Because the true vacuum is the more stable state, the universe “prefers” it, and will revert to it if given the slightest chance, just like a pebble will roll down a slope if it’s placed on one. As soon as the bubble appears, the Higgs field all around it is suddenly being shaken down to the valley floor. It’s as though that first event knocks free every precariously balanced pebble near it, and then the avalanche spreads. More and more space succumbs to the true vacuum state. Anything unfortunate enough to be in the bubble’s path is first hit by the intensely energetic bubble wall,
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