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pchang: Plasma Cosmology

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  • #1

    pchang: Plasma Cosmology

    Since you like to bring it up around here, I was wondering if you could tell me about it. What are the basics? Are there any particular assumtions y'all like to use so you get some kind of neat fluid closure? Astrophysicists like drift-ordering IIRC, so is that useful here? And do y'all pretty much ignore gravity?

    What are some good sources (I have an ok plasma reference already)? My understanding of cosmology is pretty ****ty, so I wouldn't want anything too hairy...

    Thanks.
    "Beware of the man who works hard to learn something, learns it, and finds himself no wiser than before. He is full of murderous resentment of people who are ignorant without having come by their ignorance the hard way. "
    -Bokonon
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  • #2
    The only plasma I'm interested in is of the television variety.
    Try http://wordforge.net/index.php for discussion and debate.

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    • #3
      Waste of money
      "Beware of the man who works hard to learn something, learns it, and finds himself no wiser than before. He is full of murderous resentment of people who are ignorant without having come by their ignorance the hard way. "
      -Bokonon

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      • #4
        Since this thread clearly ain't going to get any posts till pchang gets here, I'll start with an overview of plasma physics.

        What plasma is, is a bunch of really fast ions and electrons flowing together. Essentially, it's a fluid with electromagnetic forces.

        So the first step is some statistical description of this ****.

        You start with the principle of phase-space conservation. Say, you have a six dimensional space - 3 spatial and 3 velocity coordinates. And you have a distribution function, F, of ions (or electrons) in this space. And you have a region in this space. So, the time-rate of change of f plus the flux through the surface (the time derivitive of the 6-vector dotted with the 6-gradient of F) is 0 in the case of particle conservation.

        Now, you break up the flux term, and you get dF/dt + v.grad(F) + a.dF/dv = 0 (bolded are R3-vectors, . is dot product). a is the Lorentz force, (E + vxB)q/m.

        The problem with F is that it's a bunch of spiky dirac-delta functions. So we'd like to take "ensemble averages" of it.

        Define f = .

        Nother problem is that EM fields depend on the path, so that there's some correlation that needs to be accounted for. IOW:

        <a.dF/dv>=<a>.df/dv-C(f), where C's something called the colission operator (in general nonlinear) that accounts for correlations.

        Putting it all together and writing as v for simplicity:

        df/dt + v.grad(f) + q/m(E + vxB).df/dv = C(f)

        If you assume phase-space incompressibility:
        div(v) = d/dv.a = 0

        Then, you get:
        df/dt + div(vf) + q/m*d/dv.((E + vxB)f) = C(f)

        Collision operators are really hard to figure out, so what people do are just to take moments of that thing (wrt products of v) to get fluid equations. But that's enough for now. Clear as mud, eh?
        "Beware of the man who works hard to learn something, learns it, and finds himself no wiser than before. He is full of murderous resentment of people who are ignorant without having come by their ignorance the hard way. "
        -Bokonon

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        • #5
          Plasma cosmology just adds EM forces due to cosmic currents to gravity. It isn't really revolutionary however, it does require dynamic models of the universe (since static ones won't have any currents). Anything from Hans Alfven (sp?) would be good. There is some great stuff that completely explains the motion of spiral galaxies without the need for anything like dark matter or dark energy. Unfortunately, they go a bit overboard in claiming the big bang never happened and so forth.

          The only assumptions are those of scale that let us try and simulate galaxy size plasmas in a lab environment. It is fairly amazing how these lab plasmas recreate the galaxies and galaxy clusters we see in space.

          Unfortunately, I moved a bit ago and all my reference stuff is still in boxes.

          As for your equations, they are pretty much impossible to solve so in practice we use Particle in Cell computer simulations (basically Monte Carlo with EM forces added in). We also run plasmas in vacuum chambers with externally applied magnetic fields.
          “It is no use trying to 'see through' first principles. If you see through everything, then everything is transparent. But a wholly transparent world is an invisible world. To 'see through' all things is the same as not to see.”

          ― C.S. Lewis, The Abolition of Man​

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          • #6
            Lab plasmas are genearlly MHD right?
            "Beware of the man who works hard to learn something, learns it, and finds himself no wiser than before. He is full of murderous resentment of people who are ignorant without having come by their ignorance the hard way. "
            -Bokonon

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            • #7
              That is sort of a chicken and the egg question. Because MHDs are currently what are of interest, that is what is generated.
              “It is no use trying to 'see through' first principles. If you see through everything, then everything is transparent. But a wholly transparent world is an invisible world. To 'see through' all things is the same as not to see.”

              ― C.S. Lewis, The Abolition of Man​

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              • #8
                Anyway, just got in after flying. Got to sleep now.
                “It is no use trying to 'see through' first principles. If you see through everything, then everything is transparent. But a wholly transparent world is an invisible world. To 'see through' all things is the same as not to see.”

                ― C.S. Lewis, The Abolition of Man​

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                • #9
                  Cool, thanks.
                  "Beware of the man who works hard to learn something, learns it, and finds himself no wiser than before. He is full of murderous resentment of people who are ignorant without having come by their ignorance the hard way. "
                  -Bokonon

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                  • #10
                    1. How does pchang know this stuff? I thought he was a geeky bond guy like Ken?

                    2. Connect it to something I care about. Like the light bulb or the Geiger counter?

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                    • #11
                      Fusion occurs in plasmas so fusion researchers are plasma geeks. I'm not sure what's so interesting about plasma cosmology, that's what I'm here to find out.

                      pchang did this **** for PhD research I think.
                      "Beware of the man who works hard to learn something, learns it, and finds himself no wiser than before. He is full of murderous resentment of people who are ignorant without having come by their ignorance the hard way. "
                      -Bokonon

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                      • #12
                        I didn't know he was piled high and deeper...

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                        • #13
                          Once a bull drops its feces on you, other animals tend to as well.
                          "Beware of the man who works hard to learn something, learns it, and finds himself no wiser than before. He is full of murderous resentment of people who are ignorant without having come by their ignorance the hard way. "
                          -Bokonon

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                          • #14
                            Fear of being a whiney wacko

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                            • #15
                              Actually, I quit after a Master's. (I couldn't take it in Boston - there is a whole story about my eyelids freezing together one day). My major was actually Aeronautics and Astronautics, but my research was all plasma physics. Frankly, the plasma physics guys went a bit too far. Rather than just add EM to regular gravity driven cosmology, they started throwing barbs at the whole thing.

                              Some plasma physicists claim the big bang never happened and that the universe is much older and is just in the expansion phase of a perpetual expansion/shrinking oscillation. This is pretty bogus and there is no evidence for it as far as I'm concerned.

                              Some plasm physicists claim that black holes don't exist. They point to EM forces as creating galactic sized dynamos that release all the energy found spewing from galactic cores (it is released at right angles to the plane of spin). However, the process is still gravity driven, so I say there are black holes AND galactic dynamos.

                              Anyway, the math behind black holes and particle physics is too persuasive. However, the requirements for dark matter and dark energy (in large amounts) is a bit dubious to me.
                              “It is no use trying to 'see through' first principles. If you see through everything, then everything is transparent. But a wholly transparent world is an invisible world. To 'see through' all things is the same as not to see.”

                              ― C.S. Lewis, The Abolition of Man​

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