This is a book
about evolution, about flow and access to flow, and about how nature designs
itself based on what works. That nature includes human activities, pursuits,
and systems. The flow of wealth, the evolution of technology, in sports, cities,
and more are controlled by a scientific principle Bejan terms the Constructal
Law, which he first constructed in 1995. This idea is one way in which biology
and physics can be merged into one system since they are both guided by it. Bejan
gives an example that airplanes have evolved like birds in terms of wingspans,
sizes, and lengths. The law also complements other trends such as Processual
Biology, or Biology as a process. I read about half of Bejan’s previous book,
Design in Nature, which is also about the constructal law. Bejan is a
distinguished Mechanical Engineer.
This book is quite
fascinating and yet counterintuitive and perhaps a bit unsatisfying at times. It
could be Bejan’s writing style or more likely it is the difficulty of presenting
the material that supports the law, or rather the nature of the law itself. We are
perhaps just not used to seeing everything as physics, of seeing knowledge, ideas,
technology, wealth, etc. as being in the realm of physics. Despite these issues,
he makes a very good case for the constructal law.
This book is
about “evolutionary flow organization.” The constructal law is a model of flow,
or movement in nature, including in human social nature. Bejan points out
patterns and flow hierarchies inherent in flow systems. One pattern is the
S-curve of things that spread over time like river deltas, technology, and
information. Those spread rate histories follow an S-curve, which will be
explored in more detail later. The key is that flow, movement, and the spread
of things, including information, follow a slow-fast-slow curve, which gives
the graphs an S-shape.
“Two ways to flow, fast and slow, are much better than
one. The fast are the few large, and the slow are the many small. This is the
way to serve with flow an entire area or volume. We see this hierarchy
occurring naturally everywhere, from traffic in the city, to oxygen transport
in the lung and fast and slow thinking in the flow architecture of the brain.”
When phenomena are considered in the context of flow systems,
an engineering concept, one can discern that access to flow is very important.
There are natural hierarchies of flow that are not random. These occur in
natural systems and in human systems.
“Good ideas spread far, and keep on spreading. This
evolving flow of design is what “good” means. The physical measure of a good
idea is the increase of human movement that is created in one place by the
physical implementation of the idea – the flow design change, the evolution in
that place, at that time.”
Since what works is kept, the best design changes spread
naturally. Thus, he reiterates that “lIfe and evolution are physics.” He
also notes that ideas like self-organization, emergence, natural selection, and
many more, arise from this law of design in nature. The animate, and inanimate, as
well as ideas, knowledge, technology, and other pursuits, in essence, all that moves
or flows, are all subject to the law. Flow configurations that offer greater
access to flow are prioritized according to the law. Interestingly perhaps, he
also notes that the constructal law governs macroscopic behavior but not
necessarily microscopic behavior, noting that molecules, atoms, and subatomic
particles are regulated by other laws.
He notes that
human movement, including the paths of air traffic, or air mass transit has a
hierarchical geography, as does fuel consumption. He did some graphs showing
that fuel consumption correlates directly to wealth, to GDP. As humans, we
generate and consume power which allows us to move. Movement involves things.
animate, inanimate, and human-created. He notes that collaboration can be seen
as movement as it is another term for organization, where ideas flow. He notes
that the dead state is a state of equilibrium with the environment, but the
living state is one in which there is no equilibrium with the environment as
the living are pushed, pulled, heated, and cooled, and inhabited by flows and
organization. In other words, life is movement, which requires work, which
itself requires energy, usually from food. In light of this understanding, he
questions dichotomies like natural vs. artificial, nature vs. nurture, and
biological vs. non-biological. He notes that symbiosis, where mutual advantages
are cultivated or naturally arrived at occurs in both biological and
non-biological systems. He notes that flow configurations often involve few big
and many small carriers, in a natural hierarchy of organization. He states that
freedom, as freedom of movement, or freedom to change “is the most basic and
most overlooked property of nature.”
He gives an
example of the evolution of airplanes in terms of sizes and shapes. Size in
life and non-life is an evolutionary design feature. He uses the evolution of
sports in many examples, particularly how size ratios dictate how well a person
will do in certain sports like running and swimming. Bigger is often, but not
always better. Diversity is important as well as hierarchy. He notes that:
“Human & machine species evolves toward greater,
easier, more efficient, farther and longer-lasting movement.”
He defines knowledge as:
“The ability and action of the human and machine species
to effect design change.”
Knowledge spreads and can be seen as a flow system following
flow rules. He characterizes human’s adoption of fire as a design change that
enabled humans to expand their habitation and “move” to colder regions. He
notes that good ideas spread, like the use of fire, language, writing religion,
and science. The use of fire “evolved” to the heat engine so that we could
enable and control human comfort and transport’
“What works is kept, that’s evolution.” “What is good for movement, for life, is
kept.”
The diagram below
addresses flows of food, fuel, work, and heat.
.jpeg)
He suggests that we have an instinct for efficiency, for
getting more work from a similar amount of fuel. However, he also notes that
efficiency often leads to more power usage as it becomes cheaper. He talks about
systems, or all that moves, as engines that generate power connected to devices
that dissipate power – brakes. Thus, they are engine-brake systems.
“The engine produces the power, and the brake dissipates
power and transmits it as heat to the ambient.”
All that flows or spreads can be seen as emerging and evolving
flow channels that follow the S-curve of slow-fast-slow. Channels facilitate,
control, and optimize movement. He goes through many examples of seeing common
animate, inanimate, and human-created systems as flow systems that follow the
constructal law of natural design. Applying these ideas to the spread of wealth
or knowledge is perhaps less intuitive, but they too follow this design law.
Chapter 3
explores wealth as movement with purpose. He notes that flow changes are
triggered by mechanisms, and these mechanisms should not be confused with
scientific principles:
“The ‘how’ is the principle – the constructal law, the
law of life in physics. The ‘what’ are the mechanisms, and they are as diverse
as the flow systems themselves. The ‘what’ are many, and the ‘how’ is one.”
He explains that the rate of economic activity of a country,
the flow toward a better quality of life, is proportional to the rate of fuel
consumption. He says that money represents power and movement. He explores
R&D as a flow system where ‘design change’ as knowledge is what flows and
spreads. The flow of people and goods on our planet creates the natural flow architecture
we call capitalism.
“Capitalism happens. It is a natural phenomenon, and it is
good like all the natural phenomena to which humans have attached themselves,
from fire, to domesticated animals, to the use of money, air travel, and
electric power.”
Chapter 4
explores the evolution of technology. Technology liberates. Freedom facilitates
the free flow of ideas which leads to new and better technologies. Bejan uses
the example of a vehicle that moves along the landscape to explain flow. First.
The vehicle must overcome resistance to flow, namely friction. These can be depicted
as system imperfections. For most access to flow, a certain size is required. Larger
size means more weight and more weight means more fuel use. The graph below shows
imperfections and fuel penalties vs. size. The necessary trade-offs lead to an
evolved size range for moving the most weight the farthest. He sees this knowledge
of the constructal law as the key to successful biomimicry, or imitating nature
in human designs. The graph can also depict other flow systems.
.jpeg)
Technological
evolution, of course, happens on a much faster time scale than biological
evolution. According to the law, all designs evolved toward more ease of flow. He
explores the idea of miniaturization as seen in microelectronics and especially
nanotechnology, noting that miniaturization of organs in a flow system occurs in
order to increase ease of flow.
“The evolution is toward greater ‘density’ of volumetric
flow, or functionality. It is toward doing more with a smaller device,
resulting in more flow per unit of volume in that device.”
The tendency toward miniaturization reflects the tendency
toward more complexity seen in nature. He notes that evolution is also toward more,
or rather “a greater density of functionality.” He uses heat transfer as an example
where heat transfer density increases or evolves as devices improve.
He seems to
suggest that technologies always get better through time due to finding more
and more overall ease of flow, or access to flow.
“The time direction of flow organization is always the
same – it evolves, not devolves.”
He demonstrates this by noting how a plume of smoke from a
smokestack behaves, how it changes the further away it gets from the source, and
the more it mixes with the surrounding air.
He says that technological
evolution is really about the evolution of human movement along the Earth. He
explores the evolution of airplane sizes, airplane engine sizes, and the relationship
between fuel mass and airplane mass. These various size relationships and proportions,
including those recognized in biology, he says. are due to the constructal law.
“Flow architectures that offer greater access persist,
and are joined by even better ones.”
He notes that all evolution, including biological evolution,
is mainly concerned with changes that increase ease of movement.
“To summarize, technology evolution liberates us, and at
the same time it empowers us. It also affords us the ability to observe
evolution in our lifetime, and to understand that evolution is a phenomenon of
everything, of physics.”
Chapter 5 explores
sports evolution, somewhat mathematically. The evolution of shapes and sizes and the
evolution of locomotion are considered. Humans and animals that fly, swim, and
run follow the constructal law of design through these changes toward optimizing
things like speed. He goes through many examples in this chapter that prove his
points. He considers some other things in light of the law, including the
utility of stretching and yawning. Stretching is enabled by soft tissues that
are able to do so. Some stretching is indeed required and useful for optimizing
fluid flow through fluid vessels. However, too much stretching can be
counterproductive due mainly to power requirements. Combining stretching with relaxation
and rhythm has proved an ideal strategy to stretch for health optimization.
Chapter 6
explores city evolution, seeing cities as flow systems that change, or evolve, according
to the constructal law. He explores traffic in cities, both vehicle traffic and
pedestrian traffic, and how it flows through time and evolves together with the
city itself.
“Hierarchical flow architectures must emerge naturally, because
they provide easier flow access on an area.”
He notes that all of humanity’s flows are on an area or in a
volume. Traffic flow on the earth’s surface flows on an area. In line with the ‘few
large, many small’ design motif, cities too naturally exhibit this type of
hierarchical flow architecture, which is reflected in the rectangular shape of
the city block where the main road (one of few) is intersected by many small
roads. He makes the interesting observation that walking times and driving
times are often similar, although walking covers shorter distances, the two are
naturally designed so that trip times are similar. That is one way how scales are
integrated. He shows that city evolution is predictable based on flow analysis.
He considers evacuation plans, showing that they too follow the law. He also
explores urban design in the upward direction. He notes that the Occupy Wall
Street stopped the flow of cars and people in New York City due to its mainly
two-dimensional nature. Similar protest squatting in Hong Kong resulted in no stoppage
of vehicular nor pedestrian traffic due to the three-dimensional configuration
of that part of the city that includes overpasses, underpasses, and loops for both
vehicles and pedestrians.
Chapter 7 is about
growth. He mentions that one day in 2010 he was having coffee with his dean Tom
Katsouleas and they were discussing the growing use of the constructal law in
science, when Katsouleas noted that all new ideas have an S-shaped history of
growth among those who would use them. Bejan was delighted since the
constructal law had predicted such a configuration for the spreading of design
changes. As he shows in a myriad of examples from different areas of life,
non-life, and human endeavors, the S-curve of slow-fast-slow, then often final
replacement by something new, occurs in many phenomena that grow or spread. In
showing that the flow from a heat pump follows the S-curve geometry, he notes
the configuration of the S-curve as having an invasion period and a consolidation
period. The invasion phase is the initial slow part followed by the fast
consolidation phase.
.jpeg)
“Everything about this S-curve is known, because both
phases, the invasion and consolidation, are known, including their junction,
which marks the inflection point of the S. Coming from the constructal law, we
also predicted that the invading channels
should be tree-shaped as opposed to single needles. The flow from point
to volume (or area) occurs faster this way, more easily, along a steeper
S-curve.”
He notes that tributary configuration, including tree-shaped
flows and herring bone-shaped flows, offers the best flow access. S-curves are
time-history curves of flow or spread.
“The prevalence of S-curve phenomena in nature rivals
that of tree-shaped flows, which also unite the animate, inanimate, and human
realms.”
He says that this is not accidental since both show nature’s
tendency to evolve toward greater access to flow. When we hear stories about
exponential growth curves what we are really seeing is the consolidation part
of an S-curve, he suggests. He uses the example of an oil production graph. I
know from making and studying production decline curves that there is indeed an
exponential curve section rise flowed by a slow decline in the rate of
production – basically an S-curve. Of course, S-curves vary according to design
in magnitudes, some having bigger consolidation phases than others. The last
part of the S-curve where growth, spread, or flow slows after the fast consolidation
phase, is reflected in the idea of diminishing returns. These are natural
limits to further growth of those phenomena. Diminishing returns as reflected
in oil production curves such as the Hubbert Peak and in mineral production, is
a physics phenomenon, he says. He also suggests that current phenomena such as
population increases, and climate change will end up having S-curves. It is
already becoming apparent in population dynamics. We are beginning to address
climate change, so the growth rate of emissions has slowed as well.
Bejan shows that
the physics of the formation of a snowflake follows an S-curve with its
invasion and consolidation phases. He shows an S-curve of sales of new products
over time. He shows graphs of U.S. power production through time, miles driven
through time, and population through time, all having S-curves. Every new
design has its S-curve. He distinguishes growth and evolution:
“Growth is not evolution. These two are entirely
different phenomena of nature, even though both have a flow architecture that
changes over time. Growth is the sequence of changes that ‘occurs’ during the
lifetime of a flow architecture, an S-curve from no flow and zero size (birth)
to no flow at mature size (death). It is amply and correctly described as the
S-curve increase in spreading and collecting a finite space (area, volume). Evolution
is the time-oriented sequence of architectures of flow systems that belong to
the same class and maturity, for example, fully grown animals and athletes, and
fully spread river basins. Evolution occurs on a time scale much greater than
the growth (from birth to maturity) of the individual flow architecture.”
Both are about form (configuration, organization, design) but
he says distinguishing the two is vital.
The S-curve also
informs politics and science. The flow of political knowledge might be termed ‘opinion.’
These too flow like ideas and river basins, in tree shapes. He explores the
S-curves of political ideas and movements, noting that in these curves there can
be steep drop-offs on the S-curves due to things like the novelty of the ideas
wearing off and people forgetting about them. That makes the analysis more complex,
but he thinks they still follow the basic pattern.
“The evolution of government toward more openness is the
evolution toward freedom, wealth, longevity, and the rule of law, which also
means less corruption.”
“Technology, science, information, education – in one word,
culture – is how all of us unwittingly open up our channels and liberate our
flow.”
He notes that centralization
and decentralization are one design, not two and that global vs. local is also
one design, not two. They are each part of the same design. These facts allow
us to scale up according to natural flow hierarchies.
In considering
science he first notes that data is not knowledge as it requires interpretation
and utilization to become knowledge.
“Knowledge is science, and science is observing,
predicting, teaching and doing, which is the practical application of science. Observing
is the mental condensing and streamlining of the flow of observations. What is
condensed are the principles, and the most unifying among them are the first principles,
the laws of physics.”
“Knowledge is the human capacity to effect design change
that is useful to humans. Intelligence is to “see” a better design before it is
put into words, tested and built. Knowledge is the fast-forwarding of the physics
phenomenon of design generation, spread, and evolution.”
The hubs and spokes of our systems of transport,
information, and in other kinds of networks are another example of hierarchical
flow architecture.
“The evolution of design (organization) is a universal
tendency of flow systems in nature, and it happens through animate and
geophysical systems in accord with the contructal law.”
“This tendency is also recognized as self-organization,
self-optimization, increasing complexity, order, networks, and scaling.”
Evolution and design change occur along a one-directional
arrow of time so that things change from less to more access to flow. This
means that better designs follow previous designs. Is time a human creation? He
says no, since we can measure time in a fair amount of detail long before
humans even existed. The flow of knowledge is always from those who have the
knowledge to those who don’t and need it. He gives many examples in the book analyzing
the flow of ideas and knowledge. One is the spreading of the English language,
due in no small part to its simplistic grammar, which makes it easier to learn.
“In summary, knowledge is the name for two design
features that are present at the same time: idea (design change) and action (implementation
of design change).”
Chapter 10 considers death. He defines life as movement. Thus,
death would be defined as the absence or end of movement. In biology there are
relationships between lifespan and body mass, bigger animals live longer and
travel farther. He mentions the idea of ¼ power scaling prevalent in animal
design biology that involves metabolism and respiration. He notes that these
functions as measured in the ¼ power rule are about animals at rest, not locomotion.
I’m not sure I fully follow his argument here. In considering vehicle movement
or travel he notes:
“The energy conversion efficiency of the vehicle (n=W/Q)
exhibits the size effect known as economies of scale, which is valid for all power
generators and power users. Larger machines are more efficient than smaller
machines because they operate with fewer obstructions: less friction (wider
passages for fluid flow) and less heat transfer reversibility (larger surfaces
for heat transfer). The reality of economies of scale is rooted in physics.”
Larger animals and larger vehicles have greater efficiency
and longer life spans. Bigger stones roll farther. The life span of an eddy in
turbulent flow is proportional to the size of the eddy.
The last chapter
is a summary of life and evolution as physics.
“The phenomenon of evolutionary organization (design)
facilitates access for everything that flows, evolves, spreads and is collected:
reiver basins, atmospheric and ocean currents, animal life and migration and
technology, which means the evolution of the human & machine species, wealth,
and everything else that encompasses human life.”
He considers the idea of optimization, concluding that it is
what nature does.
“…optimization is the activity of making changes and
choosing between the alternatives that emerge. To opt is to make a ‘choice’… To
be able to choose one must have the ‘freedom’ to change the existing
configuration and then choose from the alternative configurations that emerge
after the change.”
He also notes
that our natural urge toward optimization is what defines what we see as “good.”
“Good is the feature of the new organization (design)
that we select after every change.”
Optimum means best. It is the best choice of those that are
available.
He notes that
mechanisms should not be confused with the constructal law. In biology, mechanisms are mutations and biological selection. In geophysics mechanisms are
soil erosion, rock dynamics, water-vegetation interaction, and wind drag. In
sports, mechanisms include training, recruitment, etc. In technology mechanisms
are things like liberty, freedom to question, innovation, etc. The physics principle
is the “how,” he says, and mechanisms are the “what.”
“The what are many, the how is one.”
He notes that the hierarchy of ‘one law, many theories,’ is
everywhere in science.
Perhaps some
future applications of the constructal law will be to fast-forward evolution
and design change in human & machine species. In flow architecture the many
small and few large work together to create an optimal system. He notes that natural
selection, adaptation, and survival, often seen as biological, are really
physical.
“The physics law of evolution is predictive, not
descriptive. This is the big difference between the constructal law and other
vies of evolution in nature…Models are acts of empiricism, not theory.”
He notes that constructal theory is not the same as
constructal law. The law is predictive while the theories are descriptive.
Below is a figure
from Bejan’s 2013 paper in Applied Physics showing the evolution and spreading
of thermodynamics.
.jpeg)
He notes Deem’s
observation that “life has evolved to evolve,” noting that “evolving
leads to better evolving.” He also explores other contemporary thought in
accord with the constructal law, noting that there are annual conferences about
the constructal law. People write papers about it. Bejan likes to read them and
at the same time follow how the law itself spreads and flows as a structure of knowledge.
He says that he would only change the constructal law in one way from his
initial 1996 declaration, to include the idea of freedom in the law. He would express
the law as follows:
“For a flow system to persist in time (to live) it must
evolve ‘freely’ such that it provides greater access to its currents.”
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