A photon is a tiny particle of light that carries energy and has zero mass. It is the smallest unit of electromagnetic radiation and is responsible for the propagation of light and other forms of electromagnetic energy.
Photons are created when an atom's electrons move from a higher energy level to a lower energy level. This can occur through various processes such as thermal excitation, chemical reactions, and radioactive decay.
The source of photon propagation is the emission of photons from an excited atom or particle. This can occur naturally, such as in stars and other celestial bodies, or artificially through devices like lasers and LEDs.
The propagation of photons can be affected by several factors, including the medium through which they are traveling, the frequency or wavelength of the photons, and any obstacles or interference that they encounter along their path.
In theory, photons can travel forever if they do not encounter any obstacles or interactions that would cause them to lose energy or change direction. However, in reality, they will eventually be absorbed by matter or scatter off particles in their path, limiting their propagation distance.