I found the subtitle of this book to be somewhat off-putting; I was expecting it would be too far towards the "gee-whizzery" pole of science writing, and indeed there is an element of that in Chown's style; still, the fact remains that present-day science does contain the most astonishing speculations and the boundary between science and science fiction was never more imprecise than it is today. (In fact, the bibliography for each chapter includes a "fiction" section.)
The book is in three parts. The first, "The nature of reality", is concerned with physics and the attempt to unite quantum theory with Einstein's theory of gravity. Chown outlines the ideas of Mark Hadley, who apparently holds that "a subatomic particle like an electron is a tiny region of spacetime so dramatically warped that it bends back on itself like a knot." These regions would constitute loops in time and would, Chown maintains, be effectively time machines. Hadley, it appears, is pretty much out on a limb with this idea, and most theorists are following the string theory trail, which Chown touches on briefly.
The second part, "Looking glass universe", is on cosmology. One chapter considers the possibility that the unknown dark matter that makes up much of the universe may consist mainly of black holes. Another is about "mirror matter": that is, matter made up of particles whose symmetry is the reverse of that of the particles of which we and our galaxy are made. Conceivably the universe could contain galaxies made up of such material but we would be unable to see them. There could even be mirror planets orbiting our own Sun, and perhaps even mirror people walking among us (though they would probably fall through to the centre of the earth). Although we could not see these things, we may be able to detect the momentary production of mirror matter in the laboratory.
Still on the cosmological theme, Chown goes on to look at the topic of parallel universes. This idea is by now familiar to aficionados of popular science, who are accustomed to reading speculations about the possibility of multiple universes in which the laws of physics differ from those in our own universe. However, Chown quotes the view of Max Tegmark, who has taken the idea further than most. Mathematicians know that there are many possible formal systems of mathematics; Tegmark has proposed that there may be actual universes corresponding to all these systems, in which case the number of possible universes is virtually infinite. Finally Chown touches on the suggestion that universes—and perhaps our own universe—could be produced by the action of super-intelligent beings.
The final section, "Life and the universe", considers the suggestion that there may be planets wandering in space, unattached to any star, but still capable of supporting at least bacterial life. Chown also looks at the Hoyle-Wickramasinghe theory that life on earth may have arrived via comets. This is by now a familiar idea to readers of popular science, and the same will be true of some of his other material, but not all.
This book would be a good choice to give to a young person interested in science. And Chown (and his publishers) are to be congratulated for including proper footnotes instead stuffing them in a cubbyhole at the back as usually happens today.