False vacuum decay is a process where the universe is in a stable state that seems “normal,” but it’s actually not the most stable state it could be. Think of it like sitting in a comfy chair that’s actually a little wobbly. If something triggers it, the chair might suddenly collapse and turn into a better one. In the universe, when this “false vacuum” decays, everything could change very quickly, and the universe would shift to a more stable state. This change could happen at any time, even though we don’t notice it yet.