Magnetoresistive RAM Updated 2025-07-16
Before Present Updated 2025-07-16
Dipole antenna Updated 2025-07-16
Radio Wave Properties: Electric and Magnetic Dipole Antennae by Harvard Natural Sciences Lecture Demonstrations (2020)
Source. The dude lights bulbs on an antenna made of a single piece of copper, powered with EM radiation. Amazing.
Dipole antenna receiver animation
. Source. 
Dipole antenna transmitter animation
. Source. 
Radar Updated 2025-07-16
Isra and Mi'raj Updated 2025-07-16
Muhammad Updated 2025-07-16
As iron sharpens iron, so one person sharpens another Updated 2025-07-16
Proverbs 27:17.
Fishers of men Updated 2025-07-16
Gospel of Matthew 4 King James Version:
18 And Jesus, walking by the sea of Galilee, saw two brethren, Simon called Peter, and andrew the Apostle his brother, casting a net into the sea: for they were fishers.19 And he saith unto them, Follow me, and I will make you fishers of men.
Man shall not live by bread alone Updated 2025-07-16
Ciro Santilli's mother loves that one. Even though she was constantly worried that if Ciro had studied physics he would be poor and starve, a factor which led him to study engineering instead, one of the greatest mistakes of his life. don't be a pussy.
Enter through the narrow gate Updated 2025-07-16
Gospel of Matthew 7:13:
Enter through the narrow gate. For wide is the gate and broad is the road that leads to destruction, and many enter through it.
Ciro Santilli really likes this one, because he feels that where many people go, it is useless to go again. It is much better to explore that which few can do, but which many will need.
The truth will set you free Updated 2025-07-16
Nielsen-Ninomiya theorem Updated 2025-07-16
Quantum field theory lecture notes Updated 2025-07-16
Lecture notes found by Googling "quantum field theory pdf":
- www.ppd.stfc.ac.uk/Pages/Dasgupta_08_Intro_to_QFT.pdf "An Introduction to Quantum Field Theory" by Mrinal Dasgupta from the University of Manchester (2008). 48 pages.
- www.thphys.uni-heidelberg.de/~weigand/QFT2-14/SkriptQFT2.pdf "Quantum Field Theory I + II" by Timo Weigand from the Heidelberg University. Unknown year, references up to 2008.
- edu.itp.phys.ethz.ch/hs12/qft1/ Quantum Field Theory 1 by Niklas Beisert
Quantum field theory lectures Updated 2025-07-16
Quantum field theory book Updated 2025-07-16
- web.archive.org/web/20150623011722/http://users.physik.fu-berlin.de/~kleinert/b6/psfiles/qft.pdf by Hagen Kleinert (2015). 1500 pages!
- The Quantum Theory of Fields by Steven Weinberg (2013) www.cambridge.org/core/books/quantum-theory-of-fields/22986119910BF6A2EFE42684801A3BDF
- Quantum Field Theory by Lewis H. Ryder 2nd edition (1996) www.amazon.co.uk/Quantum-Field-Theory-Lewis-Ryder/dp/0521478146
- Lectures of Quantum Field Theory by Ashok Das (2018) www.amazon.co.uk/Lectures-Quantum-Field-Theory-Ashok-ebook/dp/B07CL8Y3KY
- A Modern Introduction to Quantum Field Theory by Michele Maggiore (2005) www.amazon.co.uk/Modern-Introduction-Quantum-Theory-Physics/dp/0198520743
Quantum threshold theorem Updated 2025-07-16
This theorem roughly states that states that for every quantum algorithm, once we reach a certain level of physical error rate small enough (where small enough is algorithm dependant), then we can perfectly error correct.
This algorithm provides the conceptual division between noisy intermediate-scale quantum era and post-NISQ.
Quantum electrodynamics experiment Updated 2025-07-16
Experiments explained by QED but not by the Dirac equation:
- Lamb shift: by far the most famous one
- hyperfine structure TODO confirm
- anomalous magnetic dipole moment of the electron
Applications of quantum electrodynamics Updated 2025-07-16
Quantum electrodynamics Lagrangian Updated 2025-07-16
where:
- is the electromagnetic tensor
Note that this is the sum of the:Note that the relationship between and is not explicit. However, if we knew what type of particle we were talking about, e.g. electron, then the knowledge of psi would also give the charge distribution and therefore
- Dirac Lagrangian, which only describes the "inertia of bodies" part of the equation
- the electromagnetic interaction term , which describes term describes forces
As mentioned at the beginning of Quantum Field Theory lecture notes by David Tong (2007):
- by "Lagrangian" we mean Lagrangian density
- the generalized coordinates of the Lagrangian are fields
What does it mean that photons are force carriers for electromagnetism? Updated 2025-07-16
TODO find/create decent answer.
I think the best answer is something along:
- local symmetries of the Lagrangian imply conserved currents. gives conserved charges.
- OK now. We want a local symmetry. And we also want:Given all of that, the most obvious and direct thing we reach a guess at the quantum electrodynamics Lagrangian is Video "Deriving the qED Lagrangian by Dietterich Labs (2018)"
- Dirac equation: quantum relativistic Newton's laws that specify what forces do to the fields
- electromagnetism: specifies what causes forces based on currents. But not what it does to masses.
A basic non-precise intuition is that a good model of reality is that electrons do not "interact with one another directly via the electromagnetic field".
A better model happens to be the quantum field theory view that the electromagnetic field interacts with the photon field but not directly with itself, and then the photon field interacts with parts of the electromagnetic field further away.
The more precise statement is that the photon field is a gauge field of the electromagnetic force under local U(1) symmetry, which is described by a Lie group. TODO understand.
This idea was first applied in general relativity, where Einstein understood that the "force of gravity" can be understood just in terms of symmetry and curvature of space. This was later applied o quantum electrodynamics and the entire Standard Model.
From Video "Lorenzo Sadun on the "Yang-Mills and Mass Gap" Millennium problem":
- www.youtube.com/watch?v=pCQ9GIqpGBI&t=1663s mentions this idea first came about from Hermann Weyl.
- youtu.be/pCQ9GIqpGBI?t=2827 mentions that in that case the curvature is given by the electromagnetic tensor.
Bibliography:
- www.youtube.com/watch?v=qtf6U3FfDNQ Symmetry and Quantum Electrodynamics (The Standard Model Part 1) by ZAP Physics (2021)
- www.youtube.com/watch?v=OQF7kkWjVWM The Symmetry and Simplicity of the Laws of Nature and the Higgs Boson by Juan Maldacena (2012). Meh, also too basic.
There are unlisted articles, also show them or only show them.