Does light travel at different speeds?

[Burnsys]

Controlling the Speed of Light -- Up and Down
http://www.primidi.com/2005/08/20.html


Hi!, i read everywere that someone has "Slowed down" light, speeded it past the speed of light etc.

This is exactly what the EPFL team has demonstrated. Using their Stimulated Brillouin Scattering (SBS) method, the group was able to slow a light signal down by a factor of 3.6

On the other hand, they also did create "extreme conditions in which the light signal traveled faster than 300 million meters a second."
As they don't give any numbers for this upper limit, you have to trust them. Anyway, these results are important because they were achieved using off-the-shelf optical fibers, opening the way for future super fast all-optical routers

Correct me if i am wrong, but, isn't the speed of light a constant?
When the light is "slowed down" it actualy never slows down, it is just absorbed by the atoms and then emited, but light never slow down.

I am tied of this kind of articles, each time they are out, you have a lot of people totaly confused about light and special relativity

 

[J77]

The exact speed of light depends on the type of medium it's propagating in.

eg. c=3e8 m/s in a vacuum.

Though I could be wrong here - this is just what I understand by it...

 

[Burnsys]

right but can light travel in other medium that is not a vaccum?

I mean what medium is a piece of glass?? a collection of atoms, can light travel inside an atom? can light propagate on mater?

Edit: This was discused here before: https://www.physicsforums.com/showthread.php?t=122920

 

[J77]

Not answers to your specific questions, but http://en.wikipedia.org/wiki/Refractive_index

 

[russ_watters]

The simple answer is yes photons only ever travel at C. The mechanism of refraction is complicated, though.

 

[reidy]

i heard c=c/n
where n is the refractive index of the material it is propagates through

air= 1.0003
water=1.4

dont know if this is correct

 

[dimensionless]

Controlling the Speed of Light -- Up and Down
http://www.primidi.com/2005/08/20.html


Hi!, i read everywere that someone has "Slowed down" light, speeded it past the speed of light etc.





Correct me if i am wrong, but, isn't the speed of light a constant?
When the light is "slowed down" it actualy never slows down, it is just absorbed by the atoms and then emited, but light never slow down.

I am tied of this kind of articles, each time they are out, you have a lot of people totaly confused about light and special relativity

Generally speaking the speed that the light propagates through matter is slower.

I think the idea that they might light travel faster is misleading. Wasn't it only the phase velocity that they were able to accelerate? The phenomenon was accomplished with x-rays some 60 years ago.

 

[Burnsys]

Generally speaking the speed that the light propagates through matter is slower.

I think the idea that they might light travel faster is misleading. Wasn't it only the phase velocity that they were able to accelerate? The phenomenon was accomplished with x-rays some 60 years ago.

I know, but, what is matter? an electron? an atom? a proton?? does light really propagates through matter?? can light travel through a proton or an electron? or it's just absorbed and emited? in the last case it's not traveling through mater the photon just ceased to exist and later it was created again. ( i think )