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Could you say that GR is a theory of four or five dimensions?

  1. Jan 1, 2012 #1
    I don't really know much about GR, but I was just wondering about this theoretical question. I am asking this, because I think Special Relativity is a theory of four dimensions, and wasn't sure how many dimensions GR involved.
     
  2. jcsd
  3. Jan 1, 2012 #2

    Pengwuino

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    Four. Why would it be 5?
     
  4. Jan 1, 2012 #3
    Because, since space is "curved" in GR, I thought may be an addition dimension could be introduced to describe the curvature of space, but perhaps that is not counted as another dimension.
     
  5. Jan 1, 2012 #4
    Four: x, y, z, and t. What's the 5th dimension?
     
  6. Jan 1, 2012 #5
    Essentially it's all integrals with 4 elements, what makes it GRey is that the volume element changes with position in space-time
     
  7. Jan 1, 2012 #6
    E???
     
  8. Jan 1, 2012 #7

    Pengwuino

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    The 4 dimensions do describe the curvature of the space-time. For example, let's say you have a can of soda or a ball or something in the 3-dimensional world we're accustomed to. You can fully describe the curvature of those objects by using those 3 dimensions. A 4th dimension need not be introduced in this example.

    Same idea with GR, except you now are dealing with a 3+1 dimensional spacetime instead of the 3 dimensional Euclidean space of the soda can/ball example.

    If E = energy, why would E be a dimension? It doesn't measure space-time displacements.
     
  9. Jan 1, 2012 #8
    Sure it does. E alters our perception of distance.
     
  10. Jan 1, 2012 #9

    Pengwuino

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    The energy-momentum tensor in GR tells gravity, as many put it, how to curve, but that certainly does not mean it is qualified to be a dimension. A dimension has very specific meaning.
     
  11. Jan 1, 2012 #10

    Dale

    Staff: Mentor

    OK, given an inertially moving rocket in flat spacetime where, from the rocket's perspective, would the 1 J hyperplane be located?
     
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