When Einstein died, his greatest rival, Bohr, found for him words of moving admiration. When, a few years later, Bohr in turn died, someone took a photograph of the blackboard in his study. There’s a drawing on it. It represents the “box of light” of Einstein’s thought experiment. To the very last, the desire to debate, to understand more. To the very last, doubt. This permanent doubt, the deep source of science.
