On Constructal Law and Theory
This is an introduction to constructal theory, and the constructal law, discovered in 1995 and expounded by Adrian Bejan as follows:
“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.”
I first learned of constructal theory from Bejan himself, hearing him speak in 2012 of his then-recently published book, Design in Nature: How the Constructal Law Governs Evolution in Biology, Physics, Technology and Social Organizations.
As I recall, he described a crack in the ice that resembled the veins in a leaf. These hierarchical patterns, he pointed out, are everywhere in nature. Wherever something is flowing with freedom, the shape of the flow configuration will evolve toward greater efficiency, in a predictable, hierarchical and directional manner. He was designing such tree-like patterns, as an engineer, to maximize the flow of heat away from microprocessors in computers. As he described it, he realized that his designs were not copying nature, they were predicting the hierarchical flow pattern that naturally emerges. By doing so, one can anticipate and provide an optimal path to flow; thus using a law of nature to one’s advantage, and achieve a desired outcome. In the case of heat in computers, that means efficient movement of heat flow away from sensitive components.
In his research and writing, Bejan has gone on to demonstrate how the constructal law is manifest in countless familiar phenomena, previously never connected by a law of physics. Rather, these broad swaths of our world are described or ignored as mere ‘chance’ or ‘unpredictable complexity.’ Bejan shows these explanations are false.
The fundamental idea, he explained, is this:
“Everything that moves, whether animate or inanimate, is a flow system. All flow systems generate shape and structure in time in order to facilitate this movement across a landscape filled with resistance … The designs we see in nature are not the result of chance. They arrive naturally, spontaneously, because they enhance access to flow in time.”
Flow represents the movement of something relative to its environment. A flow system is defined by Bejan as one or more streams that originate from points and must find easier access to other points.
The effects of the constructal law can be seen everywhere, because they are everywhere, at all scales of space and time. Many descriptive examples will seem ‘obvious,’ but cannot be explained or predicted, based on physics, without the constructal law. Not that that stops us from writing these effects off; as complexity, chaos, or the unpredictability of nature. Constructal law shows these views to be incorrect.
Whereas Bejan has focused on many descriptive examples that we see around us as humans on Earth, I am drawn to the broadest generalization. That is, rather than looking at descriptive examples in contemporary life on earth, let’s look to the Big Bang, and the constructal law’s role in cosmology, and the evolution of the universe from what led to the elementary particles, and how they configured themselves to flow more efficiently through the universe.
Without yet getting into the defense of each of these points, which I’ll get to later, below is a list of the key theses or big ideas that I’ve taken away so far from my study of constructal theory. Some of this paraphrases Bejan directly, but some comes from me considering the implications of the constructal law in its most generalized sense.
Some Big Ideas in Constructal Theory:
The universe is a flow system. Everything in the universe is part of this universal flow system, which explodes in a hierarchical diversification of interlacing flow systems, all descending and evolving from the same source from the Big Bang.
All flow systems evolve; not only the flora and fauna of Darwin, but everything from a rock rolling down a hill, to a global social movement, or galaxy cluster. This evolution is directional, hierarchical, and predictable. The constructal theory of evolution encompasses Darwin’s biological theory of evolution, but also explains why things evolve in the direction that they do; and transcends the biological species, to explain universal evolution, not only animate but inanimate; not only individual members of species, but also e.g., social organization.
All flow systems generate shape and hierarchical structure, over time, in order to facilitate this movement through an environment that resists that flow with equal and opposite resistance. As such, the designs we see in nature are not the result of chance or chaos. They arrive naturally, spontaneously, because they enhance access to flow in time.
The universal domain of the constructal law is inclusive of energy, matter, and information. Matter is inclusive of both animate and inanimate; natural and human-made objects, as well as abstractions such as knowledge, wealth, and social organization, at all scales, obey the law of constructal flow. This universal scope applies to only the most fundamental laws of nature, putting the constructal law on a very short list of truly universal laws meeting the above criteria, along with laws of energy conservation and entropy.
If the constructal law is held up as true, it must be reconciled with quantum mechanics and general relativity, in the context of cosmology and the standard cosmological model of the evolution of the universe. Current explanations for the formation of stars and galaxies are inadequate, resting solely on gravity and wrinkles in distribution of mass. Constructal theory predicts the hierarchical evolution of matter and energy, suggesting not wrinkles, but rivulets, in the hierarchical distribution of heat in the cosmic microwave background.
The dichotomy of classical and quantum is generally framed as macro vs micro, or large and small. Key to reconciling large and small, is reconciling young and old; that is, there is a direct evolutionary, time based relationship between elementary particles and later, larger structures with progressively increasing complexity and diversity — just as particles, nuclei, atoms and molecules are all themselves evolved structures composed of more primal sub-particles. I believe that evolution is consistent with that of all other flow systems in the universe governed by the constructal law: directional and hierarchical, tending towards increasing complexity and diversity, all driven by the need of all flow systems to evolve to increase the efficiency of flow.
The efficiency of flow in a flow system has a direct relationship to the length of the lifespan on the space-time plane. The tendency to evolve towards more efficient flow is a natural tendency of everything in the universe to extend its lifespan.
All evolution of flow systems require freedom. Freedom in physics is manifest in physical symmetry across a range of transformations, aka degrees of freedom. These symmetries embody the conservation laws, and determine the distinction between what is possible and impossible in nature. It is within the possible flow configurations, the constructal law will drive evolution towards the optimum possible. Artificially imposed constraints that limit freedom to move and evolve, such as walls or authoritarian laws, also limit the ability to evolve and extend the lifespan of effected flow systems.
Going forward, my objective is to explore each of these theses in more depth, fully recognizing the need to develop the math by which to quantify, predict and validate hypotheses scientifically.
I’m writing this now because 27 years after Bejan discovered and dared to declare a fundamental universal law of nature, best-selling books by leading scholars and physicists such as Katie Mack’s The End of Everything (Astrophysically Speaking) refer to the forces that govern the evolution of the universe, without any reference to the constructal law.
I see that constructal theory remains outside the mainstream discourse in contemporary physics, astrophysics, and cosmology, and I think there are valid reasons why this is the case. In future essays I will address what I see as shortcomings in the theory, as well as alternative explanations being published in peer reviewed journals.
Prior article: Notes on Constructal Mechanics
