HOW IT BEGAN

Popular cosmology writers rarely restrain their sense of wonder, but readers who tolerate the science-fiction scenarios scattered throughout this account will not regret it.

Impey (Astronomy/Univ. of Arizona; How it Ends: From You to the Universe, 2010) writes that astronomers directly observe the past. Light from the nearest star, 25 trillion miles distant, takes about four years to arrive, so we see it as it was four years ago. Modern instruments detect galaxies whose light has traveled since near the Big Bang 14 billion years ago. Eschewing the usual Ptolemy-Galileo-Newton-Einstein chronology, Impey begins nearby and proceeds to the end of the universe, which means he moves backward in time. Our solar system condensed from the same cosmic dust that formed the sun and stars. That planets form part of the natural order seems likely as the number detected orbiting other stars approaches 1,000. Stars form, age, collapse and explode, filling space with heavier elements that make life possible or disappear into black holes, a process that may emit more energy than an entire galaxy. Until the 1920s, the universe consisted of a single immense system of stars: our galaxy. Then telescopes resolved innumerable hazy spots in the firmament as other galaxies; billions turned up. Subsequent disorienting discoveries revealed that galaxies are receding, carried away by an expanding universe whose matter is mostly invisible, propelled by newly discovered, inexplicable energy. These mysteries remain, despite the latest detectors which make out far-distant, immature galaxies present in a universe 1/20 its present age.

An astute tour of the cosmos by a skillful teacher.