One day in class, Richard Feynman was talking about angular momentum. He described rotation matrices and mentioned that they did not commute. He said that Sir William Hamilton discovered noncommutivity one night when he was taking a walk in his garden with Lady Hamilton. As they sat down on a bench, there was a moment of passion. It was then that he discovered that AB did not equal BA.(都这么着讲课...会把纯良的孩子们教坏的老师!!!