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Why did dark energy overcome dark matter to create the expanding Universe?

  1. Feb 9, 2015 #1
    Why did dark energy overcome dark matter to create the expanding universe we live in today?
     
  2. jcsd
  3. Feb 9, 2015 #2
    The density of dark matter decays as ordinary baryonic matter while dark energy has constant density. Eventually the latter would dominate to drive accelerated expansion.
     
  4. Feb 9, 2015 #3

    Chronos

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    There is no known relationship between dark energy and dark matter.
     
  5. Feb 10, 2015 #4

    Chalnoth

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    It didn't.

    The dark matter in our universe was never enough to make our universe recollapse on itself, and the first few billion years of our universe experienced essentially no impact from dark energy. What dark energy has done is make the expansion rate over the last few billion years higher than it otherwise would have been. This is because the dark energy doesn't dilute as the universe expands: its energy density stays the same.
     
  6. Feb 11, 2015 #5
    I'm sorry, my question has not been answered..

    Perhaps I should have rephrased my question as I already knew the properties of Dark Matter and Dark Energy and why it was triggered into existence during the big bang. When the big bang happened, Dark Matter and Dark Energy was described by Einstein as two opposing forces that were close in strength, eventually dark energy was stronger then dark matter and as a result; the distance between each celestial body increased at a more rapid rate.

    Why did Dark Energy dominate Dark Matter, why didn't Dark Matter win the battle against Dark Energy and cause the universe to condense instead of expand?
     
  7. Feb 11, 2015 #6

    Chalnoth

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    It's just not at all true that dark matter and dark energy are opposing forces that were close in strength. And Einstein certainly never said it (as the term dark energy wasn't coined until after his death).

    Einstein's original idea of a cosmological constant was conceived because Einstein thought the universe should be static. He used the cosmological constant to balance the matter (dark matter wasn't known at the time, either). The idea there was that matter tries to fall inward, causing the universe to collapse. The cosmological constant pushes outward. So if you have a matter density and cosmological constant that are perfectly-balanced, then you can have a universe that neither expands nor contracts.

    The problem with this idea, besides just being incorrect, is that it is unstable: a universe sitting in this configuration is just at the boundary of collapsing into a singularity or expanding forever. All it needs is for a little bit of matter in one region to migrate to another, and the whole system destabilizes.

    So this idea of dark energy balancing dark matter was never a viable model. It wasn't a good idea to begin with, and it certainly never described our universe.
     
  8. Feb 11, 2015 #7
    "It's just not at all true that dark matter and dark energy are opposing forces that were close in strength. And Einstein certainly never said it (as the term dark energy wasn't coined until after his death)."

    Einstien created the idea of Dark Matter because the laws of the universe didn't make sense without it. It was not called "Dark Matter" until after his death.

    "The problem with this idea, besides just being incorrect..."

    "So this idea of dark energy balancing dark matter was never a viable model. It wasn't a good idea to begin with, and it certainly never described our universe."

    I don't care how good of a model it is or isn't to another person, that is irrelevant as well. The fact is that Dark Matter has a small impact on the universe where as Dark Energy has a significant impact. In these terms they could be considered to have opposites properties, although technically not opposite forces I suppose.

    All I know is that at some point in the beginning of the big bang, Dark Matter and Dark Energy had opposite properties which affected the universe to expand. The properties contained with Dark Matter and Dark energy are dynamic and unfixed.

    By the way, this is a theory and not a statement demanding to be a fact. Nothing can be proven wrong or right. "Incorrect" is irrelevant.
     
  9. Feb 11, 2015 #8
    Einstein didn't come up with the idea of dark matter, he came up with the cosmological constant previously mentioned. That'd be dark energy. And you are completely forgetting inflation.
     
  10. Feb 11, 2015 #9
    (In my opinion Einstien created the idea of Dark Matter and Dark Energy because the laws of the universe didn't make sense without it. It was not called "Dark Matter" or "Dark Energy" until after his death. And yes I am taking inflation into account as well as Dark Energy and Dark Matter's impact on the universe since the big bang).

    Einstien and my opinion of what Einstien thought is not really the point. Point is I asked the question wrong and this thread is being closed in favor of another. You are probably right though because I sometimes get terms mixed up and have a bad habit of not reading before posting.
     
  11. Feb 11, 2015 #10

    PeterDonis

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    EncryptedKnight, please learn to use the Quote feature (either the +Quote button at the bottom right of each post, or the "Quote" popup that comes up when you highlight text in a post). It is extremely difficult to tell in your posts what is being quoted and what is your own response. If your posts are unreadable, nobody is going to read them.
     
  12. Feb 11, 2015 #11

    Chalnoth

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    You've still got a rather confused notion of what dark matter and dark energy do.

    Again: dark energy never "overcame" dark matter in any way, shape, or form. Neither dark energy nor dark matter is responsible for the fact that the universe is expanding. What they do do is impact how the rate of expansion has changed over time.

    For most of the history of our universe, when it was expanding the fastest, dark energy was completely irrelevant. The gravitational attraction of matter (normal and dark) slowed the expansion dramatically. When the matter density became small enough a few billion years ago, the constant density of dark energy became relevant to the expansion, essentially putting a floor on how low the expansion rate could go.

    It's entirely relevant, because your question makes no sense at all when applied to our universe.
     
  13. Feb 11, 2015 #12
    I thought dark energy was, in the form of the cosmological constant; at least that's how it's worded in numerous articles. Did I get this right?
     
  14. Feb 11, 2015 #13

    PeterDonis

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    The cosmological constant is one possible form that dark energy could take; but it's not the only one. There are other possibilities; the key feature is that all of them have positive energy density and negative pressure. That's what makes them "dark energy".

    What Chalnoth meant wasn't that dark energy and dark matter don't affect the rate at which the universe expands; they do. What he meant was that they aren't responsible for the fact that the universe is expanding; that is due to the initial conditions that came about at the end of inflation, with the universe being filled with a hot, dense plasma (because the energy released in the phase transition that ended inflation caused all kinds of particles to be created) that was expanding rapidly (because inflation greatly increased the expansion rate of the universe as a whole).
     
  15. Feb 11, 2015 #14

    Chronos

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    Bear in mind that matter and dark matter were actually winning the gravity battle until about 5 billion years ago. Expansion was actually slowing down, as expected, up to that point in the history of the universe. Dark energy gained the upper hand at that time and expansion has been accelerating ever since. This was completely unexpected when discovered by Perlmutter and Riess at the turn of the century - who were actually seeking to determine if and when the universe might ultimately recollapse. This mysterious repulsive force got saddled with the unfortunate name 'dark energy' which, of course, has proven confusing.
     
  16. Feb 11, 2015 #15

    Chalnoth

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    To be fair, some theorists suspected a small cosmological constant prior to the observations by the teams led by Perlmutter and Riess, but it is true that few people thought the idea likely. Here's one example from 1995, and I'm sure there are earlier examples as well:
    http://arxiv.org/abs/astro-ph/9504054
     
  17. Feb 13, 2015 #16
    There are several threads which discuss the precise meaning of EXPANSION

    The fabric of space-time is NOT expanding

    To quote Lee Smolin,
    What exists, is a single fabric of space-time. The whole entire fabric, from the Big Bang to Big Crunch, exists. We confuse ourselves by focusing on space-like SLICES of the fabric which we "now". The whole entire fabric exists, with no more distinction between yesterday and tomorrow, as between one place and another.

    Thus, SPACE-TIME is NOT expanding. As our sense of now passes through time, we move along our 3+1D world-lines like trains on rails. And those rails are taking us from smaller space-like slices of space-time, to larger ones.

    Imagine a vast fleet of ships encircling Antarctica. As they steam northward, towards the equator, the distances between them seem to increase. But earth and the oceans are NOT changing size in any way. And in GR, the whole course of the ships, i.e. their world-lines, are preplotted. Nothing is changing, not the ships courses, nor the earth...

    Not worldlines of particles, nor the fabric of space-TIME.

    Dark energy and mass-energy all have positive energy density. They affect the GLOBAL topological shape / form/ structure of the fabric of space-time in different ways... Mass and energy INSIDE of space-time cause it to close through time, like lines of longitude on earth which converge towards the north pole...

    Dark energy causes those lines of longitude to curve the other way, diverging outwards so as to form space-time into the shape of a vase or bowl.

    You don't need to consider negative pressures, or anything pushing anything else...
    The whole fabric of space-time is, and different kinds of energy densities affect its global topological structure differently. For discussions of standard GR, time is an illusion, and we confuse ourselves by speaking of anything stretching, expanding, changing. Space-time is shaped such that space-like slices of it are larger at later coordinate times, of clocks on world lines threading through the fabric. But the fabric is fixed and is not changing.

    You can stack big plates on small plates... That doesn't mean any plates are stretching, expanding, growing
     
  18. Feb 18, 2015 #17
    One of space's properties is that it can expand, and that means it contains Dark Energy, so (don't take my word on this as a complete answer) the more space there is the more Dark energy there is because dark energy lets space expand but Dark Matter is not necessarily found in empty space so Dark energy dominates in this case. Does that answer your question?
     
    Last edited: Feb 18, 2015
  19. Feb 18, 2015 #18

    PeterDonis

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    This is not correct; the expansion of space does not require dark matter to be present.

    This is not correct either; space can expand without dark energy being present.
     
  20. Feb 18, 2015 #19
    But Dark energy allows for it and this is one case. But how can space expand without dark energy or the cosmological constant? And I meant Dark Matter, it was a typo, by the time you read this I would have fixed it.
     
  21. Feb 18, 2015 #20

    PeterDonis

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    Um, by expanding? You are aware that there are solutions (the FRW solutions with only ordinary matter and radiation present) for an expanding universe with no dark energy and no cosmological constant, right?
     
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