THERE IS BEAUTY in simplicity. And it’s even more satisfying when that beauty condenses out of complexity. For me, the laws that tell us how gases behave are like one of those optical illusions where you think you’re seeing one thing, and then you blink and look again and see something completely different.
We live in a world made of atoms. Each of these tiny specks of matter is coated with a distinctive pattern of negatively charged electrons, chaperones to the heavy and positively charged nucleus within. Chemistry is the story of those chaperones sharing duties between multiple atoms, shifting formation while always obeying the strict rules of the quantum world, and holding the captive nuclei in larger patterns called molecules. In the air I’m breathing as I type this, there are pairs of oxygen atoms (each pair is one oxygen molecule) moving at 900 mph bumping into pairs of nitrogen atoms going at 200 mph, and then maybe bouncing off a water molecule going at over 1,000 mph. It’s horrifically messy and complicated—different atoms, different molecules, different speeds—and in each cubic inch of air there are about 500,000,000,000,000,000,000 (3 × 1020) individual molecules, each colliding about a billion times a second. You might think that the sensible approach to all that is to quit while you’re ahead and take up brain surgery or economic theory or hacking supercomputers instead. Something simpler, anyway. So it’s probably just as well that the pioneers who discovered how gases behave had no idea about any of it. Ignorance has its uses. The idea of atoms wasn’t really a part of science until the early 1800s and absolute proof of their existence didn’t turn up until around 1905. Back in 1662, all that Robert Boyle and his assistant, Robert Hooke, had was glassware, mercury, some trapped air, and just the right amount of ignorance. They found that as the pressure on a pocket of air increased, its volume decreased. This is Boyle’s Law, and it says that gas pressure is inversely proportional to volume. A century later, Jacques Charles found that the volume of a gas is directly proportional to its temperature. If you double the temperature, you double the volume. It’s almost unbelievable. How can so much atomic complication lead to something so simple and so consistent?
ONE LAST INTAKE of air, one calm flick of its fleshy tail, and the giant leaves the atmosphere behind. Everything this sperm whale needs to live for the next forty-five minutes is stored in its body, and the hunt begins. The prize is a giant squid, a rubbery monster armed with tentacles, vicious suckers, and a fearsome beak. To find its prey, the whale must venture deep into the real darkness of the ocean, to the places never touched by sunlight. Routine dives will reach 1,600–3,200 feet, and the measured record is around 1.2 miles. The whale probes the blackness with highly directional sonar, waiting for the faint echo that suggests dinner might be close. And the giant squid floats unaware and unsuspecting, because it is deaf.
The most precious treasure the whale carries down into the gloom is oxygen, needed to sustain the chemical reactions that power the swimming muscles, and the whale’s very life. But the gaseous oxygen supplied by the atmosphere becomes a liability in the deep—in fact, as soon as the whale leaves the surface, the air in its lungs becomes a problem. For every additional yard it swims downward, the weight of one extra yard of water presses inward. Nitrogen and oxygen molecules are bouncing off each other and the lung walls, and each collision provides a minuscule push. At the surface, the inward and outward pushes on the whale balance. But as the giant sinks, it is squashed by the additional weight of the water above it, and the push of the outside overwhelms the push from the inside. So the walls of the lungs move inward until equilibrium, the point where the pushes are balanced once again. A balance is reached because as the whale’s lung compresses, each of the molecules has less space and collisions between them become more common. That means that there are more molecules hammering outward on each bit of the lungs, so the pressure inside increases until the hammering molecules can compete equally with those outside. Thirty-two feet of water depth is enough to exert additional pressure equivalent to a whole extra atmosphere. So even at that depth, while it could still easily see the surface (if it were looking), the whale’s lungs reduce to half the volume that they were. That means there are twice as many molecular collisions on the walls, matching the doubled pressure from outside. But the squid might be half a mile below the surface, and at that depth the vast pressure of water could reduce the lungs to less than 1 percent of the volume they have at the surface.
Eventually, the whale hears the reflection of one of its loud clicks. With shrunken lungs, and only sonar to guide it, it must now prepare for battle in the vast darkness. The giant squid is armed, and even if it eventually succumbs, the whale may well swim away with horrific scars. Without oxygen from its lungs, how does it even have the energy to fight?
The problem of the shrunken lungs is that if their volume is only one-hundredth of what it was at the surface, the pressure of the gas in there will be one hundred times greater than atmospheric pressure. At the alveoli, the delicate part of the lungs where oxygen and carbon dioxide are exchanged into and out of the blood, this pressure would push both extra nitrogen and extra oxygen to dissolve in the whale’s bloodstream. The result would be an extreme case of what divers call “the bends,” and as the whale returned to the surface the extra nitrogen would bubble up in its blood, doing all sorts of damage. The evolutionary solution is to shut off the alveoli completely, from the moment the whale leaves the surface. There is no alternative. But the whale can access its energy reserves because its blood and muscles can store an extraordinary amount of oxygen. A sperm whale has twice as much hemoglobin as a human, and about ten times as much myoglobin (the protein used to store energy in the muscles). While it was at the surface, the whale was recharging these vast reservoirs. Sperm whales are never breathing from their lungs when they make these deep dives. It’s far too dangerous. And they’re not just using their one last breath while they’re underwater. They’re living—and fighting—on the surplus that’s stored in their muscles, the cache gathered during the time they spent at the surface.