Dark matter candidates, what chances would you give them?

  1. EL

    EL 788
    Science Advisor

    What chances would you give the different candidates to actually make up (the major constituent of) the dark matter? That is, if you were a bookmaker, what chances would you find appropriate?
    I'd find it interesting to see what you all think.

    At the moment I'll go with the following:

    LSP (50%)
    K-K DM (5%)
    Axions (4%)
    Sterile neutrinos (2%)
    Mond (2%)
    General relativity, more careful calculations (1%)
    Misinterpreted data, no dark matter needed (1%)
    Not yet suggested dark matter particle (15%)
    Other not suggested reason (15%)
    Other suggested reason (5%)
     
  2. jcsd
  3. Garth

    Garth 3,508
    Science Advisor
    Gold Member

    I guess I go with the "Other suggested reason (5%)", my suggestion being that all DM is baryonic produced in a Freely Coasting Model (FCM) as delivered by SCC.

    My suggestion to then explain where all this unseen baryonic matter resides is that roughly half of it is WHIM and roughly half IMBH's.

    However I wouldn't want to put a percentage on it. The question is how well do these alternatives match up with the observed cosmological constraints. The GP-B experiment will sort out a few alternatives in about a year's time.

    Garth
     
  4. EL

    EL 788
    Science Advisor

    Sure, but what if you actually were a bookmaker? What odds would you decide? I mean you certainly would not put 100% on your own theory (couse in that case I would bet a lot of money you were wrong...:wink: )
     
  5. Garth

    Garth 3,508
    Science Advisor
    Gold Member

    You might just lose it! :biggrin:

    Seriously, while there are problems with the standard model, not least not being able to identify a Higgs Boson/Inflaton, DM particle or DE in the laboratory, other viable alternatives ought to be studied - just in case.

    Garth
     
    Last edited: Mar 6, 2006
  6. DM Constituents

    Since I am a layman, I have no right to do this.

    Nonetheless, I put my money on a mixture of several components:

    LSP
    Axions
    Mirror Matter

    but hedge my bet with Bekenstein's MOND
     
  7. EL

    EL 788
    Science Advisor

    Sure, no doubt about that. Until we find the answer, all candidates not violating current constraints should be kept in mind. However, what I was looking for was people's personal trust in different candidates.
    Even though it may not be "scientifically correct" to rank the candidates, I would like to see what people think, just for fun...
     
  8. Chronos

    Chronos 10,117
    Science Advisor
    Gold Member

    I would like to place a side bet on WIMPS.
     
  9. EL

    EL 788
    Science Advisor

    Ok, but what chances do you give them?
     
  10. Chronos

    Chronos 10,117
    Science Advisor
    Gold Member

    Fairly good. It would explain why we have so much difficulty detecting then in particle colliders.
     
  11. EL

    EL 788
    Science Advisor

    You're all so scientifically moderate...:smile:
    What should I do to get some numbers out?:tongue2:
     
  12. Dark Matter-fuzzy thinking,bad science

    General Relativity was and remains an inspired 100 year old guess at the way things might be,only Albert Einstein(in later years dominated by divine convictions) really believed it to be the basis of the TOE.The nature of electrons,the existence of protons and the likelihood of a singular initial condition set were outside it's ambit.It presents a chillingly effective predictive algebra for narrow midz-one phyics,effectively it is local curve fitting.Go down to Planck radius or move moderately towards galactic size and the theory has no physics to accompany the expectations and predictions it makes.Dark matter is a conjectural condition,aberrations of incomplete older theories should not drive clear thinking.The candidate formally missing from your list does not involve more accurate partial theories it should be "Inadequacies of early incomplete or approximate theories to represent physical realities"and a logical response would be to see this rated at 70%
     
  13. Chronos

    Chronos 10,117
    Science Advisor
    Gold Member

    Hi jimpy, welcome to PF. I think you would find almost everyone agrees current theories are incomplete, and the likely reason it has been vexingly difficult to unite GR and QM. On the other hand, both theories are amazingly predictive at macroscopic [GR] and plankian [QT] scales. So most people are fairly certain the correct unified theory will reduce to QM at planckian scales and somehow emerge as GR at macroscopic scales. As in most human endeavors, time is the enemy. It is essentially irrelevant in quantum theory, yet indispensible in GR.

    Dark matter, however, is very much still alive these days. The fact it has not been detected in the lab is not a valid objection. Consider how long it took to validate the atom conjecture in human labs. If dark matter were a mathematical artifact introduced by a flawed theory of gravity, it would have a decidedly systematic effect on observation. But this is not observed. The evidence indicates non-baryonic matter [CDM] is just as clumpy and chaotically distributed throughout the universe as is baryonic matter. The only thing they appear to have in common is gravitational affinity - i.e., they tend to be drawn to one another. Find a big clump of baryonic matter, and it is almost a cinch you will find evidence it is embedded in an even bigger clump of CDM. The only variable is how much CDM appears to be hanging out in the hood. Oddly enough, this is frequently used to criticize the CDM conjecture - just add the right amount of CDM and all gravitational anomalies magically disappear. But isn't that exactly what you would expect if CDM really does exist - a variable amount at different locations? I would find it truly bizarre [and unbelievable] if every galaxy had the same proportion of CDM v baryonic matter. Pardon my rambling, but this is an interesting issue with many side bars to consider. Driving a stake through the heart of dark matter is simply not doable given current observational evidence - which is abundant and strikes from many directions. Science is hard. Ideas are more easily embraced than abandoned - as demonstrated by history.

    Footnote - you may find this interesting:

    Dark matter: A phenomenological existence proof
    http://www.arxiv.org/abs/astro-ph/0601489
     
    Last edited: Mar 8, 2006
  14. EL

    EL 788
    Science Advisor

    Hi jimpy.
    My list wasn't supposed to be exhausting, so everyone should feel free to come up with their own suggestions. It just reflects my current personal guess. Anyway, what you are looking for I would place under "Mond", something I have given a 2% chance to explain the dark matter problem.
    Trying to build Mond theories at the scales were we observe the dark matter problem without being in conflict with current measurements has turned out to be pretty hard, and that's why I find other candidates much more likely to make up the dark matter. Of course GR has it's range of validity, but "at the scale of the dark matter problem" I find it probable to be trustful.
    Btw, how would you divide your other 30%?
     
    Last edited: Mar 8, 2006
  15. Labguy

    Labguy 733
    Science Advisor

    I would too. Any random early formation on a large scale would be very unlikely to "parcel-out" equal proportions of matter, dark or otherwise, to what we can see today as different galaxies/clusters/superclusters. Small scale H, He and Li seem to fit initial BB conditions though and there is a fair bit of observational evidence to make that era "mainstream" today. I do see, though, a lot of mass-relation studies going on today but have to think that those that seem to indicate a constant proportion would be just as prevalent as those that don't show the same relation/proportions.
    I would go with that also. No confirmed detection yet so there is also no known limit on an upper mass and/or lifespan. If there is no limit on the mass of virtual particles from the vacuum fluctuation as per Heisenberg (there isn't a limit) then WIMPS could be very massive and often replaced with similar mass after kicking the bucket. It all isn't just going to be electrons and positrons or quark-antiquark pairs.

    Also, place emphasis on the "I" in WIMP for "Interacting". If they interact (and exist) then would we always have to think "non-baryonic"? I'm not a fan of wierd and mysterious matter lurking around in a universe blasted out of baryonic matter. Mysterious energy maybe, but not matter..:confused:
     
  16. EL

    EL 788
    Science Advisor

    Could you please elaborate this, maybe I'm just getting you wrong. Why does non-baryonic (dark) matter sound mysterious to you? I mean, we have found plenty of it already...
     
    Last edited: Mar 8, 2006
  17. Labguy

    Labguy 733
    Science Advisor

    We have seen evidence for the existence of "dark matter", but there are also other theories floating about about MOND, adjusted GR, etc. that may not require DM at all.

    But, if we accept DM, what do we have to show (yet) that it is specifically non-baryonic?
     
  18. EL

    EL 788
    Science Advisor

    E.g. constraints from the BB nucleosynthesis which only allows baryonic matter to make up a few percents of the total energy density in the universe.
     
  19. Labguy

    Labguy 733
    Science Advisor

    But maybe all the rest is energy. BB nucleosynthesis can be up to 10% baryonic matter (Ned Wright) but remember I first mentioned virtual particles from vacuum fluctuations. Also, all DM is most likely not to be of a single type; neutrinos can also contribute and they are "non-baryonic". With non-baryonic being defined as:
    I guess that would even include WIMPS and many particle-antiparticle VP pairs. So, by that definition I could agree that the DM is likely to be non-baryonic (atoms/elements), but not likely to be a type of matter unknown (or mysterious) to us. Maybe "non-atomic" would be a better description, but many of the known sub-atomic particles, already existing and virtual, are "real" particles known to us and could be candidates for DM. It seems the only requirement for all candidates is that they are gravitationally affected, hence their probable detection.
     
  20. EL

    EL 788
    Science Advisor

    That's a much higher percent than what is commonly accepted. Do you have a link to the paper?

    This is consideder as a potential source of the dark energy.

    Sure they can, and for a while they were a hot candidate. However, we now know they can just make up some percent or so of the total energy density. I.e. they have practically been ruled out.

    Of course that includes WIMPS, which are the standard example of non-baryonic dark matter.

    So you can agree WIMPS is a good candidate, but you don't like unknown candidates? In, that case, which WIMPS are you speaking of?
     
  21. Garth

    Garth 3,508
    Science Advisor
    Gold Member

    We have?

    We have plenty of evidence of Dark Matter. The only reason that this is said to be non-baryonic is the limitation on baryonic density by the standard model BBN as you later said EL.

    If we are prepared to invoke undiscovered species to make the model fit perhaps we ought also to be prepared to consider alternative BBN models such as the “Freely Coasting” model, which do not need to invoke such undiscovered species as it identifies DM as baryonic.

    Garth
     
    Last edited: Mar 8, 2006
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