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Originally Posted by yawyaw
1.Newton (and Einstein's) Gravitational field comes from E=-mGM/R = -m(Gravity Field), if M is absent in an empty universe where does the gravity field come from.
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In GR M isn't the only source of "gravity". The Einstein field equations look like
G = 8.Pi.
T
where
T is the stress-energy tensor. I really recommend that you find a decent text and read about what GR really is.
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2. If there is no "m" in an empty Universe how is the existence of the field detected. No m, no motion change of m due to gravity acceleration.
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It may be that the perspective in Misner, Thorne & Wheeler (Gravitation) has changed a bit, but in Einstein's view the universe was closed. This means that even if most of the universe was flat, you would still have regions of truly glorious curvature, and it is these regions that possess the apearance (from the point of view of GR) of the distant masses that Mach talked about.
Please read Gravitation, page 549.
