Storm in a Teacup Read online

  To my parents,

  Jan and Sue

  While I was a university student, I spent a while doing physics revision at my Nana’s house. Nana, a down-to-earth northerner, was very impressed when I told her that I was studying the structure of the atom.

  “Ooh,” she said, “and what can you do when you know that?”

  It is a very good question.

  CONTENTS

  Introduction

  1. Popcorn and Rockets

  2. What Goes Up Must Come Down

  3. Small Is Beautiful

  4. A Moment in Time

  5. Making Waves

  6. Why Don’t Ducks Get Cold Feet?

  7. Spoons, Spirals, and Sputnik

  8. When Opposites Attract

  9. A Sense of Perspective

  References

  Acknowledgments

  Index

  STORM

  in a

  TEACUP

  INTRODUCTION

  WE LIVE ON the edge, perched on the boundary between planet Earth and the rest of the universe. On a clear night, anyone can admire the vast legions of bright stars, familiar and permanent, landmarks unique to our place in the cosmos. Every human civilization has seen the stars, but no one has touched them. Our home here on Earth is the opposite: messy, changeable, bursting with novelty and full of things that we touch and tweak every day. This is the place to look if you’re interested in what makes the universe tick. The physical world is full of startling variety, caused by the same principles and the same atoms combining in different ways to produce a rich bounty of outcomes. But this diversity isn’t random. Our world is full of patterns.

  If you pour milk into your tea and give it a quick stir, you’ll see a swirl, a spiral of two fluids circling each other while barely touching. In your teacup, the spiral lasts just a few seconds before the two liquids mix completely. But it was there for long enough to be seen, a brief reminder that liquids mix in beautiful swirling patterns and not by merging instantaneously. The same pattern can be seen in other places too, for the same reason. If you look down on the Earth from space, you will often see very similar swirls in the clouds, made where warm air and cold air waltz around each other instead of mixing directly. In Britain, these swirls come rolling across the Atlantic from the west on a regular basis, causing our notoriously changeable weather. They form at the boundary between cold polar air to the north and warm tropical air to the south. The cool and warm air chase each other around in circles, and you can see the pattern clearly on satellite images. We know these swirls as depressions or cyclones, and we experience rapid changes between wind, rain, and sunshine as the arms of the spiral spin past.

  A rotating storm might seem to have very little in common with a stirred mug of tea, but the similarity in the patterns is more than coincidence. It’s a clue that hints at something more fundamental. Hidden beneath both is a systematic basis for all such formations, one discovered and explored and tested by rigorous experiments carried out by generations of humans. This process of discovery is science: the continual refinement and testing of our understanding, alongside the digging that reveals even more to be understood.

  Sometimes a pattern is easy to spot in new places. But sometimes the connection goes a little bit deeper and so it’s all the more satisfying when it finally emerges. For example, you might not think that scorpions and cyclists have much in common. But they both use the same scientific trick to survive, although in opposite ways.

  A moonless night in the North American desert is cold and quiet. Finding anything out here seems close to impossible, since the ground is lit only by dim starlight. But to find one particular treasure, you equip yourself with a special flashlight and set out into the darkness. The flashlight needs to be one that produces light that is invisible to our species: ultraviolet light, or “black light.” As the beam roams across the ground, it’s impossible to tell exactly where it’s pointing because it’s invisible. Then there’s a flash, and the darkness of the desert is punctured by a surprised scuttling patch of eerie bright blue-green. It’s a scorpion.

  This is how enthusiasts find scorpions. These black arachnids have pigments in their exoskeleton that take in ultraviolet light that we can’t see and give back visible light that we can see. It’s a really clever technique, although if you’re scared of scorpions to start with, your appreciation might be a little muted. The name for this trick of the light is fluorescence. The blue-green scorpion glow is thought to be an adaptation to help the scorpions find the best hiding places at dusk. Ultraviolet light is around all the time, but at dusk, when the sun has just slipped below the horizon, most of the visible light has gone and only the ultraviolet is left. So if the scorpion is out in the open, it will glow and be easy to spot because there isn’t much other blue or green light around. If the scorpion is even slightly exposed, it can detect its own glow and so it knows it needs to do a better job of hiding. It’s an elegant and effective signaling system—or was until the humans bearing ultraviolet torches turned up.

  Fortunately for the arachnophobes, you don’t need to be in a scorpion-populated desert at night to see fluorescence—it’s pretty common on a dull morning in the city as well. Look again at those safety-conscious cyclists: their high-visibility jackets seem oddly bright compared with the surroundings. It looks as though they’re glowing, and that’s because they are. On cloudy days, the clouds block the visible light, but lots of ultraviolet still gets through. The pigments in the high-visibility jackets are taking in the ultraviolet and giving back visible light. It’s exactly the same trick the scorpions are playing, but for the opposite reason. The cyclists want to glow; if they’re emitting that extra light, they’re easier to see and so safer. This sort of fluorescence is pretty much a free lunch for humans; we’re not aware of the ultraviolet light in the first place, so we don’t lose anything when it gets turned into something we can use.

  It’s fascinating that it happens at all, but the real joy for me is that a nugget of physics like that isn’t just an interesting fact: It’s a tool that you carry with you. It can be useful anywhere. In this case, the same bit of physics helps both scorpions and cyclists survive. It also makes tonic water glow under ultraviolet light, because the quinine in it is fluorescent. And it’s how laundry brighteners and highlighter pens work their magic. Next time you look at a highlighted paragraph, bear in mind that the highlighter ink is also acting as an ultraviolet detector; even though you can’t see the ultraviolet directly, you know it’s there because of this glow.

  I studied physics because it explained things that I was interested in. It allowed me to look around and see the mechanisms making our everyday world tick. Best of all, it let me work some of them out for myself. Even though I’m a professional physicist now, lots of the things I’ve worked out for myself haven’t involved laboratories or complicated computer software or expensive experiments. The most satisfying discoveries have come from random things I was playing with when I wasn’t meant to be doing science at all. Knowing about some basic bits of physics turns the world into a toybox.

  There is sometimes a bit of snobbery about the science found in kitchens and gardens and city streets. It’s seen as something to occupy children with, a trivial distraction which is important for the young, but of no real use to adults. An adult might buy a book about how the universe works, and that’s seen as being a proper adult topic. But that attitude misses something very important: The same physics applies everywhere. A toaster can teach you about some of the most fundamental laws of physics, and the benefit of a toaster is that you’ve probably got one, and you can see it working for yourself. Physics is awesome precisely because the same patterns are universal: They exist both in the kitchen and in the f
arthest reaches of the universe. The advantage of looking at the toaster first is that even if you never get to worry about the temperature of the universe, you still know why your toast is hot. But once you’re familiar with the pattern, you will recognize it in many other places, and some of those other places will be the most impressive achievements of human society. Learning the science of the everyday is a direct route to the background knowledge about the world that every citizen needs in order to participate fully in society.

  Have you ever had to tell apart a raw egg and a boiled egg without taking their shells off? There’s an easy way to do it. Put the egg down on a smooth, hard surface and set it spinning. After a few seconds, briefly touch the outside of the shell with one finger, just enough to stop the egg’s rotation. The egg might just sit there, stationary. But after a second or two, it might slowly start to spin again. Raw and boiled eggs look the same on the outside, but their insides are different, and that gives the secret away. When you touched the cooked egg, you stopped a whole solid object. But when you stopped the raw egg, you only stopped the shell. The liquid inside never stopped swirling around, and so after a second or so, the shell started to rotate again, because it was being dragged around by its insides. If you don’t believe me, go find an egg and try it. It is a principle of physics that objects tend to continue the same sort of movement unless you push or pull on them. In this case, the total amount of spin of the egg white stays the same because it had no reason to change. This is known as conservation of angular momentum. And it doesn’t just work in eggs.

  The Hubble Space Telescope, an orbiting eye that has been whooshing around our planet since 1990, has produced many thousands of spectacular images of the cosmos. It has sent back pictures of Mars, the rings of Uranus, the oldest stars in the Milky Way, the wonderfully named Sombrero Galaxy, and the giant Crab Nebula. But when you’re floating freely in space, how do you hold your position as you gaze on such tiny pinpoints of light? How do you know precisely which way you’re facing? Hubble has six gyroscopes, each of which is a wheel spinning at 19,200 revolutions per second. Conservation of angular momentum means that those wheels will keep spinning at that rate because there is nothing to slow them down. And the spin axis will stay pointed in precisely the same direction, because it has no reason to move. The gyroscopes give Hubble a reference direction, so that its optics can stay locked on a distant object for as long as necessary. The physical principle used to orient one of the most advanced technologies our civilization can produce can be demonstrated with an egg in your kitchen.

  This is why I love physics. Everything you learn will come in useful somewhere else, and it’s all one big adventure because you don’t know where it will take you next. As far as we know, the physical laws we observe here on Earth apply everywhere in the universe. Many of the nuts and bolts of our universe are accessible to everyone. You can test them for yourself. What you can learn with an egg hatches into a principle that applies everywhere. You step outside armed with your hatchling, and the world looks different.

  In the past, information was treasured more than it is now. Each nugget was hard-earned and valuable. These days, we live on the shore of an ocean of knowledge, one with regular tsunamis that threaten our sanity. If you can manage your life as you are, why seek more knowledge and therefore more complications? The Hubble Space Telescope is all very nice, but unless it’s also going to look downward once in a while to find your keys when you’re late for a meeting, does it make any difference?

  Humans are curious about the world, and we get a lot of joy from satisfying our curiosity. The process is even more rewarding if you work things out for yourself, or if you share the journey of discovery with others. And the physical principles you learn from playing also apply to new medical technologies, the weather, mobile phones, self-cleaning clothes, and fusion reactors. Modern life is full of complex decisions: Is it worth paying more for a compact fluorescent light bulb? Is it safe to sleep with my phone next to my bed? Should I trust the weather forecast? What difference does it make if my sunglasses have polarizing lenses? The basic principles alone often won’t provide specific answers, but they’ll provide the context needed to ask the right questions. And if we’re used to working things out for ourselves, we won’t feel helpless when the answer isn’t obvious on the first try. We’ll know that with a bit of extra thinking, we can clarify things. Critical thinking is essential to make sense of our world, especially with advertisers and politicians all telling us loudly that they know best. We need to be able to look at the evidence and work out whether we agree with them. And there’s more than our own daily lives at stake. We are responsible for our civilization. We vote, we choose what to buy and how to live, and we are collectively part of the human journey. No one can understand every single detail of our complex world, but the basic principles are fantastically valuable tools to take with you on the way.

  Because of all this, I think that playing with the physical toys in the world around us is more than “just fun,” even though I’m a huge fan of fun for its own sake. Science isn’t just about collecting facts; it’s a logical process for working things out. The point of science is that everyone can look at the data and come to a reasoned conclusion. At first, those conclusions may differ, but then you go and collect more data that helps you decide between one description of the world and another, and eventually the conclusions converge. This is what separates science from other disciplines—a scientific hypothesis must make specific testable predictions. That means that if you have an idea about how you think something works, the next thing to do is to work out what the consequences of your idea would be. In particular, you have to look hard for consequences that you can check for, and especially for consequences that you can prove wrong. If your hypothesis passes every test we can think of, we cautiously agree that this is probably a good model for the way the world works. Science is always trying to prove itself wrong, because that’s the quickest route to finding out what’s actually going on.

  You don’t have to be a qualified scientist to experiment with the world. Knowing some basic physical principles will set you on the right track to work a lot of things out for yourself. Sometimes, it doesn’t even have to be an organized process—the jigsaw pieces almost slot themselves into place.

  One of my favorite voyages of discovery started with disappointment: I made blueberry jam and it turned out pink. Bright fuchsia pink. It happened a few years ago, when I was living in Rhode Island, sorting out the last bits and pieces before moving back to the UK. Most things were done, but there was one last project that I was adamant about fitting in before I left. I had always loved blueberries—they were slightly exotic, delicious, and beautifully and bizarrely blue. In most places I’ve lived they come in frustratingly small quantities, but in Rhode Island they grow in abundance. I wanted to convert some of the summer blueberry bounty into blue jam to take back to the UK. So I spent one of my last mornings there picking and sorting blueberries.

  The most important and exciting thing about blueberry jam is surely that it is blue. I thought so, anyway. But nature had other ideas. The pan of bubbling jam was many things, but blue was not one of them. I filled the jam jars, and the jam really did taste lovely. But the lingering disappointment and confusion followed me and my pink jam back to the UK.

  Six months later, I was asked by a friend to help with a historical conundrum. He was making a TV program about witches, and he said that there were records of “wise women” boiling verbena petals in water and putting the resulting liquid on people’s skin as a way of telling whether they were bewitched. He wondered whether they were measuring something systematically, even if it wasn’t what they intended. I did a bit of research and found that maybe they were.

  Purple verbena flowers, along with red cabbage, blood oranges, and lots of other red and purple plants, contain chemical compounds called anthocyanins. These anthocyanins are pigments, and they give the plants their bright colors. There are a few diffe
rent versions, so the color varies a bit, but they all have a similar molecular structure. That’s not all, though. The color also depends on the acidity of the liquid that the molecule is in—what’s called its “pH value.” If you make that environment a little more acidic or a little more alkaline, the molecules change shape slightly and so their color changes. They are indicators, nature’s version of litmus paper.

  You can have lots of fun in the kitchen with this. You need to boil the plant to get the pigment out, so boil a bit of red cabbage in water, and then save the water (which is now purple). Mix some with vinegar, and it goes red. A solution of laundry powder (a strong alkali) makes it go yellow or green. You can generate a whole rainbow of outcomes just from what’s in your kitchen. I know: I did it. I love this discovery because these anthocyanins are everywhere, and accessible to anyone. No chemistry set required!

  So maybe these wise women were using the verbena flowers to test for pH, not bewitchment. Your skin pH can vary naturally, and putting the verbena concoction on skin could produce different colors for different people. I could make cabbage water go from purple to blue when I was nice and sweaty after a long run, but it didn’t change color when I hadn’t been exercising. The wise women may have noticed that different people made the verbena pigments change in different ways, and put their own interpretation on it. We’ll never know for sure, but it seems to me to be a reasonable hypothesis.

  So much for history. And then I remembered the blueberries and the jam. Blueberries are blue because they contain anthocyanins. Jam has only four ingredients: fruit, sugar, water, and lemon juice. The lemon juice helps the natural pectin from the fruit do its job of making the jam set. It does that because . . . it’s acid. My blueberry jam was pink because the boiled blueberries were acting as a saucepan-sized litmus test. It had to be pink for the jam to set properly. The excitement of working that out almost made up for the disappointment of never having made blue jam. Almost. But the discovery that there’s a whole rainbow of color to be had from just one fruit is the sort of treasure that’s worth the sacrifice.