Charles L. Adler is not only a physics professor but also a sci-fi and fantasy enthusiast. That is a perfect combination to find out where the boundary can be drawn between the physical reality and the fantasy of the author. But futurologists are not only the authors of fantastic novels, also scientists have proposed wild ideas. Often the energy needed to realize such a megalomanic project is a hard boundary for what is possible, but Adler also pays attention to the logistic and economic implications. Some ideas are `obviously' impossible, but this doesn't stop Adler. Several of his discussions are of the type `assume that we have solved problem x, what would be possible then?', and that leads to serious discussions of projects beyond your wildest dreams. In most cases the conclusion is that what is described in the sci-fi novel is not possible now, and that it will almost certainly never be possible in the future. That may disappoint some of the believers of the genre that see sci-fi as the evocation of our future.
The mathematics needed are at a relatively low level. The more complicated derivations are avoided by sentences of the form `solving these equations is beyond the scope of this book, but the bottom line is...'. Sometimes further exploration is left as an exercise for the reader. In this sense, this book project can also be considered as a collection of ideas to be worked out as applications of a mechanics or more general physics course. On the other hand, it is also a guide to the classics of SF literature with Arthur C. Clarke, Philip K. Dick, Ursula Le Guin, Robert A. Heinlein, Larry Niven,... movies and TV shows: 2001, A Space Odyssey, Star Trek, Babylon 5, Star Wars, Avatar,... but there are also references to scientists: Freeman Dyson, Richard Feynman, and Albert Einstein.
The book has 4 parts: (1) Potter physics, (2) space travel, (3) worlds and aliens, (4) year googol. The first part deals with the magic of Harry Potter on the basis of conservation laws of mass, energy, and momentum and on the second law of thermodynamics. If you know that about 1 gram of mass corresponds to the energy released in the Hiroshima bomb, then if one can transform a boy into a weasel, there is a lot of energy to account for the missing mass. Similarly the mending charm evoked by reparo to repair things would need a lot of energy to undo the increased entropy. It is also shown that candle light illumination will leave Hogwarts a dark place (even with thousands of candles) as well as Kleiber's law is ruling out the existence of flying monsters and dragons. The relation size-metabolism of the law limits the production energy and that prevents the existence of biological fliers of more than 20 kg.
Supposing we have solved the traveling problem, how would we be able to build or transform a planet and make it habitable? At first sight there are many planets in our universe that are at a distance from their star comparable to the earth. However that does not make it automatically habitable for us. All these planets have their own history and that can be quite different. For example the impact on our earth that wiped out the dinosaurs might be an essential contribution for us humans to have evolved as we did. Such hazards are indeed very rare. So Adler's mantra is that stars may be very much alike, but planets are as different as they can possibly be. But suppose there are such earth-like planets, how can we find them? They are dark and relatively close to a bright star. Moreover, if ever there are living humanoid aliens on it, how can we communicate and why did they not contact us? The SETI project is looking for the ET's but it was not successful so far and the Drake equation predicting the number of civilizations seeking communication have too many unknowns to be useful.
The last part is an evocation of the very distant future. Of course there are several candidates for extinction on a short horizon (global warming, nuclear war, end of petroleum resources,...) but suppose we overcome these, then the earth will be too small anyway. How can we make for example Venus or Mars habitable? How to produce soil and oxygen there. Or perhaps how can we move earth when our sun becomes too bright? Perhaps there are alternatives like the Dyson sphere (a gigantic sphere around the sun to catch practically all its energy, which would mean that we had to take the planets apart to get enough material for it) or the ringworld of Niven (a ribbon around the sun, which surprisingly would require more mass than the sphere). How stable would such constructs be? Such projects require enormous resources of energy. The Kardashev scale defines technological sophistication of civilizations on the basis of the amount of energy they can use: Type I (all of its planet), II (all of its star), and III (all of its galaxy). The final chapter is about the very end: in the `short term' (some hundred million years) the climate change cycle may wipe out humans, or asteroid impact can happen. The `medium term' expectations is the increase of our sun (only type II civilizations could overcome this). Finally there may come an end to our universe where only black holes will be around, which may eventually evaporate.
The strong point of a good science fiction adventure is that it will be recognizable for the reader. This means that it will follow the rules of physics with little exceptions. So a good SF author should also be well aware of these. At least in the so-called hard SF stories. These are the ones that Adler concentrates on. And the fan of this kind of adventures will normally be some amateur scientist as well. This is therefore a marvelous book for the fans, and why not for the possible authors as well. If you are willing to skip some of the limitations of what is possible today, then at some points, this book is at the boundary of science fiction as well. The adventure, the good heros and the bad guys, and possible love stories are missing, but the reader can easily discover them in the solution of the problems if he or she is willing to dive deeper into the facts, the problems and the mathematics,