I think…remember you heard it here first…that all our atoms and stars and galactic clusters are rushing away from each other because…
…wait for it…
Another Big Bang has happened at the heart of it all, and new matter is accelerated outward, pushing our universe outward at all inner points of origin. Being separate universes we cannot see each other. But that’s it. The cosmos has hiccuped again, and we are one in a succession of such pulses, chasing the wavefront of the universe before us. Dark matter and dark energy are the only manifestation of the other universe threaded through our own—and it keeps on happening.

Of course, I may have another theory by supper. But I enjoy wondering about such things.