The Inescapable Need for Freedom

2/17/23 Podcast

MEMS professor Adrian Bejan escaped through the Iron Curtain to pursue his dreams. Listen to discover how his freedom led him to formulate constructal theory, which connects physics to evolution through the freedom of change.

podcast cover art: tree with roots
The Inescapable Need for Freedom


Adrian  Bejan Profile Photo
Adrian Bejan Profile Photo

Adrian Bejan

J.A. Jones Distinguished Professor of Mechanical Engineering

Research Interests

Thermodynamics, applied physics, life & evolution in nature, constructal law.


Hello and welcome to Rate of Change, a podcast from Duke Engineering dedicated to the ingenious ways that engineers are solving societies toughest problems. I’m your host for today’s episode, Ken Kingery.

Adrian Bejan, the J.A. Jones Distinguished Professor of Mechanical Engineering – has made his mark as an expert on the evolution of systems – the way natural phenomena evolve in a manner that gains greater access to flow. One might also call that freedom. And having grown up under communist rule for two decades in Romana, Professor Bejan knows a thing or two about freedom.

There were no passports under communism, one could not run away. In fact, even to travel internally from city to city, one needed permission from the police station on the street. Yeah, there was police everywhere. And so I know the taste of lack of freedom, which obviously empowers me to know the taste of freedom and to value freedom. And my career, what have I achieved, actually teaches the value of freedom.


To gain his, Professor Bejan had to excel at something important enough to earn him a spot in a program that would allow him to travel abroad. Always a top student in his class, he pushed himself to be one of the top performers in school. But which subject to pursue?

Professor Bejan:

I had to choose a university that was the closest, and the closest was in my city. That university was an engineering polytechnic offering only mechanical, ship building and food engineering. I chose mechanical, so that’s how I started as a mechanical engineer. And then, two years later in 1968, in Bucharest, out of the blue, there was a math contest for scholarships in the free West. And I did perfectly. I was the only winner of six. The only one whose parents were not in the central committee of the Communist Party. And I applied to MIT. I was admitted, but that took six months. So I arrived at MIT in February, 1969. I went to classes immediately. I learned English during the first two months taking courses.

I knew right away that I was very, very fortunate. And in MIT, that’s the topic for a future book, every day was a positive shock, I mean, a surprise. Anyway, one of them was that I fell in love with thermodynamics, which I took during my second semester at MIT. That became my strength in fact. Now, my career is in thermodynamics. The words thermo and dynamics mean the science of heating and power, or power from heating, or refrigeration from the same heating because in order to have a refrigerator, you need to have a power plant that burns fuel and then makes power.


Professor Bejan focused on thermodynamics throughout his career at MIT, where he earned both a bachelor’s and doctoral degree. With his eyes set on becoming a professor, he completed a post-doctoral stint at Berkeley before joining the faculty of the University of Colorado at Boulder. Five years later in 1984, he started his tenure at Duke, where he would expand his knowledge of thermodynamics to create a new theory of physics that, he says, dictates the evolution of systems ranging from river deltas to economic hierarchies.

Professor Bejan:

In the mid 1990s, it occurred to me that thermodynamics was not sufficient to account for the nature that we all know. Not sufficient for two reasons. Thermodynamics, there’s very powerful and applicable science. It’s about black boxes called systems. The objects of nature fit in those black boxes, but they bring with them flow configuration, design and architecture. So the first aha was that the flowing form was missing in physics.

It is a phenomenon, it’s observable, it’s measurable. You can talk about it and you can teach it but it’s not in physics. And number two, missing was also the evolution of the moving form. Everything that we see is moving and changing. It is alive. In fact, everything we read in the books of history, biology, geophysics, economics, technology have been moving and changing en route to what and where they are today. Evolution means change after change in a perceptible direction, which happens to be the human perception of time. So the second aha was the evolution was missing in physics.

In order to predict the universal phenomenon of evolution, I published the constructal law, which states that for a finite size flow system, that means not infinite decimal, to persist in time, that means to live, it must evolve with freedom such that it provides easier and greater access to what flows. That was in 1996.

And yes, freedom itself has a definition. It is the word for the physical features that allow a flow system to change and evolve. No change means no evolution. And no evolution means no life, no time, meaning direction, and no future.


Professor Bejan sees this freedom to evolve – to grow in time to gain greater access to flow – as a central tenant to all living systems. And he’s applied this fundamental thought to a wide variety of disciplines that might not fit the traditional definition of being alive.

Professor Bejan:

Now, because you asked me, here are some of the simplest and most common observations that have been predicted, obviously in retrospect, by invoking thermodynamics with constructal law. Animal locomotion, which means the rhythm of the moving organs, speed, the power used, frequency of the wings, legs and the fishtail. The cross sections of blood vessels. We know they’re round or roundish, but they’re predictable. They’re everywhere in blood vessels and underground galleries for rainwater and earthworms. River basins and deltas. These are drawings of a few big channels and many small channels all carrying the same volume of rainwater.

Human movement, which I also like to call rivers of people, is a pedestrian on the landscape and that is on an area, but also in a volume in a building. The evolution of speed and body size in competitive athletics, with a constructal law when it predicts the future of records in sport. All the bookies in Las Vegas should get to know my work. In fact, some of them have called me. In fact, the bookies from Saudi Arabia called me because they’re there betting on camel races. I know nothing about camels, but I did say, tell me how tall they are and then I’ll tell you what the speed will be, okay.

The evolution of animals, airplanes, helicopters and ships. You see here, the range of sizes from the cat to the biggest oil tanker. Organ size, the prediction of that, meaning that the big engines and big hearts should, should be on big airplanes and big animals, not on the small ones. Economies of scale. It is easier to move and flow together than alone. This is an observation in economics. It is actually physics and is one of the simplest lessons that I teach. Social organization, money, periodic downturns cause crises, and hierarchy in wealth are predictable. Human perceptions with a constructal law belong in physics. The perception of freedom, beauty, time and time acceleration and time deceleration.

So beginning to put these many, let’s say developments together, the system and the environment are one system, not two. These two morph together and one shapes the other. Meanders and the rivers, nests and animals, air turbulence and the wing shape, water turbulence and the fishtail design, hand and tool and boots and feet. They are one. They belong together and they evolve together.

So I’ve been coming to the present, to the conclusion that the freedom is nature. This is why I use the word all over. Evolution never ends, contrary to people who talk about the death of the universe, because freedom to change is nature. Best, optimum, minimum, maximum, this is for people who do mathematical optimization. These things are short-lived, because freedom to change is nature. You show me the best and tomorrow I’ll tell you that’s not the best.


So you heard it here first – there’s always a better tomorrow. At least, as long as things are allowed to change. And that change requires freedom, which brings this tale back full circle to Professor Bejan’s humble beginnings in Romania.

After 42 years of living under communist rule following World War II, Romania shook the shackles suppressing their freedom to evolve in 1989. For Professor Bejan, it was a moment he had long waited for, and he hopes their relatively new-found freedom will allow the country to evolve into the future once more.

Adrian Bejan:

I was once again a citizen of Romania, because when I ran away, I was deprived of my citizenship. I had no rights in Romania. So overthrowing the communism led automatically to reinstating all the runaways. Romania is now a very lucky country. It’s totally changed.

Before Communism, before the Iron Curtain, there was no West Europe or East Europe. There was Europe, and everyone spoke French in Romania. And polite, and well dressed, and singing, and drinking. And that’s back.


That’s the show for today. I hope you’ve enjoyed hearing about how one man’s journey to freedom can inspire an entirely new way of thinking about the world through the lens of physics. If you want to learn more about constructal theory and Professor Bejan’s work, you can keep up with his progress at And if you want to here more inspiring stories such as this one, I encourage you to subscribe to this podcast. As always, thanks for listening.

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