Part 3/14:
Imagine the universe as a landscape of hills and valleys, where each point represents a state of energy. Our universe sits in a "hilltop" or a pancake-shaped valley—a local minimum—which appears stable but isn’t the absolute lowest point. Quantum mechanics allows the universe to “tunnel” through energy barriers, potentially collapsing into a lower-energy vacuum state. In such a scenario, a bubble of "new" vacuum would nucleate in space, expanding at nearly the speed of light and incinerating what we know.
Within this process, fundamental constants would change, dissolving atoms, stars, planets, and even space-time itself. The universe we see today could be wiped out in a flash, with no warning—an existential horror that challenges the very notion of cosmic stability.