B Can the speed of light change?

I had the impression that In the case of light going through a medium, the apparent speed slows down due to the rate that electrons absorb and emit photons, but that the speed of the photons as they travel unimpeded remains the same.

On the other hand, to an observer outside of the effect of a particular gravity field, the speed of light would be slower where the gravitational intensity is greater.

 

No.

 

That is a widely held, but incorrect, belief. There is a recent thread on this. I suggest a forum search.

 

Thanks. At least I know why I had that impression (might have been related to propagation inside of a laser). I wondered what percentage of light is actually captured and re-emitted while traveling through a medium such as glass.

In the case of a mirror, then almost all of the reflected light is due to interaction with the reflecting surface (some of the light is reflected by the glass). I'm wondering if there is a delay (maybe just a phase shift) of the reflected light.

 

See post #2

 

Light travels in vacuum with a constant speed which is equal to 299, 792, 458 m/s. It slows down when it travels through an optically denser medium such as glass, water, etc.