Fields of Force

The Development of a World View from Faraday to Einstein.

William Berkson

• Publisher: Routledge
• Year: 2014
• ISBN:
  9781317699309
• Edition: 1
• Topic: Historia
• Subtopic: Historia del siglo XX

This book describes the picture of reality given by Newton, and the development of the later picture of reality given by field theory. In telling this story, the author explains what problem each scientist faced, and how the process of solving them led to new discoveries. By this method he gives unique insight into the understanding of Einstein's special theory of relativity, as he explains exactly what problems led to the invention of the theory, and exactly where Einstein's solution differed from his predecessors'. A similar analysis is given of the discoveries of Faraday, Maxwell, Hertz and Lorentz. The problem-oriented approach of the book, originally published in 1974, enables the reader to share in the original creative process, and in the excitement of the discoveries. It puts physics problems into new perspective and discusses the philosophical implications of the history - an illuminating account of a great episode in the history of thought.

CHAPTER 1

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FARADAY’S PROBLEM SITUATION

FARADAY’S AIM

MICHAEL FARADAY created a new theory of the physical world, a field theory. At the same time—during the first half of the nineteenth century—he made a remarkable series of experimental discoveries about the nature of electricity and magnetism. Faraday’s questions, theories and experiments are part of one continuous story: his theories helped him to make the discoveries, the discoveries raised new questions and these questions led to further improvements in his theories. To begin the story, I shall explain how the problems Faraday tried to solve arose from Faraday’s personal aims, and from the situation in the science and philosophy of his day.

The personal aims and philosophy of a scientist have a strong influence on his choice of a research problem, and the way he goes about solving it. Faraday’s aim was a very grand one: he wanted to advance man’s understanding of the basic design of nature. For him, special problems, such as the nature of static electricity, were of interest because they might shed more light on the true picture of nature. Every particular question he immediately related to the most general problems of the nature of the universe. Faraday’s attitude is revealed by a look at his early life.

Michael Faraday was born in 1791, outside London. As his father was a blacksmith, the family was quite poor, and he had very little schooling as a child. At fourteen he was apprenticed to a bookbinder, Mr Riebau, who was a kind man and encouraged him to read books in the shop. Of the books he read he was especially interested in those on science. He mentioned later in his life that an article on electricity in The Encyclopaedia Britannica and the book Conversations on Chemistry, a popular work by Mrs Jane Marcet, had particularly roused his interest.¹

At this time Faraday had a great dream: to become one day a Natural Philosopher himself. Under the influence of this dream he began to read books on scientific method and on what makes a good scientist, and to repeat what experiments he could afford. At the same time he joined others in a self-improvement society, partly to learn to speak and write good English. During that period in England there was a movement to help educate the working class by giving lectures on science and technology. Faraday went to a series of such lectures on science by a Mr Tatum.

After these lectures, Faraday was able to get a ticket to hear a series of lectures at the Royal Institution by Sir Humphrey Davy, one of the great scientists of the day. The Royal Insititution had been founded by Count Rumford to serve as a research institute for practical arts and as a centre for the diffusion of knowledge on the practical applications of science. The Institution changed under Davy and came to be more concerned with pure science. As a result, the lectures became less for the education of the masses and more for the amusement of the educated. Nevertheless, regular lectures were given, and Faraday received the benefit of one series. He wrote up the notes he had taken, bound them carefully and gave them to Davy, saying that if there were any jobs at all he could do for him, he would be eager to try. Later, in 1813, Davy did hire Faraday as a general helper in the laboratory. Shortly after, Faraday became Davy’s assistant. Later he became Davy’s successor, and is remembered as one of the greatest scientists of all time.

Faraday’s success story is so phenomenal that it is sometimes difficult to think of him as real, especially at our distance from him in time. It is hard to imagine him, in the beginning, as a strong-willed but somewhat pathetic working class boy, trying to learn proper English and to get a job near some scientist. He was bright, ambitious and dedicated, and was also extremely courteous and anxious to be correct, as one can imagine from his attempt to rise in society and to achieve his main ambition of becoming a scientist.

Faraday was married in 1821. He had no children of his own, but he loved them: he started a yearly series of Christmas lectures for children at the Royal Institution, and had great fun giving them. Some were published, and have had a beneficial influence on teaching and on the development of children’s science literature. The Christmas lectures for children are still given today at the Royal Institution, as are the regular Friday night lectures started by Faraday.

Perhaps the most striking feature of Faraday in his later work is that he felt a constant burden of struggle for understanding, and at the same time had great dedication and love of his work. This is not to say that Faraday did not take part in the mundane activities and emotions of life, like entertaining visitors, playing with his nieces, getting angry at the pollution of the Thames, and so on. It is just that for him these activities were always subordinate to his main activity, temporary breaks in the main business of his life.

Faraday’s Experimental Researches in Electricity and his research Diary record his life’s work. They are like a history of someone who wrestled with an angel, the angel of Truth. It is as if Faraday were struggling with an opponent he could not see, but could just feel the resistance of. He kept trying to get a hold of his opponent, but could only sense his general shape, not the detail. Once in a while he could get a grip— a new successful experiment—but this was only temporary. Faraday worked almost whenever he was awake. This compulsiveness was no doubt in part responsible for his periodic mental and physical collapse after each new series of discoveries. In one way, Faraday’s life is too serious and too sad, a life to be pitied. In another way it is an effort which commands respect, and even awe: his life was a constant hymn in praise of God.

Faraday was delighted by any contribution he could make to the advance of science, however small. But his great ambition, the driving force behind most of his work, was to reveal some fundamental features of the true picture of nature. Because of his aim, he was preoccupied with those problems whose answers he thought might shed light on the most universal principles of nature. And so an important part of Faraday’s problem situation throughout his life was the group of existing speculations about the general world picture. The existing world views offered alternative constraints on the solutions to the problems he considered. He was always concerned to see which of the views could be applied most successfully in explaining experimental results, and he wanted most of all to find experiments which would be crucial tests between the alternative world views.

When Faraday began his scientific career, there was no general picture of nature from which experimental predictions could be formally deduced. So the most general theories belonged to the realm of metaphysics (as is still the case today). The competing metaphysical frameworks were those of Newton and his followers on one hand and those of the followers of Descartes and Leibniz on the other. Which among these views was best? Could one invent a new theory superior to all of them? Because metaphysics was an important part of Faraday’s problem situation, he was interested in these questions, and considered different answers in the light of the science of his time. The result of his reflection was that he leaned toward some of the anti-Newtonian views, though he was certainly not decided about these views.

In 1820 Oersted announced his discovery that an electrical current has magnetic effects. Faraday considered Oersted’s discovery in the light of the Newtonian and competing metaphysics, and carefully repeated Oersted’s experiments. As a result. Faraday made his first discovery in electro magnetism, the principle of the electric motor. To explain how Faraday was led to this and subsequent discoveries, I shall first explain the metaphysical views which formed part of his problem situation. I shall then describe the latest scientific advances in Faraday’s time, and explain why Faraday, reflecting upon these scientific theories, favoured the anti-Newtonian views. After this I shall examine the problems raised by Oersted’s discovery, and explain how Faraday’s attempt to solve these problems resulted in his first discoveries.

COMPETING WORLD VIEWS: NEWTON

The dominant world view at the beginning of the nineteenth century, when Faraday began his scientific career, was that of Newton. Newton’s ideas had been developed into a sophisticated world view by such scientists as Laplace, who was still alive when Faraday began his work. At the same time, there had been the continuous influence of the views of Descartes and Leibniz. These views offered alternatives to the Newtonian view, though not very well-developed ones.² Although some of these views were regarded with suspicion, and were felt to be anti-scientific, they were, nevertheless, very attractive to Faraday, for reasons I will explain later. Let us begin by looking at the views of Newton.

The Newtonian view is somewhat similar to Democritus’ theory: the world consists entirely of extended hard ‘corpuscles’ and empty space.³ However, there is a third entity—force. Each corpuscle has the power to ‘act at a distance’ to exert forces directly and instantaneously on all other corpuscles in the world. Newton did not present a completely coherent, unambiguous view in his own writings. For instance, he used the idea of an ether in explaining some optical effects, like ‘Newton’s rings’. Because of Newton’s many hints and ‘queries’, there was never complete agreement on what Newton’s own view really was. I believe it is correct to say that the basic picture just mentioned—extended corpuscles exerting forces at a distance across empty space—was generally regarded as Newton’s view, rightly or not. Newton had developed his theories of mechanics and gravity in accord with this basic picture.

The gravitational theory is a theory of the nature of the forces associated with the corpuscles; the mechanics describes how the forces produce motion. In the theory of gravitation, the attractive force between particles is a ‘central force’, which always acts along the line connecting the centres of the particles. The force of one corpuscle on another is always equal and opposite to the force of that other corpuscle on it. (This is a case of the law of equality of action and reaction, the third of Newton’s laws.) Finally, there is a specific law concerning the variation of the intensity of gravitational force: it is proportional to the product of the masses of the corpuscles and to the inverse square of the distance between them (F =G m₁m₂/r²). The followers of Newton hoped that all or most of these laws of gravity would apply to the forces of electricity, cohesion, chemistry, light, etc.

The Newtonians hoped also that Newton’s mechanics would apply to particles affected by other forces. A basic law of Newton’s mechanics (the second) is that a force produces a change in the momentum of a corpuscle proportional to the force’s strength (the momentum of a corpuscle is the product of its velocity and mass). Another law of mechanics is the law of inertia (the first), that a body at rest remains at rest or in uniform motion in a straight line, provided no forces act on the body. (This law can in fact be deduced from the second law.)

Once one accepts Newton’s basic metaphysical framework— corpuscles, space and forces acting at a distance—then Newton’s laws seem extremely plausible, in fact almost necessary within the framework. However, at the time it was apparent that not all the laws could be directly applied to non-gravitational phenomena, like electricity. Some compromises had to be made. When these compromises were made, the main aim was to keep the metaphysic framework intact. Let us first consider how Newton’s laws are plausible within his metaphysics and then go on to find out why the laws could not be adapted to non-gravitational forces without alteration, while examining science in Faraday’s time.

The inverse square law is very natural in Newton’s metaphysics, because it has a geometrical interpretation and so seems to follow from the character of space itself.⁴ Let me explain. Suppose one has a light source of constant intensity, a source from which water gushes out in all directions or a heat source in a uniform solid. And imagine two spheres, one bigger than the other, drawn with the source as their centre. The light, water and heat will all spread out with decreasing intensity according to the inverse square law, as can be shown from the geometry of spheres. Let us take the light source as our example. All the light as the nearer sphere will have come from the source, which is at its centre. This same light will reach the second sphere, so the same amount of light will be spread out over the first and second spheres. (The intensity of the source is supposed to be constant.) Because the second sphere is bigger, there will be less light per area; the intensity will be smaller. The ratio of the areas of the two spheres is the square of their radii. So a part of the second sphere, which is twice as far away as the first sphere, will only have one-fourth (1²/2²) of the light on it. In general, the intensity will fall off as the inverse square of the distance from the source.

If particles act directly at a distance upon each other, through a space which is empty and uniform, then it is plausible that the intensity of the force should fall off exactly in proportion to the area of a sphere’s surface at the given distance from it. If there is an intervening medium through which the forces have to pass, this medium may distort the forces. In this case it is no longer surprising that the inverse square law may fail. For example, it does not hold when a lens changes the direction of light rays comi...