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Annihilation
 
 
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Annihilation is defined as "total destruction" or "complete obliteration" of an object; having its root in the Latin nihil (nothing). A literal translation is "to make into nothing". Annihilation is the opposite of exnihilation, which means "to create something out of nothing".

In physics
Physics

Physics is the natural science which examines basic concepts such as energy, force, and spacetime and all that derives from these, such as mass, charge, matter and its Motion ....
, the word is used to denote the process that occurs when a subatomic particle
Subatomic particle

A subatomic particle is an elementary particle or composite particle particle smaller than an atom. Particle physics and nuclear physics are concerned with the study of these particles, their interactions, and non-atomic QCD matter....
 collides with its respective antiparticle
Antiparticle

Corresponding to most kinds of particle physics, there is an associated antiparticle with the same mass and opposite electric charge. For example, the antiparticle of the electron is the positively charged antielectron, or positron, which is produced naturally in certain types of radioactive decay....
. Since energy and momentum must be conserved, the particles are not actually made into nothing, but rather into new particles.






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Annihilation is defined as "total destruction" or "complete obliteration" of an object; having its root in the Latin nihil (nothing). A literal translation is "to make into nothing". Annihilation is the opposite of exnihilation, which means "to create something out of nothing".

In physics
Physics

Physics is the natural science which examines basic concepts such as energy, force, and spacetime and all that derives from these, such as mass, charge, matter and its Motion ....
, the word is used to denote the process that occurs when a subatomic particle
Subatomic particle

A subatomic particle is an elementary particle or composite particle particle smaller than an atom. Particle physics and nuclear physics are concerned with the study of these particles, their interactions, and non-atomic QCD matter....
 collides with its respective antiparticle
Antiparticle

Corresponding to most kinds of particle physics, there is an associated antiparticle with the same mass and opposite electric charge. For example, the antiparticle of the electron is the positively charged antielectron, or positron, which is produced naturally in certain types of radioactive decay....
. Since energy and momentum must be conserved, the particles are not actually made into nothing, but rather into new particles. Antiparticles have exactly opposite additive quantum number
Quantum number

Quantum numbers describe values of conserved numbers in the dynamics of the quantum system. They often describe specifically the energies of electrons in atoms, but other possibilities include angular momentum, Spin etc....
s from particles, so the sums of all quantum numbers of the original pair are zero. Hence, any set of particles may be produced whose total quantum numbers are also zero as long as conservation of energy
Conservation of energy

The law of conservation of energy states that the total amount of energy in an isolated system remains constant. A consequence of this law is that energy cannot be created or destroyed....
 and conservation of momentum are obeyed.

During a low-energy annihilation, photon
Photon

In physics, the photon is an elementary particle, the quantum of the electromagnetic field and the basic unit of light and all other forms of electromagnetic radiation....
 production is favored, since these particles have no mass. However, high-energy particle colliders produce annihilations where a wide variety of exotic heavy particles are created.

Examples of annihilation

This is an example of renormalization
Renormalization

In quantum field theory, the statistical mechanics of fields, and the theory of self-similarity geometric structures, renormalization refers to a collection of techniques used to take a continuum limit....
 in quantum field theory
Quantum field theory

Quantum field theory or QFT provides a theoretical framework for constructing quantum mechanics models of systems classically described by field or of Many-body problem....
— the field theory being necessary because the number of particles changes from one to two and back again.

When a low-energy electron
Electron

The electron is a subatomic particle that carries a negative electric charge. It has elementary particle and is believed to be a point particle....
 annihilates a low-energy positron
Positron

The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. The positron has an electric charge of +1, a spin of 1/2, and the same mass as an electron....
 (antielectron), they can only produce two or more gamma ray
Gamma ray

Gamma rays are a form of electromagnetic radiation produced by atom particle interactions, such as electron-positron annihilation or radioactive decay....
 photon
Photon

In physics, the photon is an elementary particle, the quantum of the electromagnetic field and the basic unit of light and all other forms of electromagnetic radiation....
s, since the electron and positron do not carry enough mass-energy to produce heavier particles. However, if one or both particles carry a larger amount of kinetic energy, various other particle pairs can be produced. See electron-positron annihilation
Electron-positron annihilation

Electron-positron annihilation occurs when an electron and a positron collide. The result of the collision is the conversion of the electron and positron and the creation of gamma ray photons or, less often, other particles....
.

The annihilation (or decay) of an electron-positron pair into a single photon, e+ + e- ? ?, cannot occur because momentum would not be conserved in this process. The reverse reaction is also impossible for this reason, except in the presence of another particle that can carry away the excess momentum. However, in quantum field theory
Quantum field theory

Quantum field theory or QFT provides a theoretical framework for constructing quantum mechanics models of systems classically described by field or of Many-body problem....
 this process is allowed as an intermediate quantum state. Some authors justify this by saying that the photon exists for a time which is short enough that the violation of conservation of momentum can be accommodated by the uncertainty principle
Uncertainty principle

In quantum physics, the Werner Heisenberg uncertainty principle states that certain physical quantities, like the position and momentum, cannot both have precise values at the same time....
. Others choose to assign the intermediate photon a non-zero mass. (The mathematics of the theory are unaffected by which view is taken.) This opens the way for virtual pair production or annihilation in which a one-particle quantum state may fluctuate into a two-particle state and back again (coherent superposition). These processes are important in the vacuum state
Vacuum state

In quantum field theory, the vacuum state is the quantum state with the lowest possible energy. Generally, it contains no physical particles. The term "zero-point field" is sometimes used as a synonym for the vacuum state of an individual quantized field....
 and renormalization
Renormalization

In quantum field theory, the statistical mechanics of fields, and the theory of self-similarity geometric structures, renormalization refers to a collection of techniques used to take a continuum limit....
 of a quantum field theory. It also allows neutral particle mixing through processes such as the one pictured here.

Notations


Footnotes


See also

  • Pair production
    Pair production

    Pair production refers to the creation of an elementary particle and its antiparticle, usually from a photon . This is allowed, provided there is enough energy available to create the pair ? at least the total rest mass energy of the two particles ? and that the situation allows both energy and momentum to be conserved ....