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Brian Chaboyer coauthored work using ages of old stellar clusters to constrain cosmic history. The analysis combines stellar-evolution calculations, distance estimates and uncertainty in when the clusters formed, then compares the resulting age bounds with cosmological expansion models.^[ref]

The comparison is useful because the universe must be older than its stars. It nevertheless requires the cluster's inferred stellar age and the delay before cluster formation to be distinguished.

Lawrence Krauss and Brian Chaboyer used the ages of globular clusters to test cosmological models. Their analysis combined cluster distances and stellar evolution calculations to obtain a lower bound on the age of the cosmos.

The logical comparison is simple: the cosmos must be older than the stars it contains, with additional time allowed for their formation. Combining this clock with an expansion rate constrains the cosmic equation of state and matter content. Their numerical bounds depended on the adopted stellar inputs, formation history and cosmological assumptions.^[ref]