This reminds me of this Sixty Symbols video which explains why light is slower in media such as glass than in a vacuum: https://www.youtube.com/watch?v=CiHN0ZW

This reminds me of this Sixty Symbols video which explains why light is slower in media such as glass than in a vacuum: https://www.youtube.com/watch?v=CiHN0ZWE5bk https://www.youtube.com/watch?v=CiHN0ZWE5bk The incoming light wave causes an avalanche of secondary waves through electromagnetically perturbing the individual atoms, and the superposition of all these results in a wave that seems to travel slower than the speed of light.