I was watching an XKCD “What-If” video recently and Randal off-handedly mentions the title fact as a given. Upon a further Google search I see explanations about why sound moves faster in liquids than gasses but nothing for my specific question. Is there an intuitive explanation for that fact or is it just one of those weird observable facts with no clear explanation
If I get the explanation on Wikipedia right, it’s not the photon taking a longer path, but the photon is absorbed by electons and re-emitted after a short delay. This effect is what decreases the effective speed of light in a transparent medium.