The Universe - infinite or not ?

  1. drag

    drag 1,341
    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. Yes...
     
  4. 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. I can't agree with you more, Mentat. I would say, maybe, that the universe is on the verge of infinity?[?]
     
  6. 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. 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. universe = ?
     
  9. 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. russ_watters

    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. universe = space ?
    or
    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. The big bang does not say the universe is finite or infinite.
     
  13. 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. 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. 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. 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. 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. 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. 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. Are you sure that's not just an accelerating universe?
     

  21. How about the big crunch?
     
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