I Do gravitons interact with gravitons?

[timmdeeg]

So he says implicitly that the "reduced gravitational field outside these systems" can explain the accelerated expansion of the universe.

 

[PeterDonis]

So he says implicitly that the "reduced gravitational field outside these systems" can explain the accelerated expansion of the universe.

That's how it looks to me, yes; but I'm not entirely sure whether, in his model, the term "accelerated expansion" is actually a correct description. He might be implicitly saying that what we currently think of as "accelerated expansion" is actually not accelerated, but it appears to us to be because we are modeling the evolution of the scale factor incorrectly; in Deur's model, the evolution of the scale factor might be changed so the expansion actually never is accelerated, we are just interpreting our observations incorrectly.

 

[ohwilleke]

Ah, I see.This is not correct, because here "repulsive force" would have to mean "something that causes the appearance of accelerated expansion", and that's not what a change to the matter term in the evolution equation for the scale factor does. All it does is reduce the deceleration. It does not change deceleration to acceleration. Those are qualitatively different appearances and one cannot reproduce the other.

"Repulsive force" would mean "something that causes an increase in the magnitude to the relative velocity of two masses that tends to move them farther apart from each other. Whether this means "accelerated expansion" or not would depend on exactly how one defined "expansion". Geometric terminology and force terminology are not inherently inconsistent.

 

[PeterDonis]

"Repulsive force" would mean "something that causes an increase in the magnitude to the relative velocity of two masses that tends to move them farther apart from each other.

That's the same thing as "accelerating expansion"; "accelerating" means "increasing magnitude of velocity".

As I noted in post #52, however, it's not clear to me whether Deur is actually claiming that. It seems to me that he might be saying that our universe's expansion actually is not accelerated--that the relative velocity between comoving observers is not actually increasing. He might be saying that it only appears to be increasing because our current standard model, the Lambda CDM model, is using an incorrect method of deriving the scale factor as a function of time, and when Deur's method is used instead, we find a different function of time for the scale factor, one which is always decelerating.

 

[timmdeeg]

It seems to me that he might be saying that our universe's expansion actually is not accelerated--that the relative velocity between comoving observers is not actually increasing.

I think this view fits to Deur's recent paper:

https://arxiv.org/pdf/1709.02481.pdf

This increased binding must, by energy conservation, weaken the action of gravity at larger scale. This can then be mistaken for a repulsion, i.e. dark energy. Specifically, the Friedmann equation for an isotropic and homogeneous Universe is (for a matter-dominated flat Universe) H2 = 8πGρ/3, with H the Hubble parameter and ρ the density. As massive structures coalesce, gravity is effectively suppressed at scales larger that these structures. This weakening with time results in a larger than expected value of H at early times, as seen by the observations suggesting the existence of dark energy.

 

[PeterDonis]

I think this view fits to Deur's recent paper

Yes, that's one of the statements that makes me think that. I'm still working through the actual math.

 

[timmdeeg]

I'm still working through the actual math.

Great.

Perhaps it's possible to see if in principle Deur's model predicts observations which could verify/falsify his claim.

 

[ohwilleke]

Great.

Perhaps it's possible to see if in principle Deur's model predicts observations which could verify/falsify his claim.

There are many such observations at the galaxy scale (e.g. the relationship between the extent that an elliptical galaxy is spherical and its apparent dark matter fraction, and a relationship in spiral galaxies related to disk thickness), but the dark energy/cosmology scale work is less worked out. The main prediction seems to be structure formation at an earlier time than LambdaCDM which does indeed have some support observationally.

 

[timmdeeg]

The main prediction seems to be structure formation at an earlier time than LambdaCDM which does indeed have some support observationally.

Yes, but besides that I had the Ia Supernovae data and the CMB Power Spectrum in my mind. I wonder if the depletion function which is based on anisotropy factors shouldn't in principle produce the SN data. As Deur claims that these data are "mistaken for repulsion" then I would expect that e.g. the depletion function should yield an alternative (quantitative) explanation.

 

[ohwilleke]

Yes, but besides that I had the Ia Supernovae data and the CMB Power Spectrum in my mind. I wonder if the depletion function which is based on anisotropy factors shouldn't in principle produce the SN data. As Deur claims that these data are "mistaken for repulsion" then I would expect that e.g. the depletion function should yield an alternative (quantitative) explanation.

I'm pretty much 100% certain that the answer is that Deur hasn't had the time and resources to explore a lot of those questions yet. I've corresponded with him in the past and he's basically said as much. The gravity work, while Nobel Prize material and Stephen Hawking class fame generating if it works out, doesn't have grant funding and is basically side hustle made possible by the time that his day job allows for discretionary research. So, he has to spend most of his time working on far less consequential, but better funded, activities. If I won the lottery, the first thing I'd do would be to set up grants or an endowment to support this line of research.

 

[rcarbajal68]

I am working on something similar to that of Dr. Alexandre Deur. I am also using the self-interaction of gravity. But I'm doing the self-interaction in reverse of how he's using it. And I am getting very good results in fitting to the rotation curves of the galaxies.
Sincerely.
Dr. Rigoberto Carbajal Valdez

 

[ohwilleke]

I am working on something similar to that of Dr. Alexandre Deur. I am also using the self-interaction of gravity. But I'm doing the self-interaction in reverse of how he's using it. And I am getting very good results in fitting to the rotation curves of the galaxies.
Sincerely.
Dr. Rigoberto Carbajal Valdez
This is my email.
rcarbajal68@gmail.com

Have you published anything (even a pre-print) that someone could see?

 

[PeterDonis]

I am working on something similar to that of Dr. Alexandre Deur. I am also using the self-interaction of gravity. But I'm doing the self-interaction in reverse of how he's using it. And I am getting very good results in fitting to the rotation curves of the galaxies.

As @ohwilleke has pointed out, we need a reference (a published peer-reviewed paper) in order to have a basis for discussion.

 

[DanielJoseph]

I wonder if https://www-livescience-com.cdn.ampproject.org/v/s/www.livescience.com/amp/gravitational-wave-detector-strange-bumps.html?amp_js_v=a6&amp_gsa=1&usqp=mq331AQIKAGwASCAAgM%3D#aoh=16324719503472&csi=0&referrer=https%3A%2F%2Fwww.google.com&amp_tf=From%20%251%24s&ampshare=https%3A%2F%2Fwww.livescience.com%2Fgravitational-wave-detector-strange-bumps.html is relevant at all

 

[Maarten Havinga]

If GR with self-interaction reproduces all verified MOND predictions (including the EFE) while retaining the beautiful symmetries and general framework of gauge fields and the standard model of particles:
THAT'S AWESOME!

 

[rcarbajal68]

Have you published anything (even a pre-print) that someone could see?

Good morning. I am working on that, in collaboration with another Doctor, as soon as I have something I will share it through this forum. Thank you.

 

[ohwilleke]

I wonder if https://www-livescience-com.cdn.ampproject.org/v/s/www.livescience.com/amp/gravitational-wave-detector-strange-bumps.html?amp_js_v=a6&_gsa=1&usqp=mq331AQIKAGwASCAAgM%3D#aoh=16324719503472&csi=0&referrer=https%3A%2F%2Fwww.google.com&_tf=From%20%251%24s&ampshare=https%3A%2F%2Fwww.livescience.com%2Fgravitational-wave-detector-strange-bumps.html is relevant at all

Not really.

 

[ohwilleke]

If GR with self-interaction reproduces all verified MOND predictions (including the EFE) while retaining the beautiful symmetries and general framework of gauge fields and the standard model of particles:
THAT'S AWESOME!

FWIW, this particular effort does not resolve deep inconsistencies between classical GR and the quantum mechanical foundation of the Standard Model, and indeed, can be formulated in a purely classical sense, although the motivation for the work was rooted in quantum gravity concepts. But assuming it is correct (which is hard to verify as few other in the field have examined it closely) it is indeed awesome.

 

[ohwilleke]

The latest paper in the series of papers cited earlier is the following:

Figure 2 from the paper

Field self-interactions are at the origin of the non-linearities inherent to General Relativity. We study their effects on the Cosmic Microwave Background anisotropies. We find that they can reduce or alleviate the need for dark matter and dark energy in the description of the Cosmic Microwave Background power spectrum.

A. Deur, "Effect of the field self-interaction of General Relativity on the Cosmic Microwave Background Anisotropies"
arXiv:2203.02350 (March 4, 2022).

The introduction in the body text explains:

The power spectrum of the Cosmic Microwave Background (CMB) anisotropies is a leading evidence for the existence of the dark components of the universe. This owes to the severely constraining precision of the observational data and to the concordance within the dark energy-cold dark matter model (Λ-CDM, the standard model of cosmology) of the energy and matter densities obtained from the CMB with those derived from other observations, e.g. supernovae at large redshift z. Despite the success of Λ-CDM, the absence of direct or indirect detection of dark matter particles is worrisome since searches have nearly exhausted the parameter space where candidates could reside. In addition, the straightforward extensions of particle physics’ Standard Model, e.g. minimal SUSY, that provided promising dark matter candidates are essentially ruled out.

Λ-CDM also displays tensions with cosmological observations, e.g. it overestimates the number of dwarf galaxies and globular clusters or has no easy explanation for the tight correlations found between galactic dynamical quantities and the supposedly sub-dominant baryonic matter, e.g. the Tully-Fisher or McGaugh et al. relations.

These worries are remotivating the exploration of alternatives to dark matter and possibly dark energy. To be as compelling as Λ-CDM, such alternatives must explain the observations suggestive of dark matter/energy consistently and economically (viz without introducing many parameters and fields). Among such observations, the CMB power spectrum is arguably the most prominent.

Here we study whether the self-interaction (SI) of gravitational fields, a defining property of General Relativity (GR), may allow us to describe the CMB power spectrum without introducing dark components, or modifying the known laws of nature. GR’s SI already explains other key observations involving dark matter/energy: flat galactic rotation curves, large-z supernova luminosities, large structure formation, and internal dynamics of galaxy clusters, including the Bullet Cluster. It also explains the Tully-Fisher and McGaugh et al. relations. First, we recall the origin of GR’s SI and discuss when it becomes important as well as its overall effects.

 

[Maarten Havinga]

The latest paper in the series of papers cited earlier is the following:

View attachment 298460
Figure 2 from the paper

Although I am now a great fan of Deur's theory, this last paper is not so much to my liking. It would have been great if Deur had brought it like "okay, so the CMB is explained this way by lambda CDM and if you really want to reproduce the CMB that way, in principle it can also be done without dark matter".

My issues are:

1. This CMB graph from the Big Bang is a postdiction, not a prediction. And with 6 free variables.
2. The CMB in this interpretation ought to be dampened by cosmic dust, which is not reckoned with in Lambda-CDM or Deur's paper. See Vavrycuk's paper and video.
3. The Big Bang explanation assumes inflation, which is an unfalsifiable idea for our current experimentation range.
4. I'm a believer in the bible, and there's good reason to reject the Big Bang as description of how God created the universe. An alternative explanation is given by for instance Russell Humphreys' book Starlight and Time.

In general, my great liking of Deur's theory is slightly dampened by the fact he attaches such importance to accomodating a Big Bang scenario alike to how the lambda-CDM community preaches it. For my taste this paper handles a detail not worth a paper so early in Deur's on the whole extremely prudent approach.

Nevertheless I'm a big fan of his work! :-)

 

[ohwilleke]

I'm a believer in the bible, and there's good reason to reject the Big Bang as description of how God created the universe.

There is no reason for you to investigate science in that case.

 

[PeterDonis]

I'm a believer in the bible, and there's good reason to reject the Big Bang as description of how God created the universe. An alternative explanation is given by for instance Russell Humphreys' book Starlight and Time.

Please note this is off topic here; this forum is about physics, not religion.

 

[Maarten Havinga]

There is no reason for you to investigate science in that case.

As to how the universe came into being, I do admit that for what I believe about it I don't currently need a scientific technical description of it. But it may certainly help! And if my belief doesn't match what hardcore science tells I will feel this need a lot indeed! Indeed I felt it pretty much until I found Vavrycuk's research. Belief must be factual or it is useless.

As to it being off-topic, isn't there a saying "nature doesn't care what you think?". This saying expresses the belief in an absolute entity and its order. So shouldn't you tell Newton and Einstein, who started science based on such belief?

Contrary to having no reason to investigate science, in my personal interests I've noticed this: exactly because I believe in an absolute entity that governs the laws of physics and made them, I become very curious as to how these laws work and every aspect of them. I feel they were made by the greatest genius - God, whose genius is expressed by the results of many experiments - and that makes me all the more curious.

 

[PeterDonis]

As to it being off-topic, isn't there a saying "nature doesn't care what you think?".

Yes, there is such a saying. Here are examples of applying that saying: nature doesn't care that your belief in God leads you to think that the Big Bang theory is not correct. Nature doesn't care that you've read of some alternate theory that you like better.

However, that saying is irrelevant to whether or not discussions of religion are off topic here. They are off topic here because the PF rules say so. It has nothing to do with what nature does or does not "care" about. Nor does it have anything to do with what you think.

I become very curious as to how these laws work and every aspect of them.

That's fine, and learning about that is what PF is for. But any claims about what laws you think are correct need to be based on scientific evidence.

 

[PeterDonis]

See Vavrycuk's paper and video.

And see the discussion in that thread. It gives plenty of good reasons not to believe that "cosmic dust" is a significant effect.

 

[bhobba]

As to it being off-topic, isn't there a saying "nature doesn't care what you think?". This saying expresses the belief in an absolute entity and its order. So shouldn't you tell Newton and Einstein, who started science based on such belief?

With my mentor's hat on, while I have no issues with what has been written, it must not degenerate into philosophy by forum rules. Please note it is not because we have anything against philosophy; it's just when we allowed it because we do not have an expert mentor in it, it degenerated into a mess. So please keep that in mind.

Thanks
Bill

 

[Maarten Havinga]

I will from now on adhere to this rule, didn't know about it. Therefore I won't tell you what I think of this rule, that would violate the rule.

And see the discussion in that thread. It gives plenty of good reasons not to believe that "cosmic dust" is a significant effect.

Well I've looked through the paper and Vavrycuk's video and I don't see anything unscientific in his approach. FYI, Vavrycuk supports no biblical view at all but some kind of Cyclic Cosmology. What bothers me is that people react with closing the thread and scorn for Vavrycuk, which is exactly how a scientific community should NOT react to new results and theories. Investigate everything and keep what has proven to be good. And certainly don't use scorn as a way to shrink the credibility of a theory that is unorthodox.

 

[PeterDonis]

I've looked through the paper and Vavrycuk's video and I don't see anything unscientific in his approach.

I didn't say his paper was unscientific. I said that the discussion in the other thread gives plenty of reasons not to believe that the "cosmic dust" he hypothesizes is a significant effect.

What bothers me is that people react with closing the thread and scorn for Vavrycuk, which is exactly how a scientific community should NOT react to new results and theories.

PF's primary purpose is not to discuss "new results and theories" that the scientific community is still evaluating. It is to help people understand science that is already mainstream. PF's reaction is emphatically not the same as the reaction of the "scientific community". If you want to know how other researchers in the field react to Vavrycuk, you will need to look at scientific papers, not PF.

That said, if a particular paper has issues, PF members are perfectly within their rights to point out those issues.

don't use scorn

Pointing out issues with a paper is not "scorn". Nor is pointing out that a statement made by someone who calls themselves a scientist and claims to be an expert in a field is seriously inconsistent with basic knowledge in the field.

 

[PeterDonis]

The Big Bang explanation assumes inflation

No, it doesn't. Inflation is just one hypothesis for what happened before the Big Bang (i.e., before the hot, dense, rapidly expanding state that is the earliest state of our Universe for which we have good evidence). It is not the same as the Big Bang model itself.

 

[mfb]

Investigate everything and keep what has proven to be good.

That happened, and his paper was not kept. So what's the problem?
If the proposal is weak to begin with it will be dismissed quickly. We can't spend an unlimited time on everything everyone has ever proposed anywhere. There is a time to move on. People who never realize that will keep defending something dead until they retire.

 

[Maarten Havinga]

That happened, and his paper was not kept. So what's the problem?
If the proposal is weak to begin with it will be dismissed quickly. We can't spend an unlimited time on everything everyone has ever proposed anywhere. There is a time to move on. People who never realize that will keep defending something dead until they retire.

Just list the arguments against for me. Vavrycuk had just enough time to answer 1 question, then the thread was banned.

 

[Maarten Havinga]

the earliest state of our Universe for which we have good evidence

What would falsify this earliest state? The Hubble tension? Too large structures like this one? Too big galaxies at high redshift? That if string theory is correct, the 168m Ethan Siegel gives for the universe right after inflation might be far too small to contain all those strings? It's far smaller than the scharzschild radius would be.

I think these each don't falsify the initial state entirely, correct? But still it's not settled IMO that we have conclusively proven this.

 

[PeterDonis]

Vavrycuk had just enough time to answer 1 question, then the thread was banned.

The reason for that was given in the thread.

Further discussion of that other thread is off topic here. Please stick to the topic of this thread.

 

[PeterDonis]

What would falsify this earliest state?

You can't falsify a "state". You would have to falsify the entire class of "Big Bang" models that have the universe starting from such a state and expanding to the state we have now. Note that our best current model is only one model in that class; falsifying it is not the same as falsifying the entire class of models. In particular, finding an alternative explanation for galaxy rotation curves that does not involve dark matter is not the same as falsifying the entire class of "Big Bang" models.

if string theory is correct

You protest about unproven models and yet you are bringing in string theory? I think you need to take a step back here.

the 168m Ethan Siegel gives for the universe right after inflation might be far too small to contain all those strings?

Please give a reference.

It's far smaller than the scharzschild radius would be.

Irrelevant since the spacetime geometry in Big Bang models is not the Schwarzschild geometry; the early universe in Big Bang models is rapidly expanding, not static.

Moreover, all of this is off topic for this thread. I suggest you take more time to learn basic cosmology. If you have a reference discussing issues with the Big Bang model and you would like to ask questions about it, please start a separate thread. Please keep discussion in this thread focused on the topic of this thread.

 

[Davephaelon]

I also have become enamored of Deur’s theory that explains a host of astrophysical phenomena by just a single consideration – gravitational self-interaction (SI). But I wondered if there might be a problem with gravitational lensing. Since his model dispenses with Dark Matter and the gravity field beyond a galaxy or cluster is already reduced due to SI within those structures, it would seem there wouldn’t be sufficient gravity outside such structures boundaries to induce the observed lensing. But it could be this issue is already addressed in one of his papers, which I haven’t come across.

Thinking about it some more it occurred to me that the reduced g-field outside massive astronomical structures, in his model, might lead to a sufficient gravity field gradient to induce the same space-time curvature as would be the case if the gradient were shifted into a stronger range as in the Dark Matter picture. But, I’m just guessing here how his model would handle lensing, since I’m not really sure if such a heuristic idea is compatible with General Relativity

 

[PeterDonis]

it occurred to me that the reduced g-field outside massive astronomical structures, in his model, might lead to a sufficient gravity field gradient to induce the same space-time curvature

What you are calling "gravity field gradient" is an effect of spacetime curvature, not a cause. In any case, "reduced g-field outside massive structures" is a highly heuristic and imprecise way of describing what is going on in Deur's models, and should not be used as a basis for trying to reason out their consequences. (Note also that only some of Deur's proposed models even have this property, and those are the more speculative ones, that add additional quantum gravity-type effects on top of the straightforward classical effects I describe below.)

Deur's models, in general, do not change the Einstein Field Equation and do not postulate any different "source" of spacetime curvature as compared to standard GR. His basic idea is simply taking into account properties of particular solutions of that equation (such as disk-shaped rather than spherical gravitational sources) that other researchers had ignored on the assumption that they were too small to matter, whereas Deur attempts to show that that is not the case, that those properties do matter, and that taking them into account means the visible matter in galaxies can account for things like their rotation curves, using the standard Einstein Field Equation, without having to add invisible (dark) matter to the gravitational sources. (In some of his proposed models, as noted above, he does add quantum gravity effects that aren't present in classical GR.)

 

[ohwilleke]

Deur's models, in general, do not change the Einstein Field Equation and do not postulate any different "source" of spacetime curvature as compared to standard GR. His basic idea is simply taking into account properties of particular solutions of that equation (such as disk-shaped rather than spherical gravitational sources) that other researchers had ignored on the assumption that they were too small to matter, whereas Deur attempts to show that that is not the case, that those properties do matter, and that taking them into account means the visible matter in galaxies can account for things like their rotation curves, using the standard Einstein Field Equation, without having to add invisible (dark) matter to the gravitational sources. (In some of his proposed models, as noted above, he does add quantum gravity effects that aren't present in classical GR.)

Thank you for having taken the time to read some of these papers sufficiently to understand what Deur is trying to do accurately. Your summary here expresses the gist of it clearly and succinctly. The effort you have taken to investigate and understand this not widely cited body of work is appreciated.

 

[Davephaelon]

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.

 

[Davephaelon]

I have to say this is the most interesting thread that I have read anywhere on Deur's work, which I am keenly interested in. The back and forth dialogue is very informative. I just can't help but wonder if his efforts will lead to a major paradigm shift in our understanding of nature at the largest scales.

 

[Davephaelon]

What you are calling "gravity field gradient" is an effect of spacetime curvature, not a cause. In any case, "reduced g-field outside massive structures" is a highly heuristic and imprecise way of describing what is going on in Deur's models

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.

 

[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.