# Any papers out that show the observed z vs. t?

1. Aug 22, 2011

### BillSaltLake

I know the constant ΛCDM model predicts the expansion factor a (= 1/[1+z] providing we impose the condition a = 1 now) to be of the form (sinh bt)2/3 for recent times. Are there any papers that determine either a(t) or z(t) from the supernova data, showing error bars? I think that the present observed value of a is presently higher by factor 1.12 - 1.18 than it would be if Λ = 0, and that the ΛCDM model favors the upper end (~1.18).

2. Aug 23, 2011

### Chalnoth

Cosmologists generally don't bother with such analytical approximations, and instead go for direct estimation of the densities.

Anyway, one of the most detailed current analyses of these issues can be found here:
http://supernova.lbl.gov/Union/

Of particular interest is this plot:
http://supernova.lbl.gov/Union/figures/Union2_w0-wa_slide.pdf

If $w_0=-1$ and $w_a=0$, then we have a cosmological constant. As you can see, though the errors are pretty big so far, a cosmological constant is very close to the center of the allowed region.