Re: How real are the "Virtual" partticles?

From: Arnold Neumaier (Arnold.Neumaier_at_univie.ac.at)
Date: 02/23/05 

Date: Wed, 23 Feb 2005 09:58:34 +0000 (UTC)

John C.Polasek wrote:
> On Wed, 16 Feb 2005 17:37:31 +0000 (UTC), Renan Cabrera
> <rencabla@yahoo.com> wrote:
>
>>As I read, most people say that the virtual particles are
>>not to be considered more than a mathematical tricks
>>in order to calculate the final real observable.
>
> In my opinion, virtual particles are often essential in development of
> a theory and are more than "mathematical tricks". They are now
> accepted in most fields as forming a natural bridge in the
> development. If the further analysis does not "free up" the virtual
> part, then you are left with the magic!

They are essential only in perturbation theory using
Feynman diagrams. They change their nature depending on the way
one does perturbation theory and what is resummed.

In their treatise of QED, Landau and Lifshitz discuss virtual particles
in Section 79. They start at the outset with the remark that things
depend on which kind of perturbation theory is used, and contrast
'virtual' explicitly with 'real'. Virtual particles have their
name as a contrast to 'real particles' which are observable and
hence real. And they _must_ have disappeared by the time the
calculations lead to something that can be compared with experiment.

Whence their 'reality' if there is any is like the reality of
characters in a dream. For example, just as we can fly in a dream,
virtual particles can be faster than light (since they may have
imaginary mass)...

Arnold Neumaier