Galaxy Movement

How does redshift relate to age as well as distance of galaxies?

Astronomers have deduced that the redshift of an object is not merely a representation of how fast it is moving away from us, but also how much the universe has expanded since the light we see from a distant object actually left that object. If an astronomer observes that light from a galaxy has a redshift of one, then that light left that galaxy when the universe was half its current diameter; if the redshift is two, then the universe was one-third its current diameter; if the redshift is three, then the universe was one-fourth its current diameter. This pattern continues all the way out to the edge of the observable universe: as the redshift approaches infinity, then the size of the universe approaches zero, which is the Big Bang. That means that redshift is a way to measure the cosmological age of any distant object one is observing. An astronomer can relate any fractional size of the universe with a certain number of years before the present day, and thus compute the age of the universe at the time the object is being observed.


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