In Special Relativity, a photon of frequency f is considered as a particle of mass m=h f/c2 with zero proper mass. It is experimentally verified that the photon carries momentum and exerts radiation pressure on the targets it impacts.
On the other hand, in General Relativity, it is proposed that the gravitational interaction between massive objects is due to the fact that gravitational field curves space-time. It has been verified that a massive body alters the trajectory and velocity of a beam of light that interacts with its gravitational field (Shapiro effect and gravitational lens effect). Within the frame of General Relativity, these effects are explained by proposing that photons follow geodesic trajectories within curved spaces. Obviously in this framework the mass of the photons can be considered negligible. But, in General Relativity, is the photon a massless particle?
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The mass of a photon = zero, though the photon has momentum.
H.G. Callaway
A photon is a mass of energy in a light wave that has zero mass and momentum. Comparing waves, the mass of the wave is 0, but water, the energy transfer medium for the wave, has the entire mass. A water wave is a mass of energy with zero mass. Likewise, ether(dark matter), the propagation medium for electromagnetic waves (including light waves), has total mass. In my paper(Beyond the Speed of Light – A Review of the Theory of Relativity and the Speed of Light by the Ether(Dark Matter)), I described the path of light passing through the solar gravitational field based on the ether, which has mass. The degree of space warped by the solar gravitational field was calculated using Newtonian mechanics, and the result was an accurate value that was closer to the measured value than the warp angle suggested by Einstein's theory of general relativity. All space in the universe where electromagnetic waves propagate is filled with ether. When light waves(electromagnetic waves) travel around an object with a large gravitational field, it appears to humans as a curved, distorted space. It's just a distorted path of light waves. A light wave is a mass of energy with zero mass and momentum. Thanks for reading.
The gravitational mass of a photon is equal to doubled mass of a material particle, whose energy is hf. This follows from the solution of the Einstein-Maxwell equations for directed radiation and from the application of Lagrange mechanics for analysis of the photon motion.
Preprint Dynamics of particles in a gravitational field
Article Application of Lagrange mechanics for analysis of the light-...
To state a slightly longer answer, since p is a vector (magnitude hf/c or E/c) it can be changed in direction
by a force F=dp/dt, which in fact is seen in practice. However this would be equivalent to say there is a certain mass mentioned above. Also photon forces are exerter over pallets which rotate as dp/dt, sudden change in p to -p
in a short time in reflection.
There is no rest mass but for calculational purposes you can assume a dynamical mass to get correct conclusions.
For example when giving a photon a potential energy in a gravitational field, or writting an actual gravitational force.
These points of view are calculationally correct.
If I assumed rest mass m(0) , dynamical mass of a photon would blow up, and you dont want that. So the dynamical mass
is just hf/(cc)
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