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If photons were not purely massless, their speeds would vary with frequency, with lower-energy (redder) photons moving slightly slower than higher-energy photons. Relativity would be unaffected by this; the so-called speed of light, c , would then not be the actual speed at which light moves, but a constant of nature which is the upper bound on ...
Up to now the photon structure function has only been investigated experimentally by electron scattering off a beam of quasi-real photons. The experiments use the so-called two-photon reactions at electron–positron colliders e − e + → e − e + + h, where h represents all the remaining hadrons in the final state. The kinematics chosen is ...
An FM radio station transmitting at 100 MHz emits photons with an energy of about 4.1357 × 10 −7 eV. This minuscule amount of energy is approximately 8 × 10 −13 times the electron's mass (via mass–energy equivalence). Very-high-energy gamma rays have photon energies of 100 GeV to over 1 PeV (10 11 to 10 15 electronvolts) or 16 nJ to 160 ...
Photons are massless particles of definite energy, definite momentum, and definite spin. To explain the photoelectric effect , Albert Einstein assumed heuristically in 1905 that an electromagnetic field consists of particles of energy of amount hν , where h is the Planck constant and ν is the wave frequency .
Similarly, the total energy of the system is its total (relativistic) mass times the speed of light squared. Systems whose four-momentum is a null vector (for example, a single photon or many photons moving in exactly the same direction) have zero invariant mass and are referred to as massless.
Mass–energy equivalence states that all objects having mass, or massive objects, have a corresponding intrinsic energy, even when they are stationary.In the rest frame of an object, where by definition it is motionless and so has no momentum, the mass and energy are equal or they differ only by a constant factor, the speed of light squared (c 2).
The Weyl fermion discovered in 2015 is also expected to be massless, [3] [4] but these are not actual particles. At one time neutrinos were thought to perhaps be Weyl fermions, but when they were discovered to have mass, that left no fundamental particles of the Weyl type.
At those energies and distances, very high energy gamma-ray photons have a significant probability of a photon-photon interaction with a low energy background photon from the extragalactic background light resulting in either the creation of particle-antiparticle pairs via direct pair production or (less often) by photon-photon scattering ...