To continue this discussion, this is true that gravity is important when many many particles are into the game. However, this is not the case here which is why gravity is totally ignored.
I am againnot sure to follow you when you reintroduce dark matter and dark energy, and i hence do not know what to say. You may need to clarify your thoughts first ;) apologies for this.
Anyhow, maybe discussing the basis as a start, when you will have more time, may help ^^