Equivalence Principle Misunderstanding?

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Discussion Overview

The discussion centers around the equivalence principle in the context of general relativity, exploring its formulation, limitations, and implications. Participants examine whether tidal effects can distinguish between gravitational and accelerating reference frames, and the conditions under which the equivalence principle holds true.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants argue that the equivalence principle states that no experiment can distinguish between a gravitational field and an accelerating frame, but question whether this is true given the presence of tidal effects in gravitational fields.
  • Others clarify that tidal effects are not local, suggesting that the equivalence principle applies locally, meaning it holds in small enough regions of spacetime where curvature effects are negligible.
  • There is a discussion about the definition of a uniform gravitational field, with some suggesting it must have the same proper acceleration at any height.
  • Some participants propose that the equivalence principle can be viewed as a first-order approximation, where variations in gravitational fields can be ignored to a certain extent.
  • One participant raises the idea of defining "local" based on an acceptable margin of error, proposing a practical approach to understanding local regions in spacetime.
  • There are multiple interpretations of what constitutes "local," with some emphasizing the mathematical definition while others suggest practical definitions based on measurement accuracy.
  • Participants express a desire for more precise and accurate descriptions of the equivalence principle and its limitations, indicating a need for further study.

Areas of Agreement / Disagreement

Participants generally do not reach a consensus on the interpretation of the equivalence principle, with multiple competing views and ongoing debate regarding its implications and definitions.

Contextual Notes

Limitations in the discussion include varying definitions of "local," the dependence on specific conditions for the equivalence principle to hold, and the unresolved nature of how tidal effects influence the applicability of the principle.

  • #31
Austin0 said:
Hi I have related question. Were the Rindler coordinates developed in GR from the equations there and then exported to an accelerating system in SR or is it the other way around?
I thought I read that the gamma relation to potential altitude was derived from calculations in the context of SR and were part of the process of formulating GR?.
Thanks
I did a internet search but failed to find a single reference to when Rindler actually introduced his coordinate system. If they had been developed before Einstein introduced GR in 1915, they would have provided a clue to expect a coordinate singularity or event horizon for a black hole in the GR solutions. Personally I find it fascinating that SR and the equivalence principle predicts event horizons. Unfortunately, the role of Rindler coordinates in the development of GR does not seem to get much of a mention in the historical records (or I am looking in the wrong places).
 
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  • #32
DaleSpam said:
I think that uniform means that the field corresponds to the field which would be considered uniform historically, I.e. In Newtonian gravity. They didn't attempt to reconcile it here, merely presented it as an accepted meaning.

I have been wondering if a uniform field implies a field in which neighbouring vertical lines (as measured by plumb bobs) are parallel?
 
  • #33
yuiop said:
I did a internet search but failed to find a single reference to when Rindler actually introduced his coordinate system. If they had been developed before Einstein introduced GR in 1915, they would have provided a clue to expect a coordinate singularity or event horizon for a black hole in the GR solutions. Personally I find it fascinating that SR and the equivalence principle predicts event horizons. Unfortunately, the role of Rindler coordinates in the development of GR does not seem to get much of a mention in the historical records (or I am looking in the wrong places).
Rindler coordinates are named after Wolfgang Rindler who wasn't even born until 1924, but (if the entirely unsourced Wikipedia article is to be believed(?)) was the person who invented the term "event horizon".
 
  • #34
I'm uncertain about terminology - I believe Rindler in his GR textbook says that Rindler coordinates are not a "uniform" "gravitational field".
 

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