Thursday, June 18, 2020

The lecture Feynman really wanted to give to undergraduates

For Condensed Matter Physics: A Very Short Introduction, I have started writing a chapter on "Quantum matter". It is a challenge to decide what to include, particularly given how the content needs to be accessible to a general audience. The question, "What is quantum matter?" is an interesting one. Currently, I have decided to focus on how superconductors and superfluids can exhibit macroscopic quantum effects. More on that later. 

In the process, I was reminded of the last lecture in the celebrated Feynman Lectures on Physics. These are now available online, including photos.

The Schrödinger Equation in a Classical Context: A Seminar on Superconductivity

Here is Feynman's introduction to the lecture, given on June 4, 1964. This was the last lecture in a two-year ``introductory" physics course for Caltech undergraduates.
This lecture is only for entertainment. I would like to give the lecture in a somewhat different style—just to see how it works out. It’s not a part of the course—in the sense that it is not supposed to be a last minute effort to teach you something new. But, rather, I imagine that I’m giving a seminar or research report on the subject to a more advanced audience, to people who have already been educated in quantum mechanics.

All that aside, this is a subject I want to talk about. It is recent and modern and would be a perfectly legitimate talk to give at a research seminar. My subject is the Schrödinger equation in a classical setting—the case of superconductivity.
The lecture includes a description of the quantisation of magnetic flux, the Josephson effect, Shapiro steps, and a SQUID. All of these phenomena had only been discovered in the two years before the lecture. It is striking that Feynman clearly appreciated the significance of these recent discoveries, not just for condensed matter but also for quantum theory. He concludes the lecture as follows.
These then are some illustrations of things that are happening in modern times—the transistor, the laser, and now these junctions, whose ultimate practical applications are still not known. The quantum mechanics which was discovered in 1926 has had nearly 40 years of development, and rather suddenly it has begun to be exploited in many practical and real ways. We are really getting control of nature on a very delicate and beautiful level.

I am sorry to say, gentlemen, that to participate in this adventure it is absolutely imperative that you learn quantum mechanics as soon as possible. It was our hope that in this course we would find a way to make comprehensible to you at the earliest possible moment the mysteries of this part of physics.

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