THE UNIVERSE AT MIDNIGHT

Cosmological speculations live or die on the observations of astronomers. Here, a Harvard-trained astronomer summarizes the current relations between the two disciplines.

Croswell (See the Stars, 2000) starts with the most basic observation of all, the darkness of the night sky. Explaining this quotidian phenomenon taxed the ingenuity of theorists for centuries; in an infinite universe, the night sky ought to be uniformly light. The answer provided by modern cosmology combines the finite age of the universe and the finite speed of light; we cannot see stars so far away that their light has not had time to reach us. This raises the issue of the age of the universe, a topic of considerable controversy. Until the early 1960s, some astronomers postulated that the universe was of infinite age. Confirmation of the Big Bang theory overthrew that assumption, but the exact age of the universe remained uncertain, with some calculations suggesting that the universe was younger than its oldest stars. Such paradoxes have driven cosmologists to propose a universe composed largely of invisible, perhaps extremely strange, materials. No known subatomic particles, dark stars, nor black holes seem to account for the missing mass. Just as strange is the cosmological principle (i.e., a force that arises in empty space and drives the expansion of the universe), which Einstein first proposed, then rejected as “my greatest blunder.” Current models describe a universe 14 billion years old, destined to expand forever. Croswell has a knack for creating memorable portraits of the scientists who figure in his account, and a reader will come away from him not only with a clear grasp of the current theories of our universe’s past and probable future, but a good notion of the men and women who have contributed to our understanding of it.

A solid, well-written summary of modern cosmology.