Ok…. So I’m going to try to rephrase what I just learned from this comment. Can someone tell me how far off I am? The universe is not 100% empty, so the index

Ok…. So I’m going to try to rephrase what I just learned from this comment. Can someone tell me how far off I am? The universe is not 100% empty, so the index of refraction is not 1. This could be explained by lots of phenomena like dust particles or stray radiation, etc. Because of this effect, for practical purposes, light that we see as res “travels slower” because it has traveled through more media than blue light.