absolute zero

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.