Adrian Bejan, J.A. Jones professor at the Pratt School of Engineering, reclined behind his desk, clean-shaven, sporting trim silvery hair and recouping from a four-day and three-city book tour. To his left, file cabinets and stacks of paper rise to meet the ceiling. To his right, the wall disappears behind his 16 honorary degrees from some 11 different countries.
“When last I checked, [Henry] Kissinger had 18,” he noted, with the unassuming self-confidence of someone who has invented a law of physics.
Bejan, who is one of the 100 most cited authors cited in all fields of engineering, first published on the constructal law in 1996 and has since expanded its application to almost any field. The principle defines the world as a teeming environment of flow systems—cars traveling on the highway or antelopes moving on a plain—that branch out into increasingly smaller pieces as the most efficient way to travel across a landscape.
In January, he published a book aimed at bringing his law to wider audiences. Its title indicates the broad nature of the concept—“Design in Nature: How the Constructal Law Governs Evolution in Biology, Physics, Technology, And Social Organization.”
With a background in mechanical engineering, Bejan specializes in thermodynamic design—studying, for instance, how to design computer chips that dissipate heat as efficiently as possible. He began to recognize characteristics of his designs in natural phenomena. Bejan said his “eureka” moment occurred at a 1995 thermodynamics conference in Nancy, France where he heard Nobel Prize winner and chaos theorist Ilya Prigogine refer to the apparent randomness of recurring natural tree-shaped patterns, like river basins.
“When he spoke of tree-shaped structures being the result of throwing the dice, I thought, ‘He has no idea what I know, which is that this is not the case,’” Bejan said. “If the drawing I make is the same drawing he sees everywhere in nature, then the principle that I am invoking intuitively is in fact the principle that accounts for these structures everywhere.”
On the flight back to America, Bejan condensed his new thoughts on the matter into what he would call the constructal law. According to Bejan’s research, “For a finite-size flow system to persist in time (to live), its configuration must evolve in such a way that provides easier access to the currents that flow through it.”
This principle of the constructal law can be demonstrated in the design of a river delta—gravity forces the water from higher inland elevations to the sea, but the water does not all flow in one jet. It fans out across the delta in a tree-shaped fan, in which the water covers the distance to the sea more quickly with the passage of time.
“It’s not about what flows, it’s about how the flow system acquires its configuration and why,” he said. “It’s about designing better channels through which to move.”
Bejan applies this concept of flow to systems as diverse as people moving through neighborhoods to ideas spreading through society. The law’s large reach is notable in itself—he noted that it governs the design of everything, including inanimate, animate and engineered bodies.
The breadth of the constructural law poses a certain challenge, said Tom Katsouleas, dean of the Pratt School of Engineering.
“This is pretty deep and profound and broad reaching, and I think because of that it’s a hard one for people to get their arms around,” Katsouleas said. “But like the second law [of thermodynamics], it has led to predictions in what the optimal branching should be and plants and animals and rivers have evolved to have those sorts of characteristics that have been predicted.”
Key to this expansiveness is the definition of life in constructal law. Bejan defines life through thermodynamic term, classifying anything that moves as living—a key difference from the traditional biological definition.
“A system in which nothing moves is known as a system in the dead state. It follows that anything that moves and morphs its configuration while flowing is not dead,” he said. “What do you call that which is not dead, that persists in its flow and evolution? You call that life.”
This thermodynamic definition of life can predict, for example, humanity’s continued fuel consumption in the future, Bejan said. Systems thrive on burning fuel for transport. If humans cut down on fuel consumption, it will therefore result in less movement, such as international travel and transportation. This will lead to a global slowdown.
“To argue for reducing the consumption of fuel, based on my definition of life, is to argue for death,” he said. “The history of humanity and civilization is completely oriented the other way.”
Global warming will increasingly pressure the design of global society so much that it will force a gradual change to patterns of consumption, he added, comparing it to severe smog in cities like Pittsburgh that became intolerable and prompted clean-up efforts.
Gilbert Merkx, vice provost for international affairs and director of international and area studies, met Bejan at a meeting of Duke’s international affairs committee. When Bejan showed him some diagrams of tree and river flow systems, Merkx, a professor of the practice in sociology specializing in social networks, noticed a parallel to an example in his field: patterns of immigration from Mexico to the U.S.
“Migration stream gathers people from different points, they flow together and then they spread out again,” Merkx noted. “Commuters work the same way. They live in the suburbs, they get on a trunk line to go to work, and they get off for their respective workplaces.”
The constructal law has been in publication for 16 years, and it has been the basis for publications across a broad range of subjects. The law will continue to undergo scrutiny to vie for a spot as a law of physics, Katsouleas said.
“This is exciting because he’s proposed something so fundamental, and when you have a new fundamental law, it really requires the test of time to assess its validity,” he said. “We’re in that period, and it will be exciting to see what those tests show,”
The constructal law shows that successful ideas enhance humans’ ability to flow more efficiently through systems, Bejan said. He believes the constructal law is one such idea.
“In 15 years, the constructal law has not been refuted by anybody. It is a train on which more and more scientists are climbing and publishing and actually competing with me,” he said. “Good ideas persist and keep on traveling. This is in a nutshell the origin of science, the evolution of science and the future of science.”
Get The Chronicle straight to your inbox
Signup for our weekly newsletter. Cancel at any time.