James Webb Space Telescope finds evidence for alternate theory of gravity

>We know for a fact that gravity is _not_ Newtonian, that the inverse square law does not hold

[citation needed]

The consensus is that gravity - outside of extreme mass/energy environments - works just as Newton described it to many many decimal places.

Emphasized part added because people in the replies thought that I literally think that General Relativity is somehow wrong. Don't be dense. All I'm saying is that gravity at galactic scales works as Newton described it. General Relativity has extremely tiny effect at those scales.

When you say "outside of" - that's the thing where it doesn't hold. It's interesting and not even wrong to say "these rules work in these contexts" but as far as I can tell we're looking for the scenario invariant rules.

https://en.wikipedia.org/wiki/Tests_of_general_relativity#Pe... is the example I learned in school. You don't need to be around a black hole for GR to suddenly switch on.

Newtonian gravity is an approximation. A perfectly acceptable one in many contexts, but still measurably incorrect.

These extremes exist, and GR predictions are better than Newton’s in those cases. Closest to home is mercury’s perihelion drift. We have observed black hole mergers, gravitational lensing, and GR is also an essential component in understanding the universe’s expansion(that we know from redshift and the CMB). Likely MOND will address these, but Newtonian mechanics will not get you there.

Citation needed? That's ridiculous. The empirical evidence is well over century old at this point. Start with the anomalous precession of Mercury's perihelion. That already can't be accounted for by Newtonian gravity.

You're simply wrong. There's no other way to put it. The GPS system would have been simply impossible to deploy without the general theory of relativity. There's no extreme energy or mass involved, just precision requirements that are influenced by the minuscule differences in time experienced by the surface of the earth and orbiting satellites.

Also Newton's laws famously could not account for Mercury's orbit. Mercury is just an ordinary planet orbiting an ordinary star. Nothing extreme is involved. He knew his laws were incomplete. But they were so dead-on in basically every other scenario that could be physically observed at the time that he figured there was some small tweak missing (or maybe another planetary body that hadn't been spotted yet).

We can see gravitational redshift on Harvard's campus thanks to gamma ray Mossbauer spectroscopy.

Nobody said that general relativity is "switched on" around black holes.

But ok, let me put it this way: outside of extreme energy/mass environments, gravity is described by Newton's law of gravitation with very high precision. If you look very hard, you may notice differences on the order of 10e-MANY. But for all intents and purposes, gravity is Newtonian in 99.99999% of the universe.

that's like saying the visible mass of the universe is 99% hydrogen and helium, so we don't need to learn about chemistry.

Not for all intents and purposes.

If we are asking whether MOND is useful, then the answer is probably yes. You might use it for simulations of galaxy formation where Newtonian gravity is considered a reasonable approximation today. But MOND is not a correct model of the universe. There is no place in the universe that Newtonian gravity applies, only places where the error is an acceptable trade-off for simpler calculation.

The inaccuracy of the Newtonian theory of gravity is large enough that it was already noticed by astronomers in the mid-1800s.

So you're saying we should model galaxies down to the level of individual protons? Lol.

Galactic dynamics is governed by gravity, which is Newtonian at those scales.

By the same logic, there's no place in the universe that general relativity applies either, since it breaks down at the quantum level. There's no place in the universe where any theory other than the one true grand unified theory applies, because everything else is just an approximation. At which point we're just arguing about semantics, and I don't see a reason for continuing it on my part.

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!!!).

So spacetime (interactions between mass, space, and time) are required for any sort of precision explanation. If "extreme" means planet size masses, I guess, but I generally consider our solar system pretty normal. However we cannot explain the planetary motion of mercury without relativity, so define your extreme.

But sure, newton is good enough to handle most ground based scenarios where we only care about forces at low precision.

My first thought was that we only know Cavendish's constant to a little over 4 significant figures, so how could this be right? The relativistic effects at Earth's surface would change this by only ~10^-8, so I think the challenge in refining the Cavendish gravitic constant lie elsewhere.

There are vastly different scales where the approximation is correct for newton vs general relativity. Perhaps you can define the scales that you are calling relevant so we understand what you mean.

The scale of galaxies? Which the original article is about? I feel like I need to spell out everything, but ok:

The article is about modified Newtonian dynamics (MOND), which is a theory that modifies Newtonian gravitation to fix some observed differences in galaxies' motion, without invoking dark matter. The original commenter then proclaims "haha, MOND cannot be right, because we know that Newtonian gravity is incorrect". Yeah, no shit Sherlock; it is "incorrect" because it is just a limiting case of general relativity. But that's completely besides the whole point of MOND, which tries to "fix" gravity at galactic scales, which is a Newtonian regime even with general relativity. MOND is trying to tweak the Newtonian formula at those extreme distances, and if it works, then maybe it can be worked out to be a limiting case of a "modified general relativity", just as Newtonian gravity is a limiting case of GR. Got it?

No I did not say that.

I don't think they're saying the relativistic effects don't exist, just that they're still largely unimportant compared to Newtonian effects.

For precession of perihelion of Mercury we mostly noticed because any error is cumulative over time and we could integrate over an arbitrarily wide timebase. The relativistic effects are <10^-8 of the total, around 1/10th of the change imparted by Newtonian gravity of planets much, much further away. The BepiColombo orbiter should allow us to correct for the relativistic effects of other planets' pull on Mercury, but it's expected to be a change of <10^-12.

So I guess "many, many decimal places" is in the ballpark of 6-12.

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.

Ok, then how does your chemistry comment have anything to do with the motion of galaxies? Reminder: you're commenting on an article about MOND, which is a theory that stems from trying to explain the motion of galaxies.

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"

>The consensus is that gravity - outside of extreme mass/energy environments - works just as Newton described it to many many decimal places.

It absolutely does not. Newtonian gravity occurs instantly. It has no notion of information taking time to propagate. But we know gravitational waves happen, so Newtonian gravity is wrong _at even very large scales_. If the sun disappeared Newton tells us we'd know immediately. In GR we'd know about 8 min later.

The bigger problem is not that the quantitative effect is large, but that the _qualitative_ difference of going from the instantaneous effect to one that needs to propagate is enormous. It's the whole point of relativity as a concept.

Even going to GEM as a true, non-singular linear approximation of GR would be a step up from Newton's laws, at least there we can have gravitational waves and causal flow of information.

We know that spacetime is einsteinian, not euclidean, yes. But that's not what's being discussed here. The issue is whether the force of gravity deviates from the expected 1/r^2 value. Experiments, measurements and observations within the solar system have not revealed any deviation. The precession of mercury is not due to a deviation from 1/r^2; it is due to space near the sun being bent instead of flat. Ditto GPS; we have to adjust for time dilation and curved space, but not for any deviation from 1/r^2. MOND theories predict that MOND gravity is indistinguishable from normal at short ranges less than several light years; the MOND effects only show up at distances of many light years.

Samsartor seems to think that the inverse square law does not hold at short distances (e.g. between the sun and mercury). Meindnoch agrees with mainstream physics that the inverse square law does indeed hold at short distances. You're confusing newtonian physics (busted) with the inverse square strength of gravity (still strongly supported); those are two different things. GR says gravity should be strictly 1/r^2, and this is what we observe in the solar system.

Compared to the gravitational fields galaxies orbiting other galaxies deal with Mercury orbiting the Sun is extreme. So are GPS satellites orbiting Earth.

Mass of Sun: Ms = 1.99e30 kg

Distance to Mercury from Sun: Rm = 5.83e10 m

Mass of Milky Way galaxy: Mg = 6e42 kg

Q: At what distance R from the Milky Way would something have to be to experience the same gravitational field strength from the Milky Way that Mercury feels from the Sun?

A: We want R such that Ms/Rm^2 = Mg/R^2 or R = Rm sqrt(Mg/Ms) = 1.0e17 m.

Let's convert that to lightyears. There are 9.46e15 m/ly. The final result is 10.75 ly. Note that everyplace that close to the center of mass of the Milky Way is inside the galaxy. Anything actually outside the galaxy would be at least 5000 ly away and feel a gravity field at most 1/200000th as strong as what Mercury feels.

For Earth use the same calculation from above but replace Mg with the mass of the Earth, 5.97e24 kg. That gives that the distance from Earth where something would feel the same field strength from Earth that Mercury feels from the Sun is 1.0e9 m. That's a little over 4x the radius of the orbits of GPS satellites, so GPS satellites are feeling a little under 16x the field strength from Earth that Mercury feels from the Sun.

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?

> outside of extreme energy/mass environments, gravity is described by Newton's law of gravitation with very high precision. If you look very hard, you may notice differences on the order of 10e-MANY. But for all intents and purposes, gravity is Newtonian in 99.99999% of the universe.

I meant it in the sense that "most of the cosmos runs on Newtonian gravity, therefore we can ignore GR" is similar to "most of the visible matter in the cosmos is hydrogen/helium, so we can ignore chemistry".

The interesting part is in the 0.0000001% that isn't like the others.

Thanks for bringing this up; this is the central reason why I'm skeptical of Newtonian models that predict dark matter, and why I don't think the term MOND makes sense as the simplest alternative.

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

you know what N in MOND stands for, right?

"GR says gravity should be strictly 1/r^2, and this is what we observe in the solar system"

huh?!? there are GR corrections to Newton which include terms like 1/r^3 iirc

You seem to just be arguing about the definition of "gravity" now.

That’s kinda the whole point, isn’t it? I’m just a layman, but my understanding is that the incompatibilities of GR and QM point to a need for a proper theory of gravity. Looking at the dark matter problem from a purely GR-perspective will miss that context.

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...

There are (ȓ/r^3) terms involving unit vectors, but that works out to 1/r^2 in practice. There are cubed terms in string theory and Quantum General Relativity (QGR) / Loop Quantum Gravity, but these do not apply at macroscopic distances. If you know of a url link to a non-theoretical inverse-cube effect which has actually been confirmed in lab experiments or actual observation, please post it.

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"

Huh!?! Classic GR test of Mercury periphelon precession is mainly due to inverse cube correction to Newton