Dark Cosmos: In Search of Our Universe's Missing Mass and Energy.

DARK COSMOS: In Search of Our Universe's Missing Mass and Energy DAN HOOPER

Amazingly, only 5 percent of the matter in the universe is observable as Earth, other planets, the sun, the stars, and debris. All the rest is invisible, perhaps composed of dark matter surrounded by dark energy. The search for these two elements is the fundamental task facing astrophysicists today, writes Hooper, a theoretical astrophysicist. He introduces readers to this search, defining what scientists know about the nature of dark matter and introducing candidate hiding places known as massive compact halo objects (MACHOs). Scientists infer the existence of these dark objects on the basis of their gravitational effects on visible objects in space. However, they also know that MACHOs alone wouldn't account for all dark matter, so some researchers have nominated neutrinos, other exotic particles, and even more-bizarre, extra-dimensional strings as dark matter candidates. The author then outlines the difficult notion of dark energy, a phenomenon that could explain the expanding universe and determine its fate. HarperCollins, 2006, 240 p., b&w illus., hardcover, $24.95.