While complexity researchers come from every academic discipline, in the humanities as well as the hard sciences, a hallmark of the movement is the liberation of physicists. Since Newton, physics has been focused on the inanimate, noncognitive physical world, ranging from subatomic particles to the structure of galaxies. In the process, it has developed a distinctive way of developing and manipulating mathematical models of systems. Fifty years ago, the gatekeepers of fields such as geography, biology, language and literature, and the social sciences would have told physicists to stick to their atoms and stars. Today, as the computer has enabled us to collect and process data in quantities unimaginable a generation ago, their heirs are opening the gates and inviting physicists to engage with organisms, demographics, words, and social movements, and increasing numbers of young physics PhDs are building careers without ever touching the physical systems on which their mentors were experts. In the words of one younger complexity scientist with a physics degree, “physics is whatever a physicist feels like studying.”

Geoffrey West is a physicist with traditional credentials: a theoretician specializing in subatomic particles. This book, written in nontechnical language for a popular audience, recounts how a preoccupation with the limits of human life (in particular, his own) led him to apply his professional toolbox to biological systems, and then extend his scope to other systems (cities, economies, and companies) that at first glance have little in common with mice and elephants. Two physical concepts dominate the discussion. The first is a universality class, a set of superficially different systems that obey the same mathematical laws. The second is scale invariance, the notion that a given system looks the same, from the point of view of its mathematical behavior, whatever level of distribution one uses to study it. To put the book in a sentence, West shows scale invariance across instances of the same kind of system, whether it be animals, cities, or companies, and universality by deriving this invariance from similar mechanisms across these different kinds of systems.

The first two chapters develop background concepts, including the pervasiveness of network structures in all types of systems (from circulation in animals to transportation and power distribution in cities) and the counterintuitive implications of nonlinear relations (for example, volume increases as the cube of size while surface area increases as the square), illustrated by examples ranging from why Godzilla could not exist to the failure of the Great Eastern, an oversized steamship in the 19th century.

Chapters 3 and 4 recount West’s initial explorations of scaling and universality in animal life. Many properties of animals scale with body mass with a power law whose exponent is 1/4. West’s multi-year collaboration with the ecologist Jim Brown and his student Brian Enquist led to the articulation of three properties of networks (for example, circulatory and nervous systems) that allow the theoretical derivation of this particular exponent: a) the networks must be space-filling, accessing the entire organism; b) the terminal units (biological cells) are the same size no matter what the size of the organism; and c) successful organisms have managed to optimize, minimizing their use of energy while maximizing their metabolic potential to generate energy. The theory they derived predicts that all animals follow the same growth curve, with their mass reaching a plateau, and it also predicts a limited lifetime with, surprisingly, about the same number of heartbeats for all animals with a circulatory system.

These biological properties are the result of the networks that allow organisms to function. Networks are also critical to other systems. Chapters 5 through 8 apply the same analysis to cities, sustained by networks of transportation, power distribution, and communication, while chapter 9 applies it to companies. One surprising result of the analysis is that while companies, like biological organisms, die, cities do not. The difference is that companies and organisms scale sublinearly, driven by economies of scale, while cities enable positive feedback among innovators and wealth creators, leading to superlinear growth.

The contrast between sublinear and superlinear growth reflects the age-long debate between Malthusians, who (supported by physicists focused on the second law of thermodynamics) see growth inevitably slowing and even collapsing, and economists, fascinated with the human potential for innovation as a way of overcoming each barrier that we have so far encountered. The final chapter advocates the use and extension of the theory developed in the rest of the book of developing a grand unified theory of sustainability, providing a firm analytical basis for monitoring and managing these opposing forces. An afterward sets the work described in the book in the context of the study of complex systems as championed by the Santa Fe Institute, with which West is associated and where he served as president for four years.

West has produced a work that is highly accessible to laypeople, deeply personal, scientifically stimulating, and directly relevant to today’s most pressing policy issues. It deserves a wide and thoughtful readership.

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