Finding center of universe

  1. can we find the center of the universe by measuring the deviation from theoretical value of the shape of comet's orbit when compared to real shape of comet's orbit.
     
  2. jcsd
  3. phinds

    phinds 8,736
    Gold Member

    There is no center to the universe.

    The OBSERVABLE universe has a center, and you are it.

    EDIT: you would likely find it informative to read the FAQ in the cosmology section
     
    Last edited: Nov 8, 2012
  4. Are we moving relative to the observable universe?
     
  5. phinds

    phinds 8,736
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    Wherever you are, you are the center of the observable universe, so no, we are not by definition.

    EDIT: you would likely find it informative to read the FAQ in the cosmology section
     
  6. we know that universe was created after big bang occured. then the universe would have been a point and started expanding in all direction then it have looked like a spherical ball whose surface is expanding a center. so it is meaningful to talk of center of universe isn't it
     
    Last edited: Nov 8, 2012
  7. Where's the center of a point?
     
  8. sorry. i have edited my posting now.
     
  9. phinds

    phinds 8,736
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    Absolutely not. The big bang was most emphatically NOT a point. It happened everwhere and there is no center and no edge.

    This is a bit hard to get your head around when you first hear it, but it is the case. You should read more cosmology. Try the FAQ in the cosmology section.
     
  10. Chronos

    Chronos 9,974
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    The premise the universe began as an infinitesimal point is illogical on two counts:
    1] If the universe is infinite, it was infinite from the beginning. Only the observable universe would be point-like at its inception.
    2] Unless the big bang occured in some kind preexisting space, the size of a point is undefined in the absence of external spatial coordinates.
     
  11. phinds

    phinds 8,736
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    I agree w/ what you are saying, except that I see the bolded statements as mutually contradictory. If the current observable universe started off as a dimensionless point, then it seems to me that so would have the entire universe. The observable universe likely started off REALLY small, but not as a point. Perhaps that's what you intended by "point-like" ?
     
  12. Maybe it would help to think of the universe as a big balloon. Right now we think the balloon is about ~50 billion LY 'across'. Now, going back in time, the universe gets progressively smaller and so does the balloon. The thing is, we have to think of ourselves as being on the surface of the balloon so we don't really have a center, do we? But as the universe goes back further in time, at some point in time it was say, 1 cm across. It is still that same balloon and on the surface that same point looks the same as it does if it is 50 billion light years across, the angles all go out at exactly the same angle from a point on the surface, so it doesn't matter if the universe were one micron across or 50 billion LY across, we are still on the surface so there is no center we can find.

    The idea of the balloon shows us the universe has a curvature so if we had a spacecraft that could do say a trillion times the speed of light and travel in what we think is a straight line, we would come back to the same place after X amount of time, whatever that is, say at one trillion c, assuming the universe is actually 50 E9 ly across, we would come back to our solar system in about 20 minutes even though we thought we would be traveling in a straight line. Our straight line is really a very slow curve not even noticeable if we only went from here to the closest star, Alpha Centauri or thereabouts.
     
  13. I had this conversation with John Archibald Wheeler. How would you determine the center of mass of the observable universe, at least approximately?
     
  14. Chronos

    Chronos 9,974
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    That is essentially the issue addressed by my second assertion. An infinite ensemble of infinitesimal points would collectively, and individually, be spatially undefined.
     
  15. phinds

    phinds 8,736
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    Ah ... an interesting way to look at it. I had not considered it that way before. Thanks for the clarification.
     
  16. phinds

    phinds 8,736
    Gold Member

    The approximate center of mass of the observable universe is wherever you are. Given homogeneity, I'd say the approximation is quite accurate.
     
  17. Not really. You are imagining the universe as an expanding ball, which is probably in error. The Poincare Conjecture yields possible hints about the topology of our universe. You would be better off imagining our universe mapped to the surface of a ball, like the surface of the earth. Some people used to think Vatican City, Rome, was the center of the world. Others thought it was in Ireland. Bad points could be made for either. If the earth were a perfect sphere, no matter where you were the horizon would appear equidistant in all directions, giving you the illusion you were at the center. But if you were to travel far enough in a straight line, you would return to your starting point.

    The topology of our universe is probably much like that. Also, as the sphere expands, objects appear to recede from you--just as they do in our universe at large. No point on the surface of this sphere may rightly be considered the center. But we COULD possibly use the word "center" to describe a point in time, roughly 13.7 billion years ago...
     
  18. This is a good explanation supplemented with a visual example: (Skip to 8:20)


    https://www.youtube.com/watch?v=3pAnRKD4raY
     
  19. phinds

    phinds 8,736
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    Nicely done video but I am at a complete loss to see how it has ANY bearing on this thread. What am I missing?
     
  20. Admittedly, I was responding less to the original post and more to the first post (your post) about how wherever one is in space, one is always at the centre of the universe, and I thought a visual example of the Cosmological principle would be helpful to laymen like myself. Did you skip to 8:20?
     
  21. phinds

    phinds 8,736
    Gold Member

    I watched the whole thing, thought the emphasis on black holes made it irrelevant to this thread even though there was some discussion about the center.
     
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