Isn't it "trivial" to represent/reduce any classical physics problem into a Spin-Glass which is NP-Complete?
Classical physical problems often involve real-number positions or parameter values rather than values from a discrete set (such as the integers) which would be more typical of NP-complete problems. Because of this these problems can often be NP-hard but not (or not obviously) NP-complete. For instance, we do not know whether the Euclidean TSP (for integer points in the plane, with Euclidean distances) is NP-complete, because it hinges on an unsolved problem, the complexity of comparing sums of square roots. Some other geometric problems, such as the recognition of unit distance graphs (of some relevance as an abstraction of protein folding) are complete for the existential theory of the reals, which as far as we know is a different complexity class than NP.