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Suppose I have a perfectly rigid rod of length $1$ light-year and I am running with that rod with its one end in my hand. I suddenly stop at some moment. Will the other end of the rod continue to move for at least a year(assuming information indeed travelled at the speed of light in rod)? If so, how can this happen without the elongation of the rod?

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    $\begingroup$ Correct -- it can't happen without elongation of the rod. There's more-or-less no such thing as a rigid body in special relativity. And there are lots and lots of so-called little "paradoxes" that are resolved by a rigid classical Newtonian body becoming not-so-rigid once special relativity is taken into account (e.g., car driving over a pothole from the point of view of passengers in the car versus bystanders standing alongside the road). $\endgroup$
    – eigengrau
    Feb 25, 2022 at 8:38

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