The understanding of a refractive index only cares about 'phase speed' in steady state. At least, that is what the video claims to be about. For that case, phas

The understanding of a refractive index only cares about 'phase speed' in steady state. At least, that is what the video claims to be about. For that case, phase kicks are a sufficient explanation no? I can imagine things get really weird with pulses, but that's out of scope for the video.