The Age of the Universe
30 March 2006

The Age of the Universe

 George V. Coyne, S.J., Director of the Vatican Observatory

A physics colloquium to be presented Thursday, April 27, 2006 at 4:00 p.m. in Clark Hall, Room 111.

In 1929 Edwin Hubble discovered the observational relationship that bears his name, “the Hubble law”. He found for 24 nearby galaxies that their velocities of recession, measured by the red shifts in their spectra, were directly proportional to their distances. He later extended the measurements to more galaxies at larger distances. A modern version of these pioneering observations will be discussed. In the entire history of observational astronomy this is truly a remarkable correlation. It holds true for all extra galactic objects: galaxies of all types, clusters of galaxies of all types, quasars. It is so universally true that we intuitively surmise that it is saying something fundamental about the universe itself. And it is! It is telling us that the universe is expanding uniformly.

              The largest uncertainties in determining the Hubble Law remain in two areas: accurate determination of large distances and the value of the mass density of the universe. In the last decade accurate measurements of about 70 type 1a supernovae have yielded a most remarkable result. The universe is accelerating in its expansion. Out to a redshift of about z = 0.15  the Hubble law is linear and it yields the most accurate measurement to date of the Hubble constant resulting in an age of the universe of 13.7 " 0.2 billion years. Beyond z = 0.15 there is strong evidence of a curvature in the Hubble law indicating that the universe is accelerating in its expansion.