We investigate the entropy production in the Diósi-Penrose (DP) model, one of the most extensively studied gravity-related collapse mechanisms, and one of its dissipative extensions. To this end, we analyze the behavior of a single harmonic oscillator, subjected to such collapse mechanisms, focusing on its phase-space dynamics and the time evolution of the entropy production rate—a central quantity in nonequilibrium thermodynamics. Our findings reveal that the original DP model induces unbounded heating, producing dynamics consistent with the second law of thermodynamics only under the assumption of an infinite-temperature noise field. In contrast, its dissipative extension achieves physically consistent thermalization in the regime of low dissipation strength. Using a short-time approach, we further our study to address the complete dynamics of the dissipative extension, thus including explicitly non-Gaussian features in the state of the system that lack from the low-dissipation regime.
Standard objective collapse models offer a unified approach to the quantum measurement problem but predict an unphysical, indefinite increase in the energy of the system. The dissipative Diósi-Penrose (dDP) model resolves this heating issue by introducing a linear friction mechanism. However, this modification induces complex, non-Gaussian phase-space dynamics. We rigorously establish the thermodynamic consistency of this friction mechanism -- extended to the CSL model -- across both weakly and strongly non-Gaussian regimes. Using the Wigner phase-space formalism, we go significantly beyond the quadratic approximation and, to bypass the failure of perturbative methods under strong dissipation, introduce a novel exact pseudo-spectral simulation approach. Our analysis reveals that the system subjected to the dDP mechanism does not thermalize, but rather settles into a non-equilibrium steady-state (NESS) where the asymptotic non-Gaussianity scales as the third power of the dissipation parameter
β. By evaluating the Wigner entropy production, we confirm the thermodynamic validity of the model and demonstrate that highly sensitive information-theoretic quantities require exact numerical methods to accurately capture the key non-Gaussian tails of the distribution.
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.
Abstract We investigate the phenomenology leading to the non-conservation of energy of the continuous spontaneous localization (CSL) model from the viewpoint of non-equilibrium thermodynamics, and use such framework to assess the equilibration process entailed by the dissipative formulation of the model (dCSL). As a paradigmatic situation currently addressed in frontier experiments aimed at investigating possible collapse theories, we consider a one-dimensional mechanical oscillator in a thermal state. We perform our analysis in the phase space of the oscillator, where the entropy production rate, a non-equilibrium quantity used to characterize irreversibility, can be conveniently analyzed. We show that the CSL model violates Clausius law, as it exhibits a negative entropy production rate, while the dCSL model reaches equilibrium consistently only under certain dynamical conditions, thus allowing us to identify the values—in the parameter space—where the latter mechanism can be faithfully used to describe a thermodynamically consistent phenomenon.
We investigate the Di\'osi-Penrose (DP) proposal for connecting the collapse of the wave function to gravity. The DP model needs a free parameter, acting as a cutoff to regularize the dynamics, and the predictions of the model highly depend on the value of this cutoff. The Compton wavelength of a nucleon seems to be the most reasonable cutoff value since it justifies the nonrelativistic approach. However, with this value, the DP model predicts an unrealistically high rate of energy increase. Thus, either one is forced to choose a much larger cutoff, which is not physically justified and totally arbitrary, or one needs to include dissipative effects in order to tame the energy increase. Taking the analogy with dissipative collisional decoherence seriously, we develop a dissipative generalization of the DP model. We show that even with dissipative effects, the DP model contradicts known physical facts, unless either the cutoff is kept artificially large or one limits the applicability of the model to massive systems. We also provide an estimation for the mass range of this applicability.
This note presents a conceptual modification to the Diósi–Penrose (DP) objective collapse model. The note conjectures that the timescale of wave function collapse (
τ≈ℏ/EG) is influenced not only by the gravitational self-energy (
EG) but also by the asymmetry in the "dispositional thermodynamic capacities" (
S˙disp) of the superposed branches. The proposed modification introduces a multiplicative correction factor, expressed as
τ−1≈(EG/ℏ)⋅[1+f(ΔS˙disp)], ensuring the effect vanishes when branches are thermodynamically symmetric or when
EG approaches zero. This approach is distinctly framed against the existing dissipative-collapse literature (e.g., dissipative DP and CSL variants), as it relies on a between-branch difference rather than a global dissipative term to modulate the collapse rate. The document outlines two hard constraints for this theoretical framework: Degeneracy: Canonical DP tests inherently lack thermodynamic asymmetry (
ΔS˙disp=0), meaning the correction predicts nothing beyond bare DP unless thermal asymmetries (e.g., thermal gradients or substrate proximity) are deliberately engineered. Magnitude: The correction factor must be heavily suppressed below the raw thermal scale, as naive scaling with thermal energy across a mesoscale object's phonon modes would exceed
EG by many orders of magnitude. Finally, the note addresses current barriers to empirical testing. It acknowledges that the conjecture remains practically unfalsifiable at present because the methods required to engineer
ΔS˙disp=0 are degenerate with ordinary, non-gravitational decoherence effects, and no current experimental configuration isolates the proposed mechanism from these confounds. Keywords: Diósi-Penrose Model, Objective Wave Function Collapse, Quantum Decoherence, Gravitational Self-Energy, Dispositional Thermodynamic Capacity, Quantum Foundations, Spontaneous Collapse, Dissipative Collapse.
The Cost of Reality. Does gravity have an energy bill? For decades, physicists have debated why the quantum world allows particles to exist in multiple places at once (superposition), while our everyday world does not. The Diósi–Penrose hypothesis offers a tantalizing solution: gravity itself acts as the "monitor," forcing massive objects to choose a single location. In this work, we subject this hypothesis to the ultimate accountant: Thermodynamics. Using Landauer’s Principle—the rule that erasing information requires energy—we show that if gravity "erases" quantum superpositions to create classical reality, it must pay a thermodynamic price. We calculated this price and compared it to what Einstein’s General Relativity allows gravity to pay via radiation. The result is a shocking discrepancy: the "Thermodynamic Gap." Standard gravity is roughly 50 orders of magnitude too weak to carry away the heat of reality-formation. This forces the Diósi–Penrose model into a corner with two stark experimental consequences: 1. The Heating Scenario: If the energy stays in the object, it should be getting much hotter than observed, ruling out vast swathes of the theory.2. The Cooling Scenario: If gravity does manage to pay the bill, it requires a non-standard, highly efficient mechanism we call "Dark Damping." This would manifest in the lab not as heating, but as anomalous cooling—a mysterious "vacuum friction" that sucks energy out of moving objects without thermal noise. We propose that table-top experiments with levitated nanoparticles can now hunt for this signature. We are effectively looking for the "exhaust heat" of the engine that generates our classical spacetime. If we find it, it changes our understanding of gravity. If we don't, one of the most popular explanations for quantum collapse is thermodynamically bankrupt.