Callan-Symanzik Equation

In terms of significance, the Callan-Symanzik equation is the background for the Renormalization Group Equation which is arguably one of the most important concepts from modern physics. It shows that the constants of nature are not constant and instead should be thought of as dynamical entities. The renormalization group equation is why the strong force becomes strong and how all the disparate (non-gravitational) forces of nature may unify into a single entity -- a Grand Unified Theory.