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Do we live in an open universe

  1. Oct 5, 2012 #1

    wolram

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    This paper seems to say so http://arxiv.org/pdf/1210.1183.pdf, so does this mean heat death or the big rip is assured end of the universe?

    Edit.
    From Wiki.
    If Ω < 1, the geometry of space is open, i.e., negatively curved like the surface of a saddle. The angles of a triangle sum to less than 180 degrees, and lines that do not meet are never equidistant; they have a point of least distance and otherwise grow apart. The geometry of such a universe is hyperbolic.
    Even without dark energy, a negatively curved universe expands forever, with gravity barely slowing the rate of expansion. With dark energy, the expansion not only continues but accelerates. The ultimate fate of an open universe is either universal heat death, the "Big Freeze", or the "Big Rip", where the acceleration caused by dark energy eventually becomes so strong that it completely overwhelms the effects of the gravitational, electromagnetic and strong binding forces
     
    Last edited: Oct 5, 2012
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  3. Oct 5, 2012 #2

    phinds

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    The practical differences between the big rip and the big freeze are negligible and they are both very bad, so I'm planning on being elsewhere when it happens.
     
  4. Oct 6, 2012 #3

    Chalnoth

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    Let me just say that I am immediately skeptical of anything coming from somebody who won the Templeton Prize....

    More on topic, though, as long as the dark energy continues to act like a cosmological constant (which seems most likely), whether the universe is slightly open or slightly closed is irrelevant to the future fate of the universe, as it will be driven asymptotically towards flatness.
     
  5. Oct 7, 2012 #4
    I think the difference is pretty big. Big rip is essentially a singularity while big freeze is just nothing happening.
     
  6. Oct 7, 2012 #5

    phinds

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    Again, in PRACTICAL terms, there is no difference (to a human). Dead is dead.
     
  7. Oct 7, 2012 #6

    Chalnoth

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    Well, in practical terms it's irrelevant because neither will happen before we all die anyway.
     
  8. Oct 7, 2012 #7

    phinds

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    Gosh, do you think maybe that was my POINT? Do any of your friends ever ask you if you have a sense of humor?
     
  9. Oct 7, 2012 #8

    Chalnoth

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    The way you said it (in both posts) made it sound rather like you were saying that heat death/big rip would cause our deaths, but it wouldn't matter because either way we'd be dead.
     
  10. Oct 7, 2012 #9

    phinds

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    Yes, that is EXACTLY what I was saying. I can see that my attempt at humor was a flop.

    How could you possibly interprete "I plan on being elsewhere" as anything but humor? Do you really think I believe that either event will happen in our lifetime?
     
  11. Oct 7, 2012 #10

    Chalnoth

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    Sarcasm/facetiousness very frequently doesn't come across well in writing.
     
  12. Oct 7, 2012 #11

    phinds

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    Yeah, I though it would in this case, but you're right that it often doesn't.
     
  13. Oct 23, 2012 #12
    If you continue by letting your unconscious answer that, can you notice, “How do you know the difference?”
     
  14. Oct 24, 2012 #13

    Garth

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    Well, according to the OP link, by the existence of significant magnetic fields in the universe today, that require primordial seeding.
    This isn't about the the 'Big Rip', or any other imaginative conjecture, but about a 'local' observation that seems to test whether the universe is open or not.

    Garth
     
    Last edited: Oct 24, 2012
  15. Oct 27, 2012 #14
    How is the big rip a singularity? What exactly becomes singular?
     
  16. Oct 27, 2012 #15

    Chalnoth

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    The expansion becomes infinite in rate in a finite amount of time.
     
  17. Oct 27, 2012 #16

    Chronos

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    I share your doubts, Chalnoth, nothing can increase from finite to infinitely large in a finite amount of time. Of course, logic forces me to concede nothing can go from finite to infinitely small in a finite amount of time.
     
  18. Oct 27, 2012 #17

    Chalnoth

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    Well, I think there are even bigger problems before we go that far. After all, we might simply conclude that the Big Rip ends at some finite time before the singularity. It's the difficulty in even getting that far that is a more relevant criticism.
     
  19. Oct 27, 2012 #18
    I'm still not sure what that has to do with a singularity. Is this different from a gravitational singularity?

    Edit: I just did some reading and it appears that it's the observable universe that gets infinitesimal. Is that what's meant by "singularity?"
     
    Last edited: Oct 27, 2012
  20. Oct 27, 2012 #19

    Chalnoth

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    A singularity is a point of infinite density. The entire universe would have infinite density at the big rip.
     
  21. Oct 27, 2012 #20
    That seems very counter-intuitive. Wouldn't expansion cause the Universe to become less dense as it is doing now rather than more dense, much less infinitely dense? And how would the expansion rate become infinite? What does that even mean?
     
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