How to Build a Time Machine by Paul Charles William Davies
My rating: 3 of 5 stars

I quite liked Paul Davies' "The Eerie Silence: Renewing Our Search for Alien Intelligence", which I review here . I have not found my second book by this British physicist and famous popularizer of science, "How to Build a Time Machine", as interesting. Also, while the first part of the book, which mainly focuses on "spacetime", is clear and convincing, the part dedicated mostly to wormholes seems to do less than stellar a job.

Dr. Davies first debunks the commonsense picture of time that we use in our everyday life - time whose "now is taken to be the same moment throughout the universe: your now and my now are identical wherever we are and whatever we are doing." We now learn in a college physics course that this picture is wrong, which was proven by Einstein in the so-called special theory of relativity in 1905, and exhaustively tested in various experiments. Moreover, both space and time are elastic, and gravity may be thought of not just as a force but also as a geometrical property of spacetime. Not only does gravity slows time but it affects space as well.

The author then introduces the concept of a wormhole, using the well known representation of a deformed rubber sheet. This leads to the model of a traversable wormhole depicted by a flexible two-dimensional sheet, bent so that its two ends "come close together and then get connected through the wormhole." Dr. Davies continues, explaining how passing through the wormhole makes it possible to travel back in time: "Rather than inducing time to run backward, the time traveler embarks on a journey into space that ends in the past." As he points out, Carl Sagan's novel "Contact", later made into a famous movie, was based on exactly that idea. Several additional topics are touched as well in this very short book - among others, lesser-known time-travel paradoxes and parallel universes.

I find two phrases from the book absolutely hilarious - the first one unintentionally so, I believe: "harvesting virtual wormholes from the spacetime foam". As a mathematician I love the sentence "singularities are seriously bad news." To sum up: a well written, accessible, readable book, yet somehow less satisfying than I would like.

Two and three quarter stars.


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