Penning the Physical Law of Evolution Everywhere in Nature

Adrian Bejan’s prolific academic career at Duke University has spanned four decades. Much like the laws of thermodynamics and natural evolution that he has established and taught over the years, his work has flowed freely from one big idea into another.

In hindsight, the course of his work and studies might seem obvious, and perhaps even predictable using the set of theories and laws he has developed along the way.

This fall, Bejan’s path and the contributions he has made to science along his way earned him the 2024 American Society of Mechanical Engineers Medal. The highest award that the society can bestow recognizes “eminently distinguished engineering achievement.” In Bejan’s case, the award was given specifically “for unprecedented creativity, breadth, and permanent impact on engineering; for developments in the new science of energy, motion, form, and evolution; and for building bridges to design in biological, geophysical, and sociological systems.”

To better understand what exactly that enormous range of activity encompasses, it’s useful to take a closer look at how Bejan’s work has morphed over the years.

Thermodynamics in Flowing Systems

Bejan earned all his degrees from undergraduate to doctorate at the Massachusetts Institute of Technology, where he concentrated on thermodynamics, the science of power and the design—or flow configuration—of moving things pushed by power. His graduate theses were on developing an improved thermal design of a cryogenic cooling system for rotating superconducting windings. After MIT, he became a postdoctoral Miller Fellow at the University of California, Berkeley.

Through these experiences, Bejan wrote his first two books on heat transfer through fluid flows: “Entropy Generation through Heat and Fluid Flow” published in 1982 and “Convection Heat Transfer” published in 1984. Despite his early successes in these thermal systems, Bejan felt from the start that he did not want his career to be constrained to these topics, pushing him to join Duke’s faculty in 1984.

“I knew I had two choices, to choose to stay in the same narrowly defined field, or to be happy,” Bejan said.

He attributes his success and happiness to a few rules of life and creativity, learned while being raised as a basketball player.

“Freedom is king,” Bejan espouses. “You are a somebody, a one of a kind. Question everything, freely and unafraid. Anything goes. Proceed against established method. Do not trust those who claim that ‘most scientists agree on’ anything.  Science is not about counting votes. Science is not democracy. The idea comes from one individual, not from collectivization. The idea is good if it spreads naturally, not sponsored.”

The Constructal Law

For the early part of Bejan’s career at Duke, he continued contributing fundamental insights to the disciplines of thermodynamics, fluid flow and heat transfer. In 1988, he published the first edition of his textbook “Advanced Engineering Thermodynamics,” which combined thermodynamics theory with heat transfer and fluid mechanics and introduced the method entropy generation minimization as a method of selection.

“Note that Darwin is not needed to achieve those conclusions,” added Bejan.

Soon after, his peers named two dimensionless groups the “Bejan number” in two different fields: for the dimensionless pressure difference group, in heat transfer by forced convection, and for the dimensionless ratio of fluid friction irreversibility divided by heat transfer irreversibility, in thermodynamics. From 1992 to 1996 he also published four more books in these fields.

But as he continued working closely with configurations of heat and fluid flows in various systems—both designed by humans and occurring naturally—he made a new connection that took his career into uncharted territory. He had a vision of what was missing in science: the configuration, the drawing, constantly in motion, driven by power from natural engines, and constantly changing. Missing in physics was the engine as well.

He coined the constructal law in 1995, which states that, for a finite-size flow system to persist in time—or, in his words, to live—it must evolve with freedom in such a way that it offers greater access to its flows. The ‘flows’ might be water in a river, blood vessels in a growing tumor, life over landmasses (city life) or even the periodic cycle of economic downturns.

 “The words finite-size was a jolt the other way, against the method of reductionism that dominates physics today,” Bejan said. He coined the words “to persist in time” as the definition of life of any system, biological or not, animate or inanimate, as a necessary add-on to the thermodynamics doctrine where the concept of dead state, where nothing moves or morphs, has been accepted since the late 1800s.

 “The laws of thermodynamics do not have a direction in time or for ‘entropy’—such words are jargon, and are not needed,” Bejan said. “The constructal law adds to thermodynamics a common-sense law that covers the occurrence and directionality of all design evolution in nature. Whether it’s an animate or inanimate system, everything has the same tendency to evolve, the same direction in time. With the constructal law, one is empowered to predict the evolution—the future and the past—of any flow system that has freedom to change.”

Design in Nature

With these insights in mind, Bejan has spent the latest portion of his career exploring how design processes play out both in nature and in human-centric industries. The topics are almost endless, as is his imagination and ability to connect dots that others do not see.

This “Design in Nature” concept has filled six books written over the past quarter of a century: “Shape and Structure, From Engineering to Nature” in 2000; “Design with Constructal Theory” in 2008; “Design in Nature” in 2012; “The Physics of Life: The Evolution of Everything” in 2016; “Freedom and Evolution: Hierarchy in Nature, Society and Science” in 2020; and “Time and Beauty: Why Time Flies and Beauty Never Dies” in 2022.

As Bejan describes it, his success has stemmed from his ability to identify a single phenomenon, describe it with a single law, and then invoke that law to create many theories about the world and the many systems within it. Whether it’s the evolution of the size and speed of animals, athletes, winds, rivers, and airplanes, or the Earth’s water cycle, they all adhere to the same fundamental principle that dictates how power from ‘engines’ moves everything that has freedom to move and change, to evolve and persist over time.

Most recently, Bejan says he has been working to upend various known truths that most everyone agrees with. For example, recently he demonstrated how features of flow that seem like obstacles are actually facilitators. He has made the case that ‘intangibles’ such as the human perception of both time and beauty are fundamentally rooted in physics. He showed that perfection is the enemy of evolution rather than its preferred end goal. He also showed that the so-called ‘arrow of time’ has nothing to do with the second law of thermodynamics; instead, the arrow of time is the direction spelled as ‘evolution,’ or constructal law.

Today, Bejan continues using these methods to make unexpected observations about the world around us. And he’s not alone.

This past summer saw the 14^th International Constructal Law Conference, which this time was held in Bucharest, feature dozens of speakers presented ideas stemming from Bejan’s central tenet of the role that freedom plays in evolution and nature. But of all the elder statesmen and established professors at the event, the organizers thought the best ideas were presented by Bejan’s four undergraduate students from Duke.

“None of my success would be possible without Duke, which is an oasis of freedom compared to other institutions,” Bejan said. “I describe myself as a free man, not just in freedom here at Duke, but in my world of ideas. And I’m delighted to have with me so many brilliant students.”