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B What is seen from the farthest star?

  1. Feb 2, 2017 #1
    Imagine someone in a planet at the farthest star of the farthest galaxy from ours. From that planet would the sky be a half black and the other half full of galaxies? Could a star be at the "edge" of the universe or general relativity contradicts that?
     
  2. jcsd
  3. Feb 2, 2017 #2

    russ_watters

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    General Relativity contradicts that; the universe looks basically the same no matter where you are. There is no edge.
     
  4. Feb 2, 2017 #3
    If that is true, then wouldn't that mean that the big bang that created our universe is one of many or could be inside of another bubble created by an older big bang that could be inside an even older big bang, so on and so on?
     
  5. Feb 2, 2017 #4
    Why would it mean that?
     
  6. Feb 2, 2017 #5
    There are some theories suggesting that our observable universe could be part of a larger 'multiverse'.
    However that is not necessarily true and there is no hard evidence of it.
     
  7. Feb 2, 2017 #6
    If the answer to the original question is that no matter where I stand in the expanding bubble of matter and energy created by the big bang, I see the same thing, stars galaxies and whatever, even on the very edge of that bubble, then what I look out onto beyond the bubble must have been created by a different big bang, right?
     
  8. Feb 2, 2017 #7
    That is assuming there is something outside the bubble to look out onto.
     
  9. Feb 2, 2017 #8
    Imagine you tried this with your position on a globe of the Earth. There is a "farthest point" from you, but there is nothing special about it. And you are at the farthest point from that point: Any direction you walk in would bring you closer to that point.
     
  10. Feb 2, 2017 #9
    Let's perform a thought experiment. Imagine that the Universe was smaller, only Laniakea, or even smaller, only the Local group. In this case you could be at the far edge of Andromeda and see the dark emptiness, unless you saw the Milky way on both sides. (In case that the Universe is closed, something that I don't know if is proven). It would be great if someday a telescope could see a pattern of let's see the southern universe looking at the northern universe.
     
  11. Feb 2, 2017 #10
    infinite, seem to sum this question up
     
  12. Feb 2, 2017 #11
    It's possible the edge of the observable universe is actually the edge of the entire universe. We can't see any further than 46 billion light years in any direction and really don't know for sure what's behind this horizon. However, the consensus is that we wouldn't find anything special out there.
     
  13. Feb 2, 2017 #12

    Drakkith

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    There is no expanding bubble. The expansion of space means that the distance between all unbound objects increases over time. Stop and think about that for a moment. Any object without a sufficient attractive force will, over time, move away from you. If you instantly moved 1 billion light years away you will still see objects moving directly away from you, including the location you used to be at. After moving to this new location, you lose sight of some objects that you used to be able to see in your previous location (because you've moved and their light has not had time to reach your new location yet) but you will find that new objects have now been brought into your field of view. These new objects couldn't be seen in your previous location, again because their light hadn't had time to reach that location yet.

    No matter where you go you will find the above holds true. Objects not bound to you will always be moving directly away from you and you will always find new objects entering your view as you move around the universe. This is, of course, only true if the universe is infinite in size. If not, then you may eventually come back around to your previous location (despite having moved directly away from it the whole time) or something else may happen. Current observations rule out a finite universe smaller than a certain size, with that size being some amount much larger than the observable universe. I confess I don't have a number for you.

    Additionally, please note that the big bang did not occur at a single point in space. The singularity (if it ever actually existed) existed throughout the entire universe at the same time.
     
  14. Feb 2, 2017 #13
    I agree that it is possible that what we can see is all that there is to see. It's also just as possible that it's not. I thought roughly 14 billion light years was as far as we could currently see.
     
  15. Feb 2, 2017 #14

    Drakkith

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    Such observations are already being done. So far we haven't seen the back of our own heads. :-p

    But seriously, these observations have yielded results supporting the idea that the universe is either infinite or much larger than the observable universe.
     
  16. Feb 2, 2017 #15

    russ_watters

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    You missed the last sentence of my post.
     
  17. Feb 2, 2017 #16
    Can you elaborate on that last statement? It seems to contradict most of what I have read, or maybe I didn't understand what I was reading. Either way, please explain.
     
  18. Feb 2, 2017 #17

    Drakkith

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    Yes, it is often stated that the big bang was an explosion from a single point. But according to my understanding this is not true. If we wind back time in our model of the universe, we will find that at t=0 the density of matter goes to infinity at every point in universe (which is still infinite in size). So the singularity, if it actually existed, would occur everywhere and essentially be infinite in size.

    I wish I could elaborate further, but I know very little about the details.
     
  19. Feb 2, 2017 #18
    I've never heard that before. I'd like to read about it. Can you give me a link?
     
  20. Feb 2, 2017 #19

    Drakkith

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    If I can find the thread(s) where I've seen this, I'll be sure to post a link.
     
  21. Feb 2, 2017 #20
    @Drakkith nailed it pretty well. Just because you are at the edge of the observable universe, which is relative to us on Earth, that doesn't mean you wont be able to see other matter in all directions. It is likely that the edge of the observable universe has its own observable universe that is relative to it, as @Drakkith stated that the universe is likely to be either infinite or much larger than our observable universe. As for the multiverse theory, if it did stand true, I'm not sure if you could see outside your own universe and into another. That seems beyond my current understanding of the universe. ?:)
     
  22. Feb 2, 2017 #21
    I completely understand that if I move to the edge of what we currently see I will have a new observable universe. That was never the question. Everything I've ever seen or read about the big bang explains it as a rapid expansion of energy from a singularity. From the size of an atom to a basketball in a planck second, expanding faster than the speed of light, because the expansion of space-time has no speed limit. The analogy of drawing stars on a balloon and blowing it up makes all the stars on it move away from each other, cool. If I'm on the surface e of the balloon and look up, what do I see?
     
  23. Feb 2, 2017 #22

    Grinkle

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    There is no edge. The universe looks the same no matter your position in-the-large. There are galaxies after galaxies, forever. There are not multiple finite big-bangs that over lap each other. That picture of multiple big bangs implies that there is a superstructure of infinite space-time that is populated by big bangs that sprout galaxies and stars all co-populating the same space time fabric. This is not what the expansion theory says. At one point the universe was simultaneously infinitely dense and infinitely large. It expanded and its density became less than infinity. If you find that hard to grasp, it comforts me because I find it hard to grasp. But I can grasp that expansion of an infinite universe predicts that no matter where I am in an infinite universe, I see galaxies in all directions.

    Multiverse theories postulate completely separate space-times that, if they co-exist in some over-arching fabric, that fabric is not space-time. The picture of multiple big-bangs does not reconcile the different views in this thread.
     
  24. Feb 2, 2017 #23
    The singularity is not a physical object, it represents where math breaks down and produces nonsense, (like infinite density).
    We don't actually know what happened at t=0, and the big bang theory doesn't propose an answer.
    It merely states that very shortly after whatever it is that happened the Universe must have been in a very hot dense state,
    and since then it has expanded and cooled.
     
  25. Feb 2, 2017 #24
    So the big bang did not originate from a single point, but instead originated everywhere, simultaneously, and has no edge because it is infinite. Is that the current theory?
     
  26. Feb 2, 2017 #25

    Grinkle

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    I don't know how many on this forum would agree that is the current theory. My own understanding has always been along these lines -

    The extent of the universe (finite vs infinite) has not changed over time. If it is infinite in extent now, then it has always been infinite in extent.

    The expansion theory says that at time zero the universe was infinitely dense. IMO this leads some to describe the early universe as infinitely small, which description I disagree with.

    I interpret expansion / big bang to be saying this, yes.
     
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