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Dark matter?

  1. Jul 15, 2010 #1
    im having a hard time understanding just what it actually is. I've heard about WIMPs and now quirks. But i know we can't see it, but how dose it affect us? Why does it emit no light? I've also heard about the big crunch saying that if there is too much matter in the universe it would collapse on itself, so if thats not true then dark matter is taking up about 90% of the universe's matter. And what is the difference between dark matter and dark energy?
  2. jcsd
  3. Jul 15, 2010 #2
    Hi there,

    Dark matter can be found in many different forms. You talked about the WIMPS. They are normal objects that do not emit light. Therefore, they are DARK. In our Universe, stars, in all their forms, shapes, and life stage, are mainly the only objects that emit light. The rest coudl be considered WIMPS.

    But that's not all. If you look at nuclear physics, and the different conservation principles, you will find that their are a large amount of very tiny particles that are created from every reactions. These very tiny particles are very hard to see, and even to detect, and they have a very tiny mass. But, try to imagine the amount of stars in the Universe that sustained nuclear fusion. Now, try to imagine the amount of these particles created. Eventhough they have a itsy bitsy tiny mass, it is in the amount that matters. From a fun calculation I made once (and if I remember the numbers right), there would be 1011 neutrinos passing through each kg of our body every second of the day (and night of course).

    All of these, plus all the others that we have not a clue yet, can comprise alot and alot of mass. And this mass, not being visible, is considered DARK matter.

    Hope this helps. Cheers
  4. Jul 15, 2010 #3


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    No, WIMPs are not normal matter.
    Stars and all luminous matter account for ~1% of the total mass.
    What you describe here is essentially baryonic non-luminous matter, like gas clouds or brown dwarfs and such. These make up ~3 % of the total mass/energy.
    Dark matter is another 23%. Dark matter means implicitly non-baryonic matter, i.e. not normal stuff. WIMPs are thought to be new elementary particles that interact only via gravity or the weak force. That's what most people believe Dark Matter is made of, and there is a chance that they will find them at the LHC.
    Then there's a rest of 73% that is even darker, and does not act like matter at all. Whatever it is, it's dubbed "Dark Energy". We don't know much about it, it looks like a vacuum energy would look like. We (believe to) know its equation of state: it has negative pressure and therefore acts repulsive. But that's it.
    Neutrinos (at least the known ones) are only a negligible fraction of the total energy.
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