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Dark matter dark energy

  1. Nov 26, 2012 #1
    Ok so I might sound a bit ignorant, but please bare with me. I have 2 questions

    1st I've always wondered how they know that dark matter isn't just a bunch of black holes. I mean couldn't there be a bunch of little black holes created right after the big bang. You have all these particle flying around with a high amount of energy, couldn't they form little black holes. thanks.

    2nd Space really isn't empty, It constantly has photons and other particles traveling through it, could dark energy and dark matter just be all these particles. I know I'm wrong, but I'm looking for an explanation. They way I'm thinking about it is, if you view the universe from an infinite different points of view, you would still see all the stars and what not,and this is due to the photons giving off from these stars.

    P.s. I know you can't view the universe from an infinite point of views, because technically you could only view it in different planck distances which is finite.
  2. jcsd
  3. Nov 26, 2012 #2
    According to the standard model of particle physics, all matter is composed of twelve fundamental elementary particles known as fermions. The fermions are grouped into the Quarks and the Leptons. There are also three fundamental forces: the strong force, weak force, and electromagnetic force. The cause of gravitation is widely debated. You can read more here:


    The photon is the force carrier of the electromagnetic force. It isn't matter in itself. The problem that dark matter poses is that it does not absorb or emit electromagnetic radiation at a level sufficient enough for us to see it. Its properties are different than those of the matter that we are able to see. Dark energy is believed to be the energy that is causing the accelerated expansion of the universe.
    Last edited: Nov 26, 2012
  4. Nov 26, 2012 #3


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    That would be the MACHO (Massive Compact Halo Object) hypothesis, which is heavily disfavored due to microlensing studies. Note, you can still have a lot of these objects, just not nearly enough to account for the dark matter density we observe. See: http://en.wikipedia.org/wiki/Massive_compact_halo_object

    Well the current best idea for what Dark Matter is is that it is indeed a new particle -- one which is simply electromagnetically dark. This makes sense given that a weakly interacting particle will pass through normal matter (we see this in systems like the bullet cluster), and that it can easily aggregate in halo-like formations which reproduce the observed rotation curves of galaxies.

    But think for a moment about what dark energy is. It's a substance giving rise to an acceleration of the universe, and critically, its density does NOT decrease when the universe expands. This strongly suggests that it is not due to individual particles themselves, but rather a field of constant density which permeates all of spacetime, or the so-called 'vacuum energy' (since it exists when you're classically in vacuum).
  5. Nov 27, 2012 #4
    Here's a question:

    We know that photons loose energy and are red shifted as they climb out of a gravitational well. So wouldn't gravitons also loose energy as they climb out of a gravitational well? And wouldn't this make objects farther away from galatic centers seem more massive than otherwise? I wonder if this could account for dark matter.
  6. Nov 27, 2012 #5


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    If we assume that gravitational radiation is made of gravitons, then sure -- as gravity waves are redshifted, gravitons will lose energy. But an object's gravity is not transmitted by gravitational radiation. Instead, the gravitational interaction between two bodies is mediated by spacetime curvature.
  7. Nov 28, 2012 #6
    1st. Black holes give off radiation, we can observe different types of electromagnetic fields and radiation from black holes, so we can technically observe them in a sense. Dark matter or energy doesnt give off anything, it only deflects light to your second question photons dont go right through them it gets deflected, using gravitational lensing we are able to see that some form of matter exists. And using gravitational lensing we are able to see that dark matter's gravitational pull creates the "web" where along the matter are where the galaxies are lined up. Also photons and particles cannot create the gravity needed to keep the galaxy in shape the theoryof dm and energy comes from and unaccounted gravitational and repulsive force. Gravity in the sense that to keep all our stars t constant velocity in our galaxy an others there had to be an external force dark matter. Einstein suggested our worlds will be pulled together by gravity but there is a force overpowering both dark matters gravity and visible gravity, dark energy. Photons are massless according to mass and energy theory technically and the black hole at the cetre of our galaxies doesnt create enough gravity needed either.

    Everything i said came from that documentary and another about black holes.
    Last edited by a moderator: Sep 25, 2014
  8. Nov 28, 2012 #7
    Attaboy! Once they change the dictionary we'll know we've won.
  9. Aug 24, 2013 #8
    Dark Matter was first theorized in 1933 by Fritz Zwicky but was not known as Dark Matter, it was known as the Missing Mass Problem. Zwicky measured the gravitational mass of the galaxies within the Coma galaxy Cluster. He found that the mass measured was much higher than what they would have expected. The mass of all the planets, stars, gas, dust, etc. wouldn't have such a high gravitational mass. So it was coined the Missing Mass problem.

    Vera Rubin in the 1970's was measuring the galaxy rotational rates of certain galaxies and discovered that the matter nearest the galactic core was spinning just as fast as the outermost matter. This didn't make sense because if the outermost matter was spinning just as fast as the innermost matter; the galaxy should fly apart. This was when Dark Matter was first named and we discovered what its effects are. That is keeping galaxies together.

    Scientists had guessed that it is WIMP's (Weakly Interacting Massive Particles), MACHO's (Massive Astronomical Compact Halo Objects), as well as Brown Dwarfs. But after further research none of these possible answers would have the combine mass to solve the problem. Some of the Dark Matter in galaxies might be made of WIMP's, MACHO's, and Brown Dwarfs but most of it is still unknown.

    We still are unsure of what Dark Matter is today but we believe that it is a subatomic particle yet to be discovered. We also believe that it is not made of atoms because Dark Matter does not react to the electromagnetic force. It does not interact with light making it "dark." We know it is there though because of its gravitational effects on other luminous objects.
  10. Aug 24, 2013 #9


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    Connor, it helps to check the post date on the thread. This thing hasn't been active since November of last year. :tongue:
  11. Aug 24, 2013 #10
    Yeah i see that now...but tell me that wasn't a solid answer!
  12. Aug 24, 2013 #11


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    It was an excellent answer. Drakkith is just pushing to get to 10,000 posts :smile:
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