From Eternity to Here: The Quest for the Ultimate Theory of Time

For people who want to explore deep ideas about the nature of reality, but are comfortable with the idea that they won't get solid answers, this is a great book. While the book can be read without a deep knowledge of physics, some basic understanding of physics concepts is useful, since some of the simplifications and analogies (especially in relativity, quantum physics, and cosmology) don't make it precisely clear where the line between the analogy and the real physics break down.

Physicist Sean Carroll is great at exploring complex physics topics for the general public, which he does regularly over at the Cosmic Variance blog. Now he's taken on one of the toughest topics in all of physics (the physical basis of time) in a book-length work ... and it's certainly well worth reading.

A book that focuses on such an abstract concept isn't easy to pull off, and Carroll does a great job of it ... but not a perfect one. He explores several concepts from relativity, quantum physics, and cosmology through analogies, but these analogies only go so far and it's not clear to me that a reader without a firm foundation in physics would really understand the physical corollaries. (For one example, the double slit experiment - indeed, the whole concept of quantum entanglement - is explained through reference to a cat which only ever sits on the sofa or under a table.) Despite this flaw, the basic ideas are laid out clearly enough that the reader who has a background of reading books on this topic will find the discussion easily accessible.

The emphasis of this book is on time, and specifically on the concept of the "arrow of time" - which is the idea that we see time proceeding into the future, but never into the past. In physics, the concept of time's arrow is most often tied into the concept of entropy, because the disorder of the universe increases as time moves forward. Carroll's key idea is that this results from the early universe having a very low amount of entropy, because the laws of physics imply that a universe with decreasing entropy would be possible. However, the specific low-entropy early conditions of our universe set the stage for a universe that has continually increasing entropy. The question at the heart of the book is: Why would this be the case?

This is a pretty big question, and what's nice about this book is that Carroll isn't dishonest in how he deals with it. He delves into the questions with full scientific candor, exposing to the reader the true depth with which a real scientist thinks about these questions. All too often, scientists write books that don't make it clear how open-ended the search for truth is, but Carroll leaves this clearly in the center of his narrative. He doesn't try to offer easy answers to complex problems, but instead revels in the complexity of the problems. In his own words, "it's appropriate to dwell on understanding the problem, and not become too wedded to any of the prospective solutions."

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