I have discussed tons of properties of photon in this website. The current article can be read in conjunction with; What are photons. But for other interesting ideas of photons such as why one should never say “Photon’s Rest Frame” and how in some other ways photon is really a very special particle search this website.
Photons would be produced under two mutually inclusive conditions. (1 and 2)
1. Photons are Relativistic
2. Photons are quantum Mechanical.Also (without any direct theoretical connection, but correlation through reality of nature)
3. Photons are classical only in the sense that we perceive light only when photons are produced in large numbers. So large that the laws of the small do not incur large errors because they are in large numbers. Statistically the errors are well understood and eliminated. But when they are produced in very small numbers we can not deduce their laws a priori.
[which is why Quantum Mechanics was discovered only in 1920s and not in Galileo’s time, In his time the macroscopic behavior were understood and microscopic laws can never be produced from the understanding of macro scope just like a particular individuals attribute can’t be found from a large number of individual’s group attribute]
So all in all, when the speed of charge carriers is quite large (that is; a significant fraction of 3,00,000 kms per second) or their size is quite quite small only then Photons will be produced.
That is to say photon is a quantum mechanical concept and not a classical one. eg you can’t simply add the number of photons.
Which is when we specify photons through quantum numbers and not numbers as such. Quantum numbers are already deduced by assuming quantum mechanical laws (that is; rules that are valid for very small objects and not according to our intuition from everyday world).
Plus note that; given the speed of a charge carrier (or any object) is a sizable fraction of 3,00,000 kms/second it must be really small. According to Einstein’s laws of mechanics, nothing which is quite big (eg lets say a small chalk piece) can move at such high speeds.
So it is built into nature that given Relativistic Laws were discovered its the birds of leaves of the same branch that Quantum Laws were waiting to be discovered. It went to the advantage of Einstein who himself posits awkwardly “God does not play dice”.
So you can see above point 1 and 2 are mutually inclusive (as I used the same word, mutually inclusive, above) .. But Classical world (3) is a statistical accumulation of 1 and 2. It can’t dictate 1 and 2. 1 and 2 are laws. 3 is an observation. eg 1 and 2 will decide what sort of photons will be produced and that tells us how exactly we can predict how many photons will be produced under a given situation. Photon numbers will not be conserved in 1 and 2, because its not a law of 1 and 2.
In other words observation of classical world does not lead to laws of Quantum World.*
*Pilot wave theory is eg based on such an assumption, that we can observe the classical world and predict the world of atoms and smaller. I can look at how a particular country’s citizen behave and I can predict each individual’s behavior. Then I do not know the difference between seeing a psycho killer in a crowd behaving totally sane and a killer in action away from his social role play.
Quantum Particles have totally strange laws whose classical “social role play” is what we observe as day to day phenomena. A single electron does not have enough energy to shock you but a bunch of them can kill you even if less strong in some way than the day to day forces you experience.