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What came first Gravity or Curvature

  1. Jul 23, 2009 #1

    AKT

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    I understand that Gravity is the result of spacetime curvature. All planets are spherical(almost). Planets are spherical because of gravity (partially true at least). So, seriously, what came first? If we have just mass of gas - how would it become spherical -if gravity were only because of the geometry, i.e, gravity would come in to picture only after the mass of gas takes the shape of sphere?
     
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  3. Jul 23, 2009 #2

    Fredrik

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    GR tells us the relationship between the geometry of spacetime and the motion of matter in it. It's not possible in general to specify one of those things and then determine the other thing from it. They affect each other. If you have found a solution already, and change the motion of matter slightly, this gives you a new geometry, which makes matter move in a different way, which changes the geometry again, which...you get the idea. This is the main reason why it's so hard to find solutions of Einstein's equation.
     
  4. Jul 23, 2009 #3
    Interstellar gas would float around in relatively "empty" space and as more particles approach one another spacetime gradually curves...equivalently, one could say spacetime is curved ever so slightly by gas molecules and as they drift and are "attracted" to one another they move along a curved spacetime curvature which tends to bring them together.

    on the other hand, spiral galaxies are very common and do not represent 'spherical" formation shapes...but maybe when dark matter is accounted for, the total IS rather spherical...anybody know?? Last illustration I saw pictured dark matter as spider web type formations in space.
     
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