LQG Legend Writes Paper Claiming GR Explains Dark Matter Phenomena

[strangerep]

[MTW...]

Section 20.4 stating "[...] One can always find in any given locality a frame of reference in which all local 'gravitational fields' (all Christoffel symbols . . . . disappear. No [Christoffel symbols] means no 'gravitational fields' and no local gravitational field means no 'local gravitational energy-momentum.'

Every time I read textbook statements like this I think: "But what about geodesic deviation?". That relative motion of neighboring geodesics depends on the curvature tensor and cannot be transformed away.

In Newtonian gravity, do gravitational tidal forces do work?
(Hmm, I need to review that...)

 

[PeterDonis]

That relative motion of neighboring geodesics

...is not described by Christoffel symbols, but by the curvature tensor. MTW's statement about the Christoffel symbols is basically a version of the equivalence principle: at any event in spacetime, you can always find a local freely falling frame in which there is no "gravitational field". In such a frame, the metric coefficients, to first order, will be those of the Minkowski metric; but at second order, curvature effects will appear. (If you make your local frame small enough, those curvature effects will be negligible within the confines of the frame.)

In Newtonian gravity, do gravitational tidal forces do work?

In Newtonian gravity, the Newtonian gravitational force itself does work. A fortiori so would gravitational tidal forces.

 

[strangerep]

[geodesic deviation] is not described by Christoffel symbols, but by the curvature tensor. MTW's statement about the Christoffel symbols is basically a version of the equivalence principle: at any event in spacetime, you can always find a local freely falling frame in which there is no "gravitational field". In such a frame, the metric coefficients, to first order, will be those of the Minkowski metric; but at second order, curvature effects will appear. (If you make your local frame small enough, those curvature effects will be negligible within the confines of the frame.)

Er, yes, that's of course what I meant.

In Newtonian gravity, the Newtonian gravitational force itself does work. A fortiori so would gravitational tidal forces.

Thanks -- that's what I figured.

 

[ohwilleke]

Another paper in this theme:

[Submitted on 17 Jul 2022]

Gravitational orbits in the expanding universe revisited​

Vaclav Vavrycuk

Modified Newtonian equations for gravitational orbits in the expanding universe indicate that local gravitationally bounded systems like galaxies and planetary systems are unaffected by the expansion of the Universe. This result is derived under the assumption of the space expansion described by the standard FLRW metric. In this paper, an alternative metric is applied and the modified Newtonian equations are derived for the space expansion described by the conformal FLRW metric. As shown by Vavryčuk (Frontiers in Physics, 2022), this metric is advantageous, because it properly predicts the cosmic time dilation and fits the SNe Ia luminosity observations with no need to introduce dark energy. Surprisingly, the Newtonian equations based on the conformal FLRW metric behave quite differently than those based on the standard FLRW metric. In contrast to the common opinion that local systems resist the space expansion, the results for the conformal metric indicate that all local systems expand according to the Hubble flow. The evolution of the local systems with cosmic time is exemplified on numerical modelling of spiral galaxies. The size of the spiral galaxies grows consistently with observations and a typical spiral pattern is well reproduced. The theory predicts flat rotation curves without an assumption of dark matter surrounding the galaxy. The theory resolves challenges to the ΛCDM model such as the problem of faint satellite galaxies, baryonic Tully-Fisher relation or the radial acceleration relation. Furthermore, puzzles in the solar system are successfully explained such as the Pioneer anomaly, the Faint young Sun paradox, the Moon's and Titan's orbit anomalies or the presence of rivers on ancient Mars.

Comments:	17 pages, 9 figures
Subjects:	General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO)
Cite as:	arXiv:2207.08196 [gr-qc]

 

[PeterDonis]

Another paper in this theme

So basically he's proposing that conformal time is actually the same as "experienced time" for comoving objects? He should talk to Penrose.

 

[mitchell porter]

His initial papers were quantum gravity, but he has reproduced the result in two or three recent papers classically. The insights are certainly quantum gravity inspired, but the results flow from purely classical GR. See, e.g., Alexandre Deur, "Relativistic corrections to the rotation curves of disk galaxies" (April 10, 2020) (lated updated February 8, 2021 in version accepted for publication in Eur. Phys. Jour. C).

I'm a little baffled because I don't see any relationship between this paper and his quantum gravity papers. I thought the point of the quantum gravity papers was to claim that there is a specific large quantum correction to classical GR on galactic scales, whereas this paper seems to be about a new ansatz for approximately solving "the self-gravitating disk problem in GR" - in classical GR, one would assume.

As for the other papers in this thread, I note that a lot of them (including Immirzi et al) treat the galaxy as a zero-pressure system. But Robin Hanson argues plausibly that this is conceptually wrong. In the context of Earth's atmosphere, we're used to pressure meaning the force applied by the impact of innumerable molecules. But Hanson says that in the galactic context, it refers to momentum flux. The stars orbiting the galaxy aren't colliding with anything, but their passage still creates a flow of momentum through a given region of space.

 

[PeterDonis]

Hanson says that in the galactic context, it refers to momentum flux.

He's wrong. Momentum flux is the "time-space" components of the stress-energy tensor. Pressure is the diagonal "space-space" components. They're not the same.

 

[ohwilleke]

I'm a little baffled because I don't see any relationship between this paper and his quantum gravity papers. I thought the point of the quantum gravity papers was to claim that there is a specific large quantum correction to classical GR on galactic scales, whereas this paper seems to be about a new ansatz for approximately solving "the self-gravitating disk problem in GR" - in classical GR, one would assume.

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.

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.

Indeed, one of the things, in general that makes GR difficult for students, is that the definitions of the inputs into the stress-energy tensor are formulated in a way that is not very comparable to the way that for example, Newtonian gravity and Maxwell's equations are, and wrapping your head around what is going on in that very compact form can be challenging.

Ultimately, it is just a stylistic issue. But, even for him, he had to reach the conclusion that applies in both quantum and classical formulations in the quantum formulation first, and then back out the fact that it can also follow classically second, so that it isn't actually a quantum specific effect.

In addition to the papers cited above, another work in progress paper that works out the classical GR treatment to reach the same result, which benefits from co-authors, is A. Deur, Corey Sargent, Balša Terzić, "Significance of Gravitational Nonlinearities on the Dynamics of Disk Galaxies" (August 31, 2019, last revised January 11, 2020) (pre-print). Latest update May 18, 2020. https://arxiv.org/abs/1909.00095v3 The abstract of this paper states:

The discrepancy between the visible mass in galaxies or galaxy clusters, and that inferred from their dynamics is well known. The prevailing solution to this problem is dark matter. Here we show that a different approach, one that conforms to both the current Standard Model of Particle Physics and General Relativity, explains the recently observed tight correlation between the galactic baryonic mass and its observed acceleration. Using direct calculations based on General Relativity's Lagrangian, and parameter-free galactic models, we show that the nonlinear effects of General Relativity make baryonic matter alone sufficient to explain this observation.

 

[ohwilleke]

Arguing that GEM doesn't work.

[Submitted on 20 Jul 2022]

On the rotation curve of disk galaxies in General Relativity​

Luca Ciotti (Dept. of Physics and Astronomy, University of Bologna (Italy))

Recently, it has been suggested that the phenomenology of flat rotation curves observed at large radii in the equatorial plane of disk galaxies can be explained as a manifestation of General Relativity instead of the effect of Dark Matter halos. In this paper, by using the well known weak field, low velocity gravitomagnetic formulation of GR, the expected rotation curves in GR are rigorously obtained for purely baryonic disk models with realistic density profiles, and compared with the predictions of Newtonian gravity for the same disks in absence of Dark Matter. As expected, the resulting rotation curves are indistinguishable, with GR corrections at all radii of the order of v2/c2≈10−6. Next, the gravitomagnetic Jeans equations for two-integral stellar systems are derived, and then solved for the Miyamoto-Nagai disk model, showing that finite-thickness effects do not change the previous conclusions. Therefore, the observed phenomenology of galactic rotation curves at large radii requires Dark Matter in GR exactly as in Newtonian gravity, unless the cases here explored are reconsidered in the full GR framework with substantially different results (with the surprising consequence that the weak field approximation of GR cannot be applied to the study of rotating systems in the weak field regime). In the paper, the mathematical framework is described in detail, so that the present study can be extended to other disk models, or to elliptical galaxies (where Dark Matter is also required in Newtonian gravity, but their rotational support can be much less than in disk galaxies).

Comments:	16 pages, 4 figures, ApJ, accepted
Subjects:	Astrophysics of Galaxies (astro-ph.GA); General Relativity and Quantum Cosmology (gr-qc)
Cite as:	arXiv:2207.09736 [astro-ph.GA]

 

[kodama]

Arguing that GEM doesn't work.

[Submitted on 20 Jul 2022]

On the rotation curve of disk galaxies in General Relativity​

Luca Ciotti (Dept. of Physics and Astronomy, University of Bologna (Italy))

Comments:	16 pages, 4 figures, ApJ, accepted
Subjects:	Astrophysics of Galaxies (astro-ph.GA); General Relativity and Quantum Cosmology (gr-qc)
Cite as:	arXiv:2207.09736 [astro-ph.GA]

might also apply to Deur

 

[ohwilleke]

might also apply to Deur

It might. But it isn't engaging with the same argument.

 

[kodama]

It might. But it isn't engaging with the same argument.

GEM equations are well understood in analogy to EM, and are 10-6 too weak to explain dark matter.

Are there equations of GR self-interaction directly derived from GR that would result in enough deviation from Newtonian approximation in the weak field that would explain dark matter without dark matter?

 

[ohwilleke]

GEM equations are well understood in analogy to EM, and are 10-6 too weak to explain dark matter.

Are there equations of GR self-interaction directly derived from GR that would result in enough deviation from Newtonian approximation in the weak field that would explain dark matter without dark matter?

I don't have the math and GR chops to independently confirm that, but I've read that papers that say so, they passed peer review and got published, and they make sense. I also wouldn't agree that the GEM issue is definitively resolved. Different gravity theory specialist researchers are making different assumptions and I'm not in a position to say which one's are correct.

 

[kodama]

I don't have the math and GR chops to independently confirm that, but I've read that papers that say so, they passed peer review and got published, and they make sense. I also wouldn't agree that the GEM issue is definitively resolved. Different gravity theory specialist researchers are making different assumptions and I'm not in a position to say which one's are correct.

Gravity probe B was designed to test planet Earth's GEM. it confirms it to within 0.5% but with the entire mass of planet Earth spinning on its axis is an extremely weak effect requiring extremely sensitive measurements,

 

[PeterDonis]

Gravity probe B was designed to test planet Earth's GEM.

Earth is a very different geometry from a galaxy. Earth is spherical to a very good approximation. A galaxy is not; it's a flat disk with some bulge in the center but still very different from spherical. The basic claim of the theorists who are saying that GR nonlinear effects can explain galaxy rotation curves without dark matter is that the relative order of magnitude of those effects, as compared with the usual Newtonian ones, are much larger for a flat disk than for a spherical configuration of matter. I'm not enough of an expert to independently do the calculations, but that's the basis of the claim as I understand it.

 

[kodama]

Earth is a very different geometry from a galaxy. Earth is spherical to a very good approximation. A galaxy is not; it's a flat disk with some bulge in the center but still very different from spherical. The basic claim of the theorists who are saying that GR nonlinear effects can explain galaxy rotation curves without dark matter is that the relative order of magnitude of those effects, as compared with the usual Newtonian ones, are much larger for a flat disk than for a spherical configuration of matter. I'm not enough of an expert to independently do the calculations, but that's the basis of the claim as I understand it.

MOND requires 1/r in the deep MOND regimen. could s a flat disk explains that

 

[PeterDonis]

MOND requires 1/r in the deep MOND regimen. could s a flat disk explains that

Go read the papers and see. That's basically what they are saying, but they include calculations.

 

[kodama]

Go read the papers and see. That's basically what they are saying, but they include calculations.

does MOND differ depending on location, i.e. 1/r only apply for coplanar stars and not perpendicular to galaxy

 

[PeterDonis]

does MOND differ depending on location, i.e. 1/r only apply for coplanar stars and not perpendicular to galaxy

Go read the papers on MOND and see.

 

[mitchell porter]

A lot of theories and models are being discussed at once in this thread, but (in my opinion) without any clarity or precision. It would help if we could pick out a few, and actually understand them, and how they differ. I would nominate (1) the textbook weak-field models described by Ciotti in #44 (2) Ludwig's model, as an exemplar of gravitomagnetic models (3) whatever it is that Deur is doing.

Regarding (1) and (2), Ciotti apparently carries out gravitomagnetic calculations in the context of ordinary textbook models, and obtains that the force is minuscule. But cautiously, he does not say that this refutes Ludwig, since he knows that Ludwig has a different starting point. He says only that it would be very surprising if a different kind of approximation led to such a different result from the textbook results, for weak fields.

So this raises the question that Robin Hanson tried to answer (#41, #42): exactly what is different about Ludwig's assumptions, that makes them capable of producing such a different result? Hanson proposed that it is the assumption of zero pressure, an assumption shared by several other papers cited in this thread. I am wondering if it's initial conditions: maybe if you start with large gravitomagnetic forces, they will continue to be generated, but if you don't, they won't become so strong? Surely, careful study of Ludwig's work, and careful comparison with the textbook models in Ciotti, can yield a definite answer to the question above.

As for (3), Deur's work, it is being described in this thread (#43) as a model which takes into account the "self-interaction" of gravity in general relativity; and it was even suggested (#31) that the conventional wisdom, that gravitational energy in general relativity cannot be localized, has inhibited the study of gravitational self-interaction... I am skeptical about this second claim. There has been plenty of research on nonlinearity in general relativity; there has been plenty of research on stress-energy pseudotensors and partially localized definitions of energy; are there really dramatic new empirical consequences waiting to be revealed, once these two lines of research are considered together?... I also want to understand the relationship between the classical and quantum parts of Deur's research. Hopefully all this can be disentangled with sufficient patience and care.

 

[ohwilleke]

A lot of theories and models are being discussed at once in this thread, but (in my opinion) without any clarity or precision.

Fair enough, although one of my purposes in posting the thread was to illustrate the overall state of the GR effects as DM literature which is quite a bit bigger than a lot of people realize, but apart from Deur and Ludwig, not very sustained and developed, in an effort to identify common themes and contradictions, if any, and also to demonstrate that this is not just one or two isolated individuals pursuing a research program that no one else is exploring (as well as to illustrate the concentration of the work on this research agenda in the time period since 2018 more or less).

I agree that the field itself is scattered and the people involved aren't listening to each other very much.

Deur's work is definitely the most developed line of scholarship in the GR effects cause DM phenomena research agenda, and unlike Ludwig, who is purportedly contradicted by Hanson and Ciotti, there isn't really any work out there engaging with his line of analysis for good or ill, despite the growing number of publications that Deur has made in the field.

Maybe this is because nobody inclined to do so has noticed him, but it also might be because those who have noticed intuitively believe that he must be wrong but haven't taken the time to work through the math because Deur is working with math inspired by QCD and familiar to people in that field but unfamiliar to most people in the heartland of GR theory and phenomenology. So, its a lot more work for them to dig into Deur's analysis than it is for them to work over GEM analysis that is far more familiar to them in Ludwig's papers.

Regarding (1) and (2), Ciotti apparently carries out gravitomagnetic calculations in the context of ordinary textbook models, and obtains that the force is minuscule. But cautiously, he does not say that this refutes Ludwig, since he knows that Ludwig has a different starting point. He says only that it would be very surprising if a different kind of approximation led to such a different result from the textbook results, for weak fields.

So this raises the question that Robin Hanson tried to answer (#41, #42): exactly what is different about Ludwig's assumptions, that makes them capable of producing such a different result? Hanson proposed that it is the assumption of zero pressure, an assumption shared by several other papers cited in this thread. I am wondering if it's initial conditions: maybe if you start with large gravitomagnetic forces, they will continue to be generated, but if you don't, they won't become so strong? Surely, careful study of Ludwig's work, and careful comparison with the textbook models in Ciotti, can yield a definite answer to the question above.

Along that line, one of Ludwig's assumptions, also found in the paper in #1 that started this thread, is that the system is "rotationally supported" which goes to your initial conditions speculation. GEM may not provide a good source for revving up the spin from a dead halt, but could provide the field needed to sustain it once it is going.

Intuitively, it makes more sense that the rotationally supported assumption matters, than it does that it assumes zero pressure (even though zero pressure seems like a reasonable enough assumption at face value in a spiral galaxy system).

An earlier post also noted, and I don't think it should be dropped, the importance of assumptions about the geometry of the system (disk-like in Ludwig and the paper in #1 v. spherical in many other treatments) which is almost surely a material assumption.

As for (3), Deur's work, it is being described in this thread (#43) as a model which takes into account the "self-interaction" of gravity in general relativity . . . I also want to understand the relationship between the classical and quantum parts of Deur's research. Hopefully all this can be disentangled with sufficient patience and care.

One important aspect of Deur's earlier quantum oriented work is that it is modeled in a static equilibrium model that explicitly disregards GEM effects that arise from the motion of the particles in the system. Systems not near equilibrium are expressly noted by Deur in those papers to be beyond the scope of applicability of his quantum oriented work.

(Incidentally, there is some MOND scholarship by Stacey McGaugh and others that also observes that MOND does not hold in systems not close to equilibrium and even uses a poor MOND fit as a flag that a system might be out of equilibrium. I won't cite it here as MOND itself is really off topic to this thread. This is notable, however, because, in the geometry of a spiral galaxy Deur's approach with pure GR closely approximates MOND, and Deur's approach could provide a solid GR theoretical basis for the MOND conclusions while expanding its domain of applicability in systems like galaxy clusters where MOND underperforms by resorting to the different geometry of the mass in these systems.)

In Deur's classical work, different simplifications, in addition to or in lieu of the static equilibrium assumption of the quantum work, are used in ways that less transparently differentiate gravitational field self-interaction from GEM effects. Crosta and Balasin in #2, for example, also make a static equilibrium analysis that cannot be due to GEM effects (and like Deur, have not triggered refutation papers.)

(I'm also not entirely convinced that the GEM effects aren't, through some back door in the equations, basically harnessing gravitational field self-interactions, particularly if the initial conditions in the GEM works turns out to be the key different assumption. Deur's quantum work makes it seem unlikely to me that the reverse, that his self-interaction effect is really a backdoor implicating GEM effects, is true).

Deur's recently published classical paper at #1, Alexandre Deur, "Relativistic corrections to the rotation curves of disk galaxies" (April 10, 2020) (lated updated February 8, 2021 in version accepted for publication in Eur. Phys. Jour. C)., uses a mean field approximation to do the GR analysis.

Some different methodological tools were used in the working paper, A. Deur, Corey Sargent, Balša Terzić, "Significance of Gravitational Nonlinearities on the Dynamics of Disk Galaxies" (August 31, 2019, last revised January 11, 2020) (pre-print). Latest update May 18, 2020. https://arxiv.org/abs/1909.00095v3

Some key points from the body text:

The rotation curves of several disk galaxies were computed in (Deur 2009) based on Eq. (1) and using numerical lattice calculations in the static limit (Deur 2017). . . . Although based directly on the GR’s Lagrangian, the lattice approach is limited since it is computationally costly and applies only to simple geometry, limiting the study to only a few late Hubble type galaxies at one time. To study the correlation from MLS2016 over the wide range of disk galaxy morphologies, we developed two models based on: 1) the 1/r gravitational force resulting from solving Eq. (1) for a disk of axisymmetrically distributed matter; and 2) the expectation that GR field self-interaction effects cancel for spherically symmetric distributions, such as that of a bulge, restoring the familiar 1/r 2 force.

and from the appendix:

The direct calculation of the effects of field self-interaction based on Eq. (1) employs the Feynman path integral formalism solved numerically on a lattice. While the method hails from quantum field theory, it is applied in the classical limit, see (Deur 2017). The first and main step is the calculation of the potential between two essentially static (v c) sources in the non-perturbative regime. Following the foremost non-perturbative method used in QCD, we employ a lattice technique using the Metropolis algorithm, a standard Monte-Carlo method (Deur 2009, 2017). The static calculations are performed on a 3-dimensional space lattice (in contrast to the usual 4-dimensional Euclidian spacetime lattice of QCD) using the 00 component of the gravitational field ϕµν. This implies that the results are taken to their classic limit, as it will be explained below. Furthermore, the dominance of ϕ00 over the other components of the gravitational field simplifies Eq (1) in which [ϕ n∂ϕ∂ϕ] → anϕ n 00∂ϕ00∂ϕ00, with an a set of proportionality constants. One has a0 ≡ 1 and one can show that a1 = 1 (Deur 2017).

 

[kodama]

A lot of theories and models are being discussed at once in this thread, but (in my opinion) without any clarity or precision. It would help if we could pick out a few, and actually understand them, and how they differ. I would nominate (1) the textbook weak-field models described by Ciotti in #44 (2) Ludwig's model, as an exemplar of gravitomagnetic models (3) whatever it is that Deur is doing.

Regarding (1) and (2), Ciotti apparently carries out gravitomagnetic calculations in the context of ordinary textbook models, and obtains that the force is minuscule. But cautiously, he does not say that this refutes Ludwig, since he knows that Ludwig has a different starting point. He says only that it would be very surprising if a different kind of approximation led to such a different result from the textbook results, for weak fields.

So this raises the question that Robin Hanson tried to answer (#41, #42): exactly what is different about Ludwig's assumptions, that makes them capable of producing such a different result? Hanson proposed that it is the assumption of zero pressure, an assumption shared by several other papers cited in this thread. I am wondering if it's initial conditions: maybe if you start with large gravitomagnetic forces, they will continue to be generated, but if you don't, they won't become so strong? Surely, careful study of Ludwig's work, and careful comparison with the textbook models in Ciotti, can yield a definite answer to the question above.

As for (3), Deur's work, it is being described in this thread (#43) as a model which takes into account the "self-interaction" of gravity in general relativity; and it was even suggested (#31) that the conventional wisdom, that gravitational energy in general relativity cannot be localized, has inhibited the study of gravitational self-interaction... I am skeptical about this second claim. There has been plenty of research on nonlinearity in general relativity; there has been plenty of research on stress-energy pseudotensors and partially localized definitions of energy; are there really dramatic new empirical consequences waiting to be revealed, once these two lines of research are considered together?... I also want to understand the relationship between the classical and quantum parts of Deur's research. Hopefully all this can be disentangled with sufficient patience and care.

does the energy in empty space, the cosmological constant, gravitate, and contribute to "self-interaction" of gravity in general relativity

for that matter, does the cosmological constant interact with GEM at cosmological distances

if the space of an entire galaxy that contains the cosmological constant also rotates with the galaxy, doesn't this also produce a GEM effect and also a self-interaction of gravity effect

 

[ohwilleke]

does the energy in empty space, the cosmological constant, gravitate, and contribute to "self-interaction" of gravity in general relativity

for that matter, does the cosmological constant interact with GEM at cosmological distances

if the space of an entire galaxy that contains the cosmological constant also rotates with the galaxy, doesn't this also produce a GEM effect and also a self-interaction of gravity effect

Deur is modeling GR without a cosmological constant.

 

[kodama]

Deur is modeling GR without a cosmological constant.

Emergent Gravity and the Dark Universe arXiv:1611.02269​

we argue that the positive dark energy leads to a thermal volume law contribution to the entropy that overtakes the area law precisely at the cosmological horizon. Due to the competition between area and volume law entanglement the microscopic de Sitter states do not thermalise at sub-Hubble scales: they exhibit memory effects in the form of an entropy displacement caused by matter. The emergent laws of gravity contain an additional `dark' gravitational force describing the `elastic' response due to the entropy displacement. We derive an estimate of the strength of this extra force in terms of the baryonic mass, Newton's constant and the Hubble acceleration scale a_0 =cH_0, and provide evidence for the fact that this additional `dark gravity~force' explains the observed phenomena in galaxies and clusters currently attributed to dark matter.

301 citations

Verlinde's entropic gravity proposal makes the cosmological constant central to his MOND like proposal and has 301 citations.

the energy in empty space should curve space time in GR and may even have a GEM component to it. MOND ao is related to the cc.

 

[Nik_2213]

{ My head hurts, my head hurts, my head hurts... }

Does any of these support or falsify the few String Theory versions using Teleparallel Gravity ??

 

[ohwilleke]

{ My head hurts, my head hurts, my head hurts... }

That is the joy of BSM physics! No other reason to do it really.

Does any of these support or falsify the few String Theory versions using Teleparallel Gravity ??

Not really. All of them assume basic GR and not the teleparallel gravity twist on GR.

If one or more of these work, however, it tends to weakens one of the motivations for String Theory, which is to provide a dark matter candidate particle. indeed, some narrow sense Sting Theory investigators claim that the low energy approximation of String Theory must be Supersymmetry, and one of the big arguments for the desirability of BSM Supersymmetry physics has been that it created a dark matter particle candidate. But, if it turns out that dark matter isn't necessary because it is really a GR effect, then this makes new particles that could fill out a dark sector a problem rather than a solution.

 

[mitchell porter]

like Deur, have not triggered refutation papers

I have a feeling there are far more papers with mistakes out there, than there are papers specifically spelling out the mistakes...

Anyway: the issue with all the papers in this thread, or the counterintuitive claim that they share, is the claim of strong GR effects in circumstances where (as Ciotti explains) one only expects weak effects. Any search for a mistake in a specific paper, needs to start by identifying what the alleged mechanism of the strong effects is. For example, in Ludwig it's a gravitomagnetic force that's a million times greater than what you would normally expect (I get this factor from the calculation by Garrett Lisi).

How about Deur? In "Significance of Gravitational Nonlinearities on the Dynamics of Disk Galaxies", Deur et al say:

... one may question the relevance of field self-interaction at large galactic radii r. At these distances, the missing mass problem is substantial, while the small matter density should make the self-interaction effects negligible. The answer is in the behavior of the gravitational field lines; once they are distorted at small r due to the larger matter density, they evidently remain so even if the matter density becomes negligible (no more field self-interaction, i.e., no further distortion of the field lines), preserving a form of potential different from that of Newton. Thus, even if the gravity field becomes weak, the deviation from Newton’s gravity remains.

When it comes to understanding the specific mechanism that Deur proposes, I feel that the key paper is "Self-interacting scalar fields at high temperature". He constructs scalar field theories meant to resemble QCD and GR, and argues that the force potentials they contain will have the same form in the more complex theories. That argument is certainly a natural point of scrutiny - the full theories have extra degrees of freedom, and that can completely change the dynamics.

 

[malawi_glenn]

one of the motivations for String Theory, which is to provide a dark matter candidate particle

Never read that in my string theory books.
Supersymmetric QFT particle models however can provide dark matter candidates, in some region of the models parameter spaces, but they do not have to do that per se.

some narrow sense Sting Theory investigators claim that the low energy approximation of String Theory must be Supersymmetry, and one of the big arguments for the desirability of BSM Supersymmetry physics has been that it created a dark matter particle candidate

What is a string theory "investigator"? Not someone who is a researcher? Who are these narrow sense people, and why are they narrow sensed? Supersymmetry is required in string theory to accommodate fermion particles in the low energy limit, not dark matter candidates.

 

[ohwilleke]

What is a string theory "investigator"? Not someone who is a researcher?

An investigator is basically a scientist but might include, for example, a mathematician who doesn't identify as a scientist. I chose the word to avoid using the word "scientist" for that reason. Researcher means the same thing.

Who are these narrow sense people, and why are they narrow sensed?

The narrow sense people are the people who are working directly with M-theory equations and have a very specific technical definition of what counts as string theory and this definition typically mandates supersymmetry as the low energy limit.

The broad sense people, who also often call themselves string theorists, are people who use concepts from string theory, like a massless spin-2 graviton, or 11 dimensional space, or a minimum sized one dimensional particle, or computational methods, but don't necessarily put it in the context of a specific overall comprehensive theoretical structure intended to be a complete Theory of Everything.

Supersymmetry is required in string theory to accommodate fermion particles in the low energy limit, not dark matter candidates.

Supersymmetry, by definition, supplies BSM fundamental particles. They don't always provide dark matter candidates and that wasn't the original justification for supersymmetry. But supersymmetry advocates generally touts the existence of dark matter candidates as one of the reasons to take the theory seriously and to find it desirable to pursue. If one or more of the supersymmetric fundamental particles cannot decay to SM particles, the lightest supersymmetric particle (LSP) is a prime dark matter candidate (although less so now that direct detection experiments have ruled out supersymmetric WIMPS since supersymmetric WIMPS have to interact via the weak force at the same strength as a neutrino).

Now that supersymmetric particles haven't been discovered at the masses where they would be expected to address the hierarchy problem that motivated supersymmetry in the first place, the feature that they generically provide DM candidates has become much more important in making the case of supersymmetry and by association, string theory.

 

[ohwilleke]

When it comes to understanding the specific mechanism that Deur proposes, I feel that the key paper is "Self-interacting scalar fields at high temperature". He constructs scalar field theories meant to resemble QCD and GR, and argues that the force potentials they contain will have the same form in the more complex theories. That argument is certainly a natural point of scrutiny - the full theories have extra degrees of freedom, and that can completely change the dynamics.

This would seem like more of a concern if the same result weren't reproduced with classical GR.

 

[malawi_glenn]

An investigator is basically a scientist but might include, for example, a mathematician who doesn't identify as a scientist. I chose the word to avoid using the word "scientist" for that reason. Researcher means the same thing.

Use standard lingo instead.

Supersymmetry, by definition, supplies BSM fundamental particles.

Yes but that is residual. You made it sound like (super)string theory was motivated by the need of having a dark matter particle candidate.

 

[ohwilleke]

Use standard lingo instead.

investigator is very standard lingo. I've lived in and around academia since I was a toddler. It is used all the time.

Yes but that is residual. You made it sound like (super)string theory was motivated by the need of having a dark matter particle candidate.

I said, "it tends to weakens one of the motivations for String Theory, which is to provide a dark matter candidate particle" and it is one of the modern motivations for String Theory.

 

[malawi_glenn]

it is one of the modern motivations for String Theory

I guess I have to contact my old friends at the university again and make them list the top 5 motivations for string theory. What does "modern" mean in this context?
My newest String Theory book is from 2012 (Peter Wests book), is there any newer I should get you think?

 

[ohwilleke]

I guess I have to contact my old friends at the university again and make them list the top 5 motivations for string theory. What does "modern" mean in this context?
My newest String Theory book is from 2012 (Peter Wests book), is there any newer I should get you think?

It is a motivation in arguments that there is any observational support for thinking that there is an observational evidence to motivate BSM physics that Sting Theory could explain, and hence for taking it seriously. I agree that it didn't motivate the initial formulation of the theory.

 

[mitchell porter]

This would seem like more of a concern if the same result weren't reproduced with classical GR.

Are you referring to "Relativistic corrections to the rotation curves of disk galaxies"?

Deur says in the summary that the method in this paper is "less directly based on GR’s equations than the path integral approach" (the latter refers to lattice calculations of the kind discussed in the "scalar fields" paper). He describes this new method as "a mean-field technique combined with gravitational lensing". I haven't quite figured out how it works. Although he talks about curvature, I don't see a metric anywhere in the paper.

From what I can see, he models the galaxy as a disk-shaped distribution of mass, then calculates how lines of flight radiating outward from the center would be warped by this mass distribution, then says that this is how gravitational field lines would behave due to self-interaction, and calculates a gravitational force from the flux of field lines. There must be a way of judging whether this is what GR actually predicts... At least Deur's paradigm is getting clearer to me now.