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Q&A with Adrian Bejan

Acclaimed Duke professor Adrian Bejan, one of the 100 most highly cited authors in the world regarding engineering, is credited with the development of the constructal law of design in nature. Constructal law is the view in physics that the generation of design in nature is a universal phenomenon, involved in everything from the flow of rivers to the capillaries of the circulatory system to the global distribution of wealth. The Chronicle’s Michael Lee sat down with Bejan, professor in the department of mechanical engineering and materials science, to discuss his theories and the origins of the law.

The Chronicle: How long have you been here at Duke?

Adrian Bejan: Since ’84. Soon I will have been here 30 years. I’ve been fortunate to be here, obviously. Duke is an oasis of intellectual freedom.

TC: How did you initially come up with this idea of constructal law?

AB: It happened 15 years ago. I’ve had a 40-year long career in thermodynamics, and in thermodynamics, we have essentially two working principles. One is the first law, which is the principle of the conservation of energy. And the other one is the second law, which is the principle of irreversibility…. Everything that flows by itself has the tendency to flow from high to low. But physics was not describing nature completely. I made the connection that the tendency among engineers and scientists—to create better machines, vehicles, transportation systems, etc.—is no different than what goes on in the river basin every time there is a downpour. The river basin throbs, contorts itself and improves itself. It constantly pushes the logs out of the way. It widens the channels in the right places. A city’s design does the same thing. And this extends all the way to the language of biology, which is defined by evolution. I identified [this tendency] as a distinct separate, self-standing tendency in nature.

TC: Could you apply constructal law on a cosmic scale—to planets and galaxies?

AB: Several [scientists] have written to me about this. I don’t know if they have published, but the connection with the pattern and “few large, many small,” which we see in the sky is also hierarchal. Personally, I have no doubt that the constructal law is applicable at all scales. The evolution for better and better “flowing” is happening at all scales, from the smallest capillary—30 microns—to the global scale.

TC: So your work is science, not dealing with politics?

AB: Absolutely. I want no part of the latter. My politics is that science is to be improved with better ideas.

TC: So in constructal law, how do you explain a society in which very few are very wealthy and many are not?

AB: Again, that is just one implication of the law. The answer is actually very simple. Movement on the landscape, all movement—the rivers, the winds, us—anything that moves... [occurs] because fuel is used. Fuel used is synonymous with wealth. We plotted the [gross domestic product] of all the countries versus fuel used per year. You have a [positive linear] proportionality that is crystal clear. Next, in everything that moves on the landscape, there are a few big channels [of movement] and many small channels. For example, if someone wants to fly, say from Madagascar to let’s say Greenland, that somebody always has to fly through the heart of Europe, say Paris or London. The way in which this design emerged is completely natural—there was no [United Nations] 100 years ago to say, “Listen, you should fly this way.” No, this happened the same way the river basin is formed when the rain is falling. So the burning of fuel is hierarchical. Because movement and fuel mean wealth, wealth is hierarchal. Hierarchy here can be exemplified by [wealth] or any other example you pick. The winds flow the same way. The oceanic currents flow the same way. A turbulent jet has some large eddies and many small eddies and on and on. City traffic has few large streets and many small streets. All these things that happen naturally speak of hierarchy. Yet today, you hear all this belly-aching about the fact that advanced countries are consuming too much fuel. Some countries are guzzlers of fuel. Yeah, they are. Because if the movement were not to be created in this hierarchal way, the whole globe would be slowing down.

TC: So it’s the most efficient way?

AB: Absolutely. And it’s the whole globe that has voted for it, through economic links, trade agreements. Everybody wants to be connected to flow more and more easily—meaning, in economics, to move longer for lower prices, safer, all of that. So the politically correct notion that the use of fuel should be distributed more equitably is nonsense. It is distributed equitably—in the best way—as the global community requires.

TC: Is that a Massachusetts Institute of Technology class ring? That’s a beaver, right?

AB: Yeah, this is the brass rat. I was an undergraduate, Class of ’71—I have all my degrees from MIT, and I started out [as an undergraduate]. I love this mascot.

TC: Because it is nature’s engineer?

AB: Not only that. The idea is that among all the animals, the beaver is the relentless engineer. You know, there are people who destroy his dams. Guess what he does over night? He chops new trees and makes his dam again. [Likewise], nature is not only a designer but a relentless designer.


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