55. Caesium: A Brief History Of Time

We’ll trace the history of the most important caesium-based technology all the way back to its original roots: a stick.

Featured above: Before the introduction of standard time zones, catching a train involved some significant calculating and converting.

Show Notes

Forgot To Mention: The aforementioned stick being the one stuck in the ground to cast a shadow for those sundials.

Incidentally, that same stick-based technology allowed Eratosthenes to deduce that the Earth is round. Sticks! They’re more advanced than they look!

See? If you’re reading this, rather than listening to it, you have surely noticed the decidedly non-American spelling of today’s element. Caesium is in rare company here: It is one of only two elements, the other being aluminium, which the IUPAC grants two acceptable spellings. I am an American, but I prefer to align my spelling with the vast majority of the scientific community. I have faith that my fellow citizens will be able to decipher what I’m talking about without overexerting themselves.

They’re Not All Basil Valentine: The whole “Catholic monks are why we have clocks” thing felt a little too cute when I first read it. It’s the kind of story that sounds really good; i.e., the kind that somebody probably made up. But I simply found too many sources that agreed this was the biggest impetus behind standardizing time, so there you have it.

It’s not the only reason, though. Other social pressures would have eventually led to the mechanical clock being invented by somebody, somewhy. But this is what got us there in this timeline.

Would You Call It “A Good Time?” Regarding those blushing maidens, I’ll simply quote the passage verbatim:

The directions I had for making several clocks for the country are countermanded; because no modest lady now dares to mention a word about windingup a clock, without exposing herself to the sly leers and jokes of the family… Nay, the common expression of street-walkers is, “Sir, will you have your clock wound up ?”
Virtuous matrons (the “clockmaker” complained) are consigning their clocks to lumber rooms as “exciting to acts of carnality”.

As It Should Be: Perhaps you’re familiar with the official web page for the movie Space Jam, which has remained in a state of suspended animation for the past few decades. I get similar vibes from the official event page for the Tallapoosa Possom Drop, and it is a delight to behold.

When It’s Noon On The Moon Then What Time Is It Here? You don’t need to travel east or west to visit a different time zone. You can also go up. Way, way up. Airplanes fly according to UTC, so in addition to passengers, crew, and luggage, those narrow aluminium tubes are carrying their own time zone, too.

Episode Script

Today we set upon the sixth of our table’s seven eponymous periods. That might make it sound like we’re approaching the end of our journey, but don’t worry — we’ve got a long way to go yet.

As we continue along on the periodic table, the elements get bigger, and they find more space to tuck their electrons. That’s why the first period has only two members, and why the fourth period got substantially longer with the transition metals. Now we’ll add the lanthanides.

In fact, the last two periods of the table are so long that together, they comprise over half of all the elements. So strap in, folks, because we’ll be in period six for the next year.

You’re listening to The Episodic Table Of Elements, and I’m T. R. Appleton. Each episode, we take a look at the fascinating true stories behind one element on the periodic table.

Today, we’ll take our time with caesium.

The periodic table is all about trends, and Group 1 might exhibit the most obvious trend of all: The alkali metals get increasingly reactive as we descend. With caesium, we’re handling the most reactive of all.

It’s actually more reactive than francium, the next element down in Group 1. Once the elements get as massive as francium, they start operating by a different set of rules. In this case, francium contains so many positively charged protons that it actually holds on to its negative electrons a little more tightly — making it a little less volatile than today’s subject.

And it is highly volatile. Not only will it explode with incredible force upon contact with water, it has a tendency to spontaneously burst into flame when in contact with the air.1

And that’s just for caesium’s single stable isotope, caesium-133. All the others are highly radioactive — and have even been involved with one of the most notorious accidents in history.

But you wouldn’t know any of that from its discovery. The most explosive fact about caesium’s origin story is that it was the first element discovered by spectroscopy. If you’d like to hear more about that, you’ll need to listen to the Rubidium episode, because right now we don’t have… time.

That is a very modern concern. Generally speaking, for most of human history, we’ve been far more concerned with sunsets and seasons than with seconds on stopwatches. When artificial lighting is scarce or meager, it’s just practical to do work while the sun is out, and go to bed when it’s dark.

Shorter amounts of time could be described in relative terms. Rather than saying “half an hour,” someone might say, “I’ll be back in a rice-cooking.” When an earthquake struck Santiago, Chile in 1647, the rumbling didn’t last for 45 seconds. It lasted for two credos — the amount of time it took to recite The Apostle’s Creed twice.2 3

For those who really clamored for a more absolute measure of time, there were sundials. Those had some pretty big flaws, though: They were entirely useless on a cloudy day, or, y’know, at night. But few people really depended on that information. When farmers were filling their wheelbarrows full of radishes, did they care whether it took five hours or six?4 5

There were other timepieces. Several societies invented clocks based on the carefully calibrated dripping of water, or candles that burned at a regular rate, or the hourglass. But these were little more than curiosities — and far too expensive to see any kind of widespread use. Even as civilizations built colossal monuments that functioned as calendars, when it came to small units of time, the sun in the sky was the world’s most popular clock from 1500 BCE until the Early Modern Period.6 7

The only reason the exact time became a matter of any concern at all was because the Roman Catholic Church had some very strict rules. Specifically, the devout were expected to perform a prayer called the Liturgy of the Hours at regular intervals — seven times during the day, and once in the middle of the night.8 9

So the Church was responsible for the first widespread use of clocks, which rang a loud bell when it was time to pray. That is actually why we call them “clocks” — in Medieval Latin, “clocca” means “bell.”10

Those first clocks were based on a water-driven mechanism, like the curiosities of prior centuries, but soon evolved into a design driven solely by massive weights suspended in the air.11 12

Clock towers, then, were built as a matter of function over any aesthetic preference. Hanging the weights from great height allowed the clock to run continuously for a long time, and positioning the bell high above a community made it audible over greater distances.13

Mechanical clocks solved the Liturgy of the Hours quite nicely. What surprised the Church was how useful this new invention became in secular life. Townsfolk weren’t just arranging their prayers around the bell’s toll — they could schedule business meetings and personal appointments, too. As clock technology improved, accurate timekeeping allowed sailors to calculate not only their longitude, but their latitude as well. Capable of more accurate navigation than ever before, ships could safely sail across entire oceans, fusing the Eastern and Western hemispheres into one circumnavigable globe. New empires spanned this globe as they crushed old ones beneath their feet.14 15 16 17 18

Similarly, timekeeping transformed all of science. Doctors could measure a patient’s pulse, astronomers could track a planet’s speed, and physicists could analyze the motion of the pendulum — which, in turn, led to the invention of even more accurate clocks.19 20 21

These are monumental paradigm shifts, but perhaps the biggest change brought about by the mechanical timepiece was our relationship to work. As clocks slowly became more widespread, and more accurate, workers were no longer paid according to how many goods they produced in a day. They were paid for the hours they worked — hours that were often long and grueling. And since that time was being measured so precisely, employees could be heavily penalized for a new kind of infraction called “tardiness.”22[/note] 23

These changes took hundreds of years, but they enabled transitions from agriculture to manufacturing, feudalism to capitalism — it was the beginning of the Industrial Revolution.24

Complex systems of gears jumped from clocks to factories and mills, powered by coal and steam rather than weights and springs, invigorating the economy as they blighted the landscape. But one such machine was special because it burned its fuel and and turned its cogs to traverse the landscape at speeds faster than anyone had ever seen: The locomotive.

In the same way that factories allowed a company to produce a predictable stream of high-quality goods, the tracks criss-crossing the countryside traced the fixed routes that rushed goods and passengers from place to place at regular intervals and on a strict schedule.

It made the world feel much smaller, sometimes uncomfortably so.25 The American naturalist John Muir wrote on the subject in 1872:

…our so-called trans-continental railroad is a big gun; charged with steam and cars it belches many a tourist against the targets of the golden State, — geysers, big trees, Yosemite, &c., among which they bump and ricochet, and rebound to their Atlantic homes, bruised and blurred, their memories made up of a motley jam of cascades and deserts and mountain domes, each traveller voluntarily compacting himself into the fastest cartridge of car and coach, as if resolved to see little as possible. … Thus is modern travel spiritualized. Thus are time and space … annihilated.”26

Not everyone had such a dim view of the new technology. Families who had spent generations in a single town could now buy passage to a destination thousands of miles away — and the trip’s time could be measured not in months or weeks, but in days.27 28 29 30

But this machine wasn’t exactly well oiled. Not yet. A functioning railroad system requires adherence to a pretty strict schedule, and in the early days of railroads that was nigh impossible. A standard 24-hour clock had emerged, but no two clocks were ever in agreement with each other.31 32

Locally, communities would often set their watches by the church bells. Those who lived a more rural lifestyle would be visited by traveling timekeepers, who would generously offer to disclose the time for a modest fee. In dense cities, the city set the official time every day by lowering a large ball down a tall pole precisely at noon.33 34

Nowadays, a ball drop is seen as a much more special occasion — usually one that marks the start of a new year. There’s the famous one in Times Square, of course, but pretty much every place puts its own local spin on the practice. For instance, New Orleans drops a giant fleur-de-lis in Jackson Square.35 In 2011, the New Jersey town of Seaside Heights dropped Snooki, of Jersey Shore fame,36 and every year, the Georgia town of Tallapoosa drops a stuffed possum named Spencer.37

But I digress.

Those systems worked pretty well for their communities. The problem was, until the late 19th century, every town ran by its own clock. When it was noon in Toledo, the time in Cleveland was 12:07; in Cincinnati, 12:14.38

So if the train from Toledo to Cincinnati was leaving at noon, did that mean Toledo’s noon? Or Cincinnati’s noon? Railroads tried to solve this problem by keeping their own official time, separate from any city — which meant there was another clock added to the mix. And each railroad company kept its own standard time, multiplying the confusion for passengers requiring a transfer.

This caused problems more severe than frustration. In 1853, two trains collided head-on when the conductors of both thought it was their time to use the track, killing fourteen passengers. 39

The madness finally ceased in the 1880s. The United States consolidated its patchwork of hundreds of time zones down to four, and scientists from England’s Greenwich Observatory provided one reliable and accurate time by which the rest of the world could set their clocks. The world’s official time, a standard called Universal Coordinated Time, is still anchored to the hour, minute, and second in Greenwich today.40

On November 18, 1883, clock towers along the East Coast of the United States struck their bells to mark the time as 12 o’clock noon local time… and then,a few minutes later, struck them again to mark their compliance with the newly agreed-upon time zones. The papers called it, “The Day With Two Noons.”41

The mechanical timepiece required complex machinery, inspired the invention of uniform standards, and had far-reaching social consequences. The clock didn’t just make the Industrial Revolution possible, it was a perfect illustration in miniature of everything the Industrial Revolution was.4243

Benjamin Franklin summed up the new prevailing attitude succinctly in the opening words of his essay, Advice To A Young Tradesman: “Remember that time is money.”44

We take that attitude for granted, but it is completely unlike the ways individuals and societies perceived time for the vast majority of our history as a species.

Alongside artificial lighting, high-speed travel, and long-distance communication, the mechanical clock was a symbol of humanity’s severance from the influence of nature. It could be sunny or cloudy, winter or summer, day or night — our experience of time was no longer subject to the whims of the Earth. We had turned the tables. We had harnessed the rotation of the Earth and partitioned it into 86,400 perfectly equal units of time to satisfy our ends. These triumphs demonstrated not merely our independence from the natural world, but our dominance over it.45

Eventually, though, time experts noticed a small problem: Earth’s rotation is not very constant. For one thing, it’s slowing down, the same way a spinning top slowly comes to rest, making each year about 14 microseconds longer than the one before it. There are other factors, too. Even an unusually windy year can introduce some tiny amount of variance in the equation.46 47 48 49

So in 1927, an engineer for Bell Labs named Warren Morrison devised a new way to keep time. When electricity is applied to a quartz crystal, it vibrates at a very specific — and very fast — speed. 32,768 vibrations per second, to be exact. Morrison saw that this regular, constant motion could function as a pendulum, powering clocks that would remain accurate to the second for a year or longer.50 51

That’s pretty good! Certainly good enough for most people, right?

Well, maybe. If you have a wristwatch, it probably has a quartz crystal inside. Except by the mid-twentieth century, it wasn’t just people who ran on an accurate clock. Radio signals and electrical grids and computers are all reliant on clocks that are accurate to the microsecond. Quartz wasn’t going to cut it for that task.52

Now is the time when caesium finally enters the picture. I hope you didn’t think I forgot what we’re doing here.

Element 55 keeps time pretty much the same way as quartz. Apply a little energy — microwaves, in this case, instead of an electrical current — and caesium will vibrate at a constant and shockingly fast frequency. Compared to quartz’s 32,768 hz, caesium oscillates over nine billion times per second — allowing for far greater accuracy. Rather than losing one second every couple of years, a caesium clock remains accurate for 158 million years.53 54

Such fine precision isn’t only useful in cutting-edge physics laboratories. In fact, it forms the basis of a system that’s used in many cars and just about every smartphone: GPS.

The Global Positioning System does just what it sounds like: Indicates something’s position on the globe. A network of two to three dozen satellites hang above the Earth in such a pattern that any point on the planet should be able to see at least eight of them at any given time. Each satellite carries four atomic clocks. A receiver on the ground — like a smartphone — receives timestamped signals from those satellites. By comparing the signals from at least three of them, the receiver can calculate its position on the globe within a few meters.55 56 57

GPS was exclusively for the US military upon its invention in 1978, but that changed in 1983. A South Korean passenger jet en route from Paris to Anchorage flew so close to the North Pole that their compasses malfunctioned. Completely unwittingly, the pilots made a 135-degree turn and entered prohibited Soviet airspace. Not realizing it was a civilian craft, the Soviet military fired upon the airplane, forcing an emergency landing in which two were killed.58 59 60

American authorities realized that this tragedy of errors could have been easily prevented with GPS, and later that year, allowed all the world free access to the network.

Since then, GPS has become so ubiquitous that we take it for granted. With barely any notice, our clocks have become so precise and accurate that they measure not only our whens, but also our wheres.

Caesium made a good candidate for the heart of this timepiece for the same reason it reacts so explosively with water: Its one little valence electron, dangling out there in space, so far from its nucleus, is pretty easy to keep track of.

The atomic clock debuted in the 1950s, and the technology has only improved since then. State-of-the-art atomic clocks measure the vibrations of strontium atoms instead, accurate to one second in five billion years. But the technique was pioneered using caesium, and at the National Physical Laboratory in England, element 55 remains the standard by which all time is defined.61 62 63

At least, for now.


There’s something you should know before you run off to add caesium to your collection: One of its most common isotopes is fatally radioactive.

In 1987, in Goiania, Brazil, Roberto dos Santos Alves and Wagner Mota Pereira snuck into an abandoned hospital to do a little element hunting. They weren’t collectors, per se — they were looking for potentially valuable scrap metal. A small yet heavy canister looked like just the thing, so the two carted it home and began taking it apart.64 65

Perhaps they should have known something was amiss when they both became violently ill that same night. Pereira only went to the hospital she his hand started to swell. Alves continued working. Doctors told Pereira he must’ve eaten some bad food, and he should go home and rest. Meanwhile, Alves cracked open the canister, and soft blue light spilled out.

He thought it might be some kind of gunpowder, but when he tried to light it, it would not ignite. Deciding he had learned all he could, Alves sold it to a local scrapyard.

From there, the object got passed around further. The scrapyard owner showed it to his family and friends before selling it to a second scrapyard. A six-year-old girl was delighted by the way it made her arm glow blue.

What none of these people knew was that the mysterious glowing capsule they were passing around was an enormous sample of Caesium-137.

The scrapyard owner’s wife was the first to notice that everyone who touched the metal seemed to fall ill. She alerted medical authorities, but by then, people had already been passing the caesium around for over two weeks.

Cleanup was swift and thorough. Houses were demolished and topsoil removed.

But there was nothing to do for those who had already been exposed to overwhelming levels of radiation. Pereira and Alves required amputations of an arm and some fingers. Two hundred fifty people had been irradiated by the caesium. Four of them died, including the six-year-old girl. The Director General of the International Atomic Energy Agency called the mishap “one of the world’s worst radiological incidents.”

That’s consistent with the reputation that caesium-137 has earned. It’s one of the more notorious byproducts of the 1986 Chernobyl disaster, and with a half-life of thirty years, also one of the most long-lasting. Centuries from now, the land around Chernobyl will still be measurably radioactive due to caesium-137.66

In 2019, Norwegian researchers found that a submarine that sank thirty years prior was leaking high levels of radioactive caesium — but assured the public that this was nothing to worry about. Seawater is an extremely effective insulator against radiation, rendering it harmless after only a few meters, and the wreck rests on the sea floor 1,680 meters below the surface. Perhaps more concerning are the two plutonium-tipped nuclear warheads that still lie among the wreckage.67 68 69

Sadly, atomic clocks and nuclear subs are out of reach for most of us, and caesium is frighteningly dangerous even when it’s not radioactive. If you’d like to safely add caesium to your collection, the scientific sommelier would offer a bottle of 1963 Bordeaux.

That was the last year of atmospheric nuclear weapons tests. For the prior decade-plus, mushroom clouds had been sprinkling caesium-137 dust far and wide. When it landed on French vineyards, the grapes would absorb the fallout, and it would make its way into bottles of wine. Any vintage from the mid-50s till the mid-70s will display measurable levels of gamma radiation, but bottles from 1963 have an especially atomic mouthfeel.70 71

It might be slightly easier to get your hands on a bottle from 1986. Caesium levels in wine had just about gone back to zero by then… but following the disaster at Chernobyl, caesium levels in European wines spiked for one last year.

Incidentally, none of these bottles contain enough caesium to present any kind of hazard. So if you’ve acquired one, feel free to pass it around to friends and family without fear of irradiating them. Just make sure, for your collection’s sake, that the bottle is still full when they give it back.

Thanks for listening to The Episodic Table of Elements. Music is by Kai Engel. To learn why 18th-century ladies blushed at the mention of clocks, visit episodic table dot com slash C s.

Next time, we’ll knock ’em dead with barium.

Until then, this is T. R. Appleton, reminding you that hanging on in quiet desperation is the English way.

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