Is Quantum Gravity Necessary?

Abstract

In view of the enormous difficulties we seem to face in quantizing general relativity, we should perhaps consider the possibility that gravity is a fundamentally classical interaction. Theoretical arguments against such mixed classical-quantum models are strong, but not conclusive, and the question is ultimately one for experiment. I review some work in progress on the possibility of experimental tests, exploiting the nonlinearity of the classical-quantum coupling, that could help settle this question.

based on a talk given at Peyresq Physics 11, to appear in Class. Quant. Grav

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Cited by in corpus (108)

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• Quantum Superposition of Massive Objects and the Quantization of Gravity
• Dark energy as the weight of violating energy conservation
• Gravitational Decoherence
• On the possibility of laboratory evidence for quantum superposition of geometries
• Gravitational induced particle production through a nonminimal curvature-matter coupling
• Gravitationally Mediated Entanglement: Newtonian Field vs. Gravitons
• Macroscopic Quantum Mechanics in a Classical Spacetime
• Conceptual Problems in Quantum Gravity and Quantum Cosmology
• Measurement Analysis and Quantum Gravity
• Non-Gaussianity as a signature of a quantum theory of gravity
• Quantum superposition of spacetimes obeys Einstein's Equivalence Principle
• Cosmological implications of modified gravity induced by quantum metric fluctuations
• Testing the gravitational field generated by a quantum superposition
• Gravity induced wave function collapse
• Quantum Connectivity of Space-Time and Gravitationally Induced Decorrelation of Entanglement
• Non-Paradoxical Loss of Information in Black Hole Evaporation in a Quantum Collapse Model
• Quantum correlation of light mediated by gravity
• Massive quantum systems as interfaces of quantum mechanics and gravity
• Optomechanical test of the Schrödinger-Newton equation
• Gravitationally induced decoherence vs space-time diffusion: testing the quantum nature of gravity
• Resolving the $H_0$ tension with diffusion
• Towards a formal description of the collapse approach to the inflationary origin of the seeds of cosmic structure
• Gravitational collapse of Bose-Einstein condensate dark matter halos
• White Paper and Roadmap for Quantum Gravity Phenomenology in the Multi-Messenger Era
• Schrödinger-Newton "collapse" of the wave function
• Statistical consistency of quantum-classical hybrids
• Probing the gravitational redshift with an Earth-orbiting satellite
• Breaking quantum linearity: constraints from human perception and cosmological implications
• Concept of an ionizing time-domain matter-wave interferometer
• Implications of purely classical gravity for inflationary tensor modes
• The Trilinear Hamiltonian: A Zero Dimensional Model of Hawking Radiation from a Quantized Source
• The Schrödinger-Newton equations beyond Newton
• Curvature-Restored Gauge Invariance and Ultraviolet Naturalness
• Bose-Einstein condensate strings
• Critical review of prevailing explanations for the emergence of classicality in cosmology
• Relativistic collapse dynamics and black hole information loss
• Optomechanical tests of a Schrödinger-Newton equation for gravitational quantum mechanics
• Emergent Gravity as the Eraser of Anomalous Gauge Boson Masses, and QFT-GR Concord
• Semiclassical theories as initial value problems
• Nonquantum Gravity
• Stochastic extensions of the regularized Schrödinger-Newton equation
• Black Holes: Information Loss But No Paradox
• Testing the nonclassicality of spacetime: what can we learn from Bell-Bose et al.-Marletto-Vedral experiments?
• Schrödinger's cat for de Sitter spacetime
• Reassessing the link between B-modes and inflation
• New class of generalized coupling theories
• Gravitational Decoherence, Alternative Quantum Theories and Semiclassical Gravity
• Measurable signatures of quantum mechanics in a classical spacetime
• Classical theories of gravity produce entanglement
• Hybrid quantum-classical dynamics of pure-dephasing systems
• Interacting classical and quantum particles
• Constraining quantum collapse inflationary models with current data: The semiclassical approach
• Effects of Newtonian gravitational self-interaction in harmonically trapped quantum systems
• Inference of gravitational field superposition from quantum measurements
• Semi-classical gravity phenomenology under the causal-conditional quantum measurement prescription
• Canonical bracket in quantum-classical hybrid systems
• Acceleration noise constraints on gravity induced entanglement
• Generation of quantum entanglement in superposed diamond spacetime
• On the initial value problem for semiclassical gravity without and with quantum state collapses
• Approximations for the free evolution of self-gravitating quantum particles
• Structure of Correlated Worldline Theories of Quantum Gravity
• Newtonian Semiclassical Gravity in the Ghirardi-Rimini-Weber Theory with Matter Density Ontology
• Semiclassical Self Consistent Treatment of the Emergence of Seeds of Cosmic Structure. The second order construction
• Is it time to rethink quantum gravity?
• Gravitational interaction through a feedback mechanism
• The generation rate of quantum gravity induced entanglement with multiple massive particles
• Asymptotically flat vacuum solutions in order-reduced semiclassical gravity
• Which quantum theory must be reconciled with gravity? (And what does it mean for black holes?)
• Quantum spreading of a self-gravitating wave-packet in singularity free gravity
• Mirror-induced decoherence in hybrid quantum-classical theory
• Windows on Quantum Gravity
• Enlightening the CSL model landscape in inflation
• Schrödinger's Black Hole Cat
• Semiclassical cosmology with back reaction: the Friedmann-Schrodinger equation and inflation
• Dark energy effects in the Schrödinger-Newton approach
• A dialog on the fate of information in black hole evaporation
• Spin-Spacetime Censorship
• State Swapping via Semiclassical Gravity
• Emergent universe revisited through the CSL theory
• Quantum gravity and gravitational-wave astronomy
• Emergent Quantum Mechanics at the Boundary of a Local Classical Lattice Model
• Newtonian Self-Gravitation in the Neutral Meson System
• The Role of Quantum Measurements when Testing the Quantum Nature of Gravity
• The Quantum Measurement Problem: A Review of Recent Trends
• Correlations and signaling in the Schrödinger-Newton model
• Self-gravitational dephasing of quasi-classical Stern-Gerlach trajectories
• A Solvable Model of a Nonlinear extension of Quantum Mechanics
• Quantum-Fluid Correspondence in Relativistic Fluids with Spin: From Madelung Form to Gravitational Coupling
• Probing the Schroedinger-Newton equation in a Stern-Gerlach interferometer
• Observational constraints on inflationary potentials within the quantum collapse framework
• The shadows of quantum gravity on Bell's inequality
• Cosmology with quantum matter and a classical gravitational field: the approach of configuration-space ensembles
• Testing Gravitational Self-interaction via Matter-Wave Interferometry
• Series solution of the time-dependent Schrödinger-Newton equations in the presence of dark energy via the Adomian Decomposition Method
• Entanglement and quantum teleportation under superposed gravitational fields
• Gravity as a classical channel and its dissipative generalization
• Can we detect the quantum nature of weak gravitational fields?
• Can gravity mediate the transmission of quantum information?
• Gravitational entanglement and the mass contribution of internal energy in nonrelativistic quantum systems
• Is gravitational entanglement evidence for the quantization of spacetime?
• Measurement of a quantum system with a classical apparatus using ensembles on configuration space
• Gravitational wave emission from the CMB and other thermal fields
• Proposal for a Bell Test with Entangled Atoms of Different Mass
• Seven non-standard models coupling quantum matter and gravity
• Semiclassical Gravity Beyond General Relativity: Insights from Torsion
• Dephasing and inhibition of spin interference from semi-classical self-gravitation
• Salecker-Wigner-Karolyhazy Gedankenexperiment in light of the self-gravity