Can someone please explain to me why the universe must be expanding and not contracting? Here is my take on this. The Doppler Effect tells us that we are moving faster than objects. "Behind" us, and objects "ahead" of us are moving faster still. Hence the inference of expansion. But , if objects were in a period of contraction toward a central point of origin, and curved space (I.e. Gravity) is more severe the closer you get to that central point, then the closer you got to it the faster you would recede from the objects farther away from that point. If the universe was contracting we would expect to see the same Doppler shift that we see. The space between objects would be expanding, but not necessarily the universe as a whole. Objects closer to the central point would accelerate with the curvature of space . In fact, it better explains the observation that the distance between objects is increasing. Main stream notes the increase , but infers that means there is no cycle, and that the universe will expand indefinitely, with no contraction. But they can't explain why the "expansion" would be accelerating. My hypothesis would explain that. In this hypothesis, the universe is contracting toward a central point. The distance between objects in that model would also increase. It's a period of contraction, not expansion. Edited. I know that dark energy is used to explain this acceleration of the universe's "expansion" but why is it that it has to be dark energy and expanding and not contracting as I hypothesized.