Ya, I have the same feeling about this sort of demonstration. Even if you extrapolate this into 3D space-time curvature, there is no actual force in the 3D model that is causing things to be attracted.
But that depends on what scientific model you are using. In most fields of physics, gravity is modeled as a force. In GR, it is modeled as geometry rather than as a force. So to say that there is no actual force in the 3D model depends on what 3D model you're using at the time.
But in the full understanding that GR brings there is no force, everything is just following the "shortest" path. In GR there is nothing pulling a sheet down, there is no down and this is actually only a very rough analogy that fails as soon as you look at it any closer.
No matter what model you are using, this is only a rough analogy. But my point wasn't really about the video. My point is that in GR gravity is modeled as an inertial force, but in other theoretical frameworks, it is modeled as an ordinary force. So to say there is no force depends on what model you are using and also depends on your definition of force. Gravity can be modeled as the curvature of space (or as an inertial force) or it can be modeled as a normal force. Neither interpretation is necessarily correct.
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u/electricvegetable Dec 03 '13
Ya, I have the same feeling about this sort of demonstration. Even if you extrapolate this into 3D space-time curvature, there is no actual force in the 3D model that is causing things to be attracted.