Physicist challenges quantum gravity with radical spacetime theory
Oppenheim's post-quantum model could solve dark matter and rewrite physics
1The quantum gravity wager
In 2023, physicist Jonathan Oppenheim made a 5000:1 bet against gravity being quantum. His 'post-quantum' theory maintains gravity as a classical force in continuous spacetime, directly opposing mainstream physics which assumes all fundamental forces must be quantum. This radical position stems from his belief that preserving Einstein's spacetime description is crucial for any successor theory to general relativity.
2Physics' greatest incompatibility
Modern physics faces a fundamental rift: quantum theory perfectly describes particles and forces at microscopic scales, while general relativity accurately models gravity and cosmic-scale phenomena. Yet these frameworks become mutually incompatible in extreme conditions like black holes or the Big Bang's first moments. Most physicists believe quantum gravity will resolve this, but approaches like string theory require extra dimensions and emergent spacetime.
3Oppenheim's conservative radicalism
Unlike mainstream quantum gravity theories, Oppenheim's model doesn't quantize spacetime. Instead, it introduces small random fluctuations in spacetime coordinates to reconcile quantum mechanics with general relativity. These fluctuations make time slightly unpredictable at tiny scales - a 'glitch' that surprisingly reproduces quantum mechanics' Born rule without assuming it, while potentially explaining dark matter effects.
4Dark matter connection
Oppenheim's May 2024 paper suggests spacetime fluctuations in his model could mimic dark matter's gravitational effects. Current observations show dark matter outweighs normal matter 5:1 in the cosmos, yet its nature remains unknown. While still preliminary, this aspect offers a potential solution without invoking new particles - though the effect's magnitude and properties require further verification.
5The 20p vs £1000 bet
Prominent physicists Carlo Rovelli (loop quantum gravity) and Geoff Penington (string theory) wagered against Oppenheim in 2023. If gravity proves quantum, Oppenheim owes them 20p items; if non-quantum, they owe £1000 prizes. Rovelli criticizes the model for violating both quantum mechanics and relativity, comparing it to denying Earth orbits the sun - a charge Oppenheim strongly disputes.
6Experimental pathways
Two key experiments could test the theory: 1) Attempting to entangle masses in superposition - impossible if gravity isn't quantum. 2) Measuring a superpositioned mass's response to gravity repeatedly - spacetime fluctuations should create inconsistencies. UCL's new David Potter Institute, co-led by Oppenheim, will pursue these tests using advanced quantum sensing technologies over the next decade.
7Gravitational wave constraints
The model predicts a stochastic gravitational wave background from early universe spacetime fluctuations. Existing detectors like LIGO have already constrained possible signals, narrowing the theory's parameter space. Simultaneously, lab experiments with ultracold atoms provide small-scale constraints. As Oppenheim notes, 'There's not much wiggle room' for the theory to evade empirical checks.
8Quantum measurement problem
The model's most controversial aspect involves wavefunction collapse. If an object in superposition gravitationally 'chooses' one position pre-measurement, it violates quantum uncertainty. Oppenheim's solution - fundamental spacetime randomness - troubles some colleagues who want physical causes for such fluctuations. Yet this randomness automatically generates the Born rule, solving a century-old quantum mystery.
9Schrödinger's cat analogy
Daniel Carney compares testing the theory to observing Schrödinger's cat. In quantum gravity, the cat (mass) remains in superposition (alive/dead) until measurement. In post-quantum gravity, spacetime fluctuations would rapidly collapse the superposition (making the cat alive OR dead quickly). This key difference forms the basis for experimental discrimination between the theories.
10Theoretical motivations
Oppenheim argues that after decades of failed quantum gravity attempts, paying the 'price' of spacetime randomness may be necessary. His approach uniquely preserves general relativity's spacetime description while updating quantum mechanics by explaining the Born rule's origin. This contrasts with quantum gravity theories that abandon continuous spacetime entirely - a more radical departure, in his view.
11Peer skepticism
Most physicists remain unconvinced, believing quantum gravity will ultimately prevail. Ivette Fuentes acknowledges the model's creativity but questions its randomness without physical cause. Others note that all quantum gravity approaches break general relativity in some way. The debate highlights how deeply entrenched quantum assumptions are in modern physics thinking.
12Scientific value regardless
Even skeptics like Carney recognize the theory's importance as a test case for quantum gravity assumptions. As Bose notes, without alternative models like Oppenheim's, we might not question gravity's quantum nature at all. The coming decade's experiments - made possible by quantum sensing advances - will determine whether this radical conservatism describes reality.
Original article: New Scientist — Physicist challenges quantum gravity with radical spacetime theory