On Friday, February 7, 2014 9:37:17 PM UTC, [email protected] wrote: > > > On Monday, February 3, 2014 6:27:14 AM UTC, Brent wrote: >> >> On 2/2/2014 10:12 PM, [email protected] wrote: >> >> Namely that however you jig it, there's still going to be huge spacetime >> distortion representing the sun and a tiny one representing the earth, >> which - I thought - had to bias the objectively true relation between the >> sun and the earth for the earth being gravitationally dominated by the sun >> not the other way around. >> >> >> So the question was whether one could just consider the Sun, calculate >> the spacetime metric due to its mass, and then calculate the orbit of the >> Earth as an inertial path in that metric? In that case of course the >> answer is no. The metric has to take into account the mass of the Earth as >> well as the Sun. Just as in Newtonian theory, the Sun and the Earth, and >> Jupiter and the other planets all move around their mutual center-of-mass. >> The center-of-mass is roughly near the surface of the Sun on the side >> nearest Jupiter. >> >> Brent >> > > Hi Brent - Sure, but is it ok to look at the sun and the earth together, > purely as their geometry's in spacetime, and say "that one goes around that > one" to the same sort of accuracy we can say the earth goes around the sun > without invoking relativity. Or is doing that running foul of the basic > principles in play of relativity ? > i.e. because one is visualizing what are actually two relative frames, effectively as a combined situation. the intuitive - and fragile for that as ever - the intuitive answer would be "it depends what you want to do. If you just want to say "that one goes around that one" to the same sort of accuracy we always said that about the earth and the sun, the only difference that now we intuit by looking at the geometry of a combined spacetime. The intuitive answer would be "yes you can do that no less from intuition of the geometry of spacetime than intuition of looking at a schematic of the solar system, or the Euclidean geometry of space Does relativity say that fundamental is actually the level of frames, and talking about combining frames for intuition just does not wash any more. I guess that's it in a nutshell
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