I don't think that's what agent smith meant. all this is doing is changing the refraction index of the world around us.. in most cases this is Air.. which has a refraction index of 1. It's probably higher when taken in relation to a vacuum, however, we use this as our basis and therefore the refraction is and always will be 1... This again shouldn't have any effect on non transparent materials. But if you stuck a sphere in there and made the refraction 1.33 and the refraction of the cube 1.33 the sphere should become invisible. This is all you are doing in a non photon based rendering engine.. changing the relative refraction incidents.