Double hubble: age in trouble
A key concept in modern astronomy -- the distance scale -- has been challenged by a new measurement technique. In recent years, the so-called Hubble Constant has been used to determine the distances of the farthest observable galaxies and, by assuming that they are near the periphery of the expanding universe, obtaining the age of the cosmos by dividing distance by the speed of light. Until this current challenge, the age of the universe was generally taken as about 20 billion years.
The "old" Hubble Constant, however, was determined from the measurements of the distances to rather close galaxies and then assuming that the Constant thus derived held for the entire universe. The new yardstick reaches farther out into space. It is based upon the observation that the broadening of galaxy's 21-centimeter radio emission depends upon its rate of rotation, plus the belief that the rate of rotation is proportional to its brightness! This "new" Hubble Constant is 95 kilometers/second/ megaparsec, which translates into an age of only 10 billion years for the universe. Both the 10-billion-year and 20billion-year camps claim strong supporting evidence for themselves and also point to serious difficulties in the opposing method. The stage is thus set for a delightful controversy.
(Hartline, Beverly Karplus; "Double Hubble: Age in Trouble," Science, 207: 167, 1979.)