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The Universe - infinite or not ?

  1. Mar 16, 2003 #1


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    Science Advisor

    Greetings !

    Well, I'm just a poor amatuer.
    This is the thread for you - the experts, to argue
    about it (at lenght, I hope :wink:) and for us to read your
    words of wisdom.

    Live long and prosper.
  2. jcsd
  3. Mar 17, 2003 #2
  4. Mar 17, 2003 #3
    As everyone from the original PFs knows, I do not think the universe is infinite. This is on account of the abundant proof of the BB theory (which rather clearly states that space itself is expanding, which leads me to believe that it cannot already be infinite (since something that is infinite cannot get any bigger)).
  5. Mar 17, 2003 #4
    I can't agree with you more, Mentat. I would say, maybe, that the universe is on the verge of infinity?[?]
  6. Mar 17, 2003 #5


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    Logically, there is no problem with an expanding infinite universe. If there was, physicists and mathematicians would love to know why. Intuition is not logic.
  7. Mar 18, 2003 #6
    I often agree with you Mentat but not here. I have long suspected the universe is finite but I'm having second guesses. Anyway, I never believed it to be an absolute fact. I believe in the big bang as well. However, cosmology allows for the big bang to work even with an infinite universe. The universe simply needs to have infinite size at its creation. A singularity of infinite size AND infinite density. It's weird I know.
  8. Mar 18, 2003 #7
    universe = ?
  9. Mar 18, 2003 #8
    Is the universe infinite? Well, according to the evidence, the answer is ... we don't know. And unfortunately, this may be the best answer we'll ever get. While the curvature of the universe is something that we might get a precise fix on (the data suggest a flat universe, i.e. no spatial curvature), the global topology might never be known because of the smallness of our Hubble volume. And the global topology is just as important as the curvature is in determining the size of our universe.
  10. Mar 18, 2003 #9


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    Staff: Mentor

    No... ;)

    We can detect measure the velocity of galexies quite a long distance away. The evidence we have now certainly suggests a BB like event and a finite but boundless universe.
  11. Mar 18, 2003 #10
    universe = space ?
    universe = space-time-and-so-on ?
    And...how could we find out that the universe is infinite or not ?
    Give a method...even if it's impossible to be realised...
  12. Mar 18, 2003 #11


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    The big bang does not say the universe is finite or infinite.
  13. Mar 18, 2003 #12
    Well, you are entitled to your opinion. However, to say that there can be a singularity of infinite spacial extent is contradictory, and makes no sense to me.
  14. Mar 18, 2003 #13
    You know what, you bring this up a lot, but I still disagree. Sure, BB theory may not say which it is - but isn't the idea behind the BB, that the spacial dimensions themselves are expanding? If so, then the universe cannot already be infinite, because the spacial dimensions couldn't possibly get any bigger.
  15. Mar 18, 2003 #14
    Well, for all practical purposes, it may have the potential to continue expanding infinitely. However, it will never reach infinity (if it is finite now), and so cannot really be "on the verge of infinity".
  16. Mar 18, 2003 #15


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    The important thing seems to be that expansion does not necessarily make the universe larger. This is one of the weird things you get from infinity, but it does not seem to have an inherent problem. As you noted before, each region in an infinite universe is infinitesimal compared to space as a whole. That is, each point is pretty much zero compared to the universe.

    Within any region, local expansion occurs where distances between points increases. But even though local expansion is occuring within the region, the size of that region is infintely small compared to the whole universe - and always will be. There is nothing preventing local expansion from occuring, and the size of the universe never changes. Again, this is because of the nature of infinity.
  17. Mar 18, 2003 #16
    AN IDEA!

    The universe(universe=everything) is infinite, but the spacial demensions are the ones expanding into the actual universe. It's like, what is the universe expanding into? Well, lets substitute "universe" as "subuniverse". So it's what is the subuniverse expanding into? the actual universe. I hope you understand what I mean(as I am having a hard time describing this).
  18. Mar 18, 2003 #17
    I agree with Eh, although not necessarily in the way he explained it. To me it is much simpler. An infinite number is not "the biggest number possible." An infinite number, actually, has an infinite amount of room to grow. You can add, divide, multiply infinities together and you get back another infinite number. If you didn't, you'd get all sorts of paradoxes in mathematics.

    Mentat, by saying an infinite universe can't get any bigger, you are saying an infinite universe has no more room to grow. You are implying that the universe has to have space to grow into. You know that is not the case.
  19. Mar 19, 2003 #18
    Olivers bells thesis 201 says that a universe can not expand without stretching and bursting causing a catastrophic wave of death and destruction of neutrinos and protons, the force of the rip will be 1.00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001*10Exp
  20. Mar 19, 2003 #19


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    Are you sure that's not just an accelerating universe?
  21. Mar 19, 2003 #20

    How about the big crunch?
  22. Mar 24, 2003 #21
    No, I never said that it was because it didn't have room to grow into. I said that it was because it was as big as it could possibly get.
  23. Mar 24, 2003 #22
    Re: AN IDEA!

    This is very near (if not identical) to one of the BB theories, that people bring up quite a bit, especially in threads about the incompatibility of infinite universe with BB theory.
  24. Mar 24, 2003 #23
    I understand all of this, I was talking about the idea that the spacial dimensions themselves are expanding. I had thought that this is what BB theory was all about. If this were the case, then the universe could not be infinite.
  25. Mar 24, 2003 #24
    CJames, infinity is not the biggest that you can get mathematically. But is the biggest that you can get physically.
  26. Mar 21, 2009 #25
    you gotta think outside the box man. like the universe can grow and grow. but like, what is it growing in? yknoe, what outside this box man, is the universe square? and outside of each wall is there an equal and opposite universe, or if its a circle, it wouldnt matter if you left te universe and looked at it because it wouldnt be there, you would be in a place where time and space didnt exist until you got there, and you would float forever thinking until you turned into your own universe, and you were the creator man. i swear i dont knoe what im talking about man. lmao.
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