Daniel Carney

If you want to hear me ramble about quantum noise and cosmic neutrinos, gravitational waves, and axions over zoom, this is tomorrow 4pm ET:

sites.google.com/view/hepastr...

Probably head first!

The obvious future direction is to figure out how to get a relativistic model -- i.e., recover general relativity rather than just Newton's law. Can this be done? TBD...

In brief: the models have free parameters. In some regimes, the emergent gravitational interaction is indistinguishable from the usual picture involving gravitons. But in other regimes, the thermal fluctuations are large, and you can look for this in experiments.

The basic idea is like two pistons being pushed around by an ideal gas. In our model, the pistons are massive objects, and the gas is the collection of thermalized qubits/oscillators.

This is mostly a proof-of-concept construction, but the phenomenology is really interesting, and probably general.

To do this you have to make a detailed microscopic model. In ours, there's a bunch of qubits or oscillators, and the frequencies of these depend on where massive objects are. You can engineer this so that if the qubits are thermalized, this frequency dependent coupling gives a 1/r^2 force.

Jacobson and Verlinde famously suggested that gravity could come from some kind of thermal or "entropic" interaction. But their proposals were basically classical; they don't give enough details to figure out what happens when quantized matter couples to gravity.

Our goal was to figure this out.

People tell me that the technical discussion here is better than twitter these days. So let me try that out. Here's a sort of explainer on the paper:

On the quantum mechanics of entropic forces It was conjectured thirty years ago that gravity could arise from the entropic re-arrangement of information. In this paper, we offer a set of microscopic quantum models which realize this idea in det...

Gravity could come from gravitons, like light comes from photons. Or maybe, like sound waves in a gas, it could come from the entropic dynamics of some microscopic thermal system.

But could that really work? And could it be tested?

We think so.

arxiv.org/abs/2502.17575

Almost forgot to cross post 😅

Classical-quantum scattering We analyze the framework recently proposed by Oppenheim et al. to model relativistic quantum fields coupled to relativistic, classical, stochastic fields (in particular, as a model of quantum matter c...

Could gravity be "fundamentally classical"? Akira Matsumura and I analyzed Oppenheim (@postquantum.bsky.social) et al.'s proposal. tl;dr:

A. it appears to have Lorentz-covariant scattering
B. 2—>2 scattering differs at O(1) from the usual Rutherford/Newton answer

arxiv.org/abs/2412.04839

I know. It's painful to me

small mass scattering on a large mass

Look upon my TikZ, ye mighty, and despair.