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
Interaction point whole region around the interaction point (the experimental hall) is called an interaction region. Particle colliders such as LEP, HERA, RHIC, Tevatron and LHC can host several interaction regions and therefore several experiments taking advantage of the same beam. Interaction point In particle physics, an interaction point (IP) is the place where particles collide in an accelerator experiment. The "nominal" interaction point is the design position, which may differ from the "real" or "physics" interaction point, where the particles actually collide. A related, but distinct, concept is the "primary vertex": the reconstructed location of an individual particle collision. For fixed