# Richard Feynman Quantum Electrodynamics Lecture at University of Auckland (1979) | ðŸ—– nosplit | â†‘ parent "Quantum electrodynamics bibliography" | 792, 1, 934

By Richard Feynman.

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. 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:This talk has the merit of being very experiment oriented on part 2, big kudos: how to teach and learn physics

- 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)
- 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:where$E=f(1,2,m)P=f(1,2,0)$
`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:summed over all possible $D$ Spacetime points.$cÃ—E(A,D)Ã—E(D,B)Ã—P(B,C)$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.