No need for dark matter, dark energy, MONDS, ect, nothing exotic?

[MTd2]

This guy uses lattice to calculate how gravity would behave in a non commutative aproximation. His insight is interesting given that gravitons interact among themselves pretty much like gluons.

http://arxiv.org/abs/0901.4005

I am extremely surprised of how well that describes the whole thing

 

[ZapperZ]

Isn't there something seriously missing here in this whole thing? Gravitons, and the parameters associated with it? You can almost make up anything you like to fit "the whole thing".

Compare this with the current theory of dark matter, dark energy, even MOND, etc., that are constraint by things that we already know and can verify.

Zz.

 

[MTd2]

As a original and, mainly qualitative, article, it just fitted extremelywell. He just expanded around the coupling constant, so there was no room for any adjust expect for the one used to fit the dataset.

And all models of dark matter and mond are too complicated, too much explanation, and too little things to find.

The main message for me, in this article, it is that most energy is trapped in matterless gravitational fields. I guess marcus will like this one, since a similar idea, but for cosmological constant, was presented here:

http://arxiv.org/abs/0812.3912

There, the negative pressure of cosmological constant is due to the creation of particles. Well, maybe you can say that the positive pressure of dark matter accounts for the for a weird anihilation of particles.

 

[ZapperZ]

Sorry, but I'm an experimentalist. Putting your eggs into an imaginary basket that isn't even close to being verified (and you don't even know precisely how large and how strong that basket it) is rather strange. Touting it as the being comparable, or even better, than existing concepts that have a higher degree of verification is downright foolish.

Zz.

 

[MTd2]

Since this is a beyond the standard model forums, I think trying to tell the peers about new stuff is nice thing... Otherwise, there would be no point in most of discussions about strings and LQG given that those, in a fundamental, plankian level, which also have an even lower degree of verification.

 

[humanino]

Isn't there something seriously missing here in this whole thing? Gravitons, and the parameters associated with it? You can almost make up anything you like to fit "the whole thing".

Compare this with the current theory of dark matter, dark energy, even MOND, etc., that are constraint by things that we already know and can verify.

I think you are seriously missing the point here. Dark matter of MOND make additional assumptions which this paper attempts to remove. What is being done here, is to display for everyone to see the results of a calculation under precisely reproduceable approximations. There is not new physics whatsoever. The question raised by this paper is : "if this qualitatively and quantitavely attractive picture fails, which approximation is incorrect ?". I am unable to answer this question. The lagrangian put on the lattice appears everywhere in the litterature. Being a QCD-ist, it is not suprising that I find this paper important. At the very least, if we are to accept dark matter or MOND, we should make sure that we need them.

 

[BenTheMan]

I don't understand the statement in the paper that "GM is the MORE relevant coupling to use". This is basically the only way he gets non-trivial results.

That, and he uses scalars instead of gravitons. It's not clear to me how much this effects the calculations, but drawing hard conclusions on this seems a bit dubious.

In addition, he'd have to explain why 20% of the energy density of the universe isn't accounted for.

Anyway, it seems like something that would be possible to test with astronomy---that is, he predicts that the potential is really different at long distances. In particular, the bullet cluster places strong constraints on these theories, I think.

 

[MTd2]

The author of this paper, A Deur, has an older paper, explaining some of the derivations of his model.

http://arxiv.org/abs/astro-ph/0309474

 

[MTd2]

In addition, he'd have to explain why 20% of the energy density of the universe isn't accounted for.

There were 20x more dark matter than usual matter, in some of the sampled galaxies, which agrees with the upper bound on observations:

pag. 6:

"Gaseous mass in a cluster is typically 7 times larger than the total galaxy mass. Assuming that half of the cluster galaxies are spirals or flat ellipticals we obtain for the cluster a ratio (M′/M)cluster = 18.0. Non-abelian effects make our model of cluster to appear as if composed of 94% dark matter, to be compared with the observed 80-95%.

 

[Coin]

My immediate question would be, how do they explain the bullet cluster observation? In their paper they offhandedly mention their model is compatible with the bullet cluster, but they never explain how that I can find:

7) Non-abelian effects emerge in asymmetric mass distributions. Consequently, adopting the dark matter standpoint, normal matter and dark matter distributions in space should be correlated, i.e. signs of dark matter should not be found away from systems of normal matter, or associated with homogeneous and symmetric system. This is naturally compatible with the Bullet cluster observation [10], viewed as a direct proof of dark matter existence since it is difficult to interpret in terms of modified gravity. That our mechanism is also naturally compatible with such observation, while empirical gravity law modifications are not, illustrates the importance of being conceptually correct about the observations leading to the dark matter hypothesis.

(I honestly can't even pick apart the grammar in this bit.)

It seems like the biggest problem for any MOND-alike theory (which I would think of this theory as, since it is a theory that tries to explain the dark matter evidence using a new gravity effect rather than a new type of matter) is that dark matter is used to explain such a wide variety of things these days that it is difficult for any new gravity theory to encompass all of them. In this case, as far as I can tell they provide a specific calculation for how their model solves the spiral arm problem without dark matter. This is pretty darn cool, assuming their calculations check out. But they seem to get a little messy toward the end when they try to rapidly apply their model to everything besides spiral arm rotation. They mention but gloss over the bullet cluster stuff. They try to toss together a justification for dark energy within their model with like three or four sentences of conceptual reasoning, but do not appear to have done any sort of calculation. It seems, at least from my layman's perspective, like this would all be more convincing if they either could attack the bullet cluster / dark energy type stuff with the same level of rigor with which they attack the spiral arm problem, or if they stuck to limiting the scope of the theory to stuff they can rigorously provide explanations for...

 

[BenTheMan]

There were 20x more dark matter than usual matter, in some of the sampled galaxies, which agrees with the upper bound on observations:

pag. 6:

"Gaseous mass in a cluster is typically 7 times larger than the total galaxy mass. Assuming that half of the cluster galaxies are spirals or flat ellipticals we obtain for the cluster a ratio (M′/M)cluster = 18.0. Non-abelian effects make our model of cluster to appear as if composed of 94% dark matter, to be compared with the observed 80-95%.

How does this explain the WMAP observations then?

Just ignore spiral galaxies for a minute. WMAP tells us Omega = 1. We know independently (SN observations) that the dark energy is .7, and we can calculate that baryonic matter contributes 0.05. So we're missing 0.25 before we even start calculating rotational curves.

Does anyone see what I'm confused about?

 

[MTd2]

Proportionaly, the ratio of dark matter to matter in the galaxies is 7, aproximately the same of what was found in the article. If most of the baryonic mass is found in galaxies and its vicinities, it is pretty much a good aproximate for the general situation of the universe, even in the crude aproximation used.

The article is not about a MOND, but simply the old and good General Relativity applied to a galaxy and its vicinities, in a weird aproximation.

 

[BenTheMan]

I don't care about galaxies, WMAP isn't looking at galaxies. WMAP looks at the CMB (correct me, of course, if I'm wrong about this).

How does this idea explain omega = 1? You don't need spiral galaxies to tell you that there has to be some dark matter, you can get this number as an unexplained contribution to the overall energy density of the universe.

It could be (and probably is) that they standard calculation changes in some way, but I don't know.

 

[MTd2]

Oh, I see. I get what you mean. The cosmic coincidence model is a kind of anthropic thing. Why omega=1 right now is like why the /hbar is what it is. It is just like explaining a coincidence. But anyway, trying to find an observational source for the cosmological constant is nice.

So, this is ok:

"Our approach suggests that dark energy is a consequence of energy conservation between the increased galaxy binding energy vs. the outside potential energy."

But I agree that this is not useful: "It implies a quantitative relation between dark energy and dark matter, which explains naturally the cosmic coincidence problem , that is, the dark energy and dark matter contributions needed to explain observations are similar."

He could end his article without trying to be too cool.

 

[BenTheMan]

Why omega=1 right now is like why the /hbar is what it is.

Yeah, but you can't dispute the fact that omega = 1.

 

[malawi_glenn]

Why is it ok to discuss non published articles here and nowhere else?

 

[humanino]

Why is it ok to discuss non published articles here and nowhere else?

I don't think that's a fair comment. You have in this article the details of a calculation, its results, and I think what's fair is to give a clear statement "such approximation does not hold". We are not talking about speculative theories without prediction here. We are talking about "naive" approximation to a very important problem. I think this article deserves a few minutes of attention from professionals in the field to answer it seriously.

 

[malawi_glenn]

Oh I was not commenting the article itself, I was just wondering where it is ok to discuss non published results/articles and not.

 

[MTd2]

Why is it ok to discuss non published articles here and nowhere else?

Well, we are used to it... And since most of the things here are primarily non yet verifieble stuff, we practice pear review right here. LQG and Strings are such. It is so that, they are not published for years and even so, they get importance. For exmple, the first famous BLG tri-algebra, concerning M-2 branes, was just published last week in Physics Letters, but it is really an old topic, relatively speaking. There was a consensus about its importance since it appeard o arxiv.org and important theories were built upon it, even by top guys, like Maldacena.

 

[malawi_glenn]

well, by reading the sticky forum rule for this subforum I noticed that some arxiv articles may be allowed.

Was just curios :-)

 

[MTd2]

Yeah, but you can't dispute the fact that omega = 1.

Yes, but as I said, this is not an issue, because I've agreed that it was wrong when he said his article that it was explained, because it was not. But this might be good new aproximation to GR. This could show a new mechanism to observe energy stored in gravitational fields, an it can really help to understand why omega is what it is.

 

[humanino]

Yes, but as I said, this is not an issue, because I've agreed that it was wrong when he said his article that it was explained, because it was not. But this might be good new aproximation to GR. This could show a new mechanism to observe energy stored in gravitational fields, an it can really help to understand why omega is what it is.

I don't think omega=1 is relevant in this discussion. Apart from omega=1, what other motivation do you have for dark energy ? Dark energy is only meant to bring omega back to 1. If however the motivations for dark matter are removed, I agree that the perspective on introducing dark energy changes a little bit. In this, omega is relevant here. Otherwise, if we are to realize we were wrong about dark matter, then we should think a little bit more about dark energy indeed. The author has no quantitative prediction about dark energy. Having simulations done on a personal computer with fractal (sponge-like) large scale structures is not realistic.

Again, I do not see any serious argument to sweep out this annoying paper. I could not find one myself. The way I see it, it can only be wrong in the approximations used, in particular its scalar lagrangian. So far, the only thing we have against this paper is "the lagrangian is not motivated enough". If the lagrangian were justified, the article would already be published in the most prestigious journals however !

 

[anthonyhollin]

it still doesn't cover the bullet cluster, its certainly a very neat idea (worth looking into more id say) but we can clearly see here that the gas has collided and the galaxies have passed through each other, yet the weak lensing is around the stars, hence that's where the mass is. I am pretty sure we can trust the observations telling us that that there is more mass in the inter-cluster gas than in the stars so why isn't the lensing centered on the gas in the middle if this theory is correct?

 

[humanino]

Im pretty sure we can trust the observations telling us that that there is more mass in the inter-cluster gas than in the stars

Sure, and the author acknowledges that.

so why isn't the lensing centered on the gas in the middle if this theory is correct?

He claims this is stored energy in the collapsed field lines of the gravitational field.

I have contacted with the author. His paper has been quite modified and accepted for publication in PLB. He has a "pre"diction for the Tully-Fisher relation, which in his understanding stems from the same physics as Regge slope in QCD.

 

[MTd2]

This is funny because I've remembered about this paper just last week when there were some gossips, that turned out to be true, that Fermi and HESS didn't find the peak of excess of electron/positrons at 500GeV, and that the small excess can probably indeed easily accounted by emissions of supernova remnants and nearby pulsars. anthonyhollin raised this thread from the dead precisely today, when I was discussing these issues in Marco Frasca and Tommaso's blogs:

http://marcofrasca.wordpress.com/2009/05/04/phenix-says-gluons-are-not-all-the-story/#comment-914

 

[MTd2]

I have contacted with the author. His paper has been quite modified and accepted for publication in PLB. He has a "pre"diction for the Tully-Fisher relation, which in his understanding stems from the same physics as Regge slope in QCD.

When will he update the preprint on arxiv?

 

[humanino]

When will he update the preprint on arxiv?

I asked him the question personally and got the answer : probably very soon, his paper is final and he will update arXiv within the next couple of days.

 

[robva]

The paper was updated on the arxiv server yesterday evening.

 

[Coin]

robva thanks for the update.

I continue to focus on how their model is supposed to explain the Bullet Cluster / "MACS J0025.4-1222" observations.

Non-Abelian effects emerge in asymmetric mass distributions. This makes our mechanism
naturally compatible with the Bullet cluster observation [15] (presented as a direct proof of
dark matter existence since it is difficult to interpret in terms of modified gravity): Large
non-Abelian effects should not be present in the center of the cluster collision where the
intergalactic gas of the two clusters resides if the gas is homogeneous and does not show
large asymmetric distributions. However, the large non-Abelian effects discussed in the
preceding paragraph still accompany the galaxy systems.

This seems like a significant improvement over how they addressed this issue in the previous draft. Unfortunately I am still a little lost. Can anyone help me follow the argument here? As near as I can gather they're saying that galaxies will be subject to nonabelian effects, whereas intergalactic gas will not be. So I guess the idea is there will be a large mass of intergalactic gas in each cluster which will behave differently during a collision than the rest of the matter in either cluster. And this will do... what? How would this effect result in the gravitational lensing characteristic of the bullet cluster observation?

One of course would not expect any greater detail than this paragraph provides in this particular paper, since this is an introductory paper and the goal was to model spiral arms, but I wonder if the will be running the numbers for their proposed cluster collision model in a future paper.

 

[MTd2]

Thank you very much robva. I assume that the non linear effects are due to a kind gravitational soliton, so that it stores a lot of gravitational energy to cause optical lensening. I bet this non-abelian aproximation can give rise to galactic-size versions of gluons with 0 spin.

 

[robva]

From what I understand, it is not unlike the case of QCD where the non-abelian force (strong interaction) collapses into flux tubes, resulting into confinement. As a result this binding energy is indeed stored inside the system.

As far as the gas is concerned, if the mass distribution is the gas is homogeneous, then the symmetry of the system will be such that the flux lines will all compensate each other and result in no non-abelian net effect.

 

[robva]

From what I understand, it is not unlike the case of QCD where the non-abelian force (strong interaction) collapses into flux tubes, resulting into confinement. As a result this binding energy is indeed stored inside the system.

As far as the gas is concerned, if the mass distribution is the gas is homogeneous, then the symmetry of the system will be such that the flux lines will all compensate each other and result in no non-abelian net effect.

I should have been more careful in the second paagraph. What I meant is that there will be no non-abelian net effect seen from outside the system. Like QCD, everything will stay confined. In the case of the bullet cluster, you see that the two mass maximum are offset from the two gas density spikes. Gas dominates the visible mass of the cluster so it was seen as a proof of dark matter.

In this approach however, the graviton field self interaction effects (the contact term in G^2 in the paper) will dominate this gas. This is the strength of these effects that are able to deform the space-time and bend the light to make a gravitational lens.

To sum it up, the field self-interaction plays the role of dark matter in other models

 

[robva]

In the context of the weak approximation he made in this paper, the lensing effect can not be directly computed from the lagrangien. He kept only the scalar term which can only couple with the trace of the Fmunu tensor to produce an invariant. Since this trace is zero, this model does not allow photons to couple with gravitons. It is simply necessary for future work to extent this model to rank2 tensor in order to compute lensing directly from graviton interactions. It is very difficult to compute on a lattice but some people are starting to look at it. A simpler approach is simply to use the potential he got and via a semi-classical approach do a estimate of the lensing effects. That should work fine since it is essentially what current lensing models do using the Newtonian gravity potential with extra mass coming in from dark matter.
Alexandre is going to look at that, its on his long list of things to do.

 

[MTd2]

It is very difficult to compute on a lattice but some people are starting to look at it.

So, it wasn't just me who got interested in his work?

BTW, I'd like to know how does the non abelian nature of his model relates to frame dragging.