Physicist Jim Al-Khalili Explains Role of Quantum Tunnelling in Solar Fusion

Theoretical physicist Jim Al-Khalili said that the Sun shines because of quantum tunnelling in a presentation for The Royal Institution ^[1].

This mechanism is fundamental to the existence of life on Earth. Without the ability for protons to overcome electrical repulsion, the nuclear fusion required to power the Sun would not occur, leaving the solar system dark and cold.

Al-Khalili said that the core of the Sun is the site of nuclear fusion, where hydrogen atoms fuse to create helium. However, protons carry a positive charge, which creates a powerful repulsive force known as the Coulomb barrier. Under classical physics, the temperatures and pressures inside the Sun are not high enough to force these protons together.

Quantum tunnelling provides the solution to this energy gap. In the quantum realm, particles do not have fixed positions but exist as probability waves. This allows a proton to occasionally "tunnel" through the energy barrier rather than climbing over it, effectively appearing on the other side of the repulsion to initiate fusion.

"The Sun shines because of quantum tunnelling," Al-Khalili said ^[1].

This process happens billions of times per second across the solar core. By bypassing the classical requirements for fusion, quantum tunnelling ensures a steady release of energy that sustains the Sun's luminosity over billions of years. The resulting energy travels from the core to the surface, eventually reaching Earth as sunlight.

The lecture, published by The Royal Institution in London, highlights how the smallest scales of physics dictate the behavior of the largest objects in the universe. By simplifying these complex interactions, Al-Khalili illustrates the bridge between theoretical quantum mechanics and observable astronomical phenomena.