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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.