= Richard Feynman Quantum Electrodynamics Lecture at University of Auckland (1979)
{c}
By <Richard Feynman>{parent}.
Talk title shown on intro: "Today's Answers to Newton's Queries about Light".
6 hour lecture, where he tries to explain it to an audience that does not know any modern physics. This is a noble effort.
Part of The Douglas Robb Memorial Lectures lecture series.
Feynman apparently also made a book adaptation: https://en.wikipedia.org/wiki/QED:_The_Strange_Theory_of_Light_and_Matter[QED: The Strange Theory of Light and Matter]. That book is basically word by word the same as the presentation, including the diagrams.
According to http://www.feynman.com/science/qed-lectures-in-new-zealand/ the official upload is at http://www.vega.org.uk/video/subseries/8[] and Vega does show up as a watermark on the video (though it is too pixilated to guess without knowing it), a project that has been discontinued and has has a non-permissive license. Newbs.
4 parts:
* Part 1: is saying "<photons> exist"
* Part 2: is amazing, and describes how photons move as a sum of all possible paths, not sure if it is relativistic at all though, and suggests that something is minimized in that calculation (the <action (physics)>)
* Part 3: is where he hopelessly tries to explain the crucial part of how electrons join the picture in a similar manner to how photons do.
He does make the link to light, saying that there is a function $P(A, B)$ which gives the amplitude for a photon going from A to B, where A and B are spacetime events.
And then he mentions that there is a similar function $E(A, B)$ for an electron to go from A to B, but says that that function is too complicated, and gives no intuition unlike the photon one.
He does not mention it, but P and E are the so called <propagators>.
This is likely the <path integral formulation> of QED.
On <Quantum Mechanical View of Reality by Richard Feynman (1983)> he mentions that $E$ is a <bessel function>, without giving further detail.
And also mentions that:
$$
E = f(1, 2, m) \\
P = f(1, 2, 0)
$$
where `m` is basically a scale factor.
such that both are very similar. And that something similar holds for many other particles.
And then, when you draw a <Feynman diagram>, e.g. electron emits photon and both are detected at given positions, you sum over all the possibilities, each amplitude is given by:
$$
c \times E(A, D) \times E(D, B) \times P(B, C)
$$
summed over all possible $D$ <Spacetime> points.
This is basically well said at: https://youtu.be/rZvgGekvHes?t=3349 from <Quantum Mechanical View of Reality by Richard Feynman (1983)>.
TODO: how do electron velocities affect where they are likely to end up? $E(A, D)$ suggests the probability only depends on the spacetime points.
Also, this clarifies why computations in QED are so insane: you have to sum over every possible point in space!!! TODO but then how do we calculate anything at all in practice?
* Part 4: known problems with QED and thoughts on QCD. Boring.
This talk has the merit of being very experiment oriented on part 2, big kudos: <how to teach and learn physics>
\Video[https://www.youtube.com/watch?v=Alj6q4Y0TNE]
{title=Richard Feynman Quantum Electrodynamics Lecture at University of Auckland (1979) uploaded by Trev M (2015)}
{description=
Single upload version. Let's use this one for the timestamps I guess.
* https://youtu.be/Alj6q4Y0TNE?t=2217[]: <photomultiplier tube>
* https://youtu.be/Alj6q4Y0TNE?t=2410[]: <local hidden-variable theory>
* https://youtu.be/Alj6q4Y0TNE?t=6444[]: mirror experiment shown at https://en.wikipedia.org/w/index.php?title=Quantum_electrodynamics&oldid=991301352\#Probability_amplitudes
* https://youtu.be/Alj6q4Y0TNE?t=7309[]: mirror experiment with a <diffraction grating> pattern painted black leads to reflection at a weird angle
* https://youtu.be/Alj6q4Y0TNE?t=7627[]: detector under water to explain <refraction>
* https://youtu.be/Alj6q4Y0TNE?t=8050[]: explains <biconvex spherical lens> in terms of minimal times
* https://youtu.be/Alj6q4Y0TNE?t=8402[]: mentions that for events in a series, you multiply the complex number of each step
* https://youtu.be/Alj6q4Y0TNE?t=9270[]: mentions that the up to this point, ignored:
* amplitude shrinks down with distance
* <photon polarization>
but it should not be too hard to add those
* https://youtu.be/Alj6q4Y0TNE?t=11697[]: finally starts electron interaction. First point is to add time of event detection.
* https://youtu.be/Alj6q4Y0TNE?t=13704[]: electron between plates, and mentions the word <action (physics)>, without giving a clear enough idea of what it is unfortunately
* https://youtu.be/Alj6q4Y0TNE?t=14467[]: mentions <positrons> going back in time, but does not clarify it well enough
* https://youtu.be/Alj6q4Y0TNE?t=16614[]: on the fourth part, half is about frontiers in <quantum electrodynamics>, and half full blown <theory of everything>. The QED part goes into <renormalization> and the large number of parameters of the <Standard Model>
}
\Video[https://www.youtube.com/watch?v=LPDP_8X5Hug]
{title=Richard Feynman Lecture on Quantum Electrodynamics 1/8}