= Quantum electrodynamics
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= QED
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Theory that describes <electrons> and <photons> really well, and <Richard Feynman Quantum Electrodynamics Lecture at University of Auckland (1979)>[as Feynman puts it] "accounts very precisely for all physical phenomena we have ever observed, except for gravity and nuclear physics" ("including the laughter of the crowd" ;-)).
Learning it is one of <Ciro Santilli>'s main intellectual <fetishes>.
While Ciro acknowledges that QED is intrinsically challenging due to the wide range or requirements (<quantum mechanics>, <special relativity> and <electromagnetism>), Ciro feels that there is a glaring gap in this moneyless market for a learning material that follows the <Middle Way> as mentioned at: <the missing link between basic and advanced>. <Richard Feynman Quantum Electrodynamics Lecture at University of Auckland (1979)> is one of the best attempts so far, but it falls a bit too close to the superficial side of things, if only Feynman hadn't assumed that the audience doesn't know any mathematics...
The funny thing is that when <Ciro Santilli's mother> retired, learning it (or as she put it: "how photons and electrons interact") was also one of her retirement plans. She is a pharmacist by training, and doesn't know much <mathematics>, and her <English (language)> was <having more than one natural language is bad for the world>[somewhat limited]. Oh, she also wanted to learn how <photosynthesis> works (possibly not fully understood by science as that time, 2020). Ambitious old lady!!!
Experiments: <quantum electrodynamics experiments>.
Combines <special relativity> with more classical <quantum mechanics>, but further generalizing the <Dirac equation>, which also does that: <Dirac equation vs quantum electrodynamics>. The name "relativistic" likely doesn't need to appear on the title of QED because <Maxwell's equations require special relativity>, so just having "electro-" in the title is enough.
Before QED, the most advanced theory was that of the <Dirac equation>, which was already relativistic but TODO what was missing there exactly?
As summarized at: https://youtube.com/watch?v=_AZdvtf6hPU?t=305[] Quantum Field Theory lecture at the African Summer Theory Institute 1 of 4 by Anthony Zee (2004):
* classical mechanics describes large and slow objects
* special relativity describes large and fast objects (they are getting close to the speed of light, so we have to consider relativity)
* classical <quantum mechanics> describes small and slow objects.
* QED describes objects that are both small and fast
That video also mentions the interesting idea that:
* in special relativity, we have the <mass-energy equivalence>
* in quantum mechanics, thinking along the <time-energy uncertainty principle>, $\Delta E \sim \frac{1}{\Delta t}$
Therefore, for small timescales, energy can vary a lot. But mass is equivalent to energy. Therefore, for small time scale, particles can appear and disappear wildly.
QED is the first <quantum field theory> fully developed. That framework was later extended to also include the <weak interaction> and <strong interaction>. As a result, it is perhaps easier to just <Google> for "Quantum Field Theory" if you want to learn QED, since QFT is more general and has more resources available generally.
Like in more general quantum field theory, there is on field for each particle type. In quantum field theory, there are only two fields to worry about:
* <photon> field
* <electromagnetism> field
\Video[https://www.youtube.com/watch?v=EzfFklLqDjA]
{title=Lecture 01 | Overview of Quantum Field Theory by Markus Luty (2013)}
{description=This takes quite a direct approach, one cool thing he says is how we have to be careful with adding special relativity to the <Schrödinger equation> to avoid faster-than-light information.}