Is expansion slowing down galaxies?
I’m going to introduce a small complication by way of dark energy. Yes, the universe is expanding, as an intrinsic part of the Big Bang. But from around 5 billion years ago, dark energy began to accelerate this expansion. As I understand it, the expansion of space-time is homogeneous everywhere in the universe due. Both this basic expansion and dark energy does not, at this stage, affect matter that is already gravitationally “clumped” together (i.e. the Earth itself is not getting larger due to expansion or dark energy, but the distance between the Earth and the Moon is increasing, at the rate of a few millimeters per year (the contribution of dark energy to this increase is likely extremely small)). The power of dark energy is roughly 30 proton masses per cubic meter – i.e. very small at local distances. The rate of expansion of the universe is roughly 100km/s per megaparsec (1 Parsec = 3.26 light years or 3.08568025 × 1013 kilometers), and a megaparsec is 1 million parsecs, so again
