Unification of electrodynamics and gravity from START

In order to unify electromagnetism and gravitation we derive the basic principles of both approaches from a common (geometrical) starting formulation we call START, from its structure as a Space-Time-Action Relativity Theory. Gravitation results from the epistemological approach of defining a test particle which explores the physical world in such a form that its trajectory indicates the influence of the rest of the system. Electromagnetism defines a collection of test particles, we call carriers, in interaction among themselves and with the rest of the system. Once both approaches have been formally defined we can unify gravitation and electromagnetism either within one or the other formalisms.