To keep time, you must first invent it.

1. Flicker—A piacere

Time travels in divers paces with divers persons. I’ll tell you who Time ambles withal, who Time trots withal, who Time gallops withal and who he stands still withal.
—William Shakespeare, As You Like It, III.ii.

In the cloud forests of Paek Sigma II, the inhabitants do not keep time, but stretch and slice it.

The first humans who arrived on the planet were amazed by the fauna. There’s the stone-armored petradrakon, draped in twenty thousand scales each a meter across, who lays a clutch of eggs only once every one thousand and nine times Paek Sigma II has revolved around its prime sun. There’s the glass-winged slisli fly, whose two-phased life cycle, alternating between koniphyte and nephophyte generations, lasts a brilliant seventy seconds, the average duration it takes for the living silicon snowflakes to drift from the mist-shrouded canopy to the sulfur-infused earth. There’s the deep-sea abyssal bynaasaa, who slithers no more than a centimeter in a century. There’s the red-shafted needlebeak, whose erratic, darting flight, changing direction a hundred times a second, can make a single mating pair appear to be a whole swarm to the novice observer.

On no other planet has life evolved to occupy so many timescales and niches all at once. It is a temporal Galápagos, a Mendelian garden of crisscrossing timelines.

Are they sentient? Does the petradrakon make long-lasting landscape art with the aid of erosion? Does the needlebeak compose poetry with an alphabet of movements too quick for us to parse? Does the bynaasaa leave books behind in its lightless trail, which millions of generations of slisli nephomorph larvae can read in due course when the ocean has turned into mountains?

While the question of whether the nature of the universe is continuous or discrete remains hotly debated, there is sufficient consensus that consciousness doesn’t so much flow like a smooth river as leap forward from moment to moment, a glistening frog atop a drifting lily pad.

The biological circuitry of cognition, of the machinery of life, is full of discrete steps and sinusoidal waves, alternating peaks and troughs imposed by unbending physics. Spiking neurons have refractory periods; ion channels open and close like pumping gates; neurochemical concentrations require the passage of time to change as well as to stabilize.

And so life proceeds by jerks, twitches, bounces, quivers, though we pretend otherwise. As you gaze across a vista, to give the photoreceptors in your retina the conditions to yield a steady signal and to minimize the amount of signal processing by the visual pathways, your eyes don’t glide over the visual field but hop across it in rapid saccades, leaving the brain’s visual system the task of stitching the series of flickering, fixed retinal images into one continuous, fluid scene. As you stride along, you speed up and slow down, fall toward the ground and catch yourself, teeter to one side and then totter to the other, each step a complex series of three-dimensional coordinate transformations conducted in jerky segments—nevertheless, what you perceive is only smooth, forward progress, a continuous illusion integrated from the ticktock of the body’s million billion distinct pulsing, beating, pumping, swinging, oscillating clocks.

Blending the discrete into the continuous is the glamor that brings the world as we sense it into being. Vibrations—updownupdownupdown—fuse into notes; flickers—nowyouseeit nowyoudon’t—meld into persistence of vision. Without it, we would have no motion pictures, no screens, no virtual reality, no scripted deep dreams—you never notice the ticking clock cycles that power the artificial silicon and germanium brains that give us so many simulated worlds, do you?

The smaller the flickers in our perception, the more details we notice and the longer time seems to last. So why don’t we simply slice time into the finest slivers possible, live life at the highest resolution?

There is a cost, as it turns out, to dividing time into ever-finer fractions of a second. To use a not-entirely inaccurate metaphor, the faster the frame rate of perception, the more it costs metabolically. A year seems to last so much longer for growing children, it is said, at least in part because their consciousness is processing reality faster than the slowing chronoperceptors of their aged parents—they literally experience more of the stream of time.

To the lumbering petradrakon, we are but lightning flashes, our entire life arc summed up at most with a single quadratic approximation. We burn our candle at both ends; no wonder we are born and die before the petradrakon has completed even one thought.

To the fluttering needlebeak, on the other hand, we are akin to ungainly giants trapped in viscous sap, awkward mannequins on a stop-motion set, flip books in the hands of a novice user—hours pass before we change from one pose to another, our minds as alien as the carbon dioxide glaciers on the horizon. We may live their eons, but at the expense of a metabolic frugality that makes our life dim, dull, a mere stone skipping over the river of existence, missing all the fun.

Little wonder then, that the settlers of Paek Sigma II began to look for new ways to inhabit the stream of time. Slow down or speed up—altering the metabolic clock is the only way to meet the inhabitants of the planet in their own temporal realms.

Cytonanites injected into the body build a new network of semiconducting neural sheaths; RNA lexical closures rewrite the human genome to adopt new metabolic pathways; ion pumps and protein-etched integrated circuits alter and upgrade the neuroelectronics of consciousness signal processing; blood vessel walls are strengthened with carbon nanotubes; muscles are replaced with fast-acting memory polymers; bones are converted to composite metamaterials; blood is supplanted with cellular nanomanufactories . . .

To give observers an easy way of knowing the new temporal realm they’ve moved into, each tachynaut wears an indicator device on their wrist. While these appear, superficially, like the products of haute horlogerie, closer examination reveals a key difference: instead of a harmonic oscillator in the form of a balance wheel and hairspring or a magnetic pendulum, the escapement of the “watch” is driven by a pressure plate against the inside of the wearer’s wrist, converting each pulse of the radial artery into a swing of the pallet fork. Instead of measuring the passage of seconds, the hands of the watch advance to the pace of the wearer’s heart. The faster the heart beats, the faster the hands swing around the dial.

Tachynauts literally live at different speeds from the rest of us.

Some now see the world as a darting needlebeak does: a summer in an hour, a lifetime in a day. Their heart beats so fast that it no longer sounds like a flutter, but a single note. Though they will not live to see the sun rise again, some speculate that, because they slice time so finely, they are closer to the fundamental quantum vibration of the universe. Thus, they derive more joy, sorrow, rage, surprise, and empathy from each second than most of us can experience in a lifetime.

Others, ambassadors to the petradrakon, skip over Heraclitus’ River in long, graceful arcs. To the rest of humanity, they seem to live in a perpetual state of slumber, barely distinguishable from statues, each breath spanning days, each heartbeat a somber larghissimo pianto. With such slow clocks of consciousness, they’ll likely outlive the rise and fall of would-be galactic empires, perhaps even witness the end of our species. Years are experienced in a single second; the flickering alternation of day and night fuses into a single perpetual twilight. We may think that such a life of languor, like mortally immortal Tithonus, to be not worth living, but perhaps to them, we seem like carping mayflies, lacking all sense of the scale of the divine clockwork.

All this, of course, remains conjecture. None of the explorers of other scales of time have ever returned. The modifications required to become a tachynaut are so extensive that they are irreversible. But one can’t help but wonder that even if they could return, they wouldn’t. Perhaps they find their new temporal existence much more interesting than their native realm. Or perhaps they, new converts to Marvellian metaphysics, are reluctant to inform us that lightning fast or vegetal slow, we would never have world enough, nor time.

2. Dharma—Andante con moto

We knew the world would not be the same. A few people laughed, a few people cried, most people were silent.
—J. Robert Oppenheimer

On the far side of the Moon—the one that orbits old Earth—close to the south pole, there is a large and ancient double-ringed crater, almost worn flat, called Apollo. Not named after the Greek god; not exactly. Rather, it was named to honor NASA’s Apollo program, and so the smaller, newer craters inside were given the names of astronauts and scientists who worked on the Apollo program and other NASA projects, including some who gave their lives to realize our dream of becoming a spacefaring species.

Just beyond the western rim of Apollo is another crater, rounder as well as more modest, with multiple smaller craters nestled inside its rim. This one is named after J. Robert Oppenheimer, who surely changed the world as much as the Apollo astronauts.

In this crater can be found one of the most renowned timepieces in all three hundred and sixty-eight settled planets: the End Watch, which, according to one popular interpretation of its name, counts down toward the final moment of the universe.

With such a grandiose claim, it’s natural to expect monumental construction. Certainly humanity does not lack colossal timepieces. There’s Sigetin’s “Ring of Victory,” built soon after the Third Restoration, consisting of sixty-five minor planets dragged into the same inner orbit near the system’s sun so that a different planet would transit across the solar disc for every month of the restored calendar that the revolutionaries had abolished. There’s Anyanwu’s “Progress,” consisting of a one hundred and fifty-kilometer-diameter whirling space radio beacon designed to precisely double the signals from the strongest known pulsar, PSR B0329+54, thereby commemorating the new government’s commitment to science and discovery. Every new government, revolutionary or reactionary, that comes into power seems compelled to construct something with no purpose other than to proclaim its own dominion over time, spiritual successors to the Great Pyramid or the Washington Monument, asserting an exception to the cycling tides of history, which sees power ebb as soon as it has crested a peak.

At first glance, the End Watch seems to belong to the same class as these. Viewed from a lunar cruise liner floating a few hundred kilometers above the surface, the Apollo-Oppenheimer-Leibnitz complex of craters, with their congeries of inner craters and interlocking rims, eclipsing perimeters and meshing peaks, spiraling ejecta trails and secondary impact chains, resembles nothing so much as a gargantuan version of the movements of mechanical watches, or perhaps a celestial embodiment of the Antikythera orrery. A tourist daydreaming on the lido deck, waiting for her turn to dive through the zero-g pool suspended like a giant bubble at the side of the ship, may well be forgiven for imagining the End Watch, housed somewhere below among those mountainous gears and regolithic epicycles, as some marvel of engineering, perhaps an atomic chronograph built from exotic transoganesson atoms from the island of stability entangled in a precise quantum quadrille, each step a perfect expression of the order in the very fabric of the cosmos, or perhaps a mechanical wonder constructed by a master Swiss watchmaker from diamonds and buckyballs and star metals and alchemical humors, with a googol nanogears packed into a single caliber, but in any event counting out the billions upon trillions upon duotrigintillions of seconds toward the great rip, crunch, chill, bounce, a memorial to humankind’s genius and hubris alike, a defiant rage and rave at the dying of the light.

The passenger would be very disappointed to find out that the End Watch is nothing more than a narrow, two-kilometer tunnel dug into the lunar bedrock at the center of Oppenheimer, its entrance marked by a fifteen-meter gnomon that pokes above the regolith, casting a slow-roving shadow that completes one cycle every 29.53 Earth days. Opening off the tunnel is a series of chambers, each stacked from floor to ceiling with boxes of palm-sized silicon discs with finely etched surfaces. Despite their similarity to classical integrated circuits, a closer examination reveals these discs to be neither digital nor electronic. Like those goodwill messages left by the astronauts in the Sea of Tranquility, the discs are etched with tiny text that could be read by anyone with a sufficiently powerful magnifying glass.

What is written on these discs?

There’s an entry on Joseph-Ignace Guillotin. “With my machine, I cut off your head in the blink of an eye, and you don’t feel a thing.” It notes his opposition to capital punishment, his association with the machine as an attempt to make such deaths more humane and equal, his shock and revulsion when he eventually understood that the mind survives for a few agonizing minutes beyond decapitation. His misfortune, as Victor Hugo put it, was that “he could never detach his name from his invention.” He thought he was doing the right thing, carrying out a duty.

There’s an entry on Dorothy Hae 🍁 Radhakrishnan-McCall. “I believed that artificially shortening the telomeres of enemies of the state was the most humane way to end the rebellion. I thought taking time away from their future was better than killing them in the present. I thought what I did would prevent a greater evil. Don’t we always?”

There is an entry on the designers of the last gas chamber in North America, one that used nitrogen to suffocate the condemned. They write of specifying the length, width, height of the room, of picking the color of paint on the walls, of selecting the straps to use to tie the inmate down, of choosing the thickness of the glass through which witnesses can watch them die. They speak of going home afterward to kiss their spouse, to hug their children. They speak of filling out forms, of filing them away, of meting out justice.

It’s easy to judge evil; far harder to be and judge those who do what they do in the service of righteousness.

There is an address to which people who believe they have something to contribute to the End Watch can send messages. The address is monitored by machines, not people. The messages are etched onto silicon disks by robots. When there are enough of them, the foundation legally bound to maintain the End Watch charters a lunar ferry so that a few volunteers can carry the boxes of new discs into the tunnel under the dust on the far side of the Moon, in the heart of the crater named Oppenheimer.

There is an entry on the creators of the missiles that would pierce cars and pulverize those inside with swirling blades, making sure to miss no corner in which a terrorist or his baby may hide. There is an entry on the inventors of viruses that would only kill combatants and civilians of certain ethnicities. There is an entry on the builders of bombs that would slay people but not damage their equipment. There is an entry on programmers of robots that would “neutralize” enemies without being plagued by doubt or mercy.

They speak of summer barbecues, of winter ski trips. They speak of flirting and courting and babies. They speak of games and puzzles. They speak of freedom and beauty and God. They speak of ethics workshops and transparent procedures and the alienation of modernity. They speak of an office birthday party in the conference room, before more brainstorming on how to kill more people more efficiently. Some laugh; some cry; some speak of the sweetness as well as the banality of pro patria necare.

Not all watches require gears or pendulums or trembling crystals or sweeping hands bending the flight of the arrow of time into a circle. A watch can also just be a record of the progress of causality, an expanding graveyard of dead time. For this is what the End Watch is really measuring: our seemingly unwavering faith in the idea that taking time from others can be a good thing, that the killing hand can be humane, that inventing death, the absence of time, is something that we can justify. Disc by disc, act by act, the End Watch tracks our own progress—or lack thereof—toward the end of the arc of history.

There’s an entry on Oppenheimer, with his famous quote from 1965, decades after a thousand suns glowed at Trinity, years after he had lost most of his influence and power because of suspicion that he was a Soviet spy.

The disc encodes not only the text of his interview, but also a crude encoding of the original film. Rather than relying on any ephemeral digital encoding, the film—not colorized holos, not hi-def AI reconstructions, but the original, ancient, low-quality acetate film—has been reproduced as a series of tiny rectangular images, just strokes and shading, etched along the disc rim like the jagged lip of a crater. If you spin the disc at a certain rate and watch the images through a microscope under a light flickering at twenty-four times per second, barely above the human flicker-fusion threshold, the images will fuse into a grainy scene.

“Now I am become death, the destroyer of worlds.”

Oppenheimer speaks to the camera without looking at it, perhaps trying to shape how those who come after will see the father of the atomic bomb, perhaps trying to tell himself a story that would make sense of the incomprehensible, all the while knowing that it’s impossible to bend or know the judgment of eternity.

The verse from the Bhagavad Gita, from which Oppenheimer took his own translation of a line, is chapter eleven, verse thirty-two, a speech from Lord Krishna. But “death” here is a shorthand, which says both too much and too little. An alternate translation of the full verse is more illuminating. In answer to a plea from Prince Arjuna to clarify his divine intention, Krishna tells the prince to arise and carry out his righteous duty:

I am wondrous Time,
All-devouring, annihilator of universes.
Even if you stand and wait,
Those warriors opposite, arrayed so heroically,
Will perish.

This is one of the most bleak as well as beautiful expressions of dharma, the ineluctable flow of reality itself.

If those whose voices are frozen in the End Watch had stood and waited, would a thousand suns still have burned, the death chambers still have been constructed, the guillotine blades still have fallen, the missiles and bombs and terrors and regrets still have been unleashed, in the service of righteousness, of duty, of justice, of dharma, the foundation of reality? Would we still stand paralyzed before All-Devouring Time, Annihilator of Universes? Does dharma absolve suffering? What does absolution even mean? Prince Arjuna has his answer; do we?

Year after year, the discs in the End Watch accumulate and bear witness.

3. The Time from Home—Scherzo. Allegro con brio

And yet we knew that gentle Clock
Meant nought but Going Home
—Emily Dickinson

It takes a RWB ramjet fusion rocket, the fastest mode of transport available, about seven Earth years to make the trip between Yaohan Beta and 341 Ilera, the two settled planetary systems closest to one another. A trip between Paek Sigma II and Kuulam, which sit at opposite ends of our species’ domain in space, on the other hand, requires a full four hundred and sixty-two Earth years.

With humanity so stretched out, time can no longer be universal, but must be reinvented everywhere. How can it be otherwise when BSG-216 takes longer to rotate around its own axis than to orbit around its star, while Carrie’s Planet spins so fast that its sun streaks across the empyrean like a meteor? On Narcissus, tidally locked so that its smooth, blemish-free face is always turned toward its blazing star, the settlers in the perpetual twilight of the terminator zone have no need of seasons. But on Ollumi, which doesn’t so much orbit as wander among seventeen suns and fifty-three other planets, tracking the succession of the capricious seasons and the malleable years is an adventure in itself. It’s no wonder that every world has its own calendar, its own horological tradition, its own definition of hour, day, year.

In some ways, we’ve returned to the age when the great Polynesian explorers settled the islands in the wide-open Pacific, when a departure usually meant no return, partings were mostly final, oceans divided lives, and jet lag that collapsed all time was not yet possible. Plans must be made not with merely years in view, but generations. A couple on Earth who wish to start a new life on Kuulam must understand that at least three generations will be born en route, and by the time their descendants step onto the new world, more than a century later, they, the original architects of the plan, will be gone, and their dreams and fears will no longer be the hopes and doubts of their descendants.

Even with hibernation, even with tachynauts, even if, one day, we learn to fly closer still to the speed of light, there is simply no way to bridge the vastness of space. Paradoxically, this has brought about a kind of peace. Each world is allowed to be on its own. There is no galactic empire, no practical means to gather all the scattered stars in one iron fist. We’re lucky that we live in a universe where time itself is a bulwark against tyranny, and not even a resurrected Xerxes can whip the space-time main into obedience.

To step onto an interstellar ship is to say goodbye forever to everything you’ve ever known, to pursue a dream based on news decades out of date, to take a leap of faith into a future that cannot be fathomed. The language that is spoken on arrival will not sound like the one imagined on departure. Given all that, who are the migrants who nonetheless travel between the stars?

In every community since the beginning of time, no matter how perfectly evolved or designed, there is the seed of dissatisfaction, of the desire to leave. Some will always want to walk away, even from the most utopian city. We’re happiest when we are surrounded by those who share our story, but what if our soul sings a different song, thrills to the call of another kind of music?

A mother on the remote outpost of Cel 241 sells everything she owns to secure a cabin for her and her five-year-old daughter on a ship bound for glittering Sigetin, where she hopes that her daughter, stepping off the ship as a forty year old, can receive education and be given opportunities impossible to find at home. Meanwhile, on Lada, the youngest child of a youngest child decides to give up his inheritance in exchange for a ticket to Cel 241 because he wishes to make his way without all the familial entanglements that suffocate as much as they support.

We’re at once wanderer and settler, planet and star, ship and port. We want to know our place but also be free, like an electron in the outermost orbital. Only after we’ve left does a place start to feel like home. We vacillate between being vagabond and rooted; we are, in our hearts, all strangers in our native land, permanent residents in a pan-diaspora.

Even generations after migration, we feel a connection with the land of our forebears. One of the most popular gifts new migrants bring to settlers who share the same origin is a timepiece from the old world: a clump of cesium that once sang for the laser atop Mount Gogol on Lada; a ceramic crystal oscillator tuned to the frequency of the call of the lava loon on Ori; a tuning-fork desk clock set to the New Year bells at Gohyaku Rakanji; a sundial marked with the shadows of the hours on Pele; an hourglass filled with the sand from Lusso Beach on Tau Blüte Six; a mechanical watch with a forty-one-jewel movement encased in Switzerland, with a perpetual calendar that continues to track the system devised by Maya astronomers . . .

To be sure, what’s kept by these timepieces isn’t really the time from home. Relativistic time dilation, lack of maintenance, simple drift—everything conspires to make bringing over time from one place to another a fool’s errand. Yet, there is something grand about gazing upon an artifact that contains another definition of the hour, that models the orbit of another world, that ticks to the rhythm of ancestral seasons, to the music of life from homeland.

Poets on ancient Earth spoke of people connected by threads of affection but divided by distance gazing upon the Moon, imagining that they do so at the same time, thereby entangling their hearts. Gazing upon the time from home, we, remembering the past, rooted to the present, already impatient for the future, can be permitted to imagine, for a moment, that lightyears away, our souls are entangled with those whose stories we share, one common species scattered among the stars.

4. One Second in Hilo—Tempo giusto

The Egyptians, they said, were the first to discover the solar year, and to portion out its course into twelve parts. They obtained this knowledge from the stars.
—Herodotus, The Histories, Book II, chapter 4 (Rawlinson translation, 1880)

In the town of Hilo, nestled on the northeastern coast of the Big Island of Hawaii, Earth, there is a massive, rectangular piece of black volcanic rock called the Naha Stone. It was said that whoever overturned it would unite the Hawaiian Islands. King Kamehameha the Great, by legend, accomplished this feat when he was fourteen and eventually fulfilled the prophecy. Like Arthur, who pulled the sword out of the stone, like Xiang Yu, who lifted the massive bronze ding cauldron over his head, Kamehameha changed the world in a second, when he moved what was thought immovable.

Today, the stone rests in front of a laboratory operated by the Bureau interplanétaire des poids et mesures. It is here, next to Moon-driven tides and Sun-speckled waterfalls, that the second, a fundamental SI unit, is actually measured. Inside the laboratory, atoms of cesium-133, mercury-199, ytterbium-171, rubidium-87, and many others are locked in laser cages, entangled in clouds as near absolute zero as uncertainly possible, magnetically deflected, probed with radiation, made to sing in their unique voice, an elemental chorus whose music is the most accurate clock in the known universe.

Behind the laboratory, Mauna Kea, the tallest mountain on Earth when measured from base to summit, looms a few miles away, where some of the best views of the Moon anywhere on the planet can be found.

The ancient Hawaiian calendar was based on the phases of the Moon. So important was the Moon to the life of the people that every phase—each waxing crescent, each pregnant swell, each barely there smile, each perfect circle—all thirty of them, had its own name, starting with Hilo, the first night of the new Moon, to Hoku, the full Moon that is good for fishing at sea, all the way to Muku, the Moon in shadow. A common expression compares the ignorant to small children who do not yet know the phases of the Moon.

Here, in Hilo, we see all time concentrated in one spot. The Moon is our oldest clock, the singing atoms our youngest. Between the two is a millennia-long march to invent not only more precise ways to measure time, but also to define our place in the universe.

Every schoolchild can recite at least the simplified definition of a second: “The duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the unperturbed ground state of the cesium-133 atom.”

However, before 1967, a second was defined not by reference to any atom, but by the motion of Earth itself. A second didn’t build up to hours, days, months, years, but was merely a subdivision of the day or the year, both of which were seen as more fundamental.

The earliest timepieces available to humans were also the grandest: the repeated movements of the rising Sun, the setting Moon, the spinning stars. The face of a sundial was marked into sections to divide the day into periods comparable to our hours. But as the days lengthened and shortened on the Earth’s annual journey around the Sun, so did the hours, and any subdivision thereof. A second, if it could be talked about at all, was simply an idealized, flexible fraction of an arc.

A second didn’t become real until Christiaan Huygens built the first pendulum clock in 1656. And thereafter, during the nineteenth century, the second became a base unit in systems of measurement, defined as 1/86,400 of a mean solar day.

But the Earth’s spin is inconstant. The tidal bulges reaching for the Moon, the deformation in the shape of the rubbery Earth, the advance and retreat of glaciers, the sloshing of the mantle around the dense core—the length of the day fluctuates, but overall trending longer as the Earth slows down. From the time of the earliest eclipses recorded by the Babylonian and Chinese astronomers, we know that the great clock that is the Earth has slowed down by nearly seven hours.

What to do? When our sole spinning world-timer turned out to be unreliable, we turned to a grander one: the observed positions of the stars, the Sun, and the Moon, as compared to their calculated Newtonian positions. In 1956, the world redefined the second to be 1/31,556,925.9747 of the interval it took for the Sun to return to the same apparent position in the Earth’s sky, known as a tropical year. This was the ephemeris second.

Ephemeris time, though defined by the position of the Earth with respect to the Sun, was more easily determined by observing the positions of the Moon against the background stars. One of the best places to obtain such observations, as it turned out, was here in Hawaii, where the Moon already had so many names. We left the Moon behind in our quest for precision, only to return to it like a child missing home.

But the Earth’s orbit around the Sun is also inconstant. Every second, the Sun sheds millions of tons of mass as it fuses hydrogen together, unleashing energy that, though far more powerful than the burst at Trinity, gives, rather than takes, life in the cradle of humanity. With the passage of every year, the orbit of the Earth widens, slows down.

That was when we, like Kamehameha reaching for the Naha Stone, reached for the atom. There is nothing more unchanging and constant in the cosmos.

To put the atomic definition of the second into practice, our ancestors invented the atomic clock. Like all clocks and watches, the atomic clock relies on something that oscillates, ticktock, to-and-fro. But instead of a pendulum or a balance wheel, a tuning fork or a pulsing heart, the atomic clock’s oscillator isn’t an object at all, but a beam of light. It’s an electromagnetic wave tuned to the precise frequency of the light absorbed or given off by the lone outermost electron, wandering far from the nucleus of the cesium atom, as it flips between being parallel or antiparallel to the spin of the nucleus. When the beam is tuned perfectly, that lone electron jumps in resonance, and counting off 9,192,631,770 crests in that flickering light gives you exactly one second.

We probe for the resonance of the crystalline spheres, listen for the soundless celestial music. The atomic clock is the closest we can get to the heartbeat of the Divine.

There is a great deal of beauty as well as terror in that definition. First put into place (in a slightly different form) in October 1967, just a few months after the death of Oppenheimer in February of that year, when the total amount of nuclear weapons in the world had crested to a new peak, it marked the moment when our species had simultaneously acquired the insight to peer into the fundamental clockwork that governs the universe as well as the power to annihilate ourselves in a burst of all-devouring absence of time.

The definition of the second based on the ground state radiation of the cesium atom was calculated to correspond to the length of the ephemeris second at that juncture in history. But it was a passing of the baton. Henceforth, the second would no longer be dependent on the motion of the Earth and the Sun. No matter how much further the Earth slowed, the second was freed of it.

In the end, we had to move away from the unfaithful celestial clockwork of heavenly bodies and turn toward the unchanging, invisible movement inside a single atom, an idealized lone electronic planet orbiting far in the Oort cloud of the nuclear sun, plucking the inimitable music out of the foundational strings of the universe.

It was a Galilean moment. The sword had been pulled out of the stone, the ding lifted overhead, the Naha Stone overturned. Henceforth the Earth was truly removed from the center of the universe, and the Sun decommissioned as the sole mainspring by which time would be measured. We had become a cosmic species.

This definition is why, despite all the multitudes of calendars in use on all the settled worlds, a second lasts as long in the streets of Earth as it does in the cloud forests of Paek Sigma II, spans the same duration in the deep craters of Zhurong Six as under the icy oceans of Flux IV. The hours, days, months (if they have them), and years on these worlds are built out of the same second, yet the number of seconds in each is determined by the seasons of each planet, the needs of each community.

Out of one, many.

The measurements from the laboratory behind the Naha Stone are beamed and relayed by radio waves to all the settled worlds, where, upon the signals’ arrival years or decades later, they are used to synchronize uniform time. This is what makes navigation and communication among all humanity possible, the rebbelib chart of our age.

But there is still something special about time on Earth, as our first home, our original love. We have, therefore, invented something special for it.

In the old days, it was necessary to add a second now and then to the time on Earth to allow the planet’s slowing rotation to sync up with the song of the atoms. This was clumsy, disruptive, and felt deeply inelegant. Similarly, it was necessary to add a day now and then to the Gregorian calendar to account for the fact that a tropical year didn’t divide evenly into a whole number of days—even with all the convoluted hacks, the calendar still would have eventually drifted out of sync with the course of the seasons.

None of these hacks are needed now.

During the last wave of mass migrations off the Earth, we executed a series of unprecedented mega-engineering projects: electromagnetic catapults along the equator hurled massive chunks of matter into space as a first step in the construction of interstellar island-ships; mining vessels out in the Oort cloud directed icy planetesimals into new orbits that brought them near the Earth so that they could be captured for more raw materials; atmospheric transfer wells that filled the new island-ships with hurricane-sized jets of living air. The very shape of the planet itself wobbled as we moved earth, ice, and sea in our effort to get humanity off this rock, to fulfill our destiny among the stars.

But we didn’t abandon our home. We didn’t only take and extract. We, all of us, those who left and those who stayed behind, also planned those mega-engineering projects to achieve something else. You see, with every chunk of material thrown off into space, with every planetesimal that skimmed into and was caught by the Earth’s gravity well, with every carefully considered mass shift, we were increasing the Earth’s angular moment, speeding up its rotation.

By the time the last island-ship left, a tropical year on Earth was exactly 365.25 days. The calendar could finally agree with the seasons; all that’s needed is the smallest of adjustments once every four years: a single gear in a perpetual calendar could do it.

To keep the system running smoothly, today, the Moon-gazers on Mauna Kea and the atom-conductors behind the Naha Stone feed their observations into an algorithm.

A slowdown in the rotation of the Earth is noted. The algorithm suggests more solar-desalinated water to be drawn up north to irrigate sunny Siberia and Yukon and pumped south to be added to the glaciers of Antarctica. Like a skater pulling in her arms to accelerate her spin, the redistribution of mass speeds up the Earth’s rotation. If even more angular momentum is needed, Oort cloud objects could be summoned to surf through the gravity well, contributing their kinetic energy to our whirling blue marble. With all the nudges and wobbles and swerves and turns, the Earth’s rotation catches up to the ticking of the atomic clock, and the seasons remain matched to the ancient holidays, the timeworn celebrations, the age-old stories.

It’s just a little tinkering with the celestial clockwork, an adjustment to the grandest of balance wheels. As all timekeeping enthusiasts know: any movement must be cared for and maintained.

Author’s Notes

For a possible link between metabolic rate and the perception of time, see, e.g., Healy, K., et al. “Metabolic rate and body size are linked with perception of temporal information.” Animal Behaviour 86.4 (2013): 685-696, available online at doi.org/10.1016/j.anbehav.2013.06.018.

An accessible history of the definition of the second and the development of the earliest atomic clocks can be found in Lombardi, M.A. “A Historical Review of US Contributions to the Atomic Redefinition of the SI Second in 1967.” Journal of Research of the National Institute of Standards and Technology 122 (2017), available online at doi.org/10.6028/jres.122.029.

For more on the use of ancient astronomical records to determine the deceleration in the Earth’s rotation, see Stephenson, F. R., Morrison, L. V., and Hohenkerk, C. Y. “Measurement of the Earth’s rotation: 720 BC to AD 2015.” Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 472.2196 (2016), available online at royalsocietypublishing.org/doi/pdf/10.1098/rspa.2016.0404.

For more on SI units and their definitions (including secondary representations), see the BIPM (Bureau international des poids et mesures) website (www.bipm.org/en/home) and Newell, D. B., and Tiesinga, E. “The international system of units (SI).” NIST Special Publication 330 (2019).

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