How Far Are We from the Quantum Theory of Gravity?

Abstract

I give a pedagogical explanation of what it is about quantization that makes general relativity go from being a nearly perfect classical theory to a very problematic quantum one. I also explain why some quantization of gravity is unavoidable, why quantum field theories have divergences, why the divergences of quantum general relativity are worse than those of the other forces, what physicists think this means and what they might do with a consistent theory of quantum gravity if they had one. Finally, I discuss the quantum gravitational data that have recently become available from cosmology.

106 page review article solicited by Reports on Progress in Physics

References in corpus (17)

• Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Interpretation
• Exact evolution equation for the effective potential
• Cosmology at Low Frequencies: The 21 cm Transition and the High-Redshift Universe
• Measuring the Baryon Acoustic Oscillation scale using the SDSS and 2dFGRS
• Ab-initio Determination of Light Hadron Masses
• The Ultraviolet Behavior of N=8 Supergravity at Four Loops
• Quantum Contributions to Cosmological Correlations II: Can These Corrections Become Large?
• Three-Loop Superfiniteness of N=8 Supergravity
• Loop Quantum Cosmology: An Overview
• Manifest Ultraviolet Behavior for the Three-Loop Four-Point Amplitude of N=8 Supergravity
• Is N = 8 Supergravity Ultraviolet Finite?
• Pointer states for primordial fluctuations in inflationary cosmology
• Bootstrapping One-Loop QCD Amplitudes with General Helicities
• Ultraviolet properties of Maximal Supergravity
• New Higher-Derivative $R^4$ Theorems
• Gravitons Enhance Fermions during Inflation
• All One-loop Maximally Helicity Violating Gluonic Amplitudes in QCD

Cited by in corpus (61)

• Perturbative Quantum Gravity as a Double Copy of Gauge Theory
• Simplifying Multiloop Integrands and Ultraviolet Divergences of Gauge Theory and Gravity Amplitudes
• General Relativity and Cosmology: Unsolved Questions and Future Directions
• Basics of Generalized Unitarity
• Network Cosmology
• The new lunar ephemeris INPOP17a and its application to fundamental physics
• Designing a space-based galaxy redshift survey to probe dark energy
• Using Cosmology to Establish the Quantization of Gravity
• Field Parametrization Dependence in Asymptotically Safe Quantum Gravity
• Perturbative Quantum Gravity Comes of Age
• An Optomechanical Quantum Cavendish Experiment
• D = 5 maximally supersymmetric Yang-Mills theory diverges at six loops
• Quantum correlation of light mediated by gravity
• Gravity-induced entanglement in optomechanical systems
• Limit on graviton mass from galaxy cluster Abell 1689
• Vacuum Fluctuations of a Scalar Field during Inflation: Quantum versus Stochastic Analysis
• Quantum Gravity: A Brief History of Ideas and Some Prospects
• Scalar Contribution to the Graviton Self-Energy during Inflation
• Running vacuum in QFT in FLRW spacetime: The dynamics of ${\rho }_{\mathrm{vac}}(H)$ from the quantized matter fields
• Loop Quantum Gravity
• On powercounting in perturbative quantum gravity theories through color-kinematic duality
• $d+1$ formalism in Einstein-scalar-Gauss-Bonnet gravity
• Graviton and gluon scattering from first principles
• Model Comparison tests of modified gravity from the Eöt-Wash experiment
• Quantum Stress Tensor Fluctuations of a Conformal Field and Inflationary Cosmology
• One-loop quantum electrodynamic correction to the gravitational potentials on de Sitter spacetime
• Emergent Gravity as the Eraser of Anomalous Gauge Boson Masses, and QFT-GR Concord
• Volume average regularization for the Wheeler-DeWitt equation
• Slowly Rotating Black Hole Solutions to Hořava-Lifshitz Gravity
• One loop graviton corrections to dynamical photons in de Sitter
• Time transients in the quantum corrected Newtonian potential induced by a massless nonminimally coupled scalar field
• Quantum astrometric observables I: time delay in classical and quantum gravity
• Quantum Effects of Mass on Scalar Field Correlations and Fluctuations during Inflation
• Computing the Primordial Power Spectra Directly
• Pure Gravitational Back-Reaction Observables
• The Structure of Multiloop Amplitudes in Gauge and Gravity Theories
• Precision Predictions for the Primordial Power Spectra of Scalar Potential Models of Inflation
• Spacetime and deformations of special relativistic kinematics
• From path integrals to the Wheeler-DeWitt equation: Time evolution in spacetimes with a spatial boundary
• Enhancement of quantum gravity signal in an optomechanical experiment
• On the value of the Immirzi parameter and the horizon entropy
• Gravitational waves from inspiraling black holes in quadratic gravity
• Final Thoughts on the Power Spectra of Scalar Potential Models
• On amplitudes, resonances and the ultraviolet completion of gravity
• Field-induced entanglement in spatially superposed objects
• Covariant quantum corrections to a scalar field model inspired by nonminimal natural inflation
• Effective models of quantum gravity induced by Planck scale modifications in the covariant quantum algebra
• Improving the Single Scalar Consistency Relation
• Quantum Simulation of Black Holes in a dc-SQUID Array
• Testing an Ansatz for the Leading Secular Loop Corrections from Quantum Gravity during Inflation
• The Effect of Features on the Functional Form of the Scalar Power Spectrum
• Studying Lagrangian theories with machine learning: a toy model
• Covariant Effective Action for Scalar-Tensor Theories of Gravity
• Generalizing the ADM Computation to Quantum Field Theory
• Stealth black holes in Aether Scalar Tensor theory
• Non-Gaussianity from Features
• Digital quantum simulation of cosmological particle creation with IBM quantum computers
• Gravitational dephasing in spontaneous emission of atomic ensembles in timed Dicke states
• Neutron Phase Contrast Imaging of PbWO${}_4$ Crystals for G Experiment Test Masses Using a Talbot-Lau Neutron Interferometer
• Imaging of PbWO4 Crystals for G Experiment Test Masses Using a Laser Interferometer
• Can gravity mediate the transmission of quantum information?