@imbAF Skim Section 1 and Section 61 as quick background, then Section 64 for the Bosonic case. The relativistic Klein-Gordon case sort of just modifies things by making your Fock states have creation operators for both particles and anti-particles (with an equal number) so if you understand the non-relativistic case in 64 you can make sense of KG 2nd quantization pretty quick.

KG is then basically just the Schrodinger equation for your single particle state basis, once you know this basis you almost forget about KG, now its all about using those single particle states to construct multi-particle wave function for a system of identical bosons, and (as 64 explains, because of what 61 says) it is more natural to change our variables from coordinates to occupation numbers.

Once we do that we want to define operators which change the occuption numbers, and we're basically immediately led to creation/annihilation operators and quantum field operators, and 64 makes their definitions become obvious including the square root factors, it's basically showing that usual Harmonic oscillator thing is a general feature

Chapter 1 of Walecka's Many Particle Systems book (with Fetter) is very good too, sort of fills in some of the details L&L skip when it comes to actually working out the matrix elements that suggest how we should define creation operators etc

@ACuriousMind I dont see how that can be true; (R) simply asserts that magnetic fields are vector fields, and you can simply have vector fields with singularities like cusps or whatnot

I don't see why the relativistic case should be any different than the non-relativistic one (for second quantization).

@imbAF that's not what you do, as I've mentioned already in my previous answer to your comment...

hi

@naturallyInconsistent The problem is that the question is asked at a high-school level where none of the terms are defined to a degree of precision you could actually prove anything. The relevant theorem is that the integral curves of a smooth nowhere-zero vector field never intersect. The "reason" states something like "the magnetic field is a vector field". Now, does this question expect a high-schooler to go "ah, that's not the explanation because the condition about smooth and nowhere-zero is missing"?

To me, that completely depends on what exactly they discussed in their lessons about this, it's not a question you can judge in a vacuum.

@Slereah They should have called them cornifolds

I mean I guess they do all have corners, sometimes that corner is just the empty set

could relative collapse theories be called a realisation of Kant's ideas

in relative collapse theories, physics explicitly describes ur observations of the world, instead of the world in itself

as in, there is no way to even interpret a relative collapse theory as describing the world in itself, while u could interpret e.g. classical mech or objective collapse theories that way

so relative collapse theories, if true, enforce Kant's ideas