I'd like to ask a few questions about photons, not as a professional of physics.


  1. Since it's connected to the frequency of the wave composed by the stream of photons but can be defined for a single one, what is the best way to picture this quantity?
  2. Is this physical quantity related only to photons, or at least some other fundamental particle behavior and/or nature can be described using such quantity?

Photons in media: In vacuum photons travel constantly and forever, unless perturbed, at the maximum speed of light, but in media the speed of light and thus of photons which make make it up is reduced.

  1. What is actually happening in the media so that the speed is reduced? I suppose there is some kind of interaction with its particles. I originally pictured the process as having some finite-time interaction at some places in the media and then full speed traveling in the remaining parts, so that along a finite distance one saw a global reduction, but I've been told it's not like this and I've read that an interference process takes place such that the final wave is slower. But doesn't this wave have to be made up by photons as well? If these photons are the end product of this process, shouldn't they be moving again at maximum speed? I'm a bit confused.


  • $\begingroup$ Does this answer your question? What really causes light/photons to appear slower in media? $\endgroup$ – John Rennie Oct 8 '20 at 15:41
  • $\begingroup$ "and thus of photons which make make it up is reduced." this is not correct.photons as zero mass particles always travel at velocity c. To get an intuition of how single photons buld up the classical light see this sps.ch/en/articles/progresses/… . The paths of photons differ (longer) , they have different four vectors. It is their superposition that makes up EM wave $\endgroup$ – anna v Oct 8 '20 at 19:07

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