The discussion centers on identifying which branch of physics involves the most mathematics. Participants suggest that while all branches of physics utilize mathematics, quantum mechanics is noted for its complexity, particularly at advanced levels like quantum electrodynamics (QED). String theory is highlighted for its use of novel mathematical concepts, although opinions vary on whether it qualifies as a branch of physics. General relativity and efforts to unify it with the standard model, such as m-theory and loop quantum gravity, are also mentioned as areas employing highly advanced mathematics. Overall, the consensus is that while some branches may involve more difficult math, the use of mathematics is pervasive across all areas of physics.