I think it’s typically better to understand what’s happening at the classical level before the quantum level for questions like this.

Classically, when an electromagnetic wave enters a material, the material itself responds to the electromagnetic wave because it’s composed of charged particles. The collective oscillation of this macroscopic number of charged particles itself creates an electromagnetic field. The field that you can physically observe and measure is the total electromagnetic field. Through the superposition principle, the new total field will be moving slower, and you can analyze the properties of this total field.

The reason I point this out is that intuition about quantum physics breaks down. For instance, it doesn’t necessarily makes sense to label a photon a specific ID number; photon number is not conserved. Moreover, you cannot distinguish photons of the same energy from each other: to ask if it’s the “same” photon is thus not a meaningful question to ask. Not to mention that photons don’t have classical trajectories in the usual sense, and so on.

In particular, what we conceive as a “photon” is a freely propagating quantum of light in a vacuum, without undergoing interactions. But in a medium, light is clearly very strongly with the material. Indeed, the light in the medium is physically the result of the original light wave interacting with the material. So whatever quantum particle (which is really an excitation of a quantum field) you want to use to describe what’s happening won’t behave like “ordinary” photons.

Some people will even say that you shouldn’t of think of photons like physical objects you can touch and manipulate, but rather the footprint of a quantum mechanical interaction between the electromagnetic field and whatever it is you’re talking about.

Which is all to say: photons don’t act like classical billiard balls of light, and unlike electrons are purely relativistic, so ordinary non-relativistic quantum mechanics won’t work either.

I believe protein folding can be treated with the Born-Oppenheimer approximation. Essentially, while quantum effects of the electrons in the system can be important, quantum effects of the nuclei can be neglected, and thus the nuclei are essentially treated as classical objects with definite position/momentum.

So, the quantum mechanical aspects will lie with the electronic structure; van der Waals forces, hydrogen bonds, and all that. These are all quantum phenomena.

For a high temperature gas, it would eventually instead look like a Maxwell-Jüttner distribution.

https://en.wikipedia.org/wiki/Maxwell%E2%80%93J%C3%BCttner_distribution

This happens when kT ~ mc^2 , so when the temperature is close to the rest mass energy of the particle.

However, there are effects this new distribution don’t take into account, so it has limited applicability.

I think you misunderstand what radiation is. Your question doesn’t make much sense. Electromagnetic waves aren’t matter, they don’t work like matter and can’t be “ruptured” or “destroyed”. They don’t have pieces holding them together like matter does. There’s simply nothing to break apart.

Electromagnetic waves (like radio waves, visible light, etc.) are self-propagating waves of oscillating electric and magnetic fields that travel through space. They can also travel through materials, like water or glass.

Electromagnetic waves can be absorbed by matter, where the energy of the electromagnetic wave goes into the matter that’s absorbing it. For instance, radiation from the Sun is absorbed by your skin, thus making you warm (as well as damaging some cells).

Electromagnetic waves follow the superposition principle, where if two or more electromagnetic waves are in the same region of space they can interfere. If the intensity of the radiation is increased, this is constructive interference. If the radiation intensity is decreased, this is destructive interference.

Importantly, two waves from different sources cannot perfectly destructively interfere everywhere in all space. If you have two waves and there’s a region where they perfectly cancel out, there must be another region nearby where they add up and constructively interfere. So you cannot destroy or cancel out radiation with another electromagnetic wave, all you can do is shift in space where the intensity is high or low.

You can of course stop creating an electromagnetic wave by turning off whatever the source is (e.g. turning off a flashlight), but the radiation that’s been created will already be traveling outwards.

That’s fair, cosmology and general relativity is a notable exception to all of this.

As far as we know, the speed of light as measured in vacuum has always been constant. We have not come across any experimental evidence otherwise.

Furthermore, we assume that all physical laws are the same across time and space. This is important due to Noether’s theorem, which says that symmetries in the physical laws lead to conservation laws. In this case, if the laws of physics changed with time, then energy conservation would be false; you would need very, very good evidence to claim that energy conservation is false.

As a caveat, changing the speed of light on its own isn’t very meaningful, because it’s a constant with dimensions. In physics, you can reframe all the most fundamental formulas in terms of dimensionless constants, like the fine structure constant; really, it’s these that would you want to see have changed over time or not.

For instance, if the fine structure constant changed with time, then the type of light emitted from atomic transitions would change over time as well. Meaningfully changing the speed of light would affect lots of other seemingly unrelated physics like this.

No, fusion devices cannot lead to an uncontrolled chain reaction. The reason is because the plasma needs to be confined in order to maintain the appropriate density and temperature; the Sun uses gravity to confine the plasma. In contrast, if the magnetic fields were turned off in a magnetic fusion device, the fusion plasma would just expand outwards into the wall and then cool down.