This chapter first examines the four ways in which quantum theory poses a challenge for aim-oriented empiricism. It then enumerates the six defects of the orthodox quantum theory. It also looks into the nature of the propensiton quantum theory. The last three sections of the chapter discuss one approach to developing a fully micro-realistic version of quantum theory, free of the defects which deface orthodox quantum theory. The chapter notes that this plausible view would not have been ignored if aim-oriented empiricism had been generally accepted. It argues that these defects result from failure to solve the wave/particle dilemma. The chapter suggests that theoretical physics should seriously consider the two interrelated questions in which orthodox quantum theory is so evasive: What is the nature of quantum objects? Is Nature probabilistic or deterministic?
This chapter first examines the four ways in which quantum theory poses a challenge for aim-oriented empiricism. It then enumerates the six defects of the orthodox quantum theory. It also looks into the nature of the propensiton quantum theory. The last three sections of the chapter discuss one approach to developing a fully micro-realistic version of quantum theory, free of the defects which deface orthodox quantum theory. The chapter notes that this plausible view would not have been ignored if aim-oriented empiricism had been generally accepted. It argues that these defects result from failure to solve the wave/particle dilemma. The chapter suggests that theoretical physics should seriously consider the two interrelated questions in which orthodox quantum theory is so evasive: What is the nature of quantum objects? Is Nature probabilistic or deterministic?
What sort of entities are electrons, photons and atoms given their wave-like and particle-like properties?Is nature fundamentally deterministic or probabilistic?Orthodox quantum theory (OQT) evades answering these two basic questions by being a theory about the results of performing measurements on quantum systems.But this evasion results in OQT being a seriously defective theory.A rival, somewhat ignored strategy is to conjecture that the quantum domain is fundamentally probabilistic.This means quantum entities, interacting with one another probabilistically, must differ radically from the entities of deterministic classical physics, the classical wave or particle.It becomes possible to conceive of quantum entities as a new kind of fundamentally probabilistic entity, the "propensiton", neither wave nor particle.A fully micro realistic, testable rival to OQT results.
In this paper I outline my propensiton version of quantum theory (PQT). PQT is a fully micro-realistic version of quantum theory that provides us with a very natural possible solution to the fundamental wave/particle problem, and is free of the severe defects of orthodox quantum theory (OQT) as a result. PQT makes sense of the quantum world. PQT recovers all the empirical success of OQT and is, furthermore, empirically testable (although not as yet tested). I argue that Einstein almost put forward this version of quantum theory in 1916/17 in his papers on spontaneous and induced radiative transitions, but retreated from doing so because he disliked the probabilistic character of the idea. Subsequently, the idea was overlooked because debates about quantum theory polarised into the Bohr/Heisenberg camp, which argued for the abandonment of realism and determinism, and the Einstein/Schrödinger camp, which argued for the retention of realism and determinism, no one, as a result, pursuing the most obvious option of retaining realism but abandoning determinism. It is this third, overlooked option that leads to PQT. PQT has implications for quantum field theory, the standard model, string theory, and cosmology. The really important point, however, is that it is experimentally testable. I indicate two experiments in principle capable of deciding between PQT and OQT.
The measurement problem in quantum mechanics first cropped up during the 1930s during a famous series of debates between Einstein and Bohr concerning the physical adequacy – or ‘completeness’ – of the orthodox (Copenhagen) theory.1 As we have seen, it is a topic central to Hanson’s thinking not only with regard to quantum mechanics but also for its wider bearing on the scope and limits of scientific knowledge, the theory-laden character of observations, and the underdetermination of theory by evidence.2 Thus it is frequently adduced in support of his proto-Kuhnian claim that scientists working within different paradigms must be thought of as observing different things or inhabiting ‘different worlds’.3 What I propose to do now is look in more detail at the arguments surrounding this topic and, especially, at various proposals – from Einstein down – for a realist construal of the quantum data (i.e., the empirical measurement-results) that would offer an alternative to Hanson’s idea of the uncertainty principle as placing an absolute limit on our knowledge of objects and events in the microphysical domain. Having set out his arguments already in chapters 4 and 5, I shall not make any further detailed reference to Hanson’s work but assume that the reader who has come this far will have them clearly in mind. Thus my purpose in the remainder of this book is to raise the question: what becomes of the paradigm-relativist approach to issues in the history and philosophy of science if it derives so much of its suasive force from an interpretation of quantum mechanics that has proved increasingly open to challenge?
When we are presented with apparently bizarre properties of microsystems governed by quantum mechanics (as in our discussion of the double-slit experiment in the previous chapter), we naturally ask whether it might be possible to find another theory, or at least another story to go with the equations, that would make more sense to us. We might seek a theory and a view of fundamental physical processes that would accord more with our classically based, everyday common sense. This typically takes the form of the question of the possibility of the existence of a more detailed description of atomic processes than that afforded by the wave function (that is, by the Copenhagen interpretation of the previous chapter). In this chapter we discuss some of the central interpretive problems of the Copenhagen version of quantum mechanics. Then, in the next two chapters, we look at the severe, general restrictions that are placed on any such completion of quantum mechanics and at one particular extension of quantum mechanics. First, though, we begin here with the struggle that ensued over the status of causality in quantum theory. THE COMPLETENESS OF QUANTUM MECHANICS Although the Heisenberg uncertainty principle (Section 20.4) and the lack of absolute predictive power are an inherent feature of quantum mechanics, there have been attempts to preserve an in principle completely deterministic structure for physics. Even classically, in a macroscopic sample of gas there are so many molecules that it would be hopeless, as a practical matter, to predict the future locations of all these molecules from Newton's laws of motion.
This chapter introduces two approaches to quantum mechanics, one is to follow the historical development of the theory from the first indications that the whole fabric of classical mechanics and electrodynamics should be held in doubt to the resolution of the problem. The other approach is to stand back at a point late in the development of the theory and see its underlying theoretical structure. The chapter shows that in the first approach the theory is seen gradually emerging from confusion and dilemma, while the second is a more formal approach that can still be exciting and compelling in a different sense. The chapter highlights the logic and elegance in a scheme that starts from only a few postulates, yet reveals a rich, experimentally verifiable structure. It traces some of the most fundamental concepts of the nature of matter and its behaviour that were overthrown and replaced by a puzzling but powerful new description.