Event-State Theory IX: A Programmatic Bridge Between Variational Classical Physics and Unitary Quantum Interference

Abstract Event-State Theory (EST) proposes a pre-geometric, cost-based explanatory framework for why variational structures arise so broadly in physics. EST does not claim to replace General Relativity (GR) or Quantum Mechanics (QM). Instead, it frames both as effective descriptions emerging from different uses of a single additive, real-valued history cost functional. The classical (GR-compatible) regime is characterized by dominance of extremal-cost histories (minimization), while the quantum regime is characterized by interference between many admissible histories, which requires a unitary representation of the additive cost as a complex phase. This paper is a programmatic bridge: it cleanly separates core postulates from auxiliary assumptions, identifies the precise boundary where purely positive weighting fails to generate interference, and states the minimal conditions under which complex amplitudes of the form exp⁡(iS/ℏ)exp(iS/ℏ) are forced. We outline a research program: (I) mathematical sharpening of the cost functional on discrete causal substrates, (II) derivation of continuum variational limits (GR-side), (III) derivation of unitary amplitude propagation (QM-side), and (IV) empirical diagnostics where deviations from standard models may arise.