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I Understanding the shape of the universe

  1. Dec 9, 2016 #1
    What actually means to say that the universe is spatially flat? Would it be that, if one could extend two straight rods of infinite length (assuming a universe with no boundaries and infinite amount of material for making the rods, LOL), they would remain parallel?
  2. jcsd
  3. Dec 9, 2016 #2


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    Yes. It also means angles in triangles add up to 180 degrees.
  4. Dec 9, 2016 #3
    Ok. Now, in a closed universe, what would be an interpretation for its closed form, besides angles not adding to 180°?
  5. Dec 10, 2016 #4


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    Your straight rods will converge and cross over at some large distance in any direction.

    Take note that in our presently accelerating expansion universe, even it it has a small positive spatial curvature, your rods will break long before they reach that crossover point, because they cannot extend past our Hubble radius.
    Last edited: Dec 10, 2016
  6. Dec 10, 2016 #5
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