Since dark energy and other models for explaining accelerating universe (which is quite hard to explain) are somewhat speculative, I hope that PhysicsForums rules allow some speculation on this subject. I try to keep this short. And this is also a question. Is there any serious research where accelerating universe is not explained by some internal force speeding up the expansion, but instead, some external force pulling the universe to expand? If we pull the universe from outside (whatever that means) with constant force to every direction, assuming that the force is strong enough to overcome gravitation, isn't accelerating universe just what we can expect? It would be reasonable consequence, without need for dark energy with strange properties or something similar. Surely we cannot directly observe anything outside our universe, but by studying the expansion rate or mass distribution in universe, we might get some indirect evidence to support this kind of theory.