vibrational energy that molecules retain even at the absolute zero of temperature. Temperature in physics has been found to be a measure of the intensity of random molecular motion, and it might be expected that, as temperature is reduced to absolute zero, all motion ceases and molecules come to rest. In fact, however, the motion corresponding to zero-point energy never vanishes.

Zero-point energy results from principles of quantum mechanics, the physics of subatomic phenomena. Should the molecules ever come completely to rest, their component atoms would be precisely located and would simultaneously have precisely specified velocities, namely, of value zero. But it is an axiom of quantum mechanics that no object can ever have precise values of position and velocity simultaneously (see uncertainty principle); thus molecules can never come completely to rest.