On the use of galaxies as clocks and the universal expansion

We set out to rederive the 8 Hubble parameter values obtained from estimated relative galaxy ages in Simon et al, PRD 71 (2005). We find that to obtain the level of precision claimed in $H(z)$, unrealistically small galaxy age uncertainties have to be assumed. Also, some parameter values will be correlated. In our analysis we find that the uncertainties in the Hubble parameter values are significantly larger when 8 independent $H(z)$ are obtained using Monte Carlo sampling. Smaller uncertainties can be obtained using Gaussian processes, but at the cost of strongly correlated results. We do not obtain any useful constraints on the Hubble parameter from the galaxy data employed.