Thread by @cdjarrell

This is a tweet thread summary of "The Physics of Life: The Evolution of Everything" by Adrian Bejan, a chair professor of Mechanical Engineering at Duke University amazon.com/Physics-Life-E…

Originally gaining popularity with his Constructal Law in 1996, 20 years later he described it as: "For a flow system to persist in time (to live) it must evolve freely such that it provides greater access to its currents"

[I'd sum it up as "A system that is allowed to evolve freely over time, whether alive or inanimate, will look to survive by becoming more efficient in distributing its resources." I think the idea has a lot of merit in parts but may not be Bejan’s one law to rule them all]

In a nutshell, "The Physics of Life" explores how freedom is the most basic -- yet overlooked -- property of nature. Every natural entity has a tendency to move and make it easier to move over time and relies on the freedom to change to survive

When movement stops, life generally ends. The thermodynamic definition of the dead state is when a system is in complete equilibrium with its environment. Dead state means “nothing moves”: not the system, and not its inner workings either

The opposite of this is the live state. Here the system is not in equilibrium with its environment and is constantly being pushed and pulled, heated and cooled. In nature nothing moves unless forced to and it moves relative to its environment. Movement is contrast made visible

All systems that flow -- from river basins to animal migration -- evolve yet remain imperfect. Tech evolution is about the evolving design of moving people, things, ideas, etc. across the globe. Every new technology is an abrupt change towards increasing the efficiency of flow

Technology (and science, education, and culture and others) are examples of ways we open channels and help liberate whatever flows. Peter Vadasz said, "Any society has as much freedom as the available technology can provide and support"

A society that flows is wealthy and has a greater tendency to reconfigure itself to flow more and become wealthier. There is no end to this evolving design -- there is just the time direction of the evolutionary changes and the rate at which changes are occurring

Good is a government that facilitates the movement of society, it gets better when it becomes more efficient -- opening channels, shortening and straightening paths, removing roadblocks, and reducing wait times. More openness is the evolution toward freedom

In a free market, a lot of these channels are businesses, as they allow for the better design changes to be tested and whatever is best is kept over time. That which works most efficiently survives

Let's change gears and talk about what knowledge is/isn't. Knowledge is ideas (design changes) and action (implementation). Knowledge is not a thick book filled with fancy words, it is what you do with what you learn from the book

Knowledge is not just intelligence; intelligence measures someone's ability to achieve goals in a wide range of environments. If we’re to differentiate between knowledge and intelligence, then intelligence is the capacity to possess, create, and convey knowledge

Knowledge is also not just data -- data is the plural of datum (a given), something that is known or held. Data are the facts that we accumulate based on hypotheses, observations, and measurements. Like ideas, data is useless without action

Often this action is questioning. Knowing how to come up with and investigate questions is paramount in science; cultures that encourage questioning flourish, those that don’t flounder. Bejan's advice: Encourage anything goes, welcome the amateur, and be ready to be proven wrong

Knowledge flows from high to low -- from those who have it to those who wish to acquire it. When either end has nothing to offer, there’s no potential energy difference and the flow stops. The saying goes that old news does not travel

Knowledge as a system has always evolved to flow more easily: from one-room schools/churches to universities, from libraries to journals and now the Internet. All of these were created to make the flow of knowledge easier and longer lasting

Even if an idea is great and obvious, how it is conveyed matters. A good idea sounds familiar. We all come from a culture that retains what is good and forgets what is not. "When in Rome do as the Romans do. If you can’t beat them, join them. Go with the flow"

Ideas naturally progress from simple to complex, for something complex has to have come after something simple. Yet, in order to communicate complex ideas effectively, they must be made simpler. The more widespread something is, the simpler or more efficient it is

Ex. in language, more widespread languages are understood by less widespread ones, but not necessarily the other way around. Speakers of Moroccan and Algerian dialects of Arabic understand Egyptian Arabic easily, since Arabic popular culture is produced mainly in Egypt

Ex. in sports, the most watched sports are those with the fewest words in their rule books: Soccer (FIFA) 21,891 words; Basketball (NBA) 29,581; Baseball (MLB) 46,797; Hockey (NHL) 59,065; and Football (NFL) 70,033 [What about cricket?]

The natural tendency toward easier movement is why knowledge grows. In the beginning, it spreads slowly only to a few. Later, the spreading begins a sharp rise that eventually trails off. When graphed, the evolving area of the growing flow would look like an S-curve

The idea invades society faster and faster and then consolidates slowly. How fast the idea is adopted is shown by how steep the S is; better ideas have taller and steeper S-curves, old ideas have full S-curves, fresh ideas have the beginnings and dead ideas the ends

For anything that spreads point to area, in the beginning the channels are few but large. Think of the heat’s aorta or a city’s highways – few but allowing large amounts of volume to be moved relatively quickly. They then flow to many smaller avenues

These "few large and many small" designs are viewed as whole architecture systems and are constantly concerned with improving their flow. They collaborate, adjust and go through the process again toward a better flowing system, which is also better for each subsystem as well

Anything that evolves has a hierarchy in movement. Hierarchy unites producers and users, allocated to areas in a natural vascular design that covers the globe. Hierarchy is how the flow most easily covers the available area or volume

Think about the hierarchy of streets in the city: the secret to connecting street lengths is that at all length scales, the time needed to travel slowly is roughly the same as the time needed to travel fast. The slow travel is over a shorter distance than the fast travel

[This reminds me of the movement of planets around the Sun: if you draw an asymmetrical X through its orbit, the planet will cover the smaller length of orbit in the same amount of time as it will the longer path. Think of tossing up a stick of unequal weight at its end]

Ex. time is usually proportional from walking out the door to driving on the city streets, from the streets to highways, from highways back down to time spent on streets, and finally to parking and walking in the door to work

We see this same principle in airport design (think about the ATL airport): the time to walk (short and slow) on the concourse is the same as the time to ride (long and fast) on the train. This time balance is the natural rule of construction of all urban design

Trucks move weight more efficiently on highways than they do on streets, and one truck can carry as much a hundred cars. From a per unit cost, size makes for efficiency + longer life span. We see this in everything: animals, airplanes, rivers, atmospheric jets, and rolling stones

Life can seem complicated, but really it consists of just two measurements: life span and life travel. Bigger rivers live longer and travel farther. Bigger animals live longer and travel farther. Bigger stones roll farther, and their movement lasts longer. Bigger waves as well

From mice to the whales, animals are correlated by surprisingly accurate formulas relating animal body size to flow. We even find this same pattern with man-made machines as well, as larger machines are more efficient than smaller machines, as there’s less friction per unit moved

The reality of economies of scale is rooted in physics, and means that large parts belong on large vehicles, and small parts on small vehicles. There must be a proportionality between the size of the motor vehicle and the size of the fuel load used by the vehicle

Every river basin is not unique, since they all have a rule of how they’re constructed -- the Constructal Law. Related, every human sprinter is not unique, because running for speed has a rule as well: in addition to size, a high stride frequency is also advantageous

The fastest animal sprinters (cheetahs, Arabian horses, greyhounds) have bodies with high centers of gravity. From 1900 to 2002, the average height of the fastest human sprinters has increased 2.5x faster than the average height of the human population during the same period

Bejan then goes on to say that for sprinters that are equally tall, the center of gravity in athletes of West African origin is 3% higher on average [longer legs?] than of European origin athletes, and this 3% difference in height translates into a 1.5% advantage in speed

Legs are for land, and torsos are for water. The reverse of the example above is that those equally tall athletes of European origin have on average torsos that are 3% longer, and make waves that are 3% higher, giving them a 1.5% advantage in swimming speed

In baseball, varying player heights emerge on the field since greater throwing speed is needed across greater distances (i.e. third basemen tend to be taller than the better second basemen). The team naturally allocates talent on the field, so that the team performs better

The bottom line is that bigger bodies travel faster and perform more work per distance traveled. The work requirement decreases from sea to land to air, and explains why the movement of significant animal mass around the globe has spread in the same direction over time

Anything has to have balance to succeed, however. The primary objective of commercial airplanes is to carry people and freight a certain distance while using as little fuel as possible. The amount of fuel is proportional to the work delivered by the engine over the distance

To minimize fuel used, the total force must be reduced, given two constraints: the total mass is fixed and the wings must support the weight of the whole thing. The proportionality that naturally emerges is that the wingspan should be almost equal to the plane's length

This proportionality is also seen when building fires: they end up being about as tall as they are wide. To the ancient Greeks, "pyra" means wood to be set ablaze. So, the pyramids of Egypt are literally three-dimensional renderings of how the Greeks made their fire

This evolutionary design phenomenon is universally applicable: we want greater access, more freedom, less problems and friction, and longer life. These ideals guide us, like the natural urges to feel comfort, see beauty, and experience pleasure

In the end, it is good to be dissatisfied. It is good to be hungry, to want to do better. This is why Victor Hugo’s advice is timeless: "Change your opinions, keep your principles; change your leaves, keep intact your roots"

After all, optimism goes hand in hand with making choices with purpose. In humans, this means making choices for a better life in the future. Hope sustains life, and life means movement; for without movement, there is no life

[In summary, I enjoyed Bejan’s examples of life striving for greater efficiency, and loved the discussions on balance, proportionality, freedom, and movement. But “The Physics of Life” can lose focus and claim for the Constructal Law to do too much at times] / The End

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