Can Virtual Particles in the Vacuum be Directly Detected?

[AmyS7]

Why cannot virtual particles in the vacuum be directly detected? Experiments have shown the Casimir Effect that supports the idea of virtual particles does exist. But can we also detect the presence of virtual particles directly in the vacuum? The most common virtual particle to form is photon because it has zero static mass (the havier the particle is, the shorter it exists). Therefore, once it has formed, is there a way how to detect its existence before it dissapears again? If there is not, why?

 

[Vanadium 50]

Virtual particles are not real. It's as simple as that - they are not real, so they can't be detected.

 

[humanino]

If there is not, why?

Because the probability to detect the particle vanishes when the particle is not on mass shell. Independently of whether you think virtual particles exist or not, of whether you call real particle quanta of field or whatever, what you can compute is the amplitude for a certain process with initial and final states specified. The vanishing of the amplitude away from the particle's mass occurs within Heisenberg's relations.

 

[Bob S]

It is possible to detect the effect of virtual charged particles (mostly electrons) when they are in a strong electric field. The bare (unrenormalized) charge of an nucleus is larger than the measured (renormalized) charge, but the bare charge surrounds itself with virtual particles (distances less than an electron Compton wavelength), and these virtual particles become polarized in the strong Coulomb field. This effect (vacuum polarization) is very important in electron and muon g-2 (gyromagnetic ratio) experiments, and in muonic atoms.