Gravity occupies a unique position among the fundamental forces: it is dynamical spacetime itself, requiring self-consistency at every point. General relativity encodes this through field closure, the requirement that the metric remain non-degenerate (det (g) ≠ 0) everywhere. In tetrad formulation, closure forces four basis vectors at each point to span the tangent space completely, defining a tetrahedron at each field node. Ghost-free bimetric gravity (Hassan-Rosen 2012) couples two such tetrad fields through shared boundary faces. Field coupling closure in (3+1) dimensions determines a unique minimal topology: the stellated octahedron, two tetrahedra with opposite orientations coupled at a shared origin. Deriving a covariant scalar-tensor action from that coupling hierarchy yields quantitative predictions. The topological constant k = 4 (from simplex packing in (3+1) dimensions) predicts the neutron lifetime beam-bottle discrepancy (1. 084% vs observed 1. 081%, agreement to 0. 3%) and Milky Way rotation velocity (229 km/s, exact match). Bidirectional validation across 36 orders of magnitude, from nuclear physics (10^-15 m) to galactic dynamics (10²1 m) to cosmological structure (10²6 m), with zero adjustable parameters. When dual tetrahedral field regions couple, the interaction occurs at three structural levels: field existence (1), propagation through vierbein faces (k = 4), and Hassan-Rosen bimetric channels (k² = 16). The coupling polynomial f (k) = 1 + k + k² = 21 is not phenomenological but the architecture that field coupling closure requires. Structural identification of the 16 bimetric interaction channels with the coupled face channels of the stellated octahedron yields a zero-parameter covariant completion, distinct from Hassan-Rosen bimetric gravity which contains five free functions. The resulting scalar-tensor action passes 14 empirical tests spanning GW speed (exact to 10^-15), Mercury precession, lunar laser ranging, wide binary plateaus, rotation curves, and cosmological expansion, with zero fitted parameters compared to ΛCDM's 15-20. Read for coupling depth, the hierarchy yields G = (17/13) α²1 ℏc/mₑ² (0. 12% tree-level, 0. 001% one-loop). Read for interaction breadth, it yields 1/α = 137. 036 (0. 00021% agreement). The pattern across independent tests demonstrates that the missing 85% attributed to dark matter reflects missing structure in how we model field dynamics, not missing particles. Fundamental constants are topological consequences of how gravitational fields couple in (3+1) dimensions.
Stephen Nelson (Sat,) studied this question.