What is Light? A Historical Journey from Euclid to Feynman

Understanding how light behaves is relatively easy. But what exactly is light? A wave? A particle? An emanation from God? Or a quantum excitation in a field? This is a question which has exercised some of the greatest minds of Science. Come on a journey from Euclid to Galileo and Newton; Faraday, Maxwell and Hertz; then on to Einstein’s Special Relativity; Planck, Bohr and finally to Dirac and Feynman’s Quantum Electrodynamics. Are we any the wiser?

This class will be delivered face-to-face at WEA Sydney. Enrolling students need to ensure they have read the current COVID-19 Safety Guidance that WEA Sydney has put in place before enrolling.


  • We start with a history of Science, from the Greeks to Newton, via Baghdad, Spain and the early universities. What did these early scientists/philosophers understand about the nature of light? What did Newton contribute, and what did he get wrong?
  • Faraday was the great experimenter in the emerging field of electricity and magnetism, who found it convenient to express his findings in terms of “lines of force”, or fields. While many of his contemporaries were less than impressed, the great theoretician Maxwell adapted and extended these ideas, and was able to show that light was an electromagnetic wave, as verified by Hertz. But his theory created new headaches, which were only resolved by Einstein.
  • Just when it seemed that we understood the physical world, including light, the Quantum world was opened up by a series of unexpected discoveries. We now understand that individual electrons in atoms absorb and emit individual “packets of light”: photons. So light is now a particle?
  • One of the most remarkable achievements in theoretical Physics came about when Dirac forced a shotgun marriage between Relativity and Quantum Mechanics. His equation is the basis of Feynman’s Quantum Electrodynamics: the ultimate (?) theory of electrons and light.


By the end of this course, students should be able to:

  1. Appreciate the struggle for understanding from the Greeks, via the Arabs, to the early European Universities, preparing the ground for the Scientific Revolution.
  2. Understand the work of Faraday and Maxwell, two of Einstein’s heroes.
  3. Understand the problem that Maxwell’s work created, and how it was resolved by Einstein’s Special Relativity.
  4. Understand the fundamental concepts of the Quantum world of individual electrons in individual atoms, absorbing and emitting individual photons of light.
  5. Appreciate the remarkable achievements of Dirac and Feynman, who united Special Relativity and Quantum Mechanics.

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