The end of the dark universe?

Rather than abandon the theory or complicate it such that it becomes compatible with fully classical GR, they solved a Schwarzschild-de Sitter (static spherical symmetry and an expansion term which "washes out" the extra-strength gravitational potential before it gets too strong) spacetime with a galactic mass (described simply and with some restrictions) and found that the geodesics are within a standard deviation or so of stable circular MONDian orbits. That result would relieve some of the immediate concern that their theory is unphysical, and drive them towards further study of its large-length-scale behaviour.

(In fact their result is better than some earlier attempts to make a generally covariant MOND by adding auxiliary gravitational fields to GR (see the overview by Famaey & McGaugh 2012). Postquantum-classical gravity was on a relativistic footing from the start, although exactly how diffeomorphism invariance and manifest covariance of formulations works in postquantum-classical gravity is really interesting, see <https://arxiv.org/abs/2402.17844> if you want details)

It would be interesting to see how their theory does does -- it would have to be studied numerically -- with any sort of CDM halo. Various stellar binaries are also an obvious place to look, since for sufficiently wide ones, you can't "wash out" the extra strength of the scalar potential with an expansion term. (Wide binaries are really rough on MOND too, for comparable reasons).

> it doesn't (yet?) replace anything

The authors know that. From just after Eqn (23) in the preprint <https://arxiv.org/abs/2402.19459>:

"While this study demonstrates that galactic rotation curves can undergo modification due to stochastic fluctuations, a phenomenon attributed to dark matter, it is important to acknowledge the existence of separate, independent evidence supporting ΛCDM. In particular, in the CMB power spectrum, in gravitational lensing, in the necessity of dark matter for structure formation, and in a varied collection of other methods used to estimate the mass in galaxies"

Okay, so maybe I did continue the argument a little :) I love for people working on alternative less mainstream ideas. But MOND was never very alive to begin with, let alone decades later. Let's move on.

But it's super cool that they show that a bit of randomness could explain dark matter and energy.

Personally I believe that the randomness might come from chaotic "background" gravitational waves from sources outside of universe and from times before Big Bang.

It is also not the point of peer review to judge the correctness of the theory. Reviewers check relevance, novelty, plausibility, consistency, overall correctness of methodology. "I think this is wrong" is not something an editor would accept as an argument not to publish. That's something you can write in a new paper. And I don't think Hossenfelder would like to see it not published just because she thinks it's wrong.

[0] https://arxiv.org/abs/2402.19459

The article spends about a third of its time waxing loquacious about MOND - hossenfelder's own theory - before dismissing the current paper for having equations that are just "too simple" .

Now I'm not a physicist. I'm an applied category theorist working in business process modeling of all things. But when I was reading hossenfelder's article I was hoping it would describe how oppenheim models the spectral dispersion of stochastic gravity. This is the linchpin of how oppenheim predicts physically observable phenomenon from the model.

That was missing. There have been other articles, which at least mentioned it in passing. I was hoping hossenfelder, being a physicist, could help clarify that for a wider audience. They made a choice not to.

This time around, I feel like I should point out I went back and checked and it's in 6 sentences across 3 paragraphs in a 18 paragraph article.

I don't know why you started a new account to make wildly exaggerated claims about a pretty good article, but here we are

> This presents a testable deviation from classical general relativity, potentially observable when the other terms are small, such as at low acceleration. The absence of such terms is likely to falsify this model. On the other hand since diffusion of the metric can result in stronger gravitational fields when we might otherwise expect none to be present, it raises the possibility that diffusion may explain galaxy rotation curves and galaxy formation without the need for dark matter

It certainly doesn't seem like an extreme reading to call this a MOND theory.