author : Terry Pratchett

Despite its title, this isn't a book about the science underlying Terry Pratchett's stories of Discworld -- that world runs on magic, after all -- it's about the science that governs Roundworld, our world.

It is structured as alternating chapters. The first of each pair tells the story of the Wizards at the Unseen University, and how a magical accident results in the creation of a pocket universe -- ours. With the unwilling help of Rincewind, they observe this puzzling universe as it evolves from the Big Bang to beyond our current time, and they try to understand in their own magical terms. The second of each pair of chapters then explains what the Wizards are observing from a scientific point of view.

The explanations build on ideas from Stewart and Cohen's earlier books, The Collapse of Chaos and Figments of Reality, including those of extelligence, and Ant Country. The ideas cover an enormous breadth, and because of this, there is necessarily some lack of depth, so it helps to have read the previous books to get some of this missing background.

It could also do with a "further reading" list. For example, they refer in passing to Deep Time -- that evolution operates over incomprehensibly vast periods of time, and so doesn't fit well with the kind of stories we tell about it -- and I would have liked a pointer to somewhere that explores this in more detail. There is rather a lot of this feeling that certain sentences have a lot packed into them, but with no pointer to somewhere to help the unpacking.

Lack of depth notwithstanding, I like this book. There are some nice points made about the way our high tech is beginning to look like magic from the outside, and some good discussions about the way "lies-to-children" -- over-simplified explanations -- are a necessary stepping-stone on the way to deeper explanations. [I was a bit taken aback to read on page 152: "In April 1969, Neil Armstrong stepped down onto the surface of the moon". This isn't a "lie-to-children", this is a simple factual mistake.]

In particular, I like the way the alternating fact and fiction chapters allow the separation of our current best understanding of the facts from the wildly speculative illustrative examples. The fictional details about evolution on Earth -- the rise of intelligence in certain crabs, lizards, and what not, only for them to be wiped out by the next ice age or meteor strike -- makes the point that our current civilisation is just as vulnerable to whatever the universe chooses to throw at us, but that the planet as a whole is very resilient.

So, some fascinating deep ideas lurking just round the corners. Maybe their next book will explore them further?

• The Science of Discworld, the Magic of Roundworld. Jack Cohen's talk at Reconvene '99 Eastercon

The first Science of Discworld gave us two parallel stories: the story of evolution on Earth, culminating with humanity escaping to the stars just before it was wiped out by yet another natural cataclysm, coupled with the story of the actual science behind it all. In this second volume we have the same format, with the (fictional) story being of how the humans got themselves that far, and the (scientific) story of how culture develops, and (nicely recursive here) the importance of stories within that culture.

The "plot" is this: evil misery-eating elves come to prey on the humans, by making them superstitious and thus fearful. The wizards try to stop this, but their first attempts make things even worse, until eventually they discover Shakespeare. The fun is seeing how (fiction) and why (science) they eventually succeed.

Like most Stewart and Cohen journeys, there is a lot packed into a small space, not always unpacked (or often, unpackable only if you've read previous travels), yet all fascinating nevertheless. We get excursions on chaos and complexity; on extelligence, cultural privilege, and the importance of stories; side-swipes at science, art, and religion; and loads more.

Some of the material has been covered before, but is well worth covering again and differently, because it is so import and difficult to intuit. The parts on DNA and complexity fall in this category.

Most of the work is taken up with examining the importance of stories in the development and continuation of culture. It would be interesting to speculate on how some of these ideas might be tested.

And towards the end, we get to see how science can help us make better stories, stories that are better suited to reality, rather than just how we would like things to be. Science stops us, and our stories, from fooling ourselves.

So, a fun read, and lots of food for thought (even if that food is served up as a splendid hors d'oeuvre course of masses of delightful toothfuls, rather than a good solid main course of meat and potatoes (although potatoes do play an important role...)).

In this third outing of The Science of Discworld, the authors have their usual fun, this time with evolution. The format is the same -- chapters describing how the Wizards of Discworld are trying to put right problems in their accidental creation -- our Roundworld, alternating with chapters describing the science behind it all. This time something strange has happened on Roundworld -- it seems that suddenly Darwin never wrote his Origin of Species -- and it put science back so that the people never escaped snowball earth 500 years later (don't ask -- just read the books!)

Evolution, Paley's watchmaker, and the history of Origin of Species gets an outing here -- as does a supporting cast of infinite numbers, cosmology, and complexity. It makes a fun read -- but it's probably not the best place to start, if only to understand many of the jokes about the Wizards attempts to change Roundworld.