At 81, Bob Dylan has been a celebrated artist for 60 years, which might be some kind of record. Dylan might even be the definitive post-war artist, the age when American pop culture overran much of the world. His longevity and prolixity are a big part of that success, but another part is his endless touring and his endless searching through American art, especially music, to find evidence of the wondering and wandering heart that defines modern man.