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The Edge of The Universe

  1. Jun 12, 2009 #1
    hi. im an undergraduate physicist and don't have that much exposure to cosmology but i was watching a BBC Horizon episode on M Theory and that the Big Bang was believed to be the collision of two parallel universes in the 11th dimension and that the combining of the p-brane ripples formed matter or something along the lines of that. Anyway in this scenario, there were all these parallel universes contained inside a so called "multiverse".

    I was wondering then, if we got to the edge of our universe and looked out, what would we see. i.e. if all the universes are bubbles in the multiverse, what is between teh bubbles in the multiverse?
    Also, if we get to the edge of the multiverse and look out what would we see?

    Surely the answer can't be nothing? because even nothing is something?

    cheers.
     
  2. jcsd
  3. Jun 12, 2009 #2

    marcus

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    Pretty speculative. It is an imaginative scenario but I doubt any professional scientist would admit to believing it. Just is one of many ideas on the table to be tried out.

    In standard cosmology, there is no boundary.

    The standard cosmo model, that essentially everybody uses to calculate with and fit data to, is called LCDM (lambda cold dark matter) and in that model space is either infinite or it has finite-volume boundaryless geometry like for example a hypersphere.
     
  4. Jun 12, 2009 #3
    "Can the Universe Create Itself?" This is a highly speculative (and highly technical) theory put forward by J. Richard Gott III and Li-Xin Li in the Physical Review D58 (1998) also at http://arxiv.org/abs/astro-ph/9712344. While the paper is quite technical the Introduction (which is longer than most papers) can make interesting reading. The illustrations are not part of the article; you will find them at http://arxiv.org/ps/astro-ph/9712344v1. In particular, figure 1 shows a 2 + 1 dimensional model of what they are proposing: http://arxiv.org/PS_cache/astro-ph/ps/9712/9712344v1.fig1.gif

    Cheers, Skippy
     
    Last edited by a moderator: Apr 24, 2017
  5. Jun 12, 2009 #4

    marcus

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    To speak logically, you cannot look outside because (speaking of the universe) there is no outside. It is all physical existence.

    Meaningless to speak of a "nothing" outside the universe, because there is no outside.

    Multiverse talk is mostly speculative---with made-up stuff, untestable, based on fantasized assumptions. But it does not arrive at an idea of outside the universe---it just generates a vision of a more variegated universe, with many different regions evolving according to different versions of physical law. In the multiverse fantasies I am familiar with the domain boundaries move at the speed of light and are lethal. Because there is a physically different vacuum on the other side, different particles, different physics, different dark energy. If such a boudary happened to pass thru our galaxy it would destroy it.
    Andrei Linde, an imaginative professor at Stanford, is the source of much of this. It may be stimulating to think about, and it gives graduate students something to write about. But it's not useful for ordinary work in observation-based cosmology.

    The organizers of the two most recent annual Strings conferences, Strings 2008(CERN) and Strings 2009(Rome) excluded all talks about the Multiverse and M-theory Landscape and the Anthropic principle. So the situation may be getting a bit more clear, gradually. Media like the BBC will normally be several years behind the research community, so BBC may be doing stuff about Multi which has lost most of its research interest.

    There was a nice workshop about this at Princeton last year. September I think. I might be able to get the link. Paul Steinhardt. Nima Arkani-Hamed.
     
    Last edited: Jun 12, 2009
  6. Jun 12, 2009 #5
    This is exactly what I was talking about in my thread.

    One question, would an infinite universe imply an infinite amount of matter or something like that?
     
  7. Jun 12, 2009 #6
    If the standard cosmological assumption is true: On sufficiently large scales the universe is homogeneous, then an infinite universe would necessarily contain an infinite amount of mass and energy.

    skippy
     
  8. Jun 12, 2009 #7
    Wouldnt an infinite amount of energy and mass violate the first law of thermodynamics?
     
  9. Jun 12, 2009 #8

    marcus

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    No.
    The first law does not say that the universe cannot contain an infinite amount of energy, or of mass.

    You may be under the misconception that standard cosmology says that the universe came from a finite region (which would contain a finite amount amoung of matter/energy).
    But this is not what it says. It says that the finite piece of the universe which we have so far observed, the observable, was at one time concentrated in a very dense state in a finite region. It does not say the whole universe was.

    Standard big bang cosmo allows for the present universe to be infinite--with matter more or less uniformly distributed throughout--and to have begun the expansion era as infinite (both infinite volume of space and amount of energy). It is routine. They use the infinite version of the model if any thing more than the finite.

    There is no contradiction or inconsistency, finite evolves from finite, infinite evolves from infinite. The observable chunk is always finite in either case.
    Popularizations confuse people. I think popular media accounts are responsible for most of the confusion about cosmology (and websites that oversimplify in an attempt to be helpful.)
     
    Last edited: Jun 12, 2009
  10. Jun 12, 2009 #9
    you cannot get to the edge of the universe and you cannot picture multiple universes as "bubbles" is a multiverse (object in a 3d space). the word bubble and what it actually descibes is only used to have an image for the human mind to understand these complex forms and functions of reality. concerning the edge of the universe i telly you: the edge of the universe equals the edge of your imagination! for some the universe is infinite for others very limited. there is no absolute, no absolute time, no absolute space, it is all relative to the consciousness of an aware being.
     
  11. Jun 13, 2009 #10

    Chronos

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    The edge of the universe is like a rainbow, always just beyond reach. No matter where [or when] you are in the universe, the 'edge' is equidistant in all directions. We can shrink it to a point in the past [from our persepective], but, that point may only be one of an infinite number of possibilites. This is essentially unknowable. No definitive observational test has been proposed.
     
    Last edited: Jun 13, 2009
  12. Jun 13, 2009 #11
    The real problem with multiverse theories is Mach's principle: for something to exist, it must interact with us continually (for example, virtual and real particle exchanges). Shall we say those other universes exist when they never interact with us? Can something continue to exist ~between~ the times it interacts with us (where is a neutron between two consecutive transfers of virtual photons)? If I create a machine that causes all interactions with an object to cease, have I destroyed the object? Also, some of the multiverse theories are based on the notion that there are such things as continuums and manifolds--which are strictly classical concepts. The universe is discrete. Just ask Zeno. We laugh at Zeno because he's old and quaint. But he's also right!--there's no such thing as a continuum.

    Of course, it might be that another universe IS interacting with us continually in some subtle way.
     
  13. Jun 13, 2009 #12
    So if the universe is infinite and there is indeed an infinite amount of energy, then we dont have to worry about the heat death scenario?
     
  14. Jun 13, 2009 #13

    marcus

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    Heat death is just as relevant in either case. Finite or infinite doesn't matter. What matters is density. And quality of energy.

    In either case, finite/infinite, expansion can go on indefinitely and matter can keep on getting more and more sparsely spread out.
    And civilizations (if you think about such things) can gradually utilize all the available sources of useful energy,

    Energy never gets used up, the high-grade energy gets utilized and becomes low-grade heat. Still the same amount of energy but can't do anything with it.

    This happens regardless of whether space extends infinite or whether space extends finite.
     
    Last edited: Jun 13, 2009
  15. Jun 13, 2009 #14
    For a related theory, see my nearby post CYCLIC MODEL OF THE UNIVERSE here in Cosmology.....the authors propose a repeating series of "bang" creations of finite size....

    Separately, I thought the total energy in the universe was zero...with matter radiation and so forth offset by negative gravitational potential....so I assumed whether infinite or finite makes no difference....forget where I came across that concept....

    And I don't believe I ever figured out how such "zero total energy" works in different frames of reference....
     
  16. Aug 21, 2009 #15
    Last edited by a moderator: Apr 24, 2017
  17. Aug 24, 2009 #16

    Chronos

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