I hope to have successfully argued that my proposal of a dispositional trope theory is particularly appropriate as an ontology of QFT. I have pointed out that a dispositional trope ontology suggests itself when looking at that formulation which is most significant in an ontological sense, namely AQFT.
Besides the immediate naturalness of a trope-ontological understanding of QFT in its algebraic formulation, two specific ontological problems could be solved. Both of these problems have the same structure: Although one should like to see a many-particle system as just one object or substance and although one would in general like to ascribe an unsharp localization to particles both manoeuvres are impossible as I have argued. I could show that the situation changes on a trope-ontological background. Now both wishes can be fulfilled due to a change in the ontological attitude.
A more detailed account of how dispositional trope ontology can fos-ter a more natural understanding of QFT will be given in the following conclusion to the whole thesis.
Part VI Conclusion
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Chapter 11
The Interplay of Physics and Philosophy
I begin my conclusion with some remarks on the relation of physics and philosophy when ontological questions are under consideration. If only a fraction of my investigations have been convincing they should yield ample evidence for the theses I will lay out in this chapter. In short, I claim that neither philosophy alone nor physics alone are in a position to paint a coherent picture of the general structure of the physical world that takes all relevant knowledge into account which is available today. Note, however, that this claim is not meant to imply that physics and philosophy could not be pursued without taking notice of each other. All I want to argue for is that getting a comprehensive idea of the physical world on an up-to-date level of discoveries necessitates a cooperation between physics and philosophy.
Investigating the most general structures of what there is in the world two extreme ways can be chosen and often are chosen. One of them is deeply rooted in the tradition of philosophy from ancient and medieval times to modern rationalism and idealism until the twentieth century. Pro-ponents of this way foster the idea that the structures of being qua being can be investigated by pure thinking in an a priori fashion. Some take a more modest stance and concede the necessity for at least some intuition or everyday experience. Nevertheless, defenders of the (quasi-) a priori
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dition of ontology imagine their results to be immune against any specific scientific results.
Opposed to this first way of investigating the most general structures of being is a second one. Proponents of this second way to ontology claim that only specific sciences, in particular natural sciences, are in the posi-tion to say anything about the basic entities there are and their irreducible characteristics. They contend that purely philosophical considerations on ontology are fruitlessly speculative and ill-founded and have no value in the light of ‘real scientific findings’. This pejorative stance towards ontol-ogy as a philosophical discipline has found emphatic support within some philosophical schools as well. Most notable are the British Empiricists in the seventeenth and eighteenth century and the Logical Positivists in the twentieth century.
I believe that there is some truth to be found in both ways but that they can profit from each other and even need each other eventually. Using a similar statement by Kant I think that with respect to ontological questions
‘philosophy without sciences is empty and science without philosophy is blind’. I will try to give explanations for both sides of this claim.
Why does philosophy depend on sciences when ontological matters are treated? I think that philosophy can get substantial results about our everyday ontological thinking and can uncover some hidden assumptions of our way to conceive of the world. However, when it comes to more fundamental questions about the ontological structure of the world apart from our possibly changing ways to think about it in everyday terms, it seems to me that philosophy alone comes to an end. All philosophy can do here, I believe, is to lay out a matrix of ontological options. In some cases it will be possible to exclude some of these options for internal reasons. In general, however, things are not so easy. I have the impression that most ontological conceptions have their merits with respect to those aspects which gave rise to their establishment while they have their weak points in other respects. In a situation where each conception has its successes but carries the burden of anomalies or unsolved problems as well an evaluation of different aspects becomes pivotal.
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How can physics profit from philosophical considerations about ontol-ogy? Probably the most important benefit for the physicist is not one that would help with his work. Nevertheless, I think ontological considerations can be helpful as heuristics when a theory is not completed yet as in the case of QFT due to the so far unsuccessful incorporation of gravitation.
Chapter 12
Evaluation and Comparison
12.1 General Remarks
The investigation in this thesis can be devided into two main parts. The first part consists of general ontological considerations and their founda-tions in philosophy as well as quantum physics. The second part contains investigations of some either important or promising ontological approaches to QFT. The considered approaches have emerged partly in physics and partly in philosophy. Likewise, the arguments for their evaluation came in some cases from philosophy and in other cases from physics.
Philosophical investigations about QFT form a relatively new area of philosophical research compared to similar studies in the philosophy of science and of course even more so with respect to general philosophy.
Nevertheless, philosophical questions about QFT do have a tradition both in regard to methods and contents. As I have laid out in chapter 1 this two-fold anchorage in tradition applies to the history of general philosophy as well as to modern philosophy of science.
With respect to the history of general philosophy the most prominent forerunner to questions about the ontology of QFT happens to be the same regarding methods and contents, namely the history of atomism. As regards contents the debate about atomism is the historical forerunner of ontological considerations about QFT since the atomistic point of view
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CHAPTER 12. EVALUATION AND COMPARISON 149 rests on the assumption that all natural phenomena can be reduced to a set of basic indivisible building blocks, namely the atoms. (Note that what we denote as atoms today are of course no candidates for the atoms of atomism.) The same program of reduction has always been at the core of QFT and naturally this holds for attempts of ontological analyses of QFT as well. As we saw in chapters 9 and 10 on trope ontology ‘reduction to a set of basic entities’ must be understood in a very wide sense since some revisionary ontologies like trope ontology strain the limits of this notion of reduction. Nevertheless, I rate trope ontology to be within the limits of the reduction program.
As regards methods the development of atomism can be seen as a fore-runner of ontological investigations about QFT for one general and one more specific reason. The general reason is that the development of atom-ism displays an interplay of physics and philosophy (to the extent that one can speak of two separate disciplines at all) which has gotten closer over its history. I have pointed out in chapter 1 that from ancient times to the middle ages the focus shifted from atomistic speculations as an aim in itself to the search of pragmatic explanations of natural phenomena on the basis of atomistic theories. The more specific reason why the debate about atomism is a methodological forerunner of the ontological analysis of QFT is that in both cases, atomism and QFT, the program of reduction to a set of basic building blocks was a very fruitful heuristic. It is one of the spec-tacular successes of QFT to correctly predict the existence of previously unknown particles on the basis of systematical reduction schemes.
In my main study three general kinds of arguments (which can be either positive or negative) occured. The first kind of arguments are primarily philosophical. They refer to questions of consistency, simplicity, scope etc. The second kind of arguments are those which are mainly grounded in physical requirements, such as relativistic covariance or independence from the frame of reference. It turned out, however, that a third kind of arguments is predominant in the ontological analysis of QFT. These are arguments which cannot be construed as having separable philosophical and physical components. In these cases a physical argument can radically
CHAPTER 12. EVALUATION AND COMPARISON 150 change its significance when different ontological approaches are considered.
Arguments concerning non-localizability and unsharp properties are among the most important examples.