# How is light trajectory affected by the trajectory of environment it passes through?

There's a sci-fi concept of slow light that I find very amazing:

Imagine a glass material that has index of refraction $n$ say, $3,000,000,000$ which means:

$$v_{glass} = \frac{c_{vacuum}}{n} = 0.0001 ms^{-1} = 0.1 mm\ s^{-1}$$

Simply a glass material that reduces the light propagation speed to $0.1\ mm/s$. A glass that shows what happened 10 seconds ago if it's 1 centimetre thick.

I was thinking about this and I happened to imagine a cube made of the same material, $1\times 1$ meter. Now imagine pointing a laser pointer in the cube. It's going to take $00:16:40$ for the beam to pass.

Now the question: If you move the cube around or rotate it, will you alter the beam rotation?
My guess is yes, but quantum physics doesn't always follow the rules of common sense.

I want to point out that no matter what the answer is, it's not only matter of fictional cubes but the real world too - flowing water in the river, blowing air...

• I believe so, yes. I won't make an answer to this since I could very well be wrong, but I believe it would. I appreciate that you used "light propagation speed" as opposed to "speed of light" since, of course, the photons themselves are not moving any more quickly or slowly. At any rate, I believe, yes, it would, indeed, continue in its original path relative to the cube. i.e. from top view: (1) shoot laser into left side of cube, (2)rotate it 1/2 turn, (3) the laser is now shooting out of the right side. It is important to note that once it exits the medium, it moves at $c$. Nov 19 '14 at 23:12
• Imagine this as a cool sci-fi weapon... :) Nov 19 '14 at 23:13