Peter,
Thanks. I should have explained that I really view the two questions I'd raised as separate issues (of course they're interrelated, but not necessarily directly).
I'm most interested in the second question, as in reviewing the observational evidence as best I can, it seems that the researchers identified that the redshift of photons detected from more distant objects required that expansion has accelerated. Most simply put, as I understand, they determined that galaxies at the periphery of the observed universe are receding away from us at an increased velocity, thus universal expansion is accelerating!
Again, I simply understand that the ancient light indicated greater expansion.
My resources are limited so I prefer to focus on the original source: "Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant", Riess et al.:
http://arxiv.org/abs/astro-ph/9805201v1
It states most simply: "The distances of the high-redshift SNe Ia are, on average, 10% to 15% farther than expected in a low mass density (M = 0.2) Universe without a cosmological constant."
A warning: the report is very astronomical-technical. For example, "light curve fitting methods" refers to determining where a SN observation fits in it brief period of peak emission luminosity, as it is only the observed luminosity for the consistent peak emission luminosity can be used to estimate distance. Of course the diminishment of luminosity is directly related to the distance the light has traversed, not any real distance to any observed object.
A more general source might be a summary, "The Accelerating Universe":
http://arxiv.org/abs/1010.1162
In a section "The discovery of dark energy", the author states:
"The definitive results, based on ~ 50 SN by either team that combined the nearby sample previously observed by the Calan/Tololo collaboration and the newly acquired and crucial sample of high-redshift SN, came out soon thereafter [Riess et al. (1998); Perlmutter et al. (1999)]. The results of the two teams agreed, and indicated that more distant SN are dimmer than would be expected in a matter-only universe; see Fig. 1.2. In other words, the universe's expansion rate is speeding up, contrary to expectation from the matter-dominated universe with any amount of matter and regardless of curvature."
I can understand if you are not in a position to tackle this, I think, very simple issue made very complicated by astronomers. I had hoped you could quickly point out some obvious error in my assessment, if one exists. I can certainly understand if you cannot invest your time in this issue... I thank you very much for your interest!
Jim