The Spinning Magnet

by Alanna Mitchell

  CHAPTER 16

  the lines that fill the air

  The unconventional Scottish physicist James Clerk Maxwell did understand mathematics. He read Faraday’s papers on electricity and magnetism and then, by pulling together all that was known about them, wrote four new equations in a paper published in 1861. For the first time, they described electromagnetism.

  This was a far more difficult task than simply translating Faraday’s words into math. Maxwell had to work out that not only does an electric current produce a magnetic field but so does an electric charge that is only displaced, not flowing continuously. Contained within this idea was the math to prove that space is filled with electromagnetic waves independent of any electric currents. Electricity, therefore, was a manifestation, even a subset, of the electromagnetic force. This was something the electricians of the previous century could never have imagined. When Maxwell read his equations carefully, they also told him that electricity, magnetism, and light were aspects of each other. They all behaved as waves traveling at the speed of light across space, a speed he had calculated a few years later. This was the collection of invisible lines of force that Faraday had dreamt of and partly glimpsed. Now it was enshrined in mathematics, available for all physicists to play with.

  Maxwell’s equations predicted that electromagnetic waves can be literally any length. As the physicist Neil Turok explains, the waves are just “stretched-out or shrunken-down versions of one another.” Most are invisible to humans, just as most frequencies of sound waves are inaudible, including the high frequencies of ultrasound. The electromagnetic waves we can see are far smaller than a millionth of a meter in length and they give us color. The very longest we can see are red; the shortest, violet. But there are even smaller electromagnetic waves, such as the dangerous gamma rays produced in the Large Hadron Collider, whose activities were lighting up the façade of the Niels Bohr Institute in Copenhagen when I was there, and X-rays. Extremely long waves, known as ultra-low-frequency waves, can penetrate the Earth and are used to communicate in mines. Other types include microwaves, which work in the appliance of that name but also make radar function. There is also the big group longer than microwaves called radio waves, which are put to work in cell phones, radios, and televisions. But as different as they may seem, all these waves can be described mathematically in exactly the same terms. That finding laid the groundwork for the electrical infrastructure that supports virtually all the energy and information we use in our modern world.

  Ultimately, Maxwell’s equations led to the elegant math describing the standard model of physics developed in the early 1970s. Today, if the standard model equation proves that something can be true, then it is, no matter how counterintuitive it might seem. That’s how an electron can be a particle and a vibration in a field at the same time, or how the Higgs boson was imagined before it was found. The revolution in scientific thinking this represents is vast. At the beginning of electromagnetic research, the Bible was the only truth. Natural philosophers, like Galileo, had to flout authority to make observations about nature that went against what the Bible said. Data points and logical conclusions were dangerous. Later, observational results were all that mattered; the highest scientific endeavor was to explain the world through the evidence of your own eyes. Today, the standard model equation is king, with its alarming precision and its preposterous abstractions. Observation, while not passé, is not everything.

  Here’s an example: Maxwell’s equations theoretically connected space and time, a profoundly improbable fact. That led directly to Albert Einstein’s special theory of relativity, which states that time and space are not fixed. Time does not march on, unheeding, as the poets might say. Neither are time and space separate from each other. Instead, they are a continuum, capable of adjusting themselves in order to make sure the speed of light—that is, Faraday’s tiny electromagnetic wave—is fixed.

  Einstein published his special theory of relativity in 1905 in the journal Annalen der Physik while working in a patent office in Bern, Switzerland. It was one of four remarkable papers he published that same year, known as his annus mirabilis, or miraculous year. His work that year changed the way physicists saw time, space, mass, and energy. That same year, a few hundred kilometers to the southwest, Bernard Brunhes made his trek by horse to Pont Farin in the Cantal of France to the brand-new roadcut, where he hacked away at the seam of ancient terracotta that showed that the Earth’s poles had once been on opposite sides of the planet.

  I had made a special request that James show me the entry in Faraday’s journal from the fateful day in 1831 when he wrote up his experiment with the induction ring. James pressed a code pad that allowed him into the locked archives, home not only to Faraday’s notes but also to those of Davy and other scientists who have worked at the Royal Institution over its centuries. Other researchers were ensconced there, along with the keeper of the collection. We were in the basement, just a few meters from where Faraday had worked in his magnetic laboratory.

  Box after box of scientific treasure sat on the metal shelves, tidily labeled. It was the emotional and perhaps spiritual core of the institution. Faraday’s notebooks were in sturdy, flattish brown cardboard boxes with removable lids. James, with an ease born of long practice, consulted the shelves for a few moments and then took one down and removed its lid. Inside was an elegant oblong brown leather notebook inscribed with gold lettering, evidence of Faraday’s early passion for bookbinding. James opened the volume to August 29, 1831, and held it out with a slight flourish.

  There, in sepia ink, in a sedate and beautiful hand, was Faraday’s description of the experiment that set him on the road to discovering that a magnet plus movement could make electricity, opening up the largely invisible world of electromagnetic fields snaking through the universe. Lines of script evenly spaced on a single page, written with scarcely a correction, a tidy diagram of the induction ring midway down the right-hand side.

  It seemed to me that I could see Faraday writing the lines, sitting upright and proper in his laboratory. I could imagine him puzzling over the mysteries that were slightly out of sight. And from him I could trace a path to Maxwell working out his four famous equations at his Scottish estate south of Glasgow, and from there, to Einstein in that patent office in Bern reimagining the nature of space and time, and then over to Brunhes in his slender Renaissance tower in Clermont-Ferrand, realizing that the Earth’s magnetic field was far more mercurial than anyone had imagined.

  About a hundred years later, their work, plus that of hundreds of other scientists, would unveil an electromagnetic reality that was breathtakingly more inconstant. Despite all that we now know thanks to advances in quantum physics, particle physics, geophysics, mathematics, computers, and satellite technology, we cannot predict how the Earth’s magnetic field will behave. That ability remains resolutely out of reach. But we have a few pieces of evidence. We know that the field is decaying more rapidly than many scientists had predicted. It is more unstable in the south. And if the poles are again preparing to switch places, the infrastructure that carries electrical current to our doorsteps is in danger of being damaged beyond repair.

  PART III

  core

  And what rough beast, its hour come round at last, Slouches towards Bethlehem to be born?

  —William Butler Yeats, “The Second Coming,” 1919

  CHAPTER 17

  the contorting gyre

  Despite the sweltering heat of the summer evening, the theater at the convention center in the French city of Nantes was filling up with people. They were there to hear about the journey to the center of the Earth that is, even now, in progress. The topic was a natural for citizens of Nantes. It fed into the lore of the city, once home to the writer Jules Verne. His science-fiction novel about an irascible geologist’s pilgrimage into the Earth’s core was published in 1864. Verne’s fictional geologist climbed up an extinct Icelandic volcano from which h
e descended straight into the Earth’s bowels, stumbling on an underground ocean populated with ancient monsters before finally making his way to the surface again. But today’s voyage to the underworld is not literary. It is scientific. It is fraught with implications for life and human civilization.

  Philippe Cardin was on the stage in Nantes. A physicist at the University of Grenoble in southern France, he was one of the exclusive and tight-knit group of the world’s scientists who study the machinations of the Earth’s deep interior. Most of them, which is to say, about two hundred, were gathered in Nantes for the conference they hold somewhere in the world every two years to share their newest findings. This was the second day of a week of revelations. Cardin had been tapped to give the week’s only public lecture.

  He was a gifted storyteller. The audience sat rapt as he romped his way through the history of how scientists have come to know about the enigma in the heart of the planet. He wanted to make it clear that for him, it’s not just about what’s there now. The art of reading the entrails of the Earth means reading its birth pangs, its evolution, and its future. It is to acknowledge that the Earth is alive, that it has undergone immense change, and that it must continue to change. In Cardin’s field, a longed-for goal is to be able to read what will happen next. It is elusive.

  He made a confession to his audience that surprised me. He put today’s scientific explorers of the Earth’s core into the same category as the literary explorers of old. Not just Verne, whose tales of extraordinary voyages still make him one of the most beloved novelists in the world. But also Dante Alighieri, who, in the fourteenth century, helped establish the idea within the collective human imagination that the descent into the underworld was a descent into hell. Dante banished the arch-devil Lucifer to the ice-fast lowest level of the deepest circle of suffering—mute, immobilized, abandoned. Other artists have depicted going into the underworld as the opposite: the physical and psychological search for a sacred place, where there is protection, warmth, and wonder. Scientists too, Cardin told his audience, were drawn into the earthly abyss by the allure of imagining the unknown. The quest captures them and they cannot let it go.

  The culture of the scientific world doesn’t lend itself easily to this sort of disclosure. Scientists rarely acknowledge the psychological pull their subject has on them, or the torrent of imagination their work entails. I caught up with Cardin the day after his lecture, fascinated by his willingness to name the emotional seduction of science. As we walked along the Loire River that runs through Nantes, I told him that Jacques Kornprobst had taken me to Pont Farin to show me Bernard Brunhes’s field-twisted terracotta. At once, he became voluble. He knew Kornprobst as a valued senior statesman of French geophysics. And he was unusually well informed about Brunhes, despite not having mentioned him in his talk the night before. (“Ah, yes,” he said. “Perhaps I should have talked about Brunhes!”) A few years earlier, Kornprobst had invited Cardin to give a public lecture at Vulcania, the European park of volcanism near Clermont-Ferrand, to honor the centenary of Brunhes’s discovery. It had been Kornprobst’s article on that meeting that drew me into his sphere. To prepare for the Vulcania lecture, Cardin had reread Brunhes’s work. Cardin was still marveling at what Brunhes had been able to envision back in 1905. It was like looking at a river—here he pointed to the Loire—and imagining the ocean without ever having seen it.

  Seeing the invisible has been a hallmark of geophysicists over time: How did the Earth come to be? How was that rock made? What is in the center of the planet? Why? And catching a scientific, rather than literary, glimpse of the architecture within the center of the planet has had its own peculiar narrative arc. It started with William Gilbert, who claimed in 1600 that he was the first to take a scientific look into the planet’s innermost reaches. Gilbert concluded from his experiments with terrellae, or lodestone models of the Earth, that our planet is a giant magnet with a magnetic soul that shuttles power from deep inside it all the way across its surface. It was an inspired guess then, and happened to be correct. Incorrect was his idea that the Earth’s great magnet was responsible for its ability to spin. In fact, the Earth’s need to shed heat from its inner domains makes the electrical currents that produce the magnetic field. Its spin helps to organize the field into the simple two-pole structure that allows us to use it for navigation. Later that century, Edmond Halley pushed Gilbert’s ideas further, positing that the core might be liquid and that changes within it are responsible for the magnetic soul’s constant change. That’s become the prevailing scientific consensus.

  From the center, the magnetic field spreads in unending loops from pole to pole, stretching tens of thousands of kilometers beyond Earth’s surface, forming what’s called the magnetosphere, which surrounds our planet and interacts with other magnetic fields in the universe, including the sun’s. The Earth’s vast electromagnetic field creates a protective shield around our planet, fending off solar wind and cosmic rays. On the side facing the sun, it is squashed flat by the violence of high-energy particles emanating from our mother star. The field pinches in at either pole where the loops run through the Earth’s center and then streams out the side away from the sun in protean tentacles reminiscent of a galactic squid. This odd creation, which developed when the Earth was perhaps as much as a billion years old, guards our planet from the ravages of radiation. It may even be the reason life exists on Earth.

  But how is that electromagnetic power generated within our planet’s core? Like everything else in our universe, its origin is violent. One critical component is the unpaired spinning electron.

  About 4.6 billion years ago, our solar system was just a cloud of dust and gas nestled within the universe. Then something happened—perhaps it was a nearby star exploding—to make the cloud collapse in on itself. The result was a flattened disc of gases and bits of debris, some of which collected in the middle, eventually picking up enough density to start nuclear reactions. That was the birth of our sun.

  But while the infant sun consumed most of the matter in the system, there was still a great deal of material rotating around it. As bits bumped into one another, they clumped together to form hundreds of thousands of tiny planets, called planetesimals. These were the forebears of the planets in our solar system: Earth and its siblings. Some were icy, some rocky. Near the sun it was too hot for all but the four rocky protoplanets that were to become Mercury, Venus, Earth, and Mars, and so they began to orbit closest to the sun. Farther out were the gassy formations that became Jupiter and Saturn, and farthest of all were the two dominated by ice, Uranus and Neptune (and perhaps the mysterious potential Planet Nine that scientists recently caught a theoretical hint of in the Kuiper Belt, or yet another in the theoretical Oort cloud).

  Still, the planets were accreting. As they got bigger, their gravitational pull got stronger, so they attracted even more material toward themselves. The material crashed violently into the growing planets, generating heat from the force of the collisions. That heat was locked in the planets’ cores like a giant furnace containing the savagery of their birth.

  Among the materials forming Earth and the other rocky planets was lots of iron and a little nickel. But because iron and nickel were among the heaviest elements produced in this embryonic solar system, they sank to the center of the planet while lighter material accumulated on the surface. The Earth’s center was so hot that it kept the metals liquid—too hot to carry a magnetic charge because they were above the Curie point that so fascinated Brunhes. By the immutable rules of physics, heat captured within the molten metal core needed to find a way to escape, so the Earth began shedding heat from the inside out, just as a pot of water throws off heat in the bubbles it produces across its surface when it boils. As the core succeeded in discarding heat, its innermost portion solidified, leaving the outer core liquid.

  That liquid metal of the outer core was still churning, helping to shunt heat away from the inner core while it rotated a
round its axis. That same axial rotation caused the inner-Earth liquids to dance to what’s known as the Coriolis effect. Named after a nineteenth-century French mathematician and engineer, the Coriolis force governs the spin of large bodies of liquids on the planet, including the ocean, the atmosphere, and the molten metal in the outer core. That’s why ocean gyres and hurricanes in the northern hemisphere run counterclockwise and those in the south run clockwise. They are curving as they move across the Earth’s surface. In the outer core, the Coriolis effect creates discrete north-south-running columns of liquid metal spinning on the edges of the solid inner core, another splendid mechanism for getting rid of excess heat. In addition, the atomic construction of the iron and nickel in the core makes them excellent conductors of electrical charge. Each iron atom has four unpaired electrons spinning in its outermost filled orbitals and each nickel atom has two.

  What that added up to, in this early Earth, were the magic twin elements needed to produce a dynamo—a generator of electricity that can sustain itself for billions of years: heat energy carried by a liquid, plus an electrical conductor. The dynamo produced electrical currents that flowed through the molten metal. Electrical currents, as Ørsted later showed with his copper troughs in Copenhagen, produce a magnetic field. The field that the dynamo began to produce billions of years ago cocoons us still. It is an artifact of our planet’s birth.