Abstract ‘When all is said and done, physics is only a description, not an explanation’. I have uttered similar statements many times myself in informal discussions, when my interlocutor happened to slide into an excessive praise of experimental science and an excessive contempt of other forms of human knowledge. In the mouth of Jean-Paul Fragnière, a friend and philosophy teacher who lives in the small Swiss town of Fribourg, this sentence sounds, however, the expression of a different and distant line of thought of a rivalry between human and natural sciences that is still latent in the French-speaking world, a relic of the arrogance of Positivism. We are in the massive building of Saint-Michel College – a sixteenth century Jesuit establishment, a public school for several decades; and though Jean-Paul’s classroom is a modernization of what was the granary, history weighs heavily here. For the first generations of young people educated in this school, heliocentrism was one of the hot topics; now Jean-Paul has invited me to speak to his students about quantum physics.
Abstract ‘When all is said and done, physics is only a description, not an explanation’. I have uttered similar statements many times myself in informal discussions, when my interlocutor happened to slide into an excessive praise of experimental science and an excessive contempt of other forms of human knowledge. In the mouth of Jean-Paul Fragnière, a friend and philosophy teacher who lives in the small Swiss town of Fribourg, this sentence sounds, however, the expression of a different and distant line of thought of a rivalry between human and natural sciences that is still latent in the French-speaking world, a relic of the arrogance of Positivism. We are in the massive building of Saint-Michel College – a sixteenth century Jesuit establishment, a public school for several decades; and though Jean-Paul’s classroom is a modernization of what was the granary, history weighs heavily here. For the first generations of young people educated in this school, heliocentrism was one of the hot topics; now Jean-Paul has invited me to speak to his students about quantum physics.
Abstract Leaving Saint-Michel, I take my leave of Jean-Paul who is going home, and I turn left to walk down the College Steps, a covered lane that descends into the heart of Fribourg. There, in front of the cathedral, three busy roads meet to form a roundabout. I continue my walk along the south side of the cathedral. Cars continue to stream down the road. Now that the roundabout is no longer in view, I cannot know by which route each car has entered it. In order to arrive alongside me, as it does now, this car could have taken three possible paths. I have put myself, in relation to the cars, in a situation of indistinguishability. Well then, why is the road network not a quantum interferometer? The answer is a matter of common sense – the indistinguishability of cars is only apparent, it is due to an ignorance that can easily be overcome. In order to obtain the information about the path by which each car entered the roundabout, it would suffice for me to go back a few paces or to ask the driver – neither of these steps would modify what the destination of the car will be.
Schrödinger’s equation and the “wave function” that satisfies it are the first bold brushstrokes of a new portrait of Nature that physicists gradually filled in during the middle half of the twentieth century. The emerging pattern was strange, but not entirely alien to science. It was drawn, to paraphrase Galileo, in a mathematical idiom “without some knowledge of which it is humanly impossible to understand.” While nonmathematical accounts are conceivable, I would rather at this point say more about the mathematics because it will deepen our view of the whole enterprise of modern physics. Most people never get beyond the “math is numbers and numbers are boring” barrier that hides behind it a limitless universe of beautiful things. So let us delve briefly into the nonboring side of mathematics.
Those defile the purity of mathematical and philosophical truthy who confound real quantities with their relations and sensible measures. —ISAAC NEWTON, Principia Before we say anything about quantum mechanics, let us take a quick look at the Newtonian (or ‘classical’) view of the physical universe. According to that view, nature consists of an enormous number of particles. When Newtonian physics is combined with the theory of the electromagnetic field, it becomes convenient to think of these particles as dimensionless (even if there is a kind of conceptual strain involved in trying to think of something as having a mass but not any size ), and as possessing electrical properties – negative charge, or positive charge, or neutrality. This leads to the well-known ‘solar system’ view of the atom – with the electrons whirling around the nucleons (neutrons and protons) just as the planets whirl around the sun. Out of atoms are built molecules; out of molecules, macroscopic objects, scaling from dust motes to whole planets and stars. These latter also fall into larger groupings – solar systems and galaxies – but these larger structures differ from the ones previously mentioned in being held together exclusively by gravitational forces. At every level, however, one has trajectories (ultimately that means the possibility of continuously tracing the movements of the elementary particles) and one has causality (ultimately that means the possibility of extrapolating from the history of the universe up to a given time to its whole sequence of future states).
The two towering achievements of modern physics are quantum theory and Einstein's general theory of relativity. Together, they explain virtually everything about the world we live in. But, almost a century after their advent, most people haven't the slightest clue what either is about. Did you know that there's so much empty space inside matter that the entire human race could be squeezed into the volume of a sugar cube? Or that you grow old more quickly on the top floor of a building than on the ground floor? And did you realize that 1% of the static on a TV tuned between stations is the relic of the Big Bang? These and many other remarkable facts about the world are direct consequences of quantum physics and relativity. Quantum theory has literally made the modern world possible. Not only has it given us lasers, computers, and nuclear reactors, but it has provided an explanation of why the sun shines and why the ground beneath our feet is solid. Despite this, however, quantum theory and relativity remain a patchwork of fragmented ideas, vaguely understood at best and often utterly mysterious. They have even gained a reputation of being beyond the understanding of the average person. Author Marcus Chown emphatically disagrees. As Einstein himself said, Most of the fundamental ideas of science are essentially simple and may, as a rule, be expressed in a language comprehensible to everyone. If you think that the marvels of modern physics have passed you by, it is not too late. In Chown's capable hands, quantum physics and relativity are not only painless but downright fun. So sit back, relax, and get comfortable as an adept and experienced science communicator brings you quickly up to speed on some of the greatest ideas in the history of human thought.
‘Quantum mechanics is very impressive. But an inner voice tells me that it is not yet the real thing. The theory produces a good deal but hardly brings us closer to the secret of the Old One’. These views were contained in a letter written by Albert Einstein to Max Born in December 1926. Though the following year would see the completion of work on the theoretical foundation of the modern physics of atoms and particles, Einstein was never to change his judgement and remained firmly convinced that ‘this business […] contains some unreasonableness’. He was unwilling to sacrifice his own ideas as to the cognitive scope of science even in the face of the important results being achieved by the new theory. To the undeterministic findings of quantum mechanics he opposed his belief in the ‘possibility of giving a model of reality, a theory, that is to say, which shall represent events themselves and not merely the probability of their occurrence’. For this reason he chose to live with the isolation of his scepticism and dissent, ironically accepting the reputation as a obstinate heretic that he had won over the years among his colleagues, and worked to the end on his own research programme to develop a unified field theory of rigorously causal nature. As is generally known, Einstein carried on a strong scientific and philosophical dispute with the defenders of the so-called official interpretation of quantum mechanics.
I would like to explain the motivations behind this thesis, and to acknowledge some of the people who have helped me. My general attitude to philosophy and science owes much to Cliff Hooker; like him, I defend the philosophical position known as scientific realism. This position is opposed to various other theories that I will call "narrow" empiricist philosophies. I believe that the triumph of a cogent realist philosophy of science over these (and other) theories would have beneficial effects on philosophy, on science, and in broader areas of life. Cliff Hooker has influenced this belief - he emphasises the connection between people's philosophical presuppositions and their social practices, including their scientific, economic and political practices.\n\nThe particular philosophical theory I adopt in this work owes a great deal to Malcolm Forster. Forster's theory is a realist one, and while some realists renounce any form of empiricism, Forster defends a realist philosophy of science from within an empiricist framework. He does this by developing a broader conception of empiricism than the "narrow" empiricist theories I mentioned. I support this approach.\n\nForster's theory is laid out mainly in his March, 1988 paper. This paper, which I first read in draft form, struck me as containing 'the Truth', and I became keen to work on his theory myself. His theory can be labelled a 'bottom-up' one, showing how we can build up a scientific hypothesis from the data step by step, while concentrating on how new concepts are introduced by the hypothesis. Forster's theory is based around the idea of the 'consilience of inductions', a notion introduced by William Whewell, a philosopher of science in the 19th century. Forster applies his theory to Newtonian mechanics, whereas I apply it, or a close relation of it, to quantum mechanics. Hence the title of this work.\n\nI think that the promotion of this kind of 'bottom-up' philosophy could have many positive effects - I will mention one possibility. As a science student, the dominant approach to science that I was exposed to was 'top-down', or 'hypothetico-deductive', to use the philosophical term. In the teaching of science according to this approach, the formalism of a theory is presented, then applications are worked through, deducing the consequences of the formalism in each case. By working through many examples, a student gradually gets a feel for what the concepts of the theory mean.\n\nI feel that with a bottom-up presentation of a theory, which shows how the concepts can be motivated from the data, one obtains a more thorough understanding of the concepts, and one shares some of the insight of a conceptual discovery. I would like to think that the bottom-up approach could come to have enough influence within philosophy of science to reach scientists, and eventually the educators, so that the top-down 'application based' teaching style might be complemented by a bottom-up 'concept based' approach presented alongside.\n\nAs well as benefiting from my contacts with Malcolm Forster and Cliff Hooker, I have also had great help from my supervisor, Henry Krips, and John Bigelow, who provided a good deal of supervision as well. Others I would like to thank are John Clendinnen, Alan Hajek, Stephanie Moser, David Rathbone, Richard Staley, Bill Sutherland, Carolyn Tonkin, Alexandra Towers, and Bill Wignall. Thanks go as well to my teachers and colleagues at the School of Physics at The University of Melbourne, and the departments of Philosophy. University of Western Ontario, Philosophy, Newcastle University, History and Philosophy of Science, The University of Melbourne, and Philosophy, La Trobe University. I must also thank all those friends and relatives who have suffered while I have been working on this thesis.