Second quantization by Ciro Santilli 37 Updated 2025-07-16
Second quantization also appears to be useful not only for relativistic quantum mechanics, but also for condensed matter physics. The reason is that the basis idea is to use the number occupation basis. This basis is:
Bibliography:
Like the rest of the Standard Model Lagrangian, this can be split into two parts:
Video 1.
Deriving the qED Lagrangian by Dietterich Labs (2018)
Source.
As mentioned at the start of the video, he starts with the Dirac equation Lagrangian derived in a previous video. It has nothing to do with electromagnetism specifically.
He notes that that Dirac Lagrangian, besides being globally Lorentz invariant, it also also has a global invariance.
However, it does not have a local invariance if the transformation depends on the point in spacetime.
He doesn't mention it, but I think this is highly desirable, because in general local symmetries of the Lagrangian imply conserved currents, and in this case we want conservation of charges.
To fix that, he adds an extra gauge field (a field of matrices) to the regular derivative, and the resulting derivative has a fancy name: the covariant derivative.
Then finally he notes that this gauge field he had to add has to transform exactly like the electromagnetic four-potential!
So he uses that as the gauge, and also adds in the Maxwell Lagrangian in the same go. It is kind of a guess, but it is a natural guess, and it turns out to be correct.
Video 1.
Electroweak Theory and the Origin of the Fundamental Forces by PBS Space Time (2020)
Source. Unsatisfactory, as usual.
Parity violation by Ciro Santilli 37 Updated 2025-07-16
This is quite mind blowing. The laws of physics actually differentiate between particles and antiparticles moving in opposite directions!!!
Only the weak interaction however does it of the fundamental interactions.
Some historical remarks on Surely You're Joking, Mr. Feynman section "The 7 Percent Solution".
It gets worse of course with cP Violation.
Quantum chromodynamics by Ciro Santilli 37 Updated 2025-07-16
Video 1.
Quarks, Gluon flux tubes, Strong Nuclear Force, & Quantum Chromodynamics by Physics Videos by Eugene Khutoryansky (2018)
Source. Some decent visualizations of how the field lines don't expand out like they do in electromagnetism, suggesting color confinement.
Video 2.
PHYS 485 Lecture 6: Feynman Diagrams by Roger Moore (2016)
Source. Despite the title, this is mostly about QCD.
Gluon by Ciro Santilli 37 Updated 2025-07-16
One big difference is that it carrier itself color charge.
Color confinement by Ciro Santilli 37 Updated 2025-07-16
Can be thought as being produced from gluon-gluon lines of the Feynman diagrams of quantum chromodynamics. This is in contrast to quantum electrodynamics, in which there are no photon-photon vertices, because the photon does not have charge unlike gluons.
This phenomena makes the strong force be very very different from electromagnetism.
As mentioned at Video "Are we living in the matrix? by David Tong (2020)" somehow implies that it is difficult or impossible to simulate physics on a computer. Big news!!!

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