Elastic Spacetime Theory: Deriving All Fundamental Constants from (6+2)D Geometry

We present Elastic Spacetime Theory (EST), in which spacetime is modeled as a continuous elastic medium with 6 spatial and 2 temporal dimensions — denoted (6+2) D. The theory has zero free parameters: every fundamental constant is derived from the geometry of the medium using only three empirical anchors (the speed of light c, the electron mass mₑ, and the age of the universe tᵤ). From these three inputs and the dimensional structure (Dₛ=6, Dₜ=2), we derive 22 physical quantities, including: the fine-structure constant α=1/137. 036 to <0. 01% error; the Planck-to-electron mass ratio to 0. 002%; the Higgs boson mass to 0. 12%; all three charged lepton mass ratios to sub-percent accuracy; the Planck length, gravitational constant G, and reduced Planck constant ℏ as fully derived quantities; the density and elastic modulus of the spacetime medium; and the quantum coherence length (~98 light-years). Beyond numerical derivations, the framework provides geometric explanations for: mass as a temporal offset, electric charge as a projection of that offset, vacuum transparency as 1−α, special-relativistic time dilation as geometric projection onto the temporal plane, and CPT symmetry as a geometric tautology. Competing dimensional configurations, including (3+2) D, are excluded by existing experimental data without new experiments. The theory makes eight falsifiable predictions, including a new particle at ~245–250 GeV. Three independent researchers — Lanciani (1999), the present author (2025), and Kulkarni (2026) — converged on related geometric structures without prior contact. Companion volumes: DOI 10. 5281/zenodo. 18911034