1. Standard membermenace71
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    09 Mar '14 20:57
    Black holes are not directly visible we see the effects caused by their displacement on time and space and gravitation effects


    Manny
  2. Standard membermenace71
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    09 Mar '14 20:591 edit
    Dark matter is a type of matter hypothesized in astronomy and cosmology to account for a large part of the mass that appears to be missing from the universe. ***from Wiki***

    Manny

    http://en.wikipedia.org/wiki/Dark_matter
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    09 Mar '14 21:58
    Originally posted by humy
    If it repels then we would have surely already observed this with the antimatter experiments but we didn't observe this. In addition, even if it does 'repel' matter, antimatter still annihilated matter in the experiments so, evidently, it doesn't 'repel' well enough, at least in all our experiments to date, to stop contact and annihilation thus this still begs ...[text shortened]... to mention the several other significant problems with the idea of dark matter being antimatter)
    I meant the possibility that anti-matter repels other anti-matter.
  4. Subscribersonhouse
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    09 Mar '14 22:17
    Originally posted by Metal Brain
    I meant the possibility that anti-matter repels other anti-matter.
    We can make anti-matter in small quantities but have not seen any such thing at least so far.

    My feeling is anti-matter would not go anti gravity on us, I don't think the mass inside makes any difference to the curvature of spacetime.
  5. Standard memberDeepThought
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    10 Mar '14 03:081 edit
    Originally posted by Metal Brain
    I meant the possibility that anti-matter repels other anti-matter.
    Repel how? Do you mean via electro-magnetism, in which case positrons repel other positrons, but there's nothing special about that since electrons repel electrons as they have the same charge. Or do you mean gravitationally? The main question that I've heard asked is whether anti-matter repels matter gravitationally, not whether it repels other anti-particles. I don't think that anyone seriously expects there to be an unknown force which causes anti-particles to repel each other and the known forces don't behave like that.
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    10 Mar '14 09:19
    Question:

    If we would live in a universe completely made up of anti-matter (as ours are made up of ordinary matter) - would it then be different from ours? Would we even notice it? (...provided that all the others constants are the same?)
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    10 Mar '14 09:37
    Originally posted by FabianFnas
    Question:

    If we would live in a universe completely made up of anti-matter (as ours are made up of ordinary matter) - would it then be different from ours? Would we even notice it? (...provided that all the others constants are the same?)
    I think the answer is, at least in practical everyday terms, we wouldn't notice any difference.
    But I have heard of some as yet unproven theory that the behavior of antimatter may be in some way very subtly and very slightly different from that of matter ( "matter-antimatter asymmetry" ) and, if so, there may be some experiment that allow us to measure that difference albeit with difficulty.
  8. Standard memberDeepThought
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    10 Mar '14 11:42
    Originally posted by humy
    I think the answer is, at least in practical everyday terms, we wouldn't notice any difference.
    But I have heard of some as yet unproven theory that the behavior of antimatter may be in some way very subtly and very slightly different from that of matter ( "matter-antimatter asymmetry" ) and, if so, there may be some experiment that allow us to measure that difference albeit with difficulty.
    Look up CP violation on Wikipedia. This is the asymmetry between matter and anti-matter you are thinking of. This doesn't require "new physics", it happens in the standard model and has been experimentally observed (in the 1960s) but the consequences aren't all clear - for example it appears not to be strong enough to account for the fact that there is a lot more matter than anti-matter.
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    10 Mar '14 19:35
    Originally posted by DeepThought
    Repel how? Do you mean via electro-magnetism, in which case positrons repel other positrons, but there's nothing special about that since electrons repel electrons as they have the same charge. Or do you mean gravitationally? The main question that I've heard asked is whether anti-matter repels matter gravitationally, not whether it repels other anti- ...[text shortened]... rce which causes anti-particles to repel each other and the known forces don't behave like that.
    The same way gravity attracts matter. Call it anti-gravity.
  10. Subscribersonhouse
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    10 Mar '14 21:22
    Originally posted by Metal Brain
    The same way gravity attracts matter. Call it anti-gravity.
    I would think they would have seen that in the concentration of anti-matter where it would in that case be repelled by the massive gravity in the center of galaxies and individual stars.

    The report is there is quite a bit of anti-matter right here in our solar system and there are even designs afoot to capture such local anti-matter collectors between here and the moon.
  11. Standard memberDeepThought
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    11 Mar '14 15:38
    Originally posted by Metal Brain
    The same way gravity attracts matter. Call it anti-gravity.
    The question of whether anti-matter is gravitationally attracted or repelled by anti-matter is an experimental one. Since anti-matter has positive energy and mass I see no reason why it should behave differently to normal matter in a gravitational field. I doubt that there is any way of distinguishing between matter and anti-matter based solely on their gravitational behaviour. My opinion is based on theory, there hasn't yet been an experiment, but I am confident that anti-matter falls down and not up.
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    12 Mar '14 08:591 edit
    Did Dark Matter Kill the Dinosaurs?

    http://www.scientificamerican.com/article/did-dark-matter-kill-the-dinosaurs/
    "The solar system's periodic passage through a "dark disk" on the galactic plane could trigger comet bombardments that would cause mass extinctions."

    Is this a mere speculation or is it credible?
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    12 Mar '14 09:37
    Originally posted by FabianFnas
    Is this a mere speculation or is it credible?
    Pure speculation.
    The current theory as to what killed the dinosaurs was a single large meteorite. Thus there is no evidence for an increased frequency of meteorites at that time.
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