C is the speed of light in a vacuum. This does not depend on the number of photons.
phase velocity and group velocity
c is defined as group velocity of EM wave:
I think c of one photon is less meaning.
From the point fo quantum,position of one particle is uncertain.
Re: phase velocity and group velocity
That is true, but only while in transit. The speed measured between when photon is emitted and recieved (in a vacuum) is always exactly C.
What do you mean by "vacuum", as you used it in that paragraph? I mean, the term is always used when talking about the SOL, but I don't think I have ever read a rigorus definition of "vacuum" when it is used in conjunction with the SOL.
It is sure media will effect on particles.I think there are two different phrases in physics, classical and modern.Here,measurement the former,photon the later.QM says photon is spreading in space. One can get its state function also its probability of some classical quantities,energy,momentum,etc. and other,spin,degenerate... which have not corresponding concepts in class.But when we measure,an action of classical,photon will collapse and has a certain E,M,Position,etc. In this meaning, photon is not a photon of "quantum",only classical.
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