Is the Universe Flat Without Volume?

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SUMMARY

The discussion centers on the concept of a "flat" universe in cosmology, clarifying that "flat" refers to a three-dimensional Euclidean space that is not curved, rather than implying a lack of volume. Participants highlight the common misconception that flatness equates to two-dimensionality, emphasizing that diagrams often simplify complex three-dimensional concepts into two dimensions for illustration purposes. Lawrence Krauss's lecture is referenced to further explain the distinctions between open, closed, and flat universes, reinforcing the need to understand these terms within their scientific context.

PREREQUISITES
  • Understanding of basic cosmological concepts
  • Familiarity with Euclidean geometry
  • Knowledge of dimensionality in physics
  • Exposure to lectures or discussions by physicists like Lawrence Krauss
NEXT STEPS
  • Watch Lawrence Krauss's lecture on cosmology for deeper insights
  • Research the implications of a flat universe in modern physics
  • Explore the differences between open, closed, and flat universes
  • Study the geometry of space-time and its representation in diagrams
USEFUL FOR

Students of cosmology, physics enthusiasts, and anyone seeking to understand the complexities of the universe's geometry and its implications in modern science.

ddjj77
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It's been said that the universe is flat. How can it be flat if flatness has no volume?
 
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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
 
ddjj77 said:
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?

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

 
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I thought flat was flat.
Krauss said "..it's open, closed, or flat."
 
ddjj77 said:
I thought flat was flat.
Krauss said "..it's open, closed, or flat."

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

thanks for that video
 

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