They don't just become harder, they become open problems -- open problems with a million dollar bounty on them! There is no known non-perturbative quantization

They don't just become harder, they become open problems -- open problems with a million dollar bounty on them! There is no known non-perturbative quantization of the Yang-Mills theory. http://www.claymath.org/millennium-problems/yang–mills-and-mass-gap http://www.claymath.org/millennium-problems/yang–mills-and-m...