From Eternity to Here

Starred review from November 2, 2009
No one is better equipped to take readers on a rollercoaster ride through time, space, and the origins of the universe than Caltech theoretical physicist Carroll, cofounder of Cosmic Variance, one of the top science blog sites. “We're not thinking small here,” Carroll announces with glee before launching into his topic. Time is a medium we move through and a way to sequence events. But the “Arrow of Time' is also the only feature of the universe with one irreversible direction: time goes forward. This fact plays an important role in the second law of thermodynamics: the entropy (disorderliness) of an isolated system either remains constant or increases with time. This has implications for our understanding of the “Big Bang” origins of the universe. We may not be able to travel back in time, but we can find ways to peer back across it and see clues to how the universe evolved, thanks to such discoveries as quantum mechanics and relativity theory. Carroll writes with verve and infectious enthusiasm, reminding readers that “science is a journey in which getting there is, without question, much of the fun.” Illus.

November 1, 2009
A revealing look into the fourth and thorniest dimension.

Time, a famous scientist pointed out, is nature's way of making sure everything doesn't happen at once. Carroll (Theoretical Physics/Caltech) has read all the literary and scientific writing on the subject but has plenty of his own opinions. In his debut, the author writes in accessible prose, so readers who make the effort will absorb an avalanche of information. Everyone knows one needs three dimensions to locate anything, but without the time no one can find a specific event. As a result, educated readers accept time as a legitimate dimension, yet no one can shake the feeling that it's odd. All laws of physics remain unchanged everywhere, and none assert that time can't run backward, but it never does. Carroll's explanation relies heavily on the second law of thermodynamics (to which he returns again and again), which states that all systems in the universe tend to become disorganized (increase in entropy). No law forbids an omelet from spontaneously turning back into an egg, but it's extremely unlikely. Travel in time is simple provided one travels forward. Since relativity requires moving clocks to run slower than those at rest, one can speed up time by simply traveling and then returning. Sadly, travel into the past would produce paradoxes and, the author stresses, paradoxes don't happen. Carroll delves deeper than the typical PBS science hour. Understanding time requires an acquaintance with entropy, relativity, cosmology, thermodynamics and statistical mechanics, which Carroll enthusiastically delivers at great length.

Not for the scientifically disinclined, but determined readers will come away with a rewarding grasp of a complex subject.

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August 15, 2009
A research physicist at Caltech and one of the founders of the popular group blog Cosmic Variance (http: //blogs.discovermagazine.com/cosmicvariance/), Carrollnot to be confused with biologist Sean B. Carroll ("Endless Forms Most Beautiful")expounds on a long-standing puzzle in physics. At a microscopic level the laws of physics are valid regardless of whether time runs forward or backward. However, in the real world all of us (including scientists) experience "time's arrow," which points in only one direction. More technically, scientists note that entropy (a measure of disorder) either increases or stays the same in the observable universe; it never decreases within a closed system. It appears that the universe's entropy was very low when the Big Bang occurred 14 billion years ago but has been increasing ever since. This strikes some researchers, including Carroll, as an uncomfortable oddity that needs further explanation. VERDICT Carroll employs an easygoing, colloquial style of explanation to explore challenging issues of cosmology. His approach is effective, but readers must still be willing to work through much heavy thinking. Highly recommended for fans of Stephen Hawking and those with at least some formal training in the physical sciences and/or philosophy.Jack W. Weigel, Ann Arbor, MI

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