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Exotic - "Exotic Distance Indicators All of the above...

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"Exotic" Distance Indicators All of the above methods rely on a straightforward application of the inverse-square law or the angular diameter-distance relation. There is also a range of techniques that use more involved or indirect combinations of observables. Some examples are: The Hubble time : for simple big-bang models, ages of objects (stars, radioactive nuclei) set bounds on H 0 . The age of the universe is of order the Hubble time τ H =1/ H 0 , to within a factor of order unity depending on the deceleration history of the expansion. For H 0 =50 km/s Mpc, τ H = 2 x10 10 years; for 100 km/s Mpc, 10 10 years. This must be greater than the age determined from geological and stellar-evolutionary timescales, nuclear isotopic clocks like 235 U/ 238 U, and consistent with the dynamical status of galaxies and clusters. The small amount of evolution observed in elliptical galaxies to about z=1 favors smaller H 0 in simple models (Hamilton 1985 ApJ 297, 371). One should beware subtly circular arguments - globular-cluster ages were
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