2 ms·

Sure: the Michelson-Morley interferometry experiment: https://en.wikipedia.org/wiki/Michelson–Morley_experiment https://en.wikipedia.org/wiki/Michelson–Morley_e

• ndsipa_pomu 3y ago
  Doesn't that rely on synchronising the detector with the emitter though? That's the issue that makes one-way measurements effectively a round trip measurement. Edit: looks to me like mirrors are used and it is comparing two-way speeds in different directions.
• mikewarot 3y ago
  If you look at the folded light path used in the Michelson–Morley interferometer (figure 5), you'll see that the X and Y distances traveled on both paths add to the exact same value. Thus, it would be completely insensitive to changes in the speed of light in the X or Y directions, no matter how it were rotated.
  • gumby 3y ago
    The whole point of that experiment was that it would show a difference, if such a difference existed, by projecting an interference pattern.