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Space Expansion from Dark Matter

  1. Nov 30, 2004 #1
    General Relativity GR, and Loop Quantum Gravity LQG as well, says that space is derived from the gravitational field of matter. But the total matter in the universe is constant; whereas the space of and the amount of Dark Energy in the universe is growing.

    It is supposed that most of this matter is in the form of Dark Matter. If GR and LQG are correct, then it follows that Dark Matter is indeed responsible for the expansion of the universe and that Dark Energy is really just a passive property of space.

    How can that be??? Well, we know that space is expanding at an accelerating rate. Since it incorporates an increasing amount of Dark Energy, it is tempting to assume that the acceleration is a linear effect of increasing amounts of Dark Energy. But if the gravitational field is dependent only on mass, not energy, assuming that Dark Energy has no mass-- and if GR and LQG are correct-- then universal expansion must an as yet unknown nonlinear effect of Dark Matter. Is my logic faulty?

    Any theory that makes such a prediction would be falsifiable. But it would not be a true prediction as there is already evidence of an accelerating expansion. In fact, it should be relatively easy to invent models, if not theories, that make such predictions- apparently not so.

    I have seen papers on arXiv.org that claim Dark Energy is derived from Dark Matter, but not any that attribute universe expansion to Dark Matter. Rather the linear effects of Dark Matter would cause universe contraction. It is said to be responsible for galaxy formation, clusters of galaxies and super clusters. So the linear effects dominate up to super cluster scales.

    The nonlinear effects may holistic on the scale of the universe, such as can be understood by particular values of the cosmological constant. Is the cosmological constant related to nonlinear effects of Dark Matter? Is this question valid?

    I have not seen any such theory; but I have seen solutions to the equations of GR on arXiv.org (Hamilton, etal. http://www.arxiv.org/abs/gr-qc/0411062) that predict space creation as a function of mass inflation. It happens in charged black holes where physical (baryonic) charged matter is repelled by the central (singularity) charge and is flowing outward in the black hole. When that physical flow encounters Dark Matter being absorbed by the black hole, new space is created as the physical matter passes through the Cauchy horizon.

    This GR solution predicts that the smaller the amount of Dark Matter absorbed, the larger is the inflation of the physical mass flow, a nonlinear effect. If the created space were still in our universe, perhaps in some holistic sense, then that would be a nonlinear mechanism for space expansion from Dark Matter. I have no idea how this might relate to the comic constant.
     
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  3. Dec 2, 2004 #2

    hellfire

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    I do not know what are the results of LQG, but in GR dark matter cannot account for the expansion (neither an inertia of expansion nor an accelerated expansion), because it has a positive energy density and it exerts a positive pressure or it exterts no pressure, depending on whether relativisitic or non-relativistic matter is considered.

    In GR the energy-monentum tensor determines the geometry of spacetime and both, dark matter and dark energy, have a energy-momentum tensor. On the other hand, it is also possible to have a spacetime without any energy-momentum tensor at all, at least in GR: a Minkowski spacetime or a linearly expanding space are also valid solutions in GR.
     
  4. Dec 2, 2004 #3

    turbo

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    You might want to do a CiteBase seach on "Chaplygin" and see what pops up. Chaplygin gas takes on the useful attributes of both Dark Matter and Dark Energy to fix the standard model's problems with excess apparent gravitation and expansion.

    http://citebase.eprints.org/cgi-bin/search
     
  5. Dec 2, 2004 #4

    Garth

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    There are several anomalies with the standard cosmological model, which may be at the root of your questions yanniru.

    Note Dark Energy, as it has a mass equivalent, is also a source of gravitation.

    Its existence is assumed for two reasons.
    1. To make up the density deficit between ordinary plus dark matter (Omega_matter = 0.27) and the critical density (Omega_total = 1.0) required for flatness.
    2. Its exotic equation of state, p = -rho or thereabouts, is required to explain the apparent acceleration of cosmological expansion.
    What it actually is, or what it is derived from, is anybody's guess. In the past they didn't worry about such things when they added epicycles!

    If it is attributed to the cosmological constant, then there is a problem because it is not constant, but appears to switch on and off as required.

    As to
    I would not worry, we don’t know what Dark Matter is either, so we don’t know what non-linear effects it may have! All that is known is that galaxies and galactic clusters have a greater gravitational field than standard model Big Bang nucleo-synthesis will allow, and than is visible.

    If you are interested in a different approach you may want to check out another published theory, self creation cosmology. The latest paper is: "Self Creation Cosmology - An Alternative Gravitational Theory"
    http://arxiv.org/abs/gr-qc/0405094 to be published in "Progress in General Relativity and Quantum Cosmology. " Nova Science Publishers, Inc. New York.

    Garth
     
    Last edited: Dec 2, 2004
  6. Dec 7, 2004 #5
    Do we know the GR energy-momentum tensor for DE & DM?

    "In GR the energy-monentum tensor determines the geometry of spacetime and both, dark matter and dark energy, have a energy-momentum tensor. On the other hand, it is also possible to have a spacetime without any energy-momentum tensor at all, at least in GR: a Minkowski spacetime or a linearly expanding space are also valid solutions in GR.[/QUOTE]"

    Garth,

    It is interesting that you say spacetime can exist without gravity. That seems to be in conflict with what I read in publications of the LQG community. That is a conflict I cannot resolve.

    A second interesting issue is that you claim to know the GR energy-momentum tensor for Dark Matter and Dark Energy, but admit that you do not know what Dark Matter or Dark Energy actually are. It is possible that you know what the tensor HAS TO BE to make the universe flat, and then just assume it comes from Dark Matter & Energy?

    Richard
     
  7. Dec 7, 2004 #6

    Garth

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    Actually I was just quoting the consensus opinion of the cosmology (GR)community. I have serious problems with the non-identification of DE and DM. In Self Creation Cosmology, a freely coasting cosmology, DM is baryonic and DE does not exist; as it is a Machian theory the cosmological solution requires, indeed creates, matter.

    Einstein's field equation has solutions without matter, such as either the empty universe with zero density and pressure, Milne's hyperbolic freely coasting universe R~t, or one filled only with radiation, the very early hot big bang model R~t^1/2 are well accepted models of GR cosmology.

    Garth
     
    Last edited: Dec 7, 2004
  8. Dec 7, 2004 #7

    Nereid

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    I'll just address one part of this good question ... from a wide range of high quality observations spanning several decades, a fair bit is known about Dark Matter:
    1) it's mass, in the Newtonian sense as well as GR sense
    2) much of it is certainly baryonic, in the form of gas, dust, grains, red dwarf stars, white dwarfs, brown dwarfs, rogue planets, ...
    3) at least some of it isn't baryonic, possibly most of it ... observations pointing to this conclusion are both local (both independent of GR and requiring GR) and cosmological (model-dependent).

    While there are some theories around which don't 'need' DM - e.g. MOND, Garth's SCC - they have difficulty accounting for at least some of the well established observations (note that turbo-1 has posted some other ideas here in PF, but AFAIK those ideas haven't yet been developed to the point of testability against any observations).

    [Note to Garth: I've been looking into some of the 'local' observations of DM, it's not looking good for SCC I'm afraid; nor is some of the data on low metalicity stars ... but please be patient]
     
  9. Dec 7, 2004 #8

    Nereid

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    Oh, and I forgot the DE part ... AFAIK, there are no 'local' observations which convincingly lead one to conclude 'ah ha, Dark Energy!' - its existence comes from cosmological (model) interpretations of a number of different types of (good) observations - distant supernovae, WMAP data on the CMBR, ...
     
  10. Dec 7, 2004 #9

    turbo

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    You are quite right. I'm working alone and my math skills are poor, but my ZPE model is eminently falsifiable. Here's how:

    1) Testing the Gravitational Mass of Matter vs. Antimatter

    The Athena Project is designed to produce experimentally usable quantities of anti-hydrogen. One experiment in particular is of interest – the measurement of the gravitational mass-equivalence of matter vs. antimatter. The Polarized ZPE model relies on a differential in the gravitational infall rates of matter vs. antimatter to provide the mechanics for ZPE field polarization, and is falsifiable by this experiment.

    2) Testing for the Existence of ZPE Field Polarization in Earth Orbit

    I propose adding an experiment to an Earth-orbiting platform to test the strength of the Casimir effect in various orientations. Using a conventional Casimir device with parallel conducting plates, the device should be oriented with the plates parallel to an imaginary line drawn from the orbiter to earth. A second data run should be made with the conducting plates oriented perpendicular to that line. Each data run should consist of a large enough number of orbits to allow the effects of ZPE field fluxes caused by the Sun and the Moon to be extracted and compared. The Polarized ZPE field model predicts measurable differences in Casimir force as the device traverses gradients in the ZPE field caused by these massive bodies. Subject to instrument sensitivity, the Polarized ZPE model is falsifiable by this test.

    3) Measuring the Speed of Light in a Casimir “Vacuum”

    Casimir devices produce ZPE fields that are slightly under the local ground state by using very small gaps to physically suppress the appearance of some frequencies of the ZPE spectrum. This suppressed field is somewhat below the local ZPE ground state, although it is by no means a true quantum vacuum. I propose an experiment using interferometry to compare the speed of light across a Casimir gap to that of a beam crossing an equivalent vacuum with no ZPE suppression. The Polarized ZPE model’s concept that the speed of light is dependent on the density of the ZPE field through which is propagates is falsifiable by this test. GR’s invariable speed of light in a vacuum is also falsifiable by this test. Should the ZPE model pass this test, the concept of EM aether will re-emerge and curved space-time will need a serious shake-down.

    If any of these experiments can demonstrate that the ZPE EM fields exhibit variable polarization and density in the presence of large masses, I predict that I will quickly get lots of help from very smart people with good math skills. If the Athena Project shows a differential in matter/antimatter infall rates, I hope my good friends here will pitch in and help me write convincing proposals for experiments 2 and 3.
     
  11. Dec 8, 2004 #10

    Garth

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    Thank you for your note Nereid, what observations of DM are you referring to? Remember SCC is quite happy with the existence of DM, the difference being that it identifies it as baryonic in some form or other.

    Garth
     
  12. Dec 8, 2004 #11

    Nereid

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    Garth, not enough baryons to account for all the DM that shows up in several different types of observations (I'm still wading my way through papers on the local La forest; the X-ray/optical/microwave obsevations of rich clusters may be enough on their own).
     
  13. Dec 8, 2004 #12

    Garth

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    The normal problem is the restriction SBBN theory puts on baryon nucleo-synthesis (max 4% of critical density and that is pushing it) - is this what "not enough baryons to account for all the DM" is based on?
    In which case the freely coasting model produces around Omegab = 0.2., five times the standard amount.

    Or is the problem that not enough baryons are observed? In which case SCC has a problem in identifying the nature of these 'invisible' baryons: Brown dwarfs, Jupiters, bricks, mini-black holes?? This would be no greater than the standard model's problem in identifying DM. However evidence is stacking up of Lyman Alpha forest, HI and HII in the IGM with patchy ionisation together with faint dwarf galaxies in the voids etc. to show that there is a considerable amount of ordinary 'stuff' out there.

    Garth
     
  14. Dec 8, 2004 #13

    Nereid

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    The latter Garth (well, maybe the former too, but if I concentrate on the former, there should be a lot less room for baryonic DM). Think of it like this: if 'local' observations pretty much tell us how much DM there is, and if those results are consistent with the concordance model(s) of cosmology (but not with SCC), then that's good for the mainstream interpretations, right? Either way, the 'local' results are what they are, independent of cosmological models (OK, you may need GR, maybe, partially). Further, if some of the local observations can distinguish between baryonic and 'exotic' DM, ...
     
  15. Dec 8, 2004 #14

    turbo

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    If the baryonic DM is in the form of anything more massive than Jupiter-sized planets, mini black holes, etc, shouldn't the DM halo surrounding our Milky Way (as required by the standard model) provide numerous opportunities for serendipitous observation of microlensing events? If the baryonic material is too finely divided for that, shouldn't it scatter, absorb and re-radiate the energy impinging on it? If it is primarily gaseous in nature, shouldn't we be able to see absorption lines in extragalactic spectra that grow stronger and weaker with respect to the orientation of the objects' lines of sight with the halo? My question is given the huge amount of DM required to keep our galaxy's rotation curve flat, shouldn't it be at least indirectly observable locally?
     
  16. Dec 8, 2004 #15

    hellfire

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    As far as I know a great fraction of the baryons is postulated to be in the intergalactic medium, not being part of virialized objects and with a temperature of 105 < T < 107 K (Warm Hot Intergalactic Medium). The detection seams to be a challenging task. This may be due to the fact that it lies somewhere in between the hot intergalactic x-ray gas and the lyman alpha clouds. However the actual reasons and problems are unknown to me.
     
    Last edited: Dec 8, 2004
  17. Dec 8, 2004 #16

    Chronos

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    There are some pretty severe constraints on how much of the missing matter can be baryonic. 1] baryon to photon ratio 2] primordial deuterium abundance. Not nearly enough baryonic matter could possibly have formed under BBN theory to account for the missing matter needed to explain current observations.

    As far as baryonic DM in the galactic halo, as mentioned by Turbo-1, microlensing studies have been going on for several years. Here is a recent paper by one of the more prominents groups engaged in these studies:
    http://arxiv.org/abs/astro-ph/0409167
     
  18. Dec 8, 2004 #17

    turbo

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    Thank you Chronos. Here is a relevant quote from that paper.

    If DM is baryonic, it's got to be small.
     
  19. Dec 9, 2004 #18

    Garth

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    Nereid, thank you. Yes indeed, the question is open as to what exactly local observations are telling us. Keeing the selection effect in mind and the question of how much DM is actually in the IGM and not the halo, there is a lot of work still to be done. Remember only 20% or so of the IGM metallicity can be explained by galactic out-flow.

    Thank you too turbo-1, Chronos and hellfire, the detection problems are considerable.
    However Chronos the freely coasting model, see "a simmering universe", explains deuterium abundance by another route – spallation, see " A Concordant “Freely Coasting” Cosmology ".

    Garth
     
    Last edited: Dec 9, 2004
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