Book excerpt: A.K. Dewdney takes readers on a theoretical world tour to answer the question: Did humans make up mathematics, or did mathematics make up everything, including humans? After all, mathematical formulas seem to perfectly govern the cosmos, and the ur-mathematician Pythagoras himself believed that mathematics makes up reality. Dewdney has taken it upon himself to examine this fundamental question, beginning his journey in Miletus, the ancient home of Pythagoras and other deep thinkers. There, he meets the fictional Dr. Petros Pygonopolis, the first of his guides through space and time in search of mathematical meaning in history. His journey continues with stops in the Arabian desert (for insight into ancient Islamic astronomy with Professor al-Flayli), Venice (where Maria Canzoni reveals the mysteries of atomic theory), and England (home of the "engines of thought" in the form of Alan Turing's mind machines, as explained by Sir John Brainard). Dewdney's style is accessible, his knowledge is thorough, and his sense of humor is refreshing, if a bit geeky. A Mathematical Mystery Tour is not a difficult read, although the ideas it attempts to clarify are quite abstract. The fictional tour guides at each port of call are helpful in humanizing the intimidating subject matter.