All possible paths: bringing quantum electrodynamics to classrooms

Abstract

Abstract Quantum electrodynamics was described by Feynman as the ‘jewel of physics’ [1985 QED: The Strange Theory of Light and Matter (Alix G. Mautner Memorial Lectures) (Princeton, NJ: Princeton University Press)] because of its ability to precisely describe the interaction of light and matter. It embodies the key concepts of quantum physics and yet also describes classical optics. It is normally considered to be too advanced for use in schools. Here we show that through the use of novel learning tools called phasor wheels, it is possible to make quantum electrodynamics accessible to students from middle school and higher. Our graphical approach is based on the summation of all possible paths (formally known as Feynman path integrals). It uses graphical vector addition, and gives students a deep understanding of vectors. It offers insights into the quantum world in which observations represent quantum probability density, while correctly describing the laws of classical optics. The phasor wheel is a tactile tool that allows students to compute the probability of photons arriving at a point in space and to explore phenomena such as matter–wave interference, diffraction, and reflection without any distinction between quantum or classical. To make it accessible, we combine the phasor tool with real-life analogies, and videos of single quanta interference. Needing only elementary mathematics, the approach is suitable for middle/upper secondary schools as well early undergraduate students.