Quantum tunneling is a phenomenon from quantum physics that sounds almost impossible at first: particles can pass through barriers even though, according to everyday logic, they should not have enough energy to do so. In our daily experience, this would be like a ball passing through a wall without breaking it. In the world of very small particles, however, this can actually happen.
The reason lies in the fact that particles such as electrons are not just tiny solid objects. They also behave like waves. These waves can extend slightly into a barrier. If the barrier is thin enough, there is a certain probability that the particle will appear on the other side. This process is called “tunneling”.
Quantum tunneling is not just a theoretical exception. It plays an important role in many modern technologies. Without quantum tunneling, devices such as computer chips, scanning tunneling microscopes, or many quantum technologies would not work. It also occurs in nature, for example in nuclear reactions inside the sun. This phenomenon impressively demonstrates how much the laws of the quantum world differ from our everyday experience—yet they have a real-world impact on our lives.