Light: from rays to photons

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The longest argument in physics: is light a wave or a particle? Newton's corpuscles, Young and Fresnel's decisive waves, Maxwell's electromagnetic radiation — and then Planck and Einstein forcing the particle back in as the photon. Optics is where classical physics is at its most beautiful, and where it breaks. This is the place to finally read Einstein directly: Stachel's slim collection of the five 1905 papers, with the light-quantum paper beside Feynman's QED.

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done when you can

Explain the double-slit result and why it forced the wave theory on a reluctant field.Say what the photoelectric effect showed that waves alone could not.Hold "wave and particle" as a real tension, not a slogan — and see why resolving it needs quantum mechanics.Connect an atom's sharp spectral colours (the Atoms unit) to Bohr's quantized orbits.

resources

○Light Years— Brian Clegganchor · book
○QED: The Strange Theory of Light and Matter— Richard Feynmancompanion · book
○Einstein's Miraculous Year: Five Papers That Changed the Face of Physics— John Stachel (ed.)companion · book
○Understanding Physics, Vol. 2: Light, Magnetism, and Electricity— Isaac Asimovoptional · book

sessions

unlocks The Quantum path — light is the first place quantization became unavoidable. Ibn al-Haytham (the Roots unit) opened this thread a millennium earlier. The same Einstein volume is also the primary source for special relativity and E=mc², and — via the Brownian-motion paper — for the reality of atoms.

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