The Science of Philip Pullman's His Dark Materials

CHAPTER ONE


BRIGHT MATERIALS


The secret of science, and
all the stars that shine


''She walks in beauty, like the night
Of cloudless climes and starry skies;
And all that's best of dark and bright
Meet in her aspect and her eyes:
Thus mellowed to that tender light
Which heaven to gaudy day denies.''
LORD BYRON




...her knowledge was patchy. She knew about atoms and
elementary particles, and anbaromagnetic charges and the four fundamental forces and other bits and pieces of experimental theology, but nothing about the solar system. In fact, when Mrs. Coulter realized this and explained how the earth and the other five planets revolved around the sun, Lyra laughed loudly at the joke.
However, she was keen to show that she did know some things, and when Mrs. Coulter was telling her about electrons, she said expertly, "Yes, they're negatively charged particles. Sort of like Dust, except that Dust isn't charged."
Science is explainable magic. If you were a time traveler visiting our world from the ancient past, you would think that magic was everywhere around you. Planes flying, cars moving, even frozen food would seem strange and miraculous. They are not strange magic to us because we are used to them and because we know they work by science, not magic. In ancient times, people were amazed and awed by things like rainbows and eclipses, things they had no control over. We still can't control these things, but we aren't scared of them, because we understand the science behind them.
In Philip Pullman's His Dark Materials trilogy, when Lyra visits Will's world, things like cars seem magical to her. And in Lyra's world there are things, like the alethiometer, and Dust, that seem like magic to Will. But even these things are really based on science. We are going to tell you about that science, the science of His Dark Materials. The story is all about uncovering hidden truth. The truly big magic that Philip Pullman weaves into his story is the magic that understanding things and knowing how the world works makes it less scary. He shows us that knowledge and science put you more in control of things.
This means more than understanding how a frozen pizza is made. Understanding frozen pizza is pretty smart, but the understanding behind His Dark Materials involves the whole Universe. That's where the "Dark Materials" come from. We're not talking here about the kind of material used to make a shirt or a curtain, but much more mysterious stuff, a kind of invisible matter that fills the Universe.
The worlds inhabited by Lyra, Will, and the other characters are embedded in a sea of Dust, which falls on them from space, and is real, but cannot be seen by human eyes. The characters, especially Lyra and Will, are also surrounded by a sea of knowledge. There is information about the world that they know nothing about when the story begins, but that they learn about, with the help of the alethiometer, as their adventure unfolds.
Both these images are true. Knowledge really does make the world a better place to live in. And astronomers really do have evidence that there is about ten times as much dark stuff in our Universe as there are bright stars and galaxies. Just like Dust, this dark material is not like anything ever detected on Earth. It isn't made of the kind of atoms and molecules your body is made of, or the air you breathe, or anything you have ever touched or seen. But, like Lyra, we have to know about things like atoms and electrons before we can learn about the dark materials in the Universe. And, unlike Lyra, we know a great deal about what goes on in space--not just in our Solar System, where there are actually nine planets, not six, but in the stars and galaxies beyond the planets.
THE STUFF OF THE UNIVERSE
What are atoms? Atoms are tiny particles that move around all the time, bouncing off one another and sometimes sticking together to make molecules. The discovery of atoms is the most important discovery in the whole of science. There are approximately two and a half centimeters in one inch, and an atom is only about one hundred-millionth of a centimeter across, so it would take ten million atoms side by side to stretch across the gap between two of the "teeth" on the jagged edge of a postage stamp. The oxygen molecules that you breathe in to stay alive are made of two oxygen atoms joined together. They don't just waft around gently in the air waiting for you to come along and breathe them in. When it comes to speed, they can go 50 times faster than the fastest 100-yard sprinter, and they never stop for a rest.
Oxygen molecules in the air move at about one-third of a mile per second. If they went in a straight line, they could cover more than 18 miles in a minute. But they never get a chance to go far, because they are always bouncing off other molecules in the air. The average distance they travel between collisions is just five millionths of an inch. They are so close together that they collide with other molecules three and a half billion times every second. That makes 210 billion collisions every minute. Feel free to work out how many that is in a day, a week, a century....
Atoms come in different varieties, corresponding to different kinds of material called elements. There are 92 different elements (things like oxygen, gold, or the silicon used in computer chips) that occur naturally on Earth. Because each variety of element corresponds to a different variety of atom, this means there are 92 different kinds of atoms. Everything we experience in our everyday lives is thanks to these 92 kinds of atoms interacting with each other in different ways. All the stuff around you, everywhere in the Universe, that is made of atoms is called baryonic matter.
THE LIGHT THAT SHINES
When atoms get hot, they radiate energy in the form of light--they shine. The white light that surrounds you in daylight is made of all the colors of the rainbow mixed together. In a rainbow, the colors are spread out to make a spectrum. You can do the same thing by shining light through a triangle of glass, called a prism, to make a spectrum. If you hang a prism in a window on a sunny day, it makes rainbow patterns that dance on the walls. The rainbow pattern is made because the light gets bent when it goes through the prism. Different colors are bent by slightly different amounts, so the colors get spread out. The same thing happens in raindrops to make rainbows. Raindrops are like tiny prisms.
One of the great discoveries of science in the nineteenth century was that each kind of atom shines in a particular way, making its own contribution to the rainbow spectrum of light. This role of the atom is an example of a hidden truth.
All the colors of the rainbow are made by light from shining atoms. Sodium atoms shine very brightly with yellow light. Sodium atoms in the gas in streetlights get their energy from electricity and turn it into yellow light. Every time you see that sort of yellow light, you know sodium is there, even if you can't touch it. If you ever see someone throw ordinary salt into a fire, you see a flash of the same "street lamp" yellow light. That is because salt molecules are made of sodium atoms joined to chlorine atoms (the chemical name for salt is sodium chloride).
BEYOND THE RAINBOW
On Earth, chemists can study the light from every kind of atom and measure the exact color it contributes to the spectrum. A little piece of magic turned into science. Astronomers can take this magic out into space. They measure the strength of light of different colors coming from the Sun and the stars, so they can work out what the stars are made of without ever going into space. That would have seemed like magic even a couple of hundred years ago. We actually know what the stars are made of, even though they are so far away that the light from them takes hundreds or thousands of years to get to us.
The scientific magic of the spectrum shows that all the stars--everything we can see in the Universe--are made of the same kind of atoms that we are made of. It is all baryonic matter.
STARS LIKE DUST
The Sun looks big and bright to us, and we see it in daylight, not at night. But it is an ordinary star. It is about 109 times bigger across than the Earth is and contains about 330,000 times as much material as the Earth does. It shines because, deep inside the Sun, one kind of atom (hydrogen) is being turned into another kind of atom (helium). This process is called nuclear fusion. When light atoms fuse together, they release energy. All stars shine in the same way.
The Sun looks very bright to us because it is quite close, in cosmic terms. The Earth orbits around the Sun once every year, at a distance of about 93 million miles. That's very nearly 400 times farther away from us than the Moon. But it's just next door in the Cosmos.
Other stars are just as bright as the Sun. Some of them are even brighter. But even extra-bright stars look faint to us because they are so far away. If you stood near a huge bonfire, it would look big and bright. But if you stood on a hill a few miles away and looked down on the bonfire, it would look like a tiny flickering flame. It's the same with stars, but the distances are much more than a few miles. Even stars that are quite close to us by cosmic standards are hundreds of thousands of times farther away than the Sun. And there are thousands and thousands of stars so far away that they are too faint to see at all without a telescope.
On a dark, moonless night, far from the city lights, you can see a white band of light across the sky. This is called the Milky Way. Telescopes show that the Milky Way is made up of millions and millions of stars, like a band of white dust scattered across the sky. The Sun is one of the stars of the Milky Way Galaxy. This Milky Way Galaxy is a disk of stars, shaped a bit like a huge fried egg, so big that it would take a beam of light 100,000 years to travel from one side to the other, even though light travels at 186,000 miles a second, or six trillion miles in a year. This huge distance is called a light- year. If you were as near to one of these stars as we are to the Sun, it would look as big and bright as the Sun. There are hundreds of billions of stars like the Sun in the Milky Way Galaxy.
UNIVERSES BEYOND THE UNIVERSE
But this is not the end of the story. Until the 1920s, astronomers thought that the Milky Way Galaxy was the entire Universe, everything that there is. That's less than 100 years ago. Since then, bigger and better telescopes have made it possible to look farther and farther into the Cosmos. Astronomers found that there are other galaxies, like islands in the sea of space, beyond the Milky Way. In a way, they are like other universes. But they are not the kind of other universes that Philip Pullman writes about.
The light from these galaxies tells us that they are made of ordinary stars and ordinary atoms just like the ones on Earth and in the Sun. Our Milky Way is an average-sized galaxy. Beyond the Milky Way, the Cosmos contains hundreds of billions of galaxies, each containing hundreds of billions of stars. All this bright stuff, in every star in every galaxy, is baryonic matter--it is all made of atoms. Galaxies so far away that the light we see from them left their stars even before the time of the dinosaurs here on Earth are all made of baryonic matter, just like the matter you are made of and everything you touch is made of.
All this is our kind of magic; the scientific magic of the world we live in. Philip Pullman's "Dark Materials" might seem like a different kind of magic, pure fantasy that he has invented to make a good story. The amazing thing is, though, that these Dark Materials are also part of the scientific magic of our own world. This is such an amazing story that it deserves a chapter to itself.
CHAPTER TWO


DARK MATERIALS


THE HIDDEN WORLD, AND
THE NATURE OF DUST


''There are more things in heaven and
earth, Horatio, Than are dreamt of
in your philosophy.''
WILLIAM SHAKESPEARE




"Dark matter is what my research team is looking for. No one knows what it is. There's more stuff out there in the universe than we can see, that's the point. We can see the stars and the galaxies and the things that shine, but for it all to hang together and not fly apart, there needs to be a lot more of it--to make gravity work, you see. But no one can detect it. So there are lots of different research projects trying to find out what it is, and this is one of them."


As Mary Malone explains to Lyra, there's more to the Universe than meets the eye. At one level, the Dark Materials are Dust--something that can't be seen but is really there, in Lyra's world as well as in our own. But this is also a metaphor for another kind of dark material--hidden knowledge, and hidden forces, like Mrs. Coulter and the General Oblation Board carrying out their plans in secret. And even they don't know what is really going on at a deeper level still. It's like those sets of Russian dolls with one doll inside another, inside another, and so on, right down to a tiny little doll in the middle.
Our Universe is a bit like that. When astronomers started looking at the sky and studying stars and galaxies with their telescopes, they thought that all this bright stuff was all that really mattered. But in the second half of the twentieth century, less than 50 years ago, they found out that they were wrong. They found out that there is ten times more dark matter in the Universe than all the bright stuff put together.
It's like an iceberg. When you see an iceberg floating in the sea, it looks big and white and shiny. But there is actually ten times as much ice underneath the water, hidden in the dark, where you can't see it. This is the idea behind Dust--the Dark Materials of the story. But if you can't see the dark stuff, how do astronomers know that it is there?