[s0ulphire]

> Light seems like it slows down in dense media, but light always propagates at the fastest possible speed for any physical thing. The slow down occurs when the light gets briefly absorbed by atoms and then re-emitted in the same direction.

Someone please correct me if I'm wrong, but Sixty Symbols (aka nottinghamscience) did at least 2 videos on this where they expressly pointed out that this is widely pushed but totally incorrect? https://www.youtube.com/watch?v=CiHN0ZWE5bk

[lilgreenland]

thanks! When I wrote that line I think I went with the top result of physics.stackexchange, but I'm now convinced that the phase velocity explanation is better.

Here is my updated text:

<p>While individual waves of light always move at c, light seems to move slower in dense media. This is because as the light wave propagates through a medium it produces ripples that <a href="https://www.youtube.com/watch?v=CiHN0ZWE5bk">interfere</a> in a way that slows the group velocity of the light wave.</p>