When you passed into slumber, nobody had taken a picture with a Kodak camera or used a machine that made motion pictures, or bought a device to play recorded music. By 1905, we have the first commercial versions of all three—the simple box camera, the cinematograph, and the phonograph. Now imagine dozing off for another thirty-year nap between 1990 and 2020. You would wonder at the dazzling ingenuity that we funneled into our smartphones and computers. But the physical world would feel much the same. This is reflected in the productivity statistics, which record a slowing of change as the
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