Nobody wants to touch this question I see... let me say...

Gravity remains a mystery. The "blackboard" was covered in chalk before E=MC squared emerged. All these new theories are an exercise in mathematics. The blackboard is covered in chalk again.

String theory and 11 dimensions is hardly a distillation of physics to the truth of the nature of gravity and how it relates to other forces. The acceleration of expansion of the universe is much in doubt. The red shift measurements in astronomy are skewed by things we are just finding out about. Dark matter, for example and that light does not take a straight path through the universe, and may be stretched out in wavelength, over time and distance. When we measure light from a distant star, we only a get distorted view of what was going on in the distant past. The acceleration of the expansion of the universe is likely an illusion.

                        image - wikipedia