Gravity’s Minimal Noise Level Confirmed by New Theoretical Models

Giuseppe Fabiano and colleagues at Lawrence Berkeley National Laboratory, in a collaboration between Lawrence Berkeley National Laboratory, Ochanomizu University, and Kyushu University, have classified gravitational models that do not require field quantization. This finding establishes a key threshold. Detecting gravitating systems with noise below this level would provide evidence supporting the entanglement of Newtonian gravity, offering a new pathway to test the foundations of gravitational theory. Mapping gravitational theories through Galilean invariance and Newtonian limits Systematic classification was employed to map the field of gravitational models that do not rely on the concept of gravitons, hypothetical particles mediating gravity. The motivation for exploring alternatives to graviton-based theories stems from ongoing challenges in unifying general relativity with quantum mechanics. While general relativity accurately describes gravity at macroscopic scales, its incompatibility with the probabilistic nature of quantum mechanics necessitates investigation into alternative frameworks. Adhering to established principles like Galilean invariance, the consistency of physical laws for observers in uniform motion, provided a framework for this investigation, much like a bouncing ball behaves identically on a stationary platform or a smoothly moving train. This invariance is crucial because it ensures that the predictions of the theory are independent of the observer’s inertial frame, a cornerstone of both Newtonian and relativistic physics. By demanding this consistency and accurate reproduction of Newtonian gravity on average, researchers defined rigorous boundaries for non-quantized gravitational theories. The Newtonian limit, where gravitational fields are weak and velocities are low, serves as a vital benchmark for any proposed theory of gravity, ensuring compatibility with well-established experimental observations. Gravity models beyond the standard graviton theory were investigated, focusing on those consistent with Galilean invariance and reproducing Newtonian gravity on average. This involved a detailed analysis of various theoretical approaches, including classical-quantum gravity hybrids and models based on entropic gravity, which posits that gravity arises from the tendency of systems to maximise entropy. Analysis revealed that any non-entangling model requires a quantifiable minimum amount of noise to be injected into any experimental system. This noise isn’t simply an external disturbance; it’s an inherent property of the gravitational interaction itself within these models. Should gravitating systems be measured at noise levels below this threshold, Newtonian gravity would be demonstrated as entangling. Classical-quantum gravity and entropic gravity models were examined, both predicting a small but irreducible amount of noisy evolution. The presence of this irreducible noise is a direct consequence of abandoning the quantized nature of the gravitational field, forcing a departure from the reversible dynamics characteristic of quantum mechanics. Quantifiable noise limit constrains non-quantized gravity and predicts gravitational entanglement A new, quantifiable limit of √Saa ≈10−18m/s2/ √ Hz for a pair of 1mm-separated masses has been established. This threshold represents a strong improvement over prior calculations, which lacked a systematic framework, and defines the minimum noise level inherent to any gravity theory lacking gravitons. The derivation of this limit involved careful consideration of the spectral density of the noise, quantifying the noise power per unit frequency. Detecting noise below this level would demonstrate gravitational entanglement, proving Newtonian gravity behaves quantum mechanically and fundamentally differs from classical predictions. This would have profound implications for our understanding of the universe, suggesting that gravity is not merely a classical force but is deeply intertwined with quantum phenomena. Detailed calculations of noise levels allow for a direct comparison with experimental data, moving beyond theoretical constraints to a measurable prediction relating to gravity. This noise manifests as a quantifiable, minimal decoherence, requiring its injection into any experimental system, challenging the notion that noise solely arises from interactions between objects. Decoherence refers to the loss of quantum coherence, the property that allows for quantum superposition and entanglement. Specifically, calculations demonstrate that models predicting entanglement must overcome dissipation terms, linked to single-body effects and the Newtonian interaction, alongside any non-reversibility present. These dissipation terms represent energy loss from the system, contributing to the overall noise level. The level of this noise is linked to the gravitational coupling between masses and their separation, with the derived threshold offering a means to test models against experimental results. However, these findings currently rely on idealized scenarios and do not account for all potential real-world noise sources impacting sensitive experiments, such as seismic vibrations, electromagnetic interference, and thermal fluctuations. Future work will need to address these complexities to refine the experimental verification of these predictions. Quantifying gravitational noise establishes limits for graviton-free theories A quantifiable minimum level of noise inherent to any gravity model lacking gravitons has been established, offering a new benchmark for experiments. This provides a crucial tool for evaluating the viability of alternative gravitational theories and guiding future experimental efforts. The analysis of models proposing Newtonian gravity as an entropic force reveals a reliance on parameters, mediator damping rates and bath temperatures, that remain largely unconstrained by existing observations. Entropic gravity models often introduce a ‘gravitational bath’, a reservoir of energy that mediates the entropic force. The damping rate describes how quickly fluctuations in this bath dissipate. This introduces a tension, as while the framework effectively classifies models, predicting specific noise levels requires accurate knowledge of these hidden variables, potentially limiting its immediate predictive power. Determining these parameters requires independent experimental measurements or theoretical constraints from other areas of physics. Acknowledging that pinpointing precise noise levels hinges on currently unknown parameters does not diminish the value of this work.

This research systematically classified models adhering to established physics principles, such as Galilean invariance, the consistency of laws regardless of motion, and accurately reproducing Newtonian gravity. The demonstration that any non-quantized gravity model must inject a quantifiable minimum amount of noise into experimental systems to avoid predicting gravitational entanglement, a linked fate between objects regardless of distance, was achieved. This establishes a fundamental noise level inherent to gravity theories that do not require gravitons, hypothetical particles mediating gravitational force. This work opens up a new avenue for testing the foundations of gravity, shifting the focus from searching for gravitons to precisely measuring the inherent noise in gravitational interactions. The established noise threshold provides a concrete target for future experiments, potentially revolutionising our understanding of gravity and its relationship to quantum mechanics. The research demonstrated that any theory of gravity which doesn’t rely on the exchange of gravitons must inherently possess a minimum level of noise to prevent entanglement between massive objects. This is significant because it offers a new way to test gravity, focusing on measurable noise rather than searching for elusive particles. By establishing a quantifiable noise threshold, experiments can now seek to determine if gravity operates below this level, which would suggest entanglement exists. Future work could focus on refining measurements of damping rates and bath temperatures within entropic gravity models to better predict these noise levels and guide experimental design. 👉 More information 🗞 Minimal noise in non-quantized gravity 🧠 ArXiv: https://arxiv.org/abs/2603.26075 Tags: