Deterministic microscopic laws constrain physical systems through conservation laws and boundary conditions, yet macroscopic evolution routinely exhibits irreversible collapse, destruction, and path dependence. We analyze deterministic classical and quantum systems admitting multiple metastable macroscopic trajectories under fixed global constraints and show that deterministic dynamics generally underdetermine macroscopic history. We introduce a distinction between constraint-defined macroscopic equivalence classes, fixed by invariant quantities, and metastable macroscopic trajectories, defined by dynamical stability. Using stability and basin-of-attraction arguments, we characterize collapse as a deterministic loss of metastability in which an entire macroscopic trajectory becomes dynamically inaccessible without violation of microscopic reversibility or conservation laws. Irreversible destruction corresponds to elimination of physically realizable paths rather than loss of information or coarse-grained inaccessibility. We show that explanations based solely on coarse-graining or decoherence are insufficient to account for such trajectory elimination, as they preserve admissibility of erased histories. In contrast, instability-driven trajectory destruction constitutes an ontic dynamical process, directly realized in many-body and condensed matter systems. The framework provides a unified account of irreversible macroscopic change and causal differentiation within deterministic dynamics, without invoking stochasticity, modified laws, or observer-dependent mechanisms. Deterministic laws constrain admissible macroscopic states, while instability and metastability govern the physically realizable histories connecting them.
Deterministic microscopic laws constrain physical systems through conservation laws and boundary conditions, yet macroscopic evolution routinely exhibits irreversible collapse, destruction, and path dependence. We analyze deterministic classical and quantum systems admitting multiple metastable macroscopic trajectories under fixed global constraints and show that deterministic dynamics generally underdetermine macroscopic history. We introduce a distinction between constraint-defined macroscopic equivalence classes, fixed by invariant quantities, and metastable macroscopic trajectories, defined by dynamical stability. Using stability and basin-of-attraction arguments, we characterize collapse as a deterministic loss of metastability in which an entire macroscopic trajectory becomes dynamically inaccessible without violation of microscopic reversibility or conservation laws. Irreversible destruction corresponds to elimination of physically realizable paths rather than loss of information or coarse-grained inaccessibility. We show that explanations based solely on coarse-graining or decoherence are insufficient to account for such trajectory elimination, as they preserve admissibility of erased histories. In contrast, instability-driven trajectory destruction constitutes an ontic dynamical process, directly realized in many-body and condensed matter systems. The framework provides a unified account of irreversible macroscopic change and causal differentiation within deterministic dynamics, without invoking stochasticity, modified laws, or observer-dependent mechanisms. Deterministic laws constrain admissible macroscopic states, while instability and metastability govern the physically realizable histories connecting them.
A longstanding tension in the foundations of physics concerns the coexistence of deterministic(or unitary) dynamics with the apparent reality of choice, causation, collapse, and irreversible destruction. Standard responses either deny the physical significance of freedom, modify dynamicallaws, or relocate the problem to metaphysics. This paper identifies a structural distinction betweenmetastable macroscopic trajectories (paths) and globally constrained end states (attractors) and argues that its absence underlies much of the tension. We show that local degrees of freedom can alter,destabilize, and irreversibly eliminate particular trajectories without modifying the global attractorfixed by deterministic constraints. Collapse is thereby interpreted as loss of metastability ratherthan as a violation of determinism or unitarity. On this basis, we provide a structurally consistentaccount of causal efficacy, historical collapse, and responsibility within fully deterministic dynamics. We further extend this analysis to quantum mechanics, arguing that decoherence generatesmetastable macroscopic sectors within globally unitary evolution and that ontological commitmentattaches to dynamically persistent structure rather than to arbitrary Hilbert-space decomposition.The framework introduces no stochastic postulates and no modifications of physical law, but insteadclarifies the structural level at which freedom, collapse, and irreversibility operate.
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
Physical systems often exhibit stable, repeatable regimes despite being described by equations that allow many possible trajectories. This tension is typically addressed using probabilistic language, with probability treated as a fundamental feature of evolution or as a reflection of stochastic dynamics. In this paper, we argue that probabilistic descriptions instead arise from structural underdetermination in the presence of recurrence and finite resolution. We introduce a coherence-first account in which repeated traversal of structurally admissible pathways reinforces regime stability, leading to effective regime selection without invoking randomness, agency, or additional dynamical mechanisms. Within this framework, probability collapse is not a physical event but a resolution of indistinguishability as recurrence deepens constraint. This perspective completes a structural notion of determinism: outcomes need not be fixed, but admissible regimes are finite, and repeated evolution naturally sharpens their dominance. The resulting picture reconciles deterministic dynamics with probabilistic description while preserving consistency with existing physical formalisms.
Nonintegrable Poincaré systems with continuous spectrum (so-called Large Poincaré Systems, LPS) lead to the appearance of diffusive terms in the framework of dynamics. These terms break time symmetry. They lead, therefore, to limitations to classical trajectory dynamics and of wave functions. These diffusive terms correspond to well-defined classes of dynamical processes (i.e., so-called “vacuum-vacuum” transitions). The diffusive effects are amplified in situations corresponding to persistent interactions. As a result, we have to include already in the fundamental dynamical description the two aspects, probability and irreversibility, which are so conspicuous on the macroscopic level. We have to formulate both classical and quantum mechanics on the Liouville level of probability distributions (or density matrices). For integrable systems, we recover the usual formulations of classical or quantum mechanics. Instead of being irreducible concepts, which cannot be further analyzed, trajectories and wave functions appear as special solutions of the Liouville-von Neumann equations. This extension of classical and quantum dynamics permits us to unify the two concepts of nature we inherited from the 19th century, based on the one hand on dynamical time-reversible laws and on the other on an evolutionary view associated to entropy. It leads also to a unified formulation of quantum theory avoiding the conventional dual structure based on Schrödinger’s equation on the one hand, and on the “collapse” of the wave function on the other. A dynamical interpretation is given to processes such as decoherence or approach to equilibrium without any appeal to extra dynamic considerations (such as the many-world theory, coarse graining or averaging over the environment). There is a striking parallelism between classical and quantum theory. For LPS we have, in general, both a “collapse” of trajectories and of wave functions for LPS. In both cases, we need a generalized formulation of dynamics in terms of probability distributions or density matrices. Since the beginning of this century, we know that classical mechanics had to be generalized to take into account the existence of universal constants. We now see that classical as well as quantum mechanics also have to be extended to include unstable dynamical systems such as LPS. As a result, we achieve a new formulation of "laws of physics" dealing no more with certitudes but with probabilities. The formulation is appropriate to describe an open, evolving universe.
This preprint develops a thermodynamic admissibility condition on the persistence of quantum identity in open systems. Standard quantum mechanics allows extremely large spaces of possible system histories, but only a small subset remains experimentally realisable once irreversible entropy production is taken into account. This work formalizes this as an admissibility constraint: any quantum system that preserves a stable, trackable identity over time must satisfy a finite budget on cumulative irreversible dissipation. No new forces, variables, or dynamics are added; the constraint is purely structural and compatible with existing open-systems formalisms. The paper connects this requirement with decoherence, spectrum broadcasting, quantum Darwinism, and the emergence of classical objectivity. It frames identity persistence as a pre-dynamical condition—necessary before predictions about evolution or measurement outcomes are meaningful. This structural account clarifies why only certain histories are physically realisable, how objectivity arises under irreversibility, and how thermodynamic bookkeeping parameters (such as an “identity budget”) implicitly constrain experimental practice. The result provides a unifying, thermodynamically grounded framework linking dissipative quantum processes, system architecture, and long-term identifiability.