THE UNKNOWN UNIVERSE

Updates on the universe continue to pour from the presses, but since new discoveries appear regularly, cosmology aficionados may read one every few years. They will be wise to read this latest from New Scientist contributor Clark (The Day Without Yesterday, 2013, etc.), a fellow of the Royal Astronomical Society.

The author brings the subject up to 2015 with the obligatory new discovery combined with a fine history of cosmology, and he makes it clear that our knowledge and ignorance seem to be expanding in parallel. Clark delivers the new discovery in the introduction: after spending more than two years mapping the sky in microwaves with dazzling precision, the Planck satellite has revealed subtle irregularities that can’t be explained. Unless the instruments are at fault (not a rare occurrence), “the Planck data showed ‘cosmology is not finished.’ ” Emphasizing great men and the occasional great woman, Clark begins his history in the 17th century with Kepler, Halley, and Newton, ending in the unsettling 21st, where the universe explained so brilliantly by Einstein, whose name dominates several chapters, has revealed features that he didn’t explain. Educated readers know that the term “unknown” as applied to the universe is literally true because 95 percent is invisible, detectable only because its energy and gravity influence movements of the 5 percent we see as stars and galaxies. Decades of searching for this “dark” matter and energy have failed, so some theorists wonder if tweaking the laws of gravity will eliminate the need for it. Of course, tweaking Einstein is no small matter. “Either dark matter and dark energy are real and these vast reservoirs of energy are just waiting to be found,” writes the author, “or we have to radically rethink fundamental physics.”

Since satisfying results have yet to turn up, Clark’s book ends on a cliffhanger, but readers will be entirely pleased with the experience.