Sorry to return to this subject again, but I just found a paper on Quintessence that substantiates my concerns.
My concern is that according to General Relativity(GR) and the Big Bang model, if omega was not exactly one in the beginning and very close to one for at last few billion years, we would not be here. Omega is the ratio the mass (and energy) density in the universe to the critical mass density that in GR makes the universe flat.
If omega were just a bit larger than one, the universe would immediately collapse. If it were a bit less than one, it would overexpand before stars could form. Actually, we seem to be on the verge of overexpansion right now.
The problem I saw was that most of the mass in the universe disappeared when matter and anti-matter annihilated each other early in the life of the universe, and I could not understand how omega could be maintained through this process. And there is also the problem that the omega for ordinary matter is much greater now than then.
Scientists tend not to talk about fundamental problems like this until they think they have a solution for them. This is such an example. Quintessence is being offered as a solution to that problem. Let me quote from the paper:
"Perhaps a more satisfying possibility is that the acceleration is triggered by natural events in the recent history of the universe. According to the big-bang model, the energy density in the universe was predominantly in the form of hot, relativistic particles until the universe was a few tens of thousands of years old. At that time, the universe had cooled enough that the mass energy of non-relativistic particles became more important than both their kinetic energy and the energy of radiation, resulting in a "change in the cosmic expansion rate". This marked the beginning of the "matter-dominated epoch". Only then could gravity begin to clump matter together to form stars, galaxies and large-scale structure. Is it possible that this transition triggered the onset of quintessence? "
The paper goes on to do what is called a top down analysis. They know what quintessence has to do to keep omega at one. But they do not know what it is. So quintessence is more an invention than a discovery. Alas, science often proceeds and succeeds with this kind of approach. Like the evolution of life on earth, we pretty much know how the universe evolved. We just haven't figured out why.
Here is the location of the paper I refer to: