# Existence of Virtual Particles

## Main Question or Discussion Point

As I understand it, according to the Copenhagen interpretation of QM, nothing can be said to exist until it is observed. I have also read that it is impossible to observe virtual particles in an experiment.

How is it then that virtual particles can be said to exist?

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reilly
Do a search of this forum for "virtual particles" You will find much to read and consider--including the fact that virtual particles, almost always, are artifacts of perturbation theory. The "almost always" makes allowances for resonances.
Regards,
Reilly Atkinson

Fredrik
Staff Emeritus
Gold Member
I would say that a description of what happens in terms of virtual particles is just one of many equivalent ways to describe the same thing. Virtual particles appear in the mathematics when a certain function is expanded in a series, kind of like the expansion exp(x)=1+x+x2/2+x3/6+...., but I don't think it would make sense to say that it's the individual terms in the series that describe what "actually" happens.

The statement "nothing can be said to exist until it is observed" is pretty strange. I guess you can say that, but in that case I'd rather treat that statement as a partial definition of what we mean by "existence" instead of as a statement about quantum mechanics. But I'd rather not say that at all.

malawi_glenn
Homework Helper
We can not tell wether they exists or not I think, however we can look if QED, QCD etc makes sense with experiment, and they indeed do that.

Also one has find the real counterparts of the proposed virtual particles (Z, W +/- , gluons) so that was also a gret sucess for quantum field theory.

And I am not sure wheter 'Copenhagen interpretation of QM' applies to QFT or not.

haushofer
$$E^{2} - p^{2} = m^{2}$$