I am going to ask some general questions about representation theory which may sound stupid as I don't know anything about it. How old or new is this theory? How did it come out? What is the general concensus of ths difficulty of the subject? Are there many open problems in this theory? Is it connected to modules in any way since they both deal with matrices in some way? It seems like a very general theory with deep connections to topology and analysis? How much connection has it got to physics and could it uncover some deep physical theories? I recall Matt Grime calling it 'abstract nonsense'. Why?