�鶹��Ժ

Thermodynamics revisited: Study solves 120-year-old problem and corrects one of Einstein's ideas

Nernst's theorem—a general experimental observation presented in 1905 that entropy exchanges tend to zero when the temperature tends to zero—has been directly linked to the second principle of thermodynamics in a paper in The European �鶹��Ժical Journal Plus, whose sole author is University of Seville professor José Martín-Olalla.

In addition to solving a problem posed 120 years ago, the demonstration is an extension of the consequences linked to the second principle of thermodynamics (the principle that establishes the increasing entropy of the universe). It also corrects an idea put forward more than a century ago by Albert Einstein.

The problem of the Nernst theorem arose at the beginning of the 20th century when the general properties of matter at temperatures close to absolute zero (-273°C) were being studied. Walther Nernst was awarded the Nobel Prize in Chemistry in 1920 for these studies.

As an explanation of his results, Nernst argued that absolute zero had to be inaccessible, because otherwise it would be possible to build an engine that, using absolute zero as a coolant, would convert all heat into work, going against the principle of entropy increase. Thus, he proved his theorem in 1912.

Immediately afterward, Einstein refuted this demonstration by pointing out that such a hypothetical engine could not be built in practice and, therefore, could not question the validity of the principle of entropy increase. Thus, Einstein detached the theorem from the second principle of thermodynamics and associated it to a third principle, independent of the second. This idea is now refuted.

In the demonstration presented, Professor Martín-Olalla introduces two nuances that were omitted by Nernst and Einstein: the formalism of the second principle of thermodynamics, on the one hand, requires the existence of the engine imagined by Nernst, and, on the other hand, that this machine be virtual; the engine does not consume any heat, does not produce any work, and does not question the second principle.

The concatenation of both ideas allows us to conclude that entropy exchanges tend to zero when the temperature tends to zero (which is Nernst's theorem) and that absolute zero is inaccessible.

Martin-Olalla points out that "a fundamental problem in thermodynamics is to distinguish the sensation of temperature, the sensations of hot and cold, from the abstract concept of temperature as a physical quantity. In the discussion between Nernst and Einstein, temperature was merely an empirical parameter: the absolute zero condition was represented by the condition that the pressure or volume of a gas became close to zero.

"Formally, the second principle of thermodynamics provides a more concrete idea of the natural zero of temperature. The idea is not related to any sensation, but to that engine imagined by Nernst but which has to be virtual. This radically changes the approach to the proof of the theorem."

The study points out that the only general property of matter near absolute zero that cannot be related to the second principle of thermodynamics is the cancellation of heat capacities, also compiled by Nernst in 1912. However, Martin-Olalla proposes a different formalization: "The second principle contains the idea that entropy is unique at absolute zero. The cancellation of specific heats only adds that this unique value is zero. It seems more like an important appendix than a new principle."

The professor points out that the publication of this article is a first step toward the acceptance of this novel point of view. "The students in the thermodynamics course I teach were the first to learn about this demonstration. I hope that with this publication the demonstration will become better known, but I know that the academic world has a great deal of inertia."