What is Virtual particle: Definition and 45 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.

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  1. 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...
  2. 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?
  3. J

    I Schwinger effect verified by Unruh temperature?

    According to https://arxiv.org/abs/1407.4569, equation (2.15), the Schwinger electron-positron pair production rate in Minkowski space, ##N_S##, is given in natural units by $$N_S=\exp(-\frac{m}{2T_U})$$ where the `Unruh temperature for the accelerating charge', ##T_U##, is given by...
  4. Marrrrrrr

    A Virtual Fermions and Pauli Principle

    Hi guys, Do virtual particles, when they are fermions, obey Pauli exclusion principle as real fermions do? More specifically, what I am wondering is the following: Fermion fields would have some energy at every point in spacetime due to the uncertainty principle. Now, is it possible for the...
  5. A

    I 'Real particle and virtual particle interactions' Part 2....

    Hi folks, I number of years ago, I asked a question about real particles interacting with virtual particles - since then, I've learned a little bit (maybe not too much :-), but I'm still curious about one thing. Original thread here...
  6. LarryS

    I Why must force-carrying particles be virtual?

    Why must photons, for example, that carry the EM force be virtual? Is it because they are tied to gauge invariance and that is not observable? Thanks in advance.
  7. M

    B Virtual Particle Speed: Is It Measurable?

    I'm reading up on relativity, but it confuses me. If I observe a virtual particle pop up in empty space, what sort of average speed would that particle have? It cannot depend on my reference frame, because the particle doesn't know about that. Or perhaps it does, as my observation ties it into...
  8. A. Neumaier

    Insights The Physics of Virtual Particles - Comments

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  9. J

    How does a virtual particle becomes a point interaction?

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  10. J

    I Are virtual particles real or just math filler

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  11. A

    Is Matter Created continuously?

    I've studied in many books, from which I learned that a vacuum is not truly a vacuum, that is, virtual particles are created every time. And I had also learned that the universe is left handed, that is a small non obeying in parity symmetry(individually), resulted in production of around one in...
  12. AlanKirby

    Do all exchange bosons violate energy conservation?

    Hi, so my question is along the lines of the following: Since the strong and EM forces are mediated by massless exchange particles, due to Heisenbergs uncertainty principle these forces are long range. Well, ok. But the weak force is mediated by W and Z bosons which are massive hence they can...
  13. Q

    Inside protons: origin of the sea quarks

    I have seen in many places, for example here, the statement that the proton consists of valence quarks and sea quarks. I am somewhat confused as to where this picture comes from. The sea quarks are virtual quark-antiquark pairs. I have encountered virtual particles only in the context of...
  14. L

    Qm virtual particle force on wire, acrose the universe

    What would be the virtual particle force acting on a wire, which go's from say Earth to any part of the universe reseeding away from us at near light speed, or grater ?, would it break, and how would we compute it ? Lachlan
  15. M

    What is the polarization of a virtual photon

    I read in few places that the virtual photons have longitudinal polarization while in some papers they say virtual photons have both transverse and longitudinal polarizations. Can anyone please help me to understand this
  16. B

    Understanding virtual particles

    what is the correct understanding of a virtual particle? the popular science books would have us believe that a virtual particle magically pops up out of the woodwork, steals some energy and then puts it back before it ( the particl) disappears. Like a thieving employee who steal $100 out of the...
  17. D

    What is an Exchange Particle? A-Level Physics Explained

    I really want to understand the answer to this question. Q: What is an exchange particle? A: A virtual particle that let's force act between particles in an interaction. This answer was given in my A-Level textbook but I can't for the life of me decode what it means. For example in beta minus...
  18. M

    Interpreting Casimir Effect along with Hawking's Radiation

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  19. JohnPrior3

    What are virtual particles and why do they have large implications?

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  20. M

    Destruction of virtual particles and virtual particle pairs

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  21. A

    Virtual particle creation in black holes

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  22. S

    Heisenberg's Uncertainty vs Virtual Particle Fluctuations

    I notice that many physicists say that virtual particle fluctuations occur in space "because Heisenberg's Uncertainty Principle allows them" Is this really the best form of reasoning? Isn't it actually the other way around - that because virtual particle fluctuations happen, then there is a...
  23. B

    Do virtual particle pairs interact gravitationally?

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  24. C

    Virtual Particles: Sources from Leading Universities

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  25. C

    Virtual particle production beyond the event horizon.

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  26. T

    Virtual Particle Creation Rate Near an Event Horizon

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  27. S

    Can the Big Rip affect virtual particles' annihilation process?

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  28. edpell

    Can Virtual Particle Lifetimes Be Calculated?

    Is it possible to calculate the lifetime of a virtual particle? For example is an electron and a proton form a virtual neutron that is off shell by 0.8Mev how long will it last? Is this something we can calculate? At first I would think it would be short lived because of the 0.8MeV energy...
  29. C

    Can a virtual particle create another virtual particle?

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  30. D

    Uncertainty principle, virtual particle pairs and energy

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  31. S

    Virtual particle in path integral and perturbative approaches

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  32. A

    Delay of virtual particle pair annihilation

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  33. M

    Virtual particle propagators in QFT

    I am reading a nice book (Quarks and Leptons, by Halzen and Martin) about particle physics. It states that the general form of the propagator of a virtual particle is: \dfrac{i\sum_{\text{spins}}}{p^2 - m^2} I see that this is the case for the Dirac propagator...
  34. N

    Independent virtual particle after mind experiment annihilation

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  35. A

    OMG another Virtual Particle question. Runnnn

    Hahaha, yeah I did a search on these forums for questions regarding Virtual Particles and it seems its "the horse that's been beaten to death with a stick". But, I still have questions so please try and answer them because the people on there are much more versed than me in physics. I am a...
  36. R

    Exploring the Existence of Virtual Particles: A Comprehensive Analysis

    i've been scrolling through the archives and can't get an answer if virtual particle exist or not or are real,I get different answers looking on websites.
  37. Feeble Wonk

    Virtual Particle Density in Expanding Space Time

    Please have pity on a poor ignorant layperson struggling for understanding... and keep in mind that I am mathematically impotent. I am trying to wrap my mind around the concept of expanding space-time with regard to quantum foam. Could someone please explain whether the "density" of quantum...
  38. T

    Particle or Virtual Particle: What's the Difference?

    what is the differace between a particle and a virtual particle?
  39. T

    Virtual Particle Interaction: Will Virtual Boson Leave Track?

    Suppose there's an interaction AB -> CD, that goes via a virtual W boson, my question is, will the virtual boson leaves a track in the detector even though it's virtual ?
  40. J

    Virtual particle energy-momentum

    A mentioning about virtual particle problem in my other thread just reminded me of some thoughts, which I now succeeded putting together. When calculating cross sections in QFT, we encounter terms like this \langle 0|a_{\textbf{k}'} a_{\textbf{p}'} a^{\dagger}_{\textbf{p}_1}...
  41. J

    Really a virtual particle sea?

    I've often heard the argument that vacuum is full of virtual particle pairs that get created and annihilated, but in fact the ground state of the harmonic oscillator is orthogonal to all excitation states, so shouldn't the vacuum, when in ground state, actually be empty of all particles? What is...
  42. A

    Virtual Particle Anihilation

    When a vritual particle pair anihilates, does the energy radiate away in the form of gamma rays, or is it simply used to "repay the debt" of whatever energy that was borrowed to create those particles in the first place? I would assume the latter, but I would like a confirmation on that. Thanks.
  43. M

    Virtual particle and event horizon

    Was wondering: In Hawkins's " Univers in a nutshell" book, he talks about the behavior ov virtual particle pairs around the event horizon of a black hole. My understanding is that one of the antiparticle of the pair can be absorbed by the black hole. This makes for the release of the particle (...
  44. turbo

    Orientation of virtual particle pairs in local fields?

    Can the presence of gravitational, or electro-magnetic fields cause virtual particles to arise with a preferential physical orientation? Logically, the virtual particles should not emerge in a preferred orientation if they arise spontaneously, and can't be acted upon by local fields until...
  45. O

    Real photon - virtual particle collisons

    Seems to me that in deep space real photons collide often with virtual particles. Is that a reasonable theory? If so, what are the (approximate or ball-park) statistics? What does happen? Does the putative virtual particle involved in a collision with a real photon become real? What are the...
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