Cosmic Voids and Large-Scale Structure Formation: A Pressure-Driven Gravity Approach

This thesis proposes a novel cosmological framework in which the large-scale structure of the universe - voids, filaments and sheets - emerges from pressure gradients in a relativistic superfluid vacuum. Abandoning the need for dark matter and dark energy, the Pressure-Driven Gravity (PDG) model derives gravitational effects from a compressible medium governed by a barotropic equation of state inspired by axion-like particle (ALP) field theory. We develop the theoretical underpinnings of PDG, present a relativistic extension compatible with the Tolman-Oppenheimer-Volkoff equation and derive structure formation criteria via a Jeans-like instability analysis. Numerical simulations using a modified GADGET-2 code are compared to observational data from SDSS, DESI, Planck, DES and SPT. Key observational tests - including void size distributions, two-point correlation functions, weak lensing spectra, BAO and CMB residuals - demonstrate consistency with cosmological data. Bayesian evidence is evaluated against ΛCDM, with sensitivity analyses on priors and model parameters. We address challenges including neutron star stability, CMB fine-tuning and the Hubble tension. Appendices include derivations of the Jeans scale and ALP parameter justifications. This work contributes a unified, testable alternative to standard cosmology with implications for cosmic structure formation, vacuum physics and the interpretation of high-precision data from upcoming surveys like Euclid and the Simons Observatory.