Adrian Bejan is a professor of mechanical engineering at Duke University. So why on earth are we talking to him? Bejan is the first person to articulate what could be one of the most important ideas since Darwin’s theory of evolution. He calls it the Constructal Law. It goes like this:
For a finite-size system to persist in time (to live), it must evolve in such a way that it provides easier access to the imposed currents that flow through it.
All this may sound highfalutin. But the idea is this: Systems survive when things flow better over time—all kinds of systems. In fact, this is what “life” is: flowing and changing (morphing) freely to flow/move more easily. From natural systems to human systems, when things flow better, we start to notice patterns in nature that are products of good flow. And if Adrian Bejan is right, this is one of the most important—and underappreciated—aspects of our world. Combine the insights of Hayek, the mathematics of Mandelbrot, and the biology of Darwin and you get something that might transform the way you see the world.
The Freeman: Welcome, Professor Bejan.
Adrian Bejan: Thank you for introducing the Constructal Law to your readers.
The Freeman: Why should anyone care about the Constructal Law?
Adrian Bejan: “Should”? Everyone does it already. Every human instinctively and intentionally seeks to understand and use the surroundings, to make life easier for himself or herself and for those connected to him or her. We perceive the surroundings as patterns in space (images) and in time (rhythms, sounds). Beliefs, knowledge, religion, and science came from this primordial urge.
Science, for example, began with geometry and mechanics, the science of figures, static or moving. All science has been about this design in nature, and the growing deluge of observations of this phenomenon is calling us to summarize it—that is, to compress and simplify under a single law of physics. That law is the Constructal Law. And this is why everybody benefits by knowing the law—the law of design evolution, the law that predicts the future of all flowing designs, including ours.
The Freeman: You have studied a staggering array of phenomena with this way of thinking. What kinds of things have you successfully been able to predict and explain using the constructal approach?
Adrian Bejan: Along with many colleagues worldwide, I showed that the Constructal Law predicts and unifies all animate and inanimate flow designs and evolution, for example: river basins and deltas, lungs, vegetation (roots, canopies, leaves, forests), snowflakes, streets and avenues (urban traffic), the earth’s climate, all animal locomotion (swimming, running, flying), why the bigger live longer, the wheel, the human preference for the “golden proportion,” the rigidity of the hierarchy of universities, the evolution of speed sports (“faster” calls for “bigger,” over time), and the equivalence between wealth (GDP) and movement on the world map (fuel consumption).
The Freeman: Some people see comparisons between constructal phenomena and fractals. But fractals are mathematical descriptions, or perhaps abstractions. What’s different about your work, and what makes it the stuff of science?
Adrian Bejan: Fractal algorithms are descriptive. One picks the algorithm that leads to a “drawing” that resembles a natural image. (People rarely show you the multitude of algorithms that lead to drawings that look like nothing.)
The Constructal Law is predictive: It teaches us how to discover the drawing and how to predict the evolution—the morphing—of the natural design over time. Description is empiricism and it is common, that is, diverse and abundant. But prediction involves theory, as well, and it is more rare because it unifies these abundant phenomena. Science needs both: the many small and the few large, the diversity and the unifying pattern. Both are delivered by the Constructal Law.
The Freeman: What do your biggest skeptics have to say? And how do you respond to them?
Adrian Bejan: There are no “big” skeptics. All the prominent authors of design in nature who have commented on the Constructal Law in print have been extremely supportive: see the comments cited on the cover and inside the book I wrote with J. Peder Zane, Design in Nature, both editions, hardcover and paperback.
The reality is that the Constructal Law drives a growing research movement in science. If you search “constructal” on Google Scholar today, you find 2,160 titles of scholarly articles and books, this after only 15 years of Constructal Law thinking. This research movement is global. On October 14 and 15 this year, colleagues in Nanjing, China, are hosting the 8th International Constructal Law Conference.
The Freeman: You have said, “Freedom is good for design.” At first blush, this would seem contradictory. Our readers are interested in emergent order. What do you mean by "design," and what are the implications for society?
Adrian Bejan: It is not contradictory at all—the opposite (design without freedom) is nonsense, because one cannot have design in nature (live, morphing to flow more easily over time) without freedom to change.
The water flow through a straight steel pipe is not a live system because it does not have the freedom to morph, to improve its flowing in an evolutionary manner. The steel pipe drawing is dead. The water flowing through the river channel, and through the marsh, is a living flow system. It has design, evolution, and persists in the future. In one word, it has “life,” just like all the other designs with freedom—from animal evolution to technological evolution and, obviously, societal evolution.
The Freeman: This sounds a bit like something Friedrich Hayek would have said.
Adrian Bejan: Put another way, a rigid flow system (dammed river, rigid society) is not natural and is destined to be replaced by one that is free to morph, because the future points toward configurations with greater and greater flow access. This is why freedom is good for design.
The Freeman: You have discovered an important relationship using constructal thinking: the relationship between energy and the wealth of nations. Can you help us understand this in layman’s terms?
Adrian Bejan: Look, everything that moves does so because it is being pushed or pulled. Nothing is moving by itself. The river water is pushed by the earth heat engine, which drives the climate (winds, oceans, and so on), the animal is moved by the work derived from food, and we are pushed by our engines—by the work derived from fuel. All this work is destroyed (dissipated), and the visible phenomenon is movement with evolving design.
With the Constructal Law, we had predicted that our movement on the globe should be hierarchical, with few large and many small (as in the mass traffic of airways), and that it should be increasing over time, to spread more, to bathe the world map more.
The Freeman: With a few major arteries and many minor streets and roads, for example.
Adrian Bejan: Exactly. Then we discovered that the big channels (the few large) in this global basin of human flow are the inhabitants of the affluent countries. So, because more flow means more fuel spent, we made an x-y plot with all the countries, showing (x) the annual fuel consumed versus (y) the annual wealth—i.e., the gross domestic product (GDP). We found that the intangible “wealth” is proportional to the fuel spent, which means that wealth is movement, and wealth isphysics.
The Constructal Law governs not only the hierarchical, vascular designs—i.e., few large and many small movers—but the future design, which consists of more movement over time and greater wealth and fuel consumption for every group on earth. This is why every group is racing upward on the line indicating the proportionality between energy use and wealth.
The urge to have wealth is a manifestation of the Constructal Law. It is the urge to have more movement, fewer obstacles, and more freedom.
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