Shape of the Universe: Flat or Curved?

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SUMMARY

The discussion centers on the shape of the universe, specifically the debate between flatness and curvature as described by General Relativity (GR). Participants highlight that gravity results from the curvature of spacetime, yet observations of cosmic microwave background (CMB) hot spots suggest a flat universe. The analogy of a flat rubber sheet with marbles illustrates that while massive objects create local curvature, the overall structure of the universe can remain flat. This indicates a complex relationship between local gravitational effects and the global geometry of the universe.

PREREQUISITES
  • Understanding of General Relativity (GR)
  • Familiarity with cosmic microwave background (CMB) observations
  • Knowledge of gravitational lensing phenomena
  • Basic concepts of spacetime curvature
NEXT STEPS
  • Research the implications of cosmic microwave background (CMB) measurements on cosmological models
  • Explore gravitational lensing and its effects on observing distant galaxies
  • Study the mathematical framework of General Relativity and its predictions about spacetime
  • Investigate current theories on the overall shape of the universe, including flatness and curvature
USEFUL FOR

Astronomers, physicists, cosmologists, and anyone interested in the fundamental structure of the universe and the implications of General Relativity.

moonman
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I'm not overly familiar with GR, but I have heard that gravity is basically a result of the curvature of space. Its not an attractive force so much as its a consequence of traveling on a curved surface. But I've also read that observing cosmic microwave background hot spots leads to a flat universe. So can the universe be flat, if GR claims gravity needs curves?
 
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moonman said:
Its not an attractive force so much as its a consequence of traveling on a curved surface.

Tomato, tomawto.


But I've also read that observing cosmic microwave background hot spots leads to a flat universe. So can the universe be flat, if GR claims gravity needs curves?

I think this was covered by someone else in another thread recently, but the basic idea is that massive objects are like little "dimples" in spacetime, despite its overall flatness. Imagine a large, flat rubber sheet with a few marbles resting on the surface. The marbles make an impression locally, but the overall sheet is flat. In the real world, the small-scale curvature due to gravitationally bound objects can be demonstrated with phenomena like gravitational lensing.
 

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