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Ranku
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Why is a photon considered to be its own antiparticle? What distinguishes a photon from an antiphoton? When photon and antiphoton collide do they annihilate?
Demystifier said:Actually, it would be more correct to say that antiphoton does not exist.
Ranku said:So how do you define the antiparticle of a photon, if antiphoton doesn't exist? Which of the quantum numbers of a photon are 'opposite/different' in its antiparticle?
Meir Achuz said:Particles like the photon and the pi zero that are their own antiparticles are eigenstates of the charge conjugation multiplicative operator C. The photon has eigenvalue -1, and the pi zero has eignevalue +1.
Meir Achuz said:Two photons can ( and do) annihilate into other particles in just the same way that an electron and a positron can.
SpectraCat said:Can't the same question be asked of any "force carrier" particle? Photons are (massless) carriers of the EM force, and are emitted when charge-carrying particle/antiparticle pairs annihilate. Gluons are the (also massless) carriers of the strong force, and are emitted when color-carrying particle/antiparticle pairs annihilate. So perhaps it is generally true that these massless carrier particles have no antiparticles? I guess that may be a bit ambiguous, since QCD requires 8 distinct kinds of gluons, and I guess none of them have ever been observed directly, but I have not read that they are generally organized into gluon-antigluon pairs.
Meir Achuz said:Particles like the photon and the pi zero that are their own antiparticles are eigenstates of the charge conjugation multiplicative operator C. The photon has eigenvalue -1, and the pi zero has eignevalue +1.
DrDu said:They can have different energies, but note that this depends on the reference system.
The two photons can only anihilate if they do not travel exactly in the same direction. But then you can find a reference system where one is red shifted and the other one blue shifted so that their energies coincide and they impact head on. This is analogous to the scattering of massive particles in the laboratory frame vs the rest frame of the center of mass.
Ranku said:From what I know of eigenstates, or rather energy eigenstates, is that they represent the states of a system that correspond to definite values of quantized energy. So does a photon and an antiphoton have different energies?
SpectraCat said:Can you please describe such an annihilation experiment more fully, for the case of a low energy photon, such as a 532 nm photon propagating in the +x direction and plane polarized along the y-axis in some lab-fixed frame. What are the characteristics of the "antiphoton" corresponding to this particle, and what is emitted during the annihilation event to conserve energy?
I can't see how any other particles besides more photons could be emitted in this case, and in that case, how can you tell the difference between an annihilation event and a scattering event? Of course, I am not familiar with the full "menagerie" of sub-atomic particles ... are there other candidates for emission in such an annihilation?
DrDu said:Two photons may anihilate e.g. into an electron and a positron. This requires at least two photons having 511 keV, the rest energy of the two electrons formed. I think the only anihilation process possible for visible light would be the production of a neutrino and an antineutrino which are nearly massless, which is a phantastically improbable.
DrDu said:The anihilation of two photons with the formation of an electron and a positron is just the time reverse of the anihilation of an electron and a positron to form two gamma photons.
What else do you expect to happen in the anihilation process? The energy is conserved, so new particles have to be produced.
Frame Dragger said:...And does this occur in nature?
DrDu said:Two photons may anihilate e.g. into an electron and a positron. This requires at least two photons having 511 keV, the rest energy of the two electrons formed. I think the only anihilation process possible for visible light would be the production of a neutrino and an antineutrino which are nearly massless, which is a phantastically improbable.
SpectraCat said:The two photon case is easier to think about ... basically any photon-photon interaction which has a) more than 1.022 GeV energy and b) conserves momentum (such as two counter propagating 511 MeV gamma rays) has the potential to generate spontaneous pair production.
torquil said:I think you meant 1.022MeV and 511keV
Torquil
A photon is a fundamental particle of light, while its antiparticle is known as an antiphoton. They both have the same mass and spin, but have opposite electric charge.
Photons and antiphotons can be created through various processes, such as particle-antiparticle annihilation or through certain nuclear reactions. They can also be created in high-energy collisions, such as those that occur in particle accelerators.
Photons and antiphotons have zero rest mass, travel at the speed of light, and do not experience the passage of time. They also have a wave-particle duality, meaning they can behave as both particles and waves.
Photons and antiphotons can interact with matter through a process known as pair production, where they can create an electron-positron pair. They can also be absorbed or reflected by matter, depending on the properties of the material.
Yes, photons and antiphotons have a wide range of practical applications, such as in telecommunications, solar panels, and medical imaging. They are also being studied for use in quantum computing and encryption.