Storm in a Teacup: The Physics of Everyday Life(4)

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?