When we think of particles, like electrons, we often imagine them as tiny billiard balls that must roll over a hill to get to the other side. Classical physics says that if they don’t have enough energy, they simply can’t cross the hill. But in quantum physics, there’s a strange and fascinating exception known as “quantum tunneling.” Here, particles sometimes appear on the other side of a barrier, even if they don’t have the energy to climb it.

Instead of thinking of particles as solid objects, quantum mechanics describes them more like waves spread out in space. Because of this wave-like nature, a small part of the “wave” can stretch through the barrier. If the wave on the other side is strong enough, the particle effectively “tunnels” through and appears where it classically shouldn’t be. This effect isn’t just theoretical—it’s essential for processes like nuclear fusion in the Sun and even some electronic devices in your home. Although quantum tunneling seems like magic, it’s a key ingredient in how the universe truly operates on its smallest scales.

References

Gamow, G. (1928). Quantum theory of the atomic nucleus. Zeitschrift für Physik, 51, 204–212. (Classic paper introducing the concept.)

Merzbacher, E. (1998). Quantum Mechanics (3rd ed.). Wiley. (Standard text discussing tunneling.)