They have meaning only in this precisely defined context and are meaningless otherwise. In the following, I give precise definitions of many terms, telling what they really mean as part of the technical language used in quantum field theory.

Such a discussion is begun in another Insight Article “ Misconceptions about Virtual Particles“. A further Insight Article, ” Vacuum Fluctuations in Experimental Practice”, shows the example of a recent article in the scientific literature how some authors claim the observation of vacuum fluctuations, justified only by superficial, invalid reasoning. The aim of the following exposition is a definition of physical terms essential for an informed discussion of which of these properties have a solid basis in physics, and which of these are gross misconceptions or exaggerations that shouldn’t be taken seriously. How the latter view could arise is described in the Insight Article, ” The Vacuum Fluctuation Myth”. This is partly due to misunderstandings in the terminology used, and partly due to the fact that subatomic particles manifest themselves only indirectly, thus leaving a lot of leeway for the imagination to equip these invisible particles with properties, some of which sound very magical. In discussions on the internet (including a number of Wikipedia pages) and in books and articles for non-experts in particle physics, there is considerable confusion about various notions around the concept of particles of subatomic size, and in particular about the notion of a virtual particle.

Virtual particles