Question

Is the speed of light consistent through everywhere?

Answer 1

The speed of light NEVER changes. It doesnt change even when it is in an optically dense medium. Only in this case what happens is that when the photons hit the molecules of the medium, there is a time delay before the molecule re-emits the photon in the direction it was going initially. In an optically dense medium, there are many molecules which absorb the photon and re-emits it with a delay so overall it takes longer to cover a distance through that medium. It is just like you are driving a care at 50kmph and wait for a few minutes at some points along the journey, your average speed changes but not your actual speed at an instant.

Answer 2

Speed of Light May Not Be Constant Physicists Say. Einstein's theory of special relativity sets of the speed of light, 186,000 miles per second. But some scientists are exploring the possibility that this cosmic speed limit changes

hope it helps:-)