theguy on Nostr: Right, but this difference in refractive index is between physically existing glass ...

Right, but this difference in refractive index is between physically existing glass and air in case of fibre optic. It might be something similar with ionospheric refraction, but In case of terrestrial refraction it is supposedly difference in refractive index of different layers of air in close proximity to the earth’s surface. Which I haven’t seen documented properly yet.