GR, SR and the Sagnac effect question

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Discussion Overview

The discussion revolves around the Sagnac effect and the roles of General Relativity (GR) and Special Relativity (SR) in explaining it. Participants explore the necessity and sufficiency of these theories in relation to co-rotating observers and non-inertial frames, focusing on the reasoning behind their respective contributions to understanding the effect.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants assert that GR is necessary to properly explain the Sagnac effect from a co-rotating perspective, while SR can address non-inertial observers.
  • Others argue that the Sagnac effect does not require either SR or GR, suggesting it arises simply from the movement of the receiver relative to the source along different paths.
  • A participant references a NATO explanation that claims GR is required, contributing to the confusion regarding the necessity of GR versus SR.
  • Another participant posits that neither SR nor GR are necessary for explaining the Sagnac effect, stating that both are sufficient, and even classical (Galilean) explanations can suffice.

Areas of Agreement / Disagreement

Participants express conflicting views on the necessity of GR and SR for explaining the Sagnac effect. There is no consensus on whether GR is required or if SR is adequate, leading to an unresolved discussion.

Contextual Notes

Participants highlight the complexity of the Sagnac effect and its dependence on the observer's frame of reference, but the discussion does not resolve the underlying assumptions or definitions that contribute to differing interpretations.

TheAntiRelative
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I've read in multiple locations that GR is necessary to properly explain a co-rotating perspective/observer of the experiment.

Additionally, SR can explain the experience of non-inertial observer.


The above two statements seem somewhat conflicting and leads to my question. Why is it that GR is required to properly predict the Sagnac effect. What is it that causes the SR explanation to be approximate but inadequate for an exact answer?

I'm not looking for the calculation, I'm looking for the reasoning required to say: GR takes X into account while SR does not.
 
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The sagnac effect doesn't require either SR or GR - it is simply a consequence of the fact that the receiver is moving away from the source for one path and toward the source for the other path - the path can be rectangular or circular - or even back and forth. In GPS there is always a correction for what is called the one way sagnac effect -some time correction is required for example when the satellite signal is must catch up to the receiver which moves a short distance due to the Earth's rotation during transit
 
Here is an interesting discussion of the effect.
:smile:
 
Right-On mijoon - that was the analysis i had in mind but didn't have the citation handy -
 
http://www.rta.nato.int/Pubs/RDP.asp?RDP=RTO-AG-339

There's a link to the NATO explanation that was prepared by a coalition of scientists and says GR is required... Hence my confusion.
 
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29 megabytes! :bugeye:

Maybe it will finish downloading by the time I finish my next class..
 
TheAntiRelative said:
I've read in multiple locations that GR is necessary to properly explain a co-rotating perspective/observer of the experiment.

Additionally, SR can explain the experience of non-inertial observer.


The above two statements seem somewhat conflicting and leads to my question. Why is it that GR is required to properly predict the Sagnac effect. What is it that causes the SR explanation to be approximate but inadequate for an exact answer?

I'm not looking for the calculation, I'm looking for the reasoning required to say: GR takes X into account while SR does not.

Neither SR of GR are NECESSARY.
Both are SUFFICIENT.
As an aside, classical (Galilean) explanation is also SUFFICIENT.
 

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