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Gravity Bend

  1. Nov 12, 2005 #1


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    Suppose we live in a one dimensional universe (so just a curved/straight line in 2D space). We live inside it so we can travel in one of two directions.
    Then we might consider the following scenario for how gravity works in this universe. Suppose this 1D universe starts out as a nearly straight line, with matter evenly distributed throughout. If at one point in this line there is a bigger concentration of matter, then we can imagine that at this point the line curves downward. Suppose that the matter in the vicinity of this region will have the tendency to fall down into this downward curve thus making the curve more significant, which in turn causes more matter to "fall in" and so on.
    This is nothing original here, but it's interesting to think from the perspective of a being inside this 1D universe. As he/she moves along the 1D universe, the being might eventually reach one of these downward curves. Because he/she is "inside" the line he/she will not sense this curvature visually, but will only be able to experince the acceleration it produces. Similarly, a being living in a 2D surface universe, might, in its travels in two dimensions, reach such a curvature, and though he/she will not be able to detect this curvature visually, as he/she is inside the surface, the acceleration produced by this curvature will be noticeable.
    Similarly again we can imagine that in our 3D universe (some 3D object in 4D space) these curves exist, though it's hard to visualize them because it's a curving into a fourth dimension. This means i can be travelling around in our universe, and upon reaching such a curved region, though i can't see the curvature, i will experience the acceleration produced by it.
    This seems like a pretty neat explanation for gravity, but in actuality it doesn't really explain it, because it needs gravity to make it work. Why does space curve in one direction as a function of the density of matter in that area of space? It seems that in order for this to work, the universe would need to be an object inside some other "universe" (probably shouldn't call it that), and that the gravity from this "universe" is what actually bends the space in the first universe. Has anyone any ideas why matter bends space?
    I guess what i'm asking is, when we traditionally say that matter bends space/time, is matter bending space because it's under the influence of a force, or does it bend it by itself? It seems more reasonable that gravity is not caused by the bend of space by matter, but that gravity is what actually causes this bend, because whatever bends space is what actually accelerates us when we get near the bent region.
    Last edited: Nov 12, 2005
  2. jcsd
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