HARRY POTTER AND THE PROFESSOR OF PHYSICS

Charles L. Adler. Wizards, Aliens and Starships: Physics and Math in Fantasy and Science Fiction. Princeton University Press, 2014.

Potential purchasers should be aware that this is a book to be studied rather than just an easy read. The author warns us: "I intend the book as a working book for science fiction enthusiasts who have at least a decent knowledge of algebra and know what calculus means". However, the equations used are explained so that the reader will know how they are used and why it is necessary to use careful calculation rather than relying on rough estimates, or speculating about what seems to be feasible or probable.

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The first subject dealt with is "Potter Physics", on the use or neglect of scientific principles in fantasy. There are writers, such as Ursula K. Le Guin, who invent elaborate rules for the working of magic, and others, such as J.K. Rowling whose work "contains innumerable examples of magic being used in ways that violate physical law and are also internally inconsistent".

Adler has a lot of fun with the scientific impossibilities of the details of fantasy stories. Rooms lit by candles, for example, would be rather dark in reality and he illustrates this by comparing calculations of the brightness of electric lights with that of candles. Candle-lit rooms in films look bright enough, but the film makers cheat by keeping the electric lights off screen.

Many fantasy stories contain descriptions of fantastic beasts, and we are given some interesting guidance on which ones would be physically impossible. For example, calculations show how the size of flying animals is limited by the fact that the metabolic demands of flight increase more rapidly than metabolic rate as mass increases. Thus the biggest flying birds could not be much bigger than they actually are.

Among Adler's main interests in writing this book are the possibilities of space travel and advanced space-faring peoples. So in Part II he takes a look at the economics of manned space travel as well as the physics and chemistry. He notes that some science fiction writers paid attention to the science involved in space travel but ignored the costs of the projects which they described. They came to assume that space travel would become as commonplace as air travel is today, and they included it in their stories even when the plot did not depend on it.

Space flight, though, is very expensive, especially manned space flight, and we are given some interesting calculations of the enormous amounts of energy required and the less obvious costs involved. A NASA shuttle mission costs about $450 million, the true cost of putting a payload into orbit being about 200 times higher than the cost of the fuel. As well as the expensive training required for each person going into orbit there are several dozen support personnel who stay on the ground for each one. Accidents also have to be considered. The death rate "would be absolutely unacceptable for any commercial form of transportation".

We are shown how improvements in telescopes and other equipment have made it possible to detect exoplanets (planets outside the solar system orbiting other stars), the first of these being discovered in 1993, and since then over 700 of them. It has even become possible to detect atmospheric constituents on a few of these planets. This is particularly interesting, as the detection of free oxygen would almost certainly mean that there was life on the planet.

The chapter discussing the possibility of intelligent aliens elsewhere in the galaxy is largely concerned with attempting to calculate the probabilities of their existence and whether we could ever make contact with them. The author notes, though, that recent science fiction stories have tended to depict a galaxy in which aliens are rare or non-existent, following the example of Isaac Asimov's Foundation trilogy.

There is much else in this book to interest readers interested in astronomy and astronautics and I think it will be likely to appeal to physics students. 

• John Harney