Very recently, the great Richard Feynman gave a lecture here at the University of Florida, just as he had done a year before. He appeared on 16mm film, his lecture being part of a series of lectures recorded in 1964 by the BBC entitled the “Character of Physical Law.” These lectures centered on general physics principles and were intended for the general public.

One aspect that distinguished Feynman was his uncanny talent in conveying difficult ideas clearly and memorably. His recent lecture at UF was no exception to the high quality of his teaching. Called “The Great Conservation Principles,” the subject matter was mostly familiar to beginning physics majors. However, Feynman presented the material in such a way that is not commonly taught at the introductory level. A conservation law was related as a calculation of a certain quantity, and as nature evolves with time, re-calculation of the same quantity produces the same number as before. He likened physics to a chess game, in which physicists do not know the rules of the game but are allowed to discover them through observations of the game being played. And one rule they discover is that the bishop generally remains on squares of the same color. Like the calculated quantities in conservation laws, throughout most of the game the bishop never changes color.



Among the conserved physical quantities explained in Feynman’s lecture were baryon number, angular momentum, charge, and energy. Feynman stressed the local conservation of charge – suppose two points A and B are separated by some distance. Point A has charge q and point B has no charge. If the charge at point A gradually “disappears,” can it simultaneously appear at point B? By introducing the relativity of simultaneity through the classic platform-and-train thought experiment, Feynman shows that the conservation of charge cannot be made relativistically invariant without stipulating that charge is locally conserved.

Feynman also spent considerable time on the conservation of energy. He gave a unique explanation in part by making an analogy with a child playing with 28 indestructible toy blocks. His mother is interested in counting the number of blocks at the beginning and end of each day. Some days she sees 28 blocks; other days she sees less than 28 blocks in the room. Upon further inspection, on the days where she spots less than 28, she finds the remaining blocks tossed outside the window or under a rug. The connection between this analogy and the conservation of energy is that when calculating the energy, it is important to recognize that at times some energy goes away by leaving the system and energy may also come in. To verify the conservation of energy, one must account for any energy that was taken out or put into the system. The remainder of Feynman’s lecture is notable for employing similar analogies to illustrate physics. It was also readily apparent how Feynman’s wit and enthusiasm allowed him to craft memorable and engaging lectures.