Ripples in Space

[EFLImpudence]

That's not what we are discussing; that's because of the entry and/or exit angles - reflection and refraction.

Light passing through a glass block with parallel entry and exit surfaces goes straight through so how can it have been bounced about all over the place by the molecules.

 

[Brigadier]

It's exactly what you are discussing.

A photon will not know which direction it is meant to exit the glass, when it enters it. Ergo, the "bouncing around" explanation doesn't make sense - you might as well say that the photon "tosses it off for a bit, while it's inside the glass".

 

[noseall]

The light does not slow down inside the glass, it just appears that way. The speed of light is constant. Whoever told you that it isn't is telling fibs.

 

[EFLImpudence]

It's exactly what you are discussing.

A photon will not know which direction it is meant to exit the glass, when it enters it. Ergo, the "bouncing around" explanation doesn't make sense - you might as well say that the photon "tosses it off for a bit, while it's inside the glass".

No, you are misunderstanding me.

Noseall said that the speed of light is the same inside a dense medium (glass, but not frosted); it just seems slower because it is bounced about off the molecules inside and then emerges.
If this were the case (in a rectangular block or, for that matter, a window), how does it emerge all in the same original direction?

In this case it has been refracted but, presumably not bounced about by the molecules.

The same question here:

How can it have been bounced about

 

[JohnD]

It is my understanding that the speed of light is constant in a vacuum; but when travelling through other, transparent, materials, is slower.

 

[Brigadier]

Exactly.
If photons are "bounced about", they would exit the glass every-which-way. Which would mean that there was no such thing as "clear" glass and therefore, no need for frosted glass.

 

[noseall]

It is my understanding that the speed of light is constant in a vacuum; but when travelling through other, transparent, materials, is slower.

No, the speed of light is constant. It will travel at the same speed within the glass.

 

[JohnD]

https://en.wikipedia.org/wiki/Speed_of_light#In_a_medium

"The speed at which light propagates through transparent materials, such as glass or air, is less than c; similarly, the speed of radio waves in wire cables is slower than c"

"High-frequency trading
The speed of light has become important in high-frequency trading, where traders seek to gain minute advantages by delivering their trades to exchanges fractions of a second ahead of other traders. For example, traders have been switching to microwave communications between trading hubs, because of the advantage which microwaves travelling at near to the speed of light in air, have over fibre optic signals which travel 30–40% slower at the speed of light through glass.[82]"

 

[Mikefromlondon]

Well let us assume a light entering a glass block gets deflected or whatever you want to call where it changes its direction, so naturally it is the time it takes to emerge from that glass block that may be a little later, or a delay it coming out since change of angle means a slightly longer or path, since speed = d/t, so any change in distance means the time it takes to pass through a glass block may be a few nano seconds late but the speed of the light did not alter, it just had to cover a little longer distance, so remained constant

If you were driving on a dual carriage way, at steady 40mph, you would cover a stretch of that road in say 15 seconds, if that stretch had a round about and say you negotiated it at the same 40mph, then you would take a little longer since the curves of the round about would add a few more yards. (This becomes crucial in Formula 1 racing, where matter of hundredth of a second determines world champion)

 

[Brigadier]

https://en.wikipedia.org/wiki/Speed_of_light#In_a_medium

"The speed at which light propagates through transparent materials, such as glass or air, is less than c; similarly, the speed of radio waves in wire cables is slower than c"

"High-frequency trading
The speed of light has become important in high-frequency trading, where traders seek to gain minute advantages by delivering their trades to exchanges fractions of a second ahead of other traders. For example, traders have been switching to microwave communications between trading hubs, because of the advantage which microwaves travelling at near to the speed of light in air, have over fibre optic signals which travel 30–40% slower at the speed of light through glass.[82]"

"Propagates" is the key word there. Analogous to sprint-walk-sprint-walk being slower overall than sprint-sprint-sprint-sprint, even though each sprint is the same speed.

 

[Mikefromlondon]

https://en.wikipedia.org/wiki/Speed_of_light#In_a_medium

"The speed at which light propagates through transparent materials, such as glass or air, is less than c; similarly, the speed of radio waves in wire cables is slower than c"

"High-frequency trading
The speed of light has become important in high-frequency trading, where traders seek to gain minute advantages by delivering their trades to exchanges fractions of a second ahead of other traders. For example, traders have been switching to microwave communications between trading hubs, because of the advantage which microwaves travelling at near to the speed of light in air, have over fibre optic signals which travel 30–40% slower at the speed of light through glass.[82]"

"Propagates" is the key word there. Analogous to sprint-walk-sprint-walk being slower overall than sprint-sprint-sprint-sprint, even though each sprint is the same speed.

yes the speed of light remains same but it travels through a long fiber cable bouncing off sides and so on (propagates) hence takes longer.

Watch the green arrows representing light, and you can see the light emerges later out of medium as it takes time to work its way out, and continues to travel at its optimum speed once out, so many people call this light slows down, but in reality it doesn't as it just gets held up in kind of traffic and emerges later.