Eternal Inflation: Bubble Nucleation

Eternal inflation predicts that the false-vacuum background never finishes decaying everywhere at once: true-vacuum "pocket universe" bubbles nucleate at random points and times, each one growing at close to light-speed. Because the background itself keeps expanding exponentially, a bubble's reach in comoving coordinates saturates rather than growing without bound — new bubbles keep appearing in the space left behind. This simulation draws that process directly on a 2D comoving slice: watch bubbles nucleate, grow toward their saturation radius, and occasionally collide with a neighbor, leaving a domain-wall scar exactly like the collision signatures physicists search for in the cosmic microwave background. Adjust the nucleation rate, the background's Hubble rate, and the bubble wall speed to see how each reshapes the resulting multiverse.