Experiments in Light

This is a type of love story, between scientist and subject, between physicist and the laws of the universe.

I am nine years old in the computer lab of my public elementary school, and projected against the pull-down screen is a digital visualization of the Mandelbrot set, a famous example of the fractal. It is a set of complex numbers that satisfy a seemingly simple function and set of conditions, but when visualized in a 2D plane, a startling form reveals itself. Being fourth graders, we took to calling this shape, this miracle of mathematics, a “bug.”

Bug wasn’t quite right, but it came close to capturing the general silhouette of the thing, which consisted of, to the left, a medium-sized circle (the head), in perfect contact with a greater silhouette that looked as if someone had taken another circle, pinched a point on its opposite edge and pulled it in (the body, with a little butt). Surrounding this silhouette, rendered black in the visualizer, was a corona of color, depicting the values almost meeting the conditions of the set as they drifted farther from its boundary.

The fractal nature of the Mandelbrot set becomes clear when you investigate that boundary. It is studded by smaller circles stacked on circles, which in turn sprout wiry appendages like lightning. As we zoomed in, using the cursor to snap to a region of pixels, this boundary proved to be infinite. The closer we looked, the more elements of the pattern were repeated, the form of the bug materializing again and again in what had been only a handful of pixels at first. We didn’t need to be able to make heads or tails of the math itself. This demonstration transmitted to us nine-year-olds an intuitive grasp of the geometric definition of a fractal: recursive self-similarity, magnifying a thing to discover it contains itself, contains itself, contains itself.

Fractals aren’t typical in a fourth-grade curriculum, but every Friday, a handful of the top math students of our fourth-grade class were pulled out of arithmetic and given an hour’s sneak preview of advanced mathematics and physics, including the basics of special relativity, calculus, probability, and more. The intent wasn’t that we could really learn this material, but that the exposure would spark something in us.

We had begun that Friday’s lesson at our customary spot, a lunch table dragged into the hallway outside the cafeteria. The man showing us all this—not a teacher, just a local whose face I can’t recall except for how the light reflecting off the lenses of his wireframe glasses blotted out his eyes—had used one hand to prop his little whiteboard while the other guided in black marker the first fractal of the day, a fractal tree. He drew us a Y shape, followed by more Y shapes perpetuating off the tip of each branch, until finally he was hyphenating the tips of a canopy, fine and feathery. Next, he’d sketched a crude version of the Sierpinski triangle, first drawing a large triangle, then an inverted triangle within it connecting the midpoints of each side, coloring that internal triangle black like a hole punched out and leaving three smaller triangles at each vertex. He repeated that same, simple procedure within each of those three triangles, and then again, and again, telling us, if this procedure was continued infinitely, eventually the area of the whole shape would be zero, it would be just a spindle of boundary lines.

The final fractal of the lesson, the Mandelbrot set, required more than a marker and whiteboard, so we’d gone to the computer lab, just us four, to explore its impossible topography together. I remember putting my palm on the pull-down screen’s plastic coat, the pattern of the Mandelbrot set texturing over the skin of my hand, its infinite boundary absorbing me too.

It felt like an invitation.

I consider myself lucky to have experienced mathematics and physics not only as theories, but in ways I could actually touch. I spent years trying to bring the theory of quantum mechanics into the living world, to loosen the barrier between knowledge and something more visceral. I wanted to retune my understanding of the principles underlying reality and inhabit, in the words of a friend and mentor, a quantum intuition.

In all this, I think I had one perfect moment of contact with the otherwise abstract armature of mathematical theory that governs our universe. Something that surrounds us even when we don’t see it, can’t understand it.

About ten years after that first introduction to fractals in an elementary school’s computer lab, I met someone who would bring me into much closer communion with a quantum universe. During my freshman orientation week of college, I stopped by the open house of the physics department in Wilder Hall, a staunch brick building crawled over with ivy, east of the library. The walls of its lobby were warrened by mail slots reserved for rolled-up exams and problem sets. Its black stone steps were shiny and sagging in the middle from a century of dragged feet.

The open house was on the third floor, in a small atrium with skylights. A few computers lined the edge of the room; whiteboards wriggled with Greek symbols and hasty sketches. A few dozen freshmen wandered among the physics professors and grad students. I remember mini muffins and tortilla chips. I don’t know how I got directed to Kevin, a new professor who was recruiting students to help get his lab off the ground. I’d spent the summer interning at a commercial lab in ultracold atomic physics, the same field as the work he intended to start here. I had barely handled their experiments directly, writing white papers for funding opportunities instead, but that didn’t seem to matter. He was excited to know that I had any familiarity with it at all. He was friendly but very serious, and pale in the way a lot of the physics faculty were, suggesting the hours they spent in sealed laboratories or troubleshooting on a chalkboard. For most of that summer internship, I worked outside those rooms, not in them, and it may not sound appealing, but right then being back in the lab was exactly what I wanted most.

I was just eighteen, eager to prove to myself that I belonged in a space like this, and I resolved not to let the opportunity pass. Within the first few weeks of the term, we’d found an appropriate scholarship and applied for the funding he needed to bring me on the next quarter. I started reading papers and attending weekly lab meetings with his grad student as a way to prepare.

The Wilder physics building had an auspicious history for Kevin’s research. In 1901, just a floor above his assigned lab, Ernest Fox Nichols and Gordon Ferrie Hull aimed a light at a pair of extremely delicate mirrors dangling from a quartz fiber in a vacuum. The mirrors functioned like a weather vane designed to capture light, not wind. (It’s best to think of light as a particle to understand how this happens—the surface of the mirror peppered by the blows of tiny, massless balls, and “reflection” simply a way of describing all those tiny balls bouncing off the mirror’s face.) When Hull and Nichols shone light on it, briefly, the vane twisted ever so slightly, a faint application of torque.

Thus the pressure of light was observed for the first time. Light as an instrument to manipulate the physical world. A hundred years later, in one of Wilder’s basement labs not much fancier than a brick hole tunneled out of New Hampshire granite, we were proceeding with new experiments with light, in the field of ultracold atomic physics. Kevin’s goal was to bring a small sample of atoms to within some billionths of a degree Kelvin of absolute zero—negative 273 degrees Celsius. When matter is cooled to near absolute zero, quantum effects, otherwise difficult to observe and maintain, can become stable and manifest at the “macroscopic” level, meaning even the human eye can perceive them. The first time this was done was in 1995 by Eric Cornell and Carl Wieman. In their experiment, ultracold rubidium atoms entered a fifth state of matter—beyond solid, liquid, gas, and plasma—called a Bose-Einstein Condensate, or BEC. This work won them a Nobel Prize in 2001.

The primary instrument used to make matter this cold is laser cooling. In laser cooling, light is used to exert pressure on atoms in order to slow them down. What we think of as temperature is thermal energy, and at the atomic level, that energy is kinetic, defined by the atom’s movement. With enough pressure, atoms can become so slow that they almost stop moving entirely, suspended as if in a thick “optical molasses” with just a low vibrational brrr of energy. These laser-cooled atoms are now at a temperature that is micro-Kelvins—millionths of a degree Kelvin—of absolute zero and are the first critical step to achieving a BEC.

This corner of physics I fell in love with isn’t known for its elegance. It’s mostly gnarly. The name itself—condensed-matter physics, the physics of many atoms close together interacting in complex systems—evades poetry. It is, after all, a mash-up of quantum mechanics, electromagnetism, and statistical mechanics, sometimes with a splash of particle physics, material science, and nuclear physics in the mix. And yet I loved its ugliness.

I loved how much work it was. In this field, it typically takes years for a new lab to begin producing novel research. There’s just so much infrastructure needed to catch up to the state of experimental physics. In 2014, when I joined, Kevin’s lab was already a year into its attempt to replicate Cornell and Wieman’s work of getting ultracold atoms to achieve a state of BEC. That was just step one, the foundation that would enable research into other hypothesized possibilities of condensed-matter physics.

Much of that first year had been spent on perfecting environmental necessities. The basement had been a deliberate choice. The bedrock muffled structural vibrations, whether due to students thundering out of class or just the natural stretching, shrinking, sighing of the old building. Kevin had set up a backup generator, so a power outage in a summer thunderstorm couldn’t annihilate all progress; HVAC to regulate temperature and humidity, since the laser-optic system could drift out of alignment with a fluctuation of just a few degrees. He altered the plumbing, too, to pump water into the lab that could be snaked around components in clear plastic tubes, cooling them.

After I was approved as a new researcher, I could enter the lab with a beep of my keycard. First was an anteroom, with a small workbench for electronics and an exposed array of pipes. The equipment we’d inherited but hadn’t yet cleaned sat in a pile along the left wall. There were only three of us then—Kevin, a graduate student named Sam, and me, the college freshman— each of us with our own lab shoes—special white Crocs—which we’d slip on before pausing in front of a second locked door, which led into the lab proper, to stamp a few times on a sticky doormat to remove any particulates from their soles. We’d punch in a security code, and the door would exhale with a wheeze, breaking the seal of the atmosphere inside.

The lab itself held several massive specialty tables, each covered in a tight grid of mounting screw holes so components could be attached to them in any required configuration. These optical benches, which we called floating tables, weighed several hundred pounds, but had hydraulic systems to levitate their steel tops and isolate the sensitive optical equipment from being jittered by small vibrations, like your footsteps passing by. Still, if you found yourself leaning on one corner to do your work, that corner would sag. Release, and the legs would sigh as they pumped the table level again. These tables would serve as the base of the experiment. Above them in hanging racks were stacked behemoths of instrumentation, including oscilloscopes, power supplies, and precision-control devices: a swath of gray and beige boxy faces and snarling wires.

Our goal that first year was to laser cool a trapped sample of rubidium atoms within micro-Kelvins of absolute zero, a technique called a Magneto-Optical Trap, which is a stepping stone to producing a BEC. Kevin had already acquired much of the needed equipment—a laser with a diode that would produce light near the needed frequency; parts for an ultrahigh vacuum chamber, in which the atoms, morphed into a diffuse gas, would be held; magnetic coils, which would produce the magnetic field needed for the trap; and numerous optical components, such as the lenses and mirrors and crystals we needed to calibrate the properties of the laser’s beam.

The single most relevant property to the experiment was the light’s frequency. Light interacts with individual atoms only at specific frequencies corresponding to atomic transitions—that is, the energy required to excite an electron from one orbital of the atom up into another (the s, p, d, f orbitals you learn about in chemistry). When the right frequency of light meets an atom, the atom absorbs a photon as a discrete packet of energy. In absorbing the photon, the atom also absorbs its momentum—it takes an impact—which is what we were counting on to slow it down.

My first job was to build a portable laser-optic system that would lock the laser’s diode to the correct frequency. Portable, as in it would sit on a two-foot-by-two-foot optical bench that we could haul from table to table. A laser diode emits light across a small range of frequencies, and we had to lock it to just the right one. As my point of reference, I had a clear glass tube spattered with a sample of rubidium, which I vaporized by wrapping the tube in heating pads.

I spent years trying to bring the theory of quantum mechanics into the living world, to loosen the barrier between knowledge and something more visceral. I wanted to retune my understanding of the principles underlying reality and inhabit a quantum intuition.

The goal was eventually to pass the laser through the vaporized rubidium in the tube and see absorption. Sweeping the power input of the laser diode, like you’d twist a dial to find the right radio station, would ever so slightly modify the frequency of the light produced. When the cloud of rubidium in the tube began to glow, that meant light was being absorbed, and we’d landed on the right frequency for the full experiment.

Before that could happen, however, because of other variables I needed to control for—properties like polarization, collimation, the width of the beam, etc.—the laser’s light had to traverse a jungle of optical components, those lenses and mirrors and crystals all on optical mounts with three knobs each to adjust them finely. Only when the beam was properly prepared, in all its properties, would I see the glow. This proved to be the step that took me the most time to get right.

The fluorescence of the laser was weak, meaning the detectors would be disturbed by any outside light, so I had to work in the dark. With the lights off, the basement was the blackest of blacks. (Kevin strung white Christmas lights along the shelving racks to glimmer onto the big tables and obstacles, so we had just enough light to avoid knocking anything over.) In that darkness, I only had two ways to perceive the beam: one, a little laminate card that would illuminate with a pale red dot if crossing the laser’s path; the other, a clunky infrared viewer with a trigger I had to repeatedly pump to activate.

Here is how I passed long, quiet hours: I held the viewer up to one eye, closed the other, and squeezed the trigger. Suddenly, the world was outlined in a faint, shimmering green, in which the laser formed a brilliant starburst. Squinting down the viewer, I perched one free hand on a knob, twisted slowly, and tracked a vivid green speck drifting millimeter by millimeter across the face of the next mirror.

I’d do my work in the mornings most days of the week for a few hours at a time, almost always alone in the lab. For me, it became a world within the world. In privacy, I played music over the speakers, and it boomed in my enclosed cave. I was constantly, embarrassingly talking to myself, pep talks, shit talks, cursing loudly when I couldn’t get it right—sometimes dancing when I did.

I slipped out of time, trying to let the things I worried about as a freshman student and a young woman reel away, like running the line of a kite through my fingers: poor grades on papers; hangovers and half-remembered embarrassments; meh dates the guy told our mutual friends about, while I was privately coming to terms with the fact I had no attraction toward men at all. The time a creepy junior in my class cold-emailed me: “what’s your ethnicity? you look so exotic ;).” Meanwhile, I was trying to balance athletics with lab work and coursework, which I eventually learned was a mistake. The day I quit crew, to the shock of my coach and teammates, I slunk toward Wilder, beeped in, shut the two doors behind me, and turned off the lights so I could cry in the corner, out of sight.

I found solace in the work, and much more. When I was in the lab, I could be pure math, or pure science, or pure light. My mind was often bursting from the latest proofs and problem sets, readings, lab work, presentations of guest lecturers, conversations with other students and professors—and all those other worlds bled into this dark room with me.

It happened that as I began quantum experimentation, I was also reading and writing about Jorge Luis Borges. Bent over as I manipulated the branching, circuitous path of the laser’s beam, I could picture “un laberinto de laberintos, en un sinuoso laberinto creciente que abarcara el pasado y el porvenir y que implicara de algún modo los astros” (a labyrinth of labyrinths, a sinuous, growing labyrinth that encompassed the past and the future, and in some way implicated the stars).

I treasured “The Garden of Forking Paths,” reading it back and forth between English and Spanish. I loved the way in which the protagonist’s mind unfolds, how the veil of reality peels apart like petals, and something glorious, lurking just beyond sight, is revealed. An instant of clarity and connection with a manifold universe.

In Borges’s envisioned garden, the path through time constantly bifurcates. Two paths become four, becoming eight, and so on—a vision remarkably similar to the fractal tree, with its infinitely self-similar Y-shaped branches. Despite the title’s emphasis on bifurcation, the parameters of Borges’s garden sound to me a little wilder. Take the same concept—fractal branches that split in a consistent, repeatable way—and make it three branches, not two, or make it so that the angle widens or twists with each subsequent layer, and what you eventually get is not a tree, but indeed more like a multidimensional labyrinth, organic and writhing, or like a city map written in coral growths. The paths multiply, fanning out from their origin. They soften, become sinuous, and effect a slow, spreading curve, bending even onto themselves.

This labyrinth encompasses the past and future and reaches even the stars, scooping them into its grasp. But more than that, it swallows all pasts and all futures, all destinies and possibilities unknown and unreached. It made sense to imagine it as a living thing, yes, exactly a garden. I would imagine it iridescent green and silently growing in the dark, carpeting the optical bench before me. We are all within the garden, even when we can’t perceive it.

It took me weeks to get every optical component into place. Meanwhile, Wilder Hall’s ivy turned flaming red, then the leaves died on the vine, shriveled, and dropped. The first snow swamped the steps and swallowed the bench on the lawn.

Sometimes, the beam would become misaligned, and everything I did only seemed to make it worse. While I had a definitional, textbook understanding of optics, in practice my physical instincts were bad, so I often magnified my own mistakes. And when something upstream was off, everything downstream would be dysfunctional. I had to start fresh multiple times because the particular components I’d sequenced together offered me too little wiggle room to align the beam, or—and this was even more infuriating—I’d somehow left out a pivotal step. When this happened, I’d unbolt all the optical mounts, inventorying them across the table, and sketch a new design, keeping what had worked, shedding what hadn’t. I’d look across the army of mounts—shiny mirrors, chunks of crystals, delicate lenses—and feel exhausted.

This was an iterative process, I’d remind myself, something Kevin said often. You try again and again, and you’re wrong again and again, but each time, it circles a bit closer to just right.

I was learning that science is grueling. That’s true for experimentation, and certainly true for theory. But maybe anything is grueling, when done seriously enough. I tried not to bother Kevin too much, but sometimes after getting stuck or frustrated, I’d head upstairs from the lab to see if he was in and ask for advice. His dog, a big black lab named Wolfgang, often lay panting in the corner. Wolfgang was an immediate de-stressor. I’d bury my hands in the thick folds of his neck, then reach up for a scratch behind the ears.

During my visits, Kevin could validate my frustrations and steer me toward smarter methods. He could also remind me of the broader tapestry of fundamental physics: where we were, why it mattered, what worlds of theory unknown to me our research could touch. And often, he instructed me in developing a “quantum intuition.” He meant that this work, theoretical and practical, would become easier as I internalized the theory.

Quantum mechanics is infamously nonintuitive, but what it really amounts to is that it’s misaligned with the embodied experiences we have moving about the world. Classical physics is rich with human experience. At some point long before any formal instruction of how it works, we all begin to intuit the parabola of a thrown object or the angles that pool balls chart as they collide and ricochet across a table. Even electromagnetism can be physically intuited: the sight of hair standing on end when zapped with electric current; or the magic of magnets, aligned north-north, chasing each other across the table, or, aligned north-south, snapping together.

To adopt a quantum intuition, many things you take for granted have to be unlearned. This meant that the world I knew had to be relegated to a particular regime, the macroscopic. I had to accept that, when I looked closer, things got weirder: Objects are better described as having probabilities instead of fixed, core properties. It would no longer be appropriate to say a ball (a very small, quantum-scale ball) is simply “red.” It may instead have one-half probability of being red and one-half of being green. That probability is a meaningful description of the ball. In assessing how the quantum ball interacts with the world around it, you have to take into account both probabilistic variants, even though you know, when you eventually measure the ball, only a single color will be observed. Measurement, in quantum mechanics, “destroys” a quantum state, collapsing those probabilities into a single value.

This is an unsettling proposition, and the consequences ripple outward into more quantum weirdness. But it’s worth noting that these statements actually look plainer, more approachable, in the language of mathematics. Building upon them, math will still obey its accepted laws and logic and progress toward new descriptions of systems, toward new principles of movement and force and energy. If only I could accept these foundations and align myself to a mathematical way of thinking, I could cultivate that quantum intuition through each day’s proof, problem, or experiment. The definitions I held dear—my intrinsic understandings of light, matter, and energy—would shift from classical to quantum.

This was hard work. An iterative process of learning and unlearning, not unlike how I built and unbuilt the laser-optic system. But with trust and patience, I could come to see myself as a part of that quantum world. And sure enough, by the end of winter, my intuitive understanding of our work was growing. I had finished the laser-optic system. We could reliably switch on the laser, allow its diode to thermally stabilize, and then sweep it till it locked onto the rubidium transition we needed, a pale-green glow in the infrared viewer’s window.

As the spring thaw loosened the ice and snow and the fields turned to mud, we began to work together down in the lab. Two sets of hands were required for the next part. We started on the construction of the vacuum chamber: a hulking steel apparatus that hovered like a 1950s UFO on posts bolted to the table. This was where we’d isolate an experimental sample of rubidium atoms in an ultrahigh vacuum—at less than a billionth the pressure of the atmosphere (at sea level). It had round glass windows for laser beams to shoot through and skinny viewports like spikes at off-angles. Its flanges, when not sealed by a gasket, we’d net in aluminum foil, rendering it something like a monstrous kitchen appliance.

We spent hours bolting it together, each of us taking turns awkwardly twisting around the chamber to reach every screw needed for every gasket, hands and wrists getting sore, clanging our elbows into the awful steel of both chamber and optical bench. We then filled the chamber with nitrogen, a neutral gas, and hunted for leaks, finding the spots where a flange hadn’t sunk its teeth in properly to a gasket. We hooked up a bulky, articulated vacuum to initiate the pump-down. Finally, we turned it into an oven, wrapping the chamber in super heating pads, raising its temperature to 400 degrees Celsius, which caused the metal to exhale any lingering dissolved gases or impurities.

For days, it sat baking, looming over the table, radiating intense heat. At first, the pressure sensor registered a rise in Pascals, the result of the out-gassing metal. Then it plunged, the reading dropping closer and closer to true emptiness, nothingness, the last pin-balling atoms extracted. The chamber was now ready to host the experiment.

One of the core concepts of quantum mechanics is superposition, that curious state of suspended probabilities: The cat is both dead and alive until the box is opened.

Schrödinger himself called the thought experiment “ridiculous,” but for that very reason, it still bears repeating. A cat is in a steel chamber, with a sample of a radioactive substance in a Geiger counter. If the radioactive substance decays, which is a probabilistic event—it may happen in this timeframe, it may not, we don’t know—the counter will register it and trigger a mechanism that breaks open a vial of acid, killing the cat. The cat’s life or death is therefore bound to the unknown quantum state of the radioactive particles; that is, the state of the cat is mixed or “blurred” while we imagine which outcome is true. We leave the cat for an hour and return, stand over the box, key in hand. In the act of opening, do we express some sort of power over the suspended fate of the cat?

There are two vital ideas embedded in that story. First, that before observation and measurement intercedes, the object exists in a probabilistic state. Quantum mechanics regularly asks us to accept superposition at a level of a particle—that an isolated particle, for example, is in a state of superposition that is neither “spin-up” or “spin-down” but a probabilistic mix of both. You express the state of this particle in an equation of probability amplitudes called a wave function, which you must use in all subsequent calculations around that particle.

The wave function is foundational to the theory, but it’s still a matter of debate how to interpret what it means in a physical sense. An isolated particle is abstract to think about. That makes the abstraction of the wave function seem more palatable; you just move on and do the math.

Schrödinger’s thought experiment is meant to challenge that palatability by stretching the concept of superposition into the realm of the macroscopic, the objects and other beings we interact with in everyday life.

He wants us to respond: It’s one thing to say a particle is mixed between two states, but isn’t it ludicrous to imagine that a cat is somehow alive and dead at the same time? So, what do we think is really going on inside the box?

We don’t exist in a soup of probabilities. We each carve a narrow path through the breadth of the possible—the sum of all choices we’ve made and all that were made for us.

This raises a second question about the fundamentals of quantum mechanics: Observation brings about a “collapse” of those probabilities into a single measured value (we know experimentally there would always only just one cat, alive or dead, when the box opens). Collapse is also instantaneous, which seems to violate the speed of light being the absolute maximum that anything, including information, can travel. So what exactly is this collapse? Why does it happen? Here, the theory stops short.

We used to think the universe was deterministic. That’s Newtonian, classical physics. Things either are or aren’t. If you know the exact details of how a ball is traveling across a pool table—its mass, velocity, the sideways spin it picked up off the cue tip—you can know everything about where it will go. If the universe is just a bunch of pool balls, we should be able to map out all their trajectories forward and backward in time. A universe as predictable (and dull) as clockwork.

Instead, quantum mechanics proposes a probabilistic universe, flush with the capability to surprise. Einstein struggled a lot with the theory, writing that quantum theorists “simply do not see what sort of risky game they are playing with reality.” He thought the indeterminacy of quantum mechanics was a sign, not that the universe itself was fundamentally ruled by probability and chance, but that the theory was built on bad foundations.

Despite its early controversies, many predictions of quantum mechanics have been verified experimentally in diverse and increasingly complex ways for decades. We have observed that the classically impossible does happen in the regime of the very small. In one class in college, when my attention was waning, a professor called me out. He labeled a particle with my initials, SBK, and gave it an estimate of my mass in kilograms, and then calculated at a given kinetic energy the likelihood I could spontaneously “tunnel” (blip) through a brick wall and emerge out the other side (answer: miniscule but not zero). Electrons, being both very small and energetic, can tunnel through a barrier much more easily, allowing us to measure a classically impossible “tunneling current.” 

How to interpret the mathematical architecture of quantum mechanics into a physical understanding of the universe is unresolved. Multiple interpretations have been proposed but have not led physicists to directly testable hypotheses, so they remain neither verified nor disproven, suspended between states themselves.

I was taught, by and large, the Copenhagen interpretation of quantum mechanics. Schrödinger’s cat, it would attest, is less about an undead cat, and more about the imprecision of outsider knowledge and measurement of the system within the box.

As Schrödinger put it: “There is a difference between a shaky or out-of-focus photograph and a snapshot of clouds and fog banks.” In the Copenhagen interpretation, we don’t have to accept that the cat is actually alive and dead at the same time, some unfathomable, amorphous cloud of fur. Instead, our snapshot of the cat is “blurry” only because it is out of focus. The fact we cannot make precise measurements within the box is important and has profound and unintuitive consequences, but there’s no need to feel so queasy about the fundamental nature of reality.

In other words, the Copenhagen interpretation tells us: Go ahead. You’re not playing a game with reality today. Run your experiment.

In the final weeks of that year, we split the laser’s beam into six and shot them through the viewports of the three primary axes of the vacuum chamber, so that the beams would intersect at the chamber’s heart. A fresh sample of rubidium was enclosed in a sub-
chamber, which we heated until it flowed as a diffuse gas out into the main body. We positioned two massive coils of copper wire above and below the hulking steel chamber, then sent electric current in opposite directions through them, so they produced an anti-Helmholtz magnetic field that zeroed out exactly where the laser’s beams also met.

When everything was in alignment, the laser’s photons were absorbed by the rubidium’s atoms, slowing them down into an optical molasses. The magnetic field interacted with the individual magnetic fields of the atoms, and the laser provided a push, urging the atoms to ball up in the heart of the chamber, where the field was zero and the laser’s beams coincided. The final result was a spherical cloud of rubidium cooled to within millionths of a degree Kelvin of absolute zero, a rubidium Magneto-Optical Trap.

In the greater story of the lab, this is a small moment, a footnote on the journey to the real research. It isn’t that for me. I feel like I’m supposed to model a dispassionate, rational mind. Pretend my heart wasn’t somehow entangled with that cubic centimeter of deepest chill. Pretend the thought of its nothingness was not an intoxicating thrill. This is science, not magic, but there were goosebumps on my arms. In the dark of the lab, with only the white Christmas lights strung above, I remember leaning in.

Within the viewport, centered in the shimmering steel chamber, it floats: a hazy reddish bruise of light, almost spectral, a spirit captured from an alternate dimension.

I never fell out of love with physics, not really. I just felt a gradual sinking, an acclimation almost, the isothermic relaxation of an adiabatic process. My life would be less dedicated to science, and more compelled toward its cousin, this thing called art. The love is still there, but on some days, it feels more like an old wound. I have forgotten so much of what I used to know, of what I used to be able to do. The understanding I’d tried to develop into intuition has drained out of me. I remember the shape of that knowledge, but not its content.

In moments like these, I remind myself we don’t exist in a soup of probabilities. We each carve a narrow path through the breadth of the possible—the sum of all choices we’ve made and all that were made for us.

The Copenhagen interpretation of quantum mechanics, after all, is only one of many. It is one of the most conservative, because it glosses over much of what makes quantum mechanics unsettling. What happens if you make a different choice? Leave the Copenhagen interpretation behind and accept, at face value, a simple assertion: The wave function is ontologically real. The camera is not out of focus. Instead, a cat really can be alive and dead at the same time. What, then, happens when you open the box? 

I no longer sleep well. Anxiety reared its head in my early twenties, and now hangs around even when things are otherwise going great. I fall asleep easily but in the middle of the night, somewhere between one and four in the morning, I’ll wake up, alert and fully myself and un-tired. Forced to linger, if I’m not careful in how I steer my thoughts, I’ll sift through the tendrils of dreams and dream-logic until I arrive in a state of pure, straightforward dread, imagining instead the Many Worlds Interpretation of quantum mechanics. At the moment the box opens, the universe splits in two, one world where the cat is alive, one world where it is dead.

I’ll wonder if I’m really here, wherever here is. I’ll feel all the other versions of myself sharing the bed with me. One of them didn’t just wake up; she turned over on her side, kicked a leg out from the blanket, and snoozed on. Another is sitting up, tapping an alarm silent on her phone. These versions curl over and sprawl across a variety of sheets—flannel or cotton, blue or white or gray, tattered and torn or brand new. Some of these versions sleep in cities or countries far away. Some are in a bed alone, or with a dog instead of my cat weighing down my shins—or it’s a different cat, or a different partner. Some versions are dead, moldering under the earth. Some never lived, the accident of my birth averted. For some untold, unfathomable number, their Earth resides outside the Goldilocks zone, and is scorched, barren, and an acid rain falls on its pitted surface.

When I have that dizzying thought, the material of my body alchemizes into finely spun glass. Tap me with a tuning fork and I’ll shatter. That’s how fragile our existence is, in the here and now. Fear shreds the sheets apart. It is easy to imagine falling into an abyss of time.

My mother’s mother had very few prized material objects. She and her husband lived a lean and neat life, rarely permitting clutter. As she began to fear death, she started culling her possessions even further, sorting and throwing out what she could, but in a glass cabinet in the dining room, among a few delicate pieces of porcelain and a collection of hand-painted Russian eggs, she kept a handful of matryoshke, those Russian dolls that you open by splitting them in half, within which you find another doll, who also splits in half, and you go deeper and deeper, each time thinking this will be the last (surely they can’t get any smaller), until finally there’s just a little painted nub at the heart with a round oval of a face and gleaming cartoon eyes. My fingers bluntly try to tease it apart just one more time. Please don’t let it end.

I, myself—the macroscopic, human-scale body and brain and tongue and hand that I am—am not an object directly ruled by quantum mechanics. None of us is. We are not about to phase through our seats and fall out the floor. We are not entangled with other people no matter how much we love them, a hidden state inside our souls switching at the exact instant a change comes over theirs. But sometimes, I allow myself to believe I am a probabilistic creature, best described by an evolving, imperceptible wave function, careening in full simultaneity down a chain of cascading pathways, equally real across every version of conceivable events.

You could call this a spasm of regret in the life of a could-have-been physicist. Or you could call it a fading quantum intuition, an impression left by brief contact with an indeterminate universe. Call it a silly fantasy, Hollywood schlock. Sometimes, late at night, those mathematical laws resurface with the half-remembered quality of a dream, reminding me of all that lies beyond what my embodied self can access, and I just call it a gift.