This book provides a comprehensive overview of the science, and science fiction, of time travel.  It binds together modern science, philosophy and various cultural factors relating to our understanding of time.  Although the science described is sometimes complex, there are no equations in sight.  As the authors explain:

In so doing, the authors shift towards writing a standard popular science book, condensing down the latest research findings in science and working methodically through many areas of cosmology and physics.  But then they also break up the deeper stuff with lighter sections, many of which are essentially lists of movies, books and TV shows containing time travel.  A rhythm between heavy science and light entertainment runs through the book.  A standard popular science book would not contain detailed references to fiction, like Doctor Who, for instance. 

But given that our perception of time travel, hyperspace and wormholes is greatly influenced by Hollywood, then such a digression seems appropriate.  Although these lists seemed comprehensive on first inspection, I realized that they related to English-speaking fiction only.  The authors had missed my all-time favourite time travel movie: "The Visiteurs", starring Jean Reno (1993).  It may be in French, but it's side-splittingly funny.

Anyway, the possibility of time travel is controversial, and seems to take up a surprising amount of time in the minds of professional scientists.  The very nature of time itself is debateable.  At the quantum level, is there actually a difference between the past and the future (p32)?  On the face of it we have no freedom to move in the time dimension, or the ability to control it (p45), but that does not stop us from dreaming that one day science may come up with a way around the limitations of Einstein's theories of relativity, and the various time paradoxes that that would create (the best candidate for which appears to be a provable Multiverse theory (p115)). 

Even if we don't, we humans are able to travel in time mentally, and, like other animals, our bodies have a natural capacity for time-keeping at a cellular level (p33).  Such findings took the authors in alternative directions as well - paranormal events relating to our perception of time, and further down the rabbit hole into various conspiracy theories, like Montauk, the Philadelphia Experiment, claims of Stargates and Timelines.  We learn of the claims made by Dan Burisch (p144) and Andrew Basiago's 'chrononauts' - who are alleged to have included President Obama (!?!) - and the time travel blog of one John Titer, who popped in to visit us from the year 2036 (pp136-41). 

Such far-fetched stories sit uneasily alongside serious discussions of modern physics, it must be said.  But the authors do a good job describing the work of Tesla, whose work sat somewhere in the middle.  They indicate that there are real possibilities in the idea of closed time-like curves which are theoretical paths in space-time which - like all good conversations -  return to their starting points (p91).  So perhaps melding together fact, fiction and conspiracy, when discussing time, is not so ridiculous.  After all, it was a couple of particle physicists who contemplated the intervention of baguette-wielding time travellers from the future when the LHC broke down a year or so ago at CERN.