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The photon has no electric charge, [17] [18] is generally considered to have zero rest mass [19] and is a stable particle. The experimental upper limit on the photon mass [20] [21] is very small, on the order of 10 −50 kg; its lifetime would be more than 10 18 years. [22] For comparison the age of the universe is about 1.38 × 10 10 years.
The graviton is a hypothetical tensor boson proposed to be the carrier of gravitational force in some quantum theories of gravity, but no such theory has been successfully incorporated into the Standard Model, so the Standard Model neither predicts any such particle nor requires it, and no gravitational quantum particle has been indicated by experiment.
However, there is no experimental evidence that the photon has a composite structure. Some of the problems for the neutrino theory of light are the non-existence for massless neutrinos with both spin parallel and antiparallel to their momentum outside the Einstein-Cartan torsion [13] [14] and the fact that composite photons are not bosons. [15]
According to the Big Bang theory, in the early universe, mass-less photons and massive fermions would inter-convert freely. As the photon gas expanded and cooled, some fermions would be left over (in extremely small amounts ~10 −10) because low energy photons could no longer break them apart. Those left-over fermions would have become the ...
The photon having non-zero linear momentum, one could imagine that it has a non-vanishing rest mass m 0, which is its mass at zero speed. However, we will now show that this is not the case: m 0 = 0. Since the photon propagates with the speed of light, special relativity is called for. The relativistic expressions for energy and momentum ...
It has no intrinsic spin, and for that reason is classified as a boson with spin-0. [34] The Higgs boson plays a unique role in the Standard Model, by explaining why the other elementary particles, except the photon and gluon, are massive. In particular, the Higgs boson explains why the photon has no mass, while the W and Z bosons are very
Electromagnetic radiation can be viewed in terms of particles rather than waves; these particles are known as photons. Photons do not have a rest-mass; however, photons are never at rest (they move at the speed of light) and acquire a momentum nonetheless which is given by: = =, where p is momentum, h is the Planck constant, λ is wavelength ...
The study of neutrinos is important in particle physics because neutrinos typically have the lowest rest mass among massive particles (i.e. the lowest non-zero rest mass, i.e. excluding the zero rest mass of photons and gluons), and hence are examples of the lowest-energy massive particles theorized in extensions of the Standard Model of ...