In Pursuit of the Unknown (38 page)

Hertz knew that his work was important as physics, and he published it in
Electric Waves: being researches on the propagation of electric action with finite velocity through space
. But it never occurred to him that the idea might have practical uses. When asked, he replied ‘It's of no use whatsoever . . . just an experiment that proves Maestro Maxwell was right – we just have these mysterious electromagnetic waves that we cannot see with the naked eye. But they are there.' Pressed for his view of the implications, he said ‘Nothing, I guess.'

Was it a failure of imagination, or just a lack of interest? It's hard to tell. But Hertz's ‘useless' experiment, confirming Maxwell's prediction of electromagnetic radiation, would quickly lead to an invention that made the telephone look like a children's toy.

Radio.

Radio makes use of an especially intriguing range of the spectrum: waves with wavelengths much longer than light. Such waves would be likely to retain their structure over long distances. The key idea, the one that Hertz missed, is simple: if you could somehow impress a signal on a wave of that kind, you could talk to the world.

Other physicists, engineers, and entrepreneurs were more imaginative, and quickly spotted radio's potential. To realise that potential, however, they had to solve a number of technical problems. They needed a transmitter that could produce a sufficiently powerful signal, and something to receive it. Hertz's apparatus was restricted to a distance of a few feet; you can understand why he didn't suggest communication as a possible application. Another problem was how to impose a signal. A third was how far the signal could be sent, which might well be limited by the curvature of the Earth. If a straight line between transmitter and receiver hits the ground, this would presumably block the signal. Later it turned out that nature has been kind to us, and the Earth's ionosphere reflects radio waves in a wide range of wavelengths, but before this was discovered there were obvious ways round the potential problem anyway. You could build tall towers and put the transmitters and receivers on those. By relaying
signals from one tower to another, you could send messages round the globe, very fast.

There are two relatively obvious ways to impress a signal on a radio wave. You can make the amplitude vary or you can make the frequency vary. These methods are called amplitude-modulation and frequency-modulation: AM and FM. Both were used and both still exist. That was one problem solved. By 1893 the Serbian engineer Nikola Tesla had invented and built all of the main devices needed for radio transmission, and he had demonstrated his methods to the public. In 1894 Oliver Lodge and Alexander Muirhead sent a radio signal from the Clarendon laboratory in Oxford to a nearby lecture theatre. A year later the Italian inventor Guglielmo Marconi transmitted signals over a distance of 1.5 kilometres using new apparatus he had invented. The Italian government declined to finance further work, so Marconi moved to England. With the support of the British Post Office he soon improved the range to 16 kilometres. Further experiments led to Marconi's law: the distance over which signals can be sent is roughly proportional to the square of the height of the transmitting antenna. Make the tower twice as tall and the signal goes four times as far. This, too, was good news: it suggested that long-range transmission should be practical. Marconi set up a transmitting station on the Isle of Wight in the UK in 1897, and opened a factory the next year, making what he called ‘wirelesses'. We still called them that in 1952, when I listened to the Goon Show and Dan Dare on the wireless in my bedroom, but even then we also referred to the device as ‘the radio'. The word ‘wireless' has of course come back into vogue, but now it is the links between your computer and its keyboard, mouse, modem, and Internet router that are wireless, rather than the link from your receiver to a distant transmitter. It's still done by radio.

Initially Marconi owned the main patents to radio, but he lost them to Tesla in 1943 in a court battle. Technological advances quickly made those patents obsolete. From 1906 to the 1950s, the vital electronic component of a radio was the vacuum tube, like a smallish light bulb, so radios had to be big and bulky. The transistor, a much smaller and more robust device, was invented in 1947 at Bell Laboratories by an engineering team that included William Shockley, Walter Brattain, and John Bardeen (see
Chapter 14
). By 1954 transistor radios were on the market, but radio was already losing its primacy as an entertainment medium.

By 1953, I'd already seen the future. It was the coronation of Queen Elizabeth II, and my aunt in Tonbridge had . . .
a television set!
So we piled into my father's rickety car and drove 40 miles to watch the event. I was
more impressed by Bill and Ben the Flowerpot Men than by the coronation, to be honest, but from that moment radio was no longer the epitome of modern household entertainment. Soon we, too, possessed a television set. Anyone who has grown up with 48-inch flatscreen colour TVs with high definition and a thousand channels will be appalled to hear that in those days the picture was black-and-white, about 12 inches across, and (in the UK) there was exactly one channel, the BBC. When we watched ‘the television' it really meant
the
television.

Entertainment was just one application of radio waves. They were also vital to the military, for communications and other purposes. The invention of radar (radio detection and ranging) may well have won World War II for the Allies. This top-secret device made it possible to detect aircraft, especially enemy aircraft, by bouncing radio signals off them and observing the reflected waves. The urban myth that carrots are good for your eyesight originated in wartime disinformation, intended to stop the Nazis wondering why the British were getting so good at spotting raiding bombers. Radar has peacetime uses as well. It is how air traffic controllers keep tabs on where all the planes are, to prevent collisions; it guides passenger jets to the runway in fog; it warns pilots of imminent turbulence. Archaeologists use ground-penetrating radar to locate likely sites for the remains of tombs and ancient structures.

X-rays, first studied systematically by Wilhelm Röntgen in 1875, have much shorter wavelengths than light. This makes them more energetic, so they can pass through opaque objects, notably the human body. Doctors could use X-rays to detect broken bones and other physiological problems, and still do, although modern methods are more sophisticated and subject the patient to far less damaging radiation. X-ray scanners can now create three-dimensional images of a human body, or some part of it, in a computer. Other kinds of scanner can do the same thing using different physics.

Microwaves are efficient ways to send telephone signals, and they also turn up in the kitchen in microwave ovens, quick ways to heat food. One of the latest applications to emerge is in airport security. Terahertz radiation, otherwise known as T-waves, can penetrate clothing and even body cavities. Customs officials can use them to spot drug smugglers and terrorists. Their use is a little controversial, since they amount to an electronic strip-search, but most of us seem to think that's a small price to pay if it stops a plane being blown up or cocaine hitting the streets. T-waves
are also useful to art historians, because they can reveal murals covered in layers of plaster. Manufacturers and commercial carriers can use T-waves to inspect products without taking them out of their boxes.

The electromagnetic spectrum is so versatile, and so effective, that its influence is now felt in virtually all spheres of human activity. It makes things possible that to any previous generation would appear miraculous. It took a vast number of people, from every profession, to turn the possibilities inherent in the mathematical equations into real gadgets and commercial systems. But none of this was possible until someone realised that electricity and magnetism can join forces to create a wave. The whole panoply of modern communications, from radio and television to radar and microwave links for mobile phones, was then inevitable. And it all stemmed from four equations and a couple of lines of basic vector calculus.

Maxwell's equations didn't just change the world. They opened up a new one.

 

 

 

 

The amount of disorder in a thermodynamic system always increases.

It places limits on how much useful work can be extracted from heat.

Better steam engines, estimates of the efficiency of renewable energy, the ‘heat death of the universe' scenario, proof that matter is made of atoms, and paradoxical connections with the arrow of time.

I
n May 1959 the physicist and novelist C.P. Snow delivered a lecture with the title
The Two Cultures
, which provoked widespread controversy. The response of the prominent literary critic F.R. Leavis was typical of the other side of the argument; he said bluntly that there was only
one
culture: his. Snow suggested that the sciences and the humanities had lost touch with each other, and argued that this was making it very difficult to solve the world's problems. We see the same today with climate change denial and attacks on evolution. The motivation may be different, but cultural barriers help such nonsense to thrive – though it is politics that drives it.

Snow was particularly unhappy about what he saw as declining standards of education, saying:

A good many times I have been present at gatherings of people who, by the standards of the traditional culture, are thought highly educated and who have with considerable gusto been expressing their incredulity at the illiteracy of scientists. Once or twice I have been provoked and have asked the company how many of them could describe the Second Law of Thermodynamics, the law of entropy. The response was cold: it was also negative. Yet I was asking something which is about the scientific equivalent of: ‘Have you read a work of Shakespeare's?'

Perhaps he sensed he was asking too much – many qualified scientists can't state the second law of thermodynamics. So he later added:

I now believe that if I had asked an even simpler question – such as, What do you mean by mass, or acceleration, which is the scientific equivalent of saying, ‘Can you read?' – not more than one in ten of the highly educated would have felt that I was speaking the same language. So the great edifice of modern physics goes up, and the majority of the cleverest people in the western world have about as much insight into it as their Neolithic ancestors would have had.

Taking Snow literally, my aim in this chapter is to take us out of the Neolithic age. The word ‘thermodynamics' contains a clue: it appears to mean the dynamics of heat. Can heat be dynamic? Yes: heat can
flow
. It can move from one location to another, from one object to another. Go outside on a winter's day and you soon feel cold. Fourier had written down the first serious model of heat flow,
Chapter 9
and done some beautiful mathematics. But the main reason scientists were becoming interested in heat flow was a newfangled and highly profitable item of technology: the steam engine.

There is an oft-repeated story of James Watt as a boy, sitting in his mother's kitchen watching boiling steam lift the lid off a kettle, and his sudden flash of inspiration:
steam can perform work
. So, when he grew up, he invented the steam engine. It's inspirational stuff, but like many such tales this one is just hot air. Watt didn't invent the steam engine, and he didn't learn about the power of steam until he was an adult. The story's conclusion about the power of steam is true, but even in Watt's day it was old hat.

Around 50
BC
the Roman architect and engineer Vitruvius described a machine called an aeolipile in his
De Architectura
(‘On Architecture'), and the Greek mathematician and engineer Hero of Alexandria built one a century later. It was a hollow sphere with some water inside, and two tubes poked out, bent at an angle as in
Figure 46
. Heat the sphere and the water turns to steam, escapes through the ends of the tubes, and the reaction makes the sphere spin. It was the first steam engine, and it proved that steam could do work, but Hero did nothing with it beyond entertaining
people. He did make a similar machine using hot air in an enclosed chamber to pull a rope that opened the doors of a temple. This machine had a practical application, producing a religious miracle, but it wasn't a steam engine.