Wave-Particle Duality

Historically, we might trace the issue of wave-particle duality back to the 17th century, when Isaac Newton and  Christiaan Huygens forwarded competing ideas as a description of the fundamental nature of light. Newton preferred what he called the ‘corpuscular’ or particle theory of light, while Huygens backed a wave theory of light. Given the status of Newton’s reputation, the establishment came to accept that the fundamental nature of light aligned to a particle description, although there were known anomalies that still seemed to be best described by a wave model. By the early 19th century, some of these ‘anomalies’, e.g. diffraction, were becoming increasingly problematic within the particle model. In 1801, Thomas Young performed what is now known as the double slit experiment, which renewed the debate about the wave-particle duality of light.


So, in 1864, the publication of Maxwell’s equations and the description of light as an electromagnetic wave appear to provide conclusive proof that light was indeed a wave. However, as previously outlined, Einstein would re-ignite the debate, in 1905, with the publication of a paper describing the photoelectric effect. In this paper was the suggestion that light travelled as discrete bundles of energy characterised by the relationship [E=hf], which would later be called photons. While Einstein had renewed the wave-particle debate, as early as 1905, the idea of the photon was not generally accepted. In part, we might recognise that the scientific establishment had only just consolidated its acceptance of light as a wave, based on Maxwell’s description of a electromagnetic wave; as such, there may have been little appetite to re-open the wave-particle duality debate. However, while this position concerning the duality of light would be maintain for the next 20 years, by 1922, substantial evidence in support of the photon model would be submitted in the form of Compton’s scattering. This would be further compounded, in 1924, by the publication of the doctoral thesis of Louis deBroglie in which he forwarded the idea that the wave-particle debate also encompassed matter particles as waves, as well as light waves as particles. In many respects, the debate that followed is possibly more representative of the true dawn of quantum theory and where we re-join the historic timeline in the following sub-pages: