Implications of the Wilkinson microwave anisotropy probe age measurement for stellar evolution and dark energy

The Wilkinson Microwave Anisotropy Probe (WMAP) satellite has provided a new measurement of the age of the universe, 13.7 ± 0.2 Gyr. A comparison of this limit with constraints from stellar evolution imply that the oldest globular clusters in the Milky Way have a reasonable probability of having formed significantly after reionization. At the same time, one can derive a direct upper limit of ≈3 Gyr on the time after the big bang and before globular clusters in our Galaxy formed, which significantly reduces our uncertainty since before the cosmic microwave background age estimate. The WMAP age constraint can also be shown to provide a stringent lower bound on the equation of state of dark energy. A precise value of this lower bound would require a global analysis of the WMAP parameter constraints. However, making conservative assumptions about allowed parameter ranges and correlations, one derives a lower bound of w > -1.22. Combining this with the WMAP-quoted upper limit on w thus gives a roughly symmetric 95% confidence range of w = -1 ± 0.22.