What does it mean that light 'slows down' in glass?

A link to the full video is at the bottom of the screen.

That video unpacks the mechanism behind how light slows down in passing through a medium, and why the slow-down rate would depend on color.

Editing from long-form to short by Dawid Kołodziej

[czelley]

Phase retarders were one of the most difficult parts of my optics class, this visual demonstration makes it much easier to understand the physics of how phase changes occur.

[blakeallen]

I've seen the original video twice, and this short like three times. I understand the concept pretty well at this point. I just like seeing the animation, it's so satisfying

[HenryHerkula]

It's a wonderful description of the process. Thank you for your work!

[TheOtherSteel]

How does the glass "kick" the wave back?

[guidosalescalvano]

So what is the kickback then? Absorption and re-emission by an electron shell?

[raymitchell]

Ooohh... so clearly explained! This channel truly deepens my understandings! I think now the question moves to the physical properties of the material and why the phase is shifted.

[rotaruiulian]

The explanation is correct, the graphic representation it’s almost perfect. In your graph the wavelength it’s getting shorter at the entry, then remains constant. When actually, if i’m not mistaking, in reality the wavelength it’s diminishing little by little as it goes through the medium.

[EvilTim]

This is an excellent explanation. Because we always hear two seemingly contradictory statements - 1. The speed of light is constant, and 2. Light slows down in different mediums. This can be confusing unless you understand what this video is explaining

[beboba]

You just explained one question with another question

[hanfo]

the kickback can be described as a higher force against the light. breaking power if you want. when there is no mass, there is no brakes. that’s max c in vacuum.

[JTBettencourt]

That explanation merely passes the buck.
It’s turtles all the way down.

[bangaloreindia]

How come then speed comes back higher (increased ) when it comes out of denser medium to air/vaccum?

[ehocurh]

wow man how....I never knew this. I just accepted this as a fact in high school. So good!

[_BlackSpectrum]

Nice video watched it, I had few questions, hopefully someone answers them, posted in the comment section of the main video!

[saimon]

But it doesn't explain anything. You just replaced the phrase "slow down" with "kick back"

[stephenpeters]

This guy brain is the kind i enjoy thinking from.
Matches my frequency everyother day ❤

[edmundlively]

A coaxial cable does the same thing to a radio wave because of the inductance in the conductor of the coaxial cable and the capacitance between the two conductors there is a lag. Longer. The cable the more phase shift you get .

[raghavendra]

Now please explain why glass affects the the phase of light and kicks it back

[atticuswalker]

if this were the case then the angle of refraction would reflect the width of the medium. but it dosent.
the angle of refraction reflects the difference in density between mediums. despite the thickness of the density of the space. once the light enters the glass it's. it's wavelength and direction do not change.

[raedkm]

I think its gravity force! Time is compressed with mass so we can see the relative speeds of light decreasing but its really not decreasing just the fabric of space compressed because of mass - just a thought/theory