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Thread: edge of universe

  1. #1 edge of universe 
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    I know the idea of the universe having an edge is usually easily and quickly dismissed but hear me out. From what I've read and heard there's a lot of evidence that the universe is flat (please tell me if I'm wrong), and if the big bang theory is correct (not much controversy there) it would seem to imply that the universe could not be infinitely large. Given that those two things are true then it seems to me that if you traveled through space in a straight line for long enough you would end up at some kind of boundary. Ending up where you started is not possible if the universe has no curvature, and if space is not infinite then neither would you stay within it forever. Am I wrong?


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  3. #2  
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    If space has no curvature you would probably come to some kind of boundary. However I doubt you could egress that boundary in any meaningful sense. Presumably the normal laws of physics would not apply outside any boundary.

    Also, why is the universe not curved? Remember, people used to believe the Earth was flat and had an edge you could fall off.


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  4. #3  
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    We know within a 2% margin of error that the universe is flat. This is a result of empirical evidence from a confluence of sources.

    http://map.gsfc.nasa.gov/universe/uni_shape.html


    As for an "edge," it suggests that there is something "beyond" the universe... which doesn't make sense on even a semantic level since the universe... by definition... represents absolutely everything there is.
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  5. #4  
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    As for an "edge," it suggests that there is something "beyond" the universe... which doesn't make sense on even a semantic level since the universe... by definition... represents absolutely everything there is.
    I wish i had some better words to work with, replace "universe" with "area created by the big bang" and it makes more sense
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  6. #5  
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    The way I think you grasp infinites, medlakeguy, physics doesn't.
    A pong by any other name is still a pong. -williampinn
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  7. #6  
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    Quote Originally Posted by medlakeguy
    As for an "edge," it suggests that there is something "beyond" the universe... which doesn't make sense on even a semantic level since the universe... by definition... represents absolutely everything there is.
    I wish i had some better words to work with, replace "universe" with "area created by the big bang" and it makes more sense
    According to our current knowledge, both situations are exactly the same. Everything was created by the big bang. The idea that the universe is expanding into something, is a misconception.
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  8. #7  
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    According to our current knowledge, both situations are exactly the same. Everything was created by the big bang. The idea that the universe is expanding into something, is a misconception.
    yes, but if it's flat and bounded then that's the implication isn't it?
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  9. #8  
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    Quote Originally Posted by medlakeguy
    According to our current knowledge, both situations are exactly the same. Everything was created by the big bang. The idea that the universe is expanding into something, is a misconception.
    yes, but if it's flat and bounded then that's the implication isn't it?
    The universe is thought to be flat locally (LINK) i.e Euclidean in nature, but overall it still has curvature, ie. Minkowski spacetime, especially since that is what gravity is.
    Disclaimer: I do not declare myself to be an expert on ANY subject. If I state something as fact that is obviously wrong, please don't hesitate to correct me. I welcome such corrections in an attempt to be as truthful and accurate as possible.

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  10. #9 stupid impossibles. 
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    it would make more sense though wouldn't it if the universe wasn't flat as a boundary often imply s another side which then means infinite but then how can something be infinite because surely there is a limit.
    just wondering
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  11. #10  
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    Zendra - Please note that the universe has no need to be "understandable" nor to "make sense" to us pip-squeaky humans. Just because something is not intuitive does not mean it is untrue. The universe couldn't care less about what we think, or how we believe it should operate. 8)
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  12. #11 sorry 
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    ok sorry i just like to be able to understand things
    just wondering
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  13. #12 Re: sorry 
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    Quote Originally Posted by zendra
    ok sorry i just like to be able to understand things
    I have found that there is a limit to what one can understand with basic physics knowledge. To be able to understand past a certain point, you need some training. I don't like it when that happens, but thats just the way it is, so no need for you to apologize. :wink:
    Disclaimer: I do not declare myself to be an expert on ANY subject. If I state something as fact that is obviously wrong, please don't hesitate to correct me. I welcome such corrections in an attempt to be as truthful and accurate as possible.

    "Gullibility kills" - Carl Sagan
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  14. #13  
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    Quote Originally Posted by KALSTER
    The universe is thought to be flat locally (LINK) i.e Euclidean in nature, but overall it still has curvature, ie. Minkowski spacetime, especially since that is what gravity is.
    Well if it's not flat I guess that answers my question. I just had a thought here.

    If i understand it right we think the expansion of the universe is accelerating because distant objects appear more red shifted then they should. Couldn't curvature produce the same effect?

    forgive me if i just rambled
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  15. #14  
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    Quote Originally Posted by inow
    Zendra - Please note that the universe has no need to be "understandable" nor to "make sense" to us pip-squeaky humans. Just because something is not intuitive does not mean it is untrue. The universe couldn't care less about what we think, or how we believe it should operate. 8)
    It's only "us pip-squeaky humans", or a species, rather like us, possibly thousands, millions, or even billions of light years away, that will ever have a hope of explaining, or making sense of, the universe.
    Saying "the universe couldn't care less about what we think" etc. could be interpreted as meaning the same as saying a rock couldn't care less about what we think.
    However I do understand what you mean and carrying on, in the same vein, I would much prefer to accept the words (paraphrased) of George Wald when he stated that we are the attempt of the universe to understand itself.
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    If the universe is isotropic and homogeneous on large scales, then any two observers, at any two locations, would see the same thing (on large scales). This is the "cosmological principle" in a nutshell.

    http://en.wikipedia.org/wiki/Cosmological_principle

    If the cosmological principle holds, then there can be no observer that sees an "edge," since we do not see one, and we are observers too. This is the general argument against an edge to the universe.

    It follows that if there's no edge, then there cannot be a center.

    So the cosmological principle implies that there is no edge and no center to the universe.
    "... the polhode rolls without slipping on the herpolhode lying in the invariable plane."
    ~Footnote in Goldstein's Mechanics, 3rd ed. p. 202
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  17. #16  
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    Quote Originally Posted by Dishmaster
    According to our current knowledge, both situations are exactly the same. Everything was created by the big bang. The idea that the universe is expanding into something, is a misconception.
    Surely the opening post was about whether the universe had an edge or boundary and not whether it was expanding into something.
    As a layperson I do not find it difficult to accept the universe does not have a centre or that it is not expanding into "something". However I do find it harder to envisage the lack of an edge/boundary given that space was created 14 billion years ago and is therefore not infinite in extent.
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  18. #17 Re: edge of universe 
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    Quote Originally Posted by medlakeguy
    I know the idea of the universe having an edge is usually easily and quickly dismissed but hear me out. From what I've read and heard there's a lot of evidence that the universe is flat (please tell me if I'm wrong), and if the big bang theory is correct (not much controversy there) it would seem to imply that the universe could not be infinitely large. Given that those two things are true then it seems to me that if you traveled through space in a straight line for long enough you would end up at some kind of boundary. Ending up where you started is not possible if the universe has no curvature, and if space is not infinite then neither would you stay within it forever. Am I wrong?
    Maybe it expands at such a rate that you could have to travel faster than C in order to get ahead of the expansion enough to ever reach the edge. At least, that's one possibility. If it's true, then it would explain why there is a speed limit.
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  19. #18  
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    I find it odd that most people say the universe is not expanding into anything, for it makes no sense, really (not that pesonal incredulity is ever a good starting point). If the universe as we know it is just part of something far larger, then the need to describe it as expanding into nothing is not required. That something could be another dimension or whatever rather than just empty space as would first spring to mind. For example, what is the nature of the "space" that these theoretical branes are supposed to live in like?
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  20. #19  
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    Quote Originally Posted by Dishmaster
    According to our current knowledge, both situations are exactly the same. Everything was created by the big bang. The idea that the universe is expanding into something, is a misconception.
    Perhaps it is expanding into something that was previously there. Maybe as the universe expands it replaces the "area" or "space" that the other thing once occupied.
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  21. #20  
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    Quote Originally Posted by inow
    As for an "edge," it suggests that there is something "beyond" the universe... which doesn't make sense on even a semantic level since the universe... by definition... represents absolutely everything there is.
    "Beyond" the universe may have different laws by which it operates since we often use the expression "the laws of the universe", which implies that a universe is defined by its laws. I think "reality" represents everything that exists, but "universe" does not unless all that exists is this universe with this set of laws (and characteristics).
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  22. #21  
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    We should all know, if theres one universe, theres a million more out there, long ago people thought there was one moon out there, soon they discovered there were more moon than they are people on the earth, the same goes for anything else, the problem is getting to those universes...
    the more science you know, the less crap you get.
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