Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

New study shows Dark Matter isn't needed? Relativty explains it?

  1. Oct 11, 2005 #1
    new study shows Dark Matter mat not exist? Relativty explains it?

    Look here
    http://www.space.com/scienceastronomy/051010_dark_matter.html

    Is this valid reasoning? I noticed it hadn't been submitted to peer review.
     
    Last edited: Oct 11, 2005
  2. jcsd
  3. Oct 11, 2005 #2

    EL

    User Avatar
    Science Advisor

  4. Oct 11, 2005 #3

    Garth

    User Avatar
    Science Advisor
    Gold Member

    General Relativity Resolves Galactic Rotation Without Exotic Dark Matter has been submitted to Ap.J. it will be interesting to see if it passes peer review.

    The case it makes is obvious; that the dynamics of a diffuse collection of orbiting masses, such as a spiral galaxy, has to be calculated in the non-linear theory of GR rather than the linear Newtonian theory. Apparently, and surprisingly, this has not been done before and the consequent mismatch between galactic dynamics and Newtonian theory has led to the invocation of galactic halo DM. However, Cooperstock and Tieu claim that when properly calculated there is no mis-match at all!.
    I think their calculations appear sound, although I have not checked them throroughly. However they conclude:
    I cannot concur with the absence of DM as there is other evidence for extra-galactic DM from lensing and other effects in rich cluster IGM. However it may not be exotic, if Omegabaryon ~ 0.2 - 0.3, there would be no need to invoke hypothetical exotic non-baryonic DM to explain the mass detected within galactic clusters. Such a high Omegabaryon is predicted by the strictly linear expansion model.

    Garth
     
    Last edited: Oct 11, 2005
  5. Oct 11, 2005 #4

    Garth

    User Avatar
    Science Advisor
    Gold Member

    Again:- If this analysis by Cooperstock and Tieu stands up then it would have profound implications for the 'mainstream model'. In particular there would be a problem with galaxy formation within the time scale that model allows.

    The present model relies on the quick concentration of non-interacting DM to form the potential wells into which baryonic matter can fall, which then forms the visible galaxies. However if these galactic haloes are only an artifact of inappropriate Newtonian dynamics then more time would be required for the galaxies, now seen at high z to form.

    The most extreme example of this is the Hubble ultra deep field object UDF033238.7-274839.8 aka HUDF-JD2 , a 6 x 1011Msolar galaxy at z = 6.5 when the universe was only 860 Myrs old, (age given by Ned Wright's calculator allowing for DE). Also we have high-z quasars with significant iron abundances, and iron is the last element to be formed in fusion processes, such as APM 08279+5255at z = 3.91 whose age is 2.1 Gyr when the universe was only 1.6 Gyrs old (according to LCDM model expansion).

    The strictly linear expansion model gives a universe age of 2 to 3 times the LCDM model.

    Garth
     
  6. Oct 11, 2005 #5
    Personally I suspect that the answer lies in the manner of Operation of Gravity, which is, to this date, seemingly, still unknown, in Completeness.

    It may simply be that intergalactic gravity behaves slightly dfferently then the observable gravitational interactions seen at our local scale.

    It may sum differently, it may simply be that in summing, it can drag much more of space around with it then had ever been previously thought of, if it can drag space around, then it can also drag around the contents of that space around without, persay, energy loss or general interactivity.
     
  7. Oct 11, 2005 #6

    Garth

    User Avatar
    Science Advisor
    Gold Member

    You'll need to express your ideas with a mathematically described testable theory, GR, MOND and SCC are such examples.

    But first we have to get the GR analysis right!

    Garth
     
  8. Oct 11, 2005 #7
    Really :rolleyes: so words won't do for you, interesting as that is the foundation of Mathematics, words.

    ana one ana two ana three .. .. .. .. ..

    But I appreciate your answer, for what it is worth. :approve:
     
  9. Oct 11, 2005 #8

    Garth

    User Avatar
    Science Advisor
    Gold Member

    Your concepts are fine, as points for discussion, but they will need to be quantified and not just 'hand waving'. I'm not criticising, my hands 'wave' as much as anybody's! However, having a mathematically described theory that makes testable predictions is way we separate out those ideas that 'work' and reflect reality in some way from those that are to fall by the wayside.

    Modified gravity is MOND and your "if it can drag space around" is the gravitomagnetic effect being tested at this moment by Gravity Probe B, who knows what its answer will be?

    Garth
     
  10. Oct 11, 2005 #9
    There has been a rebuttal of the paper that you can see here. The rebuttal basically says that the model is "unphysical". It's yet to be seen if this "unphysical" explanation is substantial or not.
     
  11. Oct 11, 2005 #10

    Garth

    User Avatar
    Science Advisor
    Gold Member

    Welcome to these Forums Pyro! And thank you for that link.
    In fact I do not agree with its conclusion that the Cooperstock & Tieu galaxy model is 'unphysical', the galaxy does have a disk - the galactic disk in which the spiral arms are embedded, it consists of stars, dust and gas including massive molecular clouds. The total galactic mass Cooperstock & Tieu require is 21×1010M which is totally realistic.

    Garth
     
  12. Oct 11, 2005 #11
    O.K. here it is, mathematically.

    Thanks, I was aware of how science gets done, the answer mathematically would be ∞ = 1 (No, I am NOT joking) which needs to be broken down to be effective in it's descripton of reality, otherwise, no one will understand it, it needs explaining, sorry, but it is done with words, first, then math.

    As Einstein himself stated, "Theory is that which shows us where to look" if I have a theory that is, ostensibly, complete and therefore shows 'what is' as such, then thereafter it would-could be mathematized, as to show it's validity, just that I do believe that it is not as simple as just one equation.

    The concepts I have in my head are not based upon mathematical reasonings, {Persay thought they include math knowledge} they are based upon observation{s} of reality and Lots of Currently known Scienctific evidence, after all, there is ony about ten percent of it left to know.

    LD
    .. .. .. .. Hops off .. .. .. .. .. Stage .. .. .. .. .... {Whoooops!} .. .. .. .. .. ..I'll get off of this thread now, go find turtle, he should be back, any moment now
     
  13. Oct 11, 2005 #12
    W00t? I was under the impression that astronomers/astrophysists always used GR, I mean you'd think that there is a significant difference between the two when you're talking about these kind of things.

    I'm shocked that no one has done this before.
     
  14. Oct 12, 2005 #13

    Chronos

    User Avatar
    Science Advisor
    Gold Member
    2015 Award

    Agreed, words describe what the symbols represent in a mathematical formulation. The mathematical formulation part is what appears to be missing in this example.
     
  15. Oct 12, 2005 #14

    SpaceTiger

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    :rofl:

    I love how the rebuttal paper cites "Introduction to Relativity". I'll let you guys know if we ever find dust disks distributed as a delta function in z.
     
  16. Oct 12, 2005 #15

    EL

    User Avatar
    Science Advisor

    :rofl:

    Actually, isn't it possible that this singular disk models the galaxy quite good? Would a more realistic model really give a much different result? (I'm asking because I don't know...)
     
  17. Oct 12, 2005 #16

    Garth

    User Avatar
    Science Advisor
    Gold Member

    I concur that's my point - even if their analysis leaves something to be desired the necessity of using GR rather than Newton to predict galactic rotation profiles would seem basic, don't you think?

    Garth
     
  18. Oct 12, 2005 #17

    SpaceTiger

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    In some spiral galaxies, there are disks that are relatively thin, but certainly not well-approximated by a delta function. The point in the rebuttal paper was that there was an extra source of gravity in addition to that which they were using to model the luminous matter of a "real" galaxy. In other words, they were unknowingly including dark matter. :smile:

    As for your latter question, I'm relatively sure (though I've not done the calculations myself) that the Newtonian approximation will be valid if GR is properly applied.
     
  19. Oct 12, 2005 #18

    EL

    User Avatar
    Science Advisor

    Ah, that explains a lot! Thanks. (Have to admit I didn't read the rebuttal too carefully.)


    Yes, that's what I think too.

    Anyway, it's strange that CERN newsletter took it up after the rebuttal was written...
    http://science.slashdot.org/science/...tid=160&tid=14
     
    Last edited: Oct 12, 2005
  20. Oct 12, 2005 #19

    Chronos

    User Avatar
    Science Advisor
    Gold Member
    2015 Award

    I'm going to hide behind the skirt here, Garth... Can we say with any confidence what disc model might work? I think the observational evidence is really thin. Another objection: since when did CERN jump into the fray? I don't think that is even relevant to this conversation.
     
    Last edited: Oct 12, 2005
  21. Oct 12, 2005 #20

    SpaceTiger

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Yeah, we were just talking about this at (very late) dinner. One of the guys here says he knows the people that wrote the CERN article and he says they're pretty distant from the mainstream. I wouldn't take it as an endorsement by everyone at CERN and, to my knowledge, nobody in the mainstream is taking it seriously.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: New study shows Dark Matter isn't needed? Relativty explains it?
Loading...