History of variational principles in physics involves integrals over an interval of time and (for fields) extended region of space. Moreover, in the usual formulation of classical action principles, the initial and final states of the system are fixed, e.g., In particular, the fixing of the "final" state appears to give the action principle a teleological character which has been controversial historically. This apparent teleology is eliminated in the quantum mechanical version of the action principle. History of variational principles in physics A variational principle in physics is an alternative method for determining the state or dynamics of a physical system, by identifying it as an
European Physical Journal D European Physical Journal D The European Physical Journal D: Atomic, Molecular, Optical and Plasma Physics is an academic journal recognized by the European Physical Society, presenting new and original research results. The main areas covered are: The range of topics covered in these areas is extensive, from Molecular Interaction and Reactivity to Spectroscopy and Thermodynamics of Clusters, from Atomic Optics to Bose-Einstein Condensation to Femtochemistry. The EPJ D arose from various predecessors: "Il Nuovo Cimento (Section D)", "Journal de Physique", and "Zeitschrift für Physik D". Prior to 1998, this journal was named "Zeitschrift für Physik D: Atoms, Molecules and Clusters".