• ripcord@lemmy.world
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      1 year ago

      OK, so after 1 hour:

      • How much further away are you from earth?
      • How much further away from you is the light?
      • How much further away from earth is the light?
      • It depends. The light is definitely moving at c, no matter who checks and from everyone’s perspective, but as a consequence of that the answers to those other questions change depending on how you measure. The coordinate system (technically the “reference frame”) you choose changes the answer. Even more, time isn’t the same for each frame, so you even have to specify for whom it has been 1 hour.