Are Virtual Particles Less Real?

Gregg Jaeger

doi:10.3390/e21020141

Abstract

The question of whether virtual quantum particles exist is considered here in light of previous critical analysis and under the assumption that there are particles in the world as described by quantum field theory. The relationship of the classification of particles to quantum-field-theoretic calculations and the diagrammatic aids that are often used in them is clarified. It is pointed out that the distinction between virtual particles and others and, therefore, judgments regarding their reality have been made on basis of these methods rather than on their physical characteristics. As such, it has obscured the question of their existence. It is here argued that the most influential arguments against the existence of virtual particles but not other particles fail because they either are arguments against the existence of particles in general rather than virtual particles per se, or are dependent on the imposition of classical intuitions on quantum systems, or are simply beside the point. Several reasons are then provided for considering virtual particles real, such as their descriptive, explanatory, and predictive value, and a clearer characterization of virtuality—one in terms of intermediate states—that also applies beyond perturbation theory is provided. It is also pointed out that in the role of force mediators, they serve to preclude action-at-a-distance between interacting particles. For these reasons, it is concluded that virtual particles are as real as other quantum particles.

Highlights

The notion of the virtual particle arises in the context of relativistic quantum field theory where elementary particles are considered quanta associated with fields characterized via appropriateHamiltonian or Lagrangian functions
One strong support for IV is that the consideration of quanta as virtual is due to the choice of diagrammatics and mathematical analyses applied to the situations considered, as noted in Section 2, rather than the properties of the particles themselves understood as aspects of the field having the same fundamental characteristics as non-virtual particles and differing from them primarily by not being detected as free
The question of whether virtual particles exist, like other particles in a world described by quantum field theory, is considered above in light of discussions of fundamental interactions and their previous critical analysis

Summary

Introduction

Much of the discussion below centers around scattering processes, note that neither the Lamb shift nor the anomalous magnetic moment of the electron (“g-2”) pertain only in the sort of scattering performed in collision experiments) Because arguments both for and against the existence of virtual particles crucially involve the methods of application of the mathematical formalism of quantum field theory and their connection to measurement and observation, their elements are described. For the purposes of understanding interactions, quantum systems are viewed as prepared in specific energy-momentum eigenstates |i i at some initial time t = ti and involved in scattering processes, after which, at the final time considered, particles are found away from the interaction region when the state | f i is measured. A way of avoiding this particular form of the problem might seem to be offered by redefining the virtual particle as one corresponding to a propagator in the perturbation-theoretical calculation of field interactions independently of diagrammatics, even the designation ‘virtual’ still depends on the use of that (extremely helpful but, optional) calculation technique

The Positions

The Arguments Against Virtual Particles

Virtual Particles are as Real as Others

Conclusions