ABSTRACT
The physics of elementary particles and gravitation is successfully described by Lagrangian field theory. The dynamical variables in this theory are fields ϕ(x) and the dynamics is determined by a function of the fields and their derivatives, ℒ( ϕ, ∂ μϕ), called the Lagrangian. Equations of motion are given as the Euler-Lagrange equations of the variational problem δ ϕ I = 0 for the action integral I = ∫d4 xℒ.
