disclaimer: I am not an expert, I am not a physicist, I am not an astronomer. I have no idea what I am doing.
From discussions I've read about this paper, I've been led to understand that it states specifics of three major problems/"dark spots" in gravitation:
- Gravity on quantum scales
- Accelerated expansion of the universe / dark energy
- Extra gravity in places where we don't see matter, e.g. in the rotational speed of galaxies / dark matter.
Doesn't dark matter present a much larger problem than just rotation curves? Wasn't dark matter conceptualized not because of rotation curves but to explain how the large scale structure of the universe formed?
By my understanding, he solves these 3 issues of gravity by giving the theory that when matter is created some of the information associated with space gets localized into matter. This in turns a cluster of informationless space around the matter. In his model the comparison of information associated with matter, we can calculate how big the area of space is that matches the amount of information in matter, so we can calculate how big the area of informationless space around matter is, i.e. roughly how far away from the matter you have to go until the space is again filled with information. It turns out that this distance matches experimental observations of dark matter in galaxies. His theory seems only to portray dark matter as a force due to the creation of matter, but his theory predicts the relative amount of effective dark matter to normal matter.
The limitations of his theory do come to a halting stop when you think about something like the Bullet Cluster, and if this was really hitting on the nail, it would shed some light on it.
To supplement the Einstein discussion: there is nothing in the theories of relativity that explicitly negates the potential theory of faster than light travel. It is conclusive that accelerating past c is 'forbidden', as speed ends up asymptotically approaching it as you keep accelerating.
However, things are more complicated than saying 'well, stuff could go faster than light'. An example would be putting a speed greater than c into the equations gives results such as an imaginary (in the mathematical sense) mass for the particle. We have really no idea what that would physically mean, imaginary numbers never intrude into reality anywhere else. These kinds of thing, along with the lack of any experimental evidence for any kind of greater than c effect, are a strong suggestion that faster than light travel is not really possible.
That said, these problems do not constitute a proof. Also, even if faster than light stuff doesn't happen, it's interesting to look at what our theories predict if it did.