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Universe without matter

  1. Jan 30, 2013 #1
    - Is universe without matter bigger than universe with matter?
    - Did (could) universe without matter exists before big bang?
     
  2. jcsd
  3. Jan 30, 2013 #2

    Drakkith

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    Define "bigger". What do you mean by a "bigger" universe? Current the universe can be either infinite in size or finite in size and we don't know which one it is. How can it be larger than infinite?

    We cannot talk about the universe before a point in time we call t=0. As we look further back in time (and distance) we see the universe becoming more and more dense. Eventually we reach a point where the universe has become so hot and dense that our math starts to do silly things like walk around playing a banjo behind its ear and giving us infinities for solutions. It is at this point that we smack a label on it and say "This is t=0". It is this point that our theory breaks down and no longer makes any useable predictions. In math terms this is known as a "singularity", and it is this which gives rise to the common belief that the universe was once a giant black hole. However this is very likely the result of our incomplete knowledge of physics at this scale. A theory on Quantum Gravity should resolve this and allow us to go further back.
     
  4. Jan 30, 2013 #3
    Define "bigger". What do you mean by a "bigger" universe?
    What I meant by "bigger" was if the universe(s) with matter is(are) expanding inside the universe without matter (either finite or infinite)?
    ..and thereby come to the next question if there should or could had been a universe without matter (with energy) before any possibility for "creation" of a universe(s) with matter a la Big Bang?
    Empirically, as you say, there are too little data to play with such an idea, but rationally and on a more theoretical/philosophical level, do we have any bases to assume these?
     
  5. Jan 30, 2013 #4
    Lets put it this way their are plenty of models that discuss possibilities of prior to T=0. None of these models although they can mathematically make sense have any evidence to support them other than modelled possibilities. As stated in the previous post the physics and math breaks down shortly after the expansion first started.

    One could construe that due to never being able to get information or any form of data at certain areas of the universe, ie beyond all possible observation such as the observation horizon, and inside the event Horizon then those areas can be considered different universes.
    However that again is more philisophical that scientific. I'm sure someoene will point out this forum does not support philisophical questions, for good reason lol.
     
  6. Jan 30, 2013 #5

    Chronos

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    A universe without matter is called the Milne universe. It is a special relativistic [as opposed to general relativistic] cosmological model. It is useful as a mathematical playground to examine various ideas in cosmology without that annoying gravity around to warp your space time diagrams.
     
  7. Feb 1, 2013 #6
    Let me put it this way(nothing new but still bugging many): Big bang out of nothingness just doesn't make sense!
     
  8. Feb 1, 2013 #7

    Bobbywhy

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    Postzeep, you waited for several members to comment before you got to your underlying complaint: it would have been helpful had you just stated what's bugging you in the Opening Post.

    Since it features both zero energy density and maximally negative spatial curvature, the “Empty Universe” (As Chronos points out, the Milne model) is contradicted by cosmological observations. Astronomers actually observe the universe's density parameter to be consistent with unity and its curvature to be consistent with flatness. Therefore it is nonsensical to propose an “empty universe” as real.

    Just because some process may seem to not “make sense” scientists have only observations and empirical evidence to build their understanding of nature. Allowing emotion to guide our beliefs brings only pseudoscience. Our current cosmological model does not satisfy everyone to be sure, but it is our best effort.

    Cheers,
    Bobbywhy
     
  9. Feb 1, 2013 #8

    Drakkith

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    Then you should be excited to learn that we have no idea how the universe was created. It may have been created from nothing via quantum fluctuations, it may be infinitely old and undergone countless cycles of expansion and collapse, or it may be something completely different and utterly inconceivable. We simply don't know.

    But does anything really make sense? Does a universe that is infinitely old make any more sense than one created from nothing?
     
  10. Feb 1, 2013 #9

    Chronos

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    Would it help if a scientist assured you the total energy content of the universe is exactly zero?
     
  11. Feb 2, 2013 #10
    no it does not.

    how can everyone observe light at a fixed 'c' ? That's rather crazy!

    Does space and time being dynamic 'make sense', yet they are.

    neither does quantum mechanics 'make sense' compared to our everyday macroscopic world.

    But we have theories and some observations that lead us to believe this IS the way things are.

    Richard Feynman:
     
  12. Feb 2, 2013 #11
    Postzeep: Your question is interesting even if the universe is infinite...let's set that aside for a moment....[There are different size infinities.]



    I can think of a few things to consider about relative sizes of universes...mostly initial expansion [INFLATION] and subsequent, slower, expansion. We'll restrict ourselves to descriptions based on general relativity: The general model for that is FLRW model but 'distances' are not so simple....In general more mass in our era would mean slower expansion...but it's not so simple, I don't think.

    I'm guessing the 'biggest universe is the one in which both periods have the fastest growth...the most acceleration...and retain the most. Or one in which inflation never ends. Inflation had to be 'glued on' to explain things we observe; then 'slow roll' had to be glued to inflation so it would stop!! then we add a cosmological model!! That's hw we currently model Gr based universes.

    Here is how Roger Penrose describes the initial inflationary period, right after the big bang from THE ROAD TO REALITY, pages of section 28.4. I am paraphrasing here:

    This transition is the 'slow roll' version described in Wikipedia....

    http://en.wikipedia.org/wiki/Cosmic_...roll_inflation [Broken]


    The initial inflationary expansion is theoretically driven by a negative-pressure vacuum energy density...a Higgs field....so if you want more rapid expansion, check out what increases that negative pressure vacuum energy. And once it is a big as you can make it, eliminate the 'slow roll' which brings it to an end...and it will continue forever. Of course there won't be much of interest in such a universe; certainly no life forms, for example. You can also check 'vacuum expectation value' to learn more about vacuum energy.

    The FLRW cosmological model starts moments after the inflationary period as I recall...I think that means if you want to know anything about relative sizes of universes, you'd have to decide what makes inflation the fastest, then subsequently, what keeps expansion moving the fastest....

    You can get a snapshot of some differences here:
    Use the black curve which is one distance measure, the Hubble distance.

    http://www.astro.ucla.edu/~wright/cosmo_02.htm

    scroll down the page until you come to three side by side charts across the page...
    H versus Z....

    but this is for a rather limited period of time.....
     
    Last edited by a moderator: May 6, 2017
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