But why would light "slow down"? | Visualizing Feynman's lecture on the refractive index

Summary by Krater

An exploration of why light slows down in glass and how that gives rise to the index of refraction and color dispersion, breaking down the interaction between light waves and material charges.

From the video

Answers: Why does light slow down in glass?

• index of refraction
• Snell's law
• light dispersion in prisms
• wave interference
• resonant frequency

What it concludes

• Light slows down in glass because incoming light waves interact with charges in the material, which then radiate secondary waves that interfere with the original wave and cause a phase shift.
• Different frequencies of light experience different phase shifts when interacting with material charges, which explains why blue light slows down more than red light and results in chromatic dispersion in prisms.
• When the frequency of an external driving force matches the resonant frequency of an oscillator, the amplitude of oscillation grows very large, explaining phenomena like the Millennium Bridge swaying and resonance in materials.