Recognitions:

## Speed of light through glass

 Quote by C2k I realize this post is a bit old, but Im a college student in physics and we actually went over this in a lab today. The analogy given is that youre in a car that can only go two speeds: 100mph and 0mph. When driving through the city, every stop sign, every stop light, every pedestrian and every cat, you instantaneously go from 100-0 then back to 100, causing the time it takes to go through the city to be much longer than if there were no obstacles. This analogy was related to the photons moving through a more dense medium, every time a photon encounters an obstacle, it instantaneously stops and continues (absorption-emission) at the speed of light, causing the speed of light to decrease while in a medium.. Well, not technically the speed of light, but the speed light is capable of traveling through a medium.
That's right, the only subtlety is that the "obstacles" the photons are being absorbed and reemitted by are not actually individual atoms in the medium as one might expect, instead in some weird quantum way the photon is actually being absorbed and reemitted by the lattice of atoms as a whole...see ZapperZ's post #4 on this thread.

 I think the speed of light is always the same and the "slowing down" of light is just another way to say the effective speed of light - for practical purposes you think of it as slowing down. I've read many of the technical explanations of the physics of what be happening, but approaching it from another angle, if the light were truly slowed, then when it left the glass it should remain at that same slowed speed unless some force acted on it to speed it up again right ? So theoretically if i put up a long row of glass blocks (like a long row of dominos), the light should get slower each time it hits a new glass block until it going very slow and you could see it move. I think what happens though is that when it leaves the glass, the light is back at the normal speed of light. So I really think the "slowed" speed is just a net effect.

 Quote by LexLuther I think the speed of light is always the same and the "slowing down" of light is just another way to say the effective speed of light - for practical purposes you think of it as slowing down. I've read many of the technical explanations of the physics of what be happening, but approaching it from another angle, if the light were truly slowed, then when it left the glass it should remain at that same slowed speed unless some force acted on it to speed it up again right ? So theoretically if i put up a long row of glass blocks (like a long row of dominos), the light should get slower each time it hits a new glass block until it going very slow and you could see it move. I think what happens though is that when it leaves the glass, the light is back at the normal speed of light. So I really think the "slowed" speed is just a net effect.
Yes, that's why the time delay hypothesis due to interaction with atoms is really the only feasible explanation. All proposed models boil down to that common idea.