Thank you for downloading this episode of In Our Time, for more details about in our time, and for our terms of use, please go to BBC.co.uk.

I hope you enjoy the program.

Hello, in the late 1940s a chemist in Brussels called Ilia Prigogin embarked on research

which would take him in rather surprising directions. His work concerned the energy associated with chemical reactions and in

1977 he won him a Nobel Prize in chemistry, but it also led him to write a book

about traffic management, surely one of the more startling examples of the unexpected

consequences of scientific research.

Prigagene proved something which scientists before him had doubted that it's possible to create

order from disorder. He realized that his ideas

applied not just to chemical reactions but to the wider world from city traffic

problems to how a colony of ants organises itself. Today this field of study is known as complexity.

Complexity theories study the ways in which large groups of individuals behave

collectively. Complexity only emerges a separate discipline around 40 years ago, but today it's used to study difficult

problems fields such as diverse as biology and international politics to explain the way

birds flock and how the economy works. We mean to discuss complexity

are Ian Stewart, emeritus professor of mathematics at the University of

Warwick. Jeff Johnson, professor of complexity science and design at the Urban University and Professor Eve Middleton

Kelly, Director of the Complexity Research Group at the London School of Economics.

Ian Stewart, would you begin by giving us a brief overview of what complexity is and how it's used?

It's a mathematical technique you can run computer simulations based on it, but also a point of view about systems in which large numbers of individuals interact

with each other.

And it sounds very vague in general, so let's take some examples. Think of a crowd of people moving

...