The unification of general relativity and quantum mechanics remains a central challenge of modern physics. Inflativity introduces a deterministic geometric unified field theory formulated within a four-dimensional Euclidean spatial manifold governed by observational projection limits for massless propagation. Time is defined as emergent from displacement along the fourth spatial dimension. All relativistic and quantum phenomena follow from the conservation of total four-dimensional expansion. From this invariant, the Lorentz transformation and a gravitational field equation consistent with the Schwarzschild redshift factor in the weak-field limit, are derived without invoking spacetime curvature or probabilistic collapse. The Born-rule probability relation emerges geometrically from the deterministic projection of a four-dimensional availability distribution into the observable three-dimensional domain. The resulting Inflativity Field Equation unifies relativistic dynamics, galactic rotation behaviour, and quantum measurement within a single predictive framework that yields distinct observational tests involving galaxy kinematics, photon arrival modulations, and finite black-hole interiors.