In a new publication, Professor José-María Martín-Olalla, from the Department of Condensed Matter Physics at the University of Seville, has described the direct link between the vanishing of specific heats at absolute zero—a general experimental observation established in the early 20th century—and the second law of thermodynamics. The study, published in Physica Scripta, reinterprets a 100-year-old problem and completes the consequences of the principle of increasing entropy in the universe.
The new study follows another published in the European Physical Journal Plus in June 2025, in which Professor Martín-Olalla linked Nernst's theorem (the other general property of matter at absolute zero) with the second law of thermodynamics, correcting an original idea of Einstein's. With these two papers, the two laws of thermodynamics (conservation of energy and entropy increase) would suffice to explain the macroscopic properties of matter across the entire temperature spectrum, now including absolute zero, making a third independent law unnecessary.
Specific heat is the resistance of an object to changing temperature. The vanishing of this property at absolute zero caused a stir in the scientific community in the early 20th century, as there was no explanation for it within classical physics, where a change in temperature is always associated with an exchange of energy. The vanishing of the specific heats implies that at absolute zero, a change in temperature does not require energy exchange. In 1907, Einstein used quantum physics to explain the phenomenon for the first time, which remained disconnected from the second law of thermodynamics and, together with Nernst's theorem, became the third law of thermodynamics.
Professor Martín-Olalla’s study now associates the vanishing of the specific heats at absolute zero with a consequence of the second law of thermodynamics: the stability of equilibrium, which is the property of equilibrium states to persist indefinitely until disturbed by an external action. In this way, the vanishing of the specific heats would have a "classical" thermodynamic explanation, without the need to know whether the system is quantum.
In this paper, Martín-Olalla analyses the general condition of thermal stability, which requires specific heats to be positive at temperatures other than zero, to show that this same condition requires specific heats at absolute zero to be vanished as quickly as the temperature vanishes.
"The microscopic interpretation of the vanishing of the specific heats alludes to the quantum nature of matter, but the paper shows that, in general, nature avoids situations that would lead to an unstable state at absolute zero," summarises Professor Martín-Olalla, adding that "matter behaves near absolute zero as predicted by thermal stability. There is no need for a new principle to codify regular and predictable behaviour."