Right. You might answer that the dot is not actually reaching the stars, and so is not traveling faster than the speed of light.
A similar problem, though, is a thought-experiment with a rigid rod which is one light-year long. If you rotate it with yourself as the axis, at even a small angular velocity, explain why the tip doesn’t go faster than the speed of light.
I’m guessing that “rigidity” is actually a complicated engineering sort of thing when you really look at it, so that the motion takes time to propagate down the rod.
The galaxies were just there as a visualization- I don’t think they started out as rods (but I Am Not An Astronomer).
Yep- the fundamental mechanism underlying rigidity is the electromagnetic potentials between atoms, and those can’t propagate faster than the speed of light. Typical speeds of actual propagation are significantly slower- vibrations travel at the speed of sound in that material, and so on.
Right. You might answer that the dot is not actually reaching the stars, and so is not traveling faster than the speed of light.
A similar problem, though, is a thought-experiment with a rigid rod which is one light-year long. If you rotate it with yourself as the axis, at even a small angular velocity, explain why the tip doesn’t go faster than the speed of light.
I’m guessing that “rigidity” is actually a complicated engineering sort of thing when you really look at it, so that the motion takes time to propagate down the rod.
Yep. If you tried to rotate a giant rod, it would look like a spiral.
Galaxies have much looser internal connections than a rod has.
However, this suggests that light speed puts an upper limit on the rigidity of materials.
The galaxies were just there as a visualization- I don’t think they started out as rods (but I Am Not An Astronomer).
Yep- the fundamental mechanism underlying rigidity is the electromagnetic potentials between atoms, and those can’t propagate faster than the speed of light. Typical speeds of actual propagation are significantly slower- vibrations travel at the speed of sound in that material, and so on.