4 of 4 people found the following review helpful
a review for the beginning science reader,
This review is from: From Eternity to Here: The Quest for the Ultimate Theory of Time (Paperback)If you think you are going to settle in and read about time and "what it means" from a physics perspective, be prepared for a long diversion first or to put it another way, be prepared to think about time differently. Carrol starts out with some brief observations about time and how the belief that the universe was at low entropy prior to now (maybe when it began, if you agree that it did begin and wasn't always here . . .) and is moving towards higher entropy and thus time moves forward as well (he refers to this as the arrow of time throughout the book). He states this in a much more complicated way so I'm not sure that I'm even right, but it's something like this. Then he gets into physics, first the classical stuff and then the quantum. But, most of this was far more complicated than I could understand and unlike some of the other physics books I've read, hard for me to wade through. I don't know if it was the writing style or the esoteric concepts or that it seemed to be drifting so far away from explaining a theory of time, but I would find myself just wishing the chapter would be over. But, from my perspective the book is ultimately a discussion of entropy and understanding how/why it is that the universe was at a low entropy state prior to the big bang and is moving towards a higher entropy state.
There are lots of explanations of physics in here in far more depth than most introductory books I've read, so if you are looking for discussion of Hawking radiation, black holes, the Copenhagen explanation, etc, this will provide that level of detail.
Most chapters start with a problem and Carroll attempts different hypothesis to solve the problem eventually coming to the hypothesis that is most accepted (if there is one; some problems do not have even an accepted hypothesis to solve them, according to Carroll, like speculation about many universes and a theory of quantum gravity). While I like the idea of this organization and Carroll explains historically how we've come to the current explanation it seems unnecessary to his topic. Why not tell us the accepted hypothesis and move on? I can only speculate that Carroll, one wants to provide us with the history of the idea so it is more convincing; and two, is being careful because many of these ideas are still debated (like does a black hole emit radiation; and what happens to information in a black hole?). Carroll states in the epilogue that he spent so much time on the historical and theoretical background because "we can state the problem clearly but have only a few vague ideas of what the answer might be" (p. 367).
But for the beginning reader, this level of historic detail was just overwhelming. Another stylistic convention that Carroll uses is to say, "You may be wondering why . . ." and then posit something that would seem contradictory to his conclusion. I almost never wondered whatever he was saying because I was so confused, but there were a few times when I did (like when he says our universe is heading to a high entropy state of empty space) and I was thinking, how can high entropy be empty space. He nicely answered that question.
Ultimately, Carroll does not provide an answer to the question why is the initial state of the universe at low entropy. After reviewing the available possibilities, he suggests one possible hypothesis: that maybe the universe is eternal (there is no beginning and there is no end) but just gradually and forever increasing entropy, that reaches de sitter space (empty space with positive vacuum energy) but then continues on (I hesitate to even attempt to summarize his explanation because of my level of understanding, but I think this is right). This explanation assumes the existence of baby universes that continually appear. There is no single trajectory, but space goes on forever in all directions so that the past in one is the future in another. He does address one major counter argument against this theory: there is no way to falsify the theory of the multiverse. Carroll suggests that it isn't a theory but a prediction and what we should be working on falsifying are the theories that predict the multiverse. This seems like somewhat of a copout, but maybe not.
I found this a very difficult book to get through, especially the middle. But I'm glad I read it. I imagine that as I read more books of this type, this book will add to the conversation.