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Two spaceships start accelerating at the same time and at the same rate, and they’re connected by a string. Will the string snap? This is one of the most confusing puzzles in relativity. A lot of physicists initially got it wrong, and even John Bell, who popularised the paradox, got the right answer for the wrong reasons. Most common explanations lean on length contraction. But length contraction is geometry. It’s not a physical squeezing force, so it can’t be the real cause of the stress. The real reason the string snaps has to do with acceleration, simultaneity, and the difference between what we measure in a frame and what is physically happening (proper distances). Let’s work through it carefully.



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John Bell’s original proof
https://danielhoek.com/wp-content/uploads/2019/11/Bell-How-to-teach-Special-Relativity.pdf



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