THE 4 PERCENT UNIVERSE

A superior account of how astronomers discovered that they knew almost nothing about 96 percent of the universe.

Science writer Panek (The Invisible Century: Einstein, Freud, and the Search for Hidden Universes, 2005, etc.) points out that 50 years ago astronomers assumed they understood the cosmos and its history from the big bang to galaxy formation to its ultimate fate as expansion continued. One detail remained disturbing: Galaxies were moving too fast. Since gravity controls movements, they had to be heavier than predicted. By the 1980s, this “missing mass” problem became critical as it became clear that galaxies, including ours, were rotating so fast that missing mass far outweighs visible objects such as stars. Even after eliminating gas and dust, “dark matter” represents strange particles unknown to science. Astronomers also believed that gravity was slowing expansion of the universe but debated if galaxies would reverse themselves, continue to recede ever more slowly or (the favorite theory) simply stop. Panek describes frustrating struggles with high-tech detectors, complex computer algorithms and massive telescopes to search distant galaxies for the key. The answer came in the late ’90s—expansion wasn’t slowing but speeding up. Flabbergasted astronomers understood that accelerating billions of galaxies requires immense energy. Since Einstein proved that energy and mass are equivalent, this “dark energy” makes up three-quarters of the universe. Dark energy added to dark matter reduces the familiar universe to 4 percent of the total.

Panek delivers vivid sketches of scientists, lucid explanations of their work and revealing descriptions of the often stormy rivalry that led to this scientific revolution, usually a media cliché, but not in this case.