I had questions concerning the Hubble Sphere and while researching why the Hubble sphere doesn't shrink as the universe accelerates someone informed me that the universe isn't truly accelerating in its expansion as we might conventionally think. They informed me that the universe was "accelerating" because as space expands there is more space in between two objects. However the actual expansion has been slowing down since the big bang. Perhaps he articulates it in a more coherent manner. "If we assume that the Big Bang happened everywhere and at once, at the start of the Universe, then we must understand that the entire Universe isn't expanding or moving away from a single point. Rather, every point is moving away from every other point, space is expanding at every point uniformly. So imagine that every point in space is doubling (or increasing at whatever rate - the rate is not important in this explanation). Every point is becoming more points as time progresses. Now realize the following. If we start with 20 points and after 1 second we get 40, then in the next second, 40 points are now doubling to give 80. In the first step the expansion consisted of 20 points but in the second step it is 40. This is the ABSOLUTE expansion of the Universe. You can see that the next step is then an expansion by 80 points and so on. The part that is decreasing with time is the RELATIVE rate of expansion or what I simply called "doubling" in the previous paragraph. Of course the rate is not (x2), or doubling, but I'm just using it for simplicity. So this rate is in fact decreasing. The point for point expansion of space OR how much more space can one point create in the next second. This is what is decreasing. However you must realize that even though this rate is decreasing, since we have more space to multiply in the next step, the overall expansion or the ABSOLUTE expansion is still increasing. To demonstrate, let's use our same numbers from before but with a decreasing relative expansion. So in the first step we have 20 points that expand by (x2) to give 40. Our increase was 20. In the next step, these 40 points expand by, say (x1.9), which has decreased from 2 by 0.1. In this step we get an increase from 40 points to 40 x 1.9 = 76. So we have expanded by 36 points. You can see that the overall expansion or ABSOLUTE expansion has increased from step 1 (36>20) but the RELATIVE expansion, that is the point for point expansion, has decreased from 2 to 1.9." With this is mind, it makes sense that the universe is accelerating. Why do we need dark energy to explain this rather than just saying that as there is more space then there is more space to expand into?