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Detection of motion of non characterised particles

  1. Dec 2, 2014 #1
    I have been reading on wikipedia that dark matter is made up of a not yet characterised type of sub atomic particle. Now we know that particle energies and relative positions cannot be known with precision by Heisenberg principle but we can calculate quantities like the drift velocity of charges flowing through metals so it must not be absolutely impossible to create a profile of motion of the non characterised paticles if the locations of these particles are somewhat known because they interact with weak forces. Right?
     
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  3. Dec 2, 2014 #2

    Drakkith

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    Well, we can't even narrow the particles down to an area of space smaller than about 10,000 light years, nor do we know their properties or what forces they obey other than gravity, so I don't think we can create any profile of motion. We don't even know how massive these particles may be.
     
  4. Dec 2, 2014 #3

    marcus

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    I like very much this direction of thought and it reminds me of the computer simulation studies of large scale flow and condensation of clouds of dark matter which you can see in little two minute computer movies various places. there you do see "profiles of motion" in the gradual condensation of uniform clouds into filamentary cobwebby messy-looking structure. Where the strands of DM crossed or otherwise collapsed was presumably where clusters of ordinary matter could begin to nucleate and curdle into clusters of galaxies.

    The Nobel laureate George Smoot played some of those computer animation movies of structure formation in a 15 minute lecture he gave to the TED club (technology entertainment design) a few years back. I think you can get it by googling "smoot TED".

    Dark matter seems to have served as a kind of armature or frame on which the sparser less-dense ordinary matter could gather. The dark matter's gravity helped pull the ordinary stuff together into dense enough clouds that its own gravity could take over and complete the process of condensation into clusters, galaxies, stars etc.

    So the dynamics of dark matter (its "profile of motion") was extremely important for structure formation at a certain stage.

    George Smoot was using clips from the simulations done by somebody at University of Chicago. I forget his name. I found a bunch more at his U. Chicago website one time when I looked.

    the idea of simulation studies is you have PARAMETERS for the dark matter, and they effect the computer run and what kinds of shapes develop and what kind of statistical outcomes you get about the prevalence of over densities of this or that size. You can then vary the parameters and COMPARE how well the outcome dark matter cobwebs resemble the REAL cobwebby distribution of galaxies and clusters of galaxies. The REAL distribution of ordinary matter does have that criss-cross messy look of strands and lumps and voids. And it is remarkably similar to what the computer simulations show dark matter (with observed density extrapolated back in time to early universe) would have made.
     
  5. Dec 2, 2014 #4

    Drakkith

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    Excellent point, Marcus. To be clear, are you saying the bulk motion/shape of the DM clouds can be found by looking at the distribution of visible matter?
     
  6. Dec 2, 2014 #5

    marcus

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    With simulations, at least of that sort, all I think one can hope for is verisimilitude so the way one describes the results has to be nuanced. BTW did you watch Smoot's TED talk?
    I think yes, we've discussed it several times here at PF Cosmo forum, I probably first learned of it here. It doesn't really PROVE anything (as I see it).
    You start with certain reasonable assumptions about dark matter, gross properties of a nearly uniform "gas"
    Ordinary matter is far too dilute to begin to coalesce, but there is much more DM. So starting with very slight fluctuations in its density it begins to fall together.

    They simulate this in the computer and the criss-cross mess with its clumps and voids that they get bears a striking resemblance to the way ordinary matter has gathered, One is visually comparing the observed distribution of galaxies with a DM cobweb that the computer has helped one to imagine.

    So we have to be careful and nuanced about what is claimed. We SEE a large-scale layout of galaxies and clusters of galaxies. We see filaments and voids etc. we THEORIZE that this large-scale structure could not have formed if there was just ordinary matter. there is not enough of it. We theorize that this image of a cobwebby large-scale ordinary matter structure actually REVEALS a skeleton of dark matter, whose gravity has accreted the ordinary and allowed it to coalesce into smaller scale shapes.

    Have we seen the skeleton? No, we only suppose that the galaxies decorating it reveal its overall pattern to us.

    Now we do something even more speculative and theoretical. We SIMULATE the formation of this skeleton, this large-scale structure. Oops wife asking for something, have to go. Back later. But anyway you see at each stage here we are getting farther and farther from direct observation. At the end we are relying on qualitative similarity. The same patterns, the same statistical characteristics arise in the simulated large-scale structure as we think we observe in the ordinary matter which we imagine reveals the skeleton.
    What can I say? Clever monkeys! I like it. But it is not literally direct observation for sure.
     
    Last edited: Dec 2, 2014
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