A LQG Legend Writes Paper Claiming GR Explains Dark Matter Phenomena

[wumbo]

The GEM effects are. But some of the effects that Deur is claiming (and a paper by Deur was what started this thread) are not.Take a look at the entire thread before snarking.Ok. I'm not sure I agree with it, but discussion of personal interpretations is off topic. At least I'm clear now that I don't need to look in the paper itself for those claims.I'm not sure how this paper is relevant to what we're discussing.

Don't move the goal posts -- we were discussing ciotti's paper and it's relevance to GEM effects being significant, the topic moving beyond just Duer's nonlinear claims, which I have no real opinion on.

My point is that the common interpretation of GEM's post Newton _linear_ effects being negligible is untrue, for reasons covered in perturbation theory 101.

I'm not so sure. Fig. 1 in the paper you cite does show numerically different velocity profiles vs. the Newtonian ones as a function of the parameter $\lambda$, which measures the "strength" of the GEM effects, and the corrections, as the authors state, are around 10% to 15%, so not negligible. But all of those profiles have the same general shape as the Newtonian one. None of the profiles are flatter than the Newtonian one once the "peak" is reached, which is what would be required to help reduce the disconnect between the visible matter and observed rotation curves without adding dark matter to the model. Indeed, if anything they are less flat, meaning that these corrections make the problem worse, not better.

And if personal opinions are off topic, I'll point out that in fig 1, the purple curve is flatter than the blue Newtonian curve unless your opinion of flat is very different from the common definition. You can quite clearly see the curvature of the purple curve starts to decrease (I.e. It flattens) more than the blue curve as the normalized radius increases. The Kuzmin-Toomre disk shows it especially.

Regardless, as soon as the negligible effects become non negligible the entire approximation needs to be thrown out and redone because those effects must be taken into account from the get-go. So any model of galactic rotation velocity is invalid unless it includes the basic linear extensions--let alone any nonlinear ones as Duer claims.

 

[PeterDonis]

Don't move the goal posts -- we were discussing ciotti's paper

This thread is not discussing Ciotti's paper. It started by citing a claim by Deur. It then expanded to a general discussion of possible alternate explanations for the phenomena that are attributed to dark matter. Ciotti's paper and the discussion of GEM effects is one piece of that, but not the only piece. It might be the only piece you want to discuss, but this is not your thread and it is not limited to your preferred topic.

in fig 1, the purple curve is flatter than the blue Newtonian curve

Possibly (I would want to look at the actual numbers rather than try to eyeball a graph), but it still doesn't look like an actual galaxy rotation curve. The speed falls off significantly from the peak, as it does for all the curves in the paper. In an actual galaxy rotation curve (at least in galaxies where significant amounts of dark matter are hypothesized to be present), it doesn't fall off at all; it rises to a "peak" value and then stays at that peak. None of the curves in the GEM papers look like that.

 

[wumbo]

This thread is not discussing Ciotti's paper. It started by citing a claim by Deur. It then expanded to a general discussion of possible alternate explanations for the phenomena that are attributed to dark matter. Ciotti's paper and the discussion of GEM effects is one piece of that, but not the only piece. It might be the only piece you want to discuss, but this is not your thread and it is not limited to your preferred topic.

Sure, but it _is_ on-topic and the response was to when it _did_ discuss Ciotti's paper in the context of critiquing Duer. Regardless, I think we agree that this topic is broader than just Duer's paper.

Possibly (I would want to look at the actual numbers rather than try to eyeball a graph), but it still doesn't look like an actual galaxy rotation curve. The speed falls off significantly from the peak, as it does for all the curves in the paper. In an actual galaxy rotation curve (at least in galaxies where significant amounts of dark matter are hypothesized to be present), it doesn't fall off at all; it rises to a "peak" value and then stays at that peak. None of the curves in the GEM papers look like that.

Given that Fig 1 is limited to 5 curves I can't speculate on whether there's a value of lambda that matches exactly, but I don't think you need numbers to verify that the purple curve flattens out. Would need to infer the required lambda from the observed data (if it exists). And you'd need to specify the initial mass distribution for the GEM solution which will significantly change the shape of the curve. I think Ludwig's paper chooses a different distribution, spheroidal Miyamoto-Nagai, than thin disks.

Even if it's not a perfect match, any dark matter that can be explained by "doing the math correctly" really should be eliminated from the standard models. It's kind of troubling that it hasn't been done already, especially since it's so unsophisticated mathematically.

It is noticeable that several authors take reference to Gravitomagnetism in order to explain the observed flat galactic rotation curves, e.g. while Alexandre Deur seems to be quite alone arguing the gravitational field has an energy and hence gravitates too leading to field self-interaction:

Relativistic corrections to the rotation curves of disk galaxies
https://arxiv.org/pdf/2004.05905.pdf

The reason could be that GR experts do trust Gravitomagnetism but don't trust Deur's field self-interaction which based on the heuristic that "GR and QCD have similar Lagrangians".

Duer isn't alone in saying the field itself has energy, that's the crux of the sticky bead argument. GEM is linearized so it ignores self interaction entirely. No idea if that's a valid assumption to make. Regardless, even without self-interaction you see significant contributions.

 

[PeterDonis]

Duer isn't alone in saying the field itself has energy, that's the crux of the sticky bead argument.

This is due to the fact that, in GR, two different meanings of "energy" that we are used to having go together, don't. The sticky bead argument shows that gravitational waves can do work, so they "carry energy" in that sense. But it is also true that spacetime curvature in itself has no stress-energy, and gravitational waves are spacetime curvature; so gravitational waves, and the "gravitational field" in general, do not "carry energy" in that sense.

 

[PeterDonis]

The reason could be that GR experts do trust Gravitomagnetism but don't trust Deur's field self-interaction which based on the heuristic that "GR and QCD have similar Lagrangians".

I would put it that gravitomagnetism and the GEM framework in general are already well known to be derivable from the Einstein Field Equation, whereas Deur's model is not. One thing I have not seen in any of Deur's papers, which surprises me somewhat, is an actual derivation of his proposed interactions (things like gravitational "flux tubes") from the GR Lagrangian. Deriving them from the QCD Lagrangian is, AFAIK, straightforward, so if his heuristic is correct, it should also be straightforward to show that such effects exist in GR.

 

[timmdeeg]

Duer isn't alone in saying the field itself has energy, that's the crux of the sticky bead argument. GEM is linearized so it ignores self interaction entirely. No idea if that's a valid assumption to make. Regardless, even without self-interaction you see significant contributions.

Ok, but it seems no one else claims that field self-interaction leads to increased gravity within matter distributions and decreased gravity outside matter distributions. And thus to a completely different universe as his Friedmann Equations are showing.

 

[timmdeeg]

I would put it that gravitomagnetism and the GEM framework in general are already well known to be derivable from the Einstein Field Equation, whereas Deur's model is not. One thing I have not seen in any of Deur's papers, which surprises me somewhat, is an actual derivation of his proposed interactions (things like gravitational "flux tubes") from the GR Lagrangian. Deriving them from the QCD Lagrangian is, AFAIK, straightforward, so if his heuristic is correct, it should also be straightforward to show that such effects exist in GR.

That he didn't do it "Deriving them from the QCD Lagrangian" could be a sign that it's not possible for principal reasons, e.g. lack of consistency with Gr. If it were possible though that derivation would support his claim enormously.

 

[ohwilleke]

I would put it that gravitomagnetism and the GEM framework in general are already well known to be derivable from the Einstein Field Equation, whereas Deur's model is not. One thing I have not seen in any of Deur's papers, which surprises me somewhat, is an actual derivation of his proposed interactions (things like gravitational "flux tubes") from the GR Lagrangian. Deriving them from the QCD Lagrangian is, AFAIK, straightforward, so if his heuristic is correct, it should also be straightforward to show that such effects exist in GR.

The first published paper is working from the gravitational Lagrangian.

 

[ohwilleke]

Another paper in the self-interaction paradigm rather than the GEM paradigm is this one: W.M. Stuckey, Timothy McDevitt, A.K. Sten, Michael Silberstein, "The Missing Mass Problem as a Manifestation of GR Contextuality" 27(14) International Journal of Modern Physics D 1847018 (2018). DOI: 10.1142/S0218271818470181.

 

[wumbo]

Ok, but it seems no one else claims that field self-interaction leads to increased gravity within matter distributions and decreased gravity outside matter distributions. And thus to a completely different universe as his Friedmann Equations are showing.

My understanding of Deur's papers over the years:

He's a QCD physicist, so he approaches the GR Einstein-Hilbert Lagrangian via a QFT-like Dyson series expansion to 1-loop level about flat spacetime as opposed to a "traditional" method of simplifying the PDEs down first. They are both valid but GR isn't usually handled this way, so I'm not surprised it's difficult to connect it to the literature and that he's alone in claiming this.

In doing so, he can make the analogy between QCD and GR: both are non-abelian gauge theories, with self interacting gauge Bosons, so what qualitative behavior transfers between the two? I don't believe he's using the QCD as anything more than a much more well-studied example of a self-interacting gauge theory, even if GR can't be a YM theory.

So I think he then posits that gravitational fields form something similar to flux tubes, with a non-trivial amount of mass-energy in the binding of gravitational bound systems. My guess is that he connected the 95% dark matter/energy to 5% non-dark matter/energy ratio as something analogous to the 99%-QCD binding energy to 1% quark intrinsic mass ratio. I'm not too sure about this aspect.

It's interesting, for sure, and it's nice to have an expert in perturbation theory examine GR in the same manner. That said, the notion of energy in GR is wack, so ¯\_(ツ)_/¯
edit: apparently Cooperstock still argues against the stick bead

 

[PeterDonis]

The first published paper is working from the gravitational Lagrangian.

As I recall, he doesn't actually derive the claims like flux tubes from the Lagrangian, he just writes down the GR Lagrangian and then argues by analogy with the QCD Lagrangian. It's been some time since I looked at his papers, though.

 

[timmdeeg]

My understanding of Deur's papers over the years:

...
So I think he then posits that gravitational fields form something similar to flux tubes, with a non-trivial amount of mass-energy in the binding of gravitational bound systems. My guess is that he connected the 95% dark matter/energy to 5% non-dark matter/energy ratio as something analogous to the 99%-QCD binding energy to 1% quark intrinsic mass ratio. I'm not too sure about this aspect.

Thanks for your answer, you are much deeper in the details that I (not a physicist) am able to get.

In his paper Relativistic corrections to the rotation curves of disk galaxies Deur computes numerically the distortion of the field lines which is shown in Fig. 3. whereby the bending of the field lines "increases gravity’s strength". But if so why isn't this increase a source of gravity in the "sense" of the stress-energy tensor?

If I understand the meaning of Feynman's "stick bead" correctly it is more than just a heuristic.

 

[ohwilleke]

But if so why isn't this increase a source of gravity in the "sense" of the stress-energy tensor?

In Einstein's Field Equations which he is relying upon in that paper, the self-interaction of gravity effects appear on the left hand side, not on the right hand side that include the stress-energy tensor.

 

[ohwilleke]

Deur's analysis of the self-interaction of gravitational fields addresses the Hubble tension.

One of the most important problems vexing the ΛCDM cosmological model is the Hubble tension. It arises from the fact that measurements of the present value of the Hubble parameter performed with low-redshift quantities, e.g., the Type IA supernova, tend to yield larger values than measurements from quantities originating at high-redshift, e.g., fits of cosmic microwave background radiation. It is becoming likely that the discrepancy, currently standing at 5σ, is not due to systematic errors in the measurements.

Here we explore whether the self-interaction of gravitational fields in General Relativity, which are traditionally neglected when studying the evolution of the universe, can explain the tension. We find that with field self-interaction accounted for, both low- and high-redshift data are simultaneously well-fitted, thereby showing that gravitational self-interaction could explain the Hubble tension. Crucially, this is achieved without introducing additional parameters.

Corey Sargent, Alexandre Deur, Balsa Terzic, "Hubble Tension and Gravitational Self-Interaction" arXiv:2301.10861 (January 25, 2023).

 

[mitchell porter]

How it works, according to Deur et al:

Gravitational self-interaction causes tighter binding of localized massive systems. This also leads to depletion of the gravitational field at large distances. The magnitude of gravitational depletion changes over the course of cosmic time, in a way depending on the number and type of gravitationally bound systems that have formed.

The Hubble tension can be resolved because the early universe was relatively homogeneous, so there was no gravitational depletion at high redshift; but once structure formation began, so did gravitational depletion.

A specific depletion function is proposed (equation 2, based on a 2017 paper mentioned in this thread at #136), depending on the rate and frequency of galactic mergers (parameters b and A in equation 2). The value of these parameters is inferred by fitting the depletion function to various cosmological data.

 

[member 673059]

Gravitational self-interaction as the source of the Hubble tension discrepancy is much more convincing than any of the early dark energy cosmological models proposed to resolve the Hubble Tension. It is also favored by Occam's razor over the FLRW Lambda CDM cosmological model since it doesn't assume homogeneity and isotropy for the universe. Furthermore, Deur also explains in the article why gravitational self-interaction yields a non-FLRW metric for the universe.

 

[PeterDonis]

Gravitational self-interaction causes tighter binding of localized massive systems. This also leads to depletion of the gravitational field at large distances.

So basically, the gravitational self-interaction is an additional negative contribution (same sign as the ordinary gravitational binding energy) to the mass of the system?

If this is the purported explanation for galaxy rotation curves instead of dark matter, it doesn't seem like it could work: the issue with rotation curves is that there is more mass present, based on the rotation curves, than the visible matter can account for, not less.

 

[ohwilleke]

So basically, the gravitational self-interaction is an additional negative contribution (same sign as the ordinary gravitational binding energy) to the mass of the system?

If this is the purported explanation for galaxy rotation curves instead of dark matter, it doesn't seem like it could work: the issue with rotation curves is that there is more mass present, based on the rotation curves, than the visible matter can account for, not less.

No. The concept is driven by conservation of energy.

It is easiest to explain in terms of gravitons, although the graviton mechanism isn't actually necessary and it could work equally well in terms of fields or space-time curvature that are less intuitive (to me, anyway, your mileage may vary).

In a graviton heuristic, mass-energy spews out gravitons at a fixed rate per gram or GeV/c² or whatever other unit you want to use.

Gravitational self-interaction causes more gravitons to stay within a galaxy pulling it things in the galaxy towards each other more strongly than in Newtonian gravity.

But as a result, fewer gravitons escape the galaxy to causes galaxies to be attracted to each other. Hence, the gravitational field between galaxies is weaker than in Newtonian gravity, i.e. it is depleted.

Over cosmological time scales, the average amount of gravitational depletion between galaxies represented by the depletion function looks like this (from the paper):

The more non-spherical galaxy and galaxy cluster formation takes place in the universe (which gives rise to dark matter phenomena through gravitational self-interaction), the more the gravitational pull between galaxies is depleted.

This also, incidentally, explains the cosmic coincidence, i.e. why the aggregate amount of apparent dark matter is on the same order of magnitude as the aggregate amount of apparent dark energy, in the current era.

To be clear, the dynamical effects of gravitational depletion are not exactly equivalent to dark energy or a cosmological constant on cosmological time scales, although the direction of the effect (i.e. the tendency of galaxies to move apart from each other more strongly than they would in Newtonian gravity) is the same. For example:

* Unlike the cosmological constant in LambdaCDM, the depletion of the gravitational field between galaxies is not constant and the "Hubble constant" is likewise not constant.

* Unlike dark energy, depletion of gravitational pull due to gravitational self-interaction has an asymptotic upper limit. It can't get below the point at which there is no gravitational attraction between galaxies.

 

[mitchell porter]

Actually I think the simplest intuition for the proposed mechanism is in terms of lines of gravitational flux (this is in one of Deur's papers). The galaxy is a source of gravitational flux. Because of self-interaction, the gravitational flux lines cluster together (similar to gluons forming strings in QCD). So masses up to the edge of the galaxy are absorbing more gravitational flux than there would be without self-interaction; but at a large enough distance (far beyond the edge of the galaxy, and ultimately at cosmological distances), there is less gravitational flux than otherwise, because of the extra absorption within galaxies.

So "dark energy" - a less tighly bound cosmos - is a long-distance consequence of "dark matter" - more tighly bound local systems.

@PeterDonis is that making sense?

 

[PeterDonis]

The concept is driven by conservation of energy.

So what energy is involved? That's what I'm trying to understand. Ordinary gravitational binding energy is negative: the total rest mass of a gravitationally bound system is less than the sum of the rest masses of its constituents.

What you and @mitchell porter are describing sounds like an additional effect that makes the system more tightly bound: that means its total rest mass will be less than the "standard" GR gravitational binding energy calculation would indicate, because the effect you're describing makes an additional negative contribution, i.e., it's an additional form of gravitational binding energy.

But that doesn't seem to be what galaxy rotation curves are telling us; they're telling us the masses of the galaxies are larger than a simple calculation based on the visible matter would indicate. The effect you're describing seems to be saying it should be smaller.

So "dark energy" - a less tighly bound cosmos - is a long-distance consequence of "dark matter" - more tighly bound local systems.

@PeterDonis is that making sense?

No, because more tightly bound local systems means their masses are smaller than a simple calculation based on the visible matter would indicate. But galaxy rotation curves seem to be telling us the masses of galaxies are larger than a simple calculation based on the visible matter would indicate. So the effect you're describing seems to be in the opposite direction from what the evidence indicates.

 

[PeterDonis]

"dark energy" - a less tighly bound cosmos

That's not what dark energy is. A less tightly bound cosmos--less density of ordinary matter and energy--would mean deceleration, but of a smaller magnitude. But dark energy is shown by acceleration; its equation of state is completely different from that of ordinary matter and energy.

 

[mitchell porter]

If you want to see Deur et al's own words, see page 2 of the paper in #164, starting with "One consequence of SI in QCD" (SI stands for self-interaction; the authors talk about "GR-SI", GR with self-interaction).

They are definitely saying there's no repulsive force, only an increasing screening of gravitation. It's a little like those attempts to explain the accelerating expansion as due to us being near the center of a giant void (underdensity).

 

[PeterDonis]

They are definitely saying there's no repulsive force, only an increasing screening of gravitation. It's a little like those attempts to explain the accelerating expansion as due to us being near the center of a giant void (underdensity).

Ok, so I'm understanding the basic idea correctly. I'm just not sure it's actually consistent with the data (I have the same feeling about the underdensity void arguments). But it's an open area of research; hopefully as we get more and better data and more work is done on these various models, we will be better able to distinguish between them using observations.

 

[ohwilleke]

In terms of the magnitude of the effects involved, it is also worth observing that the self-interaction effects hypothesized are second order effects that are swamped by the first order direct gravitational effects except in very weak fields.

For example, in a spiral galaxy, up to the radius where the acceleration due to the gravitational field is more than the MOND constant a₀ the self-interaction effect is just noise that is swamped by the first order, approximately Newtonian gravitational field. So, you have an enhancement of the primary approximately Newtonian gravitational field that is material only at the fringes of the galaxy where the fields are weakest. The depletion effect, likewise, is a depletion from gravitational fields experienced by observers well outside that spiral galaxy in places where that gravitational field is already extreme weak (and the depletion at the level of granularity of a single galaxy is directional with the least depletion in the plane of the spiral galaxy and the most above and below that plane - the depletion function is averaging out that directionality).

This is a much more parsimonious way to get the same effects than having a uniform scalar field that pervasively fills all of space time to generate a "dark energy" effect, or a dark matter halo of particles enveloping the entire galaxy and basically cancelling out in the central parts of the galaxy to produce the "dark matter" effect.

I also wonder if the seeming acceleration may be due to changes in the amount of depletion that is there over time.

Part of the issue is also that the astronomy data is currently interpreted in a moderately model dependent manner, and it isn't obvious that trying to quantify and explain that data in this very different model wouldn't lead to a different top level interpretation of what the raw data implies.

For example, none of the omega fractions in LambdaCDM cosmology are numbers that correspond to an actual physical reality in this model.

 

[timmdeeg]

On page 5 in https://arxiv.org/pdf/2301.10861.pdf Deur mentiones zL = 1728, whereby "zL is the redshift at the time of last rescattering". How does this make sense remembering the temperatures 3000 K at last scattering and ~ 2.7 K today?

 

[ohwilleke]

On page 5 in https://arxiv.org/pdf/2301.10861.pdf Deur mentiones zL = 1728, whereby "zL is the redshift at the time of last rescattering". How does this make sense remembering the temperatures 3000 K at last scattering and ~ 2.7 K today?

Could you spell out a bit more what contradiction or issue you're seeing? I'm not doubting that there might be one, but I'm not following your reasoning.

 

[PeterDonis]

Could you spell out a bit more what contradiction or issue you're seeing?

I suspect it's the redshift value at last scattering; the usual value given is about 1100, not 1728.

 

[timmdeeg]

Could you spell out a bit more what contradiction or issue you're seeing? I'm not doubting that there might be one, but I'm not following your reasoning.

In addition to @PeterDonis: redshift of last scattering 1728 would mean, that the plasma temperature then were about 4712 K instead of 3000 K as usually assumed. Cooling happens inverse to expansion.

I think if Deur's field self-interaction replaces $\Lambda$ then one would expect that his model yields the same relative increase of the scale factor till today as the L-CDM model does.

 

[PeterDonis]

one would expect that his model yields the same relative increase of the scale factor till today as the L-CDM model does

The relationship between redshift and scale factor, and between redshift and CMB temperature, is not model dependent; it's a general property of any FRW solution. So I would agree that we should not expect anything in Deur's proposed model to change those relationships.

 

[ohwilleke]

In addition to @PeterDonis: redshift of last scattering 1728 would mean, that the plasma temperature then were about 4712 K instead of 3000 K as usually assumed. Cooling happens inverse to expansion.

I think if Deur's field self-interaction replaces $\Lambda$ then one would expect that his model yields the same relative increase of the scale factor till today as the L-CDM model does.

Thanks for clearing that up. Redshift of last scattering is not one of those number I have stored away in the quick reference table in my head. Good point.

 

[Bandersnatch]

Why do they use the term 'last rescattering', though? Is that something different than last scattering, or just a mannerism?

Come to think of it, probably recombination and last scattering jumbled together.

 

[timmdeeg]

Why do they use the term 'last rescattering', though? Is that something different than last scattering, or just a mannerism?

Come to think of it, probably recombination and last scattering jumbled together.

I think last scattering, recombination and decoupling have all the same meaning, the short period where the universe changed from opaque to transparent. See also here post #3:

https://www.physicsforums.com/threa...diation-temperature-at-recombination.1049591/

 

[Bandersnatch]

Yes, they do. It's 'rescattering' I've never seen before.

 

[timmdeeg]

Indeed, one "last rescattering", two "last scattering", a bit weird, but seems to mean the same. I don't understand "re" anyway.

 

[PeterDonis]

I don't understand "re" anyway, because at least to my knowledge there wasn't any scattering before that time.

Yes, there was: the term "last scattering" is used precisely because that's when the scattering that had been going on until then, because the matter in the universe was plasma (electrons and ions), stopped, because the matter in the universe became neutral atoms.

 

[timmdeeg]

Yes, there was: the term "last scattering" is used precisely because that's when the scattering that had been going on until then, because the matter in the universe was plasma (electrons and ions), stopped, because the matter in the universe became neutral atoms.

Yes, thanks. I've recognized that and deleted this sentence before I've seen your answer.

 

[timmdeeg]

There is another issue with that new paper Hubble Tension and Gravitational Self-Interaction which is unclear for me.

They mention the current values:

The discrepancy presently reaches a 5σ significance: the combined high-z measurements yield 67.28 ± 0.60 km/s/Mpc while the combined low-z measurements yield H0 = 73.04 ± 1.04 km/s/Mpc [8].

But they don't mention the values which according to their model match well without tension.

How to interpret this statement:

Finally, we verify that with the constrained parameters, the GR-SI fit reproduces better the CMB power spectrum with the low-z value of H0 than with the high-z H0 determination. We also find that if H0 is left a free parameter, its best fit value agrees with the low-z determination rather than the high-z one. This indicates an absence of Hubble tension in the GR-SI model.

Does this mean that their GR-SI fit yields the low-z value ~ 73 of the Hubble constant also for the early (high-z) universe? But they don't mention that explicitly somewhere.

Any ideas?

 

[ohwilleke]

There is another issue with that new paper Hubble Tension and Gravitational Self-Interaction which is unclear for me.

They mention the current values:

The discrepancy presently reaches a 5σ significance: the combined high-z measurements yield 67.28 ± 0.60 km/s/Mpc while the combined low-z measurements yield H0 = 73.04 ± 1.04 km/s/Mpc [8].

But they don't mention the values which according to their model match well without tension.

How to interpret this statement:

Finally, we verify that with the constrained parameters, the GR-SI fit reproduces better the CMB power spectrum with the low-z value of H0 than with the high-z H0 determination. We also find that if H0 is left a free parameter, its best fit value agrees with the low-z determination rather than the high-z one. This indicates an absence of Hubble tension in the GR-SI model.

Does this mean that their GR-SI fit yields the low-z value ~ 73 of the Hubble constant also for the early (high-z) universe? But they don't mention that explicitly somewhere.

Any ideas?

In their model they aren't really predicting a Hubble constant, which, of course, isn't a constant in their model anyway. They are using the Hubble constant measurements as inputs to fit their depletion function, rather than as outputs predicted from some other inputs.

Their depletion function, a bit like the proportions of ordinary matter, dark matter, and dark energy in LCDM, isn't something that one can determine with all parameters set with precision from first principles. It is a summary description of the way a big complex system of the structure of the universe at various points in time evolved that has some free parameters to match to observations. The evolution and impacts of their depletion function, however, once you fix the parameters, can be determined more precisely.

What they are saying is that you can adjust the parameters in their model such that it is consistent with both low-z and high-z values of the Hubble "constant" thereby alleviating the tension. Hence, from their perspective, you can use the Hubble constant measurement to calibrate their deletion function's free parameters.

we verify that with the constrained parameters, the GR-SI fit reproduces better the CMB power spectrum with the low-z value of H0 than with the high-z H0 determination

This is neither here nor there, since the Hubble constant isn't a constant in their model.

It is an observation which is a bit surprising. But no really big conclusions are drawn from it. It is just mentioned.

It is surprising because you would think that the high-z Hubble constant measurement ought to produce the best CMB fit since the CMB arises at high-z.

But, it doesn't necessarily mean much.

The determination of the high-z Hubble constant value in LCDM is an output that is derived (solely) from the input of the CMB fit. This Hubble constant determination from the CMB fit is model dependent. So, it isn't necessarily that crazy that in a different model, the CMB fit would imply a modestly different inferred Hubble constant value.

Comparing Hubble constant values in a GR-SI model isn't truly an apples to apples comparison with the Hubble constant in the LCDM model. The models assign different meaning to what observations of the Hubble constant at a particular point in time mean, even though the observational measurement at a point in time is the same. And, there is no way to directly measure the Hubble constant at the time of the CMB imprint apart from looking at the CMB to determine if the Hubble constant inferred in LCDM from the CMB fit is consistent with other ways of observing it in that era.

 

[timmdeeg]

In their model they aren't really predicting a Hubble constant, which, of course, isn't a constant in their model anyway. They are using the Hubble constant measurements as inputs to fit their depletion function, rather than as outputs predicted from some other inputs.

A Hubble constant can be determined model dependent by observation. I have no clue how their "GR-SI fit" works but if they say it " ... reproduces the CMB power spectrum with the low-z value ..." doesn't seem to include a calculation of the Hubble constant. Perhaps implicitly?

I have been thinking differently. Supposed their fit includes the matter density at certain times then it should be possible the obtain the values of the corresponding Hubble constants.

Focusing at the time of the CMB makes it quite easy. Then in their model the universe is isotropic, so no field self-interaction and thus the depletion function D(z) has the value one, FIG. 1. So neglecting the K-term H² is proportional to the baryonic matter density $\rho$, resulting from the CMB data, whereas in the L-CDM model $\rho$ includes Dark Matter.
It should be possible to calculate the Hubble constant at low-z as $\rho$ goes with 1/a³ using D(z) and their CMB redshift.

That's just my reasoning, no guarantee for correctness.

 

[member 673059]

I'm slightly suspicious of their use of the value of the high redshift around 67.28 ± 0.60 in their model, because the original calculations of the Hubble constant of the Planck data measurements are based upon FLRW and Lambda; if one gets rid of FLRW and Lambda and tries to recalculate the Hubble constant from Planck data with a different model, wouldn't one get a different Hubble constant than 67.28 ± 0.60?

Unless I am reading the article wrong and they are saying that they did recalculate the Hubble constant from Planck data and ended up getting the low redshift around 73.04 ± 1.04 in their model.

 

[timmdeeg]

I'm slightly suspicious of their use of the value of the high redshift around 67.28 ± 0.60 in their model, because the original calculations of the Hubble constant of the Planck data measurements are based upon FLRW and Lambda; if one gets rid of FLRW and Lambda and tries to recalculate the Hubble constant from Planck data with a different model, wouldn't one get a different Hubble constant than 67.28 ± 0.60?

I think this is a good question. In general their model is based on the assumption that the universe is anisotropic with the exception of the early universe as shown in Fig. 1 in Hubble Tension and Gravitational Self-Interaction, where the Depletion function has the value 1 for z > 10. So that's in accordance with the L-CDM model but the matter density $\rho$ isn't. Their matter density is purely baryonic whereas the L-CDM matter density includes Dark Matter in addition.

At that time neglecting $\Lambda$ we obtain

So the deviating values of the matter densities should produce deviating values of the Hubble constant, if I see it correctly.

 

[timmdeeg]

He comes at it by analogy to QCD which is, of course, formulated as a quantum theory. And, the logic of why it should have that effect is a lot more obvious when formulated in quantum form and in a way that can exploit known analogies in QCD.

But, fundamentally, the self-interaction that matters is already present in classical GR. It is just a lot harder to see when you try to work directly with Einstein's field equations, in which, of course, the gravitational field isn't on the right hand side in the stress-energy tensor, but instead appears on the left hand side as the non-linearity in the gravitational field part.

In this paper

On the Invention of Dark Matter and Dark Energy Craig Mackay, Institute of Astronomy, Cambridge, UK.*

the author argues with the Einstein-Hilbert Lagrangian (page 6), whereby the nonlinearities take the self-interaction into account.

The polynomial comes from expanding gµν around the constant metric ηµν , with the gravitational field φµν = gµν - ηµν . The square brackets indicate sums over Lorentz-invariant terms. Setting n = 0 gives L = [δφδφ], the Lagrangian for Newtonian dynamics. This result is consequent on suppressing higher order (n>0) terms in the Lagrangian and assuming v/c <<1. This asserts that the system under consideration is homogeneous and isotropic, effectively spherically symmetric by setting the Page 7 of 15 energy-momentum tensor, Tµν to be diagonal. Nonlinearities are always part of the full Lagrangian but their effects are suppressed where the system is homogeneous and isotropic. Nonlinearities which arise in the Lagrangians for both GR and QCD are consequent on field self-interaction.
...
Most galaxies and clusters of galaxies are clearly inhomogeneous and far from uniform. The additional terms that give rise to the nonlinearity or field self-interaction start to become important when √ (GM/L) >~ 10-3 (in “natural” units, see van Remortel, N. (2016) ),where L is the characteristic scale for the system (Deur et al, 2020).

The paper doesn't seem to be peer-reviewed though.

 

[member 673059]

Barker, Hobson, and Lasenby wrote an article stating that the gravitational flux collapse effect isn't strong enough to explain the MOND/dark matter effects in galaxies:

https://arxiv.org/abs/2303.11094

Does that also weaken the gravitational depletion effect in Deur's model to the point where it isn't able to explain dark energy or the Hubble tension?

 

[PeterDonis]

Does that also weaken the gravitational depletion effect in Deur's model

The paper references some of Deur's paper, and the term "colour-confining chromoelectric flux tube model" in the abstract certainly looks to me like a reference to Deur's proposals.

 

[member 673059]

On the other hand, I think it should be possible to simply have a non-FLRW cosmological model with a depletion function without any reference to the underlying dynamics from which the depletion function is derived from.

 

[PeterDonis]

think it should be possible to simply have a non-FLRW cosmological model with a depletion function without any reference to the underlying dynamics from which the depletion function is derived from

The effects under discussion are in the dynamics of individual galaxies, which are not modeled using FRW spacetimes.

Also, while one can of course always insert a purely phenomenological function into one's model (this is what MOND does), without at least some kind of idea about underlying dynamics, one has no way of knowing whether such a function is actually physically reasonable.

 

[Adrian59]

Just to note that there appears to be two threads covering the same topic, this one and one started by kodama on Deur's gravitational thesis; but following on from post #43:

He was really arguing even in the quantum gravity papers that it was the self-interaction of the field that produces the effect.

He comes at it by analogy to QCD which is, of course, formulated as a quantum theory. And, the logic of why it should have that effect is a lot more obvious when formulated in quantum form and in a way that can exploit known analogies in QCD.

I have read the reference posted by timmdeeg, below:

In this paper

On the Invention of Dark Matter and Dark Energy Craig Mackay, Institute of Astronomy, Cambridge, UK.*

the author argues with the Einstein-Hilbert Lagrangian (page 6), whereby the nonlinearities take the self-interaction into account.

I have to say that this is the paper I would have liked to have written! Craig Mackay is an established academic from a world renowned institution. This is not a contribution that should be ignored in this debate.

 

[Adrian59]

I know I am responding to some older comments here, but I am trying to understand the terminology. It appears that at times some comments, and even some of the references are not clear. My understanding is the original use of gravito-magnetism (or GEM) were theories that did contain a definite electromagnetic component to explain galaxy dynamics, and that strictly speaking this does not apply to consideration of non-linear gravitation, as below:

I suspect Deur wasn't cited since this paper is based on Ludwig GEM proposal rather than GR self-interaction. I asked Stacy McGaugh about Ludwig proposal and he regarded it as rubbish, while GEM is real and experimentally verified by Gravity probe B, it's far too weak to explain dark matter phenomena on his blog by orders of magnitude.

Or put another way:

In General Relativity, the gravitational field a.k.a. curvature of space-time arising from gravity, doesn't necessarily arise from the stationary rest mass of nearby matter. It can arise from anything that goes into the stress-energy tensor, and the relationship between the source and the field strength (curvature magnitude) can have a non-linear relationship to the size of the mass-energy that is the source of the field (curvature).

I suppose one could be purest and say that electromagnetism has an associated energy, so must contribute to the energy-momentum tensor, but at these scales I would think like Stacy McGaugh that this was negligible. So I would consider the term gravito-electro-magnetism etc reserved for theories that make the claim of a direct electro-magnetic effect.

 

[PAllen]

I know I am responding to some older comments here, but I am trying to understand the terminology. It appears that at times some comments, and even some of the references are not clear. My understanding is the original use of gravito-magnetism (or GEM) were theories that did contain a definite electromagnetic component to explain galaxy dynamics, and that strictly speaking this does not apply to consideration of non-linear gravitation, as below:

Wrong. GEM is simply a way to write the Einstein Field Equations of GR in a way that shows analogies to Maxwell's equations. It is neither a different theory, nor does it have any relation to EM fields. It is proven to be equivalent to first order Post Newtonian approximation of GR, which is all that is needed to be used for the most precise solar system computations. In your prior post, you mention a paper quoting a Post Newtonian correction term. This term is implicitly contained in the GEM formalism.

Or put another way:
I suppose one could be purest and say that electromagnetism has an associated energy, so must contribute to the energy-momentum tensor, but at these scales I would think like Stacy McGaugh that this was negligible. So I would consider the term gravito-electro-magnetism etc reserved for theories that make the claim of a direct electro-magnetic effect.

Again, this is all a misunderstanding of what GEM is.

 

[PAllen]

Re the Ciotti paper: Can general relativity play a role in galactic dynamics?
Provides a pretty thorough counter-argument to it IMO.

I'm surprised this wasn't worked out before. Linearized gravity is well known. You can't on one hand tell me that gravity propagates at a finite speed and on the other tell me it's irrelevant at cosmological distances. Trivially, there's frame dragging inside a spherical shell of mass in GR that has absolutely no connection to anything Newtonian. The cavalier approach to turning a weakly hyperbolic set of equations into an elliptic set has always to struck me as odd. Cooperstock has an example using the van Stockum cylinder of dust: https://doi.org/10.1142/S021827181644017X

It doesn't have to explain every use of dark matter to be valid. It should be a signal to take approximations to GR with far deeper care. Numerical relativity is sorely needed.

This paper is claimed to be thoroughly refuted by https://arxiv.org/abs/2303.06115, so the debate goes on. It establishes that the homogeneous solutions are irrelevant and endorses the Ciotti paper's conclusions.