On my desk the book is open to page nine, where it says, “I stand at the window of a railway carriage which is traveling uniformly, and drop a stone on the embankment, without throwing it.” Einstein is speaking here, addressing laymen in the 1920 translation of his handy primer Relativity: The Special and General Theory. To him on the train, the stone falls in a straight line, while a pedestrian outside sees it trace a parabola. This simple act shows that motion is relative to the position of the viewer. So begins the presentation of the greatest breakthrough in modern physics, not with a formula, but a scenario. And it’s not a one-time event in the book. Einstein returns to it again and again, adding new elements with each step of the demonstration: a raven flying by, a man walking through the railway car, not sitting down. He really wants you to pretend you are there in the carriage and to see...


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