Do gravitons interact with gravitons?

[PeterDonis]

As far as "reduced g-field outside massive structures" as being "highly heuristic and imprecise way of describing what is going on in Deur's models". In comment 35 of this thread Deur states (in a quote box) "Likewise 2 in gravitational systems the increased binding due to GR's SI weakens gravity's action at large scale". He clearly is conveying this in a much more professional and exact way.

See my posts in this thread following post #35. There are multiple issues involved here.

 

[PeterDonis]

Unfortunately, I haven't been able to pin down any good info on what the baryonic mass of the various components of this system are.

The place to do that is not pop science articles or discussions (and that category includes physics stackexchange discussions, no matter what user names people claim there). You need to be looking at actual peer-reviewed papers. We have had some PF threads on the Bullet cluster that might contain useful references.

 

[ohwilleke]

Andrew Ohwilleke

I've been reading your excellent write-ups on Deur's models and was wondering if you have come across any mention of how either the quantum or classical versions of his models deal with gravitational lensing. I did a google search, but so far haven't found anything connecting gravity self-interaction and gravitational lensing.

In general relativity, the curvature of time-space induced by mass-energy affects both massive particles and massless particles, like photons. Therefore, it gives rise to gravitational lensing effects identical to those of a dark matter halo distribution that would produce the same curvature of time-space that is predicted.

 

[PeterDonis]

In general relativity, the curvature of time-space induced by mass-energy affects both massive particles and massless particles, like photons. Therefore, it gives rise to gravitational lensing effects identical to those of a dark matter halo distribution that would produce the same curvature of time-space that is predicted.

I'm not sure this is actually correct as it applies to Deur's model, because the whole point of Deur's model is that the distribution of mass-energy is not the same as it is in the dark matter model--because there is no dark matter. Therefore one would not expect the spacetime curvature to be the same either.

To put it another way: as i understand Deur's model, the key change is the connection between the mass-energy distribution, along with the spacetime curvature it produces, and galaxy rotation curves. In other words, he is claiming that the standard way of calculating the rotation curves from a given mass-energy distribution, and hence a given spacetime curvature, is wrong (because it doesn't take into account the extra GR effects that the standard calculation assumes are negligible but which Deur claims are not). But the rotation curves are the direct observable: that doesn't change when we change models from a dark matter model to Deur's alternative model. So what must change instead is the mass-energy distribution and therefore the spacetime curvature.

So if I am understanding Deur's model correctly, I would expect it to make different predictions about lensing from the dark matter model. However, I don't know how different or how easy it would be to test for the difference.

 

[ohwilleke]

I didn't mean to imply that "gravity field gradient" was the cause of spacetime curvature. I'm fully aware that in a given region of spacetime the curvature is determined by the distribution of matter and energy. My bad, I bungled it.

As far as "reduced g-field outside massive structures" as being "highly heuristic and imprecise way of describing what is going on in Deur's models". In comment 35 of this thread Deur states (in a quote box) "Likewise 2 in gravitational systems the increased binding due to GR's SI weakens gravity's action at large scale". He clearly is conveying this in a much more professional and exact way. I'll try to do that in the future.

Now back to how lensing is handled in Deur's SI models. The Bullet Cluster is one of the most studied lensing systems in astronomy so would be a great test for the SI approach. Unfortunately, I haven't been able to pin down any good info on what the baryonic mass of the various components of this system are. Popular descriptions, like in Ethan Siegel's blog, invariably state that "most" of the baryonic mass is in the ionized gas clouds between the clusters, usually cited as 90% of the system's baryonic mass. But then I came across a physics.stackexchange post titled "Bullet Cluster and Mond" where "ProfRob" states that 9% of the baryonic mass is in the form of hot gas and 11% is within the visible galaxies forming the clusters. The remaining 80% of the system's mass is in the form of Dark Matter, that is gravitationally centered on the two clusters, based on lensing data. This is drastically different than what popular expositions say.

But, if these mass ratios are correct then the dark matter in each galaxy cluster would be about 7 times the baryonic mass for each cluster. So with SI (and Mond also) dispensing with dark matter both of these models have to somehow be able to replicate the lensing that in LCDM is mostly attributed to dark matter. It seems like a pretty tall order, but hopefully Professor Deur is aware of this lensing issue and has either been able to explain it his SI paradigm or is working on it.

Deur addressed the Bullet Cluster in particular in one of his early papers. A. Deur, “Implications of Graviton-Graviton Interaction to Dark Matter” (May 6, 2009) (published at 676 Phys. Lett. B 21 (2009)).

The apparent dark matter proportion is greater than in MOND which is equivalent to an effective dimensional reduction from 3D to 2D, in clusters, because clusters effectively result (in an idealized two body case to which clusters are analogous) in a dimensional reduction from 3D to 1D in a manner analogous to QCD flux tubes.

 

[ohwilleke]

I'm not sure this is actually correct as it applies to Deur's model, because the whole point of Deur's model is that the distribution of mass-energy is not the same as it is in the dark matter model--because there is no dark matter. Therefore one would not expect the spacetime curvature to be the same either.

To put it another way: as i understand Deur's model, the key change is the connection between the mass-energy distribution, along with the spacetime curvature it produces, and galaxy rotation curves. In other words, he is claiming that the standard way of calculating the rotation curves from a given mass-energy distribution, and hence a given spacetime curvature, is wrong (because it doesn't take into account the extra GR effects that the standard calculation assumes are negligible but which Deur claims are not). But the rotation curves are the direct observable: that doesn't change when we change models from a dark matter model to Deur's alternative model. So what must change instead is the mass-energy distribution and therefore the spacetime curvature.

So if I am understanding Deur's model correctly, I would expect it to make different predictions about lensing from the dark matter model. However, I don't know how different or how easy it would be to test for the difference.

The lensing predictions ought to be quite similar. In a spiral disk, at least in the plane of the spiral disk, the gravitational pull towards the center of the galaxy is identical - the effect on ordinary matter is the same and so it out to have the same effect on photons as well. There might be a small discrepancy out of that plane, but it should be closer than a MOND expectation out of the galactic plane.

In a cluster, Deur's prediction would be that the lensing effects would be more focused than in a DM halo approach (since flux tube like fields are less diffuse), and that is consistent with observations. See Massimo Meneghetti, et al., "An excess of small-scale gravitational lenses observed in galaxy clusters" 369 (6509) Science 147-1351 (September 11, 2020). DOI: 10.1126/science.aax5164

 

[PeterDonis]

In a spiral disk, at least in the plane of the spiral disk, the gravitational pull towards the center of the galaxy is identical

"At least in the plane of the disk", yes. That's the point, which I'll emphasize by rephrasing: only in the plane of the disk is the pull identical to the ordinary Newtonian expectation. (At least, that's what Deur's model is claiming.) So only light whose trajectory lies in that same plane would be lensed the same as in a dark matter model. But that is a very small fraction of all the light passing by the galaxy from sources behind it.

 

[Davephaelon]

Andrew Ohwilleke

Thank you for responding to my query in comment #85. I saw it last night, but was too tired from the late hour and chill here in the northeast to stay awake. I’ll check out that 2009 paper that you linked.

But the paper you cited in comment #96 took me by surprise, as I said something to the same effect on March 30, 2022 at 11:42 AM, in the post: “Are there credible deviations from the baryonic Tully-Fisher relation” over at Stacey McGaugh’s Triton Station blog. But in lieu of reading those two papers, what PeterDonis said in comments #94 and #97 perfectly expresses my own concerns about Deur’s model(s) regarding lensing beyond the boundaries of either galaxies or galaxy clusters. It would be a shame if SI cannot match the empirical lensing data that is available, as it does so well with other astrophysical phenomena. Hopefully the two papers you cited will provide some plausible explanation into how SI can effectively match the lensing attributed to dark matter in large astrophysical structures.

 

[ohwilleke]

Andrew Ohwilleke

Thank you for responding to my query in comment #85. I saw it last night, but was too tired from the late hour and chill here in the northeast to stay awake. I’ll check out that 2009 paper that you linked.

But the paper you cited in comment #96 took me by surprise, as I said something to the same effect on March 30, 2022 at 11:42 AM, in the post: “Are there credible deviations from the baryonic Tully-Fisher relation” over at Stacey McGaugh’s Triton Station blog. But in lieu of reading those two papers, what PeterDonis said in comments #94 and #97 perfectly expresses my own concerns about Deur’s model(s) regarding lensing beyond the boundaries of either galaxies or galaxy clusters. It would be a shame if SI cannot match the empirical lensing data that is available, as it does so well with other astrophysical phenomena. Hopefully the two papers you cited will provide some plausible explanation into how SI can effectively match the lensing attributed to dark matter in large astrophysical structures.

We pay astronomers and astronomy collaborations and astrophysicists the big bucks to find out.

 

[Davephaelon]

Andrew,

I read the 2009 paper but didn’t notice any specific reference to lensing, although it may have been implied in the heavy math section, which I kind of skimmed over. But the other paper, (Meneghetti et al) which I was only able to read the abstract, as it was behind a paywall, grabbed my attention on your mention of “In a cluster, Deur's prediction would be that the lensing effects would be more focused than in a DM halo approach (since flux tube like fields are less diffuse), and that is consistent with observations.”. This is totally fascinating in light of a portion of the abstract of the Meneghetti et al paper:

“The large-scale gravitational lens caused by the whole cluster can be modified by smaller-scale mass concentrations within the cluster, such as individual galaxies. Meneghetti et al. examined these small-scale gravitational lenses in observations of 11 galaxy clusters. They found an order of magnitude more small-scale lenses than would be expected from cosmological simulations. The authors conclude that there is an unidentified problem with either prevailing simulation methods or standard cosmology.”

I brought up a quite similar idea at the post: “Are there credible deviations from the baryonic Tully-Fisher relation” at Tritonstation. Over there on 30 March 2022 I wrote:

“As an afterthought to the past paragraph in my previous comment it occurred to me that any lensing contour lines interior to the perimeter of either galaxy cluster (in the Bullet Cluster) could be affected by the greatly concentrated gravitational force along the “flux tubes” interconnecting the individual galaxies. That is, if a significant number of the distorted background light sources, used to map the contours, happen to intercept line segments connecting individual galaxies in the clusters, that could serve as evidence for the existence of these flux tubes. In fact, if such a case could be convincingly demonstrated it would be quite compelling evidence for Deur’s quantum gravity model.”

Looking at a composite image of the Bullet Cluster, showing the contour lines, it does appear that there are galaxies (in the left cluster) that are exterior to all but one of the contour lines. So, while I don't know if the sample of 11 clusters in the Meneghetti study included the Bullet Cluster, the Bullet Cluster looks like it may be entirely consistent with their observations.

 

[rcarbajal68]

https://physics.stackexchange.com/questions/643765/does-gravity-bend-gravity

In this link they relate gravitational lenses with the self-interaction of gravitons.