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Dark matter - maybe just water?

  1. Jan 9, 2007 #1


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    Any reason why cold dark matter isn't just ice?

    All the chemical reactions going on out there since the creation of the universe, would have created a great deal of water. Also would fit with comets being made of the same stuff.

    Just wondering...

  2. jcsd
  3. Jan 9, 2007 #2
    I have no idea what you're trying to say here
  4. Jan 9, 2007 #3


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    The missing matter isn't simply "hard to see", like cold gas or dark dust. Cold dark matter does not interact with EM radiation at all - it doesn't absorb it and it doesn't emit it (whereas water, or any other type of matter will). We only know it's there because of its interaction with gravity. It is not ordinary matter of any type we've seen before.
    Last edited: Jan 9, 2007
  5. Jan 9, 2007 #4


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    Actually nmk's is a good suggestion as to what the DM might be; but let us look at it.

    If we ask what is the baryonic content of the universe is we come up with the cosmic relative abundance mix.

    Basically the baryonic universe is made up of roughly 3/4 hydrogen, 1/4 helium and about 2% everything else by mass. Of the 2% everything else the most abundant elements are in this order: oxygen, carbon, neon and nitrogen.

    Now helium and neon are inert so the most common compound in the universe is water, mainly either as ice or vapour because liquid water is very special and rare. That is why there is so much ice in the outer solar system making comets and such.

    However, all we can have is therefore at most about 1/2% of the normal matter as ice, the rest is just mainly hydrogen and helium. That is why the gas giants are mainly composed of those elements.

    But it gets worse. There is a critical density in the standard General Relativity cosmology theory that the overall cosmological density of the universe is measured by, which is about 10-29 gms/cc.

    The total density of the universe is believed in the standard model to have this density, or be slightly denser than this. The problem is the nucleosynthesis equations of the standard Big Bang model can only produce about 4% of this critical density. In other words the total baryonic density of the universe is limited to about 4% of the total.

    Unfortunately we can see only about 0.3% of the total in the form of stars and emission nebulas.

    So there is a lot of baryonic dark matter out there, over an order of magnitude greater than that which we can see, around 0.5% (of 4%) of this BDM could well be water - ice or vapour. So, although water may be the most common compound in the universe, the maximum amount of H2O that we can have is not a lot, only about 0.02% of the total!

    Furthermore, as most of the baryonic DM is thinly distributed, most of the oxygen would not have had a chance to chemically combine with the hydrogen and so the actual amount of H2O is likely to be much less than this.

    Note that, when we talk about DM we are normally referring to the unknown non-baryonic DM needed in the standard model to make up the masses of galaxies and galaxy clusters - about 23% of the total.

    Finally of course the standard theory requires 73% of the total to be something else again, Dark Energy. You will find many threads and posts about both DM and DE in these Forums.

    With this exotic DM and DE 96% of the total density of the universe is unknown in the standard model. Whatever it is it cannot be water!

    Last edited: Jan 9, 2007
  6. Feb 18, 2007 #5
    I find it curious that because we now detect the presence of matter which does not interact with EM radiation, something otherwise never "seen" before, we jump to the assumption that it is non-barionic.

    Just looking at history, before the detection of the neutron, the idea of a chargeless particle - a particle with only mass and magnetic moment - was unheard of. If it were possible to arrange barionic particles in such a way to create a structure which had no charge AND no magnetic moment, but was only detectable via it's gravitational interaction, how would we detect it on a micro scale as apposed to the current macro-scale dark matter observations today?
  7. Oct 30, 2011 #6
    I agree with the writer but in a different way which still poses a question. We have evidence of black holes emitting water vapor that is trace able in tiny amounts. Is it possible that dark matter is just this water vapor that had dispersed and is still prevalent but un-measureable from where we are at in science, exploration, and vision? maybe even the unseen gravity that holds it all together is indeed "water?"
  8. Oct 30, 2011 #7


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    In a word, NO.
  9. Oct 30, 2011 #8
    it is the glue and universal solvent here, why not the universe where we can't even replicate the %s and grangers that the "blank" area represents?
  10. Oct 30, 2011 #9


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    I don't have a CLUE what you just said, but I can tell you for sure that your previous post tells me that you REALLY need to read up on the basics.
  11. Oct 30, 2011 #10


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    To have as big a gravitational effect as it does, dark matter must exist in very large quantities (we know how much). If it were cold dark matter, we would see it as clouds of gaseous matter. It would absorb starlight in bands according to its chemical makeup.

    It does not do this.

    (Astronomers do earn their paycheques. They do think of these things and do have reasons when they rule them out.:tongue:)
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