Skip to main content

Flow – Philip Ball ****

This is another of Philip Ball’s quirky, scholarly, illuminating studies of the patterns of nature, the second in a trilogy. The others deal with shapes and branches; this one deals with flow of all kinds, from convection in the sun to avalanches in a pile of rice.
Ball has struck popular science gold with this trilogy, because he has a subject matter that is at the same time scientifically intriguing, visually engaging, and easy for the layperson to grasp. Fluid flow – the paradigm of flow in this book – is a typical case. Eddies and turbulence are interesting for scientists because they are horribly complicated. But because they are horribly complicated, the only hope of understanding many features of fluid flow is through a kind of simple qualitative modelling, the kind that is easy to explain to a popular audience. The Kelvin-Helmholtz instability, for example, is a mechanism by which flowing water forms wavy currents. It is a simple mechanism, communicable in a picture, and it creates delicate plumed patterns in water that make great images. And like most of the patterns in this book, it crosses mediums easily – it is present in clouds as well as rivers.
It turns out, as Ball reveals in the last chapter of the book, that real turbulence is not susceptible to any simple models like the Kelvin-Helmholtz model. But this is a rare exception. And even with turbulence Ball finds a pretty way of illustrating the science: he concludes as he began the book, with a work of art. This artistic theme – the first chapter is about representations of fluid flow in Western and Eastern art, with a focus on Leonardo da Vinci – is typical of Ball’s playfulness in this trilogy, his fondness for interesting diversions. These are indeed diverting, but they can also be disorientating. In the case of this volume, I finished the first chapter without having much idea of what the book would be about.
This book is certainly about something, though, even if it that something is hard to pin it down. It’s about fluid motions, of course: aside from the relatively conventional topics of water flow and convection, we have intriguing chapters on the collective behaviour of grains (in dunes, piles, and sheets) and on the movement of flocks of animals, crowds of people, and lines of traffic. But it’s also about deeper themes, which Ball mentions now and then but never instructs us about systematically. It’s about trying to describe and understand a wide class of phenomena through a single parameter – whether it is Rayleigh’s number for describing the tendency of fluids to give convection patterns, or Reynold’s number for describing the eddy-forming habits of a liquid stream. In a vague way it is about self-organisation, the capacity of macroscopic entities to form complex patterns with no outside help except a steady influx of energy. And in a fleeting way it is also about self-organising criticality, the quality that some phenomena have of spontaneously entering highly unstable states – a quality that the now-legendary sand-pile is supposed to have.
Readers who are not interested in these themes, perhaps because they would rather see them treated front-on rather than in the occasional sidenote, will still find plenty to enjoy in this book. The simplest pleasure it offers is to witness similar patterns in disparate phenomena: lane-forming on human footpaths and in the trails of army ants; convection not just in boiling water but inside the earth, in clouds, in cereal packets, and in the regularly-spaced circular craters that shape some landscapes in Norway and Alaska. Another of the book’s pleasures is its narration of the process of science, the sequence of attacks by different scientists, using different methods, on the same problem. In Flow, Ball’s account of successive attempts to explain sand dunes is typical of his blow-by-blow coverage of the process of discovery.
The breadth and detail of Ball’s interests in this book means there are many other pleasures besides, from the historical (Faraday’s prescient thoughts on convection in grains) to the domestic (an explanation of why shaking a cereal packet drives the chunky bits to the top). The downsides are that the scientific detail is sometimes heavy-going, and that the underlying themes of the book (aside from the general idea of fluid motion) are nebulous. On a more specific note, Ball’s discussion of self-organising criticality did not ease much of my confusion about that topic. On the whole, however, Flow deserves its place in Ball’s trilogy – and that is high praise.
Hardback:  
Review by Michael  Bycroft

Comments

Popular posts from this blog

Cosmology for the Curious - Delia Perlov and Alex Vilenkin ***

In the recently published The Little Book of Black Holes we saw what I thought was pretty much impossible - a good, next level, general audience science title, spanning the gap between a typical popular science book and an introductory textbook, but very much in the style of popular science. Cosmology for the Curious does something similar, but coming from the other direction. This is an introductory textbook, intended for first year physics students, with familiar textbook features like questions to answer at the end of each chapter. Yet by incorporating some history and context, plus taking a more relaxed style in the writing, it's certainly more approachable than a typical textbook.

The first main section, The Big Bang and the Observable Universe not only covers basic big bang cosmology but fills in the basics of special and general relativity, Hubble's law, dark matter, dark energy and more. We then move onto the more speculative (this is cosmology, after all) aspects, brin…

Astrophysics for People in a Hurry – Neil deGrasse Tyson *****

When I reviewed James Binney’s Astrophysics: A Very Short Introduction earlier this year, I observed that the very word ‘astrophysics’ in a book’s title is liable to deter many readers from buying it. As a former astrophysicist myself, I’ve never really understood why it’s considered such a scary word, but that’s the way it is. So I was pleasantly surprised to learn, from Wikipedia, that this new book by Neil deGrasse Tyson ‘topped The New York Times non-fiction bestseller list for four weeks in the middle of 2017’.

Like James Binney, Tyson is a professional astrophysicist with a string of research papers to his name – but he’s also one of America’s top science popularisers, and that’s the hat he’s wearing in this book. While Binney addresses an already-physics-literate audience, Tyson sets his sights on a much wider readership. It’s actually very brave – and honest – of him to give physics such prominent billing; the book could easily have been given a more reader-friendly title such …

Once upon and Algorithm - Martin Erwig ***

I've been itching to start reading this book for some time, as the premise was so intriguing - to inform the reader about computer science and algorithms using stories as analogies to understand the process.

This is exactly what Martin Erwig does, starting (as the cover suggests) with Hansel and Gretel, and then bringing in Sherlock Holmes (and particularly The Hound of the Baskervilles), Indiana Jones, the song 'Over the Rainbow' (more on that in a moment), Groundhog Day, Back to the Future and Harry Potter.

The idea is to show how some aspect of the story - in the case of Hansel and Gretel, laying a trail of stones/breadcrumbs, then attempting to follow them home - can be seen as a kind of algorithm or computation and gradually adding in computing standards, such as searching, queues and lists, loops, recursion and more.

This really would have been a brilliant book if Erwig had got himself a co-author who knew how to write for the public, but sadly the style is mostly heavy…