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Space time

  1. Jul 4, 2011 #1
    if i consider space time to b a fabric as considered by einstein then expansion of this fabric leads in two direction
    1-if the fabric has high elasticity then the curvature of space caused by the a massive object will keep on increasing,thus the flow of time will be faster and faster
    2-if the fabric has low elasticity then the curvature will keep on decreasing thus the flow of time will be slow

    which one is correct?
  2. jcsd
  3. Jul 4, 2011 #2
    Time does not flow in a space-time representation. It is a 'static' dimension like space, and the whole space-time object is a static object. Nothing goes anywhere, and nothing changes. All the going and changing has been done and can be inspected baked into the finished loaf.

    That's the way I understand it, anyway.
  4. Jul 4, 2011 #3


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    Please don't use text-speak on PF. You're on the wrong track because your question assumes an overly literal interpretation of the rubber-sheet metaphor. Gravitational time dilation in GR depends on the difference in gravitational potential, not the curvature. Example: http://en.wikipedia.org/wiki/Pound-Rebka_experiment
  5. Jul 4, 2011 #4
    Space and time ARE variable; that is, they are not static and fixed as Newton presupposed. Only the speed of light is fixed for all inertial observers. So things are not as they superficially appear!!

    Two things affect the observed passage of time: relative speeds and gravitational potential.

    There is a nice brief summary of gravitational time dilation here:


    You can read about length contraction and time dilation here:


    Mass is not the only thing that has gravitational affects: energy (like radiation), pressure, momentum also affect gravitational attraction...as compiled in the Einstein stress energy momentum tensor which is the actual mathematical source of curvature.
    Last edited: Jul 4, 2011
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