What is Virtual particles: Definition and 189 Discussions

In physics, a virtual particle is a transient quantum fluctuation that exhibits some of the characteristics of an ordinary particle, while having its existence limited by the uncertainty principle. The concept of virtual particles arises in perturbation theory of quantum field theory where interactions between ordinary particles are described in terms of exchanges of virtual particles. A process involving virtual particles can be described by a schematic representation known as a Feynman diagram, in which virtual particles are represented by internal lines.Virtual particles do not necessarily carry the same mass as the corresponding real particle, although they always conserve energy and momentum. The closer its characteristics come to those of ordinary particles, the longer the virtual particle exists. They are important in the physics of many processes, including particle scattering and Casimir forces. In quantum field theory, forces—such as the electromagnetic repulsion or attraction between two charges—can be thought of as due to the exchange of virtual photons between the charges. Virtual photons are the exchange particle for the electromagnetic interaction.
The term is somewhat loose and vaguely defined, in that it refers to the view that the world is made up of "real particles". It is not. "Real particles" are better understood to be excitations of the underlying quantum fields. Virtual particles are also excitations of the underlying fields, but are "temporary" in the sense that they appear in calculations of interactions, but never as asymptotic states or indices to the scattering matrix. The accuracy and use of virtual particles in calculations is firmly established, but as they cannot be detected in experiments, deciding how to precisely describe them is a topic of debate.

View More On Wikipedia.org
  1. AditiShahani

    Admissions Exploring the Universe: Pursuing a PhD in High Energy Physics

    Can somebody help review my SOP. I’ve already applied to one school but have many other schools to apply to, I know it needs lots of improvement so harsh critical comments are welcomed. Thankyou. I first encountered the concept of virtual particles during my studies of the Casimir effect; I...
  2. Donut

    I Virtuals particles, vacuum and infinite energy

    Hi guys I have a question for you. Virtual particles can appear anywhere and when they have enough energy they turn into real. And if it happens long enough in a vacuum, will it remain a vacuum? If not, then is matter infinite?
  3. jcalises

    B Virtual particles and Heisenberg

    I registered yesterday in this forum with the intention of someone clarifying me how the Heisenberg uncertainty principle can explain the existence of virtual particles. More energy implies less lifetime is only possible if ΔE Δt = h/4Pi, but that's not Heisenberg's principle, the principle is...
  4. J

    I Quantum fluctuations & 'virtual particles'

    I've been reading about how language around virtual particle fluctuations is metaphorical. This is helpful: https://www.physicsforums.com/insights/vacuum-fluctuation-myth/ I'm just trying to understand a bit more from a layman's point of view. I found Matt Strassler's article 'Virtual...
  5. R

    B Why exactly do Virtual Particles not violate Conservation of energy?

    Recently I've read more about virtual particles and at first I tought that there were only doubts that virtual particles are not interpretable with the help of uncertainty principle. Furthermore it can't be used an an "excuse" for the temporary violation of the conservation of energy. Can...
  6. Ranku

    I What are the Misconceptions Surrounding Virtual Particles?

    Are the typical energies of virtual particles lower than real particles?
  7. e2m2a

    B Virtual Particles Momentum Transfer

    My understanding is that virtual particles don't really exist. However, they somehow come into existence under certain circumstances. For example, in the Casimir Effect the virtual particles on the outside of the plate now have the capacity to transfer momentum and kinetic energy to the...
  8. LuisBabboni

    I Virtual particles and Heisenberg

    Hi people. Having as uncertainty principle that ΔE Δt≥ h/4Pi, why Δt≤ h/4PiΔE to allow the existence of a virtual particle? How ≥ becomes ≤ ? I think... real particles must obey ≥ so any particle that do not obey that is a virtual particle and thus why virtual particle needs to obey Δt≤...
  9. HexHammer

    B Virtual Particles are not Dark Matter?

    So far as I understand it, a photon can split up and create particles with matter, even though the photon is massless, yes? So if a photon can be more places at the same time, it should be able to create multiple particles all at once? So how is this not Dark Matter?
  10. A

    I Virtual particle content of the vacuum state....

    Hi all, One more virtual particle question (sorry all!): for individuals who would take virtual particles as being 'real' (but unobservable), what is their understanding then of the content of the vacuum? For example, if I place a electron all by itself in the vacuum (thus making it no longer...
  11. A

    I Frank Wilczek on Virtual Particles and Summing diagrams....

    Hi all, - an initial apology - there are a large number of threads on virtual particles on the site, and I apologize for adding another one. I had two questions - on a related note, the guidance provided by @A. Neumaier's FAW on virtual particles has been highly valuable for a novice . 1) Upon...
  12. F

    B Where do virtual particles come from?

    I watched a Youtube! video on black holes, and it said that black holes evaporate via Hawking radiation. If I understood the video correctly a virtual particle can pop into existence just outside the event horizon, and that one of the resulting pair can subsequently fall back into the black hole...
  13. A

    I On-shell virtual particles and 'physical' Hilbert spaces....

    Hi all, Just a clarification question as I'm learning. It's possible to have Feynman diagrams where the internal lines (virtual particles) are in fact on shell. 'On shell' would imply 'observable,' (maybe?) but as noted in @A. Neumaier's great FAQ, only sets of Feynman diagrams have predictive...
  14. Nonametheone

    Can a virtual particle from a maget accelerate another particle on a linear path?

    Summary: Can a particle accelerator accelerate gaseous fuel? Does space-time differ for detonating ionized fuel moving near the speed of light within a magnetic field such as a particle accelerator?
  15. Ranku

    B Understanding Virtual Particles: Speed and Rest Mass

    Do virtual particles travel at the speed of light, or do they have 'virtual rest mass'?
  16. Lunct

    B Can virtual particles have an imaginary mass?

    I was talking to a physicist who said to me that virtual particles can have a mass of a constant times by i ,as in the root of -1. I have been thinking about this more and it intrigues me. I have done some research into this and can't find further details. If they have an imaginary mass does...
  17. K

    I Confused about virtual particles

    Hello! I am a bit confused about the distinction between virtual and real particles. For example a Z boson, which has a very short lifetime, in all experiments will decay to some other stable particles (i.e. it is detected through its decay). This means that it will always appear as a...
  18. M

    I Why are 'virtual particles' allowed to be 'off-shell'?

    If virtual particles are supposed to be some sort of Green's function excitation of a field following a particular Lagrangian or PDE (induced by the presence of another particle, free or virtual), then why are they allowed to be "off shell"? (Especially: Why are they allowed to be nonzero...
  19. A

    B Virtual Particles and nothingness

    According to what I have read and watched (I am new to the subject) the empty space is actually full of temporary virtual particulars that spontaneously and continuously emerge from nowhere and then disappear from the nothingness again but from where comes so much energy for so much creation of...
  20. BadgerBadger92

    B Are electrons virtual particles?

    Since electrons pop in and out of existence, are they virtual particles?
  21. RosutoTakeshi

    Superman created virtual particles?

    Comic is Superman/Batman #80 Superman explains that virtual particles are always spontaneous generated And that he's using his heat vision to (excite) the vacuum in order to accelerate the process. He's generating more virtual particles So my question is, how much energy or heat did...
  22. Malek

    B Speed of Light & Virtual Particles: Is There a Connection?

    Are there any relationships between the speed of light and the virtual particles in the vacuum? I mean that, Can I call it as a medium of propagation of a light beam?
  23. DGator86

    B Planck level effects of virtual particles

    Knowing that virtual particles appear and disappear at the Planck length, what is the effect of the annihilation on space-time where the particles used to be?
  24. P

    I Virtual particles in Feynman diagrams

    In the first diagram above, if I understand it correctly, the photon turns into an electron positron pair and then back again to a photon. However, what exactly is happening in the second diagram at the bottom left hand corner? Is the electron being converted to an electron photon pair?
  25. F

    I Two questions about "The Physics of Virtual Particles"

    Arnold Neumaier, I have 2 elementary questions about your article “The Physics of Virtual Particles”. 1. In the paragraph headed “States.” on p. 4, of 13, you talk about states of a physical system, with a mixed state specified by a Hermitian operator ρ of trace 1 acting on the Hilbert...
  26. Mcbleak

    B Expanding space time and Virtual particles

    If space time (the universe) is infinitely expanding what happens when it rips? Have we observed Virtual particles in an area and counted them? Does the expansion of space time affect the amount of Virtual particles in a particular area? Is it theoretically possible to expand space time to a...
  27. C

    I In the Casimir effect, can you slide plates unopposed by force?

    How would sliding the plates parallel to each other in order to separate them (they are prevented from contacting to avoid friction) require the same amount of energy as pulling them apart? You're not pushing against the force (the net force at the edges pulling it back is balanced by opposite...
  28. F

    I Does the path Integral contain virtual particles?

    So Feynman's path integral considers every possible path that a particle could take from start to end. In that process, there would be a path which contains a segment from, say, A to B at time t. But there could also be a path with a segment from B to A at that same time, t. If so, would this...
  29. S

    B Exploring the Existence and Energy of Virtual Particles in Quantum Mechanics

    Hello everyone, I am here today with a doubt, I first apologize for my ignorance on the subject, but come on, the uncertainty principle predicts that in the "vacuum" there are virtual particle that cancels out constantly, but my question is: which is the amount of energy that exists in this...
  30. B

    I Probability of creation of virtual particles

    Is it correct to assume that all known particles may be created as virtual particles in the vacuum? If so, is there a higher probability of a particular particle being produced than say some other particle type. For example, is an electron more likely to be created as a virtual particle than a...
  31. SlowThinker

    B Brownian motion from virtual photons?

    This a really simple question: If I have, say, 2 ions close to one another, and measure their repulsion very precisely, is the force constant, or is it a series of little pushes caused by individual virtual photons? I know there are many misunderstandings about virtual particles, but I'm not...
  32. J

    I Virtual Particles and Energy Scales

    Just a basic question which I will ask through an example: An electron and positron can scatter by annihilating to form either a virtual Z or virtual photon, either of which can then pair produce to give an electron/positron pair (amongst an infinity of other processes whose contributions need...
  33. M

    I Virtual Particles: Speed & Impact on Rocket

    Hi, quantum fluctuations enable virtual particles in space. If a rocket travels through space, these particles (real ones of antiparticle-particle pairs) could impact it. Is the effect of an impact dependent of relative speed of such particle and the rocket? For example rocket could be warmed...
  34. D

    I Virtual Particles and Charge Screening

    The following article says virtual particles don't exist or are just book keeping device. https://www.physicsforums.com/insights/physics-virtual-particles If that's the case, then how do you explain charge screening? We observe the charge of an electron to be less than the bare charge, or what...
  35. M

    B How long can a virtual particles exist in a vacuum state?

    As much as I have understood, virtual particles keep appearing and disappearing in a vacuum state. This leads to zero-point energy, Casimir effect etc. Now, I want to know if there is a lifetime (i.e. a time limit) for which these virtual particles can exist before disappearing. Also can there...
  36. A. Neumaier

    Insights The Vacuum Fluctuation Myth - Comments

    A. Neumaier submitted a new PF Insights post The Vacuum Fluctuation Myth Continue reading the Original PF Insights Post.
  37. N

    B Is dark/vacuum potential energy infinite?

    And virtual particles potential energy is infinite too? As more and more dark energy is created does this mean that the potential energy of dark energy is infinite? Does that happen for virtual particles in vacuum and vacuum energy too?
  38. Thomas Eaton

    B Virtual Particles; Making the Universe an Open System?

    The question here is simple; would the existence of virtual particles make the universe an open system? And if not, why? I thank all who consider this question for their time and would love to hear an answer.
  39. J

    I Loop Quantum Gravity and Virtual Particles....

    Hi all, Following up on another post - for a layman, can someone describe the status of virtual particles in Loop Quantum Gravity models? Since LQG avoid UV divergences, and has a different structure from field-based theories, are virtual particles still talked about? (in the context of closed...
  40. A

    I Clarify interaction between real and virtual particles....

    Hi all, I've read a number of posts on virtual particles (including one of my own), but I'm still confused about one aspect - the interaction between real and virtual particles. Say we have an electron moving from position A to position B. As the electron moves, there should be virtual...
  41. DuckAmuck

    I Black Holes and Charged Particles

    What happens when charged particles fall into a black hole? Say like N electrons fall in, giving the black hole a net charge of -N. Since light cannot escape the event horizon, I imagine electric fields cannot either, since they are mediated by photons. So is that charge effectively lost until...
  42. A

    I The Higgs and virtual particles

    I have been reading the Quantum Diaries here http://www.quantumdiaries.org/2011/03/25/an-idiosyncratic-introduction-to-the-higgs/ and in discussing the Higgs and the LHC experiment he says "The general problem is this: at the LHC, we’re smashing protons into one another. The protons are each...
  43. KarminValso1724

    B Could dark energy just be caused by virtual particles

    The tital pretty much explains it all? Why would this be impossible or not explain everything?
  44. newjerseyrunner

    B What causes recombination of virtual particles?

    In a situation like this: What causes the particle/antiparticle pair to recombine? They obviously will have opposite charge, is there a virtual photon being exchanged between them that's omitted from Feynman diagrams? That would imply that it's mathematically irrelevant, I know than these...
  45. Ranku

    I Virtual Particles: Inflation vs Present Universe

    Are virtual particles of the false vacuum during inflation indistinguishable from virtual particles of the true vacuum of the present universe?
  46. A. Neumaier

    Insights Misconceptions about Virtual Particles - Comments

    A. Neumaier submitted a new PF Insights post Misconceptions about Virtual Particles Continue reading the Original PF Insights Post.
  47. A. Neumaier

    Insights The Physics of Virtual Particles - Comments

    A. Neumaier submitted a new PF Insights post The Physics of Virtual Particles Continue reading the Original PF Insights Post.
  48. F

    I Virtual particles in Feynman diagrams and not

    I know some people here hate the subject of virtual particles. So I will try to narrow my questions. Granted, virtual particles are just attempts to describe the math and are not real in and of themselves. But there seem to be a couple of different kinds of virtual particles (in the math)...
  49. M

    Quantum non-locality and vacuum polarization

    Quantum particles are not localized before they are observed, as shown with the Young double slit experiments and those with entangled particles. On the other side, vacuum is filled with virtual particles. Are the non-localized particles responsible for the virtual particles? or only for a part...