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arXiv:2602.19377 · Classical and Quantum Gravity

Gravitational Poissonian Spontaneous Localization Model of Hybrid Quantum-Classical Newtonian Gravity: Energy Increase and Experimental Bounds

Nicolò Piccione

quant-phgr-qcSubmitted Feb 22, 2026• Announced Feb 24, 2026• 0 citations
v1 · Feb 22, 2026v2 · Sep 13, 2026
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Abstract

The Gravitational Poissonian Spontaneous Localization (GPSL) model is a hybrid classical-quantum framework in which Newtonian gravity emerges from stochastic collapses of a smeared mass-density operator. Consistency of the hybrid dynamics entails momentum diffusion and, hence, spontaneous heating. Without smearing, which enters both the collapse (measurement) and gravitational-feedback components of the dynamics, the heating rate would be divergent. Previous work assumed identical smearings for both components. Here, we treat the general case of distinct spatial smearings $g_{r_C} (\mathbf{x})$ and $g_{r_G} (\mathbf{x})$, characterized, respectively, by length scales $r_C$ and $r_G$. We characterize the spontaneous heating rate for arbitrary $g_{r_C} (\mathbf{x})$ and $g_{r_G} (\mathbf{x})$, and then discuss which smearing profiles minimize the spontaneous heating rate in relevant physical situations. Remarkably, there are situations in which, while the measurement noise remains the same, allowing $g_{r_G} (\mathbf{x}) \neq g_{r_C} (\mathbf{x})$ may reduce the feedback-induced spontaneous heating by more than 60 orders of magnitude already for $r_G = 10 r_C$. Finally, we use our results to estimate the spontaneous heating rate of neutron stars and to set new lower bounds on the model's parameters by comparing the theoretical predictions with astronomical data on temperature, radius, and mass of neutron stars.

Journal reference
Class. Quantum Grav. 43, 165005 (2026)
DOI
10.1088/1361-6382/ae92e5
Comments
11 pages plus appendices, 8 figures

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The Gravitational Poissonian Spontaneous Localization (GPSL) model is a hybrid classical-quantum framework in which Newtonian gravity emerges from stochastic collapses of a smeared mass-density operator. Consistency of the hybrid dynamics entails momentum diffusion and, hence, spontaneous heating. Without smearing, which enters both the collapse (measurement) and gravitational-feedback components of the dynamics, the heating rate would be divergent. Previous work assumed identical smearings for both components. Here, we treat the general case of distinct spatial smearings grC(x)g_{r_C} (\mathbf{x})grC​​(x) and grG(x)g_{r_G} (\mathbf{x})grG​​(x), characterized, respectively, by length scales rCr_CrC​ and rGr_GrG​. We characterize the spontaneous heating rate for arbitrary grC(x)g_{r_C} (\mathbf{x})grC​​(x) and grG(x)g_{r_G} (\mathbf{x})grG​​(x), and then discuss which smearing profiles minimize the spontaneous heating rate in relevant physical situations. Remarkably, there are situations in which, while the measurement noise remains the same, allowing grG(x)≠grC(x)g_{r_G} (\mathbf{x}) \neq g_{r_C} (\mathbf{x})grG​​(x)=grC​​(x) may reduce the feedback-induced spontaneous heating by more than 60 orders of magnitude already for rG=10rCr_G = 10 r_CrG​=10rC​. Finally, we use our results to estimate the spontaneous heating rate of neutron stars and to set new lower bounds on the model's parameters by comparing the theoretical predictions with astronomical data on temperature, radius, and mass of neutron stars.
Abstract We investigate the gravitational Poissonian spontaneous localization (GPSL) model, a hybrid classical-quantum model in which classical Newtonian gravity emerges from stochastic collapses of the mass density operator, and consistently couples to quantum matter. Unlike models based on continuous weak measurement schemes, we show that GPSL ensures vacuum stability; this, together with its applicability to identical particles and fields, makes it a promising candidate for a relativistic generalization. We analyze the model’s general properties, and compare its predictions with those based on continuous weak measurement schemes. Notably, here the gravitational feedback enters entirely through the non-Hermitian jump operators, without modifying the unitary part of the dynamics. We show that this leads to a short-range gravitational back-reaction and permits decoherence rates below those of any model based on continuous weak measurement schemes. We provide explicit examples, including the dynamics of a single particle and a rigid sphere, to illustrate the distinctive phenomenology of the model. Finally, we discuss the experimental testability of GPSL, highlighting both interferometric and non-interferometric strategies to constrain its parameters and distinguish it from competing models.
Spontaneous diffusion (i.e., nonconservation of energy) is a prominent, testable prediction of collapse and hybrid classical-quantum gravitational models. Without smearing of the mass density operator, the associated heating (or energy increase) rate diverges, yet the smearing distribution is arbitrary and, on scales much larger than the smearing length r C , much of the phenomenology is expected to be insensitive to this choice. We propose to resolve this arbitrariness as follows: for a fixed r C , select the distribution that minimizes the heating rate. Conceptually, this should identify the minimal deviation from standard quantum mechanics and provide models that, once experimentally refuted, would strongly disfavor all variants with different distributions. We apply this approach to the most investigated collapse models: GRW (for Ghirardi-Rimini-Weber), CSL (for continuous spontaneous localization), and DP (for Diósi-Penrose). Notably, the Gaussian is optimal only for the GRW case. Finally, we apply it to the Tilloy-Diósi hybrid classical-quantum model of Newtonian gravity, leading to its minimally deviating variant. This version of the model is entirely determined by only one free parameter r C , and, if experimentally refuted, would strongly disfavor any other version of it.
Abstract This paper proposes a parameter-free objective reduction theory where wavefunction collapse is induced by gravitational self-energy differences between mass distributions. Unlike Continuous Spontaneous Localization (CSL) models, which rely on phenomenological parameters, the collapse rate in this model (Γ = Eg/ħ) is uniquely determined by universal constants G and ħ. Key Highlights: Dynamical Derivation of the Born Rule: The model demonstrates that the Born probability rule emerges naturally from the martingale property of the stochastic dynamics, rather than being postulated. Experimental Consistency: The theory is shown to be consistent with current laboratory constraints, including double-slit interference experiments with large molecules (mcrit ≈ 10⁻¹⁴ kg) and loophole-free Bell inequality tests. Astrophysical Stability: Analysis confirms the stability of compact objects like neutron stars and the preservation of primordial fluctuations in the Cosmic Microwave Background (CMB). Relativistic Extension: A Lorentz-covariant field-theoretic generalization is provided, using the energy-momentum tensor to source collapse noise while respecting microcausality. The results suggest a self-contained, falsifiable framework for the transition from quantum to classical spacetime without the need for adjustable parameters.
We present a self-consistent stochastic semiclassical framework in which objective localization (collapse) of quantum states induces localized fluctuations in the stress–energy distribution that source causal gravitational wave perturbations via an Einstein–Langevin type equation. The model combines a Lindblad-averaged continuous spontaneous localization (CSL)-like dynamics with a local collapse bookkeeping field that enforces local energy–momentum conservation. Linearized analysis yields a causal wave equation for metric perturbations sourced by a stochastic tensor whose statistics are computable from collapse parameters. We derive scaling laws for expected strain statistics from a localized mass superposition, provide order-of-magnitude estimates and outline experimental strategies and model limitations. The construction avoids standard no-go objections (superluminal signaling and Page–Geilker constraints) at the ensemble level while yielding concrete, testable predictions for future high-sensitivity detectors. This model offers a phenomenological approach that can guide future experiments, assuming advancements in preparing mesoscopic superpositions and detecting subtle gravitational effects.
This memo addresses a question: In the “substrate field–soliton” model (v2 paper), canthe intuition “observation collapse = irreversible physical process” be realized as a concretedynamical collapse model? The answer is yes, but with a decisive number attached. Weprove that: (i) The master equation driven by the noise naturally derived from the masscoupling m(ϕ) is structurally isomorphic to the CSL (Continuous Spontaneous Localization) model, and the two ad hoc assumptions of CSL—mass-weighted coupling and positionbasis—are no longer assumptions in this model, but corollaries of the equivalence principleand the mass density operator; (ii) The collapse rate is proportional to Newton’s constant,Γ ∝ Gm2, realizing the motivation of the Di´osi–Penrose program that “collapse strengthis given by gravity,” though the mechanism is different (substrate noise rather than spacetime superposition instability); (iii) Decisive verdict: If the noise is taken as the quantumvacuum fluctuation of ϕ, the single-nucleon collapse rate is ∼ 10−28 s−1, which is 12 orders of magnitude smaller than the value required by GRW—the pure quantum fluctuationversion cannot solve the measurement problem. To achieve true collapse, “intrinsic probability” must be interpreted as a classical true-random component of the substrate condensate,whose power D becomes a new free parameter. In this case, the model becomes a CSL witha specific mediating field, and its heating rate directly interfaces with existing experimentalconstraints (X-ray spontaneous emission, cantilever noise, LISA Pathfinder). We presenta complete parameter space analysis, including the “localization-heating squeeze” identityP/λ = ℏ2/(2m0rC2), which explains why models with rC ∼ 1 fm are strictly ruled out, whilethose with rC ∼ 10−7 m survive.
The possibility that the collapse of the wave function in quantum mechanics is real and ultimately connected to (classical) gravity has been debated for decades with main contributions by Diósi and Penrose (DP). In particular, Diósi proposed a noise-based dynamical reduction model, which captures the same order of magnitudes for the collapse time suggested by Penrose based on heuristic arguments. This is known in the literature as the DP model (Diósi–Penrose). A peculiarity of the DP model is the prediction of spontaneous heating of matter, which can be tested without the need for massive quantum superpositions. Notably, a very similar effect is predicted by recent theoretical approaches to gravity as a classical-only information channel. Here, we reconsider the current constraints on the DP model from spontaneous heating by analyzing experimental situations not properly considered before. We argue that the parameter-free version of the DP model is close to be ruled out by standard heat leak measurements at ultralow temperatures with a conclusive exclusion likely within reach with existing technology. This result would strengthen a recent claim of exclusion inferred by spontaneous x-ray emission experiments, which relies on the somewhat stronger assumption that the DP noise field is white up to x-ray frequencies.