Quantum tunneling is a phenomenon where particles can move through a barrier that, according to classical physics, they shouldn’t be able to penetrate. Think of it as a particle performing a magic trick, as it slips through obstacles that seem impossible to penetrate.

In our everyday world, objects can’t pass through solid barriers. But the rules are different in the tiny world of quantum physics, where particles such as electrons and photons exist. Here, particles are described not just as tiny bits of matter, but also as waves. These waves don’t stop when they reach a barrier; they have a small chance of “leaking” through it and ending up on the other side. This leakage is what scientists call quantum tunneling.

To understand quantum tunneling, you need to know a bit about how particles behave in the quantum world. Unlike a tennis ball that bounces back when it hits a wall, a quantum particle doesn’t just follow one path. Instead, it explores many possible paths simultaneously due to its wavelike nature. When a particle encounters a barrier, its wave doesn’t vanish. Instead, the wave gradually decreases as it approaches the barrier, but it doesn’t drop to zero immediately. This means there’s still a small chance that the particle can appear on the other side of the barrier.

This probability is what allows quantum tunneling to occur. Even though the particle might not have enough energy to overcome the barrier in the classical sense, its wave function allows it to “tunnel” through the barrier with a small, but nonzero, probability.

The wave function exists outside the barrier. The amount is the portion of the wave function that exists on the other side of the barrier.

Quantum tunneling isn’t just a weird idea with no real-world consequences; it’s a critical part of how lots of technologies work today. For example, tunneling is crucial in the functioning of transistors, which are the building blocks of modern electronics. Without tunneling we wouldn’t have the computers, smartphones or any other digital devices that we rely on every day.

Another fascinating application of quantum tunneling is in the process that powers the sun. The sun produces energy through nuclear fusion, where atomic nuclei combine to form heavier nuclei, releasing huge amounts of energy.

Quantum tunneling plays a key role here because it allows particles to overcome the energy barrier that normally keeps atomic nuclei apart, enabling fusion to occur at the relatively low temperatures found in the sun’s core. Without quantum tunneling there would be no sunlight and no life on Earth.

Quantum tunneling challenges our everyday understanding of the world. It is a reminder that the universe operates on principles that are sometimes counterintuitive and downright strange. But despite its bizarre nature, quantum tunneling is an essential phenomenon that makes much of modern technology possible and even fuels the stars.

Quantum tunneling is like a secret passage in the quantum world, allowing particles to do the impossible. While it might seem like science fiction, it’s a real and fundamental part of the universe that plays a vital role in everything from electronics to the stars above us.

Richard Brill is a retired professor of science at Honolulu Community College. His column runs on the first and third Fridays of the month. Email questions and comments to brill@hawaii.edu.