Jerzy Kijowski
Variational Principles in Physics
It is shown that the standard derivation of field equations (Euler-Lagrange equations), based on fixing {\em a priori} the field boundary conditions, cannot be applied in the case of hyperbolic field theory, because leads to a contradiction. This contradiction has been overlooked by theoretical physicists. A remedy for this contradiction is proposed. It consists in describing Lagrangian field theory as a classical symplectic control system. Implications for various branches of physics are discussed.
