The Mechanical Origin of Atomic Structure: Primordial Pressure Entrapment and the 0.69ns Nucleation Window

This brief introduces the Universal Shell Theory (UST), a mechanical framework redefining the atom as a pressurized 3D vessel wrapped from primordial 2D energy fields. It identifies a 0.69ns nucleation window during the Big Bang that dictates atomic volume, surface vibration (charge), and neutron stability. The paper provides a mechanical solution to the "Neutron Lifetime Puzzle" and calculates skin tension constants ($\gamma$) for elements 1–20.