Captain Nemo wrote on Aug 25
th, 2021 at 11:19am:
And another thing ... if light
slows entering a denser medium (e.g. bending through glass) ... how come it speeds up again coming out?
I have seen many explanations for this and it is confusing. The one I go with is because light bumps into the atoms, gets absorbed and re-emitted. This takes time. A quantum view rather than the wave view.
It is actually not able to travel through without being absorbed at the visible frequency by bumping into atom as it is densely packed. It returns to normal speed when it exists the dense object. In air if it hits an atom, it will be re-emitted. Hence a rainbow is the light being diffracted when it hits water molecule or why the sky is blue.
However at other frequencies that are not at the frequency the atoms will absorb (the right quantum) then it will just pass through in effected. E.g. Radio wave.
Update:
Jut went to find this video I watched a few year ago.
Check out Richard Feynman's lectures on QED.
They are from the 80s but he provides the best explanation for this.
All his lectures are very informative.