Q&A: Cosmology

Q:
Is the universe expanding at about 65 miles per second?

A:
You are probably referring to the recent determinations of that the Hubble constant, which gives the rate of expansion of the universe, is 65. However, the units are not miles per hour, but kilometers per second per megaparsec. A megaparsec is a unit of distance equal to 3.26 million light years. If the Hubble constant is 65, then a galaxy 3.26 million light years away will be receding at a speed of 65 kilometers per second. One that is ten times further away, will be receding at a speed ten times greater, 650 kilometers per second. On our web site we use a Hubble constant of 60 kilometers per second, which is within the margin of error of the recent estimates. See also: http://chandra.harvard.edu/photo/cosmic_distance.html