What is the reason for the decrease in the speed of electromagnetic waves in the medium?

Question

Physics

Speed ​​decreases after all not because of collisions of a quantum with atoms of matter?
Why is this happening?

Answer 1

In a material through which an electromagnetic wave passes, a response wave arises in the opposite direction (due to the electrons in the atom). Atoms "resist" the transmitted light, much like a metal ring is deflected when a magnet is quickly brought up (a reciprocal magnetic field arises).
The vector addition of the main wave and the "response" and gives a decrease in the speed of light in the material. The more compact the material (meaning the packing density of atoms), the greater the "resistance" and the lower the speed of light.

Answer 2

because photons are re-emitted by atoms, it takes time. between atoms, light travels at the same speed - in fact, it does not go on the other