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Schrödinger's Cat, Gravitational Waves, and the Information Leak Behind Decoherence

Eran Sinbar

Published Jan 24, 2026• 0 citations
Publisher

Abstract

We propose that gravitational-wave distinguishability provides a universal, information-theoretic mechanism for decoherence in quantum superpositions involving massive systems. When alternative quantum histories imprint distinguishable gravitational radiation states into spacetime, which-branch information exists in principle even in the absence of measurement. This suppresses interference purely through unitary entanglement with the gravitational field. Unlike collapse models, this framework relies only on standard quantum mechanics and the information-carrying capacity of gravitational radiation. We argue heuristically that the Planck mass emerges as an information-theoretic crossover scale beyond which gravitationally induced decoherence becomes unavoidable. To clarify the conceptual content, we introduce a Schrödinger’s-cat–type thought experiment in which one branch of a quantum superposition produces colliding black holes and gravitational waves, while the other does not. In this limit case, spacetime itself functions as an irreversible which-branch environment. The analysis positions gravity not as a modifier of quantum mechanics, but as a universal information channel contributing to the quantum–classical transition.

DOI
10.5281/zenodo.18362963

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We propose that gravitational-wave distinguishability provides a universal, information-theoretic mechanism for decoherence in quantum superpositions involving massive systems. When alternative quantum histories imprint distinguishable gravitational radiation states into spacetime, which-branch information exists in principle even in the absence of measurement. This suppresses interference purely through unitary entanglement with the gravitational field. Unlike collapse models, this framework relies only on standard quantum mechanics and the information-carrying capacity of gravitational radiation. We argue heuristically that the Planck mass emerges as an information-theoretic crossover scale beyond which gravitationally induced decoherence becomes unavoidable. To clarify the conceptual content, we introduce a Schrödinger’s-cat–type thought experiment in which one branch of a quantum superposition produces colliding black holes and gravitational waves, while the other does not. In this limit case, spacetime itself functions as an irreversible which-branch environment. The analysis positions gravity not as a modifier of quantum mechanics, but as a universal information channel contributing to the quantum–classical transition.
An environment interacting with a system acquires information about it, e.g. about its location. The resulting decoherence is thought to be responsible for the emergence of the classical realm of our Universe out of the quantum substrate. However, this view of the emergence of the classical is sometimes dismissed as a consequence of insufficient isolation and, hence, as non-fundamental. In contrast to many other systems, a black hole can never be isolated from its Hawking radiation which carries information about its location, making this lack of isolation fundamental. Here we consider the decoherence of a "black hole Schrödinger cat"-a non-local superposition of a Schwarzschild black hole in two distinct locations-due to its Hawking radiation. The resulting decoherence rate turns out to be given by a surprisingly simple equation. Moreover, and in contrast to known cases of decoherence, this rate does not involve Planck's constant ħ.
We present a simple calculation leading to the quantum gravitationally-induced decoherence of a spatial superposition of a massive object in the linear coupling regime. The point of this calculation is to illustrate that the gravitationally-induced collapse could be of the same origin as any other collapse, i.e. due to the entanglement between the system (here a massive object) and its environment (in this case gravity, but it could well be the electromagnetic or any other field). We then point out that, in some cases, one has to be careful when concluding that matter-wave interference of large masses (to be quantified) would be prevented by their coupling to the gravitational field. We discuss how to experimentally discriminate between decoherence due to entanglement, decoherence due to classical dephasig as well as a genuine collapse of quantum superpositions (if such a process exists at all).
The gravitational decoherence field studies the suppression of coherence in quantum systems caused by effects rooted in the gravitational interaction. This models are not just important to yield interesting ideas about the search, in regimes others than the Planck scale, for the interplay between quantum mechanics and general relativity, but also from a theoretical point of view. The fact that the gravitational field can not be shielded opens the question of how strong will the gravitational ‘environment’ decohere a quantum system? and if this decoherence can somehow explain the absence of macroscopical super- positions? This thesis studies in depth the ‘Classical Channel Gravity’ (CCG) model, a recent proposal of gravitational decoherence that assumes that the gravitational interac- tion is always accompanied with an intrinsic decoherence mechanism which ensures that there is no transmission of quantum information between the parties involved. This model can be understood a series of weak continuous quantum measurements accompanied with a feedback term produced by some underlying hidden gravitational degrees of freedom. We first study all the possible emergent dynamics from collisional Markovian dynamics; these ones range from exact unitary to arbitrary fast decoherence (Zeno effect). The second part of the thesis is devoted to study the Newtonian and post Newtonian limits of the CCG model, with particular focus on the testability features of CCG. In particular, we apply this model to coupled clocks and find that the amount of decoherence predicted by CCG is the same as the decoherence that an ‘environment of clocks’ will imprint in a single clock in the context of unitary evolution. On the other hand, we find that this effect is far from being detectable with the current achieved time accuracy. However, CCG as a model for multi partite systems and two systems with very different masses seems to yield an amount of decoherence that is not only able to be detectable with current experiments but also seems to indicate that this model is ruled out. Nevertheless, we also mention potential caveats with our assumptions and discuss other physically motivated directions to further study this result. Finally, we also explore the extension of CCG for the cosmological scenario. In this context the scale factor is being decohered by test particles ‘sitting’ on spacetime. We find that this decoherence will be seen by an observer unaware of the CCG fundamental mechanism as an emergent form of dark energy filling the universe.
We present a unified and minimal theoretical framework addressing the quantum-classical transition, the measurement problem, and the emergence of the arrow of time, grounded in gravitational physics. Building on the insight that quantum superpositions of mass distributions necessarily imply superpositions of gravitational potentials, we show that such states are unavoidably associated with superpositions of proper times due to gravitational time dilation. By extending the system Hilbert space to include a temporal degree of freedom, we demonstrate that matter-time entanglement leads naturally to effective decoherence when the time degree of freedom is traced out. The resulting reduced dynamics takes the form of a Lindblad master equation derived from an underlying unitary evolution. This framework reproduces the correct microscopic and macroscopic limits, clarifies the relation to Diósi-Penrose-type models, and provides a coherent account of classicality and temporal irreversibility without postulating observers, environmental decoherence as fundamental, or objective wavefunction collapse.
Probing gravity-related decoherence with a 16 μμμg Schrödinger cat state
The Schrödinger equation predicts the validity of the superposition principle at any scale, yet we do not experience cats being in a superposition of "dead" and "alive" in our everyday lives. Modifications to quantum theory at the fundamental level may be responsible for the objective collapse of the wave function above a critical mass, thereby breaking down the superposition principle and restoring classical behavior at the macroscopic scale. One possibility is that these modifications are related to gravity, as described by the Diósi-Penrose wavefunction collapse model. Here, we investigate this model using experimental measurements on the decoherence of a Schrödinger cat state of a mechanical resonator with an effective mass of 16 micrograms.
In this paper, the authors propose a phenomenological framework for addressing the black hole information loss paradox using the Gravity Branch Model (GBM) of quantum measurements. In this approach, quantum measurement branching is dynamically constrained by local spacetime curvature, producing effective selection of semiclassically consistent trajectories. We develop Schrödinger-like and master equation formulations for the GBM, apply it to a detector of Hawking radiation, and examine how gravitationally suppressed branch proliferation modifies the apparent information content. Our analysis suggests that information loss in black holes can be reinterpreted as curvature-induced pruning of quantum measurement branches, rather than fundamental nonunitarity, with experimentally constrained coupling strengths ensuring consistency with laboratory observations.