Why Beauty is Truth (40 page)

Thinking about what could cause light rays to bend, Newton decided that the medium, not light, must be the root cause. This led him to suggest the existence of some “aethereal medium” which transmitted vibrations
faster than light.
He convinced himself that radiant heat was evidence in
favor of these vibrations, because he had established that heat radiation could traverse a vacuum. Something in the vacuum must be carrying the heat and causing refraction and diffraction. In Newton's words:

Is not the Heat of the warm Room convey'd through the Vacuum by the Vibrations of a much subtiler Medium than Air, which after the Air was drawn out remained in the Vacuum? And is not this Medium the same with that Medium by which Light is refracted and reflected, and by whose Vibrations Light communicates Heat to Bodies, and is put into Fits of easy Reflexion and easy Transmission?

When I read these words I cannot help thinking of my friend Terry Pratchett, whose series of fantasy novels set on “Discworld” satirize our own world, and whose assorted wizards, witches, trolls, dwarves, and people poke fun at human foibles. Light on Discworld travels at roughly the speed of sound, which is why the light of dawn can be seen approaching across the fields. A necessary counterpart to light is
dark
—on Discworld almost everything is reified—and dark evidently travels faster than light because it has to get out of light's way. It all makes excellent sense, even in our world, aside from the disappointing fact that none of it is true.

Newton's theory of light suffers from the same defect. Newton wasn't being stupid: his theory seemed to answer a number of important questions. Unfortunately, these answers were based on a fundamental misunderstanding: he thought radiant heat and light were two different things. He believed that when light hits a surface, it excites heat vibrations. These were variants of the same vibrations that he thought caused light to refract and diffract.

Thus was born the concept of the “luminiferous aether,” which proved remarkably persistent. Indeed, when it later turned out that light is a wave, the aether provided just the right medium for it to be a wave
in.
(We now think that light is neither wave nor particle exclusively but a bit of both—a wavicle. But I'm getting ahead of myself.)

What, though, was the aether? Newton is perfectly frank: “I do not know what this Aether is.” He argued that if the aether is also composed of particles, then they must be much smaller and lighter than particles of air or even of light—essentially for the Discworldly reason that they have to be able to get out of light's way. “The exceeding smallness of its Particles,” Newton says of the aether, “may contribute to the greatness of the
force by which those Particles may recede from one another, and thereby make that Medium exceedingly more rare and elastick than Air, and by consequence exceedingly less able to resist the motions of Projectiles, and exceedingly more able to press upon gross Bodies, by endeavoring to expand itself.”

Earlier, in his 1678
Treatise on Light
, the Dutch physicist Christiaan Huygens had proposed a different theory: light is a wave. This theory neatly explains reflection, refraction, and diffraction—similar effects can be seen, for instance, in water waves. The aether was to light as water was to waves on the ocean—the thing that moved when the wave passed. But now Newton disagreed. The debate got very confused, because both scientists were making incorrect assumptions about the nature of the alleged waves.

Everything changed when Maxwell got in on the act. And he stood on the shoulders of another giant.

Electric heating, lighting, radio, television, food processors, microwave ovens, refrigerators, vacuum cleaners, and endless items of industrial machinery all derive from the insights of one man, Michael Faraday. Faraday was born in Newington Butts, London (now the Elephant and Castle), in 1791. He was a blacksmith's son who rose to scientific eminence in the Victorian era. His father belonged to the Sandemanians, a minority Christian sect.

Faraday became an apprentice bookbinder in 1805 and began performing scientific experiments, especially in chemistry. His interest in science grew significantly when, in 1810, he became a member of the City Philosophical Society, a group of young people who met to talk science. In 1812, he was given tickets to hear the final lectures of Sir Humphry Davy, Britain's leading chemist, at the Royal Institution. Soon thereafter, he asked Davy for a job; he was given an interview, but no position was available. But after Davy's chemical assistant was soon fired for starting a fight, Faraday got his job.

From 1813 to 1815 Faraday toured Europe with Davy and his wife. Napoleon had given Davy a passport, which included a valet, so Faraday accepted that position. He was annoyed to find that Davy's wife, Jane, took the title literally and expected him to act as her servant. In 1821, events took a more favorable turn: he was promoted, and he married
Sarah Barnard, the daughter of a prominent Sandemanian. Better still, his research into electricity and magnetism was starting to take off. Following previous research of the Danish scientist Hans Ørsted, Faraday discovered that electricity flowing through a coil near a magnet produces a force. This is the basic principle underlying the electric motor.

His research interests then became swamped under administrative and teaching duties, though these had a very favorable impact. In 1826, he started a series of evening discourses on science and also initiated the Christmas lectures for young people, both of which are still running. Today the Christmas lectures are broadcast on television, one of the gadgets that Faraday's discoveries eventually made possible. In 1831, back at his experiments, he discovered electromagnetic induction. This was the discovery that changed the industrial face of the nineteenth century, because it led to electrical transformers and generators. The experiments convinced him that electricity must be some kind of force acting between material particles, and not a fluid as generally thought.

Eminence in science typically leads to the honor of an administrative post, which promptly kills off the scientific activities that are being recognized. Faraday was made scientific adviser to Trinity House, whose mission is to keep the British seaways safe for shipping. He invented a new, more efficient kind of oil-burning lamp, which produced a brighter light. By 1840, he had become an elder of the Sandemanian sect, but his health was starting to worsen. In 1858 he was given free lodgings in a “grace and favor” house at Hampton Court, the former palace of King Henry VIII. He died in 1867 and was buried in Highgate Cemetery.

Faraday's inventions revolutionized the Victorian world, but (perhaps because of his early lack of education) he was weak on theory, and his explanations of how his inventions worked were based on curious mechanical analogies. In 1831, the year Faraday discovered how to turn magnetism into electricity, a Scottish lawyer was presented with a son—his only child, as it turned out. The lawyer was more interested in managing his land holdings, but he took considerable interest in the education of young “Jamesie,” more formally known as James Clerk Maxwell.

Jamesie was bright and fascinated by machines. “How it doos?” was his standard question: How does it do that? Another was “What's the go of that?” His father, who had similar fascinations, did his best to explain.
And if the father failed to go far enough, Jamesie would ask a supplementary question: “What's the
particular
go of that?”

James's mother died of cancer when the child was nine; the loss brought father and son closer together. The boy was sent to the Edinburgh Academy, which specialized in the classics and wanted its pupils to be neat and tidy, proficient in the standard subjects, and totally lacking in original thought because that got in the way of orderly teaching. Jamesie wasn't quite what the schoolteachers wanted, and it did not help that his father, obsessed with cleanliness, had designed special clothes and shoes for the boy, including a frilly tunic bedecked with lace. The other kids nicknamed James “Dafty.” But James was stubborn and earned their respect, though he still baffled them.

The school did one good thing for James: it gave him an interest in mathematics. A letter to his father talks of making “a tetra hedron, a dodeca hedron, and two more hedrons that I don't know the wright names for.” (Presumably these were the octa and icosa.) By the age of 14 he had won a prize for independently inventing a class of mathematical curves known as Cartesian ovals, after its original inventor Descartes. His paper was read to the Royal Society of Edinburgh.

James also wrote poetry, but his mathematical talents were greater. He started at the University of Edinburgh at 16 and later continued his studies at the University of Cambridge, Britain's leading institution for mathematics. William Hopkins, who coached him for his exams, said that James was “the most extraordinary man I have ever met.”

James earned his degree and remained at Cambridge as a postgraduate student, doing experiments on light. Then he read Faraday's
Experimental Researches
and started studying electricity. To cut a long story very short, he took Faraday's mechanical models of electromagnetic phenomena and by 1864 had distilled them into a system of four mathematical laws. (In the notation of the day there were more than four, but we now use vector notation to group them into four. Some formalisms reduce these down to one.) The laws describe electricity and magnetism in terms of two “fields,” one electric and one magnetic, which pervade the whole of space. These fields describe not just the strength of electricity or magnetism at each location but the direction as well.

The four equations have simple physical meanings. Two tell us that electricity and magnetism can be neither created nor destroyed. The third describes how a time-varying magnetic field affects the surrounding electric
field, and it embodies in mathematical form Faraday's discovery of induction. The fourth describes how a time-varying electric field affects the surrounding magnetic field. Even in words, these equations are elegant.

A simple mathematical manipulation of Maxwell's four equations confirmed something that Maxwell had long suspected: light is an electromagnetic wave, a propagating disturbance in the electric and magnetic fields.

The mathematical reason was that from Maxwell's equations it is easy to derive something that all mathematicians could recognize: the “wave equation,” which as its name suggests describes how waves propagate. Maxwell's equations also predict the speed of such waves: they must travel at the speed of light.

Only one thing travels at the speed of light.

In those days it was assumed that waves had to be waves
in
something. There had to be a medium to transmit them; waves were vibrations of that medium. The obvious medium for light waves was the aether. The mathematics said that light waves had to vibrate at right angles to the direction of travel. This explained why Newton and Huygens had been so confused: they thought the waves vibrated along the direction of travel.

The theory made another prediction: that the “wavelength” of electromagnetic radiation, the distance from one wave to the next, could be
anything.
The wavelength of light is extremely short, but there ought to exist electromagnetic waves of much greater length. It was a good enough theory to inspire Heinrich Hertz to generate such waves, which we now call radio waves. Guglielmo Marconi quickly followed up with a practical transmitter and receiver, and suddenly we could talk to each other, almost instantly, across the entire planet. Now we send pictures the same way, monitor the skies with radar, and navigate with the Global Positioning System.