This paper presents a self-contained constructive argument that singles out the icosahedron, together with its symmetry group A5 and a self-similar phi-stratified hierarchy, as the unique minimal three-dimensional geometry compatible with four elementary structural requirements: discreteness, finite multiplicity per scale, non-trivial closure, and a non-solvable simple internal symmetry. Starting from a single point and proceeding step by step through lines and planar polygons to spatial closure, the author shows that only two routes survive in three dimensions: a trivial simplex route ending at the regular tetrahedron, and a pentagon-based route forced into self-similar phi-stratification, ending at the regular icosahedron. While the simplex route fails the requirement of a non-solvable internal symmetry, the icosahedron satisfies all criteria. The work establishes the identity lcm (12, 20) = 60 = |A5| as a numerical signature of icosahedron-dodecahedron duality and generates a discrete scale ladder defined by lₖ = lP * phiᵏ. Embedding the present cosmological size scale in this ladder gives a single integer order of magnitude, kₜoday approx 291. 5, supported by two mutually consistent observational reductions involving the Hubble length and the present cosmic age. The framework formulates falsifiable consequences in the form of a ln (phi) logarithmic modulation of any scale-dependent observable and identifies the spectrum of admissible fractal stages. A Python script is included in the appendix to ensure the first-principles reproducibility of all numerical claims.
Thomas Krause (Thu,) studied this question.