Microscopic unitary dynamics preserves all fine information, yet an isolated finite system can show a robust thermodynamic window in which the entropy associated with a restricted record rises. We ask why information hidden from the current record usually fails to rebuild a low-entropy macrostate. For a fixed projective record, every finite step separates exactly into the evolution predicted from the record alone and an exact correction carried by unresolved microscopic structure. The record-only contribution starts only at second order in time, so all instantaneous change of the record comes from hidden currents between macrostates. We derive the exact entropy rate, separate entropy-spreading from return-oriented currents, and resolve those currents into energy-gap amplitudes. Transitions with the same gap add coherently, revealing how the Hamiltonian and the microscopic state organize hidden information for return. In interacting mixing dynamics the current power is spread over many frequencies; free and deliberately commensurate controls progressively concentrate it, and the engineered dynamics reconstructs a low-entropy macrostate. An independent distribution-level test separates hidden dynamical activity from finite-step return, and an exact classical measure-preserving counterpart shows which parts of the construction are not uniquely quantum. Within the specified record and observation window, irreversibility is therefore not loss of microscopic information, but the failure of that information to organize currents that restore macroscopic order.
Microscopic unitary dynamics preserves all fine information, yet an isolated finite system can show a robust thermodynamic window in which the entropy associated with a restricted record rises. We ask why information hidden from the current record usually fails to rebuild a low-entropy macrostate. For a fixed projective record, every finite step separates exactly into the evolution predicted from the record alone and an exact correction carried by unresolved microscopic structure. The record-only contribution starts only at second order in time, so all instantaneous change of the record comes from hidden currents between macrostates. We derive the exact entropy rate, separate entropy-spreading from return-oriented currents, and resolve those currents into energy-gap amplitudes. Transitions with the same gap add coherently, revealing how the Hamiltonian and the microscopic state organize hidden information for return. In interacting mixing dynamics the current power is spread over many frequencies; free and deliberately commensurate controls progressively concentrate it, and the engineered dynamics reconstructs a low-entropy macrostate. An independent distribution-level test separates hidden dynamical activity from finite-step return, and an exact classical measure-preserving counterpart shows which parts of the construction are not uniquely quantum. Within the specified record and observation window, irreversibility is therefore not loss of microscopic information, but the failure of that information to organize currents that restore macroscopic order.
Decoherence and thermodynamic irreversibility are widely regarded as sufficient to explain the emergence of classical behavior from quantum mechanics. Decoherence suppresses interference between branches of the wavefunction, while entropy production provides a direction to macroscopic time. However, neither mechanism alone explains why macroscopic physics exhibits a single, persistent, globally consistent classical history rather than fragmentation into mutually incompatible record sets. In this work, we identify and formalize this unresolved issue as the classicality gap. We show that in finite systems subject to nonzero noise and irreversible record formation, decoherence and entropy production are generically insufficient to stabilize a single coherent macroscopic history. Instead, absent a history-level selection mechanism, redundant records diverge and macroscopic identity becomes ill-defined. We present a general instability result demonstrating this fragmentation tendency and introduce history-level constraint restoration as the minimal structural mechanism capable of preventing it. This mechanism operates without new microdynamics, collapse postulates, or observer dependence. We derive qualitative phase boundaries separating stable and unstable regimes and propose concrete experimental protocols on NISQ-era quantum platforms that can falsify the necessity of history selection. Our results establish that persistent classicality is not guaranteed by decoherence alone, but requires selection acting on histories under irreversible constraints. Keywords: classicality emergence, decoherence limits, record inconsistency, history instability, quantum-to-classical transition, irreversibility, entropy production, information persistence, open quantum systems, foundations of physics
Decoherence theory explains the suppression of interference between branches of a quantum state but does not explain why any particular branch persists as a stable classical history under continued environmental interaction. This unresolved gap lies at the core of the quantum measurement problem. Here we demonstrate that irreversible record formation is a necessary structural condition for the stabilization of quantum histories. Using a minimal open quantum system consisting of a measured qubit coupled to a memory degree of freedom, we show that decoherence alone fails to produce persistent measurement records in the presence of ongoing noise. By contrast, when the memory subsystem is allowed to irreversibly export entropy, stable and distinguishable records emerge robustly. We introduce an operational recordability metric based on the trace-distance distinguishability of conditional memory states and observe a pronounced transition between recordable and non-recordable regimes. These results establish that measurement outcomes do not become classical merely by decohering; they become classical only when they are irreversibly maintained. This mechanism resolves a structural incompleteness in decoherence-based accounts of measurement without invoking wavefunction collapse, observers, or interpretational postulates. Keywords: quantum measurement problem, decoherence, irreversible record formation, open quantum systems, Lindblad dynamics, classical emergence, quantum histories, record stabilization, entropy export, measurement records, trace distance, quantum information, environment-induced decoherence, thermodynamic irreversibility
Thermodynamics is useful because it lets us predict and control complex systems from a few accessible quantities when microscopic reconstruction is impractical. We ask whether this operational reduction can be less costly in a finite quantum system than in a matched classical one. We compare a few-boson Bose--Hubbard chain with its number-conserving classical-field counterpart under the same driving and the same coarse spatial record. The quantum system relaxes more in the observed particle distribution, yet the retained mean energy resolves more of the microscopic structure hidden by that record, leaving less information unusable and smaller entropy generation. We then close the process into a heat-engine cycle whose controls use only the measured mean energy and spatial record, not full state tomography; at matched thermal resources, the smaller entropy generation gives more work and higher efficiency. The advantage fades as the particle number grows toward the classical-field regime.
Complete dynamics and entropy balances of all proper subsystems need not determine global irreversibility. A three-qubit construction keeps one initial product state and every one- and two-qubit reduced semigroup fixed while changing only the organisation of energy-preserving shared phase events. The global entropy production changes, and the thermodynamic ranking of the full system against its proper subsystems reverses. Both trajectories remain separable, every compared score is positive, and interval bounds certify the opposite rankings.The comparison uses the finite-window Thermodynamic Criterion Index, the entropy reduction per unit outward entropy transfer. An exact lift identity determines when relational-information change exceeds the component deficit and the signed nonadditivity of entropy transfer. With common lower-order marginals and equal global export, a larger increment of irreducible higher-order information means an exactly equal reduction of global entropy production. At a common temperature and for an additive Hamiltonian, that information has a precise nonequilibrium free-energy value.Within the parity-contact model, fixed lower-order dynamics leave an explicit physical fibre of higher-order generators. Selective control inside this fibre changes a chosen collective decay rate. Two controllers with equal amounts of parity correlation can produce opposite thermodynamic rankings. Finite adaptive protocols confined to any fixed proper subsystem with private memory cannot identify the change; outcomes jointly retained from all three sites can reveal it. A certified pair of compatible generators gives nonzero lower bounds on the minimax absolute errors for global entropy production and the full-versus-proper yield gap, even with exact lower-order data. Complete lower-order descriptions therefore leave a physically controllable coordinate of global irreversibility undetermined.
We present a unified operational framework for the arrow of time grounded in irreversible information loss. While microscopic physical laws are time-reversal invariant, macroscopic irreversibility arises when systems overwrite metastable records. We show that recent reversible quantum-control experiments do not reverse time, but instead operate in regimes where no logically irreversible record is created. To formalize this, we introduce the **forgetting rate** (Ξcr), a coarse-grained rate defined on physically selected metastable record states (e.g., pointer states, memory registers, or macroscopic configurations). Unlike standard entropy production, which is expressed in terms of microscopic transition asymmetry, (Ξcr) captures the **rate of irreversible record overwriting**. In this formulation, entropy production obeys the lower boundS˙irr≥kBΞcr,consistent with Landauer's principle but expressed at the level of record dynamics. Within this framework, thermodynamic, quantum-measurement, psychological, and cosmological arrows emerge as substrate-dependent manifestations of Ξcr>0. Temporal asymmetry is therefore not a single global property, but a distributed feature of physical information-processing systems. The approach naturally explains the decoupling of arrows in composite systems and identifies experimentally accessible regimes where irreversibility can be locally suppressed. This work does not introduce a new microscopic law but provides a unifying, operational reformulation that connects information thermodynamics, decoherence theory, and memory dynamics through a single coarse-grained rate.
This paper develops an interpretive account of the physical life cycle of records within a consistency-history framework. Earlier papers in the series characterized a committed record as “decoherence- and thermodynamics-protected, append-only in practice.” The present paper refines and partially corrects that formulation. A physical record is not logically immutable or fundamentally append-only. It is revision-resistant in practice insofar as its information is encoded in sufficiently protected physical degrees of freedom, often—but not universally—through metastability and free-energy barriers. The central claim is structural and deliberately deflationary: there is no single thermodynamic price of a record. Record formation, passive retention, revision, logically irreversible reset, active error correction, and redundant proliferation are distinct processes with different, implementation-dependent demands. The paper therefore replaces a scalar cost with a physical record profile comprising resources, performance, and architecture: free-energy and dissipation budgets, control resources, operation and retention times, error rates, and an effective number of sufficiently independent carriers or access channels. Landauer’s principle directly constrains the logically irreversible reset component of this profile. Other record processes inherit a Landauer-type constraint only when their implementation contains a reset or another logically irreversible information-discarding step. The formation of a classical record is represented as the logically reversible, in-principle correlation of distinguishable pointer states with an initially prepared memory. This is not the cloning of an arbitrary unknown quantum state, and a complete reusable memory cycle must still account for preparation and reset. The paper further distinguishes logical commitment, physical durability, and public finality. Public finality requires an operationally significant redundancy of sufficiently independent, accessible, and durable carriers or access channels. This is an architectural requirement, not a universal additive heat cost per copy. Environmental amplification may generate redundant records without implying a universal Landauer-type price for each environmental fragment. The framework derives no result in thermodynamics or statistical mechanics. It does not derive the second law, the Landauer bound, any fluctuation theorem, the thermodynamic arrow of time, or the low-entropy boundary conditions of the universe, and it makes no independent empirical prediction. Its contribution is a disciplined decomposition of the physical processes through which records are formed, protected, revised, erased, maintained, and made publicly accessible.