Existence of Virtual Particles

  • Thread starter Bose
  • Start date
25
0

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?
 

Answers and Replies

410
0
...if a tree falls in the forest...
 
reilly
Science Advisor
1,075
0
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
Science Advisor
Gold Member
10,730
406
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. :smile:
 
malawi_glenn
Science Advisor
Homework Helper
4,782
22
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
Science Advisor
Insights Author
2,239
569
My understanding of virtual particles is this:

In quantum field theory, you can describe the amplitude of a field by a path integral ( for a heuristic motivation of this path integral, maybe you've read the first chapter of Zee's QFT in a Nutshell, that's very nice ) You can't calculate this path integral exactly, but you have to expand it in a power series and integrate term by term. In each term, you will encounter so called propagators. In these propagators, you integrate over all possible momentum. And that's not what you're used to do; for example, you're used to that a particle obeys

[tex]
E^{2} - p^{2} = m^{2}
[/tex]

So these propagators appear to describe particles with energies lying "off-shell", allowing also energies which don't obey the formula above. The particles pop up during the traveling of the field from A to B. These particles are called virtual, because they don't have to obey the energy condition. But they certainly contribute to the amplitude !
 

Related Threads for: Existence of Virtual Particles

  • Last Post
Replies
23
Views
4K
Replies
15
Views
1K
Replies
1
Views
448
Replies
7
Views
3K
Replies
14
Views
4K
  • Last Post
Replies
8
Views
2K
  • Last Post
Replies
3
Views
2K
Top