Just a clarification: galaxy rotation curves and the observed expansion of the universe are not really related. The empirically observed expansion of the Unive

Just a clarification: galaxy rotation curves and the observed expansion of the universe are not really related. The empirically observed expansion of the Universe is the motivating evidence for the existence of Dark Energy. Dark Matter, which is motivated (in part) by the inconsistencies in the rotation curves of galaxies is a separate topic. Despite sharing similarities in their names and the fact that they make up the two biggest chunks of energy/mass in the Universe, Dark Energy and Dark Matter are not actually related. The word 'dark' is really just implying that we have not yet observed anything to explain these two phenomenon.