Not much by themselves , aparently .

We try to reconstruct the scale factor a ( t ) of the universe from the SNe Ia data , i.e .
the luminosity distance d _ { L } ( z ) , using only the cosmological principle and the assumption that gravitation is governed by a metric theory .
In our hence model-independent , or cosmographic study , we fit functions to d _ { L } ( z ) rather than a ( t ) , since d _ { L } ( z ) is what is measured .
We find that the acceleration history of the universe can not be reliably determined in this approach due to the irregularity and parametrization-dependence of the results .

However , adding the GRB data to the dataset cures most of the irregularities , at the cost of compromising the model-independent nature of the study slightly .
Then we can determine the redshift of transition to cosmic acceleration as z _ { t } \sim 0.50 \pm 0.09 for a flat universe ( larger for positive spatial curvature ) .

If Einstein gravity ( GR ) is assumed , we find a redshift at which the density of the universe predicted from the d _ { L } ( z ) data is independent of curvature .
We use this point to derive an upper limit on matter density , hence a lower limit on the density of dark energy .
While these limits do not improve the generally accepted ones , they are derived only using the d _ { L } ( z ) data .