What is Virtual photon: Definition and 25 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. E

    B Virtual photons as force carriers

    (My multipart question is from a very naive perspective, so sorry if it is rife with misunderstandings. Please answer conceptually, with as few & as simple equations as possible. I think that all of the answers to these questions should be understandable to a high schooler, though maybe the...
  2. docnet

    I Can an electron in a magnetic field radiate a virtual photon?

    In Theoretical Minimum: Quantum mechanics, Leonard Susskind describes an electron in the higher energy spin state in a magnetic field radiates a photon of energy ##\hbarγ|B_0|## and flips into the lower energy spin state. I am wondering if this photon is related to the "virutal photon" that...
  3. L

    A Timescale of virtual photon interaction in particle scattering

    I'm studying the electron-proton deep inelastic scattering. In the notes that I'm studying from the author states that the time-scale for a virtual photon to interact with a proton is ##τ\sim\frac{1}{Q}##, where ##Q## is the momentum transfer with ##Q\gg M##, which is the mass of the proton. I...
  4. P

    I The virtual photon can turn into a virtual electron positron?

    for example, when does an electron repel another electron with an electromagnetic disturbance?
  5. F

    B What happens to virtual photons when an EMF is extinguished?

    Let's say I feed the same electrical signal into the opposed windings of a contrawound toroidal coil, and that this results in their individual electromagnetic fields cancelling to "zero". Can someone explain what in turn happens to the virtual photons associated with those canceled fields? For...
  6. T

    I A special relativity explanation for the Lorentz Force?

    I am still a bit puzzled by this video: Does this mean that force exerted on an electrically charged particle facilitated by moving through magnetic field B is due to special relativity, and not virtual photons acting as magnetic force carriers? Thanks
  7. Ryan Reed

    Do Electrons Excite the EMF or do the Virtual Photons?

    Do electrons excite the EM field or do they just create virtual photons that do? If you could only see EMF excitations, would you see the electrons or virtual photons coming from the electrons?
  8. nuclearhead

    Can you answer this virtual photon paradox?

    In order to get my head around virtual particles I've created the following question. Maybe some bright person can answer this. If I can answer this question I feel I would have the required understanding to explain virtual particles to other people. In the diagram below, A is a radioactive...
  9. 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
  10. 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...
  11. D

    Is a Virtual Photon Flux the Same as Ether?

    Hi, I have a thought experiment I'd like to share along with a couple of quotes. First, we consider the moment when a body goes from have exactly zero charge to a +Q charge. At that moment, by definition of E field a distance r from point charge q, we have a field propagating from point...
  12. L

    Klein Gordon & spacelike/timelike virtual photon

    Homework Statement See attachment. Homework Equations The Attempt at a Solution So I have shown that the plane wave sol'n satisfies the Klein-Gordon equation by subbing in and reducing the equation to: E^2 = p^2c^2 + m^2c^4 which reduces to: E = pc for an m = 0...
  13. J

    Mass and velocity of virtual photon in Bhabha Scattering

    Homework Statement Determine the mass of the virtual photon in each of the lowest-order diagrams for Bhabha scattering (assume the electron and positron are at rest). What is its velocity? (Note that these answers would be impossible for real photons) Note: You can "just write down" the...
  14. B

    What is a virtual photon and how is it used in quantum field theory?

    Hello all Does virtual photon have energy ? Does virtual photon travel same as speed of light ? That's energy how can calculate ? when a photon absorbed by electron , photon destroyed or changes to virtual photon ?
  15. E

    Distinction between real and virtual photon

    a.) One electron emits one real photon and it hits another electron. b.) One electron emits one virtual photon and it hits another electron. (Repulsion because of charge repulsion) What is gradual transition between cases a. and b. ? Or maybe, does it not exist?
  16. B

    What happens when a photon meets a virtual photon of the same wavelength?

    As I understand it, photons are their own anti-particle, and at all points in space there are a lot of virtual particle-antiparticle pairs being created and annhilated (perhaps infinite?), so it would seem to me that on it's journey from point A to point B that there is at least some likeliehood...
  17. N

    Is it possible a virtual photon is massive particle?

    Please teach me this problem: The classical field of real photon obey Maxwell equations,so the speed of light is c=1,therefore real photon is massless particle.But I think virtual photon maybe not obey Maxwell equations because virtual particle is the fluctuation of vacuum.So maybe virtual...
  18. S

    Weak Electron Interaction: Virtual Photon Effects?

    hi, let's suppose 2 electrons are far away each other and therefore they interact very weakly. i wonder if in such case there are as many virtual photons in the case they are very close to each other? because i know that only 1 electron in complete vacuum generates an electromagnetic field and...
  19. S

    Deriving Coulomb's Law: Exploring Virtual Photon Exchange Theory

    derive Coulombs law of electrostatic force by using virtual photon exchange theory of electrostatic field
  20. N

    Energy conservation for virtual photon

    In introducing the concept of 'virtual photon',Halzen Martin writes (ch#1,P#7) "An ekectron emits a photon (the quantum of electromagnetic field) and as a result,recoils in order to conserve momentum.it is clearly impossible to conserve energy as well,so the emitted photon is definitely not a...
  21. D

    Question: What is Virtuality for a Virtual Photon?

    What is the Virtuality for a virtual photon (Q^2). How's it defined? What is the virtual photon's frequency then? Any relations between them? Thanks. :!)
  22. E

    Kinetic energy change in virtual photon exchange

    I understand (vaguely) how momentum is exchanged via virtual photons in electromagnetic interactions. But how do the changes in kinetic energy occur? For instance, a proton and electron are at rest separated by a distance x. The proton emits a virtual photon and recoils in the direction of...
  23. S

    Calculating Virtual Photon Energy between +q and -q Charges

    Charges of +q and -q are separated by a distance L. What would be a typical energy of a virtual photon they exchange?
  24. J

    Virtual Photon Lifetime: Proton in Atom Nucleus

    QFT states that all forces are due to the exchange of virtual particles, I'm interested in photons and their role in the EM force. I was wondering what the maximum time allowed for existence of an exchange photon is when it's emmitted from a proton in the nucleus of an atom. I'm thinkin' that...
  25. L

    Electrostatic force and virtual photon exchange

    Hello, although being graduated in physics (but not being an expert on QED) I find myself embarassed in trying to explain in very simple terms how the electrostatic force arise from the exchange of virtual photon. Especially when it comes to actually reduce all calculations to the expected...