Episode 16 - Faraday and the invention of the field

Tomlin Hawthorne

Put a paperclip on the table. Now bring a fridge magnet slowly toward it. At some point, before they touch, the paperclip jumps.

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Here's the question. In the instant before it jumped, there was a gap between the magnet and the clip. A centimetre of air.

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What was in the gap?

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If you said nothing, you're in excellent company, and you've got a problem. Because if there was nothing in the gap, then the magnet reached across nothing and moved an object it wasn't touching. And if you said something, I'm going to ask you what.

Tomlin Hawthorne

The man who answered that question changed our picture of the world more than almost anyone in this series. He'd left school at thirteen and he couldn't do algebra.

Tomlin Hawthorne

Welcome to Part Four. Last time you played Twenty Questions for points, and I hope you found that the best question is always the one whose answer you can't guess. That's a bit, in Shannon's sense: one fifty-fifty surprise.

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Part Four is about light, and about what fills empty space. Five episodes. And we begin with the question I just asked. How does a magnet reach across a gap?

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But first, a villa on Lake Geneva, in June 1816.

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It was the year without a summer. A volcano in Indonesia had erupted the year before, the largest eruption in recorded history, and the ash in the upper air had dimmed the Sun across the whole northern hemisphere. In Switzerland it rained for weeks. And shut indoors by the weather at the Villa Diodati were Lord Byron, his doctor, the poet Percy Shelley, and Shelley's companion, Mary Godwin, who was eighteen.

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Byron proposed that they each write a ghost story. For days Mary couldn't think of one. And then one evening she sat listening while Byron and Shelley talked late about the latest science. About experiments in which electricity had made dead muscle move. About whether a corpse might be reanimated. She went to bed and couldn't sleep, and saw, she said, with her eyes shut, a pale student kneeling beside the thing he had put together.

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Frankenstein is a novel about electricity. We forget that, because the films added the bolts and the lightning. But the science behind it was real, and it was the sensation of the age.

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It began in Bologna in the 1780s, with Luigi Galvani, a professor of anatomy, who found that the leg of a dead frog would kick when touched with two different metals. He thought he'd discovered the fluid of life itself: animal electricity. His nephew, Giovanni Aldini, took the show on tour. In London in 1803 he was given the body of a man who'd just been hanged at Newgate, and before an audience of surgeons he applied wires to it. The jaw quivered. One eye opened. The right hand rose and clenched.

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A report says one of the spectators was so shaken that he died shortly afterwards. So that's what Byron and Shelley were talking about.

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Electricity, in 1816, was where life and matter seemed to touch. Coleridge went to lectures on it at the Royal Institution in London. He said he attended them to increase his stock of metaphors.

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And working in the basement of that same Royal Institution, washing the bottles, was a young man named Michael Faraday.

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Faraday was born in 1791 in a poor part of south London. His father was a blacksmith in bad health. The family belonged to a tiny, strict Christian sect, the Sandemanians, and Faraday stayed in it all his life. There were weeks in his childhood when his ration was one loaf of bread.

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He had almost no schooling. At thirteen he was sent out to work for a bookbinder. And here's the stroke of luck: he read the books. They came in to be bound, and in the evenings he read them. An encyclopaedia article on electricity. A popular book on chemistry by a woman called Jane Marcet, written as conversations. He started doing the experiments in the back of the shop.

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When he was twenty, a customer gave him tickets to hear the star of London science, Humphry Davy, lecture at the Royal Institution. Faraday took careful notes. Then he wrote them out in full, illustrated them, bound them himself in a handsome volume, and sent it to Davy with a letter asking for a job.

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Davy was flattered, and had no job. But a few months later his laboratory assistant got into a fist fight and was sacked. He remembered the bookbinder.

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So Faraday began as a bottle-washer. When Davy toured Europe, Faraday went along and was made to act as valet, and Davy's wife had him eat with the servants. He put up with it. Within fifteen years he was the greatest experimental scientist in Europe. People said Davy's greatest discovery was Faraday. Davy, by the end, didn't find that funny.

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But he never learned mathematics. He couldn't follow the equations in the papers of his French and German rivals. He thought in pictures. And that, it turned out, was why he saw what they'd missed.

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Let me set the scene with what was known.

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Electric charge comes in two kinds. Benjamin Franklin named them positive and negative. Like charges push each other apart. Opposite charges pull together. Rub a balloon on your jumper and it'll stick to the wall.

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And this force is strong. I mean absurdly strong. The electric force between the two particles in a hydrogen atom is stronger than the gravity between them by a factor of a one with thirty-nine zeros. Gravity is a rounding error by comparison.

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So why don't we notice it? Why is our world ruled by gravity?

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Because matter is balanced. Every lump of ordinary stuff has almost exactly as many positive charges as negative, and the pushes and pulls cancel. If they didn't, you'd know about it. Richard Feynman worked out that if you and a friend stood at arm's length, and each of you had just one per cent more electrons than protons, the force pushing you apart would be enough to lift a weight equal to the entire Earth.

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We live in a world of colossal forces in almost perfect truce. Gravity only gets a look-in because it never cancels.

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Now. In 1800 an Italian, Alessandro Volta, invented the battery, and for the first time you could have a steady flow of electricity along a wire, a current, and not just a spark.

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And in 1820 a Danish professor, Hans Christian Ørsted, noticed something during a lecture. He had a wire connected to a battery, and near it, by chance, a compass. When the current flowed, the compass needle swung.

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This was astonishing. Electricity and magnetism had been thought to be two entirely separate things. Amber and lodestone. And here was an electric current pushing a magnet around.

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The news went round Europe in weeks. And Faraday, in London, asked the obvious next question. If electricity can make magnetism, can magnetism make electricity?

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It took him ten years. He wrote in his notebook: convert magnetism into electricity. He carried a small magnet and a coil of wire in his waistcoat pocket, to fiddle with at dull meetings.

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Everyone, including Faraday, assumed that if you put a strong magnet next to a wire, a current should flow in the wire. It doesn't. You can leave a magnet beside a wire till doomsday and nothing happens.

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Then, in August 1831, he wound two separate coils of wire round opposite sides of an iron ring. One coil he connected to a battery. The other to a meter. And he noticed that at the instant he connected the battery, the needle of the meter twitched. And then fell back to zero. And at the instant he disconnected it, it twitched again, the other way.

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Not while the current was flowing. Only when it started or stopped.

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A few weeks later he tried the simplest version. A coil of wire, and a bar magnet. He pushed the magnet into the coil. A pulse of current. He held it still. Nothing. He pulled it out. A pulse the other way.

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That was the secret, and it's why everyone had missed it. A magnet doesn't make a current. A moving magnet does. A changing one. It's change that matters.

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And I want you to know that this, here, is the Industrial Revolution's second act. Every power station on Earth, coal, gas, nuclear, hydro, wind, is doing what Faraday did that autumn. Spinning magnets near coils of wire. When you switch on a kettle, you're calling on the experiment of August 1831.

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But that's not why I said he changed our picture of the world. That's this next part.

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Back to the paperclip and the gap.

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The great physicists of the day, the ones with the mathematics, had a clear view. They followed Newton. A magnet here exerts a force on a piece of iron there. The force depends on the distance. And that's all there is to say. What's in between is irrelevant. It's action at a distance, and yes, Newton himself had found that idea absurd, as we heard in episode five, but the sums worked, so people had stopped worrying.

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Faraday couldn't do the sums. So he looked.

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You've done this, perhaps at school. Put a sheet of paper over a bar magnet and sprinkle iron filings on it. Tap the paper. The filings arrange themselves into lines. Beautiful curves, sweeping out from one end of the magnet, round through the space on either side, and back in at the other end.

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The mathematicians saw that and thought: pretty. A way of visualising the force.

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Faraday saw it and thought: that's what's there.

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He came to believe that the lines were real. That the space around a magnet isn't empty. It's in a state. It's been altered, strained, filled with something, whether or not there's a paperclip nearby to feel it. He called the lines lines of force, and the whole pattern, the condition of the space, he called a field.

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So on Faraday's view, the magnet doesn't reach across the gap and grab the paperclip. The magnet changes the space around itself. That change spreads outward. And the paperclip responds to the field where it is, right at its own location. Nothing acts at a distance. Everything is local.

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If you want a picture of what a field is: think of a weather map showing temperature. At every point on the map, there's a number. That's a field, a quantity that has a value at every point in space. A magnetic field is like that, with a strength and a direction at every point.

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But here's where the picture has to break, because it matters. The temperature on the map is the temperature of something. Of the air. Faraday's field isn't a property of anything. It's there in a vacuum. It is, itself, a thing. It can hold energy. And, as we'll see next time, it can move.

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For twenty years, almost nobody took this seriously. The mathematicians were polite about it. Faraday was a superb experimenter, they said, and one must allow him his homely fancies.

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He was right, and they were wrong. And by the end of this series, I'll be telling you that fields are not just real. They're all there is. That what we call particles, the electrons and the quarks, are ripples in fields, and the fields are the furniture of the universe. That idea starts here, with a man who couldn't do algebra looking at iron filings.

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A word about the man, before we go.

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He was offered a knighthood and declined it. He was twice offered the presidency of the Royal Society and declined that. He said he wanted to remain plain Mr Faraday to the end. He turned down a fortune in consulting fees. When the government asked him to advise on making poison gas for the Crimean War, he said it was feasible, and that he would have nothing to do with it.

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And in 1825 he started a series of Christmas lectures for children at the Royal Institution. He gave nineteen of them himself. His most famous one was on the chemistry of a candle. The Christmas lectures have run every year since, apart from a gap during the Second World War, and you can watch them now.

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There's a story that the prime minister, visiting his laboratory, asked what use this electricity was. And Faraday is supposed to have said: why, sir, there is every probability that you will soon be able to tax it. It's a perfect line. I'm sorry to tell you there's no evidence he ever said it.

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The myth of the week is that a field is a convenient fiction. A mathematician's doodle. I've told you why it isn't, and next episode will prove it, when a field breaks loose from its source and travels across the room.

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And a smaller one, while we're here. People think a battery sends electricity down a wire to a bulb, where it's used up. It isn't. The same amount of current comes back along the other wire as went out. What the bulb takes is energy, not electricity. The current is the conveyor belt. The energy is what was on it.

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The question for the week.

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Years later, the mathematical genius of the next generation, James Clerk Maxwell, sat down to read Faraday's papers. He'd been warned off them. And he wrote that as he read, he saw that Faraday's way of thinking about things was a mathematical one too, even though it wasn't set out in the usual mathematical symbols.

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So what does that mean? Can you think mathematically without mathematics? Faraday reasoned about shapes and flows and what connects to what. He just never wrote an equation. Is mathematics the symbols, or is it something underneath the symbols, a way of seeing structure? You might ask the same of a composer who can't read music, or a chess player who can't explain a move.

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I'll confess an interest. This whole series rests on the hope that the answer is yes.

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Your challenge. You have, in your pocket, a rather good instrument for detecting magnetic fields. Your phone has a compass in it, and the compass is a real magnetic sensor.

Tomlin Hawthorne

Open the compass app. Now move a fridge magnet slowly round the phone, at a hand's width or so, and watch the needle follow it. You're mapping Faraday's field. Not too close, and not for long: it won't hurt the phone, but it'll confuse the compass for a while.

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Then, if you'd like to be Ørsted. Take an ordinary battery and a short piece of wire. Lay the wire across the phone, along the direction the compass is pointing. Touch the ends of the wire to the two ends of the battery for one second, no more, because it'll get hot. Watch the needle.

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That swing is what Ørsted saw in 1820. Electricity, making magnetism, on your kitchen table.

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Next time. Faraday had the picture. He needed someone to write it down. A young Scot does it, in four lines. And then he notices that the four lines predict something nobody had asked for, and it turns out to be light.