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Question on possible dark matter classification

  1. Mar 26, 2015 #1
    It is my understanding that the matter originally contained in a dying star which formed a black hole has been entirely converted to energy in the form of space time curvature. In other words the matter no longer exists and all that is left is the curvature of spacetime. Aside from my question on that topic (which is why if a sun dissappears would it's gravity stop affecting it's surroundings meaning it's surrounding space reflattens but a black holes space remains curved after the matter leaves our universe), let's just assume that kip Thorne was telling the truth and not over simplifying on the interview I saw him state this fact. Could dark matter not simply be inherent curves in the otherwise flat fabric of spacetime created by energy during the big bang just like a black holes space remains a curved manifestation of the matter converted to energy that originally created it?
  2. jcsd
  3. Mar 26, 2015 #2
    If the sun were compressed to be a black hole, this would make no difference to the Earths orbit.
    The gravity of the sun would not change.

    We don't have much clue what happens to matter once it has entered a black hole, but we can't really say it no longer exists.
    It's probably in some very different state, but still exists in some form, since the black hole still has mass.
  4. Mar 26, 2015 #3


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    Do you have a reference for the assertion in the first sentence?
  5. Mar 26, 2015 #4
    I sure do,

    Is the video I was watching the other day that made me think of this, but I also remember hearing Michio Kaku say the exact same thing. I have a bad feeling this is....an oversimplification however.
  6. Mar 27, 2015 #5


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    This is not true. Space-time curvature is the result of the presence of mass or energy. It is not energy itself. You cannot convert energy to space-time curvature.

    Matter and energy that falls into a black hole still exists in our universe. It's just behind an event horizon. This means that the mass associated with the matter and energy also still exists.

    First, space-time is not inherently flat. It is only approximately flat. On a cosmological scale space-time is curved, and it becomes a good approximation of flat space-time when you get to much smaller scales and are away from large gravitational sources. This non-flatness is one reason that the concept of energy is hard to define in GR. (As long as my meager knowledge of GR isn't wrong. Someone with more knowledge in this area is welcome to step in and elaborate/correct me)

    Second, there is no 'creation event' in the big bang theory. The big bang theory is about the evolution of the universe from a hot, dense state to a cooler, less dense state over time, a process which was driven by expansion. The big bang theory does not deal with the creation of the universe. (not directly at least) That subject remains a near-complete mystery.

    So no, that can't be what dark matter is.
  7. Mar 27, 2015 #6
    I guess that means that what was stated in the video link I posted, as well as when I've heard other physicists say that the matter no longer exists once its fallen into the black hole as it has entirely been converted into energy manifested as space-time curvature, is a gross oversimplification stemming from our inability to describe just what the heck the singularity is.

    That being said however, it is still tempting at my level of understanding to think that if gravity is simply curved space-time, then dark matter itself may just be inherent curves in the fabric of spacetime itself, with galaxies clinging on like cat-claws cling to a lattice as they grow. Is that possible classification even entertained in high level theoretical physics? If not, is there a clean cut reason why we think it has to be some type of actual quantized particle (with an extremely loose definition on what an actual particle is), or is it just common belief that it will fall under this category once discovered?
  8. Mar 27, 2015 #7


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    Google the "bullet cluster". That might help dispel some of your misconceptions.
  9. Mar 27, 2015 #8
    That was certainly an interesting read phinds! It did help straighten out a few misconceptions I had indeed. After extensive additional searching around on the internet however, I still cant seem to find an answer to my second question pertaining just to dark matter. Aside from a few theories I read over which postulate that high concentrations of matter in other universes, while constrained to its own universe is 'leaking' gravity into ours which we see as dark matter, nothing seems to indicate that spacetime having inherent flaws (in other words, it came with curves like bruises on an otherwise smooth apple) has been considered. I guess we have no reason to assume that anything but high concentrations of matter or energy can curve space, so given what we know, particle classifications of dark matter is all that makes sense.

    Regardless, thanks again for the suggested read on the bullet cluster. I had heard of it but never actually looked over the recent observations and their implications.
  10. Mar 27, 2015 #9


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    and these are totally speculative with zero evidence to support them.

    I don't think energy curves spacetime, mass does that, and by the way it is not space that is curved it is spacetime and "curved" is a bit of a loaded word. In Riemann Geometry, it's straight lines (geodesics). We call it "curved" because we are using an implied Euclidian Geometry that doesn't actually describe space-time but is what we are used to and what English is based on (for terms like curved)

    That I agree with.

    Sure ... it is, as you said, an interesting phenomenon.
  11. Mar 27, 2015 #10


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    The stress-energy tensor is what is being curved. The energy part includes both energy and mass. I'm not quite sure what the stress part is...
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