Theoretical physics has totally gone to hell. The basic density of space in our galaxy is similar to that of the area including our sun and AC i.e. about one dust mote every four miles, and the density of space between galaxies has to be vastly less than that. There is no way gravity does ANYTHING worth talking about at those distances. Gravity is the weakest force in nature and does not control the cosmos, period.
We need to find simpler explanations to the universe.
Ok, if not gravity then what other physical force creates the large-scale structures that we see in the cosmos?
It is true that gravity is a very week force. But it does becomes important when there is a large mass.
The gravity between atoms is insignificant because the mass is so mall. Between atoms electricity is a greater force, the source of chemical reactions. And at the subatomic level, gravity again is very insignificant because the mass is so small. Between subatomic particles, nuclear forces are extremely powerful, but they operate over very short distances.
But when there is a large mass like the sun, then gravity becomes a significant force in the surrounding space. And the gravitational force operates over very large distances. Over those large distances, electrical and nuclear forces are insignificant.
It seems that way sometimes. But theory must remain connected to what is more firmly established, even if it often seems wild. In other words, M-Theory, for example, connects to General Relativity in a very natural way at low energies. But M-Theory's dynamics would only be manifest at energies much higher than anything we can perhaps ever achieve. But it's a very beautiful theory. And beauty is one of the central aspects that it seems God structured the universe around.
Galactic clusters are held together by gravity and until quite recently cosmologists were unsure whether or not gravity might actually halt the expansion of the universe and lead to a Big Crunch. Gravity plays a huge role in shaping the universe.