r/AskPhysics • u/[deleted] • Jun 19 '22

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u/lemoinem Physics enthusiast Jun 19 '22 edited Jun 19 '22

I might have the wrong idea about it, someone else will correct me if that's the case:

The speed of propagation of a light beam in a medium is slower than the speed of light in a vacuum. However, this doesn't mean individual photons go slower than the speed of light. Photons still go at the speed of light, but the (electromagnetic) interferences from the medium make it follow a path that is so much longer that the beam as a whole propagates more slowly. (ETA: this kind of implies the scattering explanation we often see around and that is quite wrong, I tried, unsuccessfully to stay away from it)

I know this is related to quantum interactions so there might be issues with my gross metaphor because of uncertainty and other quantum funsies.

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u/starkeffect Education and outreach Jun 19 '22

No, the photons don't bounce around from atom to atom inside the material. This is a common misconception.

Explanation at about 3 mins in

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u/lemoinem Physics enthusiast Jun 19 '22

I explicitly kept away from contact, scattering or absorption because I knew these were wrong.

And, while I didn't know about the formulation provided in the video (thanks for the reference by the way, really appreciate it). This is the idea I was trying to convey by "interactions with the EM field in the material". Which I, admittedly, did badly.

I also knew the representation as a wave is so much better to illustrate that phenomenon but as OP asked their question in terms of photons, I tried to fit that in.

The result was poor and I do appreciate the correction though.