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## The Light-Year-Long See-Saw Conundrum

23 Dec 2014, 12:37 UTC
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Question: A lunch friend and I are debating this question.
Essentially, consider a see-saw, a board or rod with a fulcrum in the middle. This rod is made of unbendable, nondestroyable fictional material. It will not bend.
Make this rod or board one light year long. One person sits on one end, the other sits on the other. Call them A and B. A pushes down and the board appears to raise up. I say that the speed at which the “information” of movement of the board is limited to the speed of light. Therefore, from A’s perspective, the movement is immediate. But from B’s perspective, she would not rise for an entire year, until the “information” of the movement of the board would finally reach her. In effect, the board would rise and fall at the speed of light. And the effect of up and down is not automatic depending on perspective. Am I totally off base? I thank you for considering the “See-Saw” conundrum. – Mike
Answer: Well, in fact, information, which in this case is a mechanical disturbance, will travel much slower than the speed of light in a rod or board. The compression wave that represents ...