Virtual particle
A virtual particles, intermediate particles or particles in a virtual state is a concept from quantum field theory, where it is needed for the theoretical description of the fundamental interactions of elementary particles. One can imagine the virtual state of a particle as a short-lived intermediate state that occurs during an interaction of two particles that are in "normal", ie real states. The virtual particles presented as exchange particles this interaction actually only here, is in a virtual state to the outside but never visible. Thus, the electromagnetic interaction between two electrons is mediated by the exchange of a virtual photon, for example, in quantum electrodynamics. The proof is indirect: The calculated values using this approach are in the experiment with an accuracy of up to 1: confirmed 10 billion. In principle, each particle can have real states and virtual states.
Virtual particles occur in each of the three types of interaction can be described by the quantum field. Virtual particles are components of the Feynman diagrams, each play in a quantum field theoretical perturbation theory a certain term. A Feynman diagram consists of different lines, meet at nodal points, the vertices. The outer lines are distinguished ( those who have a free end ) for incoming and outgoing particles in a real state, and the inner lines (those that connect two vertices ) for virtual particles. In the context of vacuum fluctuations also Feynman diagrams are considered without external lines, ie in which particles emerge from the vacuum and disintegrate again and thus contribute to the vacuum energy. Here only come to virtual particles.
Properties
The main difference between the (real observable ) real particles and the unobservable virtual particles is that energy and momentum do not meet the energy - momentum relation in the virtual state, when the well-defined mass of the same particle in real is condition. We can therefore say that virtual particles have no mass defined, in the jargon, " they are not limited to the mass shell " (or they are not " on- shell" ). For example, transfers the virtual photon in the elastic scattering of two electrons considered in the center of mass system, only pulse, but no energy.
This property can help to illustrate the behavior of a virtual particle: Should there with the same values and in real is condition arise, the conservation of energy would be violated. After the energy-time uncertainty relation may be thought of this for sufficiently short times. The route, which could cover the particle at this time with the speed of light limits the possible radius of any effects. In low-energy processes, the range is just the Compton wavelength of the particle in question. Thus, the finite range of the nuclear forces or the weak interaction is roughly understandable. Thus, for example, is the radioactive beta decay possible because the exchange particle in question (the W boson ) can arise as a virtual particle without energy supply. Due to its large mass, it may affect only the area of a thousandth of a proton radius, however, what the relatively low transition probability and thus explains the interaction has the adjective " weak " is entered. In the same way it is also possible that evidence for the existence of very heavy particles are observed already before the reached in particle collision energy is sufficient to produce them in real is condition.
Quotes
" Virtual particles are spontaneous fluctuations of a quantum field. Real particles are excitations of a quantum field with a useful observation for stability. Virtual particles are transients that appear in our equations, but not in measuring instruments. By supplying energy spontaneous fluctuations beyond a threshold value can be increased, which causes (actually otherwise ) are virtual particles to real particles. "