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1. Prospects for a Philosophy of Nature

In the Twentieth Century, despite the advances of modern science, we are no longer sure what the world is made of. We are confident that it is made out of parts of various kinds, but it has become mysterious what these parts are made of.

  If we ask the question, `what is it to be a substance?', we might first turn to scientists for an answer, to physicists in particular. A physicist will explain how all kinds of ordinary matter are composed of small atoms, which are composed of electrons, protons, and neutrons.   Protons and neutrons are again composed of quarks, he says he believes, but when pressed as to what really are electrons and quarks, he says that he can tell you how they behave, but that he doesn't really know what they are. If he is feeling unkind, he might say `that is a meaningless question', otherwise he will say that the electrons and quarks seem to be some kind of `ultimate particles' whose existence and behaviour you just have to take on trust. `You have to start somewhere', he might add.

  But when we asked the initial question, `what is it to be a substance?', in a sense we were going straight to the question of these `ultimate particles'. We want to know what the world is really made of, and what are the ultimate individuals in the physical world.   We have a feeling that we can't go on looking for smaller and smaller constituents ad infinitum. The process of subdivision should ultimately come to a stop with the `real individuals' that are the real substances of the world. We don't know for certain if physics has yet reached the stage of looking at these ultimate substances. Of course, physicists almost always believe they have come to that stage, but that might just be because they haven't yet done the right kind of experiment.

  This means that if we want to know what these ultimate substances might be like, we have to turn to philosophy rather than to physics. We will then have to be satisfied with general principles rather than particular knowledge, because philosophers can only argue from general considerations about what is possible, and do not provide detailed knowledge about what actually occurs in particular circumstances. You may think that consideration of `mere possibilities' will not be fruitful, but you would be forgetting that every scientific theory presupposes some general framework about what is possible. Different scientific theories go along with different philosophical frameworks about what our ultimate substances might be like. The physical theories of the Greeks, of Newton and of modern quantum physics assume different philosophical ideas about substances, and these ideas are not compatible with each other. They cannot all be correct! My purpose in this book is to illuminate these different basic ideas, and to see whether there is one set of ideas which recommend themselves as reasonable, and which can help us understand the world and its peculiarities as revealed by quantum physics.

Accommodating Quantum Physics

  It is largely because of the difficulties in understanding modern quantum physics that many people have realised to need to re-examine the foundations of physics. As a result of quantum mechanics, questions have been continually raised concerning some of the deepest questions in philosophy, such as whether the world exists independently of our observations or of our minds, whether physical substances exist and/or have any definite properties, whether these properties (should they exist) are in any way knowable, and whether indeed anything could be said to have definitely happened to the exclusion of its alternatives. Many, in a kind of agnosticism, have despaired of positive answers to these questions ever being found1.1, and others have turned to philosophies where it is accepted that `objective reality' is altogether an ephemeral by-product, or an illusion of some kind1.2.

When, therefore, we do reconsider foundations, we are almost overwhelmed by the enormous range of physical theories and natural worlds that are logically possible.       Reece [1973], Jammer [1974] and Herbert [1985] survey some (but not all!) of this range. Rather than being lost in the maze of science-fiction-like realms, a better approach would be to think more carefully about the collection of general ideas which we bring to bear when we look at nature. Traditionally, these have been the four ``ultimate'' concepts used to characterise nature: matter, motion, time and space.   Leibniz was the first to point out the inadequacies in these four ``ultimates'', and how the first (`matter') was not essentially related to the other three. (We will be looking in more detail at these notions of classical physics in chapter 3.) His was merely the beginning of a long line of critiques of the ideas of physics, pointing out that the basic concepts of many theories are not properly consistent with each other. It is of course possible to argue `that even the ideals of clarity and consistency can be legitimately compromised in order to obtain other advantages'   (Edwards [1985]), but this can at best be only a temporary manoeuvre. It is only after careful consideration of the ultimate concepts we use, and the finding of a consistent set, that we can have any confidence in them as realistic descriptions of nature.

The kind of discussions here can best be called the philosophy of nature. This term is not in popular use, but it is needed in order to distinguish our endeavours from the philosophy of science, and from the philosophy of knowledge.         In the philosophy of nature we are going to consider ontological problems directly, and not let them be obscured by questions of methodology and epistemology. That is, we are going to pose and answer questions about what exists, and not be side-tracked into questions of `how can we be sure of that?', or of `how should we discover what exists in this test-tube?'. In doing this, we want to take a realistic view of our theories, at least, that is, when they have been considered carefully and found consistent and adequate. We are not taking a merely `instrumentalist' view of theories, whereby their only use is to enable correct predictions. Nor are we taking a merely `phenomenological' view of theories, whereby their only use is to describe our observations and experimental results as does a map. Of course, if a theory is realistic and correct, it will enable both correct predictions and accurate descriptions: these tasks are non-trivial and are still important!

We may picture our theories as maps of reality. If our maps of reality were comprehensive and consistent with each other, there would be little demand for further investigations in the philosophy of nature. The problem, in modern times, is precisely that our maps are fragmented, confused, and often appear to contradict each other. Physicists survive in this situation by marking various regions with large `Keep Out' signs, and learning to choose which of their opposing maps should be used in the various stages of their travels.   Richard Feynman [1967], for example, writes

I think it is safe to say that no one understands quantum mechanics. $\ldots$ Do not keep saying to yourself, if you can possibly avoid it, `But how can it be like that?' because you will get `down the drain' into a blind alley from which nobody has yet escaped. Nobody knows how it can be like that.
These practices and warnings seem more akin, however, to that of the medieval cartographers when they wrote `here be dragons'. Feynman may well have a point about the difficulties and dangers in trying to answer the question `What can the world be like such that quantum mechanics can be true of it?', but what we need therefore are suitable new instruments of analysis which are precise and versatile. We will need to extend many of our common sense ideas beyond their original scope, while at the same time always considering carefully exactly how they can still be applied.


The Philosophy of Nature

The method adopted in this book is explicitly hypothetical and deductive, rather than being an analysis either of our phenomenal experiences, or of contemporary scientific theories. I will hypothesise the existence of various things (`actual particulars' and `propensity fields', as they will be called), and then the consequences of these will be drawn out in a deductive fashion. In any hypothesising, however, I do not proceed randomly.   Both the direction and aims of much of this book are strongly influenced by Ivor Leclerc's excellent investigations (Leclerc [1972], [1986]) of the many past accounts in the philosophy of nature that have been put forward in the history of Western philosophy. He has been useful in providing critical reassessments of the fundamental issues involved in our realistic understanding of the nature of the physical world. His historical perspectives are as valuable as his re-examination of the root problems which have recurred almost unfailingly through the history of the philosophy of nature. The most common problems are those of clarifying, distinguishing and then relating the categories of
  • actual vs. potential vs. possible,
  • infinite vs. finite,
  • continuity vs. discreteness,
  • becoming vs. being,
  • substance vs. form vs. act, and
  • simple vs. compound.
It is from suggestions in his work that I derived my initial hypotheses concerning actualities and potentialities. What I am now trying to do is to present these concepts and their relations in a coherent whole. I will be analysing in more detail the categories of actuality and potentiality, and hope to flesh out the resulting categorical framework so that it has consequences of any detailed science of nature.

    The category of dispositions and potentialities is the single most important category that must be considered anew. Science has always had a kind of love-hate relation with properties in this category, accepting their necessity and usefulness, but refusing to live happily with them.   In general, it is modal properties of all kinds that cause problems. These properties deal with what might happen, and, despite their apparent remoteness and seeming unreality, we will see in the next few chapters that they have an essential role in all kinds of scientific investigations. Although various ideas of potentialities and propensities have been proposed to help solve difficulties in physics, they have been criticised as being too vague.   Hooker1.3, for example, remarks that this ``approach to quantum theory must inevitably prove less than satisfying. Any theory whatever, so far as I can see, could have its problems `solved' by this approach   -- simply because the concept of an `actualisation' of a `potential' is so vague and intrinsically not open to direct investigation of its structure.'' My aim in this book is therefore to see how potentialities etc. can be understood sufficiently precisely, and then how potentialities and dispositions can be fitted into a broad realistic view of the world.

It may be objected that I really seem to be doing speculative physics all along (or, that if not, I ought to be), but that would be to misunderstand the relation between science and the philosophy of nature. It has been remarked that quantum physics is not itself a physical theory, since it does not specify any particular laws for potentials: rather, it is a methodological and mathematical framework in which one can formulate physical theories. Similarly, the philosophy of nature is not itself a scientific theory (either methodologically or mathematically), but rather a framework in which quantum theories can be formulated and interpreted realistically. The task of the philosophy of nature is to provide a general scheme for what can reasonably be said both to exist and to be subject to change. Quantum theories then select some specific scheme, with particular laws of change in specific kinds of spaces.

As a consequence of quantum physics it has often been said that we have to give up any hope of a pictorial, literal or realistic description of what goes on in the micro-world of atomic phenomena. We seem at best to have only metaphorical and/or mathematical descriptions, without any clear idea of the reality to which they refer. Sometimes we are told1.4 that certain ideas (e.g. those of classical physics), while necessary for all our knowledge, are in fact false. At other times, it is contended that ``quantum physics conflicts with the ontological form of thought''1.5.   I will be arguing, instead, that the lack of literal and realistic ideas betrays more a lack of imagination than a lack in reality. It ought to be possible to interpret some ideas realistically, as being unequivocally and literally true -- once (of course) we have ideas which are good enough. We ought to be able to find ideas that we can interpret literally, and not be forced forever to resort to ideas based merely on mathematical formalisms or metaphors.

One important aim is to formulate a description of the world of relativity and quantum physics that is independent of classical physics,   so that we can bypass some of the unwanted legacies which have accumulated from the theories of material corpuscles. The task of this book is to produce a formulation in sufficient detail that an understanding of quantum physics begins to be possible. Even though the present investigations will not produce a complete physical theory, I hope to show that they are still valuable in providing some general ideas which are reasonable, which can be realistically interpreted, and which contribute in some part to our understanding of the world we live in and its quantum peculiarities.  

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Prof Ian Thompson


Author: I.J. Thompson (except as stated)