrade), -459.69° Farenheit, 0°Kelvin, and 0° Rankine.