## Quick Reference

A time determined by the reciprocal of the value of the Hubble constant to be about 13.7 billion years. The calculation of the Hubble constant, and hence the age of the universe, depends on which theory of cosmology is used. Usually, the age of the universe is calculated by assuming that the expansion of the universe can be described by the big-bang theory.

*Subjects:*
Astronomy and Astrophysics.