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Cambridge University Press eBooks

On the ontology of QFT

Fritz Rohrlich

Published Feb 18, 1999• 9 citations
Publisher

Abstract

Philosophical introduction The following seemingly trivial story raises important questions which lead to the philosophical issues essential for our discussion. My cat is alive and well. I can describe her by size, color, behavior, etc. I can watch her, touch her, play with her, and feed her. I know this animal is really there. But my biologist friend came to visit and informed me that my cat is really nothing but a very complicated collection of different kinds of cells in mutual interaction, and he can prove it to me by having me look through his microscope, and, if I would only let him, by dissecting my cat. But the biochemist next door has a quite different opinion: he claims that my cat is really just a very complex assemblage of organic compounds, proteins, nucleic acids, etc., etc., all in mutual interaction. He, too, can prove his claim. Of course, physicists know better: a cat, like all matter living or dead, is in last analysis really nothing but atoms bonded together to form the complicated molecules my biochemist friend is talking about. And they can prove that too. But, finally, one cannot ignore the elementary particle people who tell us that atoms are just composed of quarks, gluons, and electrons, so that a cat is really, really just a very complicated assembly of those few types of elementary particles in mutual interaction.

DOI
10.1017/cbo9780511470813.029

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Comments

S. B. Treiman

This commentator format is quite unfamiliar to me, and somewhat uncomfortable. I don't know whether I'm supposed to flatter the speakers, criticize them, grade them, or merely parrot them. Or should I go off on my own? This latter is tempting. If unleashed I could provide you with true answers to all the questions before us, philosophical, historical, physical, mathematical, physical-mathematical, and so on. But I'll bite my tongue and try to stick to the commentator role. First, a few words on the topic of the opening session this afternoon - why are philosophers interested in quantum field theory? Quantum mechanics undoubtedly abounds in genuine, deep and still unresolved philosophical questions. These are usually posed, at least in popular accounts, in the context of finite systems of nonrelativistic point particles. In preparation for the conference, I asked myself: does relativistic QFT introduce any really distinctive philosophical problems? There are several possibilities, which I can only express in low-brow form. For one thing, a field is really a collection of infinitely many degrees of freedom, one for each point in space. I can well suppose that infinity raises interesting questions for philosophers. Certainly for physicists, especially in the field theory context, it has been a great preoccupation. As we'll hear later from Jackiw, infinity has its useful aspects. Next, for systems of relativistic particles in interaction, it is no longer so easily possible to speak of measurements of position and momentum of individual particles, except perhaps in asymptotic regions.

Cambridge University Press eBooks•Feb 18, 1999•0 citations

A philosopher looks at quantum mechanics

Hilary Putnam

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).

Cambridge University Press eBooks•Apr 30, 1979•60 citations

Nonseparability and Quantum Logic

Bernard d’Espagnat

This talk is about quantum logic, and before we engage in the subject proper let me say how much I appreciate the invitation to deliver it that was extended to me by the Japanese Society for the Philosophy of Science.In particular because I feel that such a meeting is really the place that is most adequate for the discussion of these matters.Let us introduce the subject by mentioning a few general points.First of all, logics deals with propositions.Hence we shall be concerned with propositions.But in fact our interest will be exclusively focused on what is-or what should be the simplest type of propositions: the propositions by means of which a physicist expresses what he knows about a physical system.A priori, our subject should then be very simple.Indeed the elementary books about logic tell us that the rules concerning these propositions can be formalized.That, for example, the propositions can be combined by means of two rules, corresponding to and and to or, and that the resulting structure is just that of a Boolean Algebra.We would expect this to hold for any system.However, as you know, a major difficulty already creeps in at this point when we want to deal with atomic systems.This is because a very simple word such as "and" may well have no obvious meaning in that case.And when we try to force a meaning to it was sometimes encounter quite unpleasant surprises, exemplified by the Heisenberg relations.Among the founders of quantum physics the reactions to such a fact were quite varied as is well known.Some of them sort of hoped that the difficulty just came from our using the wrong concepts.For example, it is quite obvious that if we try to describe as a particle something which is really a wave, we are heading for trouble and we are bound to formulate some meaningless propositions.However, this remark did not lead to a satisfactory solution in the end.Other physicists notably the Copenhagen group took a very different standpoint.Substantially, what they said boiled to this: since we cannot "see" the elementary particles, let us refrain from formulating directly propositions bearing on them.Ultimately, there fore, all their propositions bear on the instruments; or should be interpreted in terms of such propositions.This is -it turned out a very good recipe.Of course, propositions bearing on instruments are propositions of classical, macroscopic physcis.As such, they fall -57-

Annals of the Japan Association for Philosophy of Science•Jan 1, 1977•0 citations

What are Quanta, and Why Does it Matter?

Nick Huggett

There is an emerging story about many particle quantum mechanics (MPQM) and quantum field theory (QFT) based partly on views inherited from physics, and partly on new work, especially that of Paul Teller and Michael Redhead. Three important steps in the tale go like this—(a) The transition from classical mechanics (CM) to quantum mechanics (QM) involves a significant change in particle metaphysics, (b) QFT cannot be viewed as particulate even in a MPQM sense, although (c) an ontologically enlightening understanding of QFT can be obtained from the occupation representation. Though there is some truth to all of these claims, I wish to argue that, as usually understood, they are in fact false. The ever present danger in metaphysical debates such as these is that participants will be running around on the same pitch but playing different games; some waving cricket bats at the ball, some aiming for a netball hoop and others trying for a touch-down.

PSA Proceedings of the Biennial Meeting of the Philosophy of Science Association•Jan 1, 1994•34 citations

Ontological Aspects of Quantum Field Theory

Meinard Kuhlmann, Holger Lyre, Andrew Wayne

Approaches to Ontology: Candidate General Ontologies for Situating Quantum Field (P Simons) 'Quanta', Tropes, or Processes: Ontologies for QFT Beyond the Myth of Substance (J Seibt) Analytical Ontologists in Action: A Comment on Seibt and Simons (M Kuhlmann) How Do Field Theories Refer to Entities in a Field? (S Y Auyang) Field Ontologies for QFT: A Naive View of the Quantum Field (A Wayne) Comments on Paul Teller's Book, An Interpretive Introduction to Quantum Field Theory (G Fleming) So What Is the Quantum Field? (P Teller) Relativity, Measurement and Renormalization: On the Nature of Measurement Records in Relativistic Quantum Field (J A Barrett) No Place for Particles in Relativistic Quantum Theories? (H Halvorson & R Clifton) Events and Covariance in the Interpretation of Quantum Field (D Dieks) Measurement and Ontology: What Kind of Evidence Can We Have for Quantum Fields? (B Falkenburg) Renormalization and the Disunity of Science (N Huggett) Gauge Symmetries and the Vacuum: The Interpretation of Gauge Symmetry (M Redhead) Comment on Redhead: The Interpretation of Gauge Symmetry (M Drieschner et al.) Is the Zero-Point Energy Real? (S Saunders) Two Comments on the Vacuum in Algebraic Quantum Field (M Redei).

WORLD SCIENTIFIC eBooks•Nov 1, 2002•112 citations

From Particle-in-a-Box Thought Experiment to a Complete Quantum Theory?

Jixin Chen

Einstein: God does not play dice and nothing travels faster than the speed of light. Schrödinger: My cat cannot be both dead and alive. Dirac: The existing quantum theory should not be considered to be the final solution. Feynman: How does it work? de Broglie: My matter wave has an imaginary part. Me: Great! This could be the missing piece the others have been looking for.

•Jul 26, 2023•1 citation
Philosophical introduction The following seemingly trivial story raises important questions which lead to the philosophical issues essential for our discussion. My cat is alive and well. I can describe her by size, color, behavior, etc. I can watch her, touch her, play with her, and feed her. I know this animal is really there. But my biologist friend came to visit and informed me that my cat is really nothing but a very complicated collection of different kinds of cells in mutual interaction, and he can prove it to me by having me look through his microscope, and, if I would only let him, by dissecting my cat. But the biochemist next door has a quite different opinion: he claims that my cat is really just a very complex assemblage of organic compounds, proteins, nucleic acids, etc., etc., all in mutual interaction. He, too, can prove his claim. Of course, physicists know better: a cat, like all matter living or dead, is in last analysis really nothing but atoms bonded together to form the complicated molecules my biochemist friend is talking about. And they can prove that too. But, finally, one cannot ignore the elementary particle people who tell us that atoms are just composed of quarks, gluons, and electrons, so that a cat is really, really just a very complicated assembly of those few types of elementary particles in mutual interaction.
This commentator format is quite unfamiliar to me, and somewhat uncomfortable. I don't know whether I'm supposed to flatter the speakers, criticize them, grade them, or merely parrot them. Or should I go off on my own? This latter is tempting. If unleashed I could provide you with true answers to all the questions before us, philosophical, historical, physical, mathematical, physical-mathematical, and so on. But I'll bite my tongue and try to stick to the commentator role. First, a few words on the topic of the opening session this afternoon - why are philosophers interested in quantum field theory? Quantum mechanics undoubtedly abounds in genuine, deep and still unresolved philosophical questions. These are usually posed, at least in popular accounts, in the context of finite systems of nonrelativistic point particles. In preparation for the conference, I asked myself: does relativistic QFT introduce any really distinctive philosophical problems? There are several possibilities, which I can only express in low-brow form. For one thing, a field is really a collection of infinitely many degrees of freedom, one for each point in space. I can well suppose that infinity raises interesting questions for philosophers. Certainly for physicists, especially in the field theory context, it has been a great preoccupation. As we'll hear later from Jackiw, infinity has its useful aspects. Next, for systems of relativistic particles in interaction, it is no longer so easily possible to speak of measurements of position and momentum of individual particles, except perhaps in asymptotic regions.
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).
This talk is about quantum logic, and before we engage in the subject proper let me say how much I appreciate the invitation to deliver it that was extended to me by the Japanese Society for the Philosophy of Science.In particular because I feel that such a meeting is really the place that is most adequate for the discussion of these matters.Let us introduce the subject by mentioning a few general points.First of all, logics deals with propositions.Hence we shall be concerned with propositions.But in fact our interest will be exclusively focused on what is-or what should be the simplest type of propositions: the propositions by means of which a physicist expresses what he knows about a physical system.A priori, our subject should then be very simple.Indeed the elementary books about logic tell us that the rules concerning these propositions can be formalized.That, for example, the propositions can be combined by means of two rules, corresponding to and and to or, and that the resulting structure is just that of a Boolean Algebra.We would expect this to hold for any system.However, as you know, a major difficulty already creeps in at this point when we want to deal with atomic systems.This is because a very simple word such as "and" may well have no obvious meaning in that case.And when we try to force a meaning to it was sometimes encounter quite unpleasant surprises, exemplified by the Heisenberg relations.Among the founders of quantum physics the reactions to such a fact were quite varied as is well known.Some of them sort of hoped that the difficulty just came from our using the wrong concepts.For example, it is quite obvious that if we try to describe as a particle something which is really a wave, we are heading for trouble and we are bound to formulate some meaningless propositions.However, this remark did not lead to a satisfactory solution in the end.Other physicists notably the Copenhagen group took a very different standpoint.Substantially, what they said boiled to this: since we cannot "see" the elementary particles, let us refrain from formulating directly propositions bearing on them.Ultimately, there fore, all their propositions bear on the instruments; or should be interpreted in terms of such propositions.This is -it turned out a very good recipe.Of course, propositions bearing on instruments are propositions of classical, macroscopic physcis.As such, they fall -57-
There is an emerging story about many particle quantum mechanics (MPQM) and quantum field theory (QFT) based partly on views inherited from physics, and partly on new work, especially that of Paul Teller and Michael Redhead. Three important steps in the tale go like this—(a) The transition from classical mechanics (CM) to quantum mechanics (QM) involves a significant change in particle metaphysics, (b) QFT cannot be viewed as particulate even in a MPQM sense, although (c) an ontologically enlightening understanding of QFT can be obtained from the occupation representation. Though there is some truth to all of these claims, I wish to argue that, as usually understood, they are in fact false. The ever present danger in metaphysical debates such as these is that participants will be running around on the same pitch but playing different games; some waving cricket bats at the ball, some aiming for a netball hoop and others trying for a touch-down.
Approaches to Ontology: Candidate General Ontologies for Situating Quantum Field (P Simons) 'Quanta', Tropes, or Processes: Ontologies for QFT Beyond the Myth of Substance (J Seibt) Analytical Ontologists in Action: A Comment on Seibt and Simons (M Kuhlmann) How Do Field Theories Refer to Entities in a Field? (S Y Auyang) Field Ontologies for QFT: A Naive View of the Quantum Field (A Wayne) Comments on Paul Teller's Book, An Interpretive Introduction to Quantum Field Theory (G Fleming) So What Is the Quantum Field? (P Teller) Relativity, Measurement and Renormalization: On the Nature of Measurement Records in Relativistic Quantum Field (J A Barrett) No Place for Particles in Relativistic Quantum Theories? (H Halvorson & R Clifton) Events and Covariance in the Interpretation of Quantum Field (D Dieks) Measurement and Ontology: What Kind of Evidence Can We Have for Quantum Fields? (B Falkenburg) Renormalization and the Disunity of Science (N Huggett) Gauge Symmetries and the Vacuum: The Interpretation of Gauge Symmetry (M Redhead) Comment on Redhead: The Interpretation of Gauge Symmetry (M Drieschner et al.) Is the Zero-Point Energy Real? (S Saunders) Two Comments on the Vacuum in Algebraic Quantum Field (M Redei).