We analyze gravitational collapse models within the Diósi–Penrose framework against current experimental bounds and macroscopic classicality requirements. We show that, among the six constraints considered (three interferometry bounds from MAQRO, Vienna, and Delft, and three macroscopic classicality requirements), only the Vienna bound is active in the vicinity of the optimum: the other five are satisfied with margins of 1–13 orders of magnitude and do not constrain the cutoff radius Rc. Saturating the Vienna bound alone fixes Rc = (5.3 ± 0.1) × 10^−5 m (53 µm). We present this value not as an emergent consequence of multiple independent constraints, but as the current experimental upper bound on Rc under the Diósi model with a Gaussian cutoff—the largest cutoff radius consistent with the absence of observed collapse in the Vienna levitation experiment. This is a more modest, but equally falsifiable, claim: any future experiment probing Rc ≲ 53 µm without observing the predicted collapse signature would rule out this specific parameter choice. We give the resulting testable predictions for next-generation nano-interferometry and discuss the sensitivity of the bound to the single dominant experimental input.
We analyze gravitational collapse models within the Diósi–Penrose framework against current experimental bounds and macroscopic classicality requirements. We show that, among the six constraints considered (three interferometry bounds from MAQRO, Vienna, and Delft, and three macroscopic classicality requirements), only the Vienna bound is active in the vicinity of the optimum: the other five are satisfied with margins of 1–13 orders of magnitude and do not constrain the cutoff radius Rc. Saturating the Vienna bound alone fixes Rc = (5.3 ± 0.1) × 10^−5 m (53 µm). We present this value not as an emergent consequence of multiple independent constraints, but as the current experimental upper bound on Rc under the Diósi model with a Gaussian cutoff—the largest cutoff radius consistent with the absence of observed collapse in the Vienna levitation experiment. This is a more modest, but equally falsifiable, claim: any future experiment probing Rc ≲ 53 µm without observing the predicted collapse signature would rule out this specific parameter choice. We give the resulting testable predictions for next-generation nano-interferometry and discuss the sensitivity of the bound to the single dominant experimental input.
Abstract The possibility that gravity plays a role in the collapse of the quantum wave function has been considered in the literature, and it is of relevance not only because it would provide a solution to the measurement problem in quantum theory, but also because it would give a new and unexpected twist to the search for a unified theory of quantum and gravitational phenomena, possibly overcoming the current impasse. The Diósi–Penrose model is the most popular incarnation of this idea. It predicts a progressive breakdown of quantum superpositions when the mass of the system increases; as such, it is susceptible to experimental verification. Current experiments set a lower bound R 0 ≳ 4 Å for the free parameter of the model, excluding some versions of it. In this work we search for an upper bound, coming from the request that the collapse is effective enough to guarantee classicality at the macroscopic scale: we find out that not all macroscopic systems collapse effectively. If one relaxes this request, a reasonable (although to some degree arbitrary) bound is found to be: R 0 ≲ 10 6 Å. This will serve to better direct future experiments to further test the model.
VERSION NOTE (v2, 2026-07-02): This version supersedes v1 (April 2026). The central empirical-viability claims of v1 — a thermodynamically viable collapse kernel and a favorable DESI DR1 cosmological signature — were falsified by the author's own subsequent analysis. Fixing the smearing length to its holographically mandated value forces confrontation with the full hierarchy of collapse bounds, where spontaneous-heating measurements exclude it by ~9 orders of magnitude. The work has been rewritten as a parameter-free no-go constraint. v1 is retained below for the version record but should not be cited as a viability result. ABSTRACT (v2): The Diósi–Penrose (DP) model of gravity-induced wavefunction collapse requires an ad hoc mass-smearing length, set phenomenologically at the nucleon scale, R0 ~ 1e-15 m. We show that this scale is fixed by holographic cosmological geometry: evaluating the Károlyházy metric variance over the cosmological apparent horizon, as mandated by the Bousso covariant entropy bound, yields R0 = (lP^2 RH)^(1/3) = 3.3 fm from measured constants alone — a parameter-free reproduction of the historical choice. The decoherence-time kinematics survive every current test: a quantum–classical partition at m_crit ≈ 120 m_e protects atomic chemistry (electron tau ~ 1e21 s) and matter-wave interferometry (C60: ~115 yr) while imposing definiteness on macroscopic bodies, with the ambiguous mesoscopic window falling in the macromolecular regime accessible to near-term interferometry. The standard dynamical realization does not survive. The Einstein Equivalence Principle suppresses single-nucleus dipole bremsstrahlung by a derived factor (k_X R0)^2 ≈ 3e-8, and any noise cutoff below 1e18 Hz evades the underground X-ray bound; but neither defense touches spontaneous heating, which with the standard prefactor predicts ~28 mW/kg — nine orders of magnitude above cryogenic heat-leak ceilings. The heating is charge-independent and probes THz phonons via the relative momentum diffusion of atoms separated by 1e5 correlation lengths, so it is immune to the equivalence principle and robust to any high-frequency cutoff. The framework derives exactly two temporal scales (the pixel light-crossing rate ~1e22 Hz and the horizon refresh rate ~1e-19 Hz); neither lands in the fifteen-decade escape window, and inserting one by hand reinjects the free parameter the construction eliminates. We conclude that if objective collapse is sourced by cosmological holographic geometry, it cannot be mediated by continuous stochastic momentum diffusion: a parameter-free no-go constraint forcing gravity-induced reduction toward non-dissipative or purely kinematic mechanisms.
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.
In previous works, I interpreted gravitational divergences — in both black hole singularities and quantum collapse scenarios — as limit behaviors of the classical description rather than physically realized infinities. The present paper gives this interpretation its full mathematical form. I apply the Operational Curvature Cutoff Principle (OCCP) to the gravitational self-energy integral of Penrose–Diósi collapse models, derive the maximum physically meaningful self-energy E_max = Gm²/(√π ℓ_P) from the structure of the limit process itself, and obtain a finite minimum collapse timescale τ_min = √π ℏ ℓ_P / (Gm²) > 0. The macroscopic Penrose predictions are recovered exactly. The divergence of E_grav is shown to be a limit behavior of the same kind as the Kretschmann divergence at black hole centers: a signal that the classical description has been formally extended beyond its operational domain, not a physically meaningful infinity. The central physical message is that gravity imposes a Planck-limited instability on quantum superpositions: the collapse timescale scales as τ_min ∝ 1/m², with a lower bound set by the Planck time. This work does not propose a new dynamical theory, but makes explicit what the limit-behavior interpretation requires of existing collapse models. Version history: v1: Initial submission v2: Extended with explicit Gaussian computation, mass scaling analysis (τ_min ∝ 1/m²), experimental predictions, decoherence comparison, and limitations section. v3: Four corrections and additions: (1) Fixed the d→0 limit: at d=0 the two configurations coincide and E_grav=0, as required physically. E_max is achieved in the d→∞ limit, not d→0. (2) Clarified that σ is the center-of-mass wave packet width, not the physical size R of the object. The OCCP cutoff operates at the level of the self-energy integral, not the object's geometry. (3) Showed explicitly that the OCCP cutoff is required at all length scales: even for R ≫ ℓ_P, the integral formally includes contributions from |x-y| < ℓ_P. In the macroscopic limit these contributions are negligible (not absent), and Penrose's predictions are recovered exactly. (4) Added the effective cutoff σ_eff = √(R² + ℓ_P²), which provides a single interpolating formula connecting the macroscopic τ ∝ m⁻¹ (Penrose) and Planck-scale τ ∝ m⁻² (OCCP) regimes. .
The Penrose-Diósi gravitational objective reduction criterion predicts wavefunction collapse at τ_PD = ħ/E_G where E_G = Gm²/r. Entropy-Response Gravity (ERG) modifies this criterion with zero free parameters via G_eff(r,m) = G/μ(Gm/r²a₀), where μ(x) = x/√(1+x²) and a₀ = cH₀/√(4π²−1) is derived from the Bekenstein-Hawking entropy S=A/4G. The collapse time is τ_ERG = τ_PD × μ(Gm/r²a₀) ≤ τ_PD: ERG always predicts faster collapse. At the crossover r_trans = √(Gm/a₀), where μ(1) = 1/√2 exactly: τ_ERG = τ_PD/√2. For m = 10⁻¹⁴ kg: r_trans = 74.6–79.2 nm. Current levitated nanosphere experiments have achieved ~50 nm, placing them within a factor of 1.5 of the ERG crossover. The diagnostic is the shape of τ(r): standard Penrose-Diósi gives τ∝r (linear); ERG develops a kink at r_trans with subsequent r^(3/2) steepening. The kink position is predicted from H₀ alone — not fitted. This is the first modification of the Penrose-Diósi criterion with zero free parameters, and the most concrete near-term laboratory test of quantum gravity yet proposed. ERG Preprint Letter II. Full programme: Zenodo records 19077317, 19161618, 19318665, 19415023, 19424980, 19484181, 19512503, 19537805. PRL Letter I: 10.5281/zenodo.19547151.
A model of the vacuum as a face-centered-cubic lattice predicts a two-step quantum–classical threshold, at 13.1 and 22.6 µg, from the hypothesis that a center-of-mass excitation stays coherent only while its reduced Compton wavelength is resolvable by the lattice. Collapse models also limit macroscopic coherence, so the two must be told apart by more than a scale. We derive three discriminators from the model's postulates and compute the counterpart in Diósi–Penrose collapse and in continuous spontaneous localization (CSL). The thresholds depend on total mass alone, while both collapse models depend on density. Below 13.1 µg the model predicts no intrinsic decoherence, where collapse takes 1 s for Diósi–Penrose and about a microsecond for CSL at its experimental bound, for 10⁻¹⁵ kg over 1 µm. The model predicts no measurable heating; read as position localization, its own rate scale would exceed the LISA Pathfinder bound by 66 orders of magnitude, so coherence loss above the threshold must be dephasing in the energy basis. If its effective mode mass is the relevant mass, a 16.2 µg mechanical cat state then bounds the irreversible coupling at 38 orders below its natural scale. A worked levitated-particle example and a public script complete the analysis.