The Mechanism of the Emissions/Absorptions Spectrum

Has Mathis or anyone explained the possible mechanism behind the emissions and absorption spectrum given that electrons are not considered to be "quantum tunneling" between orbitals and emitting/absorbing photons?

Yes, try this paper: http://milesmathis.com/stark.pdf and maybe this one http://milesmathis.com/arp.pdf.

Thanks for the link. I'll be honest, I still have no idea probably because I lack an understanding of Mathis' idea of spin and charge density (would not charge density simply be the density of photons themselves within a given space?).

Yes, charge density is just the number of particles per volume. Nothing esoteric about it. Spin is a bit different and does take some getting used to. Find some of Jared's videos that are linked in some posts on here. They will help you to see the motions of a particle with stacked spins. I have some apps that help too, but they need you to understand a bit first.

Can anyone explain the emission/absorption spectrum in their own terms or paraphrasing Mathis? I read the relevant papers over and over (and all the supporting papers), but they are too verbose to get a clear explanation. Nothing against Mathis' explanation, I just wonder if anyone has it nailed down.

The question might boil down to this: how does the electron (or the proton for that matter) of a hydrogen nucleus cause quantized increases in photon spin?

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With respect to the emission/absorption spectrum and how it shifts, here’s my understanding.

What’s most important isn’t the charge field density or photon emission spins. What matters most are the atoms making up the material. Take some time to look at their structure. Each is unique in number and configuration of protons - the source of the emission field we are looking at. That physical structure of the emitting protons within the atom registers in our measuring equipment as that atom’s emission spectrum. The atom itself can only recycle the photons it is receiving. You can increase or decrease the amount of energy delivered to a material under examination, such as relative cold vacuum or zapping it with electricity, but as long as the atom maintains its structural integrity, it will always present the same proton configuration and the same emission pattern. It will release energy equal to the amount of charge which it is receiving at any given time.

Please excuse my rush, I've got plenty of chores to do.
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A Break in the Quest for the Quantum Speed Limit
“When you see that, you know you’re touching on something very, very deep and fundamental.”
https://www.theatlantic.com/science/archive/2018/11/planckian-dissipation-strange-metals-superconductors-electron-speed-limit/576484/

Exactly what electrons, the carriers of electricity, are doing in strange metals isn’t known. But experts hypothesize that they may be organizing themselves into a “maximally scrambled” quantum state, in which the properties of each electron depend on those of every other. This state of maximum scrambling might allow the electrons to scatter off one another and spread energy as quickly as the laws of quantum mechanics permit.

Electrons may be organizing into a single “maximally scrambled” quantum state, capable of spreading energy at the quantum limit. It goes deeper, please let's stop there. Hooey. I believe Miles might call it very deep quantum fudge.

In my opinion, this so-called quantum electron state is an example of the same absorption/emission phenomena as I described previously. All protons, neutrons and electrons are receiving the photons present in the ‘ambient’ charge field, be it increased or decreased. Those particles will recycle that charge, at the rate in which they are receiving charge from the ambient field.
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A "maximally scrambled" state sound a hell of a lot like a charge field to me!