Reaching In

The first time I held a lodestone I was maybe eleven, in somebody's basement, and I did the thing everybody does. I picked up a paperclip, held it near, felt it go, and dropped it. Then I did it again. Then about forty more times.

Whoa, holy shit, how is this attracting metal? That's wild.

The rock is magnetite, an iron oxide, and a lodestone is a piece of magnetite that has been magnetized, usually by a lightning strike. That's the whole story of the artifact. A rock got hit by a huge current and kept the memory of it. For most of human history that rock is a curiosity. It sits in a cabinet next to the narwhal tusk and the two-headed lizard. It is a thing you show people. It does not have a theory attached to it, it does not have a mechanism, it has a demonstration and a sound effect, which is the paperclip going tick against the stone. It has that for thousands of years.

What I want you to hold onto is that this is not a small thing that later became a big thing. It was always this big. The rock was doing exactly then what it does now. It was reaching across empty space and moving matter with no contact and no explanation, in a cabinet, in front of a bored child, while nobody had any idea what was happening.

You do not get electromagnetism from a book. I have watched people try. You get some symbols and a right-hand rule and you can pass an exam with that, and you will still, in the part of your body that actually predicts things, believe that magnets are basically glue.

What builds the real intuition is fucking around with magnets and coils and charges and stuff, over months, with your hands.

Here is the sequence, roughly, and I recommend it. Get two neodymium magnets and try to push them together the wrong way. Feel the thing that is not a spring but behaves like one, and notice that the resistance climbs faster than you expect as the gap closes. Now sprinkle iron filings on paper over a bar magnet and see the lines show up, and see that they are not a metaphor. Somebody drew the field lines before anybody could compute them, and the filings drew them first.

Then wind a coil. Any wire, any nail. Run current through it and it becomes a magnet, and when you cut the current it stops being one, which is already strange because you have just made and unmade a property of matter with a switch. Then do it backwards. Take that same coil, no battery, and drop a magnet through it, and watch a voltage appear on the meter. Nothing touched. The magnet moved, and charges in the copper moved, and the two facts are the same fact.

Then hang the coil so it can swing, put it in the field of a permanent magnet, and put an audio signal through the wire. It pushes air. That is a speaker. You have just made sound out of a moving magnet, and if you run it backwards by shouting at it, you get a microphone, because a speaker is a microphone that has been asked politely.

This is the crazy coupling. Moving charges make magnetism. Changing magnetism moves charges. Each one is the source of the other, and the loop between them is not a nice analogy, it is the actual gear train of the universe, and once you have felt it in your hands a few dozen times you stop needing to be told.

It is very spooky. It moves stuff at a distance. It is alchemical and magical in a lot of ways, and I say that as someone who can write the equations. You should keep the spookiness. The equations do not dissolve it. They aim it.

In the 1860s James Clerk Maxwell wrote down the relationships between electricity and magnetism, and when he assembled them he noticed that the equations permitted a wave. Not a wave in anything. A wave of the fields themselves, an electric change making a magnetic change making an electric change, walking through empty space and holding itself up by its own bootstraps.

Then he calculated how fast that wave would travel. The speed came out of two constants that had been measured on a laboratory bench by people doing static electricity experiments with jars and coils, nothing to do with light, nothing to do with astronomy. The number that fell out was the speed of light.

Sit with that for a second, because this is the best moment in the whole history of physics and it usually gets one sentence in a textbook. A man doing algebra about magnets and wires produced a number, and the number was a thing astronomers had measured by watching Jupiter's moons come out from behind Jupiter slightly late. Two completely unrelated human activities returned the same answer, and the only way that happens is if light is an electromagnetic wave.

So light is this. The thing coming off the sun, the thing your eyes are built out of, is the same phenomenon as the paperclip going tick. Radio waves are very low frequency. Visible light turns out to just be high frequency shit. Infrared, which you feel as warmth on your face, sits between them. Ultraviolet, X-rays, gamma rays run off the other end. One phenomenon, one set of equations, and the difference between a radio station and the color red is how fast it wiggles.

That's weird. I mean, that's very unifying.

In 1887, Heinrich Hertz built the confirmation in a room. A spark jumping a gap in one circuit, and across the room, a small loop of wire with its own tiny gap, sparking in sympathy. He measured the wavelength by finding the standing waves against a metal sheet on the wall. He had made and detected an invisible thing that Maxwell had found on paper twenty years earlier and never lived to see.

Hertz was asked what it was good for. He said, essentially, nothing.

You have to understand what it feels like to be a physicist in 1890.

Mechanics is done. Newton handled that. Thermodynamics is done, and it is beautiful, and it explains steam engines and the atmosphere and why you can't get something for nothing. And now electricity, magnetism, light, radiant heat, all of it, four equations, and they are so clean you can put them on a shirt.

Hey, we've got this thing down, dude. We figured out the fundamental nature of reality. That shit was hard, Maxwell's equations, but we got them, and they're beautiful and simple, and of course it's done.

The mood was so confident that people told graduate students not to bother with physics. The story that Kelvin said the future was in the sixth decimal place is probably cleaned up in the retelling, but the sentiment is real and it is all over the record. There are two small clouds on the horizon, people said. A weird null result from an experiment about the ether, and an embarrassing problem with the color of hot objects. Details. Mop-up work.

Then it's like, oh, fuck, 20th century physics. Ah.

The cloud about hot objects is Planck in 1900, and the fix requires energy to come in discrete lumps, which nobody wants, including Planck. The cloud about the ether is Einstein in 1905, and the fix requires space and time to stop being the stage and start being participants. The same year, Einstein explains the photoelectric effect by saying light is lumpy too, which contradicts everything I just told you about waves, and is also correct. Then Rutherford fires alpha particles at gold foil and finds out the atom is almost entirely nothing with a violent speck in it. And then it gets worse, or better, depending on your disposition, and the electron gets a wavelength, and the wavelength gets a probability interpretation, and by 1927 the floor that everyone was standing on in 1890 is fully gone.

The joke is that the four beautiful equations survived all of it. Maxwell's equations are relativistic already. Einstein didn't have to fix them, he had to fix everything else so they could keep being true. They just stopped being the bottom.

That's the part that took me a long time to feel properly, and I want to hand it over cleanly. The floor opening is not a failure of the climb. Every single time humans have gotten a firm handle on a layer of reality, the handle held, and the layer underneath turned out to be stranger than the one above it. You get one thing down and it becomes the floor you stand on to reach the next thing. Then that floor opens too. There is no version of this where you arrive.

Here is the part I actually want you to do something with.

Hertz thought his apparatus was good for nothing. Within a decade, people were using spark gaps to send messages, because it turns out that if you can make an invisible wave and detect it across a room, you can make a bigger one and detect it across an ocean, and the physics does not care about your ceremony.

A spark-gap transmitter is close to the crudest possible object. You need a source of high voltage, which historically is an induction coil, which is two windings of wire around an iron core with an interrupter that keeps chopping the current, and chopping the current in the primary is what slams a big voltage into the secondary. That voltage jumps a gap between two electrodes, and the spark is a violently oscillating current that dumps energy across an enormous swath of the spectrum. Hang a wire off it. The wire radiates. You have made an event that things far away can notice.

The receiving side is the part that gets me, still, today. In 1874 Ferdinand Braun was poking at metal sulfide crystals with a metal point and found something that had no business existing in a world of nice symmetric materials. Current flowed one way through the contact and not the other. The junction rectified. He published it, and for thirty years it was a laboratory oddity of no obvious use, because nobody yet had a signal that needed rectifying.

Then radio arrived, and it needed exactly that. A radio wave arriving at your antenna wiggles up and down equally, and if you average it you get nothing. To hear it you need to cut off one half so what's left has an average that follows the sound. That is what a rectifier does, and that is what a galena crystal does. Galena is lead sulfide, an ordinary shiny gray mineral, and if you touch it with a thin bent wire and hunt around on its surface for a sensitive spot, you have a detector. The wire is called a cat's whisker, which is the correct name, because that is exactly what it looks like and exactly how gently you have to move it.

So the whole receiver is this. A long wire in the air. A coil, which with a capacitor picks which frequency you are listening to. A galena crystal, a bent wire touching it, and an earpiece. No battery. There is no power supply anywhere in a crystal set. The only energy that moves the diaphragm in your ear is energy that the transmitter put into the sky and your antenna caught, and that is why crystal sets are quiet, and why you press the earpiece hard against your head, and why the first time it works you go completely still.

I want the shape of this to land as a fact and not as a flourish. You can build a transmitter out of a coil and two electrodes and a gap of air. You can build a receiver out of a rock and a bent wire. And with those two things and some copper, two people over the horizon from each other, who cannot see each other and cannot shout to each other, can talk. Using a rock.

Do not do this part, incidentally. A spark gap sprays energy across the entire spectrum and it is thoroughly illegal to transmit with one now, for the excellent reason that it steps on everyone. That prohibition is itself a nice piece of evidence about how far this went. We banned the first radio because the sky got too crowded with the descendants of the first radio.

The transistor comes forty years after all of this, and it comes out of the same lineage. Bardeen and Brattain at Bell Labs in December 1947, two gold contacts pressed down onto a slab of germanium, a semiconductor, cousin to the galena. Point contacts on a crystal again, the same physical gesture as the cat's whisker, except this time the crystal does not merely rectify. It amplifies. A small change at one contact makes a large change in the current through the others, and once you can amplify you can build a switch, and once you can build a switch you can build all of it.

Which means the chain from the cabinet to the thing in your pocket is not a metaphor. Rock in a cabinet, iron filings on paper, four equations, sparks across a room, a bent wire on galena, gold on germanium, a billion transistors on a chip, and a phone that finds a router across the apartment by making the fields wiggle 2.4 billion times a second in a pattern the router has agreed to care about.

Wifi is a lodestone that learned to talk. It is a rock, and some copper, and a spark, all the way down, refined for a hundred and fifty years by people who wanted to hear something from far away.

There is an engraving I have loved since I was a kid, and it is the reason for the title of this chapter.

A traveler kneels at the edge of the world where the sky meets the ground, and he has pushed his head and one shoulder through the sky the way you'd push through a heavy curtain. Behind him is his ordinary landscape, trees, a village, a normal sun. Through the gap is machinery. Wheels and fire and turning things.

Everyone knows this image as medieval, as the moment some monk found the edge of the sphere. That is not what it is. Camille Flammarion put it in his book L'atmosphère in 1888, and it was made to look like a woodcut from centuries earlier, and it worked so well that it fooled essentially everybody for a hundred years. It got reproduced with the border cropped off, and the border is where the nineteenth century was hiding, and once the border was gone the fake was airtight. So it circulated as evidence that medieval people believed the sky was a solid dome, which they mostly didn't, illustrated by a picture from the decade of Hertz's spark, printed a year after the spark.

I love this more than I can say. The single most famous picture of a human discovering the limits of reality is itself a thing a human built and then successfully passed off as reality. Which is roughly the plot of this whole book.

And the image is wrong in the direction it points, which is the useful part.

There is no edge. There is no curtain and no outside and no place to poke your head through into the machinery, because you are not standing next to the machinery, you are made out of it. You have been inside the field your entire life. It is in the room with you right now, going through you, and it is what is holding your hand together, and it is what is bringing you this sentence.

So the gesture is not out. It is in. You reach into the thing you are already standing in and you find, absurdly, that it has handles.

That is the whole surprise. There is no reason a field should have handles. There is no reason a bar of iron struck by lightning should keep the strike, or that a wire moving through that memory should push electrons, or that the ratio of two constants measured on a bench should be the speed of the sun's light, or that a rock should be able to pull one half out of a wave so a person can hear a voice from over the horizon. None of that had to be available. It is available, and every single one of those handles was found by somebody with their hands on the thing, moving a bent wire across the face of a crystal, one millimeter at a time, listening.

Every handle we have found came with a floor that opened afterward. Maxwell's did. Whoever finds the next one will get the same treatment, and they will deserve it.

Go get some wire. Wind it around a nail. Drop a magnet through it and watch the needle jump, and understand that you are watching the same event that lights the sun and carries your voice and rectifies on galena, at the smallest scale it will hold still for. That twitch of the needle is the handle. It has been there the entire time, in the room with you, waiting for a hand.