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In Einstein's thought experiment (if I understand it correctly) a person in a sealed elevator in space accelerating at 9.807 m/s2 would not be able to tell the difference between that and the effect of gravity on Earth. Is there any sort of experiment the person in the elevator could do that would tell him he is feeling acceleration rather than gravity from Earth? For instance, I think that if you hung two weights from long strings some distance apart on Earth they would not be parallel. But in the elevator they would be.

Sorry if this has been asked before, but I couldn't find the answer on this forum.

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marked as duplicate by David Z Dec 18 '18 at 4:45

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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You are right. Someone in a box suspended above Earth could see that two masses hanging from strings at different locations would not see the strings as parallel, whereas a person in a box accelerating through empty space would observe parallel strings.

The issue is that these two scenarios are not related via Einstein's equivalence principal. The correct comparison would be the person accelerating through space as compared to someone in a uniform gravitational field. The Earth's gravitational field is not uniform, so it is a different scenario.

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