My respite from the slow plodding hours of renovating, dissertating, computering, was always Austin’s cold springs. Leaving the artificial over-air-conditioned box of cubicles, I melt in the warmth cooked between sun and my earth body. I seek the more nourishing cool of my watershed circulatory system, pumped by my ancestral heart, it secrets tucked securely in my DNA and felt thickly in the sweet humidity and rustling green. Nothing surpasses Barton Springs after a long day of hot, dirty renovation work, or Deep Eddy after a morning of sacrificing my body to stare at a computer screen. In these places I placate my heart, my body uncoiling from tightly bound concentration.
In this climate, by midday, sweaty bodies and tired minds seek respite from the sun-bleached heat through plunges into shadowed siestas or into liquid blue green depths—Bull Creek, Barton Springs, Deep Eddy, Hamilton Pool, Pedernales, Balmorhea. In these places, cold, impossibly blue waters gravitate and rise–as do I, as a body of water, feel their pull and inspiration. They call me to movement, from within the blissful unraveling of heat, from half-closed eyelids, contentment of sultry cicada song and sweat glistened skin. Just their promise to enliven and refresh does so.
My body cooks on a slow broil, skin pressed to sun-baked rocks or woven mats of grassy banks. Overhead, massive branching cathedral ceilings of pecan, oak, cottonwood, and sycamore delicately dance at the water’s edge, raining down shade, luring me into their darker inner embrace. Unwilling to completely abandon the sun, I park my towel at the boundary between dark and light, inhaling the sweet musk of creek and sycamore. Lulled by the musical rustling of cottonwoods, speaking to the creek, in their own shared language.
The call of the water cannot be ignored for long. Maybe you were not planning on a swim, just a Greenbelt hike or a sunbath. But the cool flow of liquid gemstones invites you to touch it. Your shoes come off unknowingly and soon the slippery stones and soft mush of creek bottom are underfoot. You are knee deep in glorious living flow of the present moment’s pressing, churning undulations, trying to keep your balance, dry land ruminations and indecision left bankside.
Sooner or later someone’s tentative, uneven, creek-walking steps give way in a splash, a shriek, and peels of laughter–the lucky devil. The delightful surprise of reason unintentionally abandoned, commitment imposed, clothes drenched, coolness surrounding. There is no resisting swimming now. Hesitation turns evangelical. Only the sly challenge of a stealthy pounce or splash to refresh dry friends remains.
Sometimes the excursions are more deliberately sought. Clothes hastily abandoned in a flying leap into the quietly awaiting buoyancy. Mid air “Whoop!” of gravitational release yields to jubilant unification in skin slap on water, joyous open arm welcome of splash, and gentle sink into a nest of bubbles, the sky and trees receding above the glassy, mirrored under surface of water. Blue surrounding, breath abated in silent, sinking, stillness.
Body contracts and expands, legs and arms, tuck in, reach out, and press back to the body, face upturned, shooting through the surface, coating of water peeling off, slicking hair, breath returns in open mouthed gasp. The solution to the chest constricting shock of this abrupt half-second, 30-degree differential is to swim hard and breathe forcefully. Explosion of churning legs and turning arms reminds my body of its inner heat, borrowed from sunshine, stored and shared through the miracle of chlorophyll.
Once acclimated, I glide silently and slowly over plant leaves: fat, thin, feathered, and twisted. They rise and fall, thicken and disperse, with the undulations of the rocky depths. I weave between and through slanted shafts of light and crisp, vertical strings of tiny, bubbled breathings–pearlescent, mirrored air lifts, inverse water drops–rising from the hidden inhabitants of the underwater forest. Ghostlike, my looming shadow worries the occasional fish or painted turtle. Small schools hover nearby, but deny my inclusion.
My skin and their scales dressed in the same fabric, made of light, woven by water. The gentle caress of brilliant, rippling, crisscross veils of sun kisses and shadows play on every surface of the underwater world–sunken pirate’s treasure, rainbows of flowing silks.
Sunlight sparkles off bubbles trailing my fingertips diving ahead, reaching to pull me forward into the length of a satisfying stretch. Surfacing, I breathe in the greenness of the pecan trees through my mouth and eyes. Laps tick off with the rhythmic slapping of arms on water, breath song strong, meditatively entranced by light’s creativity. I swim just long enough to forget my work, for my mind to relax into the rhythms of my body.
But even my rapture with sunlight through water cannot help but peak the curiosity of my metaphysician’s mind. I swim to the shallows to more closely explore water’s light weaving techniques. On my way, I dive deep, closely examining the ripples of light on the bottom and as I get closer their vibrant white glow differentiates in to a full spectrum of color. I glide over dancing rainbows.
In the shallows, on a quiet, still day, the canvas is flat and clear, whether the pale yellow, skin of limestone creek bottom or Deep Eddy’s light blue, concrete, of far away floor. This flat canvas more clearly reveals the techniques water uses to paint with light.
When water twists into whirlpools, trailing canoe paddles or a hand dragging through water, on the floor below whirlpool shadows appear as black holes. I cannot help but note that a black hole’s space-time diagram can be envisioned as a whirlpool as well. Surface bubbles, like convex space-time dents, lens light into points of bright convergence, stars dancing, blinking on, and popping off on the creek bottom stage.
These shadow projections hint at their surface undulations, 2-D images suggesting 3-D contours, so too does or our view of our cosmic neighbors hint at their underlying space-time identity. Our 3-D reality a mere shadow of space-time’s 4-D curvature. I suspect the parallels between water and space-time involve a hair more that coincidence. Water, in fact, is progeny of space-time, as are we all, forged of the same light-fabric, bound in the delicate knottings of particle orbits.
A stone dropped in in still water, ripples out in widening concentric rings. On underwater surfaces, those rings appear as alternating bands of light and shadow. The bands of light and shadow correspond to the crests and troughs of the surface water wave. The convex crests of the waves focus the light into bright patches below, just like bubbles converge light into stars. The concave troughs disperse the light, showing up as the shadows.
When two fish jump or two rocks plunk into the water near each other, two ripple circles expand out, intersecting one another in a crosshatched interference pattern. This simple, mundane phenomenon, visible anywhere there is clear water and a sunny day, in fact holds a key clue that opens the door to the mysterious hidden interior of the world around us.
As it turns out, things are not things after all.
The atoms that make up the things with which we are familiar–our bodies, furniture, dishes, computers—are actually 99% empty space. Atoms are made up of a central nucleus of protons and neutrons surrounded by concentric electron shells, not unlike a three-dimensional version of pond ripples, like spheres of light emanating from a candle. The distance between the shells and the nucleus, however, is enormous when compared to the size of the particles, like the distance between the planets in our solar system compared to the size of the planets themselves.
It seems more obvious that outer space is largely empty space. Perhaps this distinction is simply a matter of perspective, being inside looking out vs. outside looking in, much like the transparency of one’s own thought processes from an interior perspective vs. the opacity of the thought processes of another, or the transparency of the past vs. the opacity of the future. All of these instances of transparency can help us imagine opacity as a function of perspective, and thus the transparency of what seems opaque, if observed from a different perspective.
The solidity we experience in the objects that surround us is the result of an interaction of chemical bonds and electromagnetic fields that hold certain particles together and prevent others, like my hand, from passing through all their empty space. What we think of as things, are actually relationships.
These relationships are in continual flux, some slower some faster. If they change faster than us we see it, if they change slower that us it is harder for us to recognize them as a process. All objects are processes; all nouns are slow verbs; all beings are becomings; all particles are waves. This last insight, the realization that all objects are waves, is the underlying reality that the simple interference pattern of pond ripples unlocked. The signature wave interference pattern is a defining feature in the centuries long debate as to whether light is a particle or a wave.
Turns out I am not the only one who is indecisive—always torn between books and boys, head and heart, the Bay Area and Austin. When pressed on the issue of whether the fundamental unit of reality is particles or waves, Mother Nature has a hard time making up her mind too. Looks like indecision runs in the family.
The debate between whether light is made up of particles or waves, is of course part of a deeper debate between predictability and randomness, between head and heart, between objects and processes, between nouns and verbs. You see, the mind prefers particles immensely. These are nice, easily defined entities whose location and trajectory one can know, with certainty. Knowing these things makes life seem easier to predict and control. This makes the mind feel secure and confident, maybe a little too confident. It takes the unpredictable, unreasonable heart to counterbalance the hubris of the mind, as I continually re-learn.
The particle vs. wave debate is a particularly juicy venue for this debate to play out because of science’s commitment to predictability. The results of scientific inquiry are pretty hard to argue with, and even more so when they reveal the complete opposite of what was originally sought. To discover unpredictability while looking for predictability, makes a pretty solid case.
In the late 1600’s and early 1700’s Isaac Newton described the world as particles to great efficacy. He described not only how fast an apple would fall from a tree, but used the same mathematical relationships to describe how fast the earth “fell” around the sun, for the first time quantifying common laws that governed both the cosmos and our daily lives. This notion of a “billiard ball universe,” or collection of objects that interacted according to deterministic laws, known now as classical mechanics, seemed perched on the verge of being able to describe the whole universe. All we needed to know was the exact position and momentum of every particle. Then how those particles interact in both the past and future would become completely predictable. In Newton’s theory, light was also made of particles.
But particles soon revealed that they had some secrets that they were unwilling to fully divulge. Notably, each particle has a secret identity where it behaves in less than predictable ways. Like stuffed animals that come alive when no one is a looking, unobserved particles act like waves. As fairies shyly disappear into flowers upon closer inspection, waves also conform to our common-sensical observations, stifling giggles to play the role of particle when approached with a measuring device.
When held loosely and left to their own devices however, waves reveal subtle hints of their hidden nature. Like developing a relationship with a wild animal, there is a delicate balance between reaching out and letting her come to you. Too much forwardness and she runs away, but if you just go about your own business and just peek out of the corner of your eye every once in a while, you might just find yourselves nose to nose at the same watering hole when you least expect it. Or perhaps, if you pay close enough attention to learn what that wild mystery loves, then you might find a way to offer it to her, setting up a playground for her delight. This is just what British polymath Thomas Young did for the wild mystery of light in 1803.
Newton claimed that light consisted of particles, and for a hundred years no one could prove otherwise. But Young suspected that light might do things a little differently than the particles if given the chance. So he set up this playground to see if she would show off her special talents.
I do not think Thomas Young spent much time playing in creeks as a child, since he was reading by age two and familiar with around 13 languages by age 14. If he did however, he would have likely been the kid at the creek who instead of splashing around, carefully dams up a shallow pool to perform a few experiments.
As an adult, Young set up a playground for water and light called a ripple tank to study the behavior of water waves. A ripple tank is a shallow tank of water light shining through it. When a wave is generated in the tank, the crests and troughs of the wave show up as alternating bright and dark patches on the tank’s bottom. Like the play of brilliant, crisscrossing ripples at the bottom of a Texas creek or pool, the ripple tank replicates this scenario in a more controlled manner.
Young knew how waves behaved. He knew that a raindrop in a still pond sent out widening concentric rings of ripples. He knew that the ripples made by two raindrops near each other would run into each other, creating a new pattern at their intersection. Wherever two wave’s high points, or crests, cross, they would add together and create a taller bump in the waves. The waves would constructively interfere, amplifying each other. Another example of amplification happens when a boat creates a wake. When either the water or the ripple source is moving, like a rock in a stream or a boat on a lake, the circles of concentric waves stretch out into elliptical curves, bunching up the waves on one side, amplifying the ripples into one giant ripple or wake.
Deconstructive interference occurs wherever one wave’s high point, or crest, crosses the other’s low point, or trough, and they cancel each other out creating a flat place in the water. In a ripple tank, the pattern of this interference of waves became obvious in the plaid cross hatchings of light and shadow projections below–bright points where crests cross, neutral where they cancel out, and the dark shadows where troughs cross.
Young placed two oscillating points in the water. Imagine dipping two pencils in and out of the water at a consistent rate, so that they each send out continuous rings of waves. Observing the shadows below the table then reveals the interference pattern between these two wave patterns quite clearly. Young extrapolated from observing the interference pattern generated by water waves, that if light also traveled in waves it too should generate a similar interference pattern under the right conditions.
Knowing how water waves interfered with one another, Young set about to see if he could catch light acting like water. He set up a playground for light, like the water playground, to see how light would use it, to see if he could catch light behaving like a wave. He called it the double slit experiment. Instead of the ripple tank’s two oscillating wave makers he built a wall with two open passageways, on a very small scale. These small doors then could serve as the source points from which the light waves, if there were such a thing, could spread out like the waves in the ripple tank.
Young knew how particles ran through the obstacle course. They chose to go through either door with equal probability. It was a toss up which one they would choose. So if a group of particles went through the doors, about half would go through each door and they would end up in two separate groups on the other side of the wall. If light consisted of particles, then a screen set up behind the wall would catch two bright spots right behind the
Alternately, Young hypothesized that if light did indeed travel in waves, the light would go through the two slits and emanate out of each opening in broadening circles like ripples in a pond. Then the ripple’s interference pattern of amplification and nullification could be caught on a screen behind the slits as a fringe of dark and light spots.
If light was a particle, it should just show up in two bright spots directly behind the slits. If light was a wave, it should reveal the more complex fringe pattern.
Sure enough, instead of ending up on two even groups on the other side of the two doors like particles would have, light showed up very differently on the other side. Light revealed tantalizing fringe of bright and dark spots that belied the interference of waves, not the straightforward behavior of particles. In fact, the brightest spot appears not straight through either of the doors, but directly behind the wall that separates them, where one would expect all the shadow of the barrier to fall in the case of light particles.
Thus Young’s double slit experiment mounted the evidence for the wave nature of light. But, of course, the debate did not end there.
 Attributed to David Bohm
 Upon learning to swim under water, my niece, Kaelin, freshly turned 3, was spending a lot of time down there. When queried about what she saw under water, she described, “pirate’s treasure and silks!” After a moment’s reflection, I couldn’t help but agree. The ripples of light are flowing silks, and the sparkling stars of their intersection, the most precious gold.
This is an excerpt from my upcoming book “The Texture of Time”