to be offset by $\la 1$ Gyr and we obtain $w<-0.5$ at the 90% confidence level. We have also repeated the calculation using Gaussian priors for the cosmological parameters, $h=0.7 \pm 0.2$, $\Omega_m=0.25
\pm 0.2$, $\Omega_b h^2=0.02 \pm 0.01$, and find similar, but slightly more stringent constraints on $w$.

We stress here that this determination depends solely on the GC determination of the age of the universe and on the [*observed*]{} position of the first acoustic peak in the CMB power spectrum. Our constraint is slightly less stringent than that obtained by @SpergelWMAP03 from a joint likelihood analysis of [*WMAP*]{} with six external data sets ([*WMAP*]{} + CBI + ACBAR + 2dFGRS + Lyman$\alpha$ forest power spectrum + Type Ia supernovae + $H_0$ constraint from the [*HST*]{} key project), but is tighter than the CMB-only ([*WMAP*]{} + CBI + ACBAR) determination and comparable to the [*WMAP*]{} + ACBAR + CBI + [*HST*]{} constraint.

$H_0$ and $w(z)$ from the ages of unresolved stellar populations at $z=0-1.5$
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Method
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We now turn our attention to the age of the oldest objects in the universe at $z \ge 0$ as a function of redshift. As recently suggested by @JL02, these can be 