What Shape Is The World?
WHAT SHAPE IS THE WORLD?
Ian Stewart, Emeritus Professor of Mathematics, Mathematics Institute
The world is flat. It is not round. It is flat and resting upon the backs of four elephants who, in turn, stand upon the back of a giant, space-faring turtle named Great A'Tuin. This, to those who are familiar with the work of Terry Pratchett, is of course, not Earth but the Discworld – the domain in which many of his publications take place. Terry, along with Professors Ian Stewart and Jack Cohen, recently published The Science of Discworld IV. Not everything the three 'unseen academicals' discussed for this edition made it into the book and Ian Stewart was kind enough to give us a peek at the missing science of the Discworld.
Terry Pratchett, Jack Cohen and I recently completed the fourth book in the popular science series The Science of Discworld. The format of these books combines a fantasy short story, set in Terry’s Discworld, with scientific commentary about the real universe. Discworld runs on magic (things do what people want them to—if they know the right spells) and narrativium (things do what the story requires them to). It is flat, supported on four giant world-bearing elephants which stand on the back of an even larger space-faring turtle. The turtle swims through space, so it needs no further support. Our own universe, or ambiguously our planet, appears in the story as the Roundworld Project. This is a magical construct inside which magic does not work and the rules of science, the laws of nature, apply instead. The wizards of Discworld have a different idea from us regarding which world is real, but that’s their problem. They do find a world without magic puzzling: nothing seems to make sense.
This format has some very useful features for writing popular accounts of science. The main one is that since the scientific action always takes place inside Roundworld, the scientific chapters are genuine real-world science. Additionally, any scientific topic might in principle be discussed. There is no limitation to ‘explaining’ Discworld fantasy elements in terms of science, which is how most ‘science of’ books—Star Trek, Harry Potter, The X-files, Santa Claus—go about this kind of mixture. So there’s no obstacle, in principle, to us eventually getting to The Science of Discworld 42, or whatever.
In the first Science of Discworld, the wizards of Unseen University accidentally bring Roundworld into existence, and witness the origins of the universe, the solar system, the Earth, bacterial life, complex life and apes. They, unfortunately, fast-forward through the entire history of humanity, returning to Roundworld just in time to see something fleeing an approaching ice-age, leaving behind the wreckage of its space elevators.
The second book of the series sees elves invade Roundworld and disturb the course of history. But when the wizards kick them out, humanity degenerates into a primitive state and nothing interesting happens. Eventually the wizards get William Shakespeare and Isaac Newton born, and the seeds of today’s world are re-established. The third Science of Discworld relates to how interference by the Auditors of Reality, the ultimate cosmic health-and-safety officers, get Charles Darwin to write the wrong book: The Ology of Species, not The Origin. The creative tensions and debates between science and religion, which occurred in Victorian times, never happen, and humanity falls into a state of comfortable complacency. Which means they will not be inventive enough to escape that coming ice age. With difficulty, the wizards get Roundworld back on track.
The fourth, and most recent, book in the series hinges upon events in Discworld rather than Roundworld. On the Disc there is an ancient religion, Omnianism, which believes Discworld is round. Despite all the evidence, they do not believe in the turtle or the elephants. Seeing the Roundworld Project as an infringement of their theological property rights, they launch a legal case to gain custody. Naturally, the wizards dispute their claim.
This scenario allows us to examine, in the science chapters, a variety of issues. In particular, we look at how scientists can try to infer the shape of their world, or the universe itself, when they are unable to get outside it and take a direct look. For the Earth, we can now do that, but scientists mapped out the entire planet long before we could get into orbit. We still don’t have that luxury for the universe as a whole, and it’s hard to see how we could ever get it.
The commentary discusses a key feature of science, one that many non-scientists fail to appreciate: science is mainly about inference from experiments and theories, not direct observation. The ancient Greeks inferred the spherical form of the Earth thousands of years ago, by logical inference from phenomena that they could observe, such as the planet’s shadow on the Moon during an eclipse and the way boats seemed to sink below the horizon as they headed out to sea. Today we infer the temperature at the centre of the sun from our understanding of nuclear reactions, but no person or instrument has ever been there to check. The majority of scientific knowledge rests on inference, not on direct observation. Indeed, that’s what theories are for.
I don’t want to give away the contents of the book, so I’ll focus here on a short passage that we cut out, at a late stage, because the chapter about the shape of the Earth was getting too long. It illustrates how science often pursues ideas that eventually turn out to be wrong. Critics often try to convince us that this tendency means that scientists haven’t got a clue, but actually it reveals their willingness to seek fresh evidence and adapt to it. As the saying goes: “You can’t trust scientists. when new evidence comes along, they change their minds.”
The topic that we deleted concerned the short-lived hypothesis that the Earth might be expanding:Page 2 >>
Ian Stewart is Emeritus Professor of Mathematics and Digital Media Fellow at the University of Warwick. He is the co-author of the Science of Discworld series with Terry Pratchett and Jack Cohen. He is the author of several publications including ‘How to Cut a Cake’ (2006), ‘Why Beauty is Truth’ (2007) and ‘17 Equations that Changed the World’ (2012).
Image: Great A'Tuin, the Giant Star Turtle (Chelys galactica), carrying four giant elephants and the Discworld on her back. Image via fyterrypratchett.
The Science of Discworld IV: Judgement Day: It's Wizards vs Priests in a Battle for the Future of Roundworld. Terry Pratchett, Ian Stewart and Jack Cohen (2012).
ISBN : 0091949793
Why I'm going to the Discworld convention. Ian Stewart, The Guardian Books.