This is another (hopefully not tiresome) question related to the relativity of simultaneity! Suppose you have the usual train situation, but with this addition: suspended from one end of the car to the other is a long roll of paper towels. At each end there is a vial of red dye. From an the observer-on-the-embankment's perspective, two lightning flashes strike simultaneously at the front and rear of the moving train, breaking the vials. A stain spreads along each end of the paper towel strip, towards the middle. Will the observer on the embankment predict that the stains, when they meet, will meet in the exact middle of the train car? If not, why not? If so, is he correct in this prediction?(adsbygoogle = window.adsbygoogle || []).push({});

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# The spreading stain

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