I've read many of Paul Davies' books and have enjoyed them, but found About Time: Einstein's Unfinished Revolution one of those strange books that I keep drifting off while reading. This is not to say the book was boring, but there are certain books which engage me on a level which is a short slide to dreamstate, and this was one of those that I'd start one paragraph and be off in some dream “riffing” on the subject! At least this was a non-fiction book, so made it easy to figure out where I started fading, as opposed to something like Neuromaner where my brain seemed hellbent to re-write the book.
As one can guess from the sub-title, the book is pinned to Einstein's work with time. There are fascinating “I did not know that!” bits in here dealing with stuff like commercial applications of time-dilation ... a great quote: “the acid test of any weird theory is this: can you make money from it?” ... aside from various high-tech things which one might expect to have some connection to this, Davies points out that the reason that gold is, well, “gold” (as opposed to the “silvery” look of most metals), “can be traced to the effects of relativity on the motions of the electrons inside the metal that are responsible for reflecting light” ... so, there you go, time-dilation on your ring finger!
There is also interesting stuff about measuring distances in space-time, and how widely spaced events can have zero space-time separation, while events in a single locale, separate briefly in time, may have a very large (if “imaginary”, in the sense of a square root of a negative number) remove. The math involved helps explain how time could have just “switched on” at the big bang (the Hartle-Hawking theory). Davies also touches on some of the “weirdness” proposed by Feynman, where it is mathematically plausible to posit that there is but one electron (and proton and neutron) in the universe, which just move around space-time quite a lot (or, as he puts it: “seen squillions of times over”), a concept that I find fascinating as it dovetails with some spiritual theories that I've been following!
Structurally, the book looks at various topics, from a general over-view of theories of time and how it was measured (modern clocks didn't exist until developed for the Royal Navy for global navigation, and until the advent of the railroad, most people timed the day via the sun, etc., but didn't keep a “schedule” until they were likely to miss a train if they didn't!), and various concepts surrounding this. It covers “timewarps”, “black holes”, “the beginning of time”, how Einstein dealt with time, “quantum time”, “imaginary time” (as referenced above), going “backwards in time” and the possibilities for “time travel”, the concept of “now”, and various “experiments with time”, finally looking at how this is an unfinished piece of Einstein's revolution.
I have read a goodly amount in this arena, and found many things “new” in here, which is always refreshing, but because it does skip around from subject to subject, it might be hard for somebody “coming in cold" to the topic to follow along. As such, it's a bit “heavy” for an introductory overview, yet “thin” on any given subject, making the ideal target audience a narrow mid-section. Needless to say, each of the chapters here could easily be expanded and presented as a book on their own, so there is a lot of detail and context (and math) skipped to put out this volume of how time theories manifest in all these different subjects.
However, if About Time does sound interesting to you, I'd heartily recommend it! It appears to be still in print, so should be available via your local brick & mortar book vendor, but it's also available for about 1/3rd off of cover from Amazon proper, with “good” copies being available from their new/used vendors for as little as a penny (or, four bucks with shipping).