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Is the universe like a balloon?

  1. May 5, 2008 #1
    Some physicists have told me that the universe is like the surface of a balloon. Does this mean that if it were possible to travel at an infinite speed, you'd come back to the same place if you travelled straight in one direction?
     
  2. jcsd
  3. May 5, 2008 #2

    russ_watters

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    Yes. As you imply, though, there are some physical limitations that prevent you from doing it in reality.
     
  4. May 5, 2008 #3
    So the universe does not actually have an end? Why do astronomers then constantly refer to "the end of the universe"?

    And how is it possible (in theory) to return to the same point? Does this mean that the universe is bent in a fourth space-dimension that we cannot sense?
     
  5. May 5, 2008 #4

    DaveC426913

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    I've never hears an astronomer use that term unless they were tlaking about its end in time.

    Precisely.
     
  6. May 5, 2008 #5
    Wow, that's amazing! How do we know that? Or do we? Could there be creatures living in 4D space, or is that only possible in 3D world?
     
  7. May 5, 2008 #6
    Also, is it true that all galaxies are at rest in space, while the universe (and therefore the relative distances between the galaxies) expands? Doesn't this mean that the universe is filled with a kind of expanding ether (space)?
     
  8. May 6, 2008 #7
    Both of your statements are correct as for as I know :)
     
  9. May 6, 2008 #8
    In fact the 4th dimension is the time dimension as thought by Einstein & his General theory of relativity.

    But you don't really have to look for some beings living in the 4th dimension because I think there are already many of them in the cosmos!!!
     
  10. May 6, 2008 #9

    DaveC426913

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    We don't. It's a model that helps explain many things we see, but we don't really have compelling evidence

    Only wild speculation.

    The galaxies are moving wrt each other, and as well, the space is expanding. There is no aether.

    There is no evidence to support this, but we are all free to hold our beliefs.
     
  11. May 6, 2008 #10
    I have a question relating to this...
    I saw that balloon analogy of the expanding universe. But there was something I was confused about. In the balloon analogy there were dots on the balloon and as the balloon was blown up and increased in size, the space between the galaxies increased. And that was the analogy of the expansion of the universe; The galaxies are moving away from each other because space is expanding.
    I realize that the balloon analogy is a simplified model but here is where my confusion lies. On the balloon if it were blown up the dots (representing galaxies) would increase in size, and thus the relative distances apart would stay the same.
    So if space is expanding shouldn't the galaxies also be expanding, and if that is true would the distance apart not remain the same?
     
  12. May 7, 2008 #11
    So it is time that bends R^3 to a kind of 4D sphere?
     
  13. May 7, 2008 #12
    If I've got it right, the galaxies (dots) don't expand, even if dots on a balloon would expand. Only space itself expands. It is said to expand into nothing. I don't understand how that is possible.
     
  14. May 7, 2008 #13

    cristo

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    Indeed.

    I think what you mean here is that one does not need to look very far for a being living in the fourth dimension as per Einstein; that is, you are talking about the fourth dimension being temporal, as opposed to spatial. This may have caused some confusion in the thread.
     
  15. May 7, 2008 #14

    cristo

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    Time doesn't bend space: spacetime is one entity that gets deformed.
     
  16. May 7, 2008 #15

    cristo

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    kasse has got it right here: the dots in this analogy do not expand. It is perhaps a better analogy to think of sticking pieces of paper, or pennies onto the balloon to represent gravitationally bound systems.

    There is no need for there to be anything for the universe to expand into. The analogy starts to break down when you think about what the balloon is expanding into.
     
  17. May 7, 2008 #16
    What bends spacetime then? A fourth spatial dimension?
     
  18. May 7, 2008 #17

    DaveC426913

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    A better model for the analogy is, instead of drawing dots on the balloon, to glue pennies into it. As the balloon expands, the pennies do not. The solidity of the penny's metasl easily overwhelms the weak force of the balloon expanding. Likewise, the gravity of a galaxy easily overwhelms the weak force of space expanding.

    [ Edit: Sorry, missed Cristo's post saying the same thing]
     
  19. May 7, 2008 #18

    DaveC426913

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    Gravity.
     
  20. May 7, 2008 #19
    I apologize for not completing my statement... I meant something totally different...

    I was trying to say no need to search for beings living in the 4th dimension since we have enough living organisms in our surroundings!!! just joking don't take it serious :)

    Regards,

    Mubashir.
     
  21. May 9, 2008 #20
    The universe is not like a balloon.
     
  22. May 9, 2008 #21
    Your question first needs to define what is space-time. How would having a forth spatial dimension by itself bend space-time.

    Some people view space as nothing. If that is the case then what does bending nothing mean? I personally believe it to be something.

    Personally, and I am not sure if it is agreed to by the mainstream, I believe that space-time can not exist void of energy. So space is itself a manifestation of energy. The landscape of space-time is molded based on how much energy is condensed in a specific location.

    Now about your 4th spacial dimension. I have also had similar thoughts although again I am sure the mainstream would not agree but I believe that somehow a hidden dimension is involved in the curvature of space-time. This dimension somehow controls the the compression of space as it is near an energy source. However I am not sure that I even convince myself about this let alone anyone else. But in any case it is not enough just to say that if there is a 4th spacial dimension that the 4th dimension will create the curvature of space.

    I am reading a little about string theory at the moment and they seem to be high on dimensions, particularly about very small ( plank length ) dimensions that are too small for us to notice.
     
  23. May 9, 2008 #22
    its more like a balloon-only, without the balloon
     
  24. May 10, 2008 #23

    No it is nothing like a balloon. Remember that portions of our universe are expanding faster than the speed of light away from us. Even parts within our visible universe are and have always been speeding away from us at faster than the speed of light.
     
  25. May 11, 2008 #24

    DaveC426913

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    The balloon analogy simply serves to dispel a particular misunderstanding. It shows how space can expand, causing increasing distance between them, while not causing the expansion of the things within it.
     
  26. May 11, 2008 #25
    The string theory isn't a scientific theory, right? As it's not falsisiable.
     
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