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Physics
Special and General Relativity
Dark Energy vs Gravity: Expansion vs Contraction
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[QUOTE="asimov42, post: 5443399, member: 82651"] Thanks to both phinds and PeterDonis for your replies. I realize that my original post had limitations in terms of the use of 'space'. After reading "The Balloon Analogy", I may be able to phrase this slightly more clearly, but I'm not sure. My primary question is with respect to gravity, as opposed to dark energy: consider the case of the two test masses moving towards each other under gravitational attraction. In this situation, I had always understood (maybe) that the masses would be moving along trajectories bringing them together, but that this did not involve the 'contraction' of space in between them (I'm being very imprecise here, for which I apologize). Perhaps, after reading "The Balloon Analogy", I can state things this way - there has to be 'something' in between the two test masses (discussion of philosophy aside) - under gravitational attraction, does space undergo metric contraction? I realize I'm again being vague with the notion of 'space'. Said differently, if the entire universe consisted only of those two test masses with some initial spatial separation, when they 'collided' or reached each other (after some time), could the final configuration be described by a single point in spacetime? I.e., would the spacetime manifold at that time be a point with zero spatial extent? Or, would the manifold still have the original spatial extent (perhaps approximately), with the two masses at a position within that spatial extent? I'm not sure if that's clear (probably not). Here's one more attempt: if I'm skydiving, once I jump out of the plane, I'm falling along a geodesic in spacetime, where the manifold is approximately fixed (since my mass is so much smaller than that of the Earth) ... I'm getting closer to the surface of the Earth because I'm moving [B]through[/B] space(time), and not because the space in between myself and the surface is somehow 'contracting'. Am I completely off base? [/QUOTE]
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Special and General Relativity
Dark Energy vs Gravity: Expansion vs Contraction
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