Overview
If you already know classical mechanics (or relativity) and quantum mechanics, is there any more you need to learn to understand the physical world?
What are the laws of the universe? Usually students learn about a mechanical view of the universe where future behaviour can be predicted when we have sufficient information about the past and present, characterised by classical mechanics (Newton's laws of motion, and so on). Classical mechanics can be formulated in Lagrangian and Hamiltonian terms, which are more sophisticated and powerful ways of dealing with more complicated problems,
Einstein's theory of relativity essentially replaces this -- the theory is elegant and beautiful, though mathematicall
but you probably know by now that relativity is a better description. But actually quantum mechanics