I have an explanation for why the universe's expansion has been accelerating (as claimed by some astronomers).
First, I think the rubber-sheet view of how masses interact is not quite right. The rubber sheet view is that first you have this rubber sheet that's stretched taught and straight, and then you put some masses on it that dent it. Since the highest point on the sheet between any two masses is lower than the starting height of the sheet, the two masses tend to move towards eachother unless they are orbiting each other.
But this doesn't hold at extreme distances, because galaxies are not only moving apart from eachother, they are accelerating in their seperation.
I think a better view of the rubber sheet is that the rubber sheet bulges upwards. Of course, to every observer, they are at the top of the bulge. Now, masses that are near your mass will have dents that interact, and tend to draw the two together. But masses are are distant from you tend to slide down the side of the bulge, and the farther away from you, the steeper the slope (as viewed by you), and the faster they move away from you.
The question is, what is causing the rubber sheet to bulge upwards? I think that it's zero-point-energy. Just as two sheets of metal will suck together if they're placed close enough to eachother in a vacuum, due to the pressure that's exerted on them from the outside (but not on the inside, because the wavelength of ZPE won't fit between them), the pressure of ZPE causes distant objects to be forced appart. As they fall farther apart, gravity has less of an influence, but there's always ZPE.
In terms of the rubber sheet, the pressure of the zero-point-energy is essentially pushing on the underside of the sheet, bulging it upwards.