Storm in a Teacup Page 2
This book is about linking the little things we see every day with the big world we live in. It’s a romp through the physical world, showing how playing with things like popcorn, coffee stains, and refrigerator magnets can shed light on Scott’s expeditions, medical tests, and solving our future energy needs. Science is not about “them,” it’s about “us,” and we can all go on this adventure in our own way. Each chapter begins with something small in the everyday world, something that we will have seen many times but may never have thought about. By the end of each chapter, we’ll see the same patterns explaining some of the most important science and technology of our time. Each mini-quest is rewarding in itself, but the real payoff comes when the pieces are put together.
There’s another benefit to knowing about how the world works, and it’s one that scientists don’t talk about often enough. Seeing what makes the world tick changes your perspective. The world is a mosaic of physical patterns, and once you’re familiar with the basics, you start to see how those patterns fit together. I hope that as you read this book, the scientific hatchlings from the chapters along the way will grow into a different way of seeing the world. The final chapter of this book is an exploration of how the patterns interlock to form our three life-support systems—the human body, our planet, and our civilization. But you don’t have to agree with my perspective. The essence of science is experimenting with the principles for yourself, considering all the evidence available, and then reaching your own conclusions.
The teacup is only the start.
CHAPTER 1
Popcorn and Rockets
EXPLOSIONS IN THE kitchen are generally considered a bad idea. But just occasionally, a small one can produce something delicious. A dried corn kernel contains lots of nice food-like components—carbohydrates, proteins, iron, and potassium—but they’re very densely packed and there’s a tough armored shell in the way. The potential is tantalizing, but to make it edible you need some extreme reorganization. An explosion is just the ticket, and very conveniently, this seed carries the seeds of its own destruction within it. Last night, I did a bit of ballistic cooking and made popcorn. It’s always a relief to discover that a tough, unwelcoming exterior can conceal a softer inside—but why does this one make fluff instead of blowing itself to bits?
Once the oil in the pan was hot, I added a spoonful of kernels, put the lid on, and left it while I put the kettle on to make tea. Outside, a huge storm was raging, and chunky raindrops were hammering against the window. The corn sat in the oil and hissed gently. It looked to me as though nothing was happening, but inside the pan, the show had already started. Each corn kernel contains a germ, which is the start of a new plant, and the endosperm, which is there as food for the new plant. The endosperm is made up of starch packaged into granules, and it contains about 14 percent water. As the kernels sat in the hot oil, that water was starting to evaporate, turning into steam. Hotter molecules move faster, so that as each kernel heated up, there were more and more water molecules whooshing around inside it as steam. The evolutionary purpose of a corn kernel’s shell is to withstand assault from outside, but it now had to contain an internal rebellion—and it was acting like a mini pressure cooker. The water molecules that had turned to steam were trapped with nowhere to go, so the pressure inside was building up. Molecules of gas are continually bumping into each other and into the walls of the container, and as the number of gas molecules increased and they moved faster, they were hammering harder and harder on the inside of the shell.
Pressure cookers work because hot steam cooks things very effectively, and it’s no different inside popcorn. As I searched for teabags, the starch granules were being cooked into a pressurized gelatinous goo, and the pressure kept going up. The outer shell of a popcorn kernel can withstand this stress, but only up to a point. When the temperature inside approaches 360°F and the pressure gets up to nearly ten times the normal pressure of the air around us, the goo is on the edge of victory.
I gave the pan a little shake and heard the first dull pop echoing around the inside. After a couple of seconds, it sounded as though a mini machine gun was being fired in there, and I could see the lid lifting as it got hit from underneath. Each individual pop also came with a fairly impressive puff of steam from the edge of the pan lid. I left it for a moment to pour a cup of tea, and in those few seconds, the barrage from underneath shifted the lid and fluff started taking flight.
At the moment of catastrophe, the rules change. Until that point, a fixed amount of water vapor is confined, and the pressure it exerts on the inside of the shell increases as the temperature increases. But when the hard shell finally succumbs, the insides are exposed to the atmospheric pressure in the rest of the pan and there is no volume limit anymore. The starchy goo is still full of hot hammering molecules but nothing is pushing back from the other side. So it expands explosively, until the pressure inside matches the pressure outside. Compact white goo becomes expansive white fluffy foam, turning the entire kernel inside-out; and as it cools, it solidifies. The transformation is complete.
Tipping the popped corn out revealed a few casualties left behind. Dark burnt unpopped corn rattled sadly around the bottom of the pan. If the outer shell is damaged, water vapor escapes as it is heated, and the pressure never builds up. The reason that popcorn pops and other grains don’t is that all the others have porous shells. If a kernel is too dry, perhaps because it was harvested at the wrong time, there isn’t enough water inside it to build up the pressure needed to burst the shell. Without the violence of an explosion, inedible corn remains inedible.
I took the bowl of perfectly cooked fluff and the tea over to the window and stood watching the storm. Destruction doesn’t always have to be a bad thing.
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 t
o 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.
No one has ever seen the battle between a sperm whale and a giant squid. But the stomachs of dead sperm whales contain collections of squid beaks, the only part of the squid that can’t be digested. So each whale carries its own internal tally of fights won. As a successful whale swims back toward the sunlight, its lungs gradually reinflate and reconnect with its blood supply. As the pressure decreases, the volume once again increases until it has reached its original starting point.
Oddly, the combination of complex molecular behavior with statistics (not usually associated with simplicity) produces a relatively straightforward outcome in practice. There are indeed lots of molecules and lots of collisions and lots of different speeds, but the only two important factors are the range of speeds that the molecules are moving at, and the average number of times they collide with the walls of their container. The number of collisions, and the strength of each collision (due to the speed and mass of that molecule) determine the pressure. The push made by all that compared with the push from the outside determines the volume. And then the temperature has a slightly different effect.
“WHO WOULD NORMALLY be worried at this point?” Our teacher, Adam, is wearing a white tunic stretched over a happily solid belly, exactly what central casting demands of a jolly baker. The strong cockney accent is just a bonus. He pokes at the sad splat of dough on the table in front of him, and it clings on as though it’s alive—which, of course, it is. “What we need for good bread,” he announces, “is air.” I’m at a bakery school being taught how to make focaccia, a traditional Italian bread. I’m pretty sure I haven’t worn an apron since I was ten. And although I’ve baked lots of bread, I’ve never seen dough that looked like the splat, so I’m learning already.
Following Adam’s instructions, we obediently start our own dough from scratch. Each of us mixes fresh yeast with water and then with the flour and salt, and works the dough with therapeutic vigor to develop the gluten, the protein that gives bread its elasticity. The whole time we’re stretching and tearing the physical structure, the living yeast that’s carried along in that structure is busy fermenting sugars and making carbon dioxide. This dough, just like all the others I’ve ever made, doesn’t have any air in it at all—it just has lots of carbon dioxide bubbles. It’s a stretchy sticky golden bioreactor, and the products of the life in it are trapped, so it rises. When this first stage is done, it gets a nice bath in olive oil and keeps rising, while we clean dough off our hands, the table, and a surprising amount of the surroundings. Each individual fermentation reaction produces two molecules of carbon dioxide which are expelled by the yeast. Carbon dioxide, or CO2—two oxygen atoms stuck to a carbon atom—is a small unreactive molecule, and at room temperature it has enough energy to float free as a gas. Once it’s found its way into a bubble with lots of other CO2 molecules, it will play bumper cars for hours. Each time it hits another molecule, there is likely to be some energy exchange, just like a cue ball hitting a snooker ball. Sometimes one will slow down almost completely and the other will take all that energy and zoom off at high speed. Sometimes the energy is shared between them. Every time a molecule bumps into the gluten-rich wall of the bubble, it pushes on the wall as it bounces off. At this stage, this is what makes the bubbles grow—as each one acquires more molecules on the inside, the push outward gets more and more insistent. So the bubble expands until the push back from the atmosphere balances the outward push of the CO2 molecules. Sometimes the CO2 molecules are traveling quickly when they hit the wall and sometimes they’re traveling slowly. Bread bakers, like physicists, don’t care which molecules hit which walls at particular speeds, because this is a game of statistics. At room temperature and atmospheric pressure, 29 percent of them are traveling between 1150 and 1650 feet per second, and it doesn’t matter which ones they are.
Adam claps his hands to get our attention, and uncovers the rising dough with a magician’s flourish. And then he does something that is new to me. He stretches out the oil-covered dough and folds it over on itself, one fold from each side. The aim is clearly to trap air between the folds. My initial unspoken response is “That’s cheating!,” because I had always assumed that all the “air” in bread was CO2 from the yeast. I once
saw an origami master in Japan enthusiastically teaching his students about the correct application of Scotch tape to an angular paper horse, and I felt the same unreasonable outrage then as in the bakery. But if you want air, why not use air? Once it’s cooked, no one will know. I succumb to the knowledge of the expert and meekly fold my own dough. A couple of hours later, after more rising and folding and the incorporation of more olive oil than I had believed possible, my nascent focaccia and its bubbles were ready for the oven. The “air” of both types was about to have its moment.
Inside the oven, heat energy flowed into the bread. The pressure in the oven was still the same as the pressure outside, but the temperature in the bread had suddenly gone up from 68°F to 475°F. In absolute units, that’s from 293 Kelvin to 523 Kelvin, almost a doubling of temperature.* In a gas, that means that the molecules speed up. The bit that’s counter-intuitive is that no individual molecule has its own temperature. A gas—a cluster of molecules—can have a temperature, but an individual molecule within it can’t. Gas temperature is just a way of expressing how much movement energy the molecules have on average, but each individual molecule is constantly speeding up and slowing down, exchanging its energy with the others as they collide. Any individual molecule is just playing bumper cars with the energy it’s got right now. The faster they travel, the harder they bump into the sides of the bubbles, so the greater the pressure they generate. As the bread went into the oven, gas molecules suddenly gained lots more heat energy and so they sped up. The average speed shifted from 1500 feet per second to 2200 feet per second. So the outward push on the bubble walls got much harder and the outsides weren’t pushing back. Each bubble expanded in proportion to the temperature, pushing outward on the dough and forcing it to expand. And here’s the thing . . . the air bubbles (mostly nitrogen and oxygen) expanded in exactly the same way as the CO2 bubbles. This is the last piece of the puzzle. It turns out that it doesn’t matter what the molecules are. If you double the temperature you still double the volume (if you keep the pressure constant). Or, if you keep the volume constant and double the temperature, the pressure will double. The complication of having a mix of different atoms present is irrelevant, because the statistics are the same for any mixture. No one looking at the final bread could ever tell which bubbles had been CO2 and which ones had been air. And then the protein and carbohydrate matrix surrounding the bubbles cooked and solidified. The bubble size was fixed. Fluffy white focaccia was assured.