We propose a speculative but quantitatively constrained phenomenological framework in which the thermodynamic arrow of time emerges from entropy-dependent decoherence in open quantum systems. Higher environmental entropy strengthens decoherence, preferentially de- stroying quantum coherence in one temporal direction, thus providing a microscopic mechanism for irreversibility. The formalism is constructed within an effective Lindblad master-equation approach, recovering unitary quantum mechanics and standard thermodynamics in appropriate limits. A toy two-level system illustrates the emergence of coherence decay and an effective microscopic arrow of time.
We propose a speculative but quantitatively constrained phenomenological framework in which the thermodynamic arrow of time emerges from entropy-dependent decoherence in open quantum systems. Higher environmental entropy strengthens decoherence, preferentially de- stroying quantum coherence in one temporal direction, thus providing a microscopic mechanism for irreversibility. The formalism is constructed within an effective Lindblad master-equation approach, recovering unitary quantum mechanics and standard thermodynamics in appropriate limits. A toy two-level system illustrates the emergence of coherence decay and an effective microscopic arrow of time.
The concept of time presents a profound challenge at the intersection of quantum mechanics and thermodynamics. While fundamental microscopic laws are largely time-symmetric, macroscopic phenomena universally exhibit a distinct thermodynamic arrow of time, characterized by increasing entropy. This paper explores the hypothesis that quantum entanglement plays a crucial role in the emergence of this thermodynamic arrow. We review how the entanglement between a quantum system and its environment leads to decoherence, effectively driving the system towards a state of higher entropy and classical-like behavior. By analyzing concepts such as von Neumann entropy, entanglement entropy, and the Page-Wootters mechanism, we propose a theoretical framework where the degradation and spreading of entanglement act as the underlying mechanism for the perceived unidirectional flow of time. This approach offers a potential resolution to the "problem of time" in quantum gravity and provides a unified perspective on the genesis of irreversibility from the inherently reversible laws of quantum mechanics. We discuss the implications of this entanglement-driven temporal emergence for our understanding of the universe's initial low-entropy state and the fundamental nature of reality.
The problem of time’s arrow is (roughly) to understand why macroscopic physical processes typically evolve in a specific direction (the one we call “the future”) even though the underlying laws of physics describing the individual microscopic systems are time-reversal invariant. The standard answer to this problem is given by Boltzmann’s explanation of the II law of thermodynamics: a classical system starting in a non-equilibrium state spontaneously (i.e. with a high level of probability) tends towards equilibrium, thus implementing an irreversible process. However, this explanation has two drawbacks: 1. it needs a further assumption on the entropy of the initial state of the universe (past hypothesis); 2. microscopic systems (e.g. molecules in a box) should be represented as quantum states and not classical states. In this talk, I want to propose a different hypothesis to explain the origin of time’s arrow, based on quantum mechanics, specifically on decoherence theory. Differently from isolated systems, open quantum systems described by decoherence theory showirreversible behavior, as they evolve towards decoherence and von Neumann entropy increase. Is this behavior a sign of genuine irreversibility? And, if so, can this be linked to thermodynamic irreversibility?
The arrow of time paradox between quantum mechanics and thermodynamicsarises from the fundamental conflict between the time-symmetric evolution of thewave function and the irreversible increase of thermodynamic entropy. This pa?per introduces a ”small observer” model with quantum resolution capabilities andcombines quantum measurement theory with open quantum system dynamics toreveal the influence of observer scales on the perception of the arrow of time. Byestablishing a quantum master equation model for N coupled small observers, wedemonstrate the emergence of macroscopic thermodynamic entropy from micro?scopic quantum entropy production, providing a novel theoretical framework forunifying the understanding of the arrow of time. Numerical simulations based onthe quantum Darwinism framework validate the theoretical predictions.
Standard quantum mechanics describes the evolution of physical systems through unitary Schr¨odinger dynamics, while decoherence and wavefunction collapse are introduced through additional postulates or environmental interactions. Although highly successful operationally, the theory does not provide a fundamental dynamical mechanism explaining the emergence of classical localization from microscopic evolution. n this work we propose an entropy-weighted causal dynamics framework, referred to as Quantum Causal Entropy (QCE), in which each microscopic causal transition contributes both a phase increment and an entropy cost. Starting from a local causal update rule, Ψ → eiθℓ−∆SℓΨ, we derive a modified evolution equation in which the standard Hamiltonian generator is supplemented by an entropy-production operator. The resulting entropy-corrected Schr¨odinger equation takes the form iℏ dΨ dt =H − iℏλSˆΨ, where Sˆ represents the entropy rate associated with microscopic causal processes and λ is an entropy coupling constant. We show that the standard unitary Schr¨odinger evolution is recovered in the limit of vanishing entropy coupling, while finite entropy production leads naturally to decoherence, interference suppression, and effective measurement localization without invoking an explicit collapse postulate. A corresponding density-matrix evolution equation is derived, providing a thermodynamic description of coherence decay. The framework therefore provides a dynamical link between quantum evolution, information entropy, and emergent classicality, and suggests experimentally testable corrections to coherence behavior in controlled quantum systems
We present a unified and minimal theoretical framework addressing the quantum-classical transition, the measurement problem, and the emergence of the arrow of time, grounded in gravitational physics. Building on the insight that quantum superpositions of mass distributions necessarily imply superpositions of gravitational potentials, we show that such states are unavoidably associated with superpositions of proper times due to gravitational time dilation. By extending the system Hilbert space to include a temporal degree of freedom, we demonstrate that matter-time entanglement leads naturally to effective decoherence when the time degree of freedom is traced out. The resulting reduced dynamics takes the form of a Lindblad master equation derived from an underlying unitary evolution. This framework reproduces the correct microscopic and macroscopic limits, clarifies the relation to Diósi-Penrose-type models, and provides a coherent account of classicality and temporal irreversibility without postulating observers, environmental decoherence as fundamental, or objective wavefunction collapse.
This work investigates the fundamental connection between quantum mechanics and thermodynamics through the concept of the arrow of time. While the second law of thermodynamics identifies the arrow of time with the monotonic increase of entropy in isolated systems, closed quantum systems evolve unitarily and conserve von Neumann entropy, making the origin of irreversibility less apparent. Here we establish a no-go theorem proving that correlations in unknown states of closed quantum systems cannot be universally removed by any physical operation. This result demonstrates that correlation generation is inherently irreversible, providing a microscopic and universal basis for the arrow of time. In thermodynamic settings, this irreversibility ensures that heat flows spontaneously from hotter to colder subsystems, reproducing the Clausius formulation of the second law. More generally, the irreversible growth of correlations explains entropy increase, the approach to equilibrium, and decoherence as observable manifestations of the same principle. Our findings ground a quantum-mechanical foundation for the second law of thermodynamics and demonstrate the universality of the arrow of time.