LET'S GET PHYSICAL

You can use physics to describe almost anything in life

Think of physics and you most likely picture clearly defined, specific systems: atoms interacting, equations involving force, mass, and acceleration, and recent discoveries such as the Higgs boson or gravitational waves.

But why should physics be limited to such topics? After all, says Axel Kleidon, researcher at the Max-Planck-Institute for Biogeochemistry in Jena, Germany, “we live in a physics world where things have a physical function.”

There’s a long history of using physics to describe wider systems, such as Robert Ayres’ writing on how thermodynamics describes the development of socioeconomics, technological progress, and economics.

A more recent attempt to unite all manner of behavior under one simple physics law comes from Adrian Bejan, mechanical engineering professor at Duke University. He devised his Constructal Law in 1996 and has an upcoming book on the subject for a non-academic audience. Bejan, who specializes in thermodynamics, said that the laws of physics can be used to explain everything, from the flow of air in lungs to the hierarchical structure of society.

Bejan’s Constructal Law is defined as such: “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.”

In simpler language, all living systems will naturally move into configurations that allow for easier movement. It sounds deceptively straightforward, but Bejan has used his theory to discover behavior in both the natural world and manmade constructs, with these findings published in highly-regarded journals.

He has used the Constructal Law to describe the behavior of rolling stones, why humans build fires shaped the same way, why larger bodies (including animals, vehicles, and winds) live longer and travel farther, why solid growth is mapped by s-shaped graphs, the arrow of time, and why plumes and jets emerge flat but become round.

He has used the same theory to argue that both birds and airplanes have similar methods of increasing efficiency. It makes sense to study the natural and manmade world together in this way, says Kleidon. “I think it shows us that nature and human engineers deal with the same physical problems, for example, how to design something that flies well,” he adds.

Bejan insists that his law can be used to explain and predict other non-traditionally physics fields, including evolution, the flow of wealth, and the layout of streets within a city (indeed he’s not the only physicists to examine how cities are built).

It may seem strange to describe human behavior using the same laws that apply to inanimate objects, but Bejan points out that physics comes from the Latin to mean “everything that happens by itself.” He believes that one of the beauties of his law is that it applies so universally.

“Society is an organized flow system, it has an architecture, because society means people are living together—not individually or lost in the forest,” he says. “And people flowing together is easier, just like how water eventually comes together in a river flow. Physics accounts for this tendency of nature, which is also visible in human behavior.”

Kleidon is more cautious. He points out that physics might well be used to describe human social structures, “but it’s not like physics tells us what we do.”

Though Bejan’s work is compelling, his theory is far from universally accepted. Kleidon says that while Constructal Law has unearthed numerous fascinating examples, and is an elegant description of behavior, it’s not strictly formulated as a physical law.

However, the very fact that Bejan has found so many solid examples of different systems behaving as he predicts, suggests he’s onto something. At some point, Kleidon believes, physicists will find a general law that describes how all systems evolve. And though it might seem strange to study human behavior as physics, Kleidon says that, “we humans also organize in some way or another along some physical principles.”

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