Quantum Tunneling

A ball rolling toward a hill without enough energy to reach the top always rolls back — that is classical physics. In quantum mechanics, there is a small probability the particle passes through the barrier entirely.

Tunneling powers the Sun itself. Hydrogen nuclei in the solar core lack enough energy to overcome their electrical repulsion and fuse. But they tunnel through the barrier. Without quantum tunneling, the Sun would be dark and cold, and life would never have existed.