Vacuum Mechanics: Spacetime as an Elastic Medium with Finite Density, Stiffness, and Breaking Strength

We develop a framework treating spacetime as a physical elastic medium, deriving testable predictions for gravitational echoes (97.8 ms for GW150914), correlated variation of fundamental constants (ΔG/G = −4·Δα/α), and a physical mechanism for MOND (a₀ ≈ cH₀/17). Full numerical simulations and source code included.