"Discworld runs on magic." "Discworld does not run on scientific lines." Something about a flat world that sits on the backs of four elephants, that stand on the back of a giant turtle that swims through space . . . .
So, The Science of Discworld??? Basically, they are using Discworld and its magic as a foil for their discussion of real world science. This is less of a reach than it appears at first, since Discworld and many of its details are a parody of our world. For instance, magic has a basic particle, the thaum, and Unseen University has a High Energy Magic Building.
A Discworld story is woven through the book. It seems that the wizards of Unseen University, especially one Ponder Stibbons, decide to make a universe as an experiment. This is done in an old squash court. This is powered by a reacting engine, and run (sort of) by HEX, an analog of a computer. If you are not, by this time, screaming, "Noooooo!", then you need to read up on the history of science. The experiment is goosed (and, in serious scientific terms, thoroughly contaminated) when someone puts his hand into it. [He gets off light. Someone in Alan Dean Foster's The End of the Matter gets a much ruder reaction.] This universe is small enough for one man to carry on the outside, but much bigger inside. It is, of course, our universe. Time there moves much faster than on Discworld, or it would be a much longer book, but the wizards think that nothing is happening for a while. Then you get balls. Stars and planets, that is. The wizards have a hard time accepting that those huge gasballs are stars. Their stars are points of light, and their sun a small thing that goes around Discworld (Google Aristarchus, Ptolemy, Copernicus, etc.). It seems to take another while for life to appear, very much punctuated by things hitting the main focus, Earth. Intelligence is wiped out by these disasters, but reappears. It is still very primitive, and then when next they look, the planet is empty, with a cable supporting various space elevators, which network falls apart. Where did they go?
Interspersed with episodes of this are chapters on various aspects of Roundworld (Earth) science.
The universe runs on rules. More precisely, it runs, and the 'rules' describe more or less how. Science describes, not prescribes. Theories of Everything are chancy things, which usually don't describe as well as their proponents would wish.
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