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The nature of Dark Matter

  1. SUSY

    6.7%
  2. Axions

    3.3%
  3. Neutrinos

    0 vote(s)
    0.0%
  4. General relativity (more careful calculations)

    30.0%
  5. Modified theory of gravity on larger scales

    6.7%
  6. Compactified extra dimensions (Kaluza-Klein particles)

    6.7%
  7. Error corrections of the data

    0 vote(s)
    0.0%
  8. MACHOS

    0 vote(s)
    0.0%
  9. God

    6.7%
  10. Other

    40.0%
  1. Oct 7, 2005 #1

    EL

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    Which alternative do you think is the most likely to solve the Dark Matter problem?
     
  2. jcsd
  3. Oct 7, 2005 #2

    Chronos

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    In a word, the LHC. I am confident it will ring out the Higgs boson. [I'm closely guarding my prediction as a trade secret].
     
  4. Oct 7, 2005 #3

    EL

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    You think the Higgs boson will sove the Dark Matter problem?
     
  5. Oct 7, 2005 #4

    Garth

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    The Higgs boson if it is eventually detected will solve the 'Inflation problem', and turn that postulate from an epicycle, invoked to resolve shortcomings in GR, into a theory verified by laboratory experiment. it will do nothing to resolve the identity of DM.

    I voted 'other' as I maintain that DM does exist but that originally it was mainly baryonic in form, that an initial 'IGM' of Omegab ~ 0.22 formed Pop III stars which themselves left IMBHs some gas and dust. This gas and dust then formed the visible matter in the galaxies as we know them, and the IMBH's form the DM.

    Note: The Freely Coasting Cosmological model (FCM) produces a Omegab ~ 0.2 from its BBN, and Self Creation Cosmology delivers the strictly linear expansion of FCM. SCC is being tested at this moment as the GPB data is now being processed - results will be known in Summer 2006.

    Garth
     
  6. Oct 7, 2005 #5

    Chronos

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    Agreed, Garth, but that aside, would you agree some amount of 'dark matter' is necessary?
     
  7. Oct 7, 2005 #6

    EL

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    I see you don't. Have read some attempts to solve this problem by pure GR, but never really found any convincing arguments. Do you have such?
     
  8. Oct 7, 2005 #7

    EL

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    :redface:
    Agree on this.

    Ouch, forgott the IMBH alternative in the poll...
     
  9. Oct 7, 2005 #8
    Being made of dark matter myself, I find it indespensible.
     
  10. Oct 7, 2005 #9

    Garth

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    I would not claim that there is nothing left to discover in terms of exotic particles, axions or whatever. I'm just wary of using such to resolve the 'galactic rotation curve', 'cosmological missing mass' and 'large structure formation' problems of GR and thereby conclude that a 96% majority of the universe's mass inventory consists of totally unknown forms of DM and DE.

    Already we have about 1% of closure density in the form of neutrinos, who knows what else there is to find?

    Garth
     
  11. Oct 7, 2005 #10
    Could the zero point energy of quantum fields be modified by gravity? Might this explain the extra mass around galaxies and clusters, etc? Could this be the dark matter we are looking for?
     
  12. Oct 7, 2005 #11

    Garth

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    How does GR square up with QT and the ZPE, a 10140 mismatch?

    Some experiment is required, but what?

    For information Self Creation Cosmology suggests that the observed ZPE (i.e. Casimir force) is dependent on curvature and tends to zero as r -> infinity. The theory suggests that the Casimir force rounds off at a plate separation too small to be achieved within the Earth's gravitational field but the rounding off would be detectable in the Sun's gravitational field somewhere between the orbits of Jupiter and Saturn with present experimental sensitivities. An experiment could be miniaturised and placed on the 'Pluto Express' or similar to demonstrate whether "the zero point energy of quantum fields is modified by gravity" or not.

    However according to SCC this extra (and moderate) ZPE density would not be sufficient to explain DM. In SCC the DM is originally baryonic and may exist today in the form of IMBHs.

    Garth
     
    Last edited: Oct 7, 2005
  13. Oct 7, 2005 #12

    SpaceTiger

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    Dark matter is one of those things that sounds dubious to everyone when they first hear it. I can assure you, however that those of us in the field are by and large convinced of it. I can't tell you what it is, but I can say what it most probably isn't:

    1) Neutrinos - We have a limit on the mass and can calculate their approximate abundance. They appear to contribute negligibly.
    2) More careful GR - Standard GR is very well understood and I find it extremely implausible that we would have just overlooked something in modelling the systems.
    3) MOND - Although not completely dead, the theory is on its last legs. It can't seem to reproduce the CMB power spectrum or large scale structure and there is still no real theoretical motivation for the "modification" of gravity.
    4) Errors in the Data - Dark matter is a many, many-sigma statistical result at this point. There's absolutely no way to do away with it with more careful observations.
    5) MACHOs - The microlensing observations in the Milky Way halo and the low value of [itex]\Omega_b[/itex] pretty much rule this out. Primordial black holes are also a possibility, but are also almost ruled out.
     
    Last edited: Oct 8, 2005
  14. Oct 8, 2005 #13

    Chronos

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    Microlensing is the most punishing evidence in favor of DM. I was hardcore against the DM model when it first came out, but, microlensing [and to a certain extent large scale structure studies] convinced me that DM is the only logical explanation.
     
  15. Oct 8, 2005 #14
    Has it been proven that not any kind of distribution of normal, baryoinic matter could account for DM effects because normal matter would scatter light too much, whereas DM WIMPs would not?

    Could the ZPE of QFT have enough energy/mass to produce the same effects as DM. Maybe with very large volumes of space there might be enough energy to bend light and change galatic rotation curves.

    To this end, is the ZPE background independent? Or does the energy produced depend on the curvature of the spacetime in which it is calculated?

    I'm thinking that the tidal forces of a gravitational gradient (from a nearby galaxy or cluster) will increase the probability that virtual pairs will become permanently separated and survive long enough to produce gravitational effects. (Does any ZPE interact with light and cause gravity?) I think this is so for two reasons: one, the particles involved in Hawking radiation near BHs don't locally know they're near an horizon - locally all they feel is the tidal forces. And two, the equivalence principle equates accelerating frames of reference to those in a gravitational field. This being so, then the Unruh temperature effect for accelerating frames should also apply to frames in a gravitational field, right? This would give a particular temperature (and the particles that produce it) to particular gravity gradient, just as near an horizon. Then more ZPE would congregate around more massive objects (on intergalatic scales) and produce the DM effects, right?
     
    Last edited: Oct 8, 2005
  16. Oct 9, 2005 #15
    Einstein was on this track as he continued to develop his theory of General Relativity. By 1920, he was convinced that GR needed a dynamical ether to mediate gravitation and inertia. He also accepted the need for an EM ether to allow for the propagation of light through space, but did not see that the two were united. By 1924, as shown in his paper "On the Ether" he viewed the gravitational and EM ethers as one and the same and was working toward modifying GR to encompass them.

    And on magnetic fields:
    Einstein was striving for simplification and unity. A polarizable, self-interacting quantum vacuum field would very neatly serve as his GR ether, with no need for additional entities.

    Were the early "null' detections of the ether (via ether drift interferometry) actually null?

    http://redshift.vif.com/JournalFiles/Pre2001/V05NO1PDF/V05N1MUN.pdf
     
    Last edited by a moderator: Oct 9, 2005
  17. Oct 9, 2005 #16

    EL

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    I totally agree with you SpaceTiger. I can see you have answered "other". Is this because you have some special other candidate in mind, or that you just don't believe in any of the listed candidates, or simply just because you are being "scientific" and reject to answer a question you don't know the answer to?
     
    Last edited: Oct 9, 2005
  18. Oct 9, 2005 #17

    SpaceTiger

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    Mostly the latter. My intuition tells me only that the dark matter is probably a particle of some kind. Beyond that, I don't feel qualified to say anything about exactly which particle it's most likely to be.
     
  19. Oct 9, 2005 #18

    EL

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    I suspected that.:smile:

    What about if I force you to pick one kind of particle, what would your answer be then?:tongue2:
     
  20. Oct 10, 2005 #19

    Chronos

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    The DM particle most likely is very massive Probably on the order of 10 Tev - right around the Higgs mass.
     
  21. Oct 10, 2005 #20

    Garth

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    Would that be an interacting or non-interacting DM particle?

    Garth
     
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