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B Is gravity spacetime?

  1. Oct 10, 2016 #1

    wolram

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    Do you have to have mater for the gravity field,or is gravity a thing that has all ways been.
     
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  3. Oct 10, 2016 #2

    Jonathan Scott

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    In General Relativity, the stress-energy tensor (which includes energy and momentum) is the source of gravitational effects. This does not require that the energy is in the form of matter.
    I'm not quite sure what you are asking there. The gravitational effect of some amount of energy around a given location is similar regardless of its form, so there's no change when a given amount of radiation energy is converted to or from the corresponding amount of matter.
     
  4. Oct 10, 2016 #3

    wolram

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    I guess what i am trying to say is, was gravity emergent, or has it all ways been or how it came to be,for if-there was no pre existing gravitational field, all we would have is a cloud of gas
     
  5. Oct 10, 2016 #4

    Jonathan Scott

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    General relativity doesn't describe any "beginning" to gravity or any change in its rules, so according to GR it has been there at least since very shortly after the big bang (at the end of the inflation phase).

    The word "emergent" when applied to scientific properties usually refers not to a point in time but rather to higher-level phenomena which arise from simpler systems but which cannot usefully be described in terms of the components.
     
  6. Oct 10, 2016 #5

    PeterDonis

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    We don't know. Thread closed.
     
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