Dear PF Forum, I have a question that puzzles me. Galaxies are moving away from us, except Milky Way which is in collision to us in some 4 billions years. I think there are other collisions as well from any other galaxies pairs. So, 1. Galaxies are moving away from us. Are they also SPEEDING away? It's Dark energy is it, if it's true. 2. If this is true, we CAN'T say that we are at rest and they are moving (or SPEEDING), right. But,... can they feel the acceleration? Or why can't we feel the acceleration? I know if A moves against B, from B point of view it's A that moves. What if one of them is accelerating? The one who's accelerating MUST know that he's the one who accelerates, right? Thanks for any explanations.