Why Spacetime Is (3+1)-Dimensional: The Dual-Layer Answer to Physics' Unanswered Question

Version 2: Explicit distinction from Einstein's spacetime added as opening section. Einstein said space and time are equivalent. This paper says they are not equivalent — they come from different ontological layers (Koku Universe and Genki Universe). Both describe the same (3+1) universe, but explain it differently: Einstein from the geometry of curvature, this paper from the ontology of two layers. Physics has never explained why spacetime is (3+1)-dimensional. This paper proposes the Dual-Layer answer: the three spatial axes (x,y,z) correspond to the Koku Universe (刻宇宙) — generated by the three-phase rotation of the Gear Ether (Denki × Jiki × Kiko). The temporal axis (t) corresponds to the Genki Universe (元気宇宙) — the one-directional flow of Ki transmission, which is time itself. (x,y,z,t) = (刻,刻,刻,元気).