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If dark energy is a constant

  1. Feb 17, 2014 #1
    From what I have gathered, dark matter is finite, correct? The more space expands, the less dense dark matter will be. So billions or trillions of years from today, space will have expanded a lot and the density of dark matter will decrease from a universal view. But if dark energy is a constant instead of being literal matter, then wouldn't that mean dark energy would start to over-dominate dark matter's "glue" affect and eventually everything would be alone, drifting in the vacuum of space?

    I could be considered layman right now in my understanding of physics, but I would like input and discuss with you all
  2. jcsd
  3. Feb 17, 2014 #2
    the amount of energy the cosmological constant has per cubic meter is extremely small, as such it is easily overpowered by gravity. Currently its roughly 6*10-10 joules per m3. Instead of the "big rip" which is what your essentially describing, its more likely we will end up in what is referred to as" heat death. The cosmological constant is as you implied a constant, Dark matter however remains a mystery, we have no knowledge of its interactions or decays, so one cannot tell you if the amount will remain the same finite amount. However as energy can be converted to matter, processes may exist to create more.

    For that matter I've recently read papers that tried to state processes that create dark matter however those papers did not pass peer review so I will not post any reference to them here.
  4. Feb 17, 2014 #3
    I see... so it seems like we are heading towards a 'mini' big rip? Only the local galaxies will be within the visible universe many years from now. Is that accurate?
  5. Feb 17, 2014 #4


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    Local galaxies and possibly galactic clusers, yes that is the general consensus, but it is not a totally established fact simply because since dark energy isn't understood, we can't be completely sure how it will act.
  6. Feb 17, 2014 #5


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    The dark energy 'constant' only applies to the observable universe.
  7. Feb 17, 2014 #6
    Thanks, and yes I understand it's all hypothetical. While I've got your attention, I clicked the link in your signature and read how dark matter is causing inflation not expansion. Then I realize I never answered one of the most basic questions, or thought about it. If dark matter wasn't causing the expansion 8+ billion years ago, then what was?
  8. Feb 17, 2014 #7
    As far as we can tell?
  9. Feb 17, 2014 #8


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    First of all, you are talking about dark energy and using the term dark matter. A slip of the figner, I assume.

    Expansion is a result of the original actions of the universe. Dark energy is NOT causing the expansion, it is causing the ACCELERATION of the expansion. Please read my article more carefully. All of that is fully explained (well, described is probably a better term in this case than explained)
  10. Feb 17, 2014 #9
    Yes, mis-type. No where I am getting caught up is you said 8 billion years ago is when inflation began, so the 5 billion years of expansion was based solely from the force of the big bang? Gravity did not crunch in 5 billion years? That is my question
  11. Feb 17, 2014 #10
    Everything we understand in cosmology applies to the observable only. It is only an assumption that the same physics apply beyond that.
  12. Feb 17, 2014 #11


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    No, again I say, please read my article carefully. All of this is discussed. Dark energy is believe to have been around since the beginning, it's just that somewhere along the way matter became spread out enough that dark energy began to overpower gravity. Dark energy DID have an effect on the expansion before that, but it was overwhelmed by gravity (but less and less so until finally it started to dominate gravity).
  13. Feb 17, 2014 #12
    Ohh I see now! Thanks!
  14. Feb 17, 2014 #13
    this quick and simplistic article gives a general chronology of the universe


    this recent post has some further articles that will aid your understanding, as well as help clarify some of the aspects you read in Phind's signature.


    in particular I would read the following

    "What we have learned from Observational Cosmology" nice part of this article is that is very easily understood.


    if you would like an excellent tool to understand cosmology I would recommend playing around with this calculator. You can graph any of the results as well as fine tune which parameters you wish to display.


    the last link in my signature contains the user manual for the calculator, numerous examples are contained in the pinned thread "look 88 Billion years......."


    though I would jump to the later articles for the later revisions details
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