Archived Articles
- Uncertainty and nonlocality: a description of my paper with Stephanie Wehner, Science 2010.
- Quantum information can be negative: an accessible description of my paper with Horodecki and Winter in Nature.
- Sending quantum information down channels which cannot convey quantum information: A perspective in Science. A copy is available here.
- Quantum computing as free falling: A Science perspective on quantum computation as geometry. A copy is available here.
A postquantum theory of classical spacetime
Reconciling quantum mechanics with General Relativity (Einstein's theory of gravity), is one of the grand challenges of modern physics. Rather than attempting to quantise gravity, my latest research takes a different approach -- I have instead been developing a consistent theory of quantum field theory coupled to classical spacetime. I've set out why I believe it's reasonable to question whether we should quantise the spacetime metric here, and the proposal can be found in "postquantum theory of classical gravity" based on a master equation approach. With Zach Weller-Davies, we now have a path integral formulation of it. The theory is formally renormalisable, which is exciting, since it allows us to think of gravity as a theory of spacetime down to the shortest of distances.These theories do not need the measurement postulate of quantum mechanics as the Born rule follows from the dynamics. These results follow from the derivation of the most general form of evolution laws for classical systems coupled to quantum ones in 1811.03116 and 2203.01332. We have proposed an experiment, to test whether spacetime is classical via something we call, the decoherence vs diffusion trade-off. Consistent coupling of quantum fields to classical spacetime ncessarily requires the metric to have stochastic fluctuations. If these fluctuations are strong enough, they could provide an alternative explaination to the phenomena we currently regard as dark matter (see here and here).
Explainers about the postquantum theory and the experimental effort to test the quantum nature of spacetime (updated August 2024)
- An article and video explainer suitable from Quantum Magazein can be found here (July 2023).
- PBS spacetime did an episode on the postquantum theory and one on the experimental effort to test the nature of spacetime (August 2024).
- Sabine Hossenfelder can be brutal, but she was gentle with the postquantum theory (December 2023)
A sample of some of my talks on the subject
- Renormalisation of the postquantum theory of classical gravity, ICTS (August 2024)
- My talk for Quantum Gravity and All That (June 2024), kept breaking off into discussions.
- The quantum information structure of spacetime (Feb 2024)
- A post-quantum theory of classical gravity? University of Toronto Physics Colloquium, Nov 28, 2019 (for a general physics audience)
News
- We have shown that the phenomena we currently regard as dark matter could instead be explained by stochastic fluctuations in space time. We have given evidence for this, both in the context of cosmology and in galaxies). (July 2024)
- We have shown that the theory is formally renormalisable. Renormalisability is the property that the theory is valid at the shortest of distance scales. which is a big hurdle to clear. Famously, quantum gravity is not renormalisable, so its remarkable that the classical stochastic theory is. (Feb 2024)
- The paper A postquantum theory of classical gravity is now out in Phys. Rev. X, and highlighted by the editors. (Dec 2023)
- Thomas Galley has written a viewpoint in Physics Magazine on the theory, titled "Might There Be No Quantum Gravity After All?", proclaiming that "The race is on to determine whether this new proposal will win out over the established approaches". (Dec 2023)
- Here is the experimenal proposal in Nature Communications written with Carlo Sparaciari, Barbara Soda, Zachary Weller-Davies. (Dec 2023)