Can plants, animals, and cities be described with the kind of elegant mathematical laws that dictate planetary motion? In Scale: The Universal Laws of Growth, Innovation, Sustainability, and the Pace of Life in Organisms, Cities, Economies, and Companies, Santa Fe Institute physicist Geoffrey West takes readers on a tour of the mathematical rules governing systems composed of many interacting constituents. In the January issue of Physics Today, Jayanth Banavar calls Scale “an inspiring celebration of complex systems” that will “stimulate scientists to think about the patterns around us and contemplate the simplicity underlying the complexity.”
Scale lays out the power-scaling laws that describe everything from microorganism growth to the number of patents per capita in a city, providing fascinating insight into the science of complexity. In biology, the laws help predict the life spans of organisms, the maximum size of a species of tree, and the number of heartbeats per minute in animals. Some of West’s most famous work has involved modeling the growth of cities and corporations, and Scale shows that GDP, crime rates, and even walking speed scale with a city’s population. His models are increasingly of interest to city governments as they work to understand whether their safety and transit challenges are proportional to their size, or whether their cities are outliers.
West recently talked to Physics Today about how a particle physicist with the Superconducting Super Collider (SSC) came to master the laws governing organisms large and small.
PT: What led to your current interest in universal scaling laws?
WEST: After the SSC was canned in the early 1990s, I heard some colleagues saying that physics had been the science of the 20th century, but biology would be the science of the 21st. I didn’t know much biology, and so in my ignorance—maybe arrogance—I felt that biology isn’t quite the same kind of science that physics is. In physics you have underlying principles. You can make the principles quantitative; you can compute things that you can predict and do experiments to verify or to amend the theory.
I decided that I should put money where my mouth is and see if I could apply this idealized physics paradigm to an important biological question. I was always very interested in the process of aging and death. And so I asked myself the first obvious question that a physicist would ask: What sets the scale of life? Why is it that we live for 100 years or 120 years and not 10 or a billion? To my amazement, I learned that there are extraordinary scaling laws for fundamental qualities in biology, the most famous being for metabolic rate. It’s a very simple power law with this weird exponent—the metabolic rate scales with the three-quarters power of the animal’s mass.
As I started looking more closely at this, I discovered that there is a certain universality. If you look at any physiological quantity, they all scale with these simple power laws, and the exponent is always on the scale of one-quarter. This was known, but there was no deep understanding of why. It blew my mind.
PT: As you started integrating biology into your work, what was it like to communicate with people from a different discipline? Were there challenges in being a physicist talking to biologists?
WEST: It took me a long time to realize that there are different modes of doing science, different criteria of what constitutes explanation. I would say many biologists—not the ones I’ve worked with, by the way—are often content with a highly qualitative narrative. Others are content with a model or a theory. It’s almost like saying that Kepler’s laws constitute an explanation for the movement of planets. A physicist would never consider that an explanation. We want to understand where those laws came from.
And there is a part of biology that was, and in some places still is, sort of anti-theory. There’s an attitude that arguments from physics have no place in biology. A referee report for what would become a highly cited paper of mine actually said that despite its claims being convincing, this kind of work had no role in biology and should not be published.
I also did not realize how narrow physics is. Biology is such an enormous project. There’s more uniformity in physics, which is part of its strength but also part of its great weakness. Physics is narrow, yet physicists think of it as being so broad that a single theory could be a theory of everything. We can be quite arrogant.
I’ll give you an example of a cultural divide. I gave a talk at a department of biology, and at the end of my talk someone said to me, “Well this is very nice. You’ve explained a huge amount with this.” And then they said, “But what’s the point of understanding all of this? I work on crayfish. What can you tell me about the life history of crayfish?” It’s almost like giving a talk on quantum mechanics and then having someone say, “I work on rubidium, and I just don’t see how all this stuff on probabilities and the wavefunction can really teach me about rubidium.”
PT: How do you answer that kind of question?
WEST: I say, first of all, that if you are trying to deal with a problem in a very specific system, you are probably doomed to making mistakes if you do not understand the underlying general principles that are at work, whether it be in an organism or in a city. The underlying theory is idealized, like all physics in a way. The key is understanding where the baseline is and looking at how your specific system deviates from that.
PT: You’ve done some work with local politicians and civic leaders drawing from your research on cities. What has that experience been like?
WEST: One of the things I’ve most enjoyed about this stage of my work is interacting with people outside of academia. Seeing the world through different lenses has been extremely interesting, as has dealing with these very messy problems. In the city work, the most important thing is whether people who are dealing with the big questions about cities and urbanization and the future of the planet are paying attention to it. It’s been an interesting transition, to have one foot in traditional basic research and another in the world of politics, policymaking, and so on.
PT: What is your next project?
WEST: I’m working with people at UCLA to explore why it is that we sleep eight hours and not just three or four. We’re looking at how sleep changes during the growth from baby through adulthood, and how we could use that as a window to neural development.
I’m also trying to understand the structure of hunter-gatherer societies and the transition to agriculture. What made us become sedentary? I was very pleased that in 2017 I published my first paper in an anthropology journal.
The intriguing thing about scaling laws is that they provide a window onto the underlying dynamics of systems, so that they can be generalized. And that leads to my passion, which is the question of global sustainability. Can we formulate a generic framework to understand the future of the planet? Can we have open-ended growth of our socioeconomic system? Now, any physicist would tell you right off the bat that something somewhere is going to collapse. I’m trying to put all of that together in a quantitative mathematical framework that is still realistic and has predictive power.
PT: What are you reading right now?
WEST: I’m reading the 19th-century British writer Anthony Trollope. In my casual reading, I read more fiction than nonfiction as a kind of relaxing therapy. Trollope wrote a book called The Way We Live Now. It’s a very long book, but it is a fantastic mirror image of what’s going on now with the rise of capitalism, the dynamics of finance, and the social dynamics of power.
