Archive of posts on Nov 11, 2026
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Constant roundtrip average speed of light
One may be worried that the assumption of constant speed of light is in principle not verifiable from experiment because we can only measure the roundtrip average speed of light but not the single-trip speed of light. It turns out to be fine because we can always redefine the time coordinates to make the speed of light constant if the roundtrip average speed of light does not depend on the path.