Observer theories based on stueckelberg quations of motion

Stueckelberg dynamics is regarded as providing a basis for the construction of observer centered theories of particle motions. The approach involves the use of a generalized Jacobi principle to replace the four-dimensional dynamical theory of Stueckelberg by a four-dimensional geometrical theory, and then a three-dimensional dynamics is constructed from this. The causal difficulties encountered by Stueckelberg for curves which reverse direction in time appear to be absent in the present scheme.Our purpose has been to make more concrete, in a simple context, some of the ideas involved in the (conventional) causal framework recently constructed by us to deal with causal difficulties associated with hyperlight phenomena. Some insight is gained into the possible roles to be played by tachyons in a particle theory and interesting results are found involving classical Lagrangian and canonical formalisms for lightlike particles.