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Why does mass bend spacetime in a single plane?

  1. May 19, 2012 #1
    well yeah i understand that in general theory of relativity is about bending of space time. but why does the bending of spacetime itself is not relative? i mean look at these photos,
    why does spacetime was bended that way? why not sidewards? why not on top?
    just wanna know why. thanks :)

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    Last edited: May 19, 2012
  2. jcsd
  3. May 19, 2012 #2
    Welcome to PF!

    Spacetime curves in all dimensions. Those pictures are meant to provide a visual analogy.

    Here is a better image.
  4. May 19, 2012 #3


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    Staff: Mentor

    People make diagrams like that because they don't know how to make diagrams of curved four-dimensional spacetime on a two-dimensional sheet of paper (or computer screen). Do you? :wink:
  5. May 20, 2012 #4
    oh wow that's really a better picture :)
    but why do planets spiral in a single plane then?
  6. May 20, 2012 #5
    Beause of conservation of angular momentum. Deviation from a plane orbit in a two body system would imply a changing angular momentum of the system.
  7. May 20, 2012 #6
    ahh, that all makes sense now. thanks a lot! :)
  8. May 21, 2012 #7


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    Gold Member

    The curvature of space (as part of the spacetime curvature) is spherically symmetric around the source.
    Spherically symmetric: there is no force component away from the instantaneous orbital plane. So planets remain in the same orbital plane

    The orbits being planar goes back to the (spherical) symmetry.
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