- Oppenheim spent five years developing a new quantum gravity framework.
- Postquantum gravity gives spacetime itself a fundamental random element.
- The randomness strengthens at low acceleration, mimicking dark matter effects.
Jonathan Oppenheim had been sitting with an uncomfortable idea for five years before his colleagues took it seriously.
The professor of quantum gravity at University College London had proposed something unusual: a framework for uniting quantum physics with gravity that didn't give quantum properties to gravity at all. Instead, he gave gravity something stranger. Randomness.
His theory, postquantum gravity, imagines spacetime as fundamentally unstable. Not random in the ordinary sense of things we don't know, but random in the same deep, irreducible way that quantum mechanics is random. Time fluctuates. Space warps unpredictably. The future doesn't follow cleanly from the past.
What is the quantum gravity problem?
Quantum mechanics and Einstein's general relativity are the two pillars of modern physics, but they are mathematically incompatible. Quantum theory is non-deterministic, built on irreducible randomness. General relativity is deterministic, describing a smooth, continuous spacetime. Unifying them has been one of physics' central unsolved problems for nearly a century.
A Century-Old Problem, a Different Door
The standard approaches to merging quantum mechanics with general relativity, string theory, loop quantum gravity and their variants, all start from the same assumption: gravity must eventually be quantum. They try to quantize it.
Oppenheim went the other way. Gravity stays classical. Quantum mechanics stays quantum. But they interact, and that interaction is stochastic in both directions.
The mathematics, as Sabine Hossenfelder explains in this careful and occasionally self-deprecating video, allows the two kinds of randomness to coexist without contradiction. That alone is a genuine achievement. For decades, this path seemed logically blocked.
Time since last new approach
40+ years
Physicists had not found a genuinely new framework for the quantum gravity problem in more than four decades before Oppenheim's proposal.
When Randomness Looks Like Dark Matter
The more surprising claim came in a subsequent paper, co-authored with Andrea Russo, a graduate student also at UCL. They noticed something arresting about the randomness term in Oppenheim's equations.
Its effect isn't uniform. At high accelerations, near large masses, the correction is negligible. At small accelerations, in the outer regions of galaxies far from dense concentrations of matter, it becomes significant.
This is precisely the regime where dark matter becomes necessary in the standard model. The outer stars of most galaxies orbit far too quickly to be explained by visible mass alone. For decades, the solution has been to posit a vast invisible halo of dark matter. But a rival school, Modified Newtonian Dynamics (MOND), suggests the law of gravity itself changes at low accelerations.
Oppenheim and Russo found that their randomness term produces corrections that, mathematically, resemble the MOND regime. And, for good measure, they also found a contribution that looks like dark energy, the mysterious force driving the accelerating expansion of the universe.
Folks, something seems to be happening. We show that our theory of gravity can explain the expansion of the universe and galactic rotation without dark matter or dark energy.
Jonathan Oppenheim, University College London
A Promising Structure, a Technical Doubt
Hossenfelder is honest that she finds the core idea compelling. The unification attempt has real mathematical integrity. But she's skeptical of the dark matter claim.
Her objection is technical: the correction term is linear in the Newtonian potential. For a modified gravity theory to correctly reproduce the observed relationship between galactic rotation speeds and stellar mass, the equation needs to be nonlinear, with a specific 3/2 exponent. She suspects the scaling with galaxy mass won't come out right.
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→She says this with evident reluctance, noting that she may be publicly wrong in front of a large audience. It's a useful reminder of how physics actually works.
The papers were preprints, not yet peer reviewed at the time of this video. Further tests against a wider range of observations will determine whether the dark matter connection holds. The unification framework itself, that careful marriage of two kinds of randomness, is likely to attract sustained attention regardless.
Physicists had not found a genuinely new approach to this problem in more than four decades. Whether or not spacetime randomness turns out to explain galactic rotation, that alone makes Oppenheim's idea worth following.
Sources
- Sabine Hossenfelder, "New Idea Solves Three Physics Mysteries at Once: Post Quantum Gravity" (YouTube, 2024)
- Oppenheim & Russo, "Gravitationally induced decoherence vs space-time diffusion: testing the quantum nature of gravity" (arXiv, 2024)
- Oppenheim, "A postquantum theory of classical gravity?" (arXiv, 2018)
- Hossenfelder, "The End of the Dark Universe?" (Nautilus, 2024)
Fact Check: Claim-by-Claim Verification Verified
The article accurately summarizes Jonathan Oppenheim's postquantum gravity theory, its core claims from cited preprints, and Sabine Hossenfelder's balanced discussion in her video, with appropriate caveats on the dark matter explanation.
Commentary
- "40+ years" since new framework is per Hossenfelder's phrasing; prior classical-quantum coupling attempts existed but Oppenheim's stochastic formulation is presented as novel.
- Dark matter/energy explanations are preliminary mathematical observations, not confirmed by observations; article appropriately hedges with Hossenfelder's skepticism and need for tests.
- Oppenheim quote matches his public statement referenced in Hossenfelder's video.
Sources used for verification
Academic/Peer-reviewed:
- A postquantum theory of classical gravity? - arXiv
- Anomalous contribution to galactic rotation curves due to stochastic spacetime - arXiv
Other reliable sources:
Fact-checked by Perplexity Sonar Pro on 2026-03-03
