Caesar's Last Breath

INTRODUCTION

The Last Breath

Indulge me in a modest experiment. For the next few seconds try paying close attention to the air escaping your body, as if this were your last living breath on earth. How much do you really know about this air? Feel your lungs deflate and sag inside your chest. What's really going on inside there? Put your hand in front of your lips and feel how the gas escaping them has transformed inside you, growing warmer and more humid, perhaps acquiring an odor. What sort of alchemy caused that? And although your sense of touch isn't nearly discriminating enough, imagine that you can feel the individual molecules of gas pinging your fingertips, impossibly tiny dumbbells caroming off into the air around you. How many are there, and where do these molecules go?

Some don't get far. As soon as you take another breath, they come rushing back into your lungs, like waves that fling themselves onto the shore before being retracted by the sea. Others stray a little farther and make a break for freedom in the next room before returning as well, miniature prodigal sons. Most simply join the anonymous masses of the atmosphere and begin to spread around the globe. But even then, perhaps months later, a few weary pilgrims will stagger back to you. You might be a very different person between your first and second encounters with these molecules, but the ghosts of breaths past continue to flit around you every second of every hour, confronting you with every single yesterday.

Of course, you're not alone in experiencing this; the same thing happens to every other person on Earth. Moreover, your ghosts are almost certainly entangled with theirs, since they almost certainly inhaled and expelled and rebreathed a few of those very same molecules after you did—or even before you did. In fact, if you're reading this in public, you're inhaling the exhaust from everyone around you right now—secondhand breath. Your reaction to this will probably depend on the company you keep. Sometimes we enjoy this mingling of airs, as when lovers lean in and we feel their breath on our necks; sometimes we abhor it, as when the chatterbox next to us on the plane has eaten garlic for lunch. But short of breathing from a tank, we can't escape the air of those around us. We recycle our neighbors' breaths all the time, even distant neighbors'. Just as light from distant stars can sparkle our irises, the remnants of a stranger's breath from Timbuktu might come wafting in on the next breeze.

Even more startling, our breaths entangle us with the historical past. Some of the molecules in your next breath might well be emissaries from 9/11 or the fall of the Berlin Wall, witnesses to World War I or the star-spangled banner over Fort McHenry. And if we extend our imagination far enough in space and time, we can conjure up some fascinating scenarios. For instance, is it possible that your next breath—this one, right here—might include some of the same air that Julius Caesar exhaled when he died?

You know the story. The ides of March, Rome, 44 BC. Julius Caesar—pontifex maximus, dictator perpetuo, the namesake of July and the first living Roman to have his picture on a coin—enters the Senate meeting hall, looking surprisingly spry after a rough night. At a dinner party he'd attended, conversation had strayed into the rather morbid topic of the best way to die. (Caesar had declared his preference for a sudden, unexpected end.) An epileptic, he'd also slept poorly that night, and his wife had suffered ominous dreams about their house collapsing and her holding a bloodied Caesar in her arms.

As a result of all this, he almost stayed home that morning. But at the last minute he ordered his servants to ready his litter, and as his retinue made their way toward the Forum, he finally relaxed, his breath coming freer and easier. He even teased a soothsayer along the way, a man who, a month before, had prophesied doom for Caesar sometime before mid-March. Caesar filled his lungs and shouted, "The ides of March have come!" The seer answered without smiling. "Aye, Caesar, but not passed."

As Caesar entered the meeting hall, hundreds of senators rose to their feet. It was likely stuffy in there, as their mingled breath and body heat had been warming the air for some time. Before Caesar could settle into his golden chair, though, a senator named Cimber approached him with a petition asking for pardon for Cimber's brother. Cimber knew that Caesar would never grant this, but that was the point. Cimber kept begging and Caesar kept refusing, and sixty other senators now had a chance to creep forward, as if offering support. Caesar sat in the midst of them, imperial and increasingly irritated. He tried to cut off discussion, but Cimber cupped his hands on Caesar's shoulders as if to plead with him—then yanked his purple toga down, exposing Caesar's breast.

"Why, this is violence," Caesar said. He had no idea how right he was. A senator named Casca lunged with his dagger a moment later, gashing Caesar's neck. "Casca, you villain, what are you doing?" Caesar cried, still more confused than angry. But as the crowd of "petitioners" pressed in, each man pulled aside his toga, exposing a bit of skin, and opened the leather pouch on his belt where he normally kept a stylus. Rather than sixty pens, sixty iron daggers emerged. Caesar finally understood. Sic semper tyrannis.

Caesar fought back at first, but after the first few stabs the marble floor beneath his sandals grew slippery with blood. He soon got tangled in his garment and fell. At this the assassins pounced, stabbing Caesar twenty-three times in all. In looking over the body later, Caesar's doctor determined that twenty-two of the gashes were superficial. To be sure, his body would have panicked a little more with each wound, and the shock would have withdrawn blood from periphery to core, to keep oxygen flowing to his vital organs. But he still would have survived, the doctor said, if not for one of the cuts: a single stab to the heart.

According to most accounts, Caesar wrapped himself in his toga before falling, and died without a whimper. But according to one account—and it's easy to see why this account above all has captivated people for two thousand years—Caesar felt a stab in his groin just before going down, and wiped his blood-smeared eyes. In doing so he spotted his protégé Brutus amid the pack, his dagger gleaming red. Caesar took this in and murmured, "You, too, my son?," half question, half answer. He then covered himself to preserve a little dignity, and crumpled to the floor with a final, pained gasp.

So what "happened" to that breath? At first the answer seems obvious: it's gone. Caesar died so long ago that little remains of the building where he fell, much less of his body, which was cremated into ash. Even the iron daggers have likely disintegrated by now, rusting into scabs of dust. So how could something as ephemeral as a breath still linger? If nothing else, the atmosphere extends so far and wide that Caesar's last gasp has surely been dissolved into nothingness by now, effaced into the æther. You can open a vein into the ocean, but you don't expect a pint of blood to wash ashore two thousand years later.

I mean, consider the numbers. Your lungs expel a half liter of air with every normal breath; a gasping Caesar probably exhaled a full liter, a volume equivalent to a balloon five inches wide. Now compare that balloon to the sheer size of the atmosphere. Depending on where you cut it off, the bulk of the atmosphere forms a shell around Earth about ten miles high. Given those dimensions, that shell has a volume of two billion cubic miles. Compared to the atmosphere at large, then, a one-liter breath represents just 0.00000000000000000001 percent of all the air on Earth. Talk about tiny: Imagine gathering together all of the hundred billion people who ever lived—you, me, every last Roman emperor and pope and Dr. Who. If we let those billions of people stand for the atmosphere, and reduce our population by that percentage, you'd have just 0.00000000001 "people" left, a speck of a few hundred cells, a last breath indeed. Compared to the atmosphere, Caesar's gasp seems like a rounding error, a cipher, and the odds of encountering any of it in your next breath seem nil.

Before we shut the door on the possibility, though, consider how quickly gases spread around the planet. Within about two weeks, prevailing winds would have smeared Caesar's last breath all around the world, in a band at roughly the same latitude as Rome—through the Caspian Sea, through southern Mongolia, through Chicago and Cape Cod. Within about two months, the breath would cover the entire Northern Hemisphere. And within a year or two, the entire globe. (The same holds true today, naturally—any breath or belch or exhaust fume anywhere on Earth will take roughly two weeks, two months, or one or two years to reach you, depending on your relative location.)

Surely, though, wouldn't those winds have spread the breath so thin that nothing remained? Wouldn't the breadth of the breath erase it? Perhaps not. In the discussion above, we treated Caesar's breath as a single mass, a single thing. But if we drill down to the itty-bitty, this singular mass of air pixelates out into discrete molecules. So while on some level (the human level) Caesar's last breath does seem to have disappeared into the atmosphere, on a microscopic level his breath hasn't disappeared at all, since the individual molecules that make it up still exist. (Despite how "soft" air seems, most air molecules are pretty hardy: the bonds that bind their atoms together are some of the strongest in nature.) So in asking whether you just inhaled some of Caesar's last breath, I'm really asking whether you inhaled any molecules he happened to expel at that moment.

The answer of course depends on how many molecules we're talking. And with a bit of freshman chemistry, you can calculate that one liter of air at any sort of reasonable temperature and pressure corresponds to approximately 25 sextillion (25,000,000,000,000,000,000,000) molecules. That's a stupefying number, big beyond comprehension. Imagine Bill Gates cashing out his entire $80 billion fortune, converting it to $1 bills, and then stuffing them all under his mattress. Imagine then that he withdraws every individual dollar, one by one, and uses each one as seed money to found another software company. Now imagine that each of those 80 billion companies goes off like gangbusters and yields a return of $80 billion on its own. Add all that cash together—80 billion times 80 billion—and you're still four times short of the number of molecules you inhale with every breath. All the world's roads and all the world's canals and all the world's airports in the history of humankind haven't handled nearly as much traffic as our lungs do every second. From this perspective Caesar's last breath seems innumerable, and it seems inevitable that you'd inhale at least a few molecules of it in your next breath.

So which number wins out? The gargantuan number of molecules that Caesar expelled, or the insignificance of any single breath compared with the atmosphere? To answer that, it might help to consider an analogous situation, a prison break and a manhunt.

Say that all 300 inmates of Alcatraz at its peak—Al Capone, Robert "Birdman" Stroud, George "Machine Gun" Kelly, and 297 close friends—overwhelmed the guards, snagged some boats, and escaped to the mainland. Say also that, being street-smart, the fugitives flee San Francisco and (much like a gas) diffuse across the entire United States to lower their chances of capture. Say finally that you're a bit paranoid about all this, and you want to know whether any fugitive will likely wander into your hometown. Are your fears justified?

Well, the United States covers 3.8 million square miles. Given 300 inmates, that works out to around one fugitive per 125,000 square miles. My hometown in South Dakota sprawls across roughly 75 square miles of prairie, so the number of Alcatraz escapees we could expect there—divide 75 by 125,000—is 0.006. In other words, zero. We can't be sure it's zero, because one might randomly show up. But in all likelihood Alcatraz simply couldn't have flooded the country with enough thugs to make my hometown a probable sanctuary.

There are bigger prisons than Alcatraz, though. Imagine the same scenario unfolding with Cook County Jail in Chicago, which holds 10,000 inmates. Because more prisoners would be flooding the country, the odds of one matriculating in my hometown would rise to around 20 percent. Still not a certainty, but suddenly I'm sweating. The odds would of course rise still higher if the entire U.S. prison population (an incredible 2.2 million people) all escaped at once. This time the number of convicts on the lam in my hometown would jump to 43—not percent, but 43 actual fugitives. With Alcatraz, in other words, the tininess of my hometown within the vast United States kept it safe. But in an apocalyptic, nationwide prison break, the sheer number of escapees would overwhelm that tininess and all but ensure that some of the outlaws would take refuge there.

With that in mind, consider Caesar's final breath again. The molecules of air escaping his lungs are the prisoners escaping their cells. Their spread across the country is the diffusion of gas molecules into the atmosphere. And the odds of a prisoner ending up in a (relatively tiny) given town are the odds of any one molecule getting swept up in your (relatively tiny) next breath. So the question becomes: Is Caesar's final breath like Alcatraz, spilling too few molecules into the air to make a difference? Or is it like the entire U.S. prison population escaping, making it a statistical certainty?

Somewhere in between. Sort of like matter meeting antimatter, the 25,000,000,000,000,000,000,000 molecules and the 0.00000000000000000001 percent almost exactly cancel each other out. When you crunch the numbers, you'll find that roughly one particle of "Caesar air" will appear in your next breath. That number might drop a little depending on what assumptions you make, but it's highly likely that you just inhaled some of the very atoms Caesar used to sound his cri de coeur contra Brutus. And it's a certainty that, over the course of a day, you inhale thousands.

Think about that. Across all that distance of time and space, a few of the molecules that danced inside his lungs are dancing inside yours right now. And given how often we breathe (once every four seconds), this happens 20,000 times every day. Over the years you might even incorporate some of them into your body. Nothing liquid or solid of Julius Caesar remains. But you and Julius are practically kissing cousins. To misquote a poet, the atoms belonging to his breath as good as belong to you.

Mind you, there's nothing special about Caesar, either. I've heard variants of the "Caesar's breath" problem that used Jesus on the cross as the protagonist (I went to Catholic school), and really, you could pick anyone who suffered through an agonizing last breath: the masses at Pompeii, Jack the Ripper's victims, soldiers who died during gas attacks in World War I. Or I could have picked anyone who died in bed, whose last breath was serene—the physics is identical. Heck, I could have picked Rin Tin Tin or Jumbo the giant circus elephant. Think of anything that ever breathed, from bacteria to blue whales, and some of his, her, or its last breath is either circulating inside you now or will be shortly.

Nor should we limit ourselves to stories about breathing. The how-many-molecules-in-X's-last-breath exercise has become a classic thought experiment in physics and chemistry courses. But whenever I heard someone rattle on about so-and-so's last breath, I always got restless. Why not be more audacious? Why not go further and trace these air molecules to even bigger and wilder phenomena? Why not tell the full story of all the gases we inhale?

Every milestone in Earth's history, you see—from the first Hadean volcanic eruptions to the emergence of complex life—depended critically on the behavior and evolution of gases. Gases not only gave us our air, they reshaped our solid continents and transfigured our liquid oceans. The story of Earth is the story of its gases. Much the same can be said of human beings, especially in the past few centuries. When we finally learned to harness the raw physical power of gases, we could suddenly build steam engines and blast through billion-year-old mountains in seconds with explosives. Similarly, when we learned to exploit the chemistry of gases, we could finally make steel for skyscrapers and abolish pain in surgery and grow enough food to feed the world. Like Caesar's last breath, that history surrounds you every second: every time the wind comes clattering through the trees, or a hot-air balloon soars overhead, or an unaccountable smell of lavender or peppermint or even flatulence wrinkles your nose, you're awash in it. Put your hand in front of your mouth again and feel it: we can capture the world in a single breath.

That's the goal of Caesar's Last Breath—to make these invisible stories of gases visible, so you can see them as clearly as you can see your breath on a crisp November morning. At various points in the book we'll swim with radioactive pigs in the ocean and hunt insects the size of dachshunds. We'll watch Albert Einstein struggle to invent a better refrigerator, and we'll ride shotgun with pilots unleashing top-secret "weather warfare" on Vietnam. We'll march with angry mobs, and be buried inside an avalanche of vapors so hot that people's brains boiled inside their skulls. All of these tales pivot on the surprising behavior of gases, gases from lava pits and the guts of microbes, from test tubes and car engines, from every corner of the periodic table. We still breathe most of them today, and each chapter in this book picks one of them as a lens to examine the sometimes tragic, sometimes farcical role that gases played in the human saga.

The book's first section, "Making Air: Our First Four Atmospheres," covers gases in nature. This includes the formation of our very planet from a cloud of space gas 4.5 billion years ago. Later a proper atmosphere emerged on our planet, as volcanoes began expelling gases from deep inside Earth. The emergence of life then scrambled and remixed this original atmosphere, leading to the so-called oxygen catastrophe (which actually worked out pretty well for us animals). Overall the first section explains where air comes from and how gases behave in different situations.

The second section, "Harnessing Air: The Human Relationship with Air," examines how human beings have, well, harnessed the special talents of different gases over the past few centuries. We normally don't think of air as having much mass or weight, but it does: if you drew an imaginary cylinder around the Eiffel Tower, the air inside it would weigh more than all the metal. And because air and other gases have weight, they can lift and push and even kill. Gases powered the Industrial Revolution and fulfilled humanity's ancient dream of flying.

The book's third section—"Frontiers: The New Heavens"—explores how our relationship with air has evolved in the past few decades. For one thing, we've changed the composition of what we breathe: the air you inhale now is not the same air your grandparents inhaled in their youth, and it's markedly different from the air people breathed three hundred years ago. We've also started to explore the atmospheres of planets beyond our solar system, opening up the possibility that our ancestors could leave Earth altogether and start over on a planet filled with gases we can't even imagine yet.

In addition to these big stories, the book also contains a series of vignettes, collectively called "Interludes." They expand on the themes and ideas in the main chapters and explain the role that gases play in phenomena like refrigeration, home lighting, and intestinal distress. (Just for kicks, a few vignettes also stray into some not-so-everyday topics, such as spontaneous combustion and the Roswell alien "invasion.") Many of the gases featured in these sections are trace components of air—compounds that make up just a few parts per million, or a few parts per billion, of what we breathe. But in this context trace doesn't mean insignificant. Think of a glass of wine. Wine is well over 99 percent water and alcohol, but water and alcohol alone do not a wine make. Wines have scores of other flavors—hints of leather, chocolate, musk, plums, and so on. Just so, trace gases in the air add overtones and finish to the air we breathe and the stories we can tell.

If you ask people on the street what air is, you often get wildly different accounts, depending on which gases they focus on or whether they're talking about air on a microscopic or macroscopic level. That's fine: air is big enough to accommodate all those points of view. In fact, I hope this book compels you to revise your own mental picture of air, and I think your notion of air will indeed shift from chapter to chapter, leaving you with a more holistic view of it.

It's worth asking yourself what you think of air, too, because air is the single most important thing in your environment right now. You can survive without food, without solids, for weeks. You can survive without water, without liquids, for days. Without air, without gases, you'd last a few minutes at most. I'll wager, though, that you spend the least amount of time thinking about what you're breathing. Caesar's Last Breath aims to change that. Pure air is colorless and (ideally) odorless, and by itself it sounds like nothing. That doesn't mean it's mute, that it has no voice. It's burning to tell its story. Here it is.