The Elastic Onion Universe: A Complete Theory of Elastic Spacetime with Bidirectional Time, Concentric Hierarchical Structure, and Parameter-Free Derivation of the Fundamental Physical Constants

We present a complete theoretical framework in which spacetime is an elastic medium with well-defined mechanical properties, organized in a concentric hierarchical structure (the "onion"), with time flowing bidirectionally. This paper provides the full technical foundation and demonstrates that the fundamental physical constants emerge from the geometric and topological structure of this medium with zero free parameters. Part I establishes the foundations: spacetime as an elastic medium with elastic modulus Eₛt ~ 10⁸ Pa and temporal viscosity ηₜ ~ 10⁴³ Pa·s; the hierarchical onion structure with inter-layer ratio φ ≈ 2. 4 (empirically derived) ; bidirectional time (t₊, t₋) ; the Planck-scale FCC lattice with coordination z=12; and particles as topological solitons. Part II introduces the (6+2) -dimensional hypothesis: six spatial dimensions (three per temporal dimension) plus two temporal dimensions, following logically from bidirectional time. Part III presents parameter-free derivations: the fine structure constant α = 1/137. 05 (error <0. 01%) ; the Planck-to-electron mass ratio mP/mₑ with 99. 9998% precision; the reduced Planck constant ℏ; and the electric charge e. A decoherence formula validated against experimental data across 12 orders of magnitude in timescale is also derived, unifying decoherence and wavefunction collapse as the same elastic mechanism. The framework resolves dark matter (gravitational influence from higher onion layers), dark energy (elastic tension plus temporal dilation), the cosmological constant problem (natural UV cutoff from lattice structure), wave-particle duality (soliton dynamics), quantum entanglement (shared medium deformation), and the measurement problem (elastic relaxation). This is a companion technical paper to Volumes 1–2 of the Elastic Onion Universe series.