Real or Virtual Particles: Chicken or the Egg?

[sujiwun]

Do real particles "cause" virtual particles, or do virtual particles "cause" real particles?

Put another way, is it so that real particles actually exist in and of themselves and interact as normally described by transferring virtual particles with each other.

OR,

Are only virtual particles "real" in the sense of having any sort of actual existence however brief, and it is real particles that are actually just the inference of there being something there in space due to their observed interactions with other real particles also inferred to be there due their mass, charge, etc all mediated by virtual particles.

Are real particles mere consistent patterns of incidental order emergent within the chaos of brief spontaneously created random virtual particles making up the quantum foam of space?

Does this have anything to do with Symmetry Breaking and Lie groups and the relative (localized?) Lagrangian/Hamiltonian balance of KE and PE?

 

[A. Neumaier]

is it so that real particles actually exist in and of themselves

OR,

Are only virtual particles "real" in the sense of having any sort of actual existence however brief

Chicken. See https://www.physicsforums.com/showthread.php?t=460685

 

[sujiwun]

Chicken. See https://www.physicsforums.com/showthread.php?t=460685

perhaps neither...
http://en.wikipedia.org/wiki/Point_particle

 

[Dmitry67]

Interpretation dependent

 

[Phrak]

Do real particles "cause" virtual particles, or do virtual particles "cause" real particles?

What does 'cause' mean?

 

[K^2]

I'd call it an open question. We still don't know exactly what causes mass. There is evidence that all mass might be effective mass due to interaction fields between particles. At least, more and more of the rest mass of particles is shown to be such. If other fundamental charges, namely electric charge and color charge, prove to be similar, we'd be in a situation where one cannot exist without the other.

 

[DarMM]

Virtual particles are not real. If people didn't use perturbation theory there would be no discussion about virtual particles, they are not a feature of the real theory. They do not appear in a nonperturbative description.

 

[sujiwun]

What does 'cause' mean?

"The law of causality, I believe, like much that passes muster among philosophers, is a relic of a bygone age, surviving, like the monarchy, only because it is erroneously supposed to do no harm."

Bertrand Russell

 

[sujiwun]

Virtual particles are not real. If people didn't use perturbation theory there would be no discussion about virtual particles, they are not a feature of the real theory. They do not appear in a nonperturbative description.

Are the electrons and quarks, that all matter is made of - being point particles, by definition having no spatial extension - any more real?

 

[Dmitry67]

Virtual particles are not real. If people didn't use perturbation theory there would be no discussion about virtual particles, they are not a feature of the real theory. They do not appear in a nonperturbative description.

It is interpretation dependent

In SM, for example, both "real" and "virtual" particles are "just math" to describe the correlation between macroscopic events

All other definitions of "virtual" particles are sooooo Copenhagen - any definition uses words "measured", "observed", "has enough energy" (=observable), or "incoming and outgoing particles" (outgoing=detected).

I've never seen any definition of virtual particles which can be used in modern non-collapse (decoherence) theories.

 

[sujiwun]

I'd call it an open question. We still don't know exactly what causes mass. There is evidence that all mass might be effective mass due to interaction fields between particles. At least, more and more of the rest mass of particles is shown to be such. If other fundamental charges, namely electric charge and color charge, prove to be similar, we'd be in a situation where one cannot exist without the other.

How about this for a possible stochastic explanation.

The flux of quantum foam is random, so its net lagrangian should be zero.

Perhaps mass is the result of brief incidental localized emergent non-zero lagrangian - virtual particles...

where the Lagrangian, L = T-V
T = KE = change within the foam
V = PE = constancy within the foam

 

[dextercioby]

Both point particles and fields (either classical or quantum) are not real. They're only models of our reality. Nothing but elements of a mathematical modelation of an experimentally observable reality.

 

[sujiwun]

Both point particles and fields (either classical or quantum) are not real. They're only models of our reality. Nothing but elements of a mathematical modelation of an experimentally observable reality.

http://www.library.yale.edu/librarynews/ceci-n-est-pas-une-pipe.jpg

 

[DarMM]

It is interpretation dependent...

I think a discussion on what is or isn't "really real", will be pointless. Instead I will discuss what the theory itself says. All quantum field theories do not predict the existence of virtual particles. Virtual particles only appear as lines in Feynman diagrams which are attached to the perturbative formulation. What the the theory itself says are real, observable, e.t.c. are the eigenstates of the Hamiltonian, the states which label in and out going asymptotes. The theory predicts the existence of these, it does not predict the existence of virtual particles.

Whether or not the theories predictions are themselves "real" is a separate discussion, but let's not tangle it up with the observation that virtual particles are perturbative artefacts.

 

[DarMM]

Are the electrons and quarks, that all matter is made of - being point particles, by definition having no spatial extension - any more real?

I have never seen where QFT predicts that electrons and quarks are "point particles". QFT has local field interactions "at a point", but the particles themselves always have wavefunctions with finite spatial support.

 

[dextercioby]

http://www.library.yale.edu/librarynews/ceci-n-est-pas-une-pipe.jpg

I sense some irony. Anyways, the difference is that a pipe is something real. A point particle is not.

 

[sujiwun]

I have never seen where QFT predicts that electrons and quarks are "point particles". QFT has local field interactions "at a point", but the particles themselves always have wavefunctions with finite spatial support.

But does the wavefunction say anything about the size of the particles or just where they are most likely to be found?

 

[sujiwun]

I sense some irony. Anyways, the difference is that a pipe is something real. A point particle is not.

http://en.wikipedia.org/wiki/Semiosis

 

[DarMM]

But does the wavefunction say anything about the size of the particles or just where they are most likely to be found?

Well it's their spatial probability density and from it you can derive expectations and statistics for observables. Anyway, no where does any QFT predict that electrons and quarks are point particles.

 

[A. Neumaier]

Both point particles and fields (either classical or quantum) are not real. They're only models of our reality. Nothing but elements of a mathematical modelation of an experimentally observable reality.

In the same vein, even what is experimentally observable would be nothing but elements of a conceptual model of an otherwise completely incomprehensible reality.

Mathematical models at least have the advantage of being based on precise concepts.
Experimental concepts are precise only to the extent that they use the mathematical concepts.

 

[sujiwun]

Well it's their spatial probability density and from it you can derive expectations and statistics for observables. Anyway, no where does any QFT predict that electrons and quarks are point particles.

Then perhaps you can tell me what the radii are for quarks and electrons?

QFT may not predict that electrons and quarks are point particles, but, as far as I am aware it doesn't predict that they are not point particles either, and physics has no size for either of these.

 

[Phrak]

"The law of causality, I believe, like much that passes muster among philosophers, is a relic of a bygone age, surviving, like the monarchy, only because it is erroneously supposed to do no harm."

Bertrand Russell

Nice quote. One I appreciate. However, I would say that Russell was philosophizing, but doing a better job of it. Do you happen to know what publication was this from?

 

[sujiwun]

Nice quote. One I appreciate. However, I would say that Russell was philosophizing, but doing a better job of it. Do you happen to know what publication was this from?

Sorry, I can't recall where I first came across it - I just googled it.

 

[QuantumClue]

How can people state that virtual particles are not real? Of course they are real. They have calculatable effects on the energy levels of atoms. It is a small energy, but such an energy has been measured. How can you measure something that is not real?

 

[QuantumClue]

I'd say particles came from virtual particles. It is the only logical order, as it is with Chicken producing an egg.

Before any real matter was about, the vacuum was teeming with virtual particles. They live inside the vacuum, and is what makes up zero-point energy or even a Dirac sea if one can picture it.

 

[sujiwun]

I'd say particles came from virtual particles. It is the only logical order, as it is with Chicken producing an egg.

Before any real matter was about, the vacuum was teeming with virtual particles. They live inside the vacuum, and is what makes up zero-point energy or even a Dirac sea if one can picture it.

It strikes me that elementary particles such as electrons and quarks have no real existence of their own. They are essentially defined by their field effects, which are mediated by virtual particles.

No one has ever observed either, they have no descernible size, their existence is inferred from observed macroscopic effects. The same can be said of virtual particles of course, but, with both being mathematical models to help explain observable phenomena, I would suggest that virtual particles have primacy and it would be more sensible to look for a description of electrons and quarks in terms of virtual particles popping into and out of existence, than describe virtual particles in terms of what electrons and quarks are doing. Bottom up rather than top down.

 

[A. Neumaier]

How can people state that virtual particles are not real? Of course they are real.

Only people informed primarily by lay men's literature claim that. See Chapter A7 of my theoretical physics FAQ at http://arnold-neumaier.at/physfaq/physics-faq.html#A7 and the PF thread https://www.physicsforums.com/showthread.php?t=460685

They have calculable effects on the energy levels of atoms. It is a small energy, but such an energy has been measured. How can you measure something that is not real?

The Casimir energy has been measured, not a virtual particle.

 

[A. Neumaier]

Then perhaps you can tell me what the radii are for quarks and electrons?

QFT may not predict that electrons and quarks are point particles, but, as far as I am aware it doesn't predict that they are not point particles either, and physics has no size for either of these.

See the entry ''Are electrons pointlike/structureless?'' of Chapter B2 of my theoretical physics FAQ at http://arnold-neumaier.at/physfaq/physics-faq.html#pointlike

 

[QuantumClue]

Only people informed primarily by lay men's literature claim that. See Chapter A7 of my theoretical physics FAQ at http://arnold-neumaier.at/physfaq/physics-faq.html#A7 and the PF thread https://www.physicsforums.com/showthread.php?t=460685

The Casimir energy has been measured, not a virtual particle.

Well, aren't we just being a little pedantic however?

The Casimir Force, or more specifically the Lamb shift is caused by virtual particle energies. The Casimir force is in fact nothing more than an increasingly negative energy density between two plates in a vacuum via the interaction of virtual particles.

So I am interested how you can say what you say?

 

[A. Neumaier]

Well, aren't we just being a little pedantic however?

Didn't you complain about others being patronizing? Practice yourself what you preach!

The Casimir Force, or more specifically the Lamb shift is caused by virtual particle energies.

No. http://lanl.arxiv.org/abs/hep-th/0503158 derives and calculates the Casimir effect without the use of virtual particles. Thus the latter cannot be their cause.

So I am interested how you can say what you say?

I gave references for that. If you really are interested, read them!

 

[DarMM]

Well, aren't we just being a little pedantic however?

The Casimir Force, or more specifically the Lamb shift is caused by virtual particle energies. The Casimir force is in fact nothing more than an increasingly negative energy density between two plates in a vacuum via the interaction of virtual particles.

So I am interested how you can say what you say?

You can derive the Casmir force nonperturbatively, in fact I think it's done in introductory textbooks like "Quantum Field Theory in a nutshell" by A. Zee. In such a derivation there are no "virtual particles".

 

[Demystifier]

You can derive the Casmir force nonperturbatively, in fact I think it's done in introductory textbooks like "Quantum Field Theory in a nutshell" by A. Zee. In such a derivation there are no "virtual particles".

That's true. In fact, I have never seen a derivation of the Casimir effect with virtual particles. The issue is not whether Casimir effect proves the reality of virtual particles (which it certainly doesn't), but whether it proves the reality of the zero-point energy (which is controversial, especially after the Jaffe's paper). Contrary to a frequent misconception, zero-point energy has absolutely nothing to do with virtual particles.

 

[QuantumClue]

For the last few posts, especially A. Neumaier's response, this is all down to interpretation.

Quantum mechanics directly predicted the existence of virtual particles long before any other explanations where concocted - and really were only created because certain scientists did not fully appreciate this existence which seems to have been for all practical terms, has been proven experimentally. Inviting new interpretations because people do not like the idea of virtual particles seems superfluous and redundant.

 

[sujiwun]

Only people informed primarily by lay men's literature claim that. See Chapter A7 of my theoretical physics FAQ at http://arnold-neumaier.at/physfaq/physics-faq.html#A7 and the PF thread https://www.physicsforums.com/showthread.php?t=460685

The Casimir energy has been measured, not a virtual particle.

Hmmm, cool, an expert. So how are imaginary virtual particles any different from imaginary electrons?

Do electrons actually exist? Go on stick your neck out.

 

[sujiwun]

Contrary to a frequent misconception, zero-point energy has absolutely nothing to do with virtual particles.

You sure?

I'd agree that zero point energy ISN'T virtual particles and doesn't derive from virtual particles or what they are doing, but I wouldn't say it has nothing to do with them. More like the virtual particles are "anomalies" within the zero point energy field.