I've read in books and seen on television programs that the universe is expanding, and not only is it expanding it is accelerating in its expansion. I was just reading "parallel worlds" by michio kaku, and I came across the hubble constant, H. This number is the rate at which the universe is expanding. My confusion comes from the contant number of expansion, and the claim of acceleration of expansion. I've resolved the idea in my head, but wanted confirmation that it was correct. Is the universe expanding at a constant rate, and is it only the matter inbetween space that is accelerating away from each other? In which case, it would be incorrect to say the universe is accelerating. I don't know if I'm right, because I've read this phrase in many books.