Quantum Gravity
Relativity (Einstein's theory of gravity) describes the large and quantum mechanics the small, but inside black holes and at the Big Bang both are needed and the calculations break down. Candidate theories include string theory, loop quantum gravity and asymptotic safety, yet no measurement decides between them. Effects are expected only at the Planck length, far beyond any accelerator. As of October 2026 there is no breakthrough, and hope rests on indirect tests.
Open in the interactive tree →Relativity describes the large, quantum mechanics the small; inside black holes and at the Big Bang both are needed, and the calculations break down. Candidates include string theory (roughly 10^500 possible solutions), loop quantum gravity, asymptotic safety and others. Quantum-gravity effects are expected only at the Planck length (10^-35 m), far beyond any accelerator.
As of now
October 2026: no breakthrough, and no experiment separates the approaches. Hope rests on indirect tests: experiments checking whether two small bodies become entangled through gravity alone (nanodiamond interferometers and others, not yet realized), precision data on the cosmic microwave background and gamma-ray bursts. Even a successful entanglement test would not unambiguously show that gravity is quantum, because open questions of interpretation remain.
What is missing
- A measurable quantity that makes Planck-scale effects or quantum behavior of gravity visible
- A mathematically consistent, complete theory (string theory: the landscape problem; loop gravity: connection to smooth spacetime)
- An understanding of the black-hole information paradox and of the initial singularity
- Quantum control of massive objects (microgram scale) to test gravity-induced entanglement
Becomes possible once solved
- A unified theory of all forces
- The physics of the first instant of the Big Bang and of black-hole interiors
- An answer to whether space and time are fundamental or emergent
Open steps
- Gravity-induced entanglement test Low AI leveragePut two micro-scale masses into quantum superposition, shield them from decoherence, and test whether gravity alone entangles them.
- Mapping the string landscape High AI leverageCharacterize the huge set of string compactifications (about 10^500 solutions) to find which, if any, reproduce our particle content and constants.
- Black-hole information, singularity Low AI leverageUnderstand how information escapes evaporating black holes and how the initial singularity is resolved, with calculations that can be checked in toy models.
- Loop gravity and safety numerics Medium AI leverageShow that loop quantum gravity or asymptotic safety reproduces smooth spacetime at large scales, using large numerical calculations (spin-foam sums, renormalization-group flows).
- Planck-scale signatures in cosmic data Medium AI leverageFind tiny deviations from standard physics in cosmic microwave background and gamma-ray-burst data that could constrain quantum-gravity models.
Where today's AI could help
Low AI leverage. The gap is a measurable prediction and a consistent theory; AI speeds side calculations but cannot supply missing Planck-scale data.
- Compute string-compactification geometry (Calabi-Yau metrics) and scan the landscape faster
- Search for closed-form amplitude formulas and check them symbolically
- Optimize designs and noise models for tabletop gravity-entanglement experiments
- Analyze CMB and gamma-ray-burst data for tiny deviations from standard physics
Shown so far
- In February 2026 OpenAI reported that GPT-5.2 simplified low-point results and proposed a closed form for single-minus gluon tree amplitudes, which physicists then proved and checked (a related field-theory result, not gravity itself). source
- In October 2019 Ashmore, He and Ovrut showed that machine learning computes numerical Ricci-flat Calabi-Yau metrics (needed for string compactifications) one to two orders of magnitude faster than the classical algorithm. source
Prerequisites
- Theory of Relativity1905
- Quantum Mechanics1925
- Standard Model of Particles1973
- Black Hole Thermodynamics1974Black hole thermodynamics is the best clue to quantum gravity