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Given that the speed of light is the upper limit for changes to propagate through the universe; if you had a four light-year long indestructible rod and you move one end of the rod how long until the other end moves?
you're right, I meant 4 years as aboundary even if that's actually high.
Since it's a hypothetical material we don't know what max speed information can travel through it and the actual answer would be related to that, so a lower boundary at 4 years anyway.
If the material was truly somehow magically incompressible then I expect we would see some kind of time dilation so that the information could move at the right speed without deforming the rod. It would still take at minimum 4 years.
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.