The winter wouldn't end in Ankh-Morpork. Even the wizards in Unseen University were freezing. Fortunately they had Ponder Stibbons' new thaumic device ready to provide some heat… and it worked! Thaum split so amazingly well that Hex, the University's self-designed (that's why it worked better than most things in the University) computer, had to launch the Roundworld project to absorb some extra energy. In this small globe about one foot across, there lies a whole universe… maybe ours?

While The Folklore of Discworld showed how close our Earth and Discworld are, The Science of Discworld shows how different they are. So different indeed that the wizard can't even grasp the basic concepts. Rocks circling around other rocks? Life emerging on a world without a turtle and elephants? That can't possibly exist! And we don't even have narrativium and chelonium elements!

Chapter alternates. One chapter shows wizards in Unseen University devising about our weird universe and why it can't possibly work. The next chapter two known scientists, namely Ian Stewart and Jack Cohen, describe our world in a scientific way, and how very different it is from a magical world. And then back again to Discworld. This original organization is very powerful and entertaining. We read about history of sciences, philosophical questions, and even the most boring facts seem fun. A special care is taken about how we keep looking at the obvious things in the wrong way. How could people possibly think earth was flat? And what are our own errors today? So many questions, and so few answers!

Roundworld can't possibly work? But chapter after chapter, it turns out to work. Not overwhelmingly well. Civilizations keep being wiped out of the Earth by a larger rock falling on it and ice ages. How tiny and fragile we are! But life goes ever on and on. As does the reading.

• Full reference: Terry Pratchett, Ian Stewart, Jack Cohen The Science of Discworld. Ebury Press, London, 2002, 414 p. ISBN: 9780091886578.