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Spacetime, curvature, orbit, matter and reactions

  1. Sep 14, 2009 #1
    In the BBC film Einstein and Eddington, Eddington describes the theory of spacetime using a table cloth (space), a loaf of bread (sun) and a peice of fruit (a planet).

    The Bread is placed in the middle of the table cloth, this forms curves in the cloth. He then takes a peice of fruit and throws it in. The fruit oribits the bread along the curves. This shows spacetime.

    This provoked and idea in my head, The sun is a source of light, In the curves of the cloth there are shadows caused by the sun. The curves of space might have light from the sun causing a "shadow" of light particles or matter in the same way there was a shadow in the cloth. I also think this might cause a reaction as a planet orbits. the idea is rough but in theory it could work.

    Or is it all just, like Thunderbirds just string theory

  2. jcsd
  3. Sep 14, 2009 #2


    Staff: Mentor

    Well, I wouldn't take the table cloth analogy too seriously (it has big flaws) but you can get gravitational lensing, so I would think you could get other optical effects like shadows.
  4. Sep 14, 2009 #3


    User Avatar
    Science Advisor

    No this is not spacetime. This is just space (2 dimensions of it). There is no time dimension in this analogy which is crucial for the gravity model of General Relativity. Follow the links in this post, for better visualizations:

    You are completely misunderstanding the analogy here. The cloth itself represents the space in which light is propagating. So in this analogy the light from the bread (sun) would propagate only within the cloth, not outside of it. There are no shadows caused by spatial curvature around the sun, but optical distortions are possible as DaleSpam said.
    Last edited: Sep 14, 2009
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