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Keudn t1_j8hd0dv wrote

Reply to comment by Weed_O_Whirler in Light traveling through a medium that slows it. Does the same photon emerge? by TheGandPTurtle

I've always taken the explanation that "light is a propagation of a wave in the electromagnetic field, and it propagates slower through a medium than a vacuum." So from my viewpoint, its not that the photon is slowing or being absorbed and re-emitted, its simply that the speed of light in a medium is less than a vacuum. Is there a reason this interpretation would be wrong, or just yet another way to think about it?

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lucidludic t1_j8hi3wt wrote

From my perspective you have only stated the observation, this isn’t an explanation and naturally leads to questions like, “why does light propogate slower through a medium?” or “why does the speed vary depending on the medium?”

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Weed_O_Whirler t1_j8ipjyz wrote

The problem is that according to General Relativity, a massless particle must always travel at c. So when dealing with the photon nature of light, a photon cannot slow down. But of course, we know light propagates slower through a medium, so somehow you have to reconcile these things.

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MasterPatricko t1_j8j6gkn wrote

> according to General Relativity, a massless particle must always travel at c.

That's special relativity, not general relativity (yes, GR includes SR, but you get what I mean).

The fundamental wrong assumption people make is that a wavepacket of the EM field -- a photon -- in a vacuum is somehow "the same" as the wavepacket of the EM field in a complex background of charged particles, i.e. a real material made of atoms.

To make an analogy (of limited range, please don't abuse it :)): no-one is surprised that a classical gravity wave in water and a wave in honey behave differently. Why is it surprising for an EM wave? /u/Keudn 's description is classical and doesn't explain how to calculate the speed in a medium, but aside from that missing depth, strictly correct.

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Weed_O_Whirler t1_j8j8j8m wrote

I specifically talked about how there are models where the photon becomes a quasiparticle in my original answer to the question, I was simply explaining to the person who asked why there are complications when viewing EM waves moving slower.

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MasterPatricko t1_j8j9h5k wrote

Right, and I didn't contradict you on that, I'm adding to your answer there. The only mistake you made here was you have confused GR and SR.

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