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Dark matter and dark energy

  1. Nov 30, 2011 #1

    E45

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    If it existed a particle that had such properties that it both pushed away other particles of the same kind and it pushed away ordinary matter ,could this then explain dark matter and dark energy ? If the big voids of the universe was filled with such a particle, the net force of the particles in the universe would be outwards ,so the expansion would accelerate.

    If particles of this type surrounded a galaxy,they would push the edges of that galaxy inwards, so that the stars far from the center of that galaxy would increase their speed ,and it has been observed that the stars in a galaxy have a greater velocity than expected.

    In a cluster of galaxy this type of particle could push the galaxies together, allowing them to have a greater velocity than expected without escaping from the cluster,and this greater than expected speed has been observed.

    This particle could also explain the big voids in the universe,it would be a natural consequence of the particles properties.
     
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  3. Nov 30, 2011 #2

    Drakkith

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    Dark matter is not repulsive, it is attractive through gravity both with itself and to normal matter. The speed of stars orbiting a galaxy is only one phenomenon believed to be caused by dark matter. There is also things like Gravitational Lensing that must be explained.

    Also I don't believe this would fit the models for the expansion of the universe. For example, in your case the repulsive force would decrease over time at the same rate as gravitation does due to the average density of the universe decreasing. Instead we see that as the density decreases and gravity becomes weaker, the repulsive force does not. Hence we see increasing acceleration.
     
  4. Dec 1, 2011 #3

    Chalnoth

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    Unfortunately it isn't that easy. First, as Drakkith noted, dark matter produces pretty large gravitational potential wells: it attracts matter quite strongly. You also won't get dark matter that clumps if it doesn't attract itself, and the dark matter we observe is pretty clumpy.

    As for dark energy, the problem there is that matter that pushes itself away has the wrong sign to pressure. Matter that pushes itself away would experience positive pressure. Dark energy has negative pressure.
     
  5. Dec 4, 2011 #4
    Does not exists any particle that can explain the properties of dark matter or dark energy alone, less still both at once.
     
  6. Dec 4, 2011 #5

    Chalnoth

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    Uh, what? Dark matter is easily explained by a WIMP, of which many theoretical ideas have been proposed. Dark energy is most likely to be the cosmological constant, which is not a particle. But there are many scalar fields that could also do the same thing.
     
  7. Dec 6, 2011 #6
    I did mean a real particle. Of course, you can imagine hypothetical particles with all properties that you want.
     
  8. Dec 6, 2011 #7

    Chalnoth

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    (Leaving dark energy out of this, for the moment...)
    1. No particle in the standard model explains dark matter. So if it's a particle, it has to be a new particle we haven't seen in the lab before. The most reasonable numbers for a particle that would explain our cosmological observations predict that it would be extremely hard to detect anyway, so this isn't a surprise.
    2. Non-particle solutions to the dark matter problem are far more exotic than particle solutions.

    So the most reasonable conclusion is that it's probably a WIMP.
     
  9. Dec 7, 2011 #8
    That was my point.

    A lot of modern theoretical 'physics' is so safe because focuses on the experimental range that goes from the «extremely hard to detect» up to the limit of the undetectable :rolleyes:

    A more reasonable conclusion is that dark matter is a fictitious distribution of mass and thus WIMPs do not exist, what means that people's money would not be wasted in their search.
     
  10. Dec 7, 2011 #9

    phinds

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    So which of the following is it that you believe, or is it both
    (1) physicists are so stupid that they are incorrect in their conclusions regarding the existence of dark matter AND the likelihood that it is WIMPS
    (2) physicists are so corrupt that they pretend dark matter exists so they can get research money to pretend to study it.

    Oh ... there is a third possibility:

    (3) you don't know what you are talking about.
     
  11. Dec 7, 2011 #10

    Chalnoth

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    To that I say look at the evidence. It is quite conclusive.
     
  12. Dec 7, 2011 #11

    phinds

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    Chanlnoth, you are SO much more polite than I am. I should follow your example, and I DO try most of the time, but sometimes I find that, in the words of my favorite poet, e e cummings, "there is some s***, up with which I will not put".
     
  13. Dec 7, 2011 #12

    Chalnoth

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    Don't let this one example fool you ;)
     
  14. Dec 8, 2011 #13
    Effectively the several premature claims of detection have gone (although are recorded by historians of science :uhh: ) and stuff as WIMPs continue without being real particles...
     
  15. Dec 8, 2011 #14

    Chalnoth

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    What's your point? The astrophysical and cosmological observations are firm and verified.
     
  16. Dec 9, 2011 #15
    And another premature claim of observation of dark matter has gone when latest Fermi studies have found no trace of dark matter (once again)

    http://physicsworld.com/cws/article/news/48079

    But not true believer in dark matter would worry because all the tests of direct observation have failed... because the 'observations' are so «firm and verified» as the 'observations' of caloric were :rofl:
     
  17. Dec 9, 2011 #16

    Chalnoth

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    I see you are completely ignoring the cosmological evidence such as WMAP or gravitational lensing studies.
     
  18. Dec 9, 2011 #17
    Evidently neither WMAP nor gravitational lensing are direct observations of dark matter {*}. That is the reason which experiments as that reported by Physics World (link given before) have been performed and all they have failed. Not a surprise that each experiment looking for dark matter, WIMPS, and all that stuff has failed, since dark matter is so fictitious as caloric was centuries ago. And recall that many clever guys said to the ignorants that caloric had been observed in hundred of observations and experiments :rofl:

    {*} In fact, discrepancies between observation and theory are, a posteriori, interpreted as resulting from some hypothetical invisible matter.

    To say more, since you seem ignorant of the history of the scientific topic that your pretend to know. The first prediction of what WMAP would detect was done by a non-DM theory. Whereas the predictions done by DM-theory (lambda 1999 model) miserably failed and only after the observations were obtained that the DM model was modified (pure curve fitting) to adapt it to the WMAP observations a posteriori.

    However, the non-DM model predicted exactly the first and second peaks, i.e., before the observations.
     
    Last edited: Dec 9, 2011
  19. Dec 9, 2011 #18

    Chalnoth

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    Then what, pray tell, is the explanation?

    This is pure, unadulterated fantasy. The dark matter model used in nearly all WMAP data analysis is the simplest possible: zero-temperature dark matter. This model fits the data exceedingly well. There is no curve fitting done with respect to dark matter in analyzing the WMAP data, except in terms of estimating the values of the various parameters. The simplest model for WMAP uses the following parameters:

    1. Dark matter density.
    2. Normal matter density.
    3. Hubble expansion rate.
    4. Scalar spectral index (an inflation parameter).
    5. Optical depth to the CMB (basically, how transparent the universe is between us and the CMB).
    6. Amplitude of fluctuations.

    Each one of these parameters is physically-motivated. There is no "curve fitting" going on. Each one of the parameters which can be estimated independently with other experiments shows the same result for those parameters. The various extensions of this minimalist model, such as allowing spatial curvature to vary, or allowing the scalar spectral index to change with scale, so far show no evidence of deviation from this simplest description.
     
  20. Dec 10, 2011 #19
    What you call «pure, unadulterated fantasy» is just the orange line in the next figure.

    3peak06.gif

    The orange line is the prediction done by the dark-matter model before WMAP data (and Boomerang data) was known. The dark matter model was clearly falsified... unless you are blind.

    The prediction done by the non-dark matter model for both first and second peaks was remarkably verified... unless again you are blind. The third peak could not be explained because the model used then was non-relativistic, but some recent relativistic extensions seem to fit the third as well.

    Once the WMAP data was known, DM cosmologists did an exercise in curve fitting (all of dark matter is pure curve fitting) and changed the parameters of the dark matter model until fitting the data.

    Moreover, when forcing the dark matter model to fit the available data, DM cosmologists chose values for its free parameters that contradict other independent tests. For example, the baryon density assumed in the current dark matter cosmological model is much larger (about 3x) that the baryon density measured from other independent tests.

    However, if you do not assume this high value of the density then you cannot fit the WMAP data using the dark matter cosmological model, generating a contradiction.

    Therefore we have a contradictory dark matter model, which fails to explain many data (TFL, fine tunning of galactic rotation curves...) and whose hypothetical new kind of matter has been systematically not found in a large list of experiments performed since the 80s. I cited the recent results of Fermi not finding any evidence of the hypothetical dark matter, but before Fermi was Xenon100 the experiment that found nothing and before was...
     
    Last edited: Dec 10, 2011
  21. Dec 10, 2011 #20

    Chalnoth

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    Two points on this:
    1. Did you even look at the parameters for the no dark matter case? Generally the parameters for these types of "alternative" theories are completely and utterly falsified by other observations.
    2. WMAP has since measured the third peak pretty accurately, completely breaking the degeneracy between dark matter and the other parameters. The dark matter model fits, models without dark matter do not.

    Edit: Oh, and let me just point out that the baryon density discrepancy is trivially explained by just noting that most of the normal matter has not fallen into gravitational potential wells and is thus invisible.
     
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