Curved Space-time and Relative Velocity

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Discussion Overview

The discussion centers on the concept of relative velocity between moving points in curved space-time, particularly within the framework of general relativity. Participants explore the implications of parallel transport and the challenges of defining relative velocity in such a context, referencing previous threads and examples to illustrate their points.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant questions the meaningfulness of relative velocity in curved space-time, suggesting that parallel transport along different routes can yield different orientations for velocity vectors, complicating the concept.
  • Another participant provides a counterexample involving static observers in Schwarzschild spacetime, arguing that relative velocity can be computed straightforwardly for geodesic paths.
  • A participant emphasizes that the presence of sharp bends in paths used for parallel transport does not invalidate the argument regarding relative velocity.
  • One participant discusses the possibility of observing light speed from different points in curved space-time, proposing a mathematical relationship that could imply superluminal speeds under certain conditions.
  • Another participant expresses support for the arguments presented, indicating a preference for the interpretations discussed.

Areas of Agreement / Disagreement

Participants express differing views on the validity and definition of relative velocity in curved space-time. Some argue that it is well-defined under certain conditions, while others contend that it lacks a unique meaning due to the nature of parallel transport. The discussion remains unresolved with multiple competing perspectives.

Contextual Notes

Participants reference specific mathematical definitions and examples, highlighting limitations related to the assumptions of parallel transport and the implications of different paths taken in curved space-time. The discussion also touches on the complexities of measuring light speed in varying gravitational fields.

  • #331
OK, now I am completely lost. Would you stop referring to posts which refer to other posts and simply post your question in one complete post. In post 325 you referred vaguely back to post 137 where you described two spaces:

Anamitra said:
1)I consider a "Semi-hemispherical spherical" bowl with a flat lower surface[I can have it by slicing a sphere at the 45 degree latitude].A vector is parallel transported along the circular boundary a little above the flat surface[or along the boundary of the flat surface as a second example] . The extent of reorientation of the vector seems to attribute similar characteristics of the surfaces on either side of the curve.How do we explain this?

2) We come to the typical example of moving a vector tangentially from along a meridian,from the equator to the north pole and then bringing it back to the equator along another meridian, by parallel transport and then back to the old point by parallel transporting the vector along the equator. It changes its direction . Now if we make the corners "smooth" it seems intuitively that the vector is not changing its orientation. Even if it changes its orientation it is not going to be by any large amount while the curvature of the included surface remains virtually the same. How does this happen?
Your semi-hemispherical bowl with a flat lower surface and the same space but with smooth corners.

If you are not talking about those two spaces then just be explicit with your complete question in one self-contained post where you describe the issue in detail without referring back to any previous posts.
 
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  • #332
Anamitra said:
2) We come to the typical example of moving a vector tangentially from along a meridian,from the equator to the north pole and then bringing it back to the equator along another meridian, by parallel transport and then back to the old point by parallel transporting the vector along the equator. It changes its direction . Now if we make the corners "smooth" it seems intuitively that the vector is not changing its orientation. Even if it changes its orientation it is not going to be by any large amount while the curvature of the included surface remains virtually the same. How does this happen?
Thread #327 clearly refers to the above quoted problem. My subsequent postings/replies are related to the above example.
 

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