What is the speed of light inside a moving glass slab?

The speed of a photon is always c. Never faster or slower. When a photon enter a material and hits atoms of the material it gets absorbed by the atom's electron cloud and elevates a electron to a higher energy state ( photon stops). The electron falls Back to ground state emitting a new photon ( light starts). So, light starts and stops passing through a material. The speed of the photons between atoms is still c. But because of starting and stopping the AVERAGE speed I'd less than c.

The speed of light through a medium does not change with the motion of the medium. The only time you could measure the speed of the photons is between atoms and it is always c

The VACUUM speed of light is always c.

The speed of light in a medium, is controlled by the electron dances for ranges of wavelengths. Gamma and x-rays propagate at c_vacuum through all media.

Fizeau showed that visible light in water, moved at c_medium ± v_medium. Still much less than c_vacuum.

[EDIT: "I want to know WHY AND HOW the answer is still c."

You can imagine a circumstance where the medium is moving arbitrarily close to c. The electrons will be moving less than c (if they are involved). The light in between emission and reabsorption will be moving at c. Nothing moves faster than c.

There are no WHY answers in Science. We can only describe what we see, and Nature shows us a constant c:

http://physics.nist.gov/cgi-bin/cuu/Value?c

... note there is no uncertainty in that value. This constant, fixes the metre (and thereby the inch, foot, and so on).

]

The speed of light *in vacuum* is always c.

The speed of light in a medium is c/n in the rest frame of that medium. It's true that individual photons between atoms travel at c, but that's not what you're asking about. You're asking about the group velocity of the light wave.

To find the group velocity of light in the moving medium, use the relativistic velocity addition rule to combine the velocity of the medium with c/n. The answer will be less than c.

The speed of light is always same to all observers, no matter how fast he is travelling, Lorentz transformation and time dilation and many other effects will diminish the difference, and speed of light would be the same... In my frame of reference, it will always be C... but then again, in a glass slab, the cosmological constant reduces its speed... :p

and also... Scientists were able to slow down the speed of light to about 36 km/h with Bose Einstein condensate... Just a fun fact :P

Direg

apparently i am not eligible to like peoples' comments! :D .... i think mr. Oldpilot has given a real good explanation

It's dispersed but still c.