Why lightning, trees, rivers, and lungs look the same...

One of the big questions was how "living" things came to be as they are, if they weren't created that way, which Charles Darwin explained with his evolutionary theory.

However, there was no explanation for how "everything else" came to be as it is, and why they so often looked like "living", biological things.  Why do rivers, lungs, lightning and trees, and cities, airports, and highways have the same structure?   

Adrian Bejan

Distinguished Prof of

Mechanical Engineering

MIT and Duke University

Well, there are four "Laws of Thermodynamics", describing how physical quantities behave under certain conditions at "thermal equilibrium", i.e., when there is no flow between systems.  

A new "law", the "constructal" law describes how flow behaves under certain conditions in a well-researched, scientific, explanation for both biological and non-biological systems.  This was discovered and extensively demonstrated by Adrian Bejan, who published over 600 peer-reviewed articles and 28 books and has 18 honorary doctorates from universities in 11 countries.

The constructal law's key principle is "For a finite-size system to persist in time, it must evolve in such a way that it provides easier access to the imposed currents that flow through it."  "Constructal" was coined by Bejan to describe how flowing systems of all types evolve structures to increase flow access. 

Three fundamental steps are described in Bejan's "Design In Nature: How the Constructal Law Governs Evolution in Biology, Physics, Technology, and Social Organization", which Rich Doyle recommended:  

1.  Life is flow: all flow systems are living systems, the animate and the inanimate.
2.  Design generation and evolution is a phenomenon of physics.
3.  Designs have the universal tendency to evolve in a certain direction in time.

 

branches - trunk - branches
optimized constructal flow

Therefore, shape and structure arise to facilitate flow, and to ensure that the flow facilitates the functions that it exists to  perform.   

Designs evolve that allow fluids/energy/living things to flow more easily, by water, land or air, moving farther and faster for the energy consumed and then to go slowly on a shorter scale over a large area to allow critical processes to occur.

Optimized flow has "slow and short" and "fast and long" components.

photosynthesis

Trees evolved this "roots - trunk - branches" structure.  There is first "slow and short" flow for fine roots to take the water and nutrients from a large area underground through larger and larger roots.  Then it reaches the trunk where it goes "fast and long" (comparatively) until it reaches increasingly smaller branches where it goes "slow and short" to provide the materials needed for photosynthesis to occur.

       Lena river delta

           in Siberia

A similar design evolves for rivers and streams.   Drops of water fall and move slowly.  As more rain falls over a wide area, small individual branches form for "short and slow" movement.

With more rain, larger branches form, and flow becomes "fast and long" as rivers form to more efficiently move the water.  When it then spreads to cover a larger area, branches form to distribute the water "slowly and shortly".

 

With folk, we move "short" distances from our housing "slowly" until we reach larger "faster and longer" branches and trunks on trains/planes/automobiles to reach our workplace, store, entertainment event, etc.

      The "slow and short" part

           of the flow journey

Near our destination, we again flow "slowly" over "shorter" distances by walking, cab, Uber, etc., until we reach our seat, desk, work station, bar, restaurant, etc., in the "branches - trunk - branches" structure that optimizes the movement of mass and energy.

Optimal constructal flow
housing design

NYC Central Park

An optimal flow design for a city has almost perpendicular smaller branches intersecting larger and larger branches as the flow gains size and speed.

This pattern drains all areas equally.  This pattern is then reversed on the other end as the flow slows and spreads.   However, most cities perturb this optimal pattern, w/older areas, stadiums, parks, geography, etc.

One of the world's most flow efficient airports is the Atlanta Hartsfield-Jackson International.  It is almost perfectly designed by constructal principles.   Airports in Singapore, South Korea, Hong Kong and Tokyo are now designed similarly.

Optimal Airport Constructal Design 

Many designs were tried, allowing for having many planes unloading, many folk walking "slowly" for short distances, and then taking trains to travel "fast and long", then walking "slowly" again.   

Interestingly, the optimal flow design occurs when the time spent walking is equal to the time spent riding the train.  Amazingly, the optimal design for the farthest traveler is the same as the one for all of the travelers, and it is the "favorite" design of travelers.  

Cooling circuit design
for optimal heat removal

Constructal design also optimizes the removal of heat from electronic components by the most rapid and efficient flow possible.  This allows more processing functionality on the smallest real estate/substrate without damaging components from overheating, and jams more capability into our smartphones and PCs.

Heat sinks on PC

As with the other applications, the "branches and trunk" arrangement provides the best solution.

To reach as many heat source regions as possible, many "short" connections are designed to join larger "branches" perpendicularly, until they reach the "fast and long" heat-sink "trunk".

Lightning also generates a "branches - trunk - branches" structure as charge gathers "short and (kinda) slow" from many regions in a cloud and then it moves "fast and long" in a "bolt" to the ground or another cloud.  Then it goes "short and slow" into the area of the strike.  Many branches are close to perpendicular.  

This optimal perpendicular arrangement occurs when there is no unbalanced resistance to the flow.   In a river, neither the "trunk" nor the "branches" flow without impediments, changes in bank and bottom shape, highways and bridges, etc., so they evolve to fit with their environment.

Biological circulatory, pulmonary and nervous systems generate the same "branches - trunk - branches" structure for flow optimization.

Constructal calculations predict, and it is found, a 1 to 4 ratio between "mothers" and "daughters", i.e. larger and smaller branches, in low viscosity systems like rivers which use turbulent flow to move more water.   However, in animal bodies, calculations predict, and there is observed, a 1 to 2 ratio for high viscosity blood to preserve laminar flow and avoid dangerous cavitation.

Amazingly, constructal calculations demonstrate that designs of animals evolved to move mass, as a flow, further for the useful energy expended.  Changes in organ sizes, bone shapes, rhythm of breathing lungs and beating hearts, running legs, and flapping wings, for human and non-human beings can all be calculated.   

The constructal law has been successfully applied to a wide range of applications, with voluminous calculations, data bases and graphs.  Examples include:

       a)   which athletes will be successful in which sports

       b)   why the "Golden Mean Ratio" is what it is

       c)   why the Eiffel Tower is as it is

       d)   how citations affect rank of academic departments

       e)   how trees group by size in forests

       f)    how European city size distribution changed from 1600 to 2000      

BTW, the popular "Dialogues with Dominic" blogposts, were combined with unpublished later dialogues, and dialogues between Dominic, the author, and Jake, the editor, who i also worked with, into a new book "Dialogues with Dominic: A Chronicle of Inquiry and Awakening" which is on Amazon.  All proceeds are being donated and the Kindle version is free and shareable if you buy the hard copy.