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Help visualizing this concept

  1. Oct 23, 2013 #1
    I have looked at this forum for over a year. One thing that has always confused me is spatial direction in space. Thinking in terms of the balloon model: what represents the part in front/beyond if we are on the edge looking out. If we are looking out why can't we "turn around" and see the other way. I understand that when the balloon first starts expanding this is t-0 and representive of the big bang. Space is 3 dimensional why can't we see in front of us, or is this where time/speed of light is involved. Is there no real spatial model that can depict this? In the balloon model I feel we should be able to see beyond the outer latex(if we are indeed a fixated galaxy representive of a coin) and not just distant light from our past. We do a 360 rotation in space and see all parts of our galaxy from any point on the earth, whats representive of top, bottom, edge, or is there no such thing? Is this all to do with the speed of light? Please tie up my loose ends and confusion. I have the classic biology mindset, some of this hard for me to visualize.

    Thank you all for this forum,
  2. jcsd
  3. Oct 24, 2013 #2


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    Hello Adam! Welcome to PF! :smile:
    in the balloon model (2D or 3D version), there is no edge

    in 2D, we can't look "out", we can only look in 2D, ie along the surface of the balloon: we can't look in 3D

    in 3D also, we can't look "out", we can only look in 3D: we can't look in 4D

    the "3D balloon" is expanding in 4D
  4. Oct 24, 2013 #3


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    I think more accurately, the dimension being referred to is time. We can look into the past (similar to looking inward in the balloon analogy) simply by looking far away. But we cannot look at photons emitted from the future (the outward direction), because time has a definite direction.

    As for why there's a direction of time, I think Sean Carroll has written a number of good articles on the subject, such as this blog post:
  5. Oct 24, 2013 #4
    thank you both.
    this will help me better visualize other things within cosmology
    without this foundation it's hard to understand further topics


    If anyone has any further input, it would be greatly appreciated.
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