# I Are virtual particles real or just math filler

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1. Jan 4, 2016

### J-eastwood

Hello,
My question on virtual particles is quiet simple but i cannot find an answer. Are virtual particles just a filler for math or do they actually come into existence?

2. Jan 4, 2016

3. Jan 4, 2016

### DrChinese

Welcome to PhysicsForums, J-eastwood!

The generally accepted answer is: Virtual particles are artifacts of the math of Quantum Field Theory. Many find them convenient for discussion purposes. Whether they are "real" or not is something of a matter of philosophy. There is no known physical test that would further answer this question.

4. Jan 4, 2016

### A. Neumaier

I wrote here a thorough answer (see the subsection on virtual particles). Virtual particles are not more than a useful visual aid for displaying technical mathematical details without using complicated formulas. Popular claims about their alleged temporal behavior are completely unfounded.

Last edited: Jan 5, 2016
5. Jan 4, 2016

### J-eastwood

Ok thank you for the responses it helped a lot!

6. Jan 4, 2016

### jlcd

Isn't it that electric field is an exchange of virtual particles. If virtual particles are just artifacts of mathematical procedure that is not there when you use other procedure. Then what is an electric field composed of? Maybe we need to go back to Faradays where electric field are really flux lines?

7. Jan 4, 2016

8. Jan 4, 2016

### jlcd

Arnold Neumaier answer in the link is very complicated. His answer is "Observable particles. In QFT, observable (hence real) particles of mass m'>m m are conventionally defined as being associated with poles of the S-matrix at energy E=mc2'>E=mc 2 E=mc2 in the rest frame of the system (Peskin/Schroeder, An introduction to QFT, p.236). If the pole is at a real energy, the mass is real and the particle is stable; if the pole is at a complex energy (in the analytic continuation of the S-matrix to the second sheet), the mass is complex and the particle is unstable."

I'm asking about the electric field. The link is about W and Z bosons of the electroweak field. I can't relate electric field to the S-Matrix or whatever.

So what are electric field specifically? just virtual photons? Note it has no mass so can't relate this to the link that has mass. Just need a direct answer to this question. Thanks.

9. Jan 4, 2016

### Mentz114

This is a quote from the linked document which does apply to the virtual particles you ask about

10. Jan 4, 2016

### jlcd

so what is the lattice gauge theory of electric field that doesnt use the concept of virtual photons?

11. Jan 4, 2016

### bhobba

QFT starts with a field, divides it into a lot of blobs, treats each blob using standard QM, then lets the blob size go to zero. Taking the blob size to zero means you are assuming the theory is valid for all scales - even below the Plank scale where we are pretty sure our current physics breaks down. Ok - so instead of taking the blob size to zero we can make it very small and solve the resulting theory on a computer - that's lattice theory. Wonder of wonders - when you do that no virtual particles. This suggests they are simply an artefact of the methods normally used by pushing them too far.

Thanks
Bill

12. Jan 4, 2016

### jlcd

ok so what does an electric field detector detect? if its not virtual photons then what is the terms of it? lattice blob interchange?

13. Jan 4, 2016

### bhobba

The quantised EM field it couples to just like classical EM where the coupling is modelled with a coupling constant in the Lagrangian.

Thanks
Bill

Last edited: Jan 5, 2016
14. Jan 5, 2016

### vanhees71

It depends on the electric-field detector. If it's something like a CCD, it detects photons. A classical electromagnetic (wave) field from the point of view of QFT is a coherent state, i.e., the superposition of all photon-number Fock states in a specific way that describes the details of this wave field. The probability to detect a photon is given as usual by Born's rule.

15. Jan 5, 2016

### A. Neumaier

It detects the electric field. In quantum electrodynamics the basic entities are an electromagnetic field operator $A(x)$ and an electon/positron field operator $\psi(x)$. The expectation of $dA(x)$ (where $d$ denotes exterior differentiation) is the classically measurable field at any space-time point $x$, with three electric and three magnetic components. Similarly, the expectation of $e\psi(x)^*\psi(x)$ is the classically measurable charge density.

Conceptually, this is very simple, just as the quantum-classical correspondence in the Ehrenfest theorem of quantum mechanics.
Introducing virtual particles only obfuscates the picture.

16. Jan 5, 2016

### friend

If virtual particles are ONLY a tool for visualizing math procedures, then why is it not fair to use them to develop math for subjects like the Casimir effect, Hawking and Unruh radiation, screening effect on a bare point charge, etc? I don't think anyone ever mentions them as being something measurable. They always seem to be used for visualization purposes. Why (or when) is that not a fair approach for development?

17. Jan 5, 2016

### A. Neumaier

It is appropriate to use them as visual aids.
But they are treated in much of the world of nonphysicists (including many wikipedia articles) as something dynamical, which is pure science fiction.

18. Jan 5, 2016

### friend

Are there some guidelines for how to use virtual particles in theory development? For example, I'm thinking of how two charged particles might interact in terms of the screen of virtual particles that surround each. It is said that the virtual particles (vacuum fluctuations) are polarized by the presence of a bare charge. Can the theory describing the force between the particles be developed in terms of how the virtual particles are polarized by both charges together? Or would such a theory depend on some dynamics which you say does not exit for virtual particles? Yet, wouldn't polarizing the vacuum (virtual particles) be a type of dynamics? Or would polarizing the vacuum only be a way of taking into account some potential without relying on the dynamics of how each of the virtual particle pairs actually propagate through space? Is it fair to use virtual particle only in terms of the probable effect of a potential on the virtual pairs?

Last edited: Jan 5, 2016
19. Jan 5, 2016

### A. Neumaier

You use them to illustrate whatever you do on the mathematical level. The decisions what to do there must come from your mathematical and physical understanding.

20. Jan 5, 2016

### anorlunda

Wow. I just read your answer here . It was very educational, and not too difficult to read. Here is my suggestion. Add a couple of pictures and make it a PF insights article. I thinks it would be much appreciated. Also, a link to an article is presumably more permanent than a link to a post, and therefore can be cited when editing those many incorrect Wikipedia articles that you mentioned.