why only space beetwen galaxies is increasing while everything else remains the same? like for example why atoms aren't moving further away from eachother, does it have to do anything with gravity? or scale? and if the space beetwen galaxies is increasing why do they collide with eachother? is there even any speed for the expanse rate?
would it be possible that universe isn't expanding but the galaxies inside it are shrinking from their own graviity?
t. brainlet please explain it to me in simple way