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How can gravity grasp on space time?

  1. Apr 11, 2013 #1
    Hello. This topic might seem stupid, but i got interested in quantum gravity and I didn't understand how gravity grasps and distorts spacetime. So my question is, how can gravity distort spacetime?
  2. jcsd
  3. Apr 11, 2013 #2


    Staff: Mentor

    Hi medgalis, welcome to PF,

    Gravity is distorted spacetime. Your question is a little like asking how can work transfer energy. Work is a transfer of energy. So how is simply by definition.

    I am not sure what you really want to ask. Perhaps you want to know how matter can distort space-time, I.e. How can matter produce gravity. Or perhaps you want to understand what physical features of gravitation require the mathematical representation to be curved spacetime.
  4. Apr 11, 2013 #3
    Yes, that's exactly what i wanted to ask, but didn't know how to ask.
  5. Apr 11, 2013 #4


    Staff: Mentor

    Which one?
  6. Apr 11, 2013 #5
    How can matter produce gravity.
  7. Apr 11, 2013 #6
    Err, energy "distorts" space time.

    I think it's this thing that calculates how Stress energy tensor.

    This is a quote from the wiki page;

    "The stress–energy tensor is the source of the gravitational field in the Einstein field equations of general relativity, just as mass density is the source of such a field in Newtonian gravity."
  8. Apr 11, 2013 #7


    Staff: Mentor

    According to GR, anything with stress-energy produces gravity. So matter produces gravity because it has a high energy density and therefore a "large" stress-energy tensor.
  9. Apr 11, 2013 #8

    nobody really knows HOW such a thing can happen. That's likely because nobody knows exactly what gravity, nor space, nor time, nor even energy is. Sounds crazy, but all those entities apparently were 'unified' really, really early in the universe...at extremely high and unstable energy levels....meaning at those early times all the entities were the same.....maybe roughly like a 'quantum foam' if you know that term....

    In any case, those early unstable conditions underwent a 'spontaneous symmetry breaking'
    and, voila, everything you see around you emerged or developed. So today we see a bunch of characteristics around us and are trying to figure out how they are related. For example, in special relativity Einstein deduced that space and time are not constants as they superficially appear to us....He grabbed relationships from Lorentz and Fitzgerald and Maxwell and with brilliant insights concluded: the speed of light is constant, not space, not time!!

    But as already noted in prior posts, it turns out we HAVE codified our observations about how most of gravity works...we have math that matches observations.....via the Einstein stress energy tensor and field equations, for example...these seem to capture MOST situations.... from most of black holes to most of the universe.....not bad!!

    But what happens to gravity space and time at 'singularities' is not yet understood.....so the progress continues.
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