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Layers of Scientific Understanding poster

Click to enlarge the image. Find a copy of the small right-column print toward the bottom of this screen. To purchase the BIG (3’x5′) paper poster, please email

Quotation at poster’s upper left: One thing I have learned in a long life: that all our science, measured against reality, is primitive and childlike—and yet it is the most precious thing we have.  – Albert Einstein

“About this poster,” at upper right: Principal subjects of science appear in this poster as geological strata.  Psychology rests atop biology because—as far as we know—psychological events are a special class of biological events.  So, psychology is “grounded” in biology.  Biology, in turn, is grounded in chemistry.  And chemistry is grounded in physics.  Finally, all these branches of science rest on the deepest stratum, philosophy.  Each major subject reveals three substrata that describe “structures” of differing scale, large to small.  Each such structure refers laterally to a crucial scientific theory that underlies our understanding of the universe at that level. 

The Layers of Scientific Understanding poster was designed by Jon Lomberg, chief artist for Carl Sagan’s acclaimed television series Cosmos.  The poster was conceived and written by Tucker Hiatt, executive director of Wonderfest, with crucial expert advice from:

Alex Filippenko, Department of Astronomy, University of California, Berkeley

Walter Freeman, Division of Neurobiology, University of California, Berkeley

Philip & Phylis Morrison, Department of Physics, Massachusetts Institute of Technology

Frank Sulloway, Department of Psychology, University of California, Berkeley

Dan Werthimer, Space Sciences Laboratory, University of California, Berkeley

Richard Zare, Department of Chemistry, Stanford University

R2-D2’s image appears courtesy of Lucasfilm Ltd.  STAR WARS © 1977 & 1997 Lucasfilm Ltd. & ™.  All rights reserved.  Used under authorization.

Production of this poster was facilitated by Branson School and the David and Lucile Packard Foundation.  The poster copyright is held by Wonderfest, the San Francisco Bay Area Beacon of Science.


Full text of the poster’s right-most sector follows:



Memetics is the emerging social science of meme evolution through natural selection.  A meme (rhymes with dream) is a unit of culture.  It is a piece of information that passes from mind to mind, and that undergoes mutation, selection, and replication.  Examples of memes are ideas, tunes, styles, principles, customs, myths, techniques.  As Earthlings transfer biological information via genes, so too do we transfer cultural information through memes.  For example, the idea of democracy is a relatively fresh-faced meme.  It now thrives in many cultures, mutating slightly as it leaps from mind to mind across the generations and across national boundaries.  Of course, the democracy meme constantly competes with other ideas of government for a niche in other cultures, and in ours.  No meme is guaranteed survival.


Evolutionary Psychology

The evolution of life via natural selection implies that behavior has evolved alongside physiology.  Evolutionary psychologists try to understand behavior by identifying the evolutionary survival value of various behaviors.  For example, affection for offspring has obvious survival value among primates (humans, apes, monkeys).  Early primates that did not adore their babies would have allowed more offspring to die during times of environmental stress.  Then fewer primate babies would have reached puberty, and fewer would have had offspring themselves. For rodents, however, affection for offspring has less survival value.  Since rodent offspring are plentiful and the length of time they spend in a state of helplessness is quite short, rodent behavior has not evolved to include a deep affection for offspring.


Psycho-Neural Identity

PNI theory holds that psychological events (perceptions, thoughts, feelings, memories, etc.) correspond to brain events.  I.e., every subjective mental phenomenon—from the smell of cinnamon to the meaning of a joke—is a manifestation of neural activity in the brain.  Neuroscientists have not yet identified the precise set of neuron activities that gives rise to any particular subjective experience.  The so-called neural correlate of the smell of cinnamon and the neural correlate of your favorite “knock-knock joke” remain a mystery.  Nevertheless, PNI is supported by tremendous indirect evidence, and is considered to be the cornerstone of modern neuroscience.  Its startling implications include the assertion that all aspects of consciousness—though they may feel very different—are purely manifestations of neural activity.




Evolution through Natural Selection

Perhaps the most important principle of biology—and the most momentous idea in science— holds that all life on Earth evolved from simpler forms.  Evolution occurs via three steps: variation, selection, reproduction.  Charles Darwin and Alfred Wallace described natural selection as that fundamentally undirected process by which the environment “selects” (allows to live and reproduce) individuals who—by accident of genetic variation—have favorable gene-borne traits.  The idea of evolution through natural selection enriches and broadens our understanding of life.  In fact, according to eminent biologist Theodosius Dobzhansky, “Nothing in biology makes sense except in the light of evolution.”



The largest unit of life is, arguably, the organism.  (Some biologists say that communities of organisms—even the entire biosphere of Earth—can be alive.)  Of course, just defining “life” is famously difficult.  Perhaps the key trait that distinguishes a living system from any other system is its ability to derive energy and structure from its environment and thereby maintain itself.  In accord with the laws of thermodynamics, the energy taken in by an organism equals the energy removed from its environment.  But the structure achieved with that energy never exceeds the destruction wrought upon the environment during that energy transfer.  Life is messy.  This ability of organisms to create and maintain their structure (at the greater expense of the their environment) is called autopoiesis.



The smallest unit of life is the cell.  Cells perform two crucial, life-defining functions: they metabolize (i.e., acquire energy and matter to maintain themselves) and they reproduce.  Usually, metabolism specifically refers to the creation and/or manipulation of proteins, the structural building blocks of life.  Physicist Freeman Dyson has proposed that Earth’s first genuine lifeforms emerged when self-maintaining, haphazardly-growing “protein creatures” merged with short-lived, self-replicating “nucleic acid creatures.”  The union of self-maintainer and self-replicator, speculates Dyson, may have produced the first primitive cell.  Biochemists have, so far, been unable to build such creatures from scratch in the laboratory.




DNA Coding

Molecules do amazing things.  Some, when in the proper environment, can even copy themselves.  Important examples are the nucleic acids of heredity, DNA and RNA.  Of course, reliable reproduction is possible only with a reliable mechanism for information storage.  In living systems, these chemical stores of information are the genes.  A gene is a portion of a DNA molecule that encodes information for the structure of a particular protein.  Proteins, in turn, are the building blocks of cells.  But to understand how the totality of proteins can produce an individual, we need to know much more than even the total information content of our genes, i.e. our genome.  We need to know the laws governing the complex self-organizing processes of cells.  The discovery of these laws remains a great ongoing challenge of biochemistry.


Atomic Theory

Our concept of the atom has come a long way since Democritus hypothesized the existence of these basic units of matter.  We now know that atoms are themselves composite particles, having an outer electron “cloud” that surrounds a tiny nucleus of protons and neutrons.  Atoms come in 92 naturally occurring varieties, the elements, each differing from the others in its number of protons.  The elements’ ability to combine varies periodically with the number of protons.  The conceptual organization of elements in the Periodic Table is one of the crowning achievements of chemistry.  Proper understanding of the Periodic Table allows us to understand how atoms combine to make molecules and, in turn, how molecules combine to make all of ordinary matter, from paramecia, to people, to planets.


Statistical Mechanics

Even the simplest atom is remarkably complex.  However, we can often treat atoms as tiny “Newtonian” billiard balls that obey simple statistical laws when large numbers of atoms interact.  The resulting theory of matter, statistical mechanics, encompasses two important laws of thermodynamics.  The 1st law amounts to the famous law of energy conservation: the quantity of energy in an isolated system of particles never changes.  The 2nd law of thermodynamics, in its imprecise form, says something even more surprising about energy: the quality of energy in an isolated system always decreases.  Potential energy has the highest quality; thermal energy (“heat”) the lowest.  Thus, the 2nd law describes the eventual degradation of all forms of energy into disordered, random molecular motion.




General Relativity

Gravity dominates the large-scale structure of the universe.  Our prize theory of gravity, called general relativity, describes gravity not as a force but as the curvature of space.  The overall curvature of space has been decreasing ever since the Big Bang hurled matter far and wide. Today, we are surprised to see how matter has coalesced into intricate structures despite this expansion.  On the one hand, the laws of physics explain the formation of galaxies, stars, and planets quite nicely.  On the other hand, the fundamental constants that must go into those laws to explain structure seem very improbable.  Many astronomers find these structure-enabling constants so unlikely that they hypothesize a huge number of other universes in which intricate structures do not arise!


Classical Mechanics

Everyday objects—from the microworld of molecules to the macroworld of blood, sweat, and tears—obey Newton’s laws of motion.  These laws describe how masses respond to the forces that act upon them; they constitute the heart of classical mechanics.  Just two forces dominate our day-to-day activities: familiar gravity and surprising electromagnetism.  Electromagnetism gives rise to all the forces discussed in chemistry: ionic bonding, Van der Waals forces, gas pressure, etc.  It also gives rise to all the everyday forces (except gravity) discussed in physics: friction, contact forces, magnetism, etc.  Light is electromagnetic, as well.  Sound and heat are, too, in that they rely on molecular interactions.  Thus, our senses, our muscular actions, and even our brain activity all rely on electromagnetism for their ultimate explanation.  We are electromagnetic creatures.


Quantum Mechanics

Many laws of classical physics fail to work in the realm of objects smaller than about 1 nanometer.  This is the realm of quanta—of subatomic particles that obey the strikingly unintuitive laws of quantum mechanics.  Such particles have only certain precise “quantized” values of physical traits.  This guarantees, for example, that every hydrogen atom is exactly alike and that the entire Periodic Table is exactly as it is.  But, at the same time, quantum mechanics demands that quanta not have well-defined traits when in isolation.  Only by interaction with large numbers of other particles do quantum traits undergo decoherence and gain precise values.  The greatest triumph of quantum mechanics is the Standard Model of matter and forces.  It describes point-like particles, quarks and leptons, that interact according to the rules of quantum field theory to make up all of ordinary matter.





Scientists seek explanations of the things they observe.  The primary attribute of a good explanation is its ability to pass the test of experiment.  Secondary attributes that distinguish good explanations include coherence, scope, simplicity, and elegance.  Accordingly, scientists ask a great deal of their very best explanations.  Such explanations earn the title theory.  In common, everyday language, a theory may be little more than an educated guess.  In science, however, a theory is as good as it gets!  A theory must agree in detail with experiment, cohere with all explanations of related phenomena, encompass a broad range of phenomena, include no unnecessary steps, and, finally, inspire a subjective sense of beauty.


Reason, Skepticism, & Consensus

Science demands careful reasoning; wishful thinking must yield to evidence and logical analysis.  Every day, we face the temptation to see what we want to see in nature.  Scientists have learned that a relentless skepticism is the best way to avoid error.  However, at the same time, scientists must be open to the incredible strangeness and subtlety of the world.  A proper combination of skepticism and open-mindedness is, ideally, the goal of every scientist.  Scientists must also be on the lookout for wholesale fraud.  Fortunately, replication of key experiments and the risk of censure by the scientific community usually succeed in keeping scientists honest.  Alleged observations become facts only after a slow, quasi-democratic process takes place among perhaps thousands of specialists around the world.


Scientific Realism

Science begins with observation.  Virtually every scientist assumes that perceptions, observations, and experiments pertain to an objective reality that exists outside the mind of the scientist. Scientific realism holds that the universe really is a certain way, and that we can come to know that way through careful observation.  Scientific knowledge may never encompass any aspect of reality perfectly.  Further, science may never come anywhere near ultimate reality.  But scientific models certainly seem to approach ultimate observable reality, and they do it better and better every day.  Slowly, asymptotically, and sometimes fitfully, science approaches important truths of the world.  And the value of these models cannot be overstated.  Recall the words of Einstein: “All our science, measured against reality, is primitive and childlike—and yet it is the most precious thing we have.”