Chapter 1 introduces the ideas of tensed and tenseless time: this distinction contrasts the common sense view that time flows from an under-defined future through the instantaneous present to a fixed past, vs. the classical physics view that ‘now’ is simply an index into a pre-existing space-time block universe, where there is no flow of time as such. This chapter may put off the casual reader, as it includes much conceptual hand-wringing on the meaning of words. It is a reminder of why science uses precise models expressed in mathematical language, with its clear semantics and rules of inference, rather than ordinary language discussion.

Chapters 2-7 are far better. A conceptually clear explanation of special and general relativity, with a discussion of time travel (closed timelike curves) and mechanisms such as wormholes for accomplishing it.

Chapter 8 changes gear as Lockwood introduces the Hamiltonian approach to classical mechanics, and phase spaces. Chapters 9 and 10 form an extended discussion about the role of entropy in time asymmetry, placed in a historical context. Again interesting and clear.

Things get murky again in chapters 11-13. These purport to be a discussion about why we remember the past, but not the future, but the discussion is shapeless, visiting a number of topics in a meandering fashion.

Chapter 14 brings us to Quantum Mechanics. As is the fashion these days, we are taken briskly through the ‘old quantum mechanics’ to Hilbert spaces and energy eigenstate superposition as the driver of time-varying quantum probabilities. We are then brought to the Measurement Problem, the EPR paper and the various interpretations of QM. This is all pretty brisk, and the reader really needs to have had prior exposure to the Hilbert space formulation of QM to follow what is going on here. Lockwood, like David Deutsche, is a supporter of the ‘many worlds’ interpretation of QM - he prefers a variant model comprising an ‘actuality’ dimension. In chapter 15 he explains why this model (space-time-actuality) can resolve time travel paradoxes. Chapter 16 is a clear conceptual discussion of string/M-theory and loop quantum gravity - the two main unification thrusts in current physics.

Chapter 17 suddenly goes off in an new direction, focusing on the neurological and philosophical basis of our psychological construct of the present moment. This is an extended period - Lockwood thinks about a second - called ‘the specious present’. The chapter ends in an obscure philosophical debate on ‘the temporal mode of presentation’. And that’s it, the book ends.

Read this book for the explanations of relativity, quantum mechanics and current frontier thinking in fundamental physics, where it is first-rate. The chapters which deal specifically with philosophical issues probably appeal to a different audience: they seem irritating and nit-picking to this reviewer - why not translate the discussions into formal models where they can be analysed properly?

Finally, a number of issues are not well analysed or resolved, such as the nature of causality, the subjective view of time flowing and the reasons why we don’t remember the future. Surely these are not purely philosophical issues, disconnected from our best physical theories? The lack of a concluding chapter is also a serious omission. Finally, you would need a degree in maths or a science subject to really engage with this book.