Thirty-one years ago [1949], Dick Feynman told me about his "sum over histories" version of quantum mechanics. "The electron does anything it likes," he said. "It just goes in any direction at any speed, forward or backward in time, however it likes, and then you add up the amplitudes and it gives you the wave-function." I said to him, "You're crazy." But he wasn't. --Freeman J. Dyson, 1983 Oh my life is changing everyday In every possible way And oh my dreams it's never quite as it seems 'cause you're a dream to me Dream to me --Cranberries, 〈Dreams〉