The ghosts of breaths past continue to flit around you every second of every hour, confronting you with every single yesterday.
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.
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?
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Caesar’s Last Breath. The Epic Story of the Air around us. by Sam Kean
get it from Amazon