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A Is the universe really flat?

  1. May 22, 2017 #1
    It's been said that the universe is flat. How can it be flat if flatness has no volume?
     
  2. jcsd
  3. May 22, 2017 #2

    PeroK

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  4. May 22, 2017 #3
    Maybe "flat" isn't the right term; 2-dimensional would be more accurate (see attached image). What would you call a shape with no thickness? Volumeless?
    Universe shape.JPG
     
  5. May 22, 2017 #4

    PeroK

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    Those are 2D surfaces. The reason that a lot of diagrams use 2D to represent the universe is that, although you could represent the "flat" universe as a 3D box, you can't draw a curved 3D surface (you'd need 4D for that, which we don't have).

    So, these diagrams lose a dimension in order to illustrate the concept of curved space.

    It's interesting that you've taken the concept of "flat" so literally.
     
  6. May 22, 2017 #5

    PeroK

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    PS Lawrence Krauss explains this right at the start of his lecture here:

     
  7. May 22, 2017 #6
    I thought flat was flat.
    Krauss said "..it's open, closed, or flat."
     
  8. May 22, 2017 #7

    PeroK

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    No, "flat" in cosmology means 3D but not curved. "Flat" in everyday speech means 2D.

    That is an intellectual hurdle you are going to have to jump.
     
  9. May 22, 2017 #8

    davenn

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    thanks for that video
     
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