# GR, SR and the Sagnac effect question

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.

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 earths rotation during transit

Here is an interesting discussion of the effect.

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 [Broken]

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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jtbell
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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.