
599
Appendix 4: Noether’s Theorem
In Chapters 4 and 5, we note that symmetries of the Lagrangian or Hamiltonian gave rise to con-
stants of the motion; such parameters are of utmost importance in the analysis. However, the con-
stants of the motion do not always come from the obvious symmetries of the Lagrangian nor do they
always have a simple form. Often they are expressed by complicated functions of coordinates and
momenta, which are invariant in time.
It is therefore desirable to develop a general approach that is not limited by the specic details of a
given situation. Such a formalism was found in 1918 by the noted mathematician Emmy Noet