velocity of light in materials

[michel123456]

Question: does the velocity of light remain an invariant when it goes through a material?

 

Explaining the question: It is known that C is an invariant when C is speed of light in vacuum.

It is also known that C has other values when it goes through materials (water, glass): is it still a constant regardless of the velocity of the observer / material or is it "linked" to the material?

Edited August 16, 2016 by michel123456

[studiot]

Well it rather depends what you mean by constant.

 

In vacuo the speed is the same for all wavelengths (frequencies) in all directions, and incidentally is the maximum speed for light.

So we don't normally consider these as important variables.

 

Introducing a material introduces complications.

 

Firstly the material itself may not be homogeneous so the passage of light will be affected as the material composition changes.

 

But even given a homogeneous material its effect may not be isotropic in that the refractive index may vary with direction.

 

Finally the speed is now a frequency dependent quantity, in any direction, but is fixed or 'constant' in that direction for as long as the material remains homogeneous and the light frequency is fixed.

[michel123456]

My question is:

If the different observers in other frames, moving with respect to the material, will they measure the same velocity of c inside the material?

[swansont]

My question is:

If the different observers in other frames, moving with respect to the material, will they measure the same velocity of c inside the material?

No. The invariant is c, which is the speed in vacuum.

 

You can travel at the speed of light in a material. The light will not be moving with respect to you.

[michel123456]

No. The invariant is c, which is the speed in vacuum.

 

You can travel at the speed of light in a material. The light will not be moving with respect to you.

Ah.

So the vacuum plays a role in the invariance.