I have a big claim for this book – almost scarily big. This is the book Stephen Hawking’s A Brief History of Time should have been. Let me explain. Despite being the absolute classic of the genre, Hawking’s book has two huge flaws. Firstly it doesn’t do what it says on the tin. It has lots of great stuff to tell us about relativity and black holes and much more. But it doesn’t really tell us anything much about time.
Secondly, BHoT isn’t the most readable of popular science books. It is infamously a book that many have started but few have finished. When you look at the concepts it covers there’s nothing too scary (at least, by modern popular science standards), but it isn’t put across in a way that’s easy to pick up.
So we come to Sean Carroll’s book. And it is a joy. It really does tell us about time, better than anything I’ve ever read. To be fair, most of the content is about entropy and the second law of thermodynamics (which ought to be better understood, and is strongly time-related) with a good dose of relativity and quantum theory thrown in. But it really does explore the nature of time.
As for the second issue with BHoT, there is good news and bad when we put From Eternity to Here (I title I hate, by the way) alongside it. This book explains significantly more complex matters than Hawking’s does. But it does so much more clearly. I’m not saying it is all an easy read. You have to read it slowly and carefully – so some readers will definitely be put off – but it hugely repays the effort. I particularly like the way that Carroll not only presents with the orthodox picture, but his own personal views, making it clear where these vary from many other physicists and cosmologists, but nonetheless making powerful points.
Of course it’s not perfect. It is occasionally a trifle obscure. There are occasions the mask of accessibility slips and he forgets who he is talking to. The section on coarse graining, microstates and macrostates, for example, would be better suited to an undergraduate lecture than the intended readership. And I particularly disliked Carroll’s cat and dog analogy for quantum theory, which I found more confusing than just talking about the particles that feature in the theory. The analogy was both cringe-making and confusing.
I also think Carroll (to be fair, like quite a few scientists) needs to take a look at his dictionary when it comes to his approach to paradoxes. ‘Paradoxes are impossible,’ he bluntly states. No they are not – you are thinking of fallacies. Although paradox is sometimes applied in this sense, the better meaning is something that appears impossible but is actually true, something that runs counter to common sense. (Which is why the author is also wrong moaning about EPR being called a paradox.)
A final mini-moan – I wish he had told us how the ekpyrotic universe (see Endless Universe) fitted with his entropy-based analysis of different models of the universe, as he totally ignored it. But these are minor concerns in what is a tour-de-force of popular science writing in the ‘you really need to read this carefully and think about it’ school (as opposed to ‘sit back and enjoy it.’) Highly recommended.