Genius_ The Life and Science of Richard Feynman - James Gleick [216]
It is the analysis of circulating or turbulent fluids. If we watch the evolution of a star, there comes a point where we can deduce that it is going to start convection, and thereafter we can no longer deduce what should happen… . We cannot analyze the weather. We do not know the patterns of motions that there should be inside the earth.
No one knew how to derive this chaos from the first principles of atomic forces or fluid flow. Simple fluid problems were for textbooks, he told the freshmen.
What we really cannot do is deal with actual, wet water running through a pipe. That is the central problem which we ought to solve some day.
Feynman designed his lectures as self-contained dramas. He never wanted to end by saying, “Well, the hour is up, we will continue this discussion next time …” He timed his diagrams and equations to fill the sliding two-tier blackboard so definitively that an image of the final chalk tableau seemed to have been in his head from the start. He chose grand themes with tentacles that spread into every corner of science: Conservation of Energy; Time and Distance; Probability … Before a month was out he introduced the deep and timely issue of symmetry in physical laws. His approach to the conservation of energy was revealing. This principle was never far from the consciousness of a working theoretical physicist, yet most textbooks let it arise in passing, toward the end of chapters on mechanical energy or thermodynamics. First they would note that mechanical energy is not conserved, since friction inevitably drains it away. Not until the Einsteinian equivalence of matter and energy does the principle fully come into its own.
Feynman took the conservation of energy as a starting point for discussing conservation laws in general (as a result, his syllabus managed to introduce the conservation of charge, baryons, and leptons weeks before reaching the subject of speed, distance, and acceleration). He put forward an ingenious analogy. Imagine, he said, a child with twenty-eight blocks. At the end of every day, his mother counts them. She discovers a fundamental law, the conservation of blocks: there are always twenty-eight.
One day she sees only twenty-seven, but careful investigation reveals one under the rug. Another day she finds twenty-six—but a window is open, and two are outside. Then she finds twenty-five—but there is a box in the room, and upon weighing the box and weighing individual blocks she surmises that three blocks are inside. The saga continues. Blocks vanish beneath the dirty water of a bathtub, and further calculations are needed to infer the number from the rising water level. “In the gradual increase in the complexity of her world,” Feynman said, “she finds a whole series of terms representing ways of calculating how many blocks are in places where she is not allowed to look.” One difference, he warned: in the case of energy, there are no blocks—just a set of abstract and increasingly intricate formulas which must always, in the end, return the physicist to his starting point.
With the vivid analogies and large themes immediately came computation. In the same one-hour lecture on the conservation of energy, Feynman had his students calculating potential and kinetic energy in a gravitational field. A week later, when he introduced the uncertainty principle of quantum mechanics, he not only conveyed the philosophical drama of this “inherent fuzziness” in the description of nature but