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Virtual Particles

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Virtual Particles

A one-loop vacuum polarization. A photon (the squiggly line) splits into a proton and anti-proton (the loop) and then meet back up, destroy each other, returning to their photon state.

Public Domain (from Wikimedia Commons)
Definition:

Virtual particles are particles that come into existence for a limited time. They are predicted by the equations governing quantum physics and these predictions are strongly confirmed by and consistent with physical evidence and experimental results.

There are a number of ways that virtual particles come up in physics. Some of the most notable are:

Gauge Bosons

In quantum physics, forces result from the interactions of quantum fields, which can also be represented by particles called bosons. (These particular types of bosons are called gauge bosons, because the exact theory that describes them is called gauge theory.) The gauge bosons for the four fundamental forces are:
  • Photons - Electromagnetic interactions between charged particles in which the particles create short-lived photons, which exist just long enough to exchange the information between the charged particles.
  • Gluon - Gluons are the gauge boson that mediate the strong nuclear force.
  • W Boson and Z Bosons - There are two different types of gauge bosons that are involved in mediating the weak nuclear force.
  • Graviton - The graviton is a theoretical particle that is incorporated as a gauge boson in most theories of quantum gravity. Gravitons have not been detected or confirmed experimentally yet.

Virtual Particle Pairs

One of the most curious concepts in quantum physics is the idea that particles can spring out of nothingness. It turns out a region of empty space (containing no energy, in theory) can bring into existence a pair of particles: a normal particle and its related antimatter particle (or antiparticle). Since the energy associated with the creation of the particle and the energy associated with the creation of the anti-particle is negative, these two particles together contain a net energy of zero. The universe essentially "allows" them

This is demonstrated in the graphic at the top right, which shows a portion of a Feynman diagram where this takes place. The Feynman diagram from left to right represents particles moving forward through time. The photons are represented by the squiggly lines. The circle represents a particle and antiparticle coming into existence. (The bottom arrow, which moves backward in time, represents the antiparticle.) When they meet up they annihilate each other, emitting a new photon.

Though this seems amazing, but it has been tested and confirmed through experiments to detect the Casimir effect. The existence of these sort of virtual particle pairs provided the basis for one of Stephen Hawking's most startling claims, that black holes actually emit a form of radiation (aptly called Hawking radiation).

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