Abstract Quantum field theory (QFT) is the union of quantum mechanics and Einstein’ s special theory of relativity. QFT is the most fundamental physical theory and provides the answers to questions about the basic structure of the physical world. However, the way QFT describes the world is so different from the way our senses present it to us that it requires an overhaul of philosophic categories and arguments. How can we know the microscopic world without a satisfactory measurement theory? What are the general conditions of the world that make possible such knowledge? What are the presuppositions of physical theories? Dr.Auyang argues that the current relational substantial debate on space-time is inadequate and the observer-observed distinction in quantum interpretations illusory because they are hampered by philosophical constructs too narrow to accommodate the complicated structures of modern philosophical theories. Modern physical theories have incorporated many presuppositions of empirical knowledge, and consequently the theories inform us about the general nature of the world and out relation to it, in addition to information about elementary particles. The conceptual structure of QFT is extracted and articulated in commonsense terms, and used to answer many longstanding philosophical questions.
Abstract Quantum field theory (QFT) is the union of quantum mechanics and Einstein’ s special theory of relativity. QFT is the most fundamental physical theory and provides the answers to questions about the basic structure of the physical world. However, the way QFT describes the world is so different from the way our senses present it to us that it requires an overhaul of philosophic categories and arguments. How can we know the microscopic world without a satisfactory measurement theory? What are the general conditions of the world that make possible such knowledge? What are the presuppositions of physical theories? Dr.Auyang argues that the current relational substantial debate on space-time is inadequate and the observer-observed distinction in quantum interpretations illusory because they are hampered by philosophical constructs too narrow to accommodate the complicated structures of modern philosophical theories. Modern physical theories have incorporated many presuppositions of empirical knowledge, and consequently the theories inform us about the general nature of the world and out relation to it, in addition to information about elementary particles. The conceptual structure of QFT is extracted and articulated in commonsense terms, and used to answer many longstanding philosophical questions.
Quantum field theory (QFT) can be analyzed in terms of its mathematical structure, its conceptual system for physical descriptions, or its basic ontology. The analysis can be done logically or historically. In this chapter, only the genesis of the conceptual foundations of QFT relevant to its basic ontology will be treated; no discussion of its mathematical structures or its epistemological underpinnings will be given. Some conceptual problems, such as those related to probability and measurement, will be discussed, but only because of their relevance to the basic ontology of QFT, rather than their intrinsic philosophical interest. Here, by basic ontology I mean the irreducible entities that QFT is invented to describe. The often mentioned candidates for the basic ontology of QFT, in fact of the physical world, are the discrete particle and the continuous field. Another possible candidate (the spacetime point) has also been suggested recently (Redhead, 1983). Since the aim of this chapter is to analyze the historical process in which the conceptual foundations of QFT were laid down, rather than the logical structure of QFT which philosophers of the present day treat, no discussion of the last possibility will be given. The content of this chapter involves the formation and interpretation, in a roughly chronological order, of the concepts of the wave function, quantization, quantization of the field, the vacuum, interactions between fields, and renormalization. The first two topics will be discussed in relation to the quantization of the field, with their role being taken as the starting point of the conceptual development of QFT.
This two-tier conference signals a new phase of philosophers' interest in quantum field theory, which has been growing noticeably in the last few years. However, some prominent physicists have shown their deep suspicions against ignorant philosophers' intrusion into their profession, and have expressed their hostility quite openly. In the philosophy community, some prominent philosophers of physics have also expressed their suspicions against the rationale of moving away from the profound foundational problems raised by Einstein and Bohr, Bohm and Bell, such as those concerning the nature of space-time and measurement, possibility and implications of hidden variables and nonlocality, and stepping into the technical complexity of quantum field theory, which is only an application of quantum mechanics in general without intrinsically distinct philosophical questions to be explored. In order to dispel these suspicions, it is desirable to highlight certain aspects of quantum field theory which require philosophical reflections and deserve further investigations. This discussion intends to suggest that philosophers can learn many important lessons from quantum field theory, and may be of some help in clarifying its conceptual foundations. At this stage of crisis that quantum field theory is experiencing now, the clarification may contribute to the radical transformation of our basic concepts in theoretical physics, which is necessary for a happy resolution of the crisis and the emergence of a new promising fundamental physical theory. Generally speaking, philosophers are interested in the metaphysical assumptions adopted by science and the world picture suggested by science.
…the quantum theory of fields is the contemporary locus of metaphysical research. (Stein 1970, p. 285) It is now generally recognized that Quantum Field Theory (QFT), after many vicissitudes and a period of almost total neglect, has emerged during the last ten years as a triumphant framework in which to do elementary particle physics. If philosophers are prepared to use current physical theory as a guide to resolving metaphysical questions (and that is a big “If”), then QFT is what philosophers should all be studying. But the subject is notoriously.recondite, and philosophers are busy people, so the objective of the present paper is to cut through all technicalities and try to tell in as straightforward a way as possible just what QFT has to say about “reality”.
Modern scientists describe the universe in terms of two basic partial theories: firstly, the general theory of relativity proposed by Albert Einstein, and secondly, the theory of quantum mechanics. This theory introduces an immense reality and simultaneously creates complex questions for the world of physics. Quantum mechanics is an incompletable knowledge however scientists are finding the basic theories from this theory. They propose complex mathematical expressions from quantum mechanics to prove the basic law of atoms. Quantum mechanics is the entire knowledge of subatomic particles such as electrons, protons, and neutrons. Quantum mechanics reveals that what we see is just a part of a deeper reality. Then we can grasp from this theory that the material world is not the completed reality; there are other things beyond human physical senses. The concept of quantum mechanics describes particles that can exist in multiple states. The concept of quantum mechanics is directly proportional to contemporary world technologies. The super specialty of this theory is that scientists cannot be explained universe without quantum mechanics. The uncertainty principle of Heisenberg in quantum mechanics suggests that there are limits to what we can know about a particle state of an atom. Humans cannot yet find out what it looks like and how we can imagine the existence of subatomic particles in an atom. That was an unseen dynamite for humans' perspective observation of the material world.
Quantum field theory is the ultimate expression of quantum mechanics. Its formalism provides the framework for all modern fundamental theories about the nature of matter. However, it involves difficult and intricate mathematics, which is why physics students don’t generally come across it until postgraduate level, and then only if their subject specialism requires the insights that it provides. In ordinary quantum theory, observable properties are represented by Hermitian operators, with eigenstates that form a basis for the expansion of a system’s states. Philosophers have been debating the correctness of such arguments, but now it seems that experimental science has come along and shown that, at the quantum level at least, the objects we study have no substance to them, independent of their properties. In classical physics, interactions between particles can be considered by either an examination of forces or from the potential energies involved.
In this introductory chapter, which actually is the core of the entire book, we make a serious effort to bring together a variety of ideas from philosophy and physics. We first lay the epistemological foundations for our approach to particle physics. These philosophical foundations, combined with tools borrowed from the amazingly sophisticated, but still not entirely satisfactory, mathematical apparatus of present-day quantum field theory and augmented by some new ideas, are then employed to develop a mathematical representation of fundamental particles and their interactions. In this process, also the relation between “fundamental particle physics” and “quantum field theory” is going to be clarified. This first chapter consists of two voluminous sections: a number of philosophical contemplations followed by a discussion of mathematical and physical elements . The reader might wonder why these massive sections are not presented as two separate chapters. The reason for keeping them together is the desire to emphasize the intimate relation between these two sections: the selection and construction of the mathematical and physical elements is directly based on our philosophical contemplations. The beauty of the entire approach is a fruit of this intimate relationship. The presentation of the material in this chapter is based on the assumption that the reader has a basic working knowledge of linear algebra and quantum mechanics. If that is not the case, the reader might want to consult the equally entertaining and serious introduction Quantum Mechanics: The Theoretical Minimum by Susskind and Friedman [4]. The book Quantum Mechanics and Experience by Albert [5] offers a fascinating introduction with a strong focus on the measurement problem. An almost equation-free discussion of the history and foundations of quantum mechanics can be found in the book Einstein, Bohr and the Quantum Dilemma: From Quantum Theory to Quantum Information by Whitaker [6]. Complex vector spaces, Hilbert space vectors and density matrices for describing states of quantum systems, bosons and fermions, canonical commutation relations, Heisenberg's uncertainty relation, the Schrodinger and Heisenberg pictures for the time evolution of quantum systems, as well as a basic idea of the measurement process are all referred or alluded to in Section 1.1; these basics of quantum mechanics are recapped only very briefly in Section 1.2. The crucial construct of Fock spaces is explained in a loose way in Section 1.1.3 and later elaborated in full detail in Section 1.2.1.