The resulting implication was that what we had come to think of as “gravity” between two objects was really just the acceleration that results when the mass of the objects bends the space and time around them. A common metaphor to visualize general relativity involves heavy balls on an elastic surface, as explained by biographer Walter Isaacson, who asks his reader to “picture what it would be like to roll a bowling ball onto the two-dimensional surface of a trampoline. Then roll some billiard balls. They move toward the bowling ball not because it exerts some mysterious attraction but because
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