What is a virtual particle?

Question

Could you give some examples, and relate the virtual particles to the field or interaction they are involved with?

Answer 1

A virtual particle is a subatomic particle whose existence violates the principle of conservation of energy but is allowed to exist for a short time by Heisenberg's uncertainty principle.

In physics, a virtual particle is a particle-like abstraction used in some models of quantum field theory. Virtual particles exhibit some of the phenomena that real particles do such as conservation of charge. Virtual particles cannot be directly detected, and they do not necessarily respect some of the most fundamental laws associated with physical particles. The concept of virtual particles necessarily arises in the perturbation theory of quantum field theory where interactions between real particles are described in terms of exchanges of virtual particles. Any process involving virtual particles admits a schematic representation known as a Feynman diagram which facilitates understanding of calculations.

In other words, their kinetic energy may not have the usual relationship to velocity, indeed, it can be negative. The probability amplitude for them to exist tends to be cancelled out by destructive interference over longer distances and times. They can be considered a manifestation of quantum tunnelling.

There are two principal ways in which the notion of virtual particles appear in modern physics. They appear as intermediate terms in Feynman diagrams; that is, as terms in a perturbative calculation. They also appear as an infinite set of states to be summed or integrated over in the calculation of a semi-non-perturbative effect. In the later case, it is sometimes said that virtual particles cause the effect, or that the effect occurs because of the existence of virtual particles.

Examples :

* The Coulomb force between electric charges. It is caused by exchange of virtual photons. In symmetric 3-dimensional space this exchange results in inverse square law for force,
* The spontaneous emission of a photon during the decay of an excited atom or excited nucleus; such a decay is prohibited by ordinary quantum mechanics and requires the quantization of the electromagnetic field for its explanation,
* The Casimir effect, where the ground state of the quantized electromagnetic field causes a weak, short-range attraction between a pair of electrically neutral metal plates,
* The van der Waals force, which is essentially the Casimir effect between two atoms,
* Vacuum polarization, which involves pair production or the decay of the vacuum, which is the spontaneous production of particle-antiparticle pairs (such as electron-positron),
* Hawking radiation, where the gravitational field is so strong that it causes the spontaneous production of photon pairs (with black body energy distribution) and even of particle pairs.

Answer 2

An electron can be a virtual particle. For example, light can scatter off of light via an exchange of virtual electrons. A virtual particle is one which has to borrow energy from the uncertainty principle in order to exist at all. It can only exist for a short period of time (inversely proportional to the energy borrowed). You won't see the particle itself, but it can mediate interactions between other real particles. That said, most electrons you will actually find in the world (living in atoms and in metals) are not virtual. They have all their energy and can stick around indefinitely.

Answer 3

when u see someting it is by means of a virtual photon