Can virtual particles become real?

We often come across the need to explain how fundamental physics works to the general public unfamiliar with the physical and mathematical prerequisites. We usually end up with analogies – a powerful tool which can, without explanation, give the audience a rough idea of how the thing works. But analogies can only be taken seriously so far – attempts to use them to explain complicated phenomena usually lead to apparent paradoxes, misunderstanding and confusion.

The same thing has been happening over and over on this forum with virtual elementary particles. See, when physicists speak of virtual particles, they refer to a specific type of fluctuation in the quantum field – the same field that gives rise to ordinary (real) elementary particles. That fluctuation has a precise mathematical meaning as a part of the asymptotic series, describing a fundamental object in the theory – the scattering matrix describing interactions between real elementary particles. That's why an analogy is usually employed: those fluctuations are said to be "virtual particles" which "mediate" interactions.

This analogy addresses the correct issues, and tells an unprepared audience a lot about the underlying phenomena. But it is only an analogy, and it has its limitations. Most of the newbie questions about virtual particles can and should be addressed in the full mathematical framework which is interacting Quantum Field Theory. Any kind of explanation involving virtual particles is just hand-waving.

Virtual particles have no dynamics. The latter is always tied to a state, which - unlike virtual particles - necessarily respects causality. Hence they cannot ''become'' anything. See https://www.physicsforums.com/insights/misconceptions-virtual-particles/

Talk about virtual particles doing something is therefore always just an illustration of some underlying formula, without any intent of physical accuracy.