kenstauffer

Where do Photon's come from?

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When the filament in a lightbulb has current pass thought it the filament heats up, causing it to glow and give us light.

In atomic theory, the atoms in the filament are excited, the electrons in the atoms go to a higher orbital shell then quickly return to more stable state, this is when the energy is released in the form of a photon.

Where are the photons coming from? Are the photons "inside' the fillament, inside the electrons, inside the atom or what?

Can this go on forever? Will a particular closed system (except for the light being emitted) run out of photons?

(presumably the energy source would be fixed in this closed system, so that when the enrgy source depletes the generation of light would also cease. But is this limiting condition? or could you have a large enough battery such that the supply of photons depletes before the battery?)

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The real physical processes of photon creation and annihilation are poorly understood by the standard theories. There exists a great deal of complicated mathematical processes that, in some theories like quantum field theory, describe cetain behaviors of group particle processes to a high degree. But such mathematical descriptions are not, in themselves, real physical descriptions of the process.

In general, the electromagnetic potential is considered the basic field of the photon, with photons emerging from a quantization of the field. But the creation and annihilation operators that are used are are really just a mathematical device that are used to construct operators that deal with interactions between particles. These are "observables," such as the total energy of the electromagnetic field in a specific region. The photon number operators describe how many photons are in a given state, but the mathematics leads to infinities when you attempt to count the exact number in a given region. So to get a finite result, a sort of smearing function is used, and the result is just an approximation based on the means used to smear the region boundaries. This might give you some idea how the mathematical processes, which, in fact, are extremely useful, do not necessarily connect to the real physical processes that occur, even though there is an "observable" photon number operator relationship which links the number of photons to the total energy.

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kenstauffer:

You asked "Where are the photons coming from? ... Will a particular closed system ... run out of photons?".

There is no reason to believe that the photons exist in any form before they are emitted. There is no evidence that a system will ever run out of photons.

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