It appears that the Dark Energy concept was born out of a need to explain the two major observational phenomenons (increasing rate of expansion of the Universe and the faster-than-expectated-rotation of the galactic outer-rim). If I'm not mistaken, this also has to do with gravity seemingly trending towards 1/r rather than 1/r2 with more distance. That said, I'm curious as to what other phenomenons it explains? For example, does it also explain (better) the Pioneer Anomaly and the precession of the perihelion of Mercury? Also, has anyone considered the possibility that the Dark Energy IS THE ONLY SOURCE of Gravity rather than separating the Matter/Dark-Matter as the other sources? For example, Is it wrong to speculate that the Dark Energy, with it's negative-pressure, is the source of gravity with the Matter simply being a region of space-time (due to presence of localized energy) where such gravity is more concentrated (i.e. gravity well)? I ask this question without having any means to formulate it given that it's been a long-long-time since I took Calculus in college.