The Birth of Time: How Astronomers Measure the Age of the Universe

How can we measure the age of the universe? Renowned astronomer Gribbin (Almost Everyone's Guide to Science, etc.) answers this question by describing both the early guesswork and later refinements that finally converged on an answer. He masterfully explains the techniques to measure astronomical distances available to both ancient and modern astronomers, from simple triangulation to the regular pulsation of Cepheid stars. By the 1950s, physicists understood in detail the fission reaction that occurs in the Sun and calculated its age to be 4.5 billion years. This understanding spawned new theories on the creation and ages of stars. Still, the oldest measurable star only provides a lower limit to the age of the universe. It took the realization that the universe is expanding--the measurement of the ""red shift"" of light from distant stars--to give a closed-ended estimate of its age. The measurement of the rate of expansion, the ""Hubble Constant,"" is the Holy Grail that Gribbin spends the latter half of the book refining. This quest, which concludes with Gribbin's own research, does finally arrive at an age for the universe, but it is the journey, not the destination, that makes the trip worthwhile. In the end, Gribbin's conclusions seem no more mysterious than if he had determined the age of a tree by simply counting the rings. The text is written clearly and concisely for the general reader, yet nevertheless manages to educate on a wide range of topics in physics. Illustrations. (Apr.)