Expansion Freedom Theory v6.9: Principle of Least Action and Principle of Feedback — Alternating Dominant Principles by Scale

Expansion Freedom Theory (EFT) is a cosmological framework proposing that the universe's fundamental tendency is expansion and mutual recession, not attraction. What is conventionally called gravity is reinterpreted as the gradient of Expansion Parallax — the speed differential between expanding space and slower-moving matter. This paper (v6.9) introduces two governing principles and demonstrates that they alternate in dominance by scale. At sub-galactic scales, the Principle of Least Action dominates, recovering Newtonian mechanics and general relativity exactly. Beyond a critical scale, a self-reinforcing feedback loop between matter arrangement and relational spatial geometry takes over as the dominant principle. Extending the Principle of Least Action into the feedback-dominated regime — as all existing theories do — is identified as the structural root cause of the dark matter and dark energy problems. Within this framework: (1) flat rotation curves arise naturally from a spherical-to-cylindrical geometric transition without invoking additional mass; (2) dark matter profiles (NFW, Burkert, isothermal) are reinterpreted as a spectrum of geometric transition rates, not matter distributions; (3) the Bullet Cluster separation is evidence for the independent inertia of spatial geometry, not dark matter particles; (4) large-scale structure formation is accelerated by self-reinforcing feedback without dark matter seeds; and (5) the equation v²/r = g_EP + g_FB directly measures feedback intensity from existing rotation-curve data. The paper also establishes structural analogies with fluid Reynolds number (laminar/turbulent flow ↔ feedback/least-action regimes) and gradient descent in machine learning (unidirectional convergence cannot spontaneously close feedback loops; divergent background + local convergence can) Korean version also included..