Why light slows in water and glass
Fermilab · Explainer · 10 min · 2019 · YouTube title: Why does light slow down in water?
Why it's here
HN commenters link it to correct the widespread misconception about why light slows in a medium.
What it covers
Fermilab's Don Lincoln explains why light travels slower in water and glass. He knocks down common wrong explanations such as absorption and re-emission, then gives the wave-mechanics reason tied to refractive index.