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7. REMAINING ISSUES FOR MEASURING t0

What are the ages of the oldest objects in the Universe? In this context, we need to keep in mind that it is currently only a useful working hypothesis that the Galactic globular clusters are representative of the oldest objects in the Universe (e.g. see Freedman 1995 for a more detailed discussion). Currently, the sample of objects for which direct (i.e. main-sequence-fitting) ages can be measured is limited to our own Galaxy and a small number of satellites around our own Galaxy. It is at least conceivable that in denser environments in the early Universe, star formation could have proceeded earlier than for Galactic globular clusters. At this time, there is no direct information with which to constrain the true dispersion in (or upper limit to) ages in environments outside the nearest galaxies in our own Local Group. There are, for example, no giant elliptical galaxies in the Local Group. Although considerable effort is now being invested in finding potential ways to lower the Galactic globular cluster ages, there is reason to keep in mind that the expansion-age discrepancy could potentially be even worse than is currently being discussed.