I am a bit confused by your answer. I am not sure to follow what you are explaining.
Gravity does not need particles to exist. It is there, and everything couples to gravity. Graviton is known as the potential particle mediating gravitational interactions, but it has not been observed up to now.
Now, to come back to the second point, mass in indeed not a particle. It is a property of each particle. It works both for elementary objects and composite systems. For the latter, the binding energy indeed plays a role.
Taking the quark example, protons hold together thanks to the strong force, via numerous quark and gluon exchanges. No gravity here. The role of gravity is exactly zero.
But all of this has nothing to do with the expansion of the universe. And the latter cannot be converted into matter. At least to my knowledge (please show me an article to read about that so that I could get further pieces of information).
I'm not surprised that you are confused with my reply. By training you are a Physicist, I am not. I can only simulate my thoughts and they always seem to come up with other perspective views. Have patients with me. You say everything couples to gravity, I take the view everything physical is gravitational. I am also aware that the potential gravity particle has not bin observed (yet). I agree with you that the strong forces which hold the quarks together have zero gravity, but the whole system in itself is again gravitational. Put it in an empty room with something nearby which has less mass, it will be attracted to the object with higher mass. The expansion of the Universe is trying to find equilibrium by falling to a lower energy state. Dose that mean that the vacuum energy, is a higher energy state? Spontaneous particles come into being and are annihilated with their counter parts in very small time intervals. As we know, mater without space is not possible and matter has to be some kind of derivative of space because both came from the same singularity. I have no literature on this subject. String theory likes to fold 11 dimensions also in theory. But when considering the Planck scale and the smallest known particles, there is lots of room for speculation. No need for a response, but I would love to hear one. I suppose its getting philosophical now. Thanks for your time. That is also why there must be some kind of correlation between our visible universe ( its mass ) and the vacuum energy state from which the singularity had its beginning or not.
The key point that may be missing in your reasoning is that the gravitational strength is proportional to the involved mass. The quark or proton masses are thus way too small to be gravitationally relevant. Even if a gravitational force exists, it can be approximated to zero compared to anything else.
I like discussing with you, I need people with expertise. It drives the thought process, but I will not take anymore time of yours except I have to comment on your last reply. I agree with you that on the particle level gravity is neglect-able, but it is the sum of the parts that make a difference as long as the individual parts are not zero. It seems to be similar with the Dark Matter problem and Dark Energy which is even larger. You are looking for small Anti-Particles which in the sum cause the orbits of the stars to be stable. The Dark Energy, … dose it have something to do with the vacuum energy? It (DE), some how is the reason that everything got started in the first place. I once visited the University for two months in Master Classes as a Guest (Germany Ulm) to find out why Professors think the way they do. Well if one can't model it with some algorithm you have a problem. That's my problem, I can't do the Math but I did learn a lot. It seems I would have to start from scratch but I'm too busy with the Cryptocurrencies. Thanks again it was a lot of fun for me.
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 ^^