The Quantum Vacuum Universe: Linear and Nonlinear Effects of Quantum Vacuum Composite Stiffness

We present the Quantum Vacuum Universe (QVU) as a unified physical framework in which gravity and cosmic expansion arise from the intrinsic stiffness of spacetime. The Quantum Vacuum Composite Stiffness Response (QVCSR) provides a covariant constitutive law that links the gravitational field with the internal stress of the vacuum, characterized by a universal acceleration scale aQV ≃ 1.09 × 10−10 m s−2. Two regimes naturally emerge. In the linear regime, where accelerations are large compared to aQV, the QVCSR reproduces Newtonian and general-relativistic dynamics and yields an effective cosmological term that drives the observed cosmic acceleration. In the nonlinear regime, where g ≲ aQV, the same stiffness law produces self-gravitating excitations of the vacuum—Qvions—that act as relativistic gravitational solitons with de Sitter-like cores and 1/r acceleration tails. These structures reproduce the flat rotation curves of galaxies, the baryonic Tully– Fisher relation, and lensing signatures commonly attributed to dark matter, without introducing new particles. Thus, phenomena ascribed to both dark energy and dark matter emerge as complementary manifestations of a single quantum vacuum stiffness field governed by aQV. We present relativistic field equations, stability conditions, and observational tests spanning rotation curves, wide binaries, lensing, and potential CMB/BAO signatures of Qvion distributions.