A single mechanism, endemic to the standard model of physics, is proposed to explain wavefunction collapse, classical motion, dissipation, equilibration, and the transition from pure quantum mechanics through open system decoherence to the natural regime. Spontaneous events in the neighborhood of a particle disrupts correlation such that large many-particle states do not persist and each particle collapses to a stable mode of motion established by its neighbors. These events are the source of thermal fluctuation and drive diffusion. Consequently, evolution is not deterministic, unitary or classically conservative; diffusion toward a steady state occurs incessantly in every system of particles, though slowed under unnatural experimental conditions that suppress these events. Mean properties of a system evolve as particles jump between single-particle modes, producing observed transport laws and equilibrium properties without additional postulate or empirical factors. These modes are localized in dense material, yielding classical characteristics. Boltzmann's equal probability postulate is valid only when comparing results of nonrelativistic observers.
A single mechanism, endemic to the standard model of physics, is proposed to explain wavefunction collapse, classical motion, dissipation, equilibration, and the transition from pure quantum mechanics through open system decoherence to the natural regime. Spontaneous events in the neighborhood of a particle disrupts correlation such that large many-particle states do not persist and each particle collapses to a stable mode of motion established by its neighbors. These events are the source of thermal fluctuation and drive diffusion. Consequently, evolution is not deterministic, unitary or classically conservative; diffusion toward a steady state occurs incessantly in every system of particles, though slowed under unnatural experimental conditions that suppress these events. Mean properties of a system evolve as particles jump between single-particle modes, producing observed transport laws and equilibrium properties without additional postulate or empirical factors. These modes are localized in dense material, yielding classical characteristics. Boltzmann's equal probability postulate is valid only when comparing results of nonrelativistic observers.
The emergence of classical behavior and the origin of thermal equilibrium are two central problems in the foundations of physics. In the standard accounts, both phenomena are typically explained through interactions with an external environment: decoherence suppresses quantum interference, while coupling to a thermal bath drives relaxation toward equilibrium. Over the last decades, however, it has become clear that equilibration and thermalization can arise even in fully isolated quantum systems, in the operational sense that the expectation values of relevant observables remain close to equilibrium values for most of the time. Here, we ask whether the same intrinsic equilibration mechanism can also account for the emergence of classical behavior. Using rigorous bounds on equilibration in closed systems, we derive sufficient conditions under which a time-evolved pure state becomes, for most times, operationally indistinguishable from a classical mixture associated with a chosen physical property. We identify two complementary routes to such operational classicality: either the chosen property almost commutes with the system Hamiltonian or the observables used to probe the system lose access to the remaining coherence after equilibration. Our results show that classical behavior need not be confined to the energy basis and may emerge even when substantial coherence remains present in the equilibrium state. This establishes a direct connection between two foundational questions: the origin of thermalization in isolated quantum systems and the quantum-to-classical transition
This work proposes a conceptual and ontological reformulation of classical dynamics, thermodynamics, and quantum mechanics based on a single postulate: dissipation is a fundamental property of all physical processes. Traditional dynamics relies on the idealization of isolated, reversible systems, yet no real physical system satisfies such conditions. By introducing an intrinsic dissipative energy term into the equations of motion, we suggest that dissipation entails an irreversible loss of physical information, from which a classical uncertainty principle naturally follows. Stationary states are reinterpreted as zero‑dissipation configurations, lacking internal temporal evolution, thereby offering an ontological basis for quantization, non‑locality, and the Heisenberg uncertainty principle. Quantum mechanics can thus be viewed as the mathematical description of these stationary states and of the dissipative transitions connecting them. The framework is conceptually consistent with fluctuation‑dissipation theory, open‑system quantum dynamics, decoherence theory, and relaxation phenomena in NMR spectroscopy. Several experimental proposals are outlined to discriminate this ontological model from both classical mechanics and standard quantum mechanics.
Abstract The quantum measurement problem—the absence of any dynamical mechanism connecting continuous wavefunction evolution to discrete empirical outcomes—has persisted since the foundations of quantum theory. Decoherence explains interference suppression but cannot explain outcome selection: the diagonal density matrix remains an improper mixture until one outcome is actualized. We propose that collapse is a physical phase transition in the coupled system–apparatus field. The order parameter ψ, constructed as a coarse-grained collective coordinate of apparatus degrees of freedom, evolves under Ginzburg–Landau dynamicswith a symmetry-breaking potential. When the coherence pressure γ exceeds a critical threshold γc, the symmetric phase(superposition) becomes unstable and the field crystallizes into one of the discrete stable minima (eigenstates). We derive the critical coupling from microscopic system–apparatus Hamiltonians, obtaining γc ∼ (√Ng)−1 where N is the number of apparatus degrees of freedom and g is the coupling constant. This scaling explains why macroscopic apparatus collapse wavefunctions while microscopic interactions preserve coherence. The Born rule Pn = |cn|2 is preserved through this dynamical selection mechanism: attractor basin geometry under probability-conserving flow converts probabilistic weights into definite outcomes without altering the underlying probabilities. The theory yields four falsifiable predictions absent from standard quantum mechanics: critical slowing near γc, hysteresis in the collapse–recoherence cycle, metastable supercooled superpositions, and transient Jacobian spikes at the moment of collapse. We provide quantitative estimates for superconducting qubit readout, predicting collapsetimes of order 100 ns with critical slowing observable within current experimental precision. This framework provides a concrete existence proof, within a controlled effective-theory regime, that collapse dynamics can be constructed from standard quantum mechanics plus statistical mechanics, requiring no modification to the Schr¨odinger equation.
Classical statistical mechanics relies on the ergodic hypothesis, which states that a system explores the entire allowed phase space during its time evolution. Pure quantum states are at odds with this concept as they remain in a single quantum state even if the system's parameters are suddenly altered. However, in a generic many-body system, coherent dynamics drive local thermalization of its subsystems. In this case, any local observable appears thermal and can be described by a statistical ensemble even though the full state remains pure. The key to understanding the phenomenon of quantum thermalization lies in the entanglement properties of the system: The presence of entanglement creates local entropy that validates the use of statistical physics.\nIn this thesis, we experimentally study the emergence of statistical mechanics in a quantum state and observe the fundamental role of quantum entanglement in facilitating this emergence. We perform microscopy on an evolving quantum system, and we see thermalization occur on a local scale while we measure that the full quantum state remains pure.\nThe only known robust exception from the paradigm of quantum thermalization is provided by disordered systems. In this case, the particle transport ceases through the system, preventing the formation of a sufficient amount of entanglement required for thermalization. However, if the many-body system is interacting, the state develops non-local quantum correlations that are inaccessible to any local observable. These correlations spread exponentially slowly in time throughout the entire system and are considered a hallmark feature of many-body-localized states.\nIn order to study the interplay between thermalization and localization in our system, we develop novel methods for high fidelity state preparation and readout. We achieved an exquisite isolation of our system from the environment, which allows us to monitor coherent many-body dynamics over multiple decades of time evolution.\nWe experimentally realize such a many-body localized system and observe the formation of non-local quantum correlations, while the particle transport is frozen in the system. Our work experimentally establishes many-body localization as a qualitatively distinct phenomenon from localization in non-interacting, disordered systems.
We study the back-reaction of quantum systems onto classical ones. Taking the starting point that semi-classical physics should be described at all times by a point in classical phase space and a quantum state in Hilbert space, we consider an unravelling approach, describing the system in terms of a classical-quantum trajectory. We derive the general form of the dynamics under the assumptions that the classical trajectories are continuous and the evolution is autonomous, and the requirement that the dynamics is linear and completely positive in the combined classical-quantum state. This requirement is necessary in order to consistently describe probabilities, and forces the dynamics to be stochastic when the back-reaction is non-zero. The resulting equations of motion are natural generalisations of the standard semi-classical equations of motion, but since the resulting dynamics is linear in the combined classical-quantum state, it does not lead to the pathologies which usually follow from evolution laws based on expectation values. In particular, the evolution laws we present account for correlations between the classical and quantum system, which resolves issues associated with other semi-classical approaches. In addition, despite a breakdown of predictability in the classical degrees of freedom, the quantum state evolves deterministically conditioned on the classical trajectory, provided a trade-off between decoherence and diffusion is saturated. As a result, the quantum state remains pure when conditioned on the classical trajectory. To illustrate these points, we numerically simulate a number of semi-classical toy models, including one of vacuum fluctuations as a source driving the expansion of the universe. Finally, we discuss the application of these results to semi-classical gravity, and the black-hole information problem.
The quantum–classical divide remains one of the most persistent conceptual challenges in modern physics. Conventionally, this transition is explained through decoherence— the environment-induced loss of phase coherence via interaction with external degrees of freedom. While phenomenologically successful, decoherence theory does not provide a fundamental mechanical substrate for why quantum behavior emerges preferentially at small scales and vanishes systematically at large ones. It remains a statistical account rather than a mechanistic one. The Absolute Medium (AM) framework offers an alternative foundation by re-conceptualizing spacetime not as an abstract arena, but as a Universal Force Continuum— a baseline of potential energy that precedes and underlies physical matter. In this formulation, the vacuum is characterized not by emptiness but by structured tension, where the “graininess” emerges from equilibrium conditions within the continuum itself.This graininess is quantified by the Energetic Net, defined by the fundamental length scale Lfund ≈ 3.34 nm. This scale represents the characteristic spacing at which the continuum’s tension reaches local equilibrium, creating a natural lattice structure. The continuum is neither rigid nor fluid in conventional terms, but exists in a state of dynamic equilibrium where its tension field supports both wave-like propagation and particle-like anchoring. This intrinsic structural property of the vacuum introduces a natural scale separation that defines two distinct dynamical regimes:• Slippage (Quantum) Regime (d < Lfund, m < mcrit): Particles interact with the continuum through local tension fluctuations without engaging its equilibrium structure. Their motion is governed by stochastic variations in the continuum’s potential field, yielding emergent quantum behavior.• Bulk-Coupled (Classical) Regime (d ≥ Lfund, m ≥ mcrit): Objects span multiple equilibrium nodes of the continuum, engaging its fundamental structure. They must displace the continuum’s equilibrium configuration, triggering deterministic volumetric coupling that recovers classical mechanics. This proposal replaces abstract decoherence with a concrete mechanical transition rooted in the continuum properties of the vacuum. It offers a first-principles explanation for the emergence of both quantum and classical dynamics from a unified energetic continuum, with the transition governed by intrinsic properties of the medium rather than external interactions.