Mass of Earth/Sun: Comparing in Different Frames

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SUMMARY

The discussion centers on the paradox of mass measurement in a two-body system, specifically the Earth-Sun system, where each body can be considered at rest relative to the other. Participants argue that without a third reference body, it is impossible to definitively assign mass to either body, as observations of orbital speed and separation are inherently relative. The conversation references the Sagnac effect and Einstein's Machian thought-experiments, concluding that mass cannot be uniquely defined in a two-body system without external reference points, which are necessary for establishing boundary conditions in General Relativity.

PREREQUISITES
  • Understanding of General Relativity (GR)
  • Familiarity with the Sagnac effect
  • Knowledge of Newtonian gravity principles
  • Concept of Mach's principle in physics
NEXT STEPS
  • Explore the implications of Mach's principle in modern physics
  • Investigate the Sagnac effect and its applications in measuring rotation
  • Study the concept of inertial frames in General Relativity
  • Examine boundary conditions in gravitational systems and their significance
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Physicists, students of theoretical physics, and anyone interested in the foundations of gravitational theory and the nature of mass in relativistic contexts.

  • #31
PeterDonis said:
Even though the density and curvature are infinite there?

Yes.
 
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  • #32
bcrowell said:
Yes.

Hmm...okay, at least I'm clear about your position. I don't think it's a very common position to take (as I understand it, the "standard" position in GR is that singularities, such as the initial singularity of the FRW models and the r = 0 singularity of the Schwarzschild interior, are a sign that the theory breaks down, and a better theory is needed to cover such cases--presumably some kind of quantum gravity theory), but in the absence of any actual experimental evidence concerning singularities, I can't say it's ruled out.
 

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