The Origin of the Refractive Index: Feynman's Physics Explained
Why does light seem to slow down in glass? The light itself is not slowing; rather, its electric field makes the electrons in the glass jiggle, and those jiggling electrons radiate their own little waves. The field you actually observe inside the glass is the sum of the original wave and all these tiny re-radiated ones. Their interference produces a new wave that looks like the original but with a shifted phase — which we measure as a slower speed.
The big idea
Light 'slows' in glass because atoms re-radiate and reshape the wave.
Think about it
If the light wave never truly slows down, what does the 'speed of light in glass' really describe?
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