There are many stories of how Feynman did fairly profound work in an offhand way. Two that I can remember: 1. A number of times, young professors would visit w

There are many stories of how Feynman did fairly profound work in an offhand way. Two that I can remember: 1. A number of times, young professors would visit with him when they were in town to give a lecture, and would discuss a recent result they had come up with, and Feynman would say that reminded him of something, pull out a sheet of paper from his drawer, and say effectively, "yes, looks like your result is correct". 2. A more specific version of that was captured in the link below, when Feynman worked out blackhole radiation on a blackboard with some grad students over lunch. The blackboard was erased and the result lost until Hawking published the same result a year later, propelling him to fame (deserved, of course). http://nautil.us/blog/the-day-feynman-worked-out-black_hole-radiation-on-my-blackboard http://nautil.us/blog/the-day-feynman-worked-out-black_hole-... He was a gifted theoretician with an ability to see how/why things worked and had the mathematical ability to express that understanding rigorously.