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B The granularity of space-time curvature

  1. Nov 24, 2017 #1
    I wonder if someone would field a beginner's muse I had: If gravity is just an illusion of the curvature of space caused by mass, does not the matter within that space follow the curve? and what is the granularity of that curvature? Does the curvature exist in the space between the nucleus and the electrons? Is the nucleus itself curved? Are the electrons curved?
  2. jcsd
  3. Nov 24, 2017 #2


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    I'm not sure it's correct to say that gravity is an illusion. Rather, for a long time we interpreted it as a force, but now we regard it as curved spacetime. Matter does, indeed, follow curved paths as a result.

    However, exactly how gravity works on the quantum scale is an open question. We don't have a complete answer, largely because we haven't done experiments precise enough to detect gravity at that scale.
  4. Nov 24, 2017 #3


    Staff: Mentor

    It isn’t an illusion. And I am pretty sure that no professional source characterized it that way.
  5. Nov 24, 2017 #4


    Staff: Mentor

    Mass (more generally, stress-energy) doesn't curve space, it curves spacetime.
  6. Nov 25, 2017 #5


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    I wouldn't say that gravity is an illusion, but I would say it's a consequence of the curvature of space-time. I'm not sure what you mean by "matter within that space follows the curve", though there is a well known remark by Wheeler.
    Note that for technical reasons Wheeler says "matter" and not "mass". That is because there are other properties of matter other than "mass" that contribute to space-time curvature.

    The curvature, in the form of the Riemann curvature tensor, does exist in the empty space where there is no matter. For example, the sun is a lump of matter, and it causes space-time curvature here on the Earth, which we can see and measure directly in terms of the tidal forces that are present on the Earth. An instrument known as the "gravity gradiometer", and also as the "Forward mass detector" can use these local tidal force measurements to detect the presence and distribution of distant masses. The underlying theory has practical usage for the purposes of oil exploration.

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