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Universe is nothing?

  1. May 5, 2015 #1
    Dear PF forum,

    I once read that the universe IS nothing. And "FROM", too.
    But I like to ask about "IS".
    They say that "Gravity" is negative energy. So if you add all the masses and energies and gravity, it would be zero.
    What I'd like to ask is this.
    A. Is all Mass + Energy + Gravity = 0?
    B. Is all Mass + Energy + Dark Matter + Dark Energy + Gravity = 0?
    C. Is all Mass + Energy + Dark Matter + Dark Energy + x + Gravity = 0?
    - Is there any other factor beside Mass + Energy + Dark Matter + Dark Energy + Gravity?
    - If so, what is "x"?
    D. Or we should say X + Y = 0?
    - Is the factors is correct? What is X + Y produces zero? Is that Gravity? Mass? Energy? Something else?
    E. How is Gravity" negative energy? (if this is true)
    F. Is it true that the universe is "nothing"? (Remember, I'm not asking about "from", but "is" :smile:)

    Thanks for taking some efforts to answer


    Steven
     
  2. jcsd
  3. May 5, 2015 #2

    PeterDonis

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    The concept of "gravitational energy" can only be defined in certain situations. In the case of cosmology, it only works if the universe is closed (so that it has finite spatial volume). (AFAIK this model also only works if there is no dark energy; see below.) To the best of our current knowledge, our universe is not closed, so this kind of model does not apply to our universe.

    Even when the model does apply, it doesn't really tell you anything. It gives an equation for something that can be called "total energy of the universe" and says that it is zero. But this equation is really an identity; it doesn't tell you anything about the dynamics of the universe.
     
  4. May 5, 2015 #3

    Chronos

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    The zero energy universe is basically an accounting trick.The idea came out of quantum physics where particles and anti particles can spontaneously pop into existence for a short period of time limited by their mass. See http://www.webcitation.org/6SOdzjRHd for discussion.
     
  5. May 6, 2015 #4

    bapowell

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    It's maybe more correct to say that the universe is flat to within half a percent. That's not the same as knowing that it's not closed.
     
  6. May 6, 2015 #5
    Hello again Bapowell. Thanks for taking effort answering me.
    You've answered my question about Observable Universe, remember? :smile:

    Hello Chronos, glad to meet you again. Last time you've responded to my posting "Big Bang Temperature and Observable Universe"

    Hello PeterDonis. Is it true if that the total energy of the universe is really zero?

    Anybody?

    Thanks for giving me answer then and later :smile:
     
  7. May 6, 2015 #6

    bapowell

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    Hello, Stephanus. This is not currently known. As Peter mentions above, the concept of "total gravitational energy" only applies in select circumstances. If the universe is closed, it can be said to have zero total energy; however, we don't know the global geometry of the universe because we can only observe the geometry of the observable universe. The observable universe appears flat to a high degree, but this is only a local probe.
     
  8. May 7, 2015 #7

    Chronos

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    Einstein insisted the universe must be closed after realizing his field equations were otherwise ill behaved.
     
  9. May 7, 2015 #8

    PeterDonis

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    Ill-behaved in what way? The current best-fit cosmological model has the universe being spatially infinite, and the EFE works fine.
     
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