By Sean Carroll
Dutton Adult (January 7, 2010)
Most of you will know Sean Carroll, who blogs at Cosmic Variance. Sean is a Senior Research Associate at CalTech and his research focuses on cosmology, general relativity and the standard model, as well as extensions thereof. He has written a textbook on General Relativity, and the lecture notes that gave rise to the book are available online. I've met Sean a few times, he's an interesting person and gives great talks. Sean has a special interest in the arrow of time, and that is also the topic of book “From Eternity to Here.” The arrow of time is, in a nutshell, the question why the past is different from the present.
I bought the book for three reasons. One is that for many years I've been using the PDF version of his lecture notes as a handy quick reference when on travel and had a bad consciousness for never buying the book. The second one is that from reading Sean's blog I know he writes well. The third reason is that adding a second book to the order rendered delivery free.
“From Eternity to Here” is a very well written book that communicates a lot of science, both textbook science and contemporary science, while at the same time being amazingly accurate. The biggest part of the book - all but the last chapter - is dedicated to accurately framing the question. Why is it interesting to ask why the past was what it was? What exactly is it that we don't understand? How do we get a grip on the problem? For this, Sean covers first of all the second law of thermodynamics, then special relativity, general relativity, cosmology, quantum mechanics, black hole physics, and finally inflation and the multiverse. In the last chapter, he then discusses possible solutions to the question he has posed and puts forward his own solution as the most plausible one. Along the way he scratches on topics like the vacuum energy, structure formation, the AdS/CFT duality and magnetic monopoles.
Sean is very careful with distinguishing between established science and unconfirmed speculations. The only glitch is the section on the holographic principle where he fails to point out that there is no experimental evidence for such a feature of Nature to be true in all generality. I am somewhat sick of being misinterpreted on this point so let me be very clear here. All I am saying is that, absent experimental evidence, scientists should be very careful with what they put forward as a true description of Nature. Theoretical evidence can very easily be biased simply because a topic that attracts attention may mount one-sided “evidence.” This can never replace actual tests of a hypothesis. The holographic principle certainly does not rest on the same basis as ΛCDM or the Schrödinger equation and I wish its status had been framed more clearly. Anyway, Sean needs the holographic counting of degrees of freedom for the rest of his argument.
I was very pleased that Sean's explanations of physical concepts are not as superficial and vague as one frequently finds in popular science books. He does not shy away from the phase space, using logarithms, and discusses the amplitude of the wave function. The chapter on quantum mechanics however somewhat suffers from the overuse of cats and dogs. The book has plenty of footnotes with additional explanations, and offers many references so that the interested reader will easily be able to find the relevant keywords and dig deeper, should they wish so. On several occasions I took a note that Sean had forgotten to point out a specific assumption that entered his argument or left out some exceptions. In every single case, these points were later addressed, so I am left with nothing to complain about.
I personally don't have a large interest in the topic and don't care very much about the whole discussion. I think the question is ill-posed and when we have a better understanding of quantum gravity we'll see why. Sean's book didn't succeed in increasing my interest. Nevertheless, it was a pleasure to read. Sean has a good sense of humor, but doesn't overdo it. The story he tells is also well embedded into its scientific history and I learned a thing or two here that I hadn't known before. Both the historical and the philosophical aspects however play a secondary role and don't take over the scientific discussion. All together, the book is very well balanced and a recommendable read. It has something to offer for anybody who has an interest in modern cosmology and/or the arrow of time. I'd give this book 5 out of 5 stars.
From January through April, Sean offered a book club at his blog, each weak discussing another chapter. You might find this a useful addition to the book itself.