Thermodynamics, the branch of physics concerned with the description of macroscopic bodies, heat exchange and the conversion of different forms of energy is based on four laws: the zeroth law, which states that bodies in thermal contact reach a state of thermal equilibrium, the first law, which postulates the energy conservation and establishes the way in which different forms of energy transform into each-other, the second law, which states that the entropy increases or stays constant in time in any isolated system, and, finally, the third law (or Nernst postulate), which states that the entropy of any system approaches a constant minimum when temperature approaches 0 K. One of the direct consequences of the third law is that the specific heat of any system converges to zero when its temperature decreases to zero Kelvins. Here we show that the third law is violated in a wide class of fermionic systems, by calculating the specific heat and showing that it diverges to infinity when the absolute zero temperature is approached. Until now, no exception to these four laws is know in physics. These findings ask for the revision of one of the most fundamental laws of nature.
Thermodynamics, the branch of physics concerned with the description of macroscopic bodies, heat exchange and the conversion of different forms of energy is based on four laws: the zeroth law, which states that bodies in thermal contact reach a state of thermal equilibrium, the first law, which postulates the energy conservation and establishes the way in which different forms of energy transform into each-other, the second law, which states that the entropy increases or stays constant in time in any isolated system, and, finally, the third law (or Nernst postulate), which states that the entropy of any system approaches a constant minimum when temperature approaches 0 K. One of the direct consequences of the third law is that the specific heat of any system converges to zero when its temperature decreases to zero Kelvins. Here we show that the third law is violated in a wide class of fermionic systems, by calculating the specific heat and showing that it diverges to infinity when the absolute zero temperature is approached. Until now, no exception to these four laws is know in physics. These findings ask for the revision of one of the most fundamental laws of nature.
A system, or a set of systems, is said to be in thermal equilibrium when no net flow of heat energy occurs between its constituent parts when they are connected by a path permeable to heat (a diathermal wall).1 This condition is the endpoint of a spontaneous process: if two bodies at different temperatures are brought into thermal contact, energy will flow from the higher-temperature object to the lower-temperature object until this flow ceases and the equilibrium state is achieved.3 Within a single system, thermal equilibrium is characterized by a temperature that is both spatially uniform (the same at all points) and temporally constant (unchanging over time).4 This uniformity of macroscopic properties—such as temperature and pressure—is what defines the state of the system.1 It is important to distinguish this from the broader state of thermodynamic equilibrium. Thermal equilibrium (uniform temperature) is a necessary component, but full thermodynamic equilibrium also requires mechanical equilibrium (uniform pressure) and diffusive equilibrium (uniform chemical potential).6 Systems can achieve thermal equilibrium without achieving full thermodynamic equilibrium.6 The Zeroth Law of Thermodynamics: The "Discovery" of Temperature The concept of temperature, while intuitive, requires a formal physical principle to exist as a measurable, fundamental property. This principle is the Zeroth Law of Thermodynamics. Although it was formulated and named after the First and Second Laws, its foundational role was recognized as a logical prerequisite for the entire structure of thermodynamics.8 The law states: If system A is in thermal equilibrium with system C, and system B is in thermal equilibrium with system C, then systems A and B are in thermal equilibrium with each other.1 In this construction, system C plays the role of a thermometer.13 The profound implication of this law is mathematical: it establishes thermal equilibrium as a transitive relation 9, or more formally, an equivalence relation.14 In mathematics, any equivalence relation partitioning a set of objects implies the existence of a common, scalar property shared by all members of a given equivalence class. The Zeroth Law thus proves the existence of a scalar function of state—a property we call temperature—that is common to all systems in mutual thermal equilibrium.9 The law is, therefore, the fundamental basis for defining temperature and building consistent, reproducible temperature scales.1 This axiomatic foundation also provides the logical origin for one of temperature's most critical characteristics: it is an intensive property. An intensive property is one that does not depend on the size or amount of the system.15 If a large system 'A' is in internal thermal equilibrium 6, any two parts of it, subsystems 'A1' and 'A2', must also be in thermal equilibrium with each other. By the Zeroth Law, a thermometer 'C' that is in thermal equilibrium with the whole system 'A' must also be in thermal equilibrium with 'A1' and 'A2' individually.13 The thermometer, therefore, gives the same reading for all three. This demonstrates that the temperature of a system in thermal equilibrium is the same as the temperature of any part of it.16
Abstract The third law of thermodynamics has two classical formulations: Nernst’s heat theorem (entropy change ΔS→0 as T→0) and the unattainability principle (absolute zero cannot be reached in a finite number of steps). Quantum statistical mechanics challenges Nernst’s theorem through residual entropy in systems such as quantum spin liquids and spin ice, which retain nonzero entropy even as T→0. Landauer’s principle connects information erasure with heat dissipation, implying that reaching absolute zero is equivalent to deleting all information from a system. This paper proposes that physical reality comprises two information-carrying sectors—the material phase (Ξ) and the information phase (Ω)—governed by strict conservation of total information. Within this framework, absolute zero is reinterpreted as the global information ground state of two-phase information settlement: it is both the absolute zero point of material-phase information capacity and the material embodiment of the minimal information potential of the information phase. Residual entropy is not an exception to the third law, but an inevitable manifestation of information conservation at the absolute zero boundary. Starting from the principle of least action incorporating two-phase coupling, we derive a quantitative condition for the unattainability of absolute zero and demonstrate that the decoherence rate of a quantum system near absolute zero is systematically modulated by the information-phase coupling parameter. The framework yields three testable predictions: a scaling relation between decoherence rate and information-phase coupling strength at ultra-low temperatures, entropy accumulation near quantum critical points corresponding to enhanced information-phase potential density, and a temperature scaling law for the coherence time of time crystals. This work unifies the third law of thermodynamics with quantum measurement, black hole information processing, dark energy cosmology, quantum entanglement, and the Higgs mechanism under a single cross-scale information settlement paradigm. Keywords: absolute zero, third law of thermodynamics, residual entropy, information conservation, Landauer’s principle, decoherence, quantum spin liquid, time crystal
The second law of thermodynamics places constraints on state transformations. It applies to systems composed of many particles, however, we are seeing that one can formulate laws of thermodynamics when only a small number of particles are interacting with a heat bath. Is there a second law of thermodynamics in this regime? Here, we find that for processes which are approximately cyclic, the second law for microscopic systems takes on a different form compared to the macroscopic scale, imposing not just one constraint on state transformations, but an entire family of constraints. We find a family of free energies which generalize the traditional one, and show that they can never increase. The ordinary second law relates to one of these, with the remainder imposing additional constraints on thermodynamic transitions. We find three regimes which determine which family of second laws govern state transitions, depending on how cyclic the process is. In one regime one can cause an apparent violation of the usual second law, through a process of embezzling work from a large system which remains arbitrarily close to its original state. These second laws are relevant for small systems, and also apply to individual macroscopic systems interacting via long-range interactions. By making precise the definition of thermal operations, the laws of thermodynamics are unified in this framework, with the first law defining the class of operations, the zeroth law emerging as an equivalence relation between thermal states, and the remaining laws being monotonicity of our generalized free energies.
In a series of papers, we intend to take the perspective of open quantum systems and examine from their nonequilibrium dynamics the conditions when the physical quantities, their relations, and the laws of thermodynamics become well defined and viable for quantum many-body systems. We first describe how an open-system nonequilibrium dynamics (ONEq) approach is different from the closed combined system + environment in a global thermal state (CGTs) setup. Only after the open system equilibrates will it be amenable to conventional thermodynamics descriptions, thus quantum thermodynamics (QTD) comes at the end rather than assumed in the beginning. The linkage between the two comes from the reduced density matrix of ONEq in that stage having the same form as that of the system in the CGTs. We see the open-system approach having the advantage of dealing with nonequilibrium processes as many experiments in the near future will call for. Because it spells out the conditions of QTD's existence, it can also aid us in addressing the basic issues in quantum thermodynamics from first principles in a systematic way. We then study one broad class of open quantum systems where the full nonequilibrium dynamics can be solved exactly, that of the quantum Brownian motion of N strongly coupled harmonic oscillators, interacting strongly with a scalar-field environment. In this paper, we focus on the internal energy, heat capacity, and the third law. We show for this class of physical models, amongst other findings, the extensive property of the internal energy, the positivity of the heat capacity, and the validity of the third law from the perspective of the behavior of the heat capacity toward zero temperature. These conclusions obtained from exact solutions and quantitative analysis clearly disprove claims of negative specific heat in such systems and dispel allegations that in such systems the validity of the third law of thermodynamics relies on quantum entanglement. They are conceptually and factually unrelated issues. Entropy and entanglement will be the main theme of our second paper on this subject matter.
We study two small quantum systems coupled to the same reservoir which is in thermal equilibrium. By studying the particle density and the energy density in the two systems before and after they contact each other, we find that the two systems are not in thermal equilibrium with each other. Our result shows that the zeroth law of thermodynamics is broken in small quantum systems at low temperatures. Therefore, the traditional way of defining temperature fails due to the breakdown of the transitive relation of thermal equilibrium. Then we show a different way of defining temperature by attaching an auxiliary site, which plays the role of a thermometer, to the small quantum system.