James Webb Space Telescope finds evidence for alternate theory of gravity

Easy there champ. Noone is shitting on general relativity.

All I'm saying is that the effect of general relativity at galactic scales is so minuscule, that galactic dynamics is - for all intents and purposes - governed by the Newtonian limit of gravity.

If you propose that gravity doesn't behave like the Newtonian limit at those scales, then you're contradicting general relativity as well, since the far-field limit of the Schwartzschild metric is literally Newton's inverse square law.

In layman terms, modified Newtonian gravity, that the article talks about, is an attempt to explain why galaxies don't rotate the way they should according to Newton (and Einstein, because at those distances the two are the same!!!).

I had the impression that "shitting on general relativity" was exactly what MOND was about. That is, it starts from the position that Einstein is wrong, and searches for ways to support that.

The Wikipedia article on MOND literally starts with galaxy rotation curves: https://en.m.wikipedia.org/wiki/Modified_Newtonian_dynamics

There's zero mention of MOND being a rejection of general relativity.

OF COURSE, any tweaking of Newton's formula at galactic scales will necessarily invalidate general relativity, since general relativity predicts Newton's formula at those scales! But MOND tries to work backwards: they propose a modification of the far-field Newtonian formula, and the belief is that it can eventually be worked out to be a limiting case of a "modified general relativity", for lack of a better name. Just how Newtonian gravity was eventually worked out to be a limiting case of a theory called general relativity.

Can you explain how MOND shits on GR? My understanding is it's more like. "GR is mostly right but...". As for MOND being exclusively Newtonian, yeah. In terms of solving the math, you gotta crawl, walk, run. Let's not kid ourselves, GR invokes way harder math than algebra and simple integral calculus. TeVeS Is a first attempt at "walk", let's say, but even it might not be correct even if adjusting gravity may be correct.

If someone emerges with a proof that the two systems are irreconcilable then yeah you have an argument that it's "shitting on GR"

We already know that one must not use Newtonian gravity on the galaxy scale. For example, properly accounting for GR effects is enough to explain the observed rotational curve for our Galaxy without the need for any dark matter hypothesis.

Similarly there are papers that tries to explain the effects attributed to dark matter on the scale of tenths and hundreds megaparsecs using just proper accounting of GR effects. They are rather speculative, but still they show that even on very huge distances Newtonian approximation may not be valid.

Hi! Physics BS, but they let me take some grad courses, including a Spacetime and Relativity class. I can help.

The word "mass" is used in physics in three different general contexts. First, we have mass in mass-energy, as in "how much energy can I get for trading in this mass?" Mass-energy is the coin paid as the price of existence. If it exists, it has mass-energy. Mostly mass for us. Mostly. We can skip that one for now.

The second context of mass is inertial. Mass has the property of inertia, of resisting a change in its direction or speed. It resists stopping if it is motion, and if it is stopped, it resists moving. The degree of the resistance is also called mass. Put a pin in this one.

The third context of mass is gravitational. Two masses, attracting one another because a force between them, a force which is not based on charge or the relatively nearby exchange of some more exotic bosons, no, just attraction based on how much mass is present. Nothing more special.

Now, curiously, values of each one of these seem to agree!

Einstein's absolute core concept in general relativity, the idea from which all else is built, is that inertial mass is identical to gravitational mass, not merely in number, but so fundamentally intertwined that there is no real difference between them, other than being two faces of the same coin. Now, that does not sound like much, but it gives birth to experiments such as an elevator which is falling toward versus an elevator floating far from gravitational sources, and that they are, from the inside of the elevator, impossible to differentiate.

Einstein then constructs general relativity from this, that the "m" in "F = ma" is identical to the first m in "F = -G m1 * m2 / r^2"

In MOND, the two ms are not identical, they only appear close most places, and so you cannot construct general relativity atop it. You will get most correct approximations but you're missing out in some cases.

> For example, properly accounting for GR effects is enough to explain the observed rotational curve for our Galaxy without the need for any dark matter hypothesis.

Do you have some references handy for this? Or are you talking about the work of Deur?

> There's zero mention of MOND being a rejection of general relativity.

you know what N in MOND stands for, right?

See references in https://en.m.wikipedia.org/wiki/Galaxy_rotation_curve right before See also section. For more speculative paper about behavior of galaxy clusters see https://www.scirp.org/journal/paperinformation?paperid=12663...

Do yourself a favour and check your "speculative paper" in google scholar, look at who cites this and the author's related papers, and notice that it's exclusively self-citations. Do yourself another favour and absorb: "Scientific Research Publishing (SCIRP) is a predatory[1][2][3] academic publisher of open-access electronic journals, conference proceedings, and scientific anthologies that are considered to be of questionable quality.[4][5][6]...In 2021 Cabells' Predatory Reports described SCIRP as a "well-known predatory publisher".[2] In the Norwegian Scientific Index the publisher and all of its journals have a rating of 0 (non-academic).[18]". SCIRP itself wildly claims an OALibJ impact factor of 1.18.

The References in your "speculative paper" include at least five citations of the same author's previous work, at least one of which didn't even find its way into SCIRP's OALJ, and does not cite the Ludwig paper.

The full text also has such writing and editing gems, in the published version, as "the disk, the bugle and the halo of dark matter" immediately before eqn 23.

The paper's central argument is not obviously worth untangling, because the decomposition into the g and k fields (eqn 10) isn't Lorentz-invariant which raises questions about higher speed observables like cosmic rays, lensed background, "kicked" post-merger BHs, and even stars flung out of globular star clusters. There is no general transform avaiable in his equations of motion between two subsystems (e.g., outer stars and inner stars) related by a Lorentz boost. As far as I can tell the notational approach (and even the expression "gravitic field" to stand for the the gravitomagnetic field B_g) is unique to the author. It's so atypical (for quite ordinary equations) that I'd be surprised if there was any sort of reviewer or editor at all.

The author <https://people.epfl.ch/stephane.lecorre/> is a computer engineer in the university's architecture department, and claims a master's degree in theoretical physics <https://www.researchgate.net/profile/Stephane-Le-Corre-2>. I admire his continuing interest in and even investigations of "Astrophsics" (sic), but would not point to him as a persuasive expert as you have.

The Ludwig paper (EPJC 2021) is by comparison cited by 60, only a couple of which are self-cites. Whatever take one might have on Springer's approaches to open access journals, EPJC has an IF of almost 5.

Ludwig is an electrical engineer and plasma physicist. With the many cites on his set of related papers, it's clear he was not ignored by virtue of not being an astrophysicist or relativist. So we can't blame Le Corre's background for the lack of published engagement with his no-dark-matter-needed papers.

I don't think that Ludwig's gravitomagnetic vortex model is particuarly interesting in galaxy rotation curves because the fall-off off of the Lorentz force pulling outer margins of the galaxy inwards must have some arbitrary per-galaxy cutoff that also suppresses wild lensing effects at the cutoff point; we're interested mainly in doppler corrections on the HII spectrum rather than luminous stars (we don't necessarily need DM to explain flat rotations for the outer stars - we do need DM for rotating HI gas well beyond those outer stars) so the cutoff point is beyond the optical limb (meaning we should see wild lensing even in HST/WFC3); the gravitomagnetic effects must be smaller than the gravitoelectric effects (and capturing that somewhat in (v/c)^2 terms corrections to Newtonian/Keplerian orbits (v ~ 0.001 c in Andromeda-like galaxies) should be on the order of 10^-6 whereas in this approach we'd need corrections on the order of 10^-5 and higher for lower-mass lower-v dwarfs); and because the formulation does not work well with elliptical and irregular galaxies (both of which can have low circumferential rotational support - blobs of gas move radially in and out) without treating them differently from discoids (and when you do that in this approach you get divergences at galactic cores); and even for discoids there must be a minimum rotational support. More prosaically, the problem with the model is to avoid having to stabilize satellite dwarfs around a galaxy: you have to make the attractive Lorentz force not pull them right into the parent's middle and you have to avoid having satellites tear the crap out of the outer orbits of the parent galaxy's HI gas.

The paper's central idea certainly does not succeed as a general theory for flat rotation curves of HI dust as opposed to stars in circular orbits in a thin-disc plane.

However Ludwig's wasn't an obviously misguided idea, the paper's arguments are pretty clear, he's done follow-on work that is interesting, and the academic dialogue it produced is well deserved. But to say that anyone could use this paper to point to which mathematical object in GR (or which physical aspect of GR) stabilizes the relevant HI and dwarf orbits is, I wager, a huuuuge stretch.

Finally, quoting you:

> For example, properly accounting for GR effects is enough to explain the observed rotational curve for our Galaxy without the need for any dark matter hypothesis

This is not at all borne out by your choice of papers. Ludwig's text doesn't even mention the Milky Way.

Why would they not be identical? You'd change either the Fg function or adjust F=ma (more common). The weak equivalence principle holds in MOND IIUC. You can't make a statement about the strong equivalence principle until the resolution of MOND with GR is well-defined, in which case the strong equivalence principle may still hold.

Anyways, to claim that failing equivalence principle is disqualifying is begging the question since support of the equivalence principle depends on the observations... And already we observe the rotation curves are "messed up". If that means EP is violated, so be it?

You wouldn't argue against a symmetry violation like CP because "it makes the cute rule fail"