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arXiv:1206.5781

Environment Induced Time Arrow

János Polonyi

Published Jun 25, 2012• 6 citations
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Abstract

The spread of the time arrows from the environment to an observed subsystem is followed within a harmonic model. A similarity is pointed out between irreversibility and a phase with spontaneously broken symmetry. The causal structure of interaction might be lost in the irreversible case, as well. The Closed Time Path formalism is developed for classical systems and shown to handle the time arrow problem in a clear and flexible manner. The quantum case is considered, as well, and the common origin of irreversibility and decoherence is pointed out.

DOI
10.48550/arxiv.1206.5781

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The spread of the time arrows from the environment to an observed subsystem is followed within a harmonic model. A similarity is pointed out between irreversibility and a phase with spontaneously broken symmetry. The causal structure of interaction might be lost in the irreversible case, as well. The Closed Time Path formalism is developed for classical systems and shown to handle the time arrow problem in a clear and flexible manner. The quantum case is considered, as well, and the common origin of irreversibility and decoherence is pointed out.
It is shown in the framework of a harmonic system that the thermodynamical time arrow is induced by the environmental initial conditions in a manner similar to spontaneous symmetry breaking. The Closed Time Path formalism is introduced in classical mechanics to handle Green functions for initial condition problems by the action principle, in a systematic manner. The application of this scheme for quantum systems shows the common dynamical origin of the thermodynamical and the quantum time arrows. It is furthermore conjectured that the quantum-classical transition is strongly coupled.
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 role of the environment initial conditions in the breaking of the time reversal symmetry of effective theories and in generating the soft irreversibility is studied by the help of Closed Time Path formalism. The initial conditions break the time reversal symmetry of the solution of the equation of motion in a trivial manner. When open systems are considered then the initial conditions of the environment must be included in the effective dynamics. This is achieved by means of a generalized ϵ-prescription where the non-uniform convergence of the limit ϵ → 0 leaves behind a spontaneous breakdown of the time reversal symmetry.
The role of the environment initial conditions in the breaking of the time reversal symmetry of effective theories and in generating the soft irreversibility is studied by the help of Closed Time Path formalism. The initial conditions break the time reversal symmetry of the solution of the equation of motion in a trivial manner. When open systems are considered then the initial conditions of the environment must be included in the effective dynamics. This is achieved by means of a generalized ϵ\epsilonϵ-prescription where the non-uniform convergence of the limit ϵ→0\epsilon\to0ϵ→0 leaves behind a spontaneous breakdown of the time reversal symmetry.
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.
Coherence, Entropy, and the Arrow of Time: Why Time Has a Direction in a Phase Ontology (Phase Ontology — Part V) proposes a phase-centered explanation for one of physics’ strangest asymmetries: microscopic laws are largely time-symmetric, yet macroscopic reality is not. Cups shatter but do not reassemble; heat flows from hot to cold; correlations decay; memories accumulate. This paper argues that the arrow of time becomes conceptually clear once phase coherence is treated as ontologically primary. In this framework, time is not fundamental. It emerges operationally from countable phase evolution in physical clocks (all clocks are oscillators) and from synchronization between systems. A shared “global time” is therefore a relational structure sustained by coherence, not a background substance that governs dynamics. The paper then reframes entropy growth as the loss of accessible phase information in open systems. As systems interact with environments that contain many degrees of freedom, phase correlations disperse outward and become physically inaccessible, even if not destroyed in principle. Decoherence is elevated from a technical detail to the central engine of macroscopic irreversibility: reversing decoherence would require re-phasing an astronomically large environment, which is practically impossible. Building on Part III, the paper also interprets measurement as phase locking: once a macroscopic coupling stabilizes one local configuration, alternative phase possibilities are effectively dispersed into the environment. Classical definiteness and temporal irreversibility are thus treated as two faces of the same process—coherence flow. This manuscript is Part V of a seven-part series (Parts I–VII). It connects Parts I–IV to time asymmetry and points forward to Part VI (mass, inertia, gravitation) and Part VII (experimental implications and falsifiability).