We present a theoretical framework in which gravity becomes repulsive when the gravitational force reaches a maximum value, known as the Planck force. This inner flip from attractive to repulsive gravity at extreme field strengths resolves three fundamental problems in physics. First, it explains why the Big Bang did not immediately re-collapse under its own gravity: when the entire massof the observable universe was compressed within a radius of approximately 24cm, the gravitational force exceeded Fmax, triggering repulsive gravity and driving explosive expansion. Second, it eliminates the singularity inside black holes, replacing the infinite-density point with a finite-density core at the inner flip radius rmin. Third, it establishes a minimum mass for black hole formation of approximately 250 grams, below which the repulsive core extends beyond the would-be event horizon, preventing collapse. Thisminimum mass directly contradicts the standard primordial black hole hypothesis, which allows black holes of arbitrarily small mass. Our theory uses only two well-established constants G and c and the SI base unit of 1 kg, requiring no new particles, no inflaton field, and no exotic matter.