The Big Questions: Physics (2 page)

‘I do not know what I may appear to the world,’ he wrote, ‘but to myself I seem to have been only like a boy playing on the sea-shore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me.’

ISAAC NEWTON

If there is one aspect of physics’ achievements that Newton perhaps appreciated less than most, it was the subject’s ability to slice through mysticism and superstition. Newton was a great alchemist and a biblical scholar; he considered his writings on the Old Testament book of Daniel his greatest work. Whenever physics threatened to cast doubts upon spiritual matters, Newton would cringe. ‘I have studied these things – you have not,’ was his constant retort to astronomers’ criticisms of religion. Newton left
room for God’s work in the mechanism of his ‘clockwork heavens’ but the march of physics soon displaced the divine hand. When the Emperor Napoleon questioned Pierre-Simon Laplace about his newly published treatise on celestial mechanics, he remarked on the absence of God in the mechanism. ‘I have no need of that hypothesis,’ Laplace replied. The point of physics, in many ways, is to find what, in the universe, is explicable by a set of laws, and the simpler the laws the better.

Until around 600
BC
, civilizations developed technologies but thought little about how to make sense of the world: that was for the prophets and the sages. Then came the Milesians. The city of Miletus, on the west coast of modern Turkey, was home to a mode of thought that would be recognizable to today’s scientists as a thirst for real, first-hand understanding. Rather than having the universe’s secrets obscured by mystical religious concerns, the Milesians sought laws to explain the phenomena of nature, and came up with theories for the causes of Earthquakes, lightning and the structure of the universe, among other things.

The Milesians debated these theories openly, considered how they might be tested, and accepted the results of experiments as the arbiter of truth. Anaximenes of Miletus is credited with performing the world’s first scientific experiment. His observations of how the temperature of exhaled breath seems to vary depending on whether the lips are pursed or wide open, led him to conclude that compression causes cooling, and expansion causes heating.

The fact that Anaximenes was exactly wrong here is another lesson in the point of physics. It teaches us that we cannot ever be sure of anything that is ‘received wisdom’; accepted theories, and even ‘facts’ about how things in the universe work, are often proved wrong, and supplanted by new ideas. These, too, are open to falsification. Physics is a process of testing everything – especially those things we most want to be true.

It is for this reason that physics is somewhat devoid of ‘scientific saints’. It is not so much a discipline of ideas as a discipline
of consensus arrived at through the gathering of experimental evidence. Those who fail to accept the results of experiments – and do not provide good reasons why others should join them on the ‘wrong’ side of the fence – tend to be given short shrift.

The physicists Albert Einstein and Richard Feynman provide a suitable illustration of the way physics is bigger than any physicist. Though now venerated as a public icon, Einstein did not die a hero to other physicists. On the contrary, his later life is remembered with a tinge of regret at his ultimate quest. Einstein’s best-known work was done early in his career. He made a seminal
contribution to quantum theory with the experimental discovery of the photon, the quantum of energy (see
What is Light?
).

This destroyed the centuries-old view that light must be a wave. Then his special theory of relativity changed our notion of time. His elucidation of the idea that mass and energy are interchangeable (see
Why Does E = mc
²
?
) was a revelation about the fundamentals of matter. The general theory of relativity rewrote Newton’s gravitational work after nearly four centuries of acceptance (see
Why Does an Apple Fall?
).

After that, though, Einstein’s views grew irrelevant to physics. The quantum revolution changed the face of the subject, but Einstein refused to accept quantum theory as a useful way to describe the universe. He spent his later years working, to no avail, on a theory that would unite electromagnetism and relativity and render quantum theory an unnecessary innovation. The number of physicists who would work with him and support him dwindled throughout his life.

Richard Feynman is perhaps the second most famous physicist after Einstein. He was a great popularizer of the subject, a great and innovative thinker, and – most significantly of all – remains a great hero to those working in the field. Feynman never reached Einstein’s dizzy heights of achievement, but he did more than most, contributing to the creation of quantum electrodynamics, or QED, a theory that describes the interactions of light and matter (see
What is Light?
). It is widely feted as our most successful theory of physics.

‘The first principle is that you must not fool yourself – and you are the easiest person to fool.’

RICHARD FEYNMAN

One of Feynman’s greatest strengths as a physicist was his ability to listen to the convictions of his peers, bow to the law of evidence, and admit that he was always working from a position of ignorance. He famously said that, ‘The first principle is that you must not fool yourself – and you are the easiest person to fool.’ His
unwillingness to fool himself is summed up in his appraisal of the theory that became Einstein’s downfall. ‘I think I can safely say that nobody understands quantum mechanics,’ he wrote in
The Character of Physical Law
. ‘Do not keep saying to yourself, if you can possibly avoid it, ‘But how can it be like that?’ because you will get … into a blind alley from which nobody has yet escaped. Nobody knows how it can be like that.’

This is the reason the older Einstein is not revered by physicists, and Feynman is. While Einstein led himself into a blind alley, Feynman admitted his limited understanding, and followed others as they made forays into new territory. This is another component of the point of physics: progress by building on the achievements of others. As Newton put it, ‘If I have seen further it is only by standing on the shoulders of giants.’

‘If I have seen further it is only by standing on the shoulders of giants.’

ISAAC NEWTON

Thanks to quantum theory, physics has even taken the extraordinary step of defining some limits for itself. The Heisenberg uncertainty principle (see
Is Everything Ultimately Random?
) sets in stone the fact that there are limits to what physics can tell us about a system.

When we examine the equations that govern the motion of an electron, say, we can see how they tell us its momentum, or its velocity. There is no means by which they can tell us, precisely, about both the momentum and the velocity, however. The two can be found to only a finite precision.

Werner Heisenberg saw the practical side of this: there are limits to what our experiments can reveal. Bounce a photon of light off the electron, and you can infer its position, but the photon will have imparted some momentum to the electron, too. Thus the act of determining the position of the electron creates an uncertainty in the value of its momentum. Conversely, a measurement of momentum will always create an uncertainty in a
particle’s position. Whether you look at theory or experiment, there are strict limitations to what we can find out. Physics, in many ways, is a humble discipline. But there’s plenty to be humble about, as the physicists behind the atomic bomb will testify.

If you had posed the question ‘what is the point of physics?’ to Western governments after the Second World War, you would have been greeted by disbelief that you even had to ask. Physics was everything, as the war had shown. Physics had given us fantastic technological innovations: radar, computers, the atomic bomb, and, of course, televisions and microwave ovens. Physics was set to be the driver of economies, and the protector of nations. Pose the same question to physicists, however, and you might have got a rather more subdued response.

Immediately after the first test of the atomic bomb in New Mexico, the Harvard physicist Kenneth Bainbridge turned to Robert Oppenheimer, the project leader. ‘Now we’re all sons of bitches,’ he said. Oppenheimer was dealing with his own mixed emotions: decades later, he admitted they all knew at that moment that the world would never be the same. And yet, Oppenheimer said, put in the same situation, he would do it all again. ‘If you are a scientist, you cannot stop such a thing,’ he said in his retirement speech in 1945. ‘If you are a scientist, you believe that it is good to find out how the world works … that it is good to turn over to mankind at large the greatest possible power to control the world.’

Is this the point of physics: to gain control over the world? It is true that physics – or at least the industrial application of physics – has created the modern world. If our age can be defined by one thing, it is probably the microelectronics revolution: television, computing, the Internet, and mobile communications, to mention but a few aspects. All of it was built on the back of physics. To be more specific, it was built on the back of silicon technology. During the Second World War, the developers of radar worked to create ever-purer crystals of silicon and germanium for the equipment. Physicists – above all the ones employed by Bell Labs
in the USA – continued that development after the war, learning how to turn them into ‘semiconductors’ and incorporate them into technologies that had previously required inefficient and bulky valve amplifiers. By 1952, the first silicon-based electronics products had hit the market: low-power and highly portable devices, such as hearing aids and pocket radios. A year later, the first transistor-driven computer appeared. Shortly after that, people started to refer to the concentration of electronics companies in a small area of northern California as ‘Silicon Valley’.

It is not hard to see the impact of physics on our lives. Lasers provide a specific example. Lasers also came from Bell Labs, and stemmed from wartime research into radar technology. Since their invention in 1957, they have become ubiquitous in everyday life. CD and DVD players, fibre-optic communications systems such as the telephone network, supermarket checkout scanners, eye surgery and laser printers are just a few of the applications.

So, is the development of technology the point of physics? Not at all. The technological revolutions of the 20th century came about as a result, ultimately, of the discovery – or invention, if you prefer – of quantum theory. That was the result of trying to unravel things no one understood, such as why the spectrum of radiation emitted by an oven at 100 celsius was the same as the spectrum of radiation emitted by anything else at 100 celsius, rather than specifically trying to invent new devices.

In essence, our modern electronic technologies, come from quantum theory, which came from thermodynamics, the study of heat. That arose from the study of gases – and so on. Physics is a self-sustaining chain reaction: every discovery provokes another set of questions, which provoke new discoveries. As George Bernard Shaw once said, ‘science never solves a problem without creating ten more’.