Dark matter and antimatter

Discussion in 'Astronomy, Exobiology, & Cosmology' started by ash64449, Nov 6, 2012.

  1. ash64449 Registered Senior Member

    Hello friends,
    I want to precisely understand what dark matter is. Is Dark Matter a matter that is not visible but have gravitational effects? Why is Dark Matter not visible? Can Dark Matter be really big? I mean can it have considerable amount of mass or does it have negative mass? And I have Heard of Antimatter that it can annihilate energy when in contact with matter.But Why do they annihilate energy on contact? Since Antimatter is opposite of Matter,Does it have negative mass?
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  3. Neverfly Banned Banned

    You're on fire today...
    Don't we all...
    Currently, Dark Matter is more hypothetical than established, although I've come to learn that may be a gray area.
    Dark Matter is hypothesized to be WiMPS.:

    There have been many experiments performed to try to indirectly observe dark matter and BruceP posted a link a while back that left me scratching my chin.
    It's not confirmed, however.
    Yes. It is not invisible, but it is very difficult to detect. Bear in mind where it is (Far away in outer space).
    If dark matter is composed of Weak Interacting Particles, it won't have a reaction with matter that we can easily see. This includes a reaction with light. It's not invisible, just far away and doesn't really have detectable properties other than gravitational attraction.
    Assuming your asking can a lot of it be in one area, even if there is very little in another area-we would assume yes.
    It does not have any kind of "Negative Mass."
    Anti-matter has an opposite charge, not opposite mass. Anti-matter is identical in every way to its matter counterpart, only with the opposite charge.
    Anti-matter counterpart to an electron is a positron. Electrons have a negative charge, positrons have a positive charge.
    So why annihilate? When they annihilate, they can release photons, gamma rays, etc- these are considered to be massless.
    Conservation of energy and momentum. An electron cannot decay into a photon because a photon has no charge and an electron has a negative charge. Charge is conserved and the electron has no lower state to jump into.
    Collide it with a positron, however, and the charges cancel eachother. Since they cancel out charges, photons can now be produced. Matter is energy and energy must be conserved and remember, energy cannot be created or destroyed. It only changes state.
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  5. brucep Valued Senior Member

    Dark Matter has been directly detected in weak lensing observations. Over six years ago. This was the first and this paper has been cited 200 x's. So we know it exists and WMAP tells us how much. We know it acts gravitationally [duh] but very weak electromagnetically if at all. I say very weak based on Robert Foot's proposal Mirror Dark Matter. The Mirror Dark Matter would be awesome if confirmed.
    A direct empirical proof of the existence of dark matter
    Robert Foot, University of Melbourne Talk at Italy-Australia Symposium
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  7. RoccoR Registered Senior Member

    et al,


    Rather than being this invisible matter, is it possible that there is a huge amount of planetary size objects just floating alone with the galaxies that accounts for the extra gravity?

    Most Respectfully,
  8. mathman Valued Senior Member

    No. The ratios of H1 to He4 and H2 (produced in big bang) tells us that there is much too little baryonic matter to account for dark matter.
  9. brucep Valued Senior Member

    There's no evidence for that over the years of astrophysical observation. For example it would have been noticed by perturbation of local paths.
  10. brucep Valued Senior Member

    Good answer.
  11. RoccoR Registered Senior Member

    brucep, mathman, et al,

    Thanks. I was musing about the observations on the curve of spiral galaxies and gravitational lensing.


    I had not realized that we knew the exact ratio of elements [(primordial H, H2, He3, He4, and Li7) (indeed all the elements)] conjured through the Big Bang Nucleosynthesis (BBN) model relative to the detectable non-Baryonic material .

    Does Baryonic Matter include all normal matter; or, are there particles like electrons and neutrinos that are different?

    From reading some of Prof Zwicky's old material, he thought there might be an electromagnetic connection. I assume that, since the 1970's, this has been ruled out. That a galaxy does not have sufficient spin to generate a continuous electric field by dragging non-Baryonic Material. Is that correct?

    (I apologize if my questions are too elementary.)

    Most Respectfully,
  12. brucep Valued Senior Member

    R_you're great.

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