Contacts Between High Energy Physics and Other Fields of Physics : Springer : 9783709185001 : 3709185009 : 10 Jan 2012 : The equations of quantum mechanics, let alone those of quantum field theory, are sufficiently complex to solve that various approximation schemes are both welcome and desirable. In applications to quantum field theory, renorm­ alized perturbation theory has long been the predominant calculational tool, and it has even tended to shape the entire conceptual outlook on such problems as well. How­ ever, the apparently irreconcilable conflict between strong interaction physics and perturbation theoretic calculations has given way in the past few years to some fairly revolut­ ionary (at least for field theory) modes of formulation and calculation. The fires of this revolution have been fed by exact solutions of special classical systems, [1] notably the sine-Gordon equation, and an appreciation of the relevance of classical solutions of nonlinear systems as starting points