Vibrating Universe

"Gravitational waves are fundamentally different. Not only is a gravitational wave a side-to-side, lateral wave like light, not a longitudinal wave like sound, but it isn’t a ripple through objects in spacetime; it passes through spacetime itself. When a gravitational wave passes by, spacetime squeezes and contracts. This oscillation influences matter, which exists in spacetime – but doesn’t require matter to be able to travel. It’s quite demeaning to gravitational waves to call their detection ‘hearing the sound of black holes in space’ as some have done. By comparison, sound is a trivial local effect. Gravitational waves make the universe itself vibrate."

- Brian Clegg (1955 - )
Gravitational Waves

Web of Conjectures

"Before Einstein, geometry was thought to be part of the laws. Einstein revealed that the geometry of space is evolving in time, according to other, deeper laws ... It is important to absorb this point completely. The geometry of space is not part of the laws of nature. There is therefore nothing in those laws that specifies what the geometry of space is. Thus, before solving the equations of Einstein's general theory of relativity, you don't have any idea what the geometry of space is. You find out only after you solve the equations.

...

We have to find a way to unfreeze time-to represent time without turning it into space. I have no idea how to do this. I can't conceive of a mathematics that doesn't represent a world as if it were frozen in eternity. It's terribly hard to represent time, and that's why there's a good chance that this representation is the missing piece.

...

What we have, in fact, is not a theory at all but a large collection of approximate calculations, together with a web of conjectures that, if true, point to the existence of a theory."

- Lee Smolin (1955 - )
 The Trouble with Physics

Paradoxes and Contradictions

"We can pull atoms apart, peer back at the first light and predict the end of the universe with just a handful of equations, squiggly lines and arcane symbols that normal people cannot fathom, even though they hold sway over their lives. But it's not just regular folks; even scientists no longer comprehend the world. Take quantum mechanics, the crown jewel of our species, the most accurate, far-ranging and beautiful of all our physical theories. It lies behind the supremacy of our smartphones, behind the Internet, behind the coming promise of godlike computing power. It has completely reshaped our world. We know how to use it, it works as if by some strange miracle, and yet there is not a human soul, alive or dead, who actually gets it. The mind cannot come to grips with its paradoxes and contradictions. It's as if the theory had fallen to earth from another planet, and we simply scamper around it like apes, toying and playing with it, but with no true understanding."

- Benjamín Labatut (1980 - )
When We Cease to Understand the World

Transcending the Subject

"The fact that these highly abstract notions coalesce in such refined harmony is absolutely mind-boggling. It points to something rich and mysterious lurking beneath the surface, as if the curtain had been lifted and we caught glimpses of the reality that had been carefully hidden from us. These are the wonders of modern math, and of the modern world.

...

The interaction between math and physics is a two-way process, with each of the two subjects drawing from and inspiring the other. At different times, one of them may take the lead in developing a particular idea, only to yield to the other subject as focus shifts. But altogether, the two interact in a virtuous circle of mutual influence.

...

The essence of mathematics lies in its freedom.” Mathematics teaches us to rigorously analyze reality, study the facts, follow them wherever they lead. It liberates us from dogmas and prejudice, nurtures the capacity for innovation. It thus provides tools that transcend the subject itself."

- Edward Frenkel (1968 - )
Love and Math: The Heart of Hidden Reality

Time and Memory

"This is the disconcerting conclusion that emerges from Boltzmann’s work: the difference between the past and the future refers only to our own blurred vision of the world. It’s a conclusion that leaves us flabbergasted: is it really possible that a perception so vivid, basic, existential—my perception of the passage of time—depends on the fact that I cannot apprehend the world in all of its minute detail? On a kind of distortion that’s produced by myopia? Is it true that, if I could see exactly and take into consideration the actual dance of millions of molecules, then the future would be “just like” the past?

...

Temporality is profoundly linked to blurring. The blurring is due to the fact that we are ignorant of the microscopic details of the world. The time of physics is, ultimately, the expression of our ignorance of the world. Time is ignorance.

...

I am my mother’s caresses, and the serene kindness with which my father calmly guided me; I am my adolescent travels; I am what my reading has deposited in layers in my mind; I am my loves, my moments of despair, my friendships, what I’ve written, what I’ve heard; the faces engraved on my memory. I am, above all, the one who a minute ago made a cup of tea for himself. The one who a moment ago typed the word “memory” into his computer. The one who just composed the sentence that I am now completing. If all this disappeared, would I still exist? I am this long, ongoing novel. My life consists of it."

- Carlo Rovelli (1956 - )
The Order of Time

Quantum Realities

"To understand this new frontier, I will have to try to master one of the most difficult and counterintuitive theories ever recorded in the annals of science: quantum physics. Listen to those who have spent their lives immersed in this world and you will have a sense of the challenge we face. After making his groundbreaking discoveries in quantum physics, Werner Heisenberg recalled, 'I repeated to myself again and again the question: Can nature possibly be so absurd as it seemed to us in these atomic experiments?' Einstein declared after one discovery, 'If it is correct it signifies the end of science.' Schrödinger was so shocked by the implications of what he'd cooked up that he admitted, 'I do not like it and I am sorry I had anything to do with it.' Nevertheless, quantum physics is now one of the most powerful and well-tested pieces of science on the books. Nothing has come close to pushing it off its pedestal as one of the great scientific achievements of the last century. So there is nothing to do but to dive headfirst into this uncertain world. Feynman has some good advice for me as I embark on my quest: 'I am going to tell you what nature behaves like. If you will simply admit that maybe she does behave like this, you will find her a delightful, entrancing thing. Do not keep saying to yourself, if you can possibly avoid it, 'But how can it be like that?' because you will get 'down the drain,' into a blind alley from which nobody has yet escaped. Nobody knows how it can be like that.'"

- Marcus du Sautoy (1965 - )
 The Great Unknown

Geometrodynamics

"The universe does not exist “out there,” independent of us. We are inescapably involved in bringing about that which appears to be happening. We are not only observers. We are participators. In some strange sense, this is a participatory universe. Physics is no longer satisfied with insights only into particles, fields of force, into geometry, or even into time and space. Today we demand of physics some understanding of existence itself."

- John Archibald Wheeler (1911 - 2008)

Time and Space

"Because of the hazy, nondefinite character of quantum physics (called the Heisenberg uncertainty principle), at the dimensions of the Planck length, space and time churn and seethe, with the distance between any two points wildly fluctuating from moment to moment, and time randomly speeding and slowing, perhaps even going backward and forward. In such a situation, time and space no longer exist in a way that has meaning to us."

- Alan Lightman (1948 - )
Probable Impossibilities

 

Full of Fire

"When primitive man gained control over fire, it was a great step. However, the Universe is full of fire; consider the stars. Because we can think, and nothing else on our planet seems to be able to do so, it is natural for us to hold our intellectual prowess in great esteem. However, it may be that information processing, instead of being the sole province of us humans and our machines, may be a part of almost everything else in physics. Life itself, is clearly mediated by digital information; the genetic code. Digital Mechanics assumes that physics is also a process based on informational processes. We may need to rid ourselves of the prejudice that purposeful, thought related action is exclusively the domain of humans or perhaps aliens similar to humans. There are kinds of thinking that are qualitatively unimaginable to us though we can think about it quantitatively. We should not be afraid to consider intellectual activity as the driving force behind the creation of the Universe. By a close and quantitative examination of the possible parameters of Digital Mechanics, we can arrive at reasonable guesses as to what might be the purpose behind the creation of a universe like ours. That, in turn, can lead us towards intelligent speculations about Other, the space that contains the engine of our world."

- Edward Fredkin (1934 - 2023)
A New Cosmogony

Manifest Form

"The harmony of the world is
made manifest in Form and Number,
and the heart and soul and all the
poetry of Natural Philosophy are embodied
in the concept of mathematical beauty.

...

Cell and tissue, shell and bone, leaf and flower, are so many portions of matter, and it is in obedience to the laws of physics that their particles have been moved, moulded and confirmed... Their problems of form are in the first instance mathematical problems, their problems of growth are essentially physical problems, and the morphologist is, ipso facto, a student of physical science."

- D’Arcy Wentworth Thompson (1860 - 1948)
On Growth and Form

Observer-Centric Virtualities

"Your Universe is in consciousness. And it’s a teleological process of unfolding patterns...The totality of your digital reality is what your conscious mind implicitly or explicitly chooses to experience out of the infinite.

...

Self-causation of reality becomes apparent when a phenomenal mind, which is a web of patterns, conceives a novel pattern and perceives it. All mass-energy, space-time itself emerge from consciousness. Those are epiphenomena of consciousness.

...

Mind instantiates oneself into matter. In a mathematical sense, matter is an “in-formed” pattern of mind. Time is emergent, and so is space. If space-time is emergent, so is mass-energy. All interactions in our physical world is computed by the larger consciousness system. In short, mind is more fundamental than matter. All realities are observer-centric virtualities."

- Alex M. Vikoulov, Theology of Digital Physics

Neither Time nor Space

"The scene of action of reality is not a three-dimensional Euclidean space but rather a four-dimensional world, in which space and time are linked together indissolubly. However deep the chasm may be that separates the intuitive nature of space from that of time in our experience, nothing of this qualitative difference enters into the objective world which physics endeavors to crystallize out of direct experience. It is a four-dimensional continuum, which is neither "time" nor "space". Only the consciousness that passes on in one portion of this world experiences the detached piece which comes to meet it and passes behind it as history, that is, as a process that is going forward in time and takes place in space."

- Hermann Weyl (1885 - 1955)

Cartesian Fallacy

"The universe is wider than our views of it."

- Henry David Thoreau (1817 - 1862)

"Logic does not lead us from the fact that we are an integral part of the web of life to certain norms of how we should live. However, if we have the deep ecological experience of being part of the web of life, then we will (as opposed to should) be inclined to care for all of living nature. Indeed, we can scarcely refrain from responding in this way. 

By calling the emerging new vision of reality 'ecological' in the sense of deep ecology, we emphasize that life is at its very center. This is an important issue for science, because in the mechanistic paradigm physics has been the model and source of metaphors for all other sciences. 'All philosophy is like a tree,' wrote Descartes. 'The roots are metaphysics, the trunk is physics, and the branches are all the other sciences.'

The systems view of life has overcome this Cartesian metaphor. Physics, together with chemistry, is essential to understand the behavior of the molecules in living cells, but it is not sufficient to describe their self-organizing patterns and processes. At the level of living systems, physics has thus lost its role as the science providing the most fundamental description of reality. This is still not generally recognized today. Scientists as well as nonscientists frequently retain the popular belief that 'if you really want to know the ultimate explanation, you have to ask a physicist,' which is clearly a Cartesian fallacy. The paradigm shift in science, at its deepest level, involves a perceptual shift from physics to the life sciences."

- Fritjof Capra (1939 - ) and Pier Luigi Luisi (1938 - )
The Systems View of Life: A Unifying Vision

"Nature is an infinite sphere
whose center is everywhere and
whose circumference is nowhere."

- Blaise Pascal (1623 - 1662)

Improvisational Nature

"Perhaps the answers to these questions require fundamental advances at the interface of physics, the arts, and neuroscience. The deep links between musical form and physical form may be unveiled by understanding how both kinds of knowledge-music and physics-arise together in human brains and nowhere else. After all, brains, regardless of how mysterious they are, are the most complex structures in the universe.

...

It is amusing to speculate that the reason why music has the ability to move us so deeply is that it is an auditory allusion to our basic connection to the universe. If our cosmic origins are seated in sound patterns, is it too far-fetched to think that music viscerally enables us to tap into those origins?

...

What if there were a vibrational pattern
in the early universe capable of
generating the current complex
structure that we live in,
the complex structures that we are?
And what if these structures
had an improvisational nature."

- Stephon Alexander (1971 - )
The Jazz of Physics

Whirling Light

"Rotating systems often break axisymmetry; were it not so, there would be no hurricanes. There are steadier examples: the skirts of the 'whirling dervish' carry cusped wave patterns which seem to defy gravity and common sense.

...

We consider a rotating, conically symmetric surface made out of a sheet of material that is constrained not to stretch or compress in two dimensions, but is perfectly flexible with respect to bending in the third. The symmetry of the surface permits an additional material flow to be superimposed on the rotation of the surface, leading to Coriolis forces. The equations describing this system yield a three-parameter family of exact solutions, some of which bear a close resemblance to the patterns on a dervish's skirt. We find that the Coriolis terms that arise from the additional flow are crucial for these types of patterns to exist.

...

The results widen our understanding of the dynamics of flexible objects and of pattern formation in rotating systems. They may also shed some light on previously known instabilities of turbine disks and hard disks. Finally, they bring a bit of science into the otherwise nebulous world of the mystic, and address a phenomenon that has been observed with aesthetic pleasure for hundreds of years."

- J. Guven, J. Hanna and M. Müller,
"Whirling skirts and rotating cones,"
New Journal Of Physics (Nov, 2013)

Postscript. The images in the diptych that I took with my iPhone recently (of light reflecting off of cars parked onto the walls of a local garage) reminded me of Rumi's "Whirling Dervishes," about which you can read here and here (in considerably less technical detail than the one you'll find if you follow the link to the physics journal!)

“You are water, whirling water,
Yet still water trapped within,
Come, submerge yourself within us,
We who are the flowing stream.
...
We came whirling out of nothingness,
scattering stars like dust...
The stars made a circle,
and in the middle,
we dance.”

- Rumi (1207 - 1273

Vedantic Complementarity

"The very nature of the quantum theory ... forces us to regard the space-time coordination and the claim of causality, the union of which characterizes the classical theories, as complementary but exclusive features of the description, symbolizing the idealization of observation and description, respectively."

- Niels Bohr (1885 - 1962)

"The general opinion in theoretical physics had accepted the idea that the principle of continuity ("natura non facit saltus"), prevailing in the microscopic world, is merely simulated by an averaging process in a world which in truth is discontinuous by its very nature. This simulation is such that a man generally perceives the sum of many billions of elementary processes simultaneously, so that the leveling law of large numbers completely obscures the real nature of the individual processes."

- John von Neumann (1903 - 1957)
Mathematical Foundations of Quantum Mechanics

"The plurality that we perceive is only an appearance; it is not real. Vedantic philosophy... has sought to clarify it by a number of analogies, one of the most attractive being the many-faceted crystal which, while showing hundreds of little pictures of what is in reality a single existent object, does not really multiply that object."

- Erwin Schrödinger (1887 - 1961)

Communicating the Joys of Doing Photography

“A great photograph is one that fully expresses
what one feels, in the deepest sense,
about what is being photographed.”
- Ansel Adams (1902 - 1984)

To my ever-patient readers, I will dispense with my usual (and likely tiresome) "excuses" for yet another prolonged period of inactivity on my blog. Suffice to say, that photography is something I am able to pursue only as time - i.e., "day job" constraints - allow; and to which I look forward to soon returning. But this is not to say that the pleasures of photography are ever far from my mind (or soul); even as the making of photographs goes through the inevitable crests and troughs of daily realities. It is in this spirit that I offer not one of my own recent photographs (since there are none I dare share), but instead introduce - and provide links to - a few prodigiously talented YouTube photographers/storytellers that I'm sure my kind readers would enjoy spending some quality time with. By "talented," I mean that these photographers are not just gifted artists (something that is immediately obvious by looking at their online portfolios), but that they all possess a preternatural gift of (seemingly effortlessly) conveying the joy of doing photography through visual narrative. As I wallow in my current state of creative non-being, I have repeatedly turned to these "YouTubers" for inspiration, solace, and the simple pure pleasure of immersing myself in beautiful imagery. (To be clear: though I sense a deep creative kinship with each of these storytellers, I do not know nor have I ever met any of them, except through the videos and portfolios they post online.)

So, who are these magnificent "aesthetic storytellers"? I follow about a dozen or so photographers on YouTube (and there are certainly many more that deserve attention), but the ones whose channels I go back to again and again - and why I always smile when my iPhone notifies me that a new video has been posted - are: Henry Turner, Thomas Heaton, Nigel Danson, Simon Booth, and Gary Gough. 

First and foremost, these are all magnificent photographers, in the purest sense of the word; i.e., if they did nothing but stare into a camera each week and pull up whatever new images they produced since their last video, it would still be a privilege to view. But each of them does so much more (as explained below). Overall, their channels are mostly landscape oriented (which is easy to understand, since they all live in the U.K. and are within easy reach of the Lake District, the Scottish Highlands and the Isle of Skye, among other spectacular places), but it would be foolish to blindly categorize the imagery that any of these photographers produce as "just landscapes," for their artistic sensibilities and repertoires run considerably deeper.

"Photography for me is not looking, it's feeling.
If you can't feel what you're looking at,
then you're never going to get others to
feel anything when they look at your pictures."
- Don McCullin (1935 - ) 

Turner, who is my favorite (for reasons I'll immediately explain), has a bit less experience than some of the others in this esteemed group (Turner posted his first video only four years ago, while Heaton's first is seven years old and Gough's eight), but - my oh my - what a God-given gift Turner has to inspire even time- and weather-beaten old photographers such as myself (for whom straggling down a short slope at a local park to get to a "shot" depends more on the state of my 61yo knees than how good the shot is that I think I might get!). Turner's joy of photography - his utter delight in just being out and about in nature, hiking, exploring, doing photography (or, sometimes, just looking, with his camera still in the bag) - infuses each and every frame of the videos he posts. He comes across as a genuinely unassuming, humble and creative soul; his instinctive reaction to beauty appears deeply visceral (on at least one occasion, I recall seeing him shed a tear because of what he was "seeing"). His infectious enthusiasm for being/reveling in nature is utterly mesmerizing and intoxicating (in a good way)! I challenge you to watch any of Henry's videos without discovering a smile on your face, and finding yourself in a relaxed, meditative state of mind after seeing his trademark signoff - "Out!" - at the end. Turner is an impassioned, sometimes humorously self-deprecating, master photographer and storyteller; and his stunning videos are experiential wonders. A few of my favorites are: Isle-of-Sky, Stop complaining about the conditions, and What landscape photography gives.

Heaton is the first "YouTuber" I became a devoted follower of a few years ago, and - as is true for the others in this group - I rarely miss any of his episodes. He is both a consummate photographer and an experienced, and creative, YouTuber. Indeed, I am often left in awe at the care he takes in putting together and editing his videos. All are masterful, and are a treat to experience. His 2021 two-part series recounting his north-to-south hike on Scotland's Isle-of-Skye (part 1 and part 2) is one of my personal favorites. Heaton is as comfortable - and gifted at - capturing "Wagnerian" epic like vistas, the likes of which most of us will never get to see (simply because we lack the will or stamina, or both, to trek up some mountainside hours before a glorious sunrise reveals itself at its peak!), as he is at finding quiet abstract compositions of nothing but sand on some otherwise nondescript beach.

"Great photography is about depth of feeling, not depth of field."
- Peter Adams

Danson, who started his channel about five years ago, has a quiet and inviting demeanor. The relaxing tone of his voice and cadence gently lulls you into a creatively receptive state of mind, as he explores the practice and philosophy of what it means to "do photography." Endearingly, he is often accompanied on his "adventures" by his adorable English Springer Spaniel, Pebbles. (Equally endearing, at least to me, is that Danson and I share a love of physics: Danson's Ph.D. is in optics, mine is in complex systems.) While Danson is a superlative all-around landscape photographer (and founded the World Landscape Photographer competition in 2020), his work with trees is among the most accomplished I've ever seen. A few favorites: woodland photography, trees of scotland, and woodland photography tips.

Simon Booth, whose channel I have only recently "discovered" (but who has been uploading video content for five years), is both a landscape and wildlife photographer with over 30 years experience. Like Danson, he a scientist; specifically, an ecologist. His research interests often play an integral part in his adventures, as he uses his scientific knowledge to help guide his aesthetic choices. Dedicated viewers of his channel learn as much about the flora and fauna of the places he saunters in as they do about the creative process. His graceful unassuming manner belies a keen eye for composition. If ever there was a photographer who can find a photograph where others see nothing - with the magical ability to transform (what to most people's eyes, even to other photographer's eyes, is) an "uninteresting" leaf or fungus into an otherworldly, exquisitely beautiful image - it is Simon. He is a master of turning the "ordinary" into the extraordinary! A few of my favorite Simon Booth videos are: hidden gems, summer photography, and looking beyond the obvious.

"Don’t shoot what it looks like.
Shoot what it feels like."
- David Alan Harvey (1944 - )

Gough is a landscape, commercial, wedding, and portrait photographer, though his YouTube channel is focused mainly on landscape. What I love about Gough's videos is an amalgam of what I admire about what all five of my favorite YouTube photographers do so well. He is a talented artist, unassuming and unarrogant, knowledgeable about the art and craft of photography, takes his work seriously but not always himself doing it, and is a wonderful story teller. Gough is also a dedicated experimentalist, by which I mean that he often injects an element of "play" into his photography; such as when he recently challenged a $20 (old, old, so very old) camera to taking long exposures, combined wide-angle and telephotos shots of a railroad track and train into a single image, and discussed shooting landscapes in poor light. Gary's channel also include wonderful video tutorials on myriad specific topics; watching them is akin to being part of a master workshop (albeit, remotely, observing and learning, but - alas - unable to interact; and Gary's cheerful and inviting "video personality" certainly makes one want to engage with on a personal level). 

It is often said (as evidenced by the quotes above) that what distinguishes a "fine art" photographer from someone who merely takes "snapshots" is (in part) the ability to create an image that shows the viewer not just the "thing" or "place" the photographer was looking at, but to convey what the photographer experienced, emotionally (even spiritually) while engaged in the creative process that led to capturing the image. Each of the YouTubers introduced above shines in this regard! They all have a gift for story telling and for expressing their obvious love of being out in nature and capturing its beauty. YouTube may even be the perfect medium for communicating what it feels like to do photography, since it directly shows the photographer in his or her element; provided, of course, that there is something worth communicating, and that the photographer is skilled in doing so. YouTube provides a powerful new channel through which a special group of artists - those who are skilled equally in image making and storytelling - can engage with their followers; not by just showing them finished products of their work, but by taking viewers along with them on the walks (or hikes) the photographers themselves went on as they find and create their images. But you do not have to take my word that these five "photographer storytellers" are among the very best at communicating the joys of photography on their YouTube channels; just follow the links and enjoy the journey! 😊

Mathematical Beauty

"The harmony of the
world is made manifest
in Form and Number,
and the heart and soul
and all the poetry of
Natural Philosophy are
embodied in the concept
of mathematical beauty."

- D'Arcy Wentworth Thompson (1860 - 1948)

Postscript. As may be the case with many of you, my day-job constraints leave me precious little time to devote to purely aesthetic pleasures (notwithstanding those that occasionally overlap with more mathematical pursuits). Sometimes, as now, even my weekend time is filled mostly with staring at gibberish on a computer screen, and pounding away at my keyboard to produce picture-less reams of technical reports (even as I day-dream of month-long photo-safaris in far-away lands). Thus, the short walks my wife and I take through our neighborhood after breakfast each day have become immeasurably important physical and spiritual oases for me. The simple pleasure of encountering beautifully haphazard arrangements of natural forms rejuvenates and nourishes my soul. The images in the triptych above were taken no more than a few minutes apart during a walk that itself lasted less than a half hour. But what a joy it is to stumble upon such humble transcendent beauty hiding in plain sight! The great polymath Thompson's book, On Growth and Form (the first edition of which came out in 1917, and which to this day remains an extraordinarily beautiful book to read) is essentially a 1100+ page erudite argument that biology can be reduced to mathematics (a sentiment that a much younger version of myself would have been happy to accept): "It behooves us always to remember that in physics it has taken great men to discover simple things. They are very great names indeed which we couple with the explanation of the path of a stone, the droop of a chain, the tints of a bubble, the shadows in a cup. It is but the slightest adumbration of a dynamical morphology that we can hope to have until the physicist and the mathematician shall have made these problems of ours their own." For those of you interested in exploring (taking a deep-dive, really, into) the broader entanglement of art and science, here are some slides I used for a 2017 presentation at a Humanities and Technology Association conference (held that year in Newport, RI). This lecture is one of three I've given in (relatively) recent years during which I wore both of my hats, as physicist and photographer. The other two lectures were given at the American Center for Physics (College Park, MD in 2009) and at the Morrison House (Alexandria, VA in 2011).

Ceaselessly Creative

"The past three centuries of science have been predominantly reductionist, attempting to break complex systems into simple parts, and those parts, in turn, into simpler parts. The reductionist program has been spectacularly successful, and will continue to be so. But it has often left a vacuum: How do we use the information gleaned about the parts to build up a theory of the whole? The deep difficulty here lies in the fact that the complex whole may exhibit properties that are not readily explained by understanding the parts. The complex whole, in a completely nonmystical sense, can often exhibit collective properties, “emergent” features that are lawful in their own right.

...

This web of life,
 the most complex system
we know of in the universe,
breaks no law of physics,
yet is partially lawless,
ceaselessly creative."

- Stuart Kauffman (1939 - )

Why is the sky blue?

"[Why is the sky blue?] ... It’s a question every toddler asks, but it is also one that most great scientists since the time of Aristotle, including da Vinci, Newton, Kepler, Descartes, Euler, and even Einstein, have asked... One of the things I like most about this explanation—beyond the simplicity and overtness of the question itself—is how long it took to arrive at correctly, how many centuries of effort, and how many branches of science it involves.

Aristotle is the first, so far as we know, to ask the question about why the sky is blue, in the treatise On Colors; his answer is that the air close at hand is clear and the deep air of the sky is blue the same way a thin layer of water is clear but a deep well of water looks black. This idea was still being echoed in the 13th century by Roger Bacon. Kepler too reinvented a similar explanation, arguing that the air merely looks colorless because the tint of its color is so faint when in a thin layer. But none of them offered an explanation for the blueness of the atmosphere. So the question actually has two, related parts: why the sky has any color, and why it has a blue color.

...

The sky is blue because the incident light interacts with the gas molecules in the air in such as fashion that more of the light in the blue part of the spectrum is scattered, reaching our eyes on the surface of the planet. All the frequencies of the incident light can be scattered this way, but the high-frequency (short wavelength) blue is scattered more than the lower frequencies in a process known as Rayleigh scattering, described in the 1870’s. John William Strutt, Lord Rayleigh, who also won the Nobel Prize in physics in 1904 for the discovery of argon, demonstrated that, when the wavelength of the light is on the same order as the size of the gas molecules, the intensity of scattered light varies inversely with the fourth power of its wavelength. Shorter wavelengths like blue (and violet) are scattered more than longer ones. It’s as if all the molecules in the air preferentially glow blue, which is what we then see everywhere around us.

Yet, the sky should appear violet since violet light is scattered even more than blue light. But the sky does not appear violet to us because of the final, biological part of the puzzle, which is the way our eyes are designed: they are more sensitive to blue than violet light.

The explanation for why the sky is blue involves so much of the natural sciences: the colors within the visual spectrum, the wave nature of light, the angle at which sunlight hits the atmosphere, the mathematics of scattering, the size of nitrogen and oxygen molecules, and even the way human eyes perceive color. It’s most of science in a question that a young child can ask."

- Nicholas Christakis (1962 - )
This Explains Everything (John Brockman, ed., 2013)