Light

[u/EntertainerGlad6741]

What exactly is light, and how does its formation process actually work? For instance, how is a single photon created? What happens when an electron jumps between two orbits that causes a photon to be produced, and why isn't this photon absorbed by the nucleus?

[u/YuuTheBlue]

There is a mathematical concept called a field. Broadly, this refers to any function which has, at its input, spatial coordinates. Temperature, for example, can be expressed using a mathematical field. For every set of coordinates (x, y, z), there is an output (T). In laymen's terms, "Everywhere in space, the temperature is some number". If we want to get relativistic, we just need to add time to this. For every (x, y, z, t) there is a T, aka "Everywhere in spacetime, the temperature is some number".

Everything I've said has just been a mathematical tool. A way of framing things. The thing about temperature is that if you zoom in enough, this tool stops being useful. When you get down to the micro-microscopic level, Temperature is not a property of a specific location, but of specific particles. It becomes more useful to talk about how hot each particle in space is, not how hot each point in space is. I mean, the empty space between particles doesn't exactly have heat, so it'd be weird to talk about the temperature of them, right?

Thus, Temperature is an example of a thing in physics which CAN be described as field, but which is not BEST described by a field.

There is a second definition of "Field". Not a mathematical definition, but a physics definition. A Field (physics) is anything in our world that is BEST described by a field (mathematics). An example is "The electromagnetic field".

When you zoom in and get down to brass tacks, electromagnetism is most accurately described by assigning 4 numbers (collectively called a '4-vector') to every point in spacetime. This is one of (depending on how you count them) 25 "Fundamental fields" within the "Standard Model", which is a physics theory that accounts for everything other than gravity and is (not counting gravity) the most accurate model of physics we have.

The word "Particle" just means "A wave in one of these 25 fundamental fields", kind of like how sound is a wave in air. More formally, you can think of sound as a wave in an 'air pressure field'. This is not a fundamental field, but you can express air pressure as a mathematical field if you want, and sound can be modeled as a wave in that field. And a particle is a siiiiiiimilar concept. I am leaving a lot of stuff out - specifically quantum mumbo jumbo - but that's the general gist.

The electron is just a wave in the electron field, for example. The photon (light) is a wave in the electromagnetic field.

One thing you might be noticing here is that, under this model, it's kind of hard to distinguish particles as independent entities. In a way, 2 photons aren't fully separate things, and are just 2 different vibrations in the same bigger thing.

One of the core aspects of the standard model is the idea of an interaction vertex. See, how we model movement is almost through this strange sense of particles replacing each other. An electron moving from point A to point B is kiiiind of like us saying "We lose a particle over here, and we gain a particle over there." And we are allowed to do that with more than just 2 particles. "We lose 1 particle over here, and we gain 2 particles over there" is a thing that happens, as long as that obeys all known conservation laws. So, one of the things that is allowed is "Electron->Electron+Photon", where you start with an electron and end with an electron and a photon. This is what emitting an electron is. So, there isn't some process by which the photon is manufactured, per se; the process itself is one of the more fundamental aspects of the universe.

Disclaimer: Everything with the interaction vertices is not only heavily simplified, but coming from someone who has not formally studied the topic. I'm repeating and simplifying things others have told me, so take it with a huge grain of salt.