Comments by "Lepi Doptera" (@lepidoptera9337) on "Proč se světlo může "zpomalit" a proč závisí na barvě | Optické hádanky 3" video.

Photons don't travel at all. That's just a failed mental model that shows its weakness in situations like this where it makes no sense whatsoever. What you are noticing here is not a problem with the quantum mechanical description of light in solids but a problem with the semi-classical notion of photons as tiny moving particles of light. One can, unfortunately, not even use the simple quantum mechanical picture of a photon as an irreversible energy transfer. That only works for emission and absorption phenomena and optical refraction is neither. At the quantum level refraction is a very complex multi-quantum phenomenon that requires us to analyze the solid as a series of coupled harmonic oscillators. It can be done and it has been done, but it's usually a bridge too far, both for laymen and undergrad physics students. I have a book about the topic somewhere. I gave up reading it after the first dozen pages (I am a high energy physicist by training), the theoretical details are that boring and tedious.
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It's not the electrons that are causing this phenomenon, at least not directly. It's a collective excitation of the crystal lattice which gets polarized. The correct theoretical explanation is, unfortunately, much more complex on the quantum level than e.g. the conductivity of metals or semiconductors and if we really wanted to take this on correctly, then we would also see effects like Raman spectra and solid state laser theory drop out of the math. That's why we usually simplify this problem to the classical level, which for most optical and materials applications is perfectly sufficient. In terms of math this brings us from coupled quantum mechanical linear oscillators to classical polarization.
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Technically "charges" do not matter in optical media for visible light. What matters is bulk polarization.
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@destroya3303 Why not? Optical properties are usually not caused by free charges. They are caused by the polarizability of the medium. The more polarizable a medium is, the higher the epsilon_r and the lower the effective speed of light in that medium. Frequency dependent polarizability leads to chromatic effects (like the very pretty "fire" of diamonds, but it's bad thing if we want to make lenses for optical instruments). There are rare cases of natural materials where free charges do, indeed, play a role. Have you seen fluorescing diamonds? They have a pretty blue hue when exposed to UV light. (even though this fluorescence lowers the value for jewelry because it reduces the visibility of the actually desired chromatic effect). If I remember correctly it's caused by a so called color center, which is an electron that is trapped at the site of a nitrogen dopant atom in the diamond's carbon lattice. Other examples where free charges matter for optical materials are LCDs. There the free charges on the electrodes in the screen cause an electric field that re-orients the chiral molecules of the liquid crystals.
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It's a linear superposition of many different frequencies and polarizations. Nothing a Fourier transform can't handle (if you are OK with the notion of randomized phases).
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Momentum conservation.
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Light slows down because it stops being light. What's inside an optical medium does not obey relativistic equations and it is not light but a quasi-excitation between the electromagnetic field and the internal degrees of freedom of the medium.
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Momentum conservation.
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If you do that you end up with the wrong result because that is not how this works.
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@Harrykesh630 Because this is a collective polarization effect. You don't need particles for that.
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@Harrykesh630 Refraction is a completely classical dielectric bulk phenomenon. There is no need to drag charge quantization into it.
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@Harrykesh630 You saw it on the internet, so it must be true, right? How old are you? Less than six or over eighty? Those are the only user groups who can be excused for believing every bit of bullshit they see on the internet. The little ones are still naive, the old ones already have dementia. Everybody else is required to check everything against textbooks and the primary literature. ;-) Grant's channel description that claims "physics is adjacent to math" should already have given you the chills. Physics has absolutely nothing to do with math (except that it's the foundation of math and that it abuses its notation). Some mathematicians are completely oblivious to what physicists really mean when they use the equivalence sign. :-)
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@Harrykesh630 Physics uses the language of math but it means something entirely different with it. In F=ma the mathematicians only see three variable (or two variables and a constant). Physicists see three completely different phenomena: acceleration, inertia and force. The equation defines how we measure force through acceleration and inertia or how we can measure inertia through acceleration and force or how we can measure acceleration through force and inertia. You can't get that out of the mathematical equation, at all. That's knowledge about the world that is entirely external to the mathematical symbols. Grant's channel is fine, as long as he sticks to things he actually knows, which is math. Physics is not math. It's much more than that. It's millions, if not billions of actual experiences about the world.
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