Sean Carroll’s From Eternity to Here sets out to explain the nature of time, particularly what’s known as the “arrow of time,” the fact that we experience time as a flow in only one direction, from the past into the future. This is a daunting prospect, as just setting up the question requires a discussion of just about every important physics discovery of the 19th and 20th centuries. Carroll manages to make it all readable, though, and whether or not you end up agreeing with his preferred approach, you’ll leave the book with a clearer sense of the problems and the physics involved in the nature of time.
From Eternity to Here is a little unusual in that it is not just a popular-level explanation of well settled physical questions, but a book-length argument in favor of a particular theory of the universe. This is much less common in the science side of academia than in the humanities, where the scholarly monograph is one of the standard units of academic production. Scientists, for the most part, don’t write books, and as a result the interested reader usually needs to piece together a full argument from a large set of journal articles and a great deal of background knowledge. It’s a pleasure to see everything laid out in one place like this.
The humanities style is probably fitting, as the subject matter often straddles the border between physics and philosophy. Any book asking questions like “What should the Universe look like?” ought to contain a healthy amount of philosophy, and this delivers, along with a rich assortment of literary and cultural allusions, delivered with dry humor.
While the book is ultimately an argument in favor of a very particular physical model of the universe, it is not an intimidatingly mathematical work. Carroll includes citations of most of the critical papers in modern theoretical physics, but the text here doesn’t involve anything more daunting than scientific notation (inescapable when you’re dealing with a book about the entire universe) and the occasional logarithm (which are explained clearly and concisely in an appendix).
While the book contains an excellent summary of all the major theories of modern physics, the key concept here is the notion of entropy, and the key scientific figure in the story is Ludwig Boltzmann, who first explained entropy as a measure of the “disorder” of a system. Carroll recasts the question of the arrow of time as primarily a problem of thermodynamics, and the second law of thermodynamics in particular. The arrow of time is inextricably bound up with the increase of entropy in the universe, and Carroll makes a case that the crucial question in cosmology ought to be “Why was the entropy of the early universe so low?” This puts a very different slant on the usual questions about the cause of the Big Bang and the eventual fate of the universe, and suggests a very different answer.
The final section of the book runs through a large number of possible explanations put forth for the origin and fate of the universe, and makes an argument for Carroll’s own preferred model, in which our universe is just one of many “baby universes” spawned from quantum fluctuations in an eternally existing “multiverse.” One may not find the arguments in favor of the multiverse picture as the most satisfying of these options entirely convincing– something that I hope we will discuss a bit in this book salon– but just setting up the questions makes this a very thought-provoking book.
From Eternity to Here provides an excellent and highly readable survey of pretty much the entire history of physics, and uses it to attempt to explain pretty much the entire history of the universe. While it may or may not convince you that physicists have glimpsed the “ultimate theory of time,” it’s a book that asks deep questions and provides thoughtful answers, and that alone makes it a rewarding read.