absolute zero

Science Dictionary
absolute temperature scale  
A temperature scale having absolute zero as the lowest temperature. Absolute temperature scales only have positive numbers. The Kelvin scale and the Rankine scale are absolute temperature scales. Compare relative temperature scale.
American Heritage
Science Dictionary
absolute zero  
The lowest possible temperature, at which all molecules are have the least possible amount of kinetic energy. Absolute zero is equal to 0°K, -459.67°F, or -273.15°C. At temperatures approaching absolute zero, the physical characteristics of some substances change significantly. For example, some substances change from electrical insulators to conductors, while others change from conductors to insulators. Absolute zero has never been reached in laboratory experiments. See also Bose-Einstein condensate, zero-point energy.

Our Living Language  : The temperature of a substance is determined by the average velocity of its molecules: the faster they move, the warmer the substance. At absolute zero molecules have minimal kinetic energy (or zero-point energy) and heat energy cannot be extracted from them. The molecules are not motionless, however, due to the uncertainty principle of quantum mechanics, which entails that the atoms cannot have both a fixed position and zero momentum at the same time; instead, the molecules of a substance at absolute zero are always "wiggling" in some manner. Absolute zero is zero degrees Kelvin, equal to -273.15 degrees Celsius and -459.67 degrees Fahrenheit. The coldest known place in the universe is the Boomerang Nebula, where the temperature is -272° Celsius. Scientists at Massachusetts Institute of Technology have gone much lower than that by using laser traps and other techniques to cool rubidium to 2 × 10-9 degrees Kelvin.

The American Heritage® Science Dictionary
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