In chapter 2 of Quantum Clear we provided our answer to the all important question What is physics? And we concluded that the crux of it all is Nature . Furthermore, we reaffirmed the implicit dictum, known even before the time of Newton, that the experiment is the voice of Nature. That is how Nature communicates with us. Hence, it is important to recognize that … the experiment is the ethos of physics . From a quantum perspective, this is only natural since quantum mechanics was born from the experiment (Planck). Not only that, but as expressed by Born, the principles of quantum mechanics ‘were found by a slow and tedious process of interpreting experimental results.’ Here, it is from this perspective that we look at general trends in physics, theoretical physics in particular, and we conclude with a simple observation: it is time to return to the old ways, it is time to return to the experiment .
In chapter 2 of Quantum Clear we provided our answer to the all important question What is physics? And we concluded that the crux of it all is Nature . Furthermore, we reaffirmed the implicit dictum, known even before the time of Newton, that the experiment is the voice of Nature. That is how Nature communicates with us. Hence, it is important to recognize that … the experiment is the ethos of physics . From a quantum perspective, this is only natural since quantum mechanics was born from the experiment (Planck). Not only that, but as expressed by Born, the principles of quantum mechanics ‘were found by a slow and tedious process of interpreting experimental results.’ Here, it is from this perspective that we look at general trends in physics, theoretical physics in particular, and we conclude with a simple observation: it is time to return to the old ways, it is time to return to the experiment .
Quantum theory has passed through three distinct stages during its evolution. The first is generally referred to as ‘old quantum theory’. During a period roughly between 1900 and 1925 Planck, Bohr and Einstein, among others, grappled with various experimental and theoretical crises by patching up classical mechanics with some new quantum ideas applied as band-aids. This is not to disparage the work; it was vitally important, and you can only do what is possible at the time. The quantum world is very different to the picture painted by classical physics. That being the case and given the extreme nature of some of these differences, we might question the wisdom of accepting the quantum view. Scientists can be quite disparaging about philosophy, sometimes while in the process of espousing, quite stridently, a philosophical position of their own. The chapter also presents an overview on the key concepts discussed in this book.
The difficulties of the old quantum theory were largely dispelled by the development of quantum mechanics in the 1920s. First Heisenberg (1925) developed the rather abstract matrix mechanics and soon after Schro¨dinger (1926; see also Eckart, 1926) developed the physically more appealing wave mechanics. Subsequently he showed them to be mathematically equivalent. The physicists were greatly relieved; now they had once again a mathematical formalism that enabled the results of experiments to be calculated. It was possible to move forward. It is certainly a very elegant and indeed beautiful formalism, and does enable the results of many physical measurements to be calculated with great accuracy. It is used daily by atomic and nuclear physicists; there is no other way to make calculations. From the earliest days there has been intense debate about the interpretation of quantum mechanics, and it shows no signs of being settled; if anything it is becoming more intense over the years. As Penrose has remarked, no one understands quantum mechanics. Feynman (1967; see also Sykes, 1994) also admitted that ‘nobody understands quantum mechanics’, and Einstein once remarked: ‘I have thought a hundred times as much about the quantum problems as I have about general relativity theory’ (Pais, 1994, p. 57). It should therefore be evident that the most that can be done here is to try to show where the real difficulties lie, and how the failure to recognize that quantum mechanics is an essentially statistical theory has led to a series of confusing quantum paradoxes. It is just these paradoxes that have often been used to support theological speculations. It is useful to ask what ‘understanding quantum mechanics’ actually means. Certainly it means being able to calculate the results of many measurements. The same applies to Newton’s theory of gravitation, which we understand in the sense that we can use it as a basis of calculation, although we do not really understand the gravitational force itself. Very often, especially in modern physics, the mathematical formalism does not give us the sort of intuitive physical feeling for what is going on that we often obtain from classical mechanics. Perhaps we can never achieve more than this for quantum mechanics. In classical mechanics we can assume that a property that is measured objectively exists prior to the interaction of the measuring apparatus with the observed system. Quantum mechanics, however, ‘is incompatible with the proposition that measurement discovers some unknown but pre-existing property’ (Peres, 1997, p. 14). There is an important distinction between mysteries and absurdities. We may be forced to live with mysteries, but there is no reason why we should put up with absurdities such as the wave-particle duality, tunnelling through potential barriers, acausal events and the collapse of the wave function. These are the quantum paradoxes that will be discussed later on. They arise within the Copenhagen interpretation of quantum mechanics and are solved by other interpretations. These alternative interpretations enable us to make conjectures about what is going on, even though we cannot understand it in detail. This is acceptable and a stimulus to further research. It is certainly difficult enough to understand quantum mechanics, but there is no need to try to visualize logical absurdities in the effort to do so. Quantum mechanics is a mathematical formalism that makes it possible to calculate the results of some experiments. Anything more than this, such as questions about the interpretation of what is measured and whether it tells us what is actually going on in the system being studied, belongs to philosophy. Thus we are concerned here with what is essentially a philosophical debate; if it were just a matter of physics the debate would have been settled long ago. One of the difficulties is that it invokes the results of experiments and uses the language of quantum mechanics. Inevitably this language uses philosophical terms and then it is easy to give the impression that the philosophical propositions are in some way entailed by the physical results. These in turn can influence theological thinking. In order to be quite clear which arguments are justified and which are not, it is essential to separate the three levels of discourse: physical, philosophical and theological. Our task is to relate these together, and this immediately raises the traditional problems of the philosophy of science, including the relation of experiment to theory, and of theory to explanation. We begin by discussing experiments, distinguishing between those that are real and those that are imaginary.
‘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.
The essence of quantum mechanics involves indistinguishability , superposition , Heisenberg's uncertainty principle , nonlocality of the photon , and Born's rule . As a whole, these concepts integrate the indeterminacy of quantum mechanics. Indistinguishability and superposition are quantum concepts that together with probability amplitudes are crucial coherent concepts that are part of the first layer of quantum mechanics. Albeit functioning at the mathematical unmeasurable realm of quantum physics, these concepts, nevertheless, faithfully reflect the reality of experimental configurations. Heisenberg's uncertainty principle, nonlocality of the photon, and Born's rule manifest themselves in the second layer of quantum mechanics: the measurable realm . Here, all these five concepts are considered from the experimentalist's perspective. This chapter concludes with the observation that the essence of quantum mechanics is closely and intrinsically entangled with the ethos of physics: the experiment .
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).
Abstract Einstein’s lasting conviction that quantum mechanics was not a theory of principle did not impede him from recognizing that this theory was highly successful. As early as 1927, he publicly expressed his judgment that wave mechanics is ‘in amazing agreement with the facts of experience’ [ E1]. In 1936 he wrote, ‘It seems clear … that the Born statistical interpretation of the quantum theory is the only possible one’ [E2], and in 1949 declared, ‘The statistical quantum theory [is] the most successful theory of our period’ [E3]. Then why was he never convinced by it? I believe Einstein indirectly answered this question in his 1933 Spencer lecture-perhaps the clearest and most revealing expression of his way of thinking in later life. The key is to be found in his remarks on Newton and classical mechanics. In this lecture [E4], Einstein noted that ‘Newton felt by no means comfortable about the concept of absolute space, … of absolute rest … [and] about the introduction of action at a distance.