Why Information Grows: The Evolution of Order, from Atoms to Economies César Hidalgo, New York 2015: Basic Books, 256 pp. $ 26.99. ISBN: 0141978031, 9780141978031

Why should economic and human geographers read a book titled Why Information Grows: The Evolution of Order from Atoms to Economies? C esar Hidalgo is a statistical physicist at MIT, and the book makes ample references to matter, energy, and thermodynamics. But open it and you will see that its central question has kept human geographers busy for decades: why do economies grow faster in some part of the world than in others? To answer, Hidalgo crosses disciplines and draws inspiration from Shannon and Prigogine while building on the work of Smith and Granovetter. What comes out of this ambitious exchange between natural and social sciences is a key message: economies grow because information grows. Building on Shannon’s information theory, Hidalgo defines information as ‘the order embodied in codified sequences, such as those found in music or DNA, while knowledge and knowhow refer to the ability of a system to process information’ (p. 165). It essentially refers to order, from the particular arrangement of atoms in an airplane to the structure of the DNA double helix and it follows that more complex arrangements, like human beings or cars, contain more bits of information than simple ones, like single cell organisms or kitchen tools. These concepts of order, arrangements, structure, and complexity are the building blocks of the book. Before focusing on the economy, Hidalgo explores the evolution of order in the physical world. To grow, information needs energy to emerge, matter to be stored, and computational abilities of matter to adapt and evolve. Computational abilities are particularly important, as they refer to the ability to process information, a shared ability between humans and cells. The reader might wonder how this section connects with economic growth. Starting from the physical world, Hidalgo shows what it looks like to observe the world through the lens of physics, chemistry, and biology. It also reminds us that the growth of information in the economy is a by-product of the growth of information at a much bigger scale and it makes clear that evolution in the biological world is a relentless march towards greater complexity. This analogy is important as it allows us to understand that economies grow and evolve through the embodiment of increasingly large amounts of information into increasingly complex physical objects. Hidalgo calls this phenomenon ‘crystallized imagination’, and he compares apples (from trees) and Apples (from Steve Jobs) to illustrate the idea. The main difference is that apples first existed in the world and then in our head, while Apples first existed in our head and then in the world. Apples are crystallised imagination, and it is through this process that economies grow. But the thought-provoking idea is that complex products require more than one head: ‘Our need to form networks, however, emerges from one important consideration: the limited ability of humans to embody knowledge and knowhow’ (p. 179). Hidalgo refers to this human limitation as the ‘personbyte’ theory, stating that the complexity of an economic activity reflects the size of the network to execute it. The computers that process information in the economy are not isolated individuals, they are networks of individuals. Given the complexity of an economic activity, these computers can be households, teams of inventors, firms, cities, regions or countries. This vision contrasts with the neoclassical homo economicus but fits very well with the conceptualisation of cities