Abstract
A virtual particle is an elementary particle in a quantum field theory that serves to symbolise the interaction of its counterparts, the so called real particles. In the last 20 years, philosophers of physics have put forth several arguments for and against an interpretation of virtual particles as being like ordinary objects in space and time. In this article, I will attempt to systematise the major arguments and argue that no pro-argument is ultimately satisfactory, and that only one contra-argument—that of superposition—is sufficient to deny the realistic interpretation of virtual particles. The secondary aim of this paper is to argue that even the philosophical considerations of virtual particles overestimate their role in that these entities are merely pictorial descriptions of a mathematical approximation method. This description, while helpful, is not necessary to understand particle interactions. In the end, quantum field theory is not the place to explain what actually happens in the very centre of an individual particle interaction.
Zusammenfassung
Unter virtuellen Teilchen versteht man Elementarteilchen einer Quantenfeldtheorie, die die Wechselwirkung ihrer Gegenstücke – den sogenannten reellen Teilchen – symbolisieren sollen. Wissenschaftstheoretiker haben in den vergangenen zwanzig Jahren viele Argumente für und gegen eine realistische Interpretation von virtuellen Teilchen zusammengetragen. Realistische Interpretation meint dabei, daß virtuelle Teilchen so existieren wie gewöhnliche Gegenstände in Raum und Zeit. Mein Anliegen in diesem Aufsatz ist es, die Hauptargumente dieser Debatte zu systematisieren und zu zeigen, daß keines der Argumente für die Existenz virtueller Teilchen überzeugt, und daß nur eines der Gegenargumente – das Superpositionsargument – ausreicht, um die die realistische Interpretation virtueller Teilchen zu widerlegen. Ein zweites Ziel dieses Aufsatzes ist es zu zeigen, daß die philosophischen Erwägungen die Rolle dieser Entitäten überschätzen, da sie eher einer bildhafte Beschreibungen einer mathematischen Näherungsmethode entnommen sind. Diese Beschreibung ist bei aller Anschaulichkeit nicht notwendig, um Teilchenwechselwirkungen zu berechnen und physikalisch zu verstehen. Am Ende sind Quantenfeldtheorien nicht der Ort, an dem aufgeklärt wird und werden kann, was tatsächlich bei einer einzelnen Teilchenwechselwirkung geschieht.
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Notes
One exception may be Bjorken and Drell 1965, chapter 17 on perturbation theory. It leads us to Feynman diagrams, but without any mentioning and investigation of virtual particles.
The author is indebted to Henning Schröder (University of Rostock), Ewald Reya (University of Dortmund), and Gerhard Ecker (University of Vienna) for indispensable discussions as well as to Paul Tellers Interpretive Introduction to Quantum Field Theory (Princeton, 1995).
The reader may forgive the author for not displaying in an example some steps from the Lagrangian to the perturbation expansions and then to correlating graphical elements of Feynman diagrams. This is done in Bjorken and Drell’s Relativistic Quantum Fields, pp. 74 ff. (New York, 1965). For the purpose of this paper it would be to much to explain why the intermediate steps are mathematically necessary, but philosophically negligible.
Although I will return to virtual particles in the third section, with respect to the argument of this essay the above elementary description will suffice.
Eidelman et al. 2004 (the main publication of the particle data group).
See, e.g., Worrall (1994).
Halzen and Martin 1984, p. 8.
Nachtmann 1990, p. 99.
Frauenfelder and Henley 1975, p. 16f.
Feynman and Henley 1965.
Redhead 1988, p. 9.
Weingard 1988, 45f.
Redhead 1988, p. 20.
See the literature on the measurement of the anomalous magnetic moment given above.
See the quotations above.
Stöckler (1990), 130 f., my translation.
Cao (1997), p. 23 (footnote 10), p. 204.
ibid., p. 204.
Still it is worth being astonished about all that, but does not lead to any arguments against the reality of EPR-correlation, state-superpositions, and so on.
Harré 1988, p. 68.
ibid., p. 66.
Weingard 1988, p. 45.
Bunge (1970).
ibid., p. 508.
Weingard 1988, p. 44f.
Teller 1995, p. 138.
Röhl 2005, p. 474, my translation. The original statement contains a footnote about the source of the transfer theory of causality.
See Itzykson and Zuber 1980, pp. 138–142. Both the Casimir-effect and the Lamb-shift are given as examples without “particle interpretation” (p. 138).
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Fox, T. Haunted by the Spectre of Virtual Particles: A Philosophical Reconsideration. J Gen Philos Sci 39, 35–51 (2008). https://doi.org/10.1007/s10838-008-9066-9
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DOI: https://doi.org/10.1007/s10838-008-9066-9