The Fundamental Fields Theorem

This theorem proves that gravity is the only classical interaction field capable of structural closure in principle. All other classical interaction fields are shown to be necessarily open, requiring external charge sectors or regime-dependent prescriptions. The result is structural rather than phenomenological and follows from minimal requirements of classical covariance, conservation, and exhaustion under symmetry, without assuming specific dynamics or actions. The result is independent of phenomenology, specific actions, or model fitting, and provides the logical foundation for the downstream Ananke (Gravitational Closure) Theorem.