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Not the centre of the universe.

  1. May 4, 2005 #1
    I'm having trouble getting my head around the universe not having a centre, can anyone maybe explain it to me or give me a good analogy or something? I need another "Ahhh, I geddit!" moment (better than sex. Sometimes o:) ). I can feel it teetering just on the edge of my mind... BTW, I wasn't really sure where to post this topic, sorry if this is the wrong place for it.
     
  2. jcsd
  3. May 4, 2005 #2
    Ok. It was once said tht the universe is infinitly big. If this is so then it is impossible to define a centre. Thats just one theory
     
  4. May 5, 2005 #3
    the general acceptance of time and the universe, now, is that they are finite but have no "barrier". So, maybe there's no center of the universe because it just isn't like how we imagen it: like a round circular ball. maybe it's open, flat, curved........
     
  5. May 18, 2005 #4
    Hmmmm.... But still....Nope, it's blagging my 'ed. Is it even possible for me to be able to conceptualise this? Or is it something that'll take a lot of studying for me to grasp?
     
  6. May 18, 2005 #5

    Pengwuino

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    I dunno how closely the two are related, but do we know where the big bang might have taken place?
     
  7. May 18, 2005 #6

    JamesU

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    I don't know if that's a good way of explaining it. There are an infanite amount of positive and negative numbers, but we can define a middle, zero
     
  8. May 18, 2005 #7

    Pengwuino

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    But theres no "negative" universe.
     
  9. May 18, 2005 #8

    JamesU

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    How do we know what's negative and what isn't? "negative" numbers are a way of explaining other numbers than the normal ones.
     
  10. May 18, 2005 #9

    Pengwuino

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    theres nothing abnormal about a negative number though. Also, unless we can define what a negative universe is, theres no way of figuring out where the negative and positive universe converge like we do with numbers.
     
  11. May 18, 2005 #10

    HallsofIvy

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    I can settle that for you very simply: of course, the universe has a center: I am the center of the universe!
     
  12. May 18, 2005 #11
    :rofl: :rofl: I so badly wanted to make that joke but I was worried it might make the question look like an elaborate set-up!
     
  13. May 18, 2005 #12
    its prolly a GR reference...every frame is moving except the Empty space frame...but then some people don't believe there exists this empty space so no center of universe =]
     
  14. May 18, 2005 #13

    honestrosewater

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    Do you mean there is no center of expansion? There is a common balloon analogy which is nice (of course, like most analogies, if don't read too much into it). Have you heard it? Edit: Oh, there is another 3D analogy with raisins in dough.
    This looks like a good explanation.
     
    Last edited: May 18, 2005
  15. May 19, 2005 #14
    It should be: There is no center of expansion.


    There is probably a center of the universe. But it is a meaningless point in space. But space is also too big to find it so no one cares. And with relativity it is even harder to find it because time (dilation) makes everything very confusing.
     
  16. May 19, 2005 #15
    I ain't saying you're wrong, but that is very contrary to everything I've ever read. The universe is expanding from a point, and as such, every point in the universe was once in this point.
    Einstein believed space to be infinite but bounded... if you could head in a straight line for long enough you may end up back where you started. I don't think everyone agrees on this.
    The balloon analogy, as long as you don't take it too literally, is still the best I reckon. A balloon's surface expands as you blow it up - but where is the centre of the balloon's surface? Nowhere - every given distance on the surface balloon is expanding at the same rate as any other equal distance.
    I used to transfer this analogy to the universe and think that the universe is expanding into a fourth spacial dimension, but apparently I was very wrong. Then I thought it was expanding into the time dimension but that's probably no better. That's no doubt why they say not to take the balloon analogy seriously.
     
    Last edited: May 19, 2005
  17. May 19, 2005 #16

    honestrosewater

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    If you suspect the center of the universe probably exists, would you share your definition of it? For instance, the center of a line segment is the point equidistant from its endpoints.
    Wouldn't that point then be the center of expansion? As I understand things, galaxies are not moving through space as pieces from an explosion would move through the air. Rather, the space between galaxies is itself expanding. But I'm not a physicist, astronomer, or cosmologist, and there are plenty of them around here to straighten it out.
    I think most confusion about the balloon analogy results from it being a 2D model of a 3D concept. People forget or don't realize this and think the center of the 3D balloon would be the center of the universe or other such extrapolations.
     
  18. May 19, 2005 #17
    I wonder what you read or if you misunderstood me. If space is unbounded and finite (so the other way you think Einstein claimed it is, because that doesn't make sense to me. I think you flipped them around.) it is 3d surface on a 3d object. Like a 2d surface on the 3d sphere(ballon).

    This is incorrect. It didn't expand from a point, the point itself expanded.

    You can take it quite literally.


    Now about expanding. When the universe is expanding no object is moving in space. The universe as a whole is changing. All the universe is stretched. The space inbetween the galaxies grows bigger because of this stretching. You could say the universe is the same shape as before the big bang, only bigger. So the universe isn't expanding, its being stretched. (Except, it will not snap back.)

    An inflating balloon does not expand from a point. Every point on the balloon itself expands.

    I am not sure what you mean by this. Unless an object is frozen in time(its own time, not some other frame of reference its time), which has never been observed, it is already moving in the time dimension.

    About the center of the universe. Since we do not know the shape of the universe we do not know if it has a center. It might have, but its pretty meaningless in itself. It has no function. Its just a point in empty cold dead space.
     
    Last edited: May 19, 2005
  19. May 20, 2005 #18
    Mmm. Did I get my words mixed up? Whichever is akin to a line on a circle. I thought that was infinite (you can go on and on forever) but bounded (you may come back to where you started). In what way is a 3D surface on a 3D object like a 2D surface on a 3D object?

    Okay, I think we mean the same thing, but perhaps saying them in ways that make sense to us. A singularity is dimensionless, so it has no dimensions to expand, hence I put it the way I did. But I think we have the same picture in our heads.

    Dammit, can I or can't I? I get different answers from different people. Last thing I was told is that the balloon analogy can't be taken too literally as its 2D surface is wrapped around a 3D volume. If the analogy held, the universe would be a 3D space volume wrapped around a 4D space... (what's the word for 4D spaces?). I was told this was incorrect, and that there is no fourth spacial dimension that we are expanding into or around. Harrumph!

    Okay, this is getting a little far-fetched. The universe isn't expanding? Are you sure that's the consensus? I have not heard of the stretch model of the universe. Also, saying the universe, a 3D volume, is the same shape as the singularity, a 0D point, would not to me seem logical. Furthermore, "before the big bang"? What before is there? I think you're kind of going out on a limb here.

    I don't get it... you say the balloon analogy holds, but the surface of the balloon does not have a centre. Then you say the universe may have a centre.
     
  20. May 20, 2005 #19
    I'm not quite sure this has been posted before but the way I learned the universe has no centre is like ths:

    It's basicly all down to special relativity. Saying that you cannot ever be sure of the fact that you are standing still, since there's always another reference frame in witch you are moving. Now, if there would be a centre of the universe it would be perfectly standing still, simply because a centre of any body could ofcourse never be moving around, even not when the body itself is expanding. Second of all, if it was possible to actualy stand inside this centre it would be possible for you to determine if something is, or is not moving because your view from the centre of the universe would be something like an absolute reference frame of the universe. Einstein says this is not possible. If you would be flying around in your spaceship and you would get to what you think is the centre of the universe you would not be able to tell wether it is you who is moving or that it is the centre of the universe that is moving. But since the centre of the universe cannot be moving, and can never be sure of your own movement, this problem cannot be solved.

    So if you accept special relativity you must accept that there can be no such thing as a centre of the universe.
     
  21. May 22, 2005 #20

    mathwonk

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    does the euclidean plane have a center? does it bother you?
     
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