Talk:Virtual particle

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Real vs. virtual[edit]

I've got a question for the physicists here. I've always wondered about so-called "virtual photons." Is there REALLY any difference between real photons and virtual photons? What I mean is this: when we detect a photon with our eye or some instrument, the photon coming in excites some electrons into some higher energy states, or causes induced relaxation of some excited state, or whatever...but basically all the photon did before it "died" was move a charged particle (the electron). This is the same as what a virtual photon does! So, the only difference that I can see is that with a virtual photon, we consider that we observed a charged particle change its trajectory, whereas with a "real" photon, we claim that we observed a photon hitting our detector. But, really, they're the same thing? Comments?

Ed Sanville 04:32, 23 Dec 2004 (UTC)

As described in the article, virtual particles occur strictly as intermediate steps in interactions. If your photodetector was triggered, something other than the virtual particle provided the initial energy for the triggering. The collision of two electrons is a good example for this: the force that the two electrons experience as they approach each other is carried by disturbances in a sea of virtual photons, but the change in trajectory of one electron is caused by exchange of energy and momentum with the other electron. The virtual photons acted solely as intermediaries. (ObCaveat: I'm still hazy on where the energy recovered from the work done by the pressure produced by the Casimir effect between plates whose separation distance is being changed comes from.)--Christopher Thomas 06:53, 12 Jun 2005 (UTC)
"virtual particles occur strictly as intermediate steps in interactions" But doesn't that depend on what you characterize as "the interaction?" For example, in my above example of a photon hitting a detector, you could consider the interaction to be between the particle that emitted the photon, and the particle in the detector that absorbed it. If you considered that to be the interaction, then it would seem that the photon has now become a virtual photon... is there some other requirement for a photon to be "virtual?" Ed Sanville 21:39, 17 April 2006 (UTC)
There are formal definitions of real vs. virtual photons. If you're using Feynman diagrams, virtual particles are ones that don't enter or leave the diagram (or alternatively, particles that do enter or leave the diagram are the real ones). If I recall correctly it was User:Linas who gave another description that treated virtual particles as the mathematical artifacts you get when you quantize behavior of forces in a certain way (via perturbation theory), with alternate ways of treating the problem removing the virtual particles, but leaving the real ones. My best advice for telling which is which is to treat any interaction over a distance as being mediated by real particles, as the range of interaction for virtual particles is very, very short (the simplified explanation which I was given was that they couldn't exist long enough for it to be _possible_ to measure them, due to uncertainty principle effects providing the loophole in conservation laws that the simplified explanation uses to handwave their existence in the first place). This is mostly-true down to scales approaching the size scale at which the Casimir effect becomes important, for photons, or scales comparable to the size of a nucleon, for things like mesons and gluons. One of the lurking physicists can give you a much clearer answer than I can. --Christopher Thomas 23:39, 17 April 2006 (UTC)
Ed's reasoning is correct: in a certain philosophical sense, there is no distinction between real and virtual photons. Chris Thomas' answer is correct as well: in practical matters, there's a clear distinction, and one has to cook up intriguing and confusing thought experiments to blur the distinction. linas 04:39, 20 April 2006 (UTC)
OK, thank you Chris Thomas and linas, this is one of those things I've always wondered about, and I wanted to get the consensus from the people who actually study these things. Ed Sanville 12:27, 20 April 2006 (UTC)
Me, I don't think electrons are real. Electrons are just perturbation theory to explain how cathode ray tubes work. They're just a fiction needed to make the calculations agree with reality. :-)WolfKeeper 01:25, 6 October 2007 (UTC)

I would just like to thank the person who wrote this: "Furthermore, in the photon's frame of reference, no time elapses between emission and absorption. This statement illustrates the difficulty of trying to distinguish between "real" and "virtual" particles as mathematically they are the same objects and it is only our definition of "reality" which is weak here." Excellent quote! Itistoday 06:52, 19 June 2006 (UTC)

I would question the last statement, someone clarify... time would elapse if the photon were in a slowing medium. To keep it simple make it water, more complicated, make it the LHC. Slowing the speed below the cmax would change the photon's frame of reference and allow time to pass?Cyberchip (talk) 18:21, 5 January 2015 (UTC)

Sad state of physics[edit]

If Einstein lived today he'd have become an alcoholic at the ridiculous state of physics. I was the person who added the last paragraph of the introduction which called into question the foundation for the origin of virtual particles. I put it there based on my own understanding of physics, and though I didn't cite a reference I thought it was an innocuous commentary that just gave more context to the subject. After all, a virtual particle has never been observed, and by its own clever conception it cannot even exist if its observed. If that's not a catch 22 situation I guess they don't exist. I now see that the writing is "literally" on the wall that a citation is required. Well, I don't have one other than my own published writing and I refuse to cite my own writing based on a general cringing at self promotion.

So Wolfkeeper, remove that paragraph if you must and we can all chalk it up as a further example of physics moving in lockstep over the cliff. Physics has now become so absurd that as long as you cite an important person as ignorant as oneself you can pontificate on anything, including multiverses which by definition, being separate universes, have no causality with our own. What a sad situation where a science beloved by many of us has been taken over by accountants without the slightest shred of common sense or genuine intuition. 09:28, 4 December 2007 (UTC)

I was going to leave it, or just remove some of the weasel words, but based on the evidence presented above, I'm taking it out entirely.- (User) WolfKeeper (Talk) 10:10, 4 December 2007 (UTC)
Oh and BTW, in physics we don't play 'count the universes' any more than we play 'count the atoms'. We play 'count the assumptions'. That's how physics works, that's how it has always worked.- (User) WolfKeeper (Talk) 10:26, 4 December 2007 (UTC)

Virtual particles – logical fallacy

I notice there is no citation for the initial summary or for virtual particles at all.

One citation (raymond) is already dead. I hope that wasn’t the one this article depended upon. The powerpoint has no direct or source references. The Gilman cite has no direct or source references. The references on phonons and photon are not about particles with mass.

This means the article has zero direct or source references to its definition.

Yet somehow this wiki article has wrongly reversed the Burden Of Proof to the skeptic.

That’s a logical fallacy called Burden Of Proof reversal.

The proper burden of proof is on the proposer – not the skeptic.

I agree with whoever “added the last paragraph of the introduction which called into question the foundation for the origin of virtual particles.”

I think that until a direct or source reference to virtual particles can be found – that introduction should be revived (though I’ve never read it and can’t find it in history -- Dec 2007). — Preceding unsigned comment added by (talk) 21:03, 11 August 2012 (UTC)

"but based on the evidence presented above, I'm taking it out entirely." In other words, Wolfkeeper, you are mad so you are you using that as an excuse to take out needed contextual counterbalance on the subject of virtual particles. Another sad commentary on the state of discourse in physics today. Your actions follow your emotion of the moment rather than logical thought processes. 19:19, 4 December 2007 (UTC)
No, it was mainly the fact that you admitted you were never, ever going to cite it, together with your admission that it was OR; but if you give us a link here to any published paper we can still evaluate it for notability, but otherwise it's staying gone because it's unverifiable.- (User) WolfKeeper (Talk) 19:57, 4 December 2007 (UTC)
Wolfkeeper, you are not thinking logically, but emotionally. Otherwise you'd realize the absurdity of talking about the "verifiableness" of my comments. We are talking about a subject, virtual particles, whose main definition is that they aren't verifiable. Haven't you figured out yet that all you are protecting on this subject is the idea of "precedence", in which a cockamamy idea which by definition couldn't be proved became accepted without proof. If you had any sense at all you'd realize the burden of proof is on you and the people who have accepted this idea. Virtual particles are a bookkeeping mechanism required because of our ignorance of what is really going on in this area of physics. Why are you pretending that it isn't, and instead acting like the burden of proof in denying the "bookkeeping" reality isn't on you and not me. You are just compounding ignorance with stubornness. 20:37, 4 December 2007 (UTC)
Hey, the main point of quarks is that they aren't verifiable, either. Does that make them a mere bookkeeping device? For that matter, you've never seen an isolated real photon, let alone a virtual one. Are "real" photons mere bookkeeping devices to "explain" that energy is absorbed out of the EM field only in chunks? Why not just leave it at that, instead of making the "chunks" into clunky particles? And now, let's start on electrons. Ever seen one? How do you know they aren't just a bookkeeping device? And even more importantly, why doesn't we agree to let bookkeeping have two p's, so we can have four sets of double letters in a row, instead of just three? SBHarris 18:03, 6 February 2008 (UTC)
To take a more everyday argument, when you unevenly cool a lump of iron, internal forces are set up which don't have any external effects, you never have internal forces entering or leaving the lump of iron, and internal forces never appear in a non perturbative calculation, so it's questionable whether internal forces exist at all, right? It's just a bookkeeping thing; but you can measure the distortions due to them. And lumps of iron frequently crack open due to them.- (User) WolfKeeper (Talk) 18:25, 6 February 2008 (UTC)
The argument against virtual particles in the article is of this same form, and is completely unreferenced.- (User) WolfKeeper (Talk) 18:25, 6 February 2008 (UTC)
SB,Being a physician it seems strange to me that you would try to correct a physicist's arguments about physics. I don't try to correct your ideas about medicine. I'm referring to your comments on the discussion page about "virtual particles". What you are doing in that discussion is taking ideas that have been superceded and taken them as gospel. I'm sure there are things in medicine that I could quote from a 40 year old book, and do it in the most literal way and pretty much offend you by telling you that you are a quack because you don't agree with me. Well, that's what you and many other people are doing on the subject of virtual particles. To get a better idea of what is really going on in physics read the wiki article "zero-point field" which I've contributed about 90 percent of. (talk) 09:30, 31 January 2009 (UTC)
Being a physician I'd be glad to be taught by a real physicist. Are you one? What are your credentials? My name is on my userpage. All I see from you is a mix of IP-hopping like I'd expect from a banned sock or a vandal. Surely if you're an authority on physics you'd be proud of that? And people wouldn't laugh at you, but would take you seriously, like new-age guru Hal Puthoff? Wups, no, strike that: they do laugh at Puthoff, even though he is a physicist. Free energy suppression consipracy and New Age. My, my. Is this where physics is, today? From reading all the unreferenced stuff in the zero-point field article I'd guess perhaps you are Puthoff. If so, good luck, but the community of respectable physicists (not to mention physicians) is not backing you, and you well know it. PS: Where's your free energy, baby? We need it. SBHarris 21:14, 31 January 2009 (UTC)

Six years later and this stuff still finds people squabbling. I still think we can call virtual particles 'virtual' by a basic Webster's definition of the concept. The point being we don't have a direct word for an imaginary complex abstract vector or a group of them in non-conjugated or translated, rotated (whatever) form. Will we ever finish the Pauli exclusion principle and its unobservables.

I'd prefer to use virtual. Of course I feel it's absolutely required that laymen even have a basic concept of the formation of eigenvectors, and symmetry breaking, etc. Thank goodness from the references we're starting to understand this and define it. It's a concept that needs strict definition for sake of discussing exceptions and complementary subjects. Perhaps this subject can gain enough legitimacy in defining terms that people won't feel threatened, and can start signing things even. Can we at least agree that 'virtual particles' exist, even if they're not real?! Or when we really understand everything going on in the background are we going to encorporate 'virtuality' or complex imaginary particles into the 'real' realm. I think that would just be a confusion to a layman. As referenced by reality and existence, I prefer the concept of observable, indirectly observable, and unobservable. Although, I hope some day we will indirectly observe the unobservable too. Entanglement should definitely be included here as far as something virtual happening. I think entanglement describes the only locally non-local effect around. I could give my reasons; but, I would be surprised even if I did and people couldn't refute it, you'd find a citation anywhere. The attitude nowadays would have had even Einstein and Tesla kicked out from making inclusions into Wikipedia today at some point in their life. Sad state indeed!Cyberchip (talk) 22:11, 5 January 2015 (UTC)

Explaining the relation to off/on shell would clear up everything instantly.[edit]

After an evening of reading I connected the dots from virtual particle to off the mass shell. I can't believe it was so hard to find an explanation of this anywhere on the net. I thin an explanation like the following, would clear things up for many newbies:

Yeah, I think not too many understand the difference philosophically. The page On/off shell is not very good either, being mostly just mathematics. Discusing virtual vs real particles as if vitual means imaginary or unreal, is not very useful. I think the word "virtual" here is not a very good name for the "particles". My (I'm not very much of a quantum physicist) understading of "virtual" is more like the particles being vague or incomplete (of shell) and in many ways more wave-like than classical particle-like. The jargon itself does not help much in understading this philosofically, and it is easy to get the impression that the physicists that originally discovered these consepts in the mathematics, did not really know how to interpret it very well either. Yikkayaya (talk) 21:25, 14 June 2015 (UTC)

Article has deteriorated[edit]

The wording has become mushy and less encyclopedic. A re-vert to ~2 years ago would be a quantum improvement. Or it should be incrementally improved.

Spope3 (talk) 15:12, 25 December 2014 (UTC)

I agree, Chjoaygame's massive lead (also lacking links and citation) about virtual particles being just a purely mathematical trick to fulfill conservation laws, is highly misguiding. The understanding lies in the concept of on/off mass shell. Though something along the line "Some physicists interpret virtual particles as .....[citation needed], while some physicists interprets virtual particles as being mathematical consepts[citation needed]", might fit in, as indeed the best experimental techniques are very far from measureing at the simultaneous time and space resolution required to "see" vitual particles. Yikkayaya (talk) 21:25, 14 June 2015 (UTC)
A pity SBHarris ran away. Yikkayaya (talk) 21:29, 14 June 2015 (UTC)
Added expert needed tag Yikkayaya (talk) 18:25, 2 August 2015 (UTC)
I am very skeptical of expert tags. If you are going to add one, you should ask a specific question and link to a section on the talk page devoted to discussing that question. It seems that the biggest controversy on this page is whether virtual particles are real. RockMagnetist(talk) 21:39, 3 August 2015 (UTC)
Comparing a version from yesterday with one from two years ago, the main change is in the lead, while the body has mostly been rearranged. It appears that a couple of years of wrangling over the lead has been, if anything, counterproductive; meanwhile, the body has remained disorganized and poorly supported by citations, and no one seems to care enough to do something about that. Yesterday, I improved some of the existing citations and added some new high-quality citations. A lot more of this should be done, and the grocery list in Virtual particle#Manifestations should be organized. For example, one of the obvious themes is that (whether they are real particles or just mathematical constructs) virtual particles mediate the fundamental forces. This could have its own section - and should have plenty of citations! These are the kinds of edits that lead to lasting improvement. RockMagnetist(talk) 21:39, 3 August 2015 (UTC)
It is good to read Editor RockMagnetist's sober and constructive post. One can happily agree with his admirable advice, that better references are desirable. Perhaps it may not be too easily followed. It is not easy to find many reliable secondary sources, such as student textbooks, that give direct explicit or deliberate systematic accounts of the term 'virtual particle'. I spent some time finding the three that I offered, and I agree that they are not all that may be desired. Often when it used, the term is not extensively discussed as such. Some specialists recommend avoidance of the term.
One may remember that Heisenberg said that the inner workings of subatomic reactions are not directly observable.
At the risk of suggesting further discussion that would lead to conceptual considerations that may be inappropriate here, perhaps I may say a little more. The word 'virtual' is not a synonym for the word 'short-lived'. The word 'virtual' is not a synonym for the phrase 'not real'. But in the present context, the word 'virtual' is not too far from being a synonym for 'not concretely observable'. In many customary physical discussions, the word 'real' is not explicitly defined. It is general usage that what is concretely observed is real. On the other hand, to say that something is not concretely observed is not to say that it is not real. To say that something is real is not to say that it is not a mathematical construct. One would not wish to say that the physical quantity 'action' is not real, but one would not say that is concretely observed. The word 'real' is not a synonym for the phrase 'materially concretely existent'.
It is my view that virtual particles are 'real' insofar as they refer to theoretically valid possible mechanisms of concretely observed physical processes. But they are by definition not actually observed as such. In my view, a virtual particle is real if it provides a valid contribution to an account of concrete observations. That is not the same thing as saying that as such, in itself, it has concrete material existence.Chjoaygame (talk) 03:08, 4 August 2015 (UTC)
@Chjoaygame: It is clear from past discussions that you are very interested in the question of how real virtual particles are. Instead of discussing this in general terms, let's look at some claims in a particular section (see below). RockMagnetist(talk) 18:13, 4 August 2015 (UTC)

Pair production[edit]

The section Pair production has some claims that bear on the reality/nonreality of virtual particles. I looked for citations that discuss the relevance of the Unruh effect to virtual particles, but in the sources I found they weren't mentioned. Similarly, the article on vacuum decay doesn't mention virtual particles at all. Can anyone find sources that explicitly relate these phenomena to virtual particles? RockMagnetist(talk) 18:13, 4 August 2015 (UTC)

See also[edit]

see The Physics of Virtual Particles — Preceding unsigned comment added by 2001:62A:4:2F00:223:24FF:FE74:F329 (talk) 18:24, 29 March 2016 (UTC)

Suggestion to split the page[edit]

There should be two different pages on virtual particles, one called virtual particles (physics), and one called virtual particles (popular science). The meanings assigned are completely different in both cases, and mixing up these different notions causes considerable confusion and misunderstandings. See "Misconceptions about Virtual Particles"

The same applies for the treatment of virtual particles in various related pages, in particular [se below]

I don't know about a split, but this would be a really helpful section in themain article. 2601:647:4501:2510:A50B:52A3:3E37:1D2D (talk) 06:01, 18 July 2016 (UTC)

History / anti-particle confusion[edit]

The last sentence in the intro about virtual particles being unrelated to anti-particles seemed like a non-sequitur, until I got down to the "History" section, which seems to be entirely about anti-particles (or, even more confusingly, solid-state electron holes) -- and some comments here indicate that either these concepts are very frequently confused, or I am not understanding something properly.

So, I'm just removing the history section.

2601:647:4501:2510:A50B:52A3:3E37:1D2D (talk) 05:57, 18 July 2016 (UTC)