| Sumario: | Recent work in the physics literature demonstrates that, in particular classes of rotating spacetimes, physical light rays in general do not traverse null geodesics. Having presented this result, we discuss its philosophical significance, both for the clock hypothesis (and, in particular, a recent purported proof thereof for light clocks), and for the operational meaning of the metric field. 1 Introduction 2 Fletcher's Theorem 2.1 Maudlin on the clock hypothesis in special relativity 2.2 Fletcher's result in special relativity 2.3 Fletcher's theorem in general relativity 3 Electromagnetism and the Geometrical-Optical Limit 3.1 Maxwell's equations in curved spacetime 3.2 The geometrical-optical limit 3.3 Rotating spacetimes 3.4 Aren't Gödel spacetimes unphysical? 4 The Clock Hypothesis and Chronogeometry 4.1 Natural and mathematical observations 4.2 Clock registry discord 4.3 Chronogeometry 5 Conclusion
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