[AntonioLao]

It took a very long time (about 30 years) for physicists to gradually accept the fact that absolute entropy exists. At absolute zero of temperature the absolute entropy is also absolutely zero. This phenomenological limit is known as the heat theorem or Nernst’s theorem or simply stated as the 3rd law of thermodynamics. It is theoretically believed that an atom or molecule with zero entropy exists in only one quantum state. Its energy is known precisely with absolute certainty. This does violate the uncertainty principle. On the other hand, since absolute zero cannot be measured by finite steps of temperature decreases (see principle of unattainability, pp 92-93, Pauli Lectures on Physics, Volume 3, Thermodynamics and the Kinetic Theory of Gases, Dover Edition, 2000), quantum mechanics (QM) remains valid in the infinitesimal positive neighborhood of zero. However, at absolute zero it can only imply a return to determinism as envisioned by Einstein for completing QM.

Seemingly, it is this implied violation of the uncertainty principle that prevented any mention of Nernst’s theorem in most books on QM. However, Pauli, Schrödinger, Fermi, Feynman, and many others accepted it as a true physical law without bothering to give a rigorous proof. Nonetheless, zero temperature is not equivalent to zero heat. Since heat is just a form of thermal energy and zero thermal energy means thermal equilibrium, input equals output for a closed system. Nernst developed his theorem in 1906 in order to understand the idealized nature of any chemical equilibrium. It was probably for this reason that he was awarded the 1920 Nobel Prize for chemistry instead of physics.