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

  1. Jan 27, 2009 #1

    MTd2

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    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
     
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  3. Jan 27, 2009 #2

    ZapperZ

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    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.
     
  4. Jan 27, 2009 #3

    MTd2

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    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.
     
  5. Jan 27, 2009 #4

    ZapperZ

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    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.
     
  6. Jan 27, 2009 #5

    MTd2

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    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.
     
  7. Jan 27, 2009 #6
    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.
     
  8. Jan 27, 2009 #7
    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.
     
  9. Jan 27, 2009 #8

    MTd2

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  10. Jan 27, 2009 #9

    MTd2

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    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%.
     
  11. Jan 27, 2009 #10
    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:

    (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...
     
  12. Jan 27, 2009 #11
    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?
     
  13. Jan 27, 2009 #12

    MTd2

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    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.
     
  14. Jan 27, 2009 #13
    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.
     
  15. Jan 27, 2009 #14

    MTd2

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    Oh, I see. I get what you mean. The cosmic coincidence model is a kind of antropic 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.
     
  16. Jan 28, 2009 #15
    Yeah, but you can't dispute the fact that omega = 1.
     
  17. Jan 28, 2009 #16

    malawi_glenn

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    Why is it ok to discuss non published articles here and nowhere else?
     
  18. Jan 28, 2009 #17
    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.
     
  19. Jan 28, 2009 #18

    malawi_glenn

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    Oh I was not commenting the article itself, I was just wondering where it is ok to discuss non published results/articles and not.
     
  20. Jan 28, 2009 #19

    MTd2

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    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.
     
  21. Jan 28, 2009 #20

    malawi_glenn

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

    Was just curios :-)
     
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